Title of Invention

ELECTRO-OPTICAL SENSING DEVICE FOR DETECTING THE PRESENCE OF AN ANALYTE IN A MEDIUM AND METHOD THEREFOR

Abstract An electro-optical sensing device for detecting the presence and concentration of an analyte in a liquid or gaseous medium includes a pair of indicator elements positioned to receive radiation from a radiation source and transmit radiation to a pair of photosensitive elements. The indicator elements each contain indicator molecules having an optical characteristic responsive to the presence of an analyte; however, one of the indicator elements is covered by an analyte-impermeable chamber that renders the indicator element insensitive to the presence of the analyte in the medium outside the chamber so that it can be used as a reference to cancel environmental and systemic variables that affect both indicator elements. The chamber preferably holds an analyte-containing fluid in contact with the reference indicator element so that the indicator elements operate under nominally identical conditions. The indicator element used to measure the analyte in the external medium is preferably also covered, but in a manner that provides direct contact between the analyte and the indicator element.
Full Text ELECTRO-OPTICAL SENSING DEVICE FOR DETECTING THE
PRESENCE OF AN ANALYTE IN A MEDIUM AND METHOD
THEREFOR
BACKGROUND OF THE INVENTION
Filed of the invention
(0001] The invention relates to electro-optical sensing devices for detecting the presence or
concentration of an analyte in a liquid or gaseous medium. More particularly, the invention relates
to an electro-optical sensing device having a signal channel responsive to the presence of an analyte
in a liquid or gaseous medium and a reference channel that is not responsive to the presence of the
analyte in the medium
[0002] U.S PatentNo. 5,517313, the disclosure of which is incorporated herein by reference,
describes an electro-optical sensing device that detects the presence and amount of an analyte using
fluorescence of an indicator molecule. Broadly speaking, in the context of the field of the present
invention, indicator molecules are molecules having one or more optical characteristics affected by
the local presence of an analyte. In one embodiment of the device according to U.S. Patent No.
5,517,313. a light source is located at least partially within a layer of material containing indicator
molecules that fluoresce when illuminated by the light source. Alternatively, the light source is
located at least partially within a wave guide layer such mat light emitted by the source strikes and
causes the indicator molecules to fluoresce. A high-pass filter allows fluorescent light emitted by
the indicator molecules to reach a photosensitive element while filtering out scattered light from the
light source.
[0003] The fluorescence of the indicator molecules employed in the device described in U.S.
PatentNo. 5,517,313 is modulated, Le., attenuated or enhanced, by the local presence of an analyte.
For example, the orange-red fluorescence of the complex tris(4,7-diphenyl-1,10-
phenanthroline)ruthenium(II) perchlorate is quenched by the local presence of oxygen. Therefore,
this complex can be used advantageously ss the indicator molecule in an oxygen sensor. Indicator
molecules whose fluorescence properties are affected by various other analytes are known as well.
[0004] In the sensing device described in U.S. PatentNo. 5,517,313, the material conraining the
indicator molecules is permeable to the analyte. Thus, the analyte can diffuse into the material from
the surrounding test medium, thereby affecting the fluorescence of the indicator molecules. The
light source, indicator molecule-containing material, high-pass filter, and photodetector are
configured such that fluorescent light emitted by the indicator molecules impacts the photodetector
such that an electrical signal is generated mat is indicative of the concentration of the analyte in the
surrounding medium.
[0005] In order to make accurate measurements based on a single variable, such as analyte
concentration, the design of the sensing device must isolate the effects of analyte concentration from
all other variables that may influence operation of the device. One way to do this is to measure all
other influential variables using specific transducers, and assuming the relationship is well defined
and predictable, compensate for these factors mathematically. Importantly, this method requires a
means of measuring the influential variable specifically, and a detailed mathematical model
describing and predicting its behavior over time.
[0006] In the example of the indicator molecule Ruthenium tris-biphenylphenanthroline, for
example, the relationship between indicator fluorescence and oxygen concentration is described by
the Stem-Volmer equation:

where I/Iq is an intensity ratio, pOj is oxygen concentration, and K,, is the Stem-Volmer constant
If the output from a sensor constructed using this type of indicator were recorded from within an
environment which isolated all variables except oxygen concentration, we should see a plot as
shown in FIG. 1. One can employ the Stem-Volmer plot as shown to measure an intensity in the
presence and absence of oxygen (the anaryte) and then find the corresponding oxygen concentration
from the x-axis using the plot as a calibration curve.
[0007] In reality, however, Kgy is a function of temperature, and in most practical applications,
the temperature of the test medium can be expected to change substantially. The temperature can
also change very rapidly. To account for the temperature sensitivity of Kgy, the Stern-Vohner
relationship can be represented by a series of curves, as shown in FIG. 2, corresponding to different
temperatures.
[0008] Introduction of a second variable such as teanperature mus makes measurement of the
first variable (i.e., analyte concentration) much more difficult It is necessary to know the
temperature accurately in order to know which of the Stern- Volmer plots to use for finding the
correct oxygen concentration from a measured intensity value.
[0009] An example of another influential variable is signal drift. Drift is less predictable than
temperature because a multitude of known, and often, unknown, factors are causative. One of many
such drift examples is illustrated by photo-oxidation in the case of the indicator Ruthenium tris-
biphenylphenarrthroline. Photo-oxidation, or photo-bleaching, is a well described degradation
which occurs when a (typically photochemical) reaction occurs between the indicator and ambient
oxygen. (In the case of the indicator Ruthenium tris-biphenylphenanthroline, the photodegradation
occurs due to singlet oxygen.) This degradation reaction results in the covalent and permanent
alteration of the indicator molecular structure. Once oxidized, the indicator loses it known
performance characteristics and its sensitivity to the intended analyte. If a variable drift component
due to photo-oxidation is superimposed over the previous temperature dependent variable shown in
FIG. 2, the result is a complex plot of the type shown in FIG. 3. FIG. 3 shows what a Stern-Volmer
calibration plot looks like under the influence of only three variables - changing oxygen
concentration, changing temperature, and changing amplitude as a result of ongoing drift due to
photo-oxidative degradation. It is not possible to know which of the plots to use for finding oxygen
concentration without knowledge of the temperature and the amount of degradation experienced by
the sensor.
[0010] Yet another example of error that may be introduced is from variable excitation light
levels. Since the excitation light source directly "pumps" the fluorescence detected from the
indicator, any fluctuation or degradation in the source light will directly be introduced as error into
the calibration. Light source drift can be caused by transient changes in the sensor power supply or
due to simple operational life degradation in the light source itself Some means of correcting for
this drift is necessary to making an accurate analyte measurement from sensor-supplied data.
[0011] From the above, it will be appreciated that, in order to design an electro-optical sensing
device for the purpose of measuring a single analyte, some means of correcting for kinetic,
molecular stability, and system influences which would otherwise introduce error into the
measurement is required. These influential factors can become complex and are highly
interdependent For example, an increase in temperature will also tend to increase the rate of
degradation due to photo-oxidation. There are many more known and often unknown influential
factors than the three examples described The result is a very complex and difficult to understand
series of interdependent variables that directly affect the accuracy of a measurement by an electro-
optical sensing device.
[0012] One method of correcting for the matrix of potential variables is to construct a reference
channel that is responsive to all variables except the presence of the analyte in the external
environment. The output from the reference channel may then be used to cancel the effect of such
variables on the sensing channel, for example by taking the ratio of the sensing and reference
channel outputs. In the absence of any change in the amount of analyte in the external
environment, this ratio should remain constant over time so that, if the ratio is plotted, the result
would be a flat line. This ensures that any change in the output ratio is due entirely to any change
in the amount of analyte in the external environment.
[0013] Several examples of using a reference channel in this manner during analyte detection are
known in the art. For example, U.S. Patent No. 3,612,866, the entire disclosure of which is
incorporated herein by reference, describes a fluorescent oxygen sensor having a reference
channel containing the same indicator chemistry as the measuring channel, except that the
reference channel is coated with varnish to render it impermeable to oxygen. Indian Patent
Application No. IN/PCT/2001/00300, filed March 16,2001, and entitled "An optical-based sensor
for determining the presence or concentration of an analyte" (which issued as Indian Patent No.
199317 on June 09, 2006), the disclosure of which is incorporated herein by reference, discloses
another fluorescent oxygen sensing device having a reference channel that starts out with the
same base chemistry as the sensing or signal channel but is further processed to block oxygen
diffusion, for example by coating the reference channel with a material that is impermeable to
oxygen.
[0014] This approach, however, may induce other differences between the channels that cannot be
canceled by taking the ratio of the outputs. For example, the output from the reference channel
may be increased or decreased due to reflectivity of the coating material. If the gain stages for
each channel are designed the same, one could be running at substantially higher levels than the
other due to differences in reflectivity. In addition ambient light that might be present in the
external environment at the same wavelength as the fluorescent emission would probably not be
picked-up by the reference channel and, thus, would probably not be canceled.
[0015] Yet another difference may stem from the fact that surface chemical properties of the
coating create the dominant properties of the reference channel whereas the chemical properties
of the indicator material or matrix create the dominant properties of the sensing channel.
Susceptibility to dust and condensation, chemical compatibility, and wear, would be expected to
create other differences.
[0016] It is also expected that mechanical micro-thermal influences driven by surface turbulence
would be different in a reference channel that has been "blanketed" and protected. Moreover,
specific absorption or diffusion characteristics may be different. The rate of photo-oxidation
would be expected to be dramatically different as the light scattering or absorbing influence from
the coating may intensify the excitation flux on the indicator molecule. This would result in
different rates of photo-bleaching thereby removing a key benefit sought from use of the reference
channel.
[0017] Importantly, the inherent solubility of the analyte within the coating material will establish
the concentration as seen by the reference channel. For example, if the analyte is oxygen, the
inherent solubility of the coating material for oxygen will be the oxygen level maintained at the
interface between the coating material and the top surface of the reference channel. Assuming this
solubility results in an equilibrium concentration much less than the concentration of oxygen in
air, then the reference channel will "see" a relatively anoxic environment. It will therefore
perform as if it were in an anoxic environment. If the indicator molecule were a Ru complex as
mentioned above, then the fluorescence of the reference channel will be much greater than the
signal channel at sensor baseline because of the inverse relationship between oxygen quenching
and fluorescence intensity. Further, because there is less oxygen in equilibrium with the reference
channel on average in this example, the rate of photo-oxidation (beyond the previously described
light scatter influence) will be reduced by the ratio of oxygen in the coating versus oxygen in air.
Any chemical reaction with alteration of, or inclusion of, the chemical components of the coating
material within the indicator matrix upon initial application will alter the performance
characteristics relative to the signal channel.
[0018] FIG. 4 illustrates an optical sensing device 10 of the same general type as described in
Indian Patent No. 199317 having an excitation source 12 in the form of an LED mounted on a
substrate 14 within a housing 16, a pair of indicator membranes 18A and 18B mounted over
openings 20A and 20B formed in the housing, and a pair of photosensitive elements 22 A and 22B
on opposite sides of the LED. The indicator membranes have the same base chemistry, however,
me indicator membrane shown on the right in FIG. 4 is coated with a material 24 that is
impermeable to oxygen in an attempt to form a reference channel.
[0019J FIG. 5 is a graph of actual test results for a sensing device of me type shown in FIG. 4
illustrating significantly diflerent responses for the signal and reference channels over an extended
period of time during which the sensing device is exposed to ambient air having a constant oxygen
concentration. It can be seen that the ratio of the signal and reference channel outputs is not a flat
line as desired, but an increasing function that makes interpretation of the results complex.
[0020] In addition to the foregoing, there are other rnemods of using a reference during analyte
detection. For example, U.S. Patent Nos. 4,861,727 and 5,190,729, the entire disclosures of which
are incorporated herein by reference, describe oxygen sensors employing two different lanthanide-
based indicator chemistries that emit at two different wavelengths, a terbium-based indicator being
quenched by oxygen and a europium-based indicator being largely unaffected by oxygen. U.S.
Patent No. 5,094,959, the entire disclosure of which is also incorporated herein by reference,
describes an oxygen sensor in which a single indicator molecule is irradiated at a certain wavelength
and the fluorescence emitted by the molecule is measured over two different emission spectra
having two different sensitivities to oxygen. Specifically, the emission spectra which is less
sensitive to oxygen is used as a reference to ratio the two emission intensities. U.S. Patent Nos.
5,462,880 and 5,728,422, the entire disclosures of which are also incorporated herein by reference,
describe a radiometric fluorescence oxygen sensing method employing a reference molecule that is
substantially unaffected by oxygen and has a pnotodecomposition rate similar to the indicator
molecule. Additionally, Muller, B., etcd., ANALYST, Vol. 121, pp. 339-343 (March 1996), the
entire disclosure of which is incorporated herein by reference, describes a fluorescence sensor for
dissolved COj, in which a blue LED light source is directed through a fiber optic coupler to an
indicator channel and to a separate reference photodetector which detects changes in the LED light
intensity.
[0021] In addition, U.S. Patent No. 4,580,059, the entire disclosure of which is incorporated
herein by reference, describes a fluorescent-based sensor containing a reference light measuring cell
for measuring changes in the intensity of the excitation light source — see, e.g., column 10, lines 1,
et seq. Furthermore, U.S. Patent No. 4,617,277, the entire disclosure of which is also incorporated
herein by reference, describes an absorbance-based sensor for carbon monoxide, in which a
reference element reflects light from a source to a reference photoceU to detemrae when a
measuring element needs replacement due to irreversible color change.
[0022] There remains a need in the art for an electro-optical sensing device with a reference
channel that responds in essentially the same manner as the measuring charmel to aU environmental
and systemic factors except the presence of an analyte of interest in the external environment
SUMMARY OF THE INVENTION
[0023] A first aspect of the present invention is generally characterized in an electro-optical
sensing device for detecting the presence and concentration of an analyte in an ambient fluid (i.e.,
liquid or gaseous medium) including a pair of indicator elements positioned to receive excitation
radiation from a radiation source and to transmit resufant radiation to a pair of photosensitive
elements. The indicator elements each contain indicator molecules having an optical characteristic
responsive to the presence of an analyte; however, one of the indicator elements is covered by an
analyte-impermeable chamber that renders the indicator element insensitive to the presence of the
analyte in the external environment so that it can be used as a reference to cancel environmental and
systemic variables that affect both indicator elements. The chamber preferably holds an analyte-
containing fluid in contact with the reference indicator element so that the indicator elements
operate under nominally identical conditions. The indicator element used to measure the analyte in
the external medium is preferably also covered, but in a manner that provides direct contact between
the analyte and the indicator element
[0024] The reference can be used to compensate or correct for: changes or drift in the
component operation intrinsic to the make-up of the sensing device; environment conditions
external to the sensor; or combinations thereof. For example, the reference can be used to
compensate or correct for internal variables induced by, among other things: aging of the radiation
source; changes affecting the performance or sensitivity of the photosensitive elements;
deterioration of the indicator molecules; changes in the radiation transmissivity of the indicator
elements, etc. In other examples, the reference can be used to compensate or correct for
environmental variables (e.g., variables influenced by factors external to the device, such as
temperature), that could affect the optical characteristics or apparent optical characteristics of the
indicator molecule irrespective of the presence or concentration of the analyte.
[0025] Another aspect ofthe present invention is generally characterized in an electro-optical
sensing device including a radiation source that emits radiation; first and second photosensitive
elements configured to receive radiation and output an electrical signal in response thereto; first and
second indicator elements positioned to receive radiation from the radiation source and to transmit
radiation to the first and second photosensitive elements, respectively, the indicator elements each
containing indicator molecules with an optical characteristic responsive to the presence of an
analyte; and an analyte-impermeable chamber covering at least a portion ofthe second indicator
element so as to render the second indicator element insensitive to the presence ofthe analyte in a
medium external to the device; whereby the ratio of output signals from the first and second
photosensitive elements can be used to measure the presence and concentration ofthe analyte in the
external medium.
[0026] The chamber of me sensing device can be filled with an analyte-containmg fluid. The
fluid can be a liquid (e.g., water) or a gas (e.g., air). The analyte-containing fluid can be ofthe same
type as the external medium or ofa different type. If the analyte is a gas, the partial pressure ofthe
analyte in the chamber fluid is preferably within the range of expected partial pressures ofthe
analyte in the surrounding medium.
[0027] An example ofa suitable indicator molecule is tris(4,7-diphenyl-l,10-
phenanthroline)ruthenium(TO perchlorate.
[0028] The device can include a housing mounting the first and second indicator elements, the
first and second photosensitive elements, and the radiation source. An aiialyte-impermeable cover
can be mounted on the housing to define at least a portion of the chamber covering the second
indicator element If an opening is formed in the housing, the second indicator element and the
cover can be mounted on opposite sides ofthe opening to define the chamber therebetween. The
cover can include a plug that extends into the opening. The cover can be formed of any suitable
material but is preferably formed of metal. An analyte-penneable first cover can also be mounted
on the housing over the first indicator element if desired. The first cover can include a bore formed
therethrough to provide fluid communication between the first optical indicator element and the
external medium. First and second openings can be formed in the housing, with the first indicator
element and the first analyte-penneable cover being mounted on opposite sides of the first opening,
and the second indicator element and the analyte-impermeable second cover being mounted on
opposite sides of the second opening to define the chamber therebetween. The first and second
covers are preferably substantially similar in configuration with the exception of Ihe bore.
[0029] Still another aspect of the present invention is generally characterized in a method of
detecting an analyte in a fluid medium using an electro-optical sensing device having a first
indicator element exposed to the fluid medium and a second indicator element at least partially
covered by an analyte-impermeable chamber that renders the second indicator element insensitive to
the presence of the analyte in the fluid medium so mat it can be used as a reference to cancel
environmental and systemic variables mat affect bom indicator elements.
[0030] Some of the advantages of the present invention over the prior art include increased
accuracy, enhanced mechanical protection of the indicator elements, ease of manufacturing, and
prevention of contamination including condensation.
[0031] The above and other objects, features and advantages will be further appreciated based on
the following description in conjunction with the attached drawings.
BRIEF DESCRIPTION OF THEjDRAWINGS
[0032] These and other objects of die invention will be apparent from the detailed description of
the invention and the following figures, which are given by way of example and not limitation, and
in which:
[0033] FIG. 1 is a graph iUustratmg the Stern-Volmer relationship between oxygen
concentration and light intensity emitted by a fluorescent oxygen indicator molecule.
[0034] FIG. 2 is a graph illustrating the effect of temperature on the Stem-Volmer relationship.
[0035] FIG. 3 is a graph illustrating the combined effects of temperature and photodegradation
on the Stern-Volmer relationship over time.
[0036] FIG. 4 is a sectional side view of arelated electro-optical sensing device having an
optical reference channel coated to prevent diffusion of an analyte therethrough;
[0037] FIG. 5 is a graph demonstrating the effects of temperature and photodegradation over
time for the signal and reference channels of the electro-optical sensing device shown in FIG. 4;
[0038] FIG. 6 is a perspective view, partly cutaway, showing an embodunent of an electro-
optical sensing device according to the present invention;
[0039] FIG. 7 is a sectional side view, taken through line 7-7 in FIG. 6, showing further details
of the electro-optical sensing device; and
[0040] FIG. 8 is a graph demonstrating the effects of temperature and photodegradation over
time for the signal and reference channels of the electro-optical sensing device shown in FIGS. 6
and 7.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0041] An electro-optical sensing device 100 according to the present mvention is illustrated in
FIGS. 6 and 7. Sensing device 100 generally includes a signal channel with an indicator element
102A and a photosensitive element 104A, a reference channel with an indicator element 102B and a
photosensitive element 104B, and a radiation source 106 providing excitation radiation for both the
signal and reference channels. The indicator elements 102A and 102B each include an indicator
layer or membrane containing indicator molecules havmg one or more optical characteristics mat
are affected by the local presence of an analyte. The indicator membrane 103A of the signal
channel is exposed to an exterior of the device and is thus responsive to the local presence of an
analyte in the external environment or medium. The indicator membrane 103B of the reference
channel is covered and is thus not responsive to the local presence of an analyte in the external
environment Since the membranes are similar in all other respects, a ratio of the outputs from the
signal and reference channels will cancel-out changes common to both channels, such as changes in
operation intrinsic to the sensing device and/or environment changes external to the sensing device,
leaving only those changes in the signal channel output due to presence of the analyte. The
foregoing aspects of the sensing device are similar to those used in the dual channel electro-optical
sensing devices described in the aforementioned U.S. Patent No. 6,330,464. In accordance with the
present invention, however, the sensing device 100 is configured to define a hermetically sealed
chamber 108, preferably holding an analvte-containing fhnd 110 in direct contact with the indicator
membrane 103B of the reference channel. If the fluid 110 in the chamber 108 contains the same
type of analyte contained in the external environment, such an arrangement ensures that the
response over time of the reference channel to changes in the radiation source, the temperature of
the external environment, and photo-oxidation of the membrane are essentially the same as or
similar to the response of the signal channel thereto. At the same tinxe, the hermetic seal iro
reference channel from changes in the concentration of the analyte in the external environment so
mat environmental factors other man analyte concenttao^n can be canceled om by using the ratio of
the signal and reference channel outputs as described above.
[0042] In the ulusttaled embodiment, the sigruri
100 are incorporated in a chip-like package with leads 112 extending therefrom for providing
power, signals, etc., to and/or from the device. The illustrated package includes a device substrate
114 m the form ofaretfangular Tainted cu^^ 112 disposed along
opposite edges of the substrate, and a housing 116 mounted on the substrate between the rows of
leads. In a preferred embodiment, the substrate 114 is formed of an alumina ceramic. Discrete
components can be electrically connected to the substrate, for example using commonly available
solder paste or conductive epoxy such as, for example, ABLEBOND 84 from Ablestick Electronic
Materials.
[0043] Housing 116 includes a generally rectangular top wall 118 and two side walls 120Aand
120B depending downwardly from opposite edges of the top wall. Bottom edges of the sidewalls
120A and 120B are configured to mount on a top surface of substrate 114 so as to maintain me top
wall 118 in vertically spaced relation to the substrate. The housing 116 can be formed of any
material suitable for use in the environment of interest but is preferably formed of a relatively rigid
plastic or metal material to improve accuracy by maintaining the top wall and substrate in vertically
spaced, parallel planes. The entire region R between the housing 116 and me substrate 114 can be
empty but preferably contains a waveguide material such as, for example, Epoxy Technologies
301™ which has good optical characteristics, although other suitable materials can be used. The
complete optical path (i.e., between the radiation source, the indicator membranes, and the
photosensitive elements) is preferably refractive index matched so that maximum light capture with
rnjnjmal internal reflection losses occur.
[0044] First and second openingsl22A and 122B are formed through the top wall 118 of the
housing 116 at spaced locations to communicate with the indicator membranes 103A and 103B.
The openings 122A and 122B are preferably arranged symmetrically on the top wall 118 so that the
indicator membranes 103A and 103B are subjected to similar conditions. In the illustrated
embodiment, for example, the openings 122A and 122B are bom arranged along a lorigrtudinal axis
of the housing 116 equidistant from opposite edges of the top wall 118. The openings 122A and
122B are shown as identical circular holes that are somewhat smaller than the indicator elements
102A and 102B; however, the shape and/or size of the openings can be varied to accommodate
different types of elements.
[0045] Indicator elements 102A and 102B are disposed within the housing 116 adjacent the
openings 122A and 122B formed in the top wall 118 thereof. The indicator elements 102A and
102B shown in mis embodiment include rectangular substrates 105A and 105B, respectively, mat
are somewhat larger man the openings 122A and 122B so mat peripheral portions of the substrates
can be affixed to an interior surface of the housing 116 around the openings to form a hermetic seal.
As mentioned above, indicator elements 102A and 102B also include indicator molecules having
one or more optical characteristics mat are affected by the local presence of an analyte. The
indicator molecules are preferably part of a membrane or layer 103 A and 103B formed on a central
portion of a respective substrate 105A and 10SB in alignment with openings 122A and 122B. The
membrane substrates 10SA and 10SB are preferably formed of the same material and with the same
thickness so that the indicator elements exhibtt similar thermal properties. In an exemplary
embodiment, the membrane substrates are formed of an optically transparent material such as
borosilicate glass and the membrane includes an inorganic polymer support matrix termed sol-gels
or ormosils, into which the indicator molecule is immobilized or entrapped. These materials and
techniques are well known (See, e.g.: McDonagh et al., "Tailoring of Sol-Gel Films for Optical
Sensing of Oxygen in Gas and Aqueous Phase", Analytical Chemistry, Vol. 70, No. 1, Jan. 1,1998,
pp. 45-50; Lev. O. "Organically Modified Sol-Gel Sensors", Analytical Chemistry, Vol. 67, No. 1,
Jan. 1,1995; MacCraith et al., "Development of a LED-based Fibre Optic Oxygen Sensor Using a
Sol-Gel-Derived Coating", SPIE, Vol 2293, pp. 110-120 C94); Shahriari et al., "Ormosil Thin
Films for Chemical Sensing Platforms", SPffi, VoL 3105, pp. 50-51 C97); Krihak et al., "Fiber Optic
Oxygen Sensors Based on the Sol-Gei Coating Technique", SPDE, Vol. 2836, pp. 105-115 C96), the
entire disclosures of which are each incorporated herein by reference). These types of materials can
be applied to the appropriate indicator element substrate by a number of techniques that are well
known in the art, such as dipping, swabbing, squeegeeing, silk screening, pad printing, vapor
deposition, ink-jet printing, etc. In an alternative embodiment, one or both of the indicator elements
can be formed without a dedicated substrate, for example by mounting an indicator membrane
directly on a cover, an encapsulant, or some other part of the device.
[0046] A preferred indicator molecule for sensing oxygen is tris(4,7-diphenyl-l,10-
phenanthroline) ruflienium (H) j>en^crate molecule, discussed on column 1, lines 16-19, of U.S.
Patent No. 5,517,313. It is contemplated that me membranes can include a variety of other
materials as set form in the aforementioned U.S. Patent No. 6,330,464, incorporated herein by
reference.
[0047] The radiation source 106 is mounted on the substrate 114 at an appropriate location to
excite the indicator molecules on each of the indicator elements 102A and 102B. To maintain
commonality between the channels, the radiation source 106 is preferably located equidistant from
each of the indicator elements 102A and 102B. Any suitable radiation source can be used; however,
a tight-enntting diode (LED) is preferred. The wavelength of the radiation emitted by the source is
dependent upon the type of indicator molecule employed. For example, in the case of the ruthenium
molecule referenced above, it is preferred that the radiation source emit light in the blue or ultra-
violet bands, for example at 460nm. While the radiation source 106 is shown centrally located
between the photosensitive elements 104A and 104B and the indicator elements 102A and 102B,
the radiation source may be otherwise located, as long as adequate excitation is provided to the
signal and reference channel membranes.
[0048] Photosensitive elements 104A and 104B are mounted on the device substrate 114 on
opposite sides of the radiation source 106 in general nHgrnnmt with indicator elements 102A and
102B, respectively. Silicon photo-diodes, such as for example part no. 150-20-002 from Advanced
Photonics, Inc., are preferably provided as the photosensitive elements, and are preferably flip chip
mounted using ball bonds and conductive epoxy. Optical filters 124A and 124B are preferably
provided for each of the photosensitive elements. In an exemplary embodiment, each optical filter
is formed using a high-pass filter epoxy, such as LP-595 filter resin available from CVI Laser
Corporation, with, for example, a 600nm cutoff corresponding to the ruthenium molecule
fluorescent emission. In another exemplary embodiment, each optical filter is fabricated from
commercially available filter sheet stock. The optical filters preferably separate fluorescent
emission from the indicator membranes from the excitation energy of the radiation source. In an
alternative embodiment, each optical filter can be formed using a bandpass filter that rejects
wavelengths outside a predetermined range. Bandpass filters are commercially available from
numerous vendors and allow the device to operate in environments with ambient light
[0049] A cover 126B is mounted over the reference channel opening 122B in spaced relation to
the indicator element 102B to define the hermctiwilly-sealed cliamber 108 that isolates the re
channel from changes in the concentration of the anaryte m me exteriial environment vvdu^e emuring
that the reference channel responds like the signal channel to otner environment changes external to
the sensing device (e.g., temperature) as well as changes in operations intrinsic to the sensing device
(e.g., photodegradation and fluctuations in the power source). In the illustrated embodiment, the
reference channel cover 126B includes a cylindrical plug 128B configured to fit within the opening
122B and a circular flange 130B extending radially outward from an upper or top end of the plug.
As best seen in Fig. 7, the plug 128B fits snugly in the opening 122B and extends part way through
the thickness of the housing wall 118 such that a gap is maintained between a bottom of the plug
and the indicator membrane. The circular flange 130B extending radially outward from the top of
the plug 128B defines a lower annular contact surface adapted to contact an upper or outer surface
' of the housing 116 completely around the circumference of the opening 122B so that an hermetic
seal can be formed that will prevent migration of analyte-contaming fluids from the external
environment into the chamber. The reference channel cover 126B can be formed of any suitable
TP> conductivity so that the fluid in the chamber will experience temperature changes similar to the
fluid in me external environment It can also be advantageous for the material to have high
reflectivity. Examples of suitable material* for the cover include, but are not limited to, metals such
as brass, aluminum, and steeL It is also contemplated that insulating and semi-insulating materials
such as plastics and ceramics can be used. When the external environment includes background
radiation coinciding with the wavelength of interest, it may be desirable for the cover to be formed
of a transparent material so that such background radiation can be canceled. The cover 126B can be
affixed to the housing 116 using any technique capable of producing an hermetic seal, but is
preferably bonded using an adhesive suitable for the particular housing and cover materials.
[0050] It will be appreciated that the presence of the sealed chamber 108 above the reference
indicator element 102B can result in the channels being unbalanced due to the enhanced thermal
insulation provided by the fluid-filled gap and the additional light reflected by the cover 126B. To
compensate for these effects, the sensing device 100 is shown with an optional signal channel cover
126A mounted over the signal channel opening 122A. The signal channel cover 126A is identical
to the reference channel cover 126B described above but is modified to permit direct contact
between the signal channel indicator dem illustrated embodiment, the cover 126A is rendered porous by forming a bore 132 through the
cover. The bore 132 is preferably much smaller than the size of the opening 122A (e.g., less than
about 50% of the opening area) to mimic the reflectance ai*l thermal properties of the ref^^
channel cover 126B. While a single bore 132 is shown, it will be appreciated mat any number of
channels or bores may be formed in the signal channel cover. Alternatively, or in addition to bores,
grooves may be formed across the annular contact surface in communication with flutes or openings
formed in the plug to provide fluid communication between the indicator element 102 A of the
signal channel and the external environment
[0051] While the sensing device 100 can be fabricated in a variety of ways by those skilled in
the art based on this disclosure, one exemplary method of making the device shown in FIGS. 6 and
7 is as follows. The circuit substrate 114 can be custom manufactured but is preferably of a type
(e.g., alumina ceramic or fiberglass) that can be obtained commercially from a large number of
vendors. Circuits including components such as amplifiers, filters and inductors can be formed on
the substrate 114 in any conventional manner, such as by bonding the components directly onto the
substrate, for example using commonly available solder paste or conductive epoxy such as
ABLEBOND 84 from Ablestick Electronic Materials. The circuit components can then be wire
bonded, if necessary, to complete the circuit connections. Silicon photo-diodes, such as, for
example, part no. 150-20-002 from Advanced Photonics, Inc., can be used as the photosensitive
elements 104A and 104B, and axe preferably flip chip mounted onto the substrate using ball bonds
and conductive epoxy. Filters 124A and 124B can be formed using optical filter material, such as,
for example, LP-595 from CVI Laser Corporation or commercially available sheet stock. The filters
124A and 124B can be formed separately and bonded to the photosensitive elements 104A and
104B, or the filters can be formed directly on the photosensitive elements. As mentioned above, the
radiation source 106 is preferably mounted on the substrate 114 between the photosensitive
elements 104A and 104Bin symmetrical relation to the indicator elements 102Aand 102B.
[0052] The indicator elements 102A and 102B and covers 126A and 126B can be attached to the
housing 116 in any suitable manner but are preferably bonded using adhesives suitable for the
respective materials. A preferred method of fabricating the housing assembly includes bonding the
indicator elements 102A and 102B to an interior surface of the housing 116 such tbat the indicator
molecules contained by the membranes &ce outwardly of the housing through the respective
openings 122A and 122B in the housing and bonding me covers 126A and 126B to an exterior
surface of the housing over the openings. Preferably, me step of bonding or otherwise sealing the
reference cover 126B is performed in an environment having properties appropriate for the
environment in which measurements are to be taken. Alternatively, the chamber can be filled with a
fluid that is different from the external medium (so long as, in the case of a gaseous analyte, the
partial pressure of the analyte in the chamber fluid is within the range of expected partial pressures
of the analyte in the external medium). For example, it has been found mat a device with an air-
filled reference chamber can be used effectively to detect dissolved oxygen over a wide range of
partial pressures in a liquid medium such as water or blood.
[0053] The housing 116 can be attached to the substrate 114 in any conventional manner but is
preferably bonded thereto using an adhesive. An optically transparent encapsulant 134 can be
injected into the space R between the housing 116 and the substrate 114 to serve as a waveguide
and, together with the covers 126A and 126B, provide environmental protection for the circuitry. If
the housing 116 is formed of a relatively flexible material, the encapsulant 134 can also help
mair|fait> spatial alignment of optical components such as the membranes and me photosensitive
elements.
[0054] An exemplary operation of the electro-optical sensing device 100 shown in FIGS. 6 and 7
is as follows. The sensing device 100 is positioned in an environment or medium of interest to
measure the concentration of an analyte in the medium. In an exemplary embodiment, the
environment is ak within a respiratory circuit and the analyte is oxygen. When a measurement is
desired, power is supplied to the radiation source 106 to cause the source to emit radiation in the
sensing device. In the illustrated embodiment, power is drawn from an external source via the leads
112. It will be appreciated, however, that power can be provided from an internal power source
such as a battery or from an external source via an induction circuit formed in the sensing device as
described in the aforementioned U.S. Patent No. 6,330,464, incorporated herein by reference.
[0055] The radiation emitted by the radiation source 106 propagates wito me sensing device
(as shown generally by arrows in FIG. 7) and reaches both the signal membrane 103Aandthe
reference membrane 103B. Indicator molecules contained by these respective membranes are
excited by the radiation and, in turn, radiate light back into the sereing device (as also shown
generally by arrows). The light radiated by the indicator membranes 103A and 103B is modulated
(i.e., attenuated or enhanced) by the local presence of an analyte. For example, h is known that the
orange-red fluorescence of the complex tris(4,7- perchlorate is quenched by the local presence of oxygen. As mentioned above, the sealed chamber
108 in the sensing device holds a fluid 110 with a suitable concentration of analyte in direct contact
with the reference membrane 103B whereas the signal channel is exposed to the external
environment or medium. Thus, modulation of the light radiated from the signal membrane 103A
should be due in part to changes in the amount of analyte present in the external environment
whereas modulation of the light radiated from the reference membrane 103B should be due entirely
to other factors such as temperature, photo-oxidation, and fluctuations in the power source. Since
the covers 126A and 126B mounted over each of the openings 122A and 122B in the housing 116
are substantially similar in structure, these other factors should similarly affect both channels.
[0056] It should be understood that, in the case of gaseous analyte, the above sensing device
actually measures the partial pressure of the analyte, the behavior of which is widely understood
Although the sensing device measures partial pressure, this is readily converted to concentration, if
desired, using known techniques.
[0057] Light from each of the indicator elements 102A and 102B propagates through the sensing
device to a corresponding photosensitive element 104A or 104B via a filter 124A or 124B. Filters
124A and 124B are configured to allow the light emitted by the indicator molecules to reach the
photosensitive elements 104A and 104B while filtering out scattered light from the radiation source
(and, depending upon circumstances, ambient ligbl that may interfere wim the signal).
Photosensitive elements 104A and 104B generate electrical outputs in response to the light received
from the indicator elements 102A and 102B, respectively. These outputs can be transmitted directly
to an external device via the leads 112 for processing and/or processed internally using circuits
formed in 1he sensing device 100 before transmission. An output proportional only to analyte
concentration in the external environment can be obtained by taking the ratio of the signal and
reference channel outputs since factors other than analyte concentration will tend to affect both the
signal and reference channels in equal measure and, thus, be canceled.
[0058] FIG. 8 shows actual test data of signal and reference channel outputs for a sensing device
100 as shown mHGS. 6 aal 7 havmg a reference c The test was conducted
under the same conditions described above in connection wffli the sensing device 10 as shown in
FIG. 4. As can be seen, the reference and signal channel outputs A and B for device 100 respond in
like manner over time to environmental and systemwdiangessou^theiatioof thec^itputs C will
always be a flatline absent changes in analyte concentration m the external medium. Theratiocan
thus be used to provide an output proportional only to analyte change.
[0059] It is contemplated that the sensing device 100 illustrated in FIGS. 6 and 7 can be
modified in a variety of ways. For example, the size and/or shape of the packaging can be modified
to suit various applications. The packaging can include leads as shown or any other means for
establishing connections with external devices including, without limitation, wireless connections
established using radio-frequency (RF) transmitters and receivers. The device can be powered by an
internal source such as a battery or by an external source via leads, induction, or some other
mechanism.
[0060] The configuration and arrangement of the various features of the device can also be
varied. For example, the openings in the top wall of the housing can be circular as shown,
rectangular, or have any other configuration. The openings can be arranged anywhere in me
housing but are preferably symmetrically arranged relative to the radiation source to ensure
commonality between the signal and reference channels. Similarly, the indicator elements can be
rectangular as shown, circular, or have any other configuration. The indicator membranes can be
carried on a substrate or mounted on other parts of the device such as the covers. 'When a separate
membrane substrate is used it can be a plate-like member as sbx>wn, a wavegdde material fusing me
space between the internal components of the device, or have any other suitable configuration. In
addition, the indicator elements can be disposed above or below the top wall of the housing, within
an opening formed in the top wall of the housing, or in pockets formed in the encapsulant Also, a
baffle or partition can be positioned between the indicator elements to inhibit "cross-talk" of light
radiated from the signal and reference channel membranes. Such a baffle would preferably be
impervious to radiation mat could affect the photosensitive elements.
[0061] The housing can have any configuration to support the various components of the device.
For example, the housing can include one or more walls that extend from the substrate to support
indicator elements in spaced relation to the photosensitive elements. Preferably, the space
between the excitation source, indicator elements, and photosensitive elements is filled with an
encapsulant formed of a waveguide material. If an encapsulant is used, the encapsulant can serve
as the housing to support the operational components without the use of walls.
(0062] While the use of fluorescent indicator molecules to measure oxygen is described above, it
should be understood that other types of indicator molecules and combinations thereof can be
used depending on the particular analyte of interest. For example, light-absorbing indicator
molecules, such as those described in U.S. Patent No. 5,512,246, the disclosure of which is
incorporated herein by reference, can be used to measure polyhydroxyl compounds such as
sugars, including glucose. In another example, indicator molecules, such as those described in
U.S. Patent No. 6,344,360, Indian Patent Application No. 987/KOLNP/2003, filed July 31,2003,
U.S. Patent Application Serial No. 10/028,831 filed December 28, 2001 and U.S. Provisional
Patent Application Serial No. 60/363,885 filed March 14,2002, the disclosures of which are
incorporated herein by reference, can be used to measure vicinal diols, polyhydroxyl compounds
such as sugars, including glucose. In some circumstances it may be possible to utilize fluorescent
indicator molecules in one of the membranes while using light-absorbing indicator molecules in
the other of the membranes. In most cases, however, the signal and reference membranes will
both use like indicator molecules, such as described herein.
[0063] Preferably, both the reference channel and the signal channel include a cover mounted
over a corresponding opening formed in the sensing device housing. The signal channel cover is
preferably similar to the reference channel cover but can be of significantly different design so
long as adequate commonality is achieved. The signal channel can also be operated without a
cover if desired. The reference and signal channel covers can include planar members that sit
flush against a surface of the housing, convex members that define a space adjacent a surface of
the housing, plugs that fit within openings in the housing, or any combination of the foregoing.
The covers can also be formed as an integral part of the housing.
[0064] In another embodiment, the device can be provided with multiple radiation sources (e.g.,
LEDs) disposed within the same housing or in different housings mounted on the same substrate.
In yet another embodiment, the device can be modiied so as to include a plurality of signal
membranes (e.g., to measure the same or different analytes) and/or a plurality of reference
membranes (eg., to measure the same or different optical properties). In addition, while the
embodiment shown herein has only two channels (Le., a signal channel and a reference channel),
other embodiments could contain multiple signal channels and/or multiple reference channels.
[0065] The ability of mis device to measure oxygen levels from inhaled and exhaled respiratory
gases has significant medical utility. For example, the device can be utilized in conjunction with
flow or volume measuring devices to determine the uptake and release of respiratory gases, enabling
the measurement of critical medical parameters such as metabolic rate (calorie expenditure),
indirect cardiac output based on the Fick principle (first described in theory by Adolph Fick in
1870), pulmonary function, and onset of shock. Many of these medical diagnostic determinations
require the measurement of the partial pressure respiratory gases at the very end of an exhalation
(known as end-tidal p02 or end-tidal pC02 levels). While the illustrated example is preferably used
for the measurement of oxygen, the sensing device can easily be modified to measure other analytes,
for example by use of different indicator membranes.
[0066] It will be appreciated that the sensing device of the present invention can be used in any
environment having one or more anarytes mat can be sensed. For example, the sensing device can
be employed in mediums made up of solid, liquid or gaseous mediums or combinations thereof
The reference chamber is preferably filled with a medium corresponding to the external medium but
can be filled with any type of medium. For example, tests have shown that a sensing device with a
sealed reference chamber filled with air can be used to measure oxygen concentration in a liquid
environment In some cases, it may be desirable to create a vacuum in the chamber.
[0067] While the sensing device has been described above as measuring intensity, it is also
possible to detect the presence and concentration of an analyte by measuring fluorescence decay
time with the device.
[0068] While the invention has been described in detail above, the invention is not intended to
be limited to the specific embodiments as described. It is evidem that nwse skilled in the art may
now make numerous uses and modifications of and departures from the specific embodiments
described herein without departing from the inventive concepts.
We Claim:
1. An electro-optical sensing device for detecting the presence of an analyte in a
medium, said sensing device comprising:
a. a radiation source that emits radiation;
b. a first and a second photosensitive elements configured to receive radiation
and output an electrical signal in response thereto;
c. a first and a second indicator elements positioned to receive radiation from the
radiation source and to transmit radiation to said first and second photosensitive elements,
said first and second indicator elements each containing indicator molecules with an optical
characteristic responsive to the presence of an analyte; and
d. a hermetically sealed chamber covering said second indicator element so as to
render said second indicator element insensitive to the presence of the analyte in a medium
external to the device,
wherein said first indicator element is in fluid communication with said external
medium and said second indicator element fs not in fluid communication with said external
medium, and
wherein said hermetically-sealed chamber contains an analyte-containing fluid in
contact with said second indicator element.
2. The sensing device as claimed in 1, having a housing, wherein said first
and second indicator elements, said first and second photosensitive elements, and said
radiation source are mounted in said housing.
3. The sensing device as claimed in 1, having an analyte-impermeable cover
mounted on the housing which defines at least a portion of the chamber covering the second
indicator element.
4. The sensing device as claimed in 1, having an analyte-permeable cover
mounted on the housing over the first indicator element.
5. The sensing device as claimed in 4, wherein said analyte-permeable cover has a
bore formed therethrough to provide fluid communication between the first indicator
element and the external medium.
6. The sensing device as claimed in 1, wherein said first indicator element and said
first photosensitive comprise a signal channel, and wherein said second indicator element
and said second photosensitive element comprise a reference channel.
7. The sensing device as claimed in 1, wherein said analyte-containing fluid is a
liquid.
8. The sensing device as claimed in 1, wherein said analyte-containing fluid is a
gas.
9. The sensing device as claimed in 1, wherein an analyte in said analyte-containing
fluid is the same type of analyte to be detected in the external medium.
10. The sensing device as claimed in 1, wherein an analyte in said analyte-containing
fluid is a different type of analyte than the analyte to be detected in the external medium.
11. The sensing device as claimed in 1, wherein said indicator molecule has an
optical characteristic responsive to the presence of oxygen.
12. The sensing device as claimed in 11, wherein said indicator molecule is tris (4,7-
diphenyl- 1, 10-phenanthroline) ruthenium (II) perchlorate.
13. A method for detecting an analyte of interest in a medium, said method
comprising :
a. providing an electro-optical sensing device containing a first and a second
indicator elements each containing indicator molecules haying an optical characteristic
responsive to the presence of an analyte and positioned to receive excitation radiation from
a radiation source and to transmit resultant radiation to a pair of photosensitive elements,
and wherein said first indicator element is covered by a cover having at least one bore
therethrough and said second indicator element is covered by an analyte-impermeable,
hermetically-sealed chamber that renders the second indicator element insensitive to the
presence of the analyte in the medium external to the device;
b. introducing a medium to contact said first indicator element through the bore
in said cover;
c. activating said radiation source to emit radiation to said first and second
indicator elements,
d. optically detecting an optical response of said first and second indicator
elements; and
e. evaluating said response to determine the presence or concentration of at least
one analyte of interest in the sample,
wherein said response detected from said second indicator element is used as a
reference to cancel variables that affect both said first and second indicator elements.



An electro-optical sensing device for detecting the presence and concentration of an analyte in a liquid or gaseous
medium includes a pair of indicator elements positioned to receive radiation from a radiation source and transmit radiation to a pair
of photosensitive elements. The indicator elements each contain indicator molecules having an optical characteristic responsive to
the presence of an analyte; however, one of the indicator elements is covered by an analyte-impermeable chamber that renders the
indicator element insensitive to the presence of the analyte in the medium outside the chamber so that it can be used as a reference to
cancel environmental and systemic variables that affect both indicator elements. The chamber preferably holds an analyte-containing
fluid in contact with the reference indicator element so that the indicator elements operate under nominally identical conditions. The
indicator element used to measure the analyte in the external medium is preferably also covered, but in a manner that provides direct
contact between the analyte and the indicator element.

Documents:

1549-kolnp-2003-abstract.pdf

1549-KOLNP-2003-AMENDE CLAIMS.pdf

1549-KOLNP-2003-AMENDED PAGES.pdf

1549-kolnp-2003-assignment 1.1.pdf

1549-kolnp-2003-assignment.pdf

1549-KOLNP-2003-CANCELLED PAGES.pdf

1549-kolnp-2003-claims.pdf

1549-KOLNP-2003-CORRESPONDENCE 1.1.pdf

1549-KOLNP-2003-CORRESPONDENCE 1.3.pdf

1549-KOLNP-2003-CORRESPONDENCE-1.2.pdf

1549-kolnp-2003-correspondence.pdf

1549-kolnp-2003-description (complete).pdf

1549-KOLNP-2003-DRAWINGS.pdf

1549-kolnp-2003-examination report.pdf

1549-KOLNP-2003-FORM 1.pdf

1549-kolnp-2003-form 18 1.1.pdf

1549-kolnp-2003-form 18.pdf

1549-kolnp-2003-form 2.pdf

1549-KOLNP-2003-FORM 27.pdf

1549-kolnp-2003-form 3 1.1.pdf

1549-kolnp-2003-form 3.pdf

1549-kolnp-2003-form 5 1.1.pdf

1549-kolnp-2003-form 5.pdf

1549-KOLNP-2003-FORM-27.pdf

1549-kolnp-2003-gpa 1.1.pdf

1549-kolnp-2003-gpa.pdf

1549-kolnp-2003-granted-abstract.pdf

1549-kolnp-2003-granted-claims.pdf

1549-kolnp-2003-granted-description (complete).pdf

1549-kolnp-2003-granted-drawings.pdf

1549-kolnp-2003-granted-form 1.pdf

1549-kolnp-2003-granted-specification.pdf

1549-KOLNP-2003-OTHERS.pdf

1549-KOLNP-2003-PETITION UNDER RULE 137.pdf

1549-KOLNP-2003-REPLY TO EXAMINATION REPORT.pdf

1549-kolnp-2003-specification.pdf


Patent Number 243358
Indian Patent Application Number 1549/KOLNP/2003
PG Journal Number 41/2010
Publication Date 08-Oct-2010
Grant Date 07-Oct-2010
Date of Filing 28-Nov-2003
Name of Patentee SENSORS FOR MEDICINE AND SCIENCE, INC.
Applicant Address 12321 MIDDLEBROOK ROAD, GERMANTOWN, MD
Inventors:
# Inventor's Name Inventor's Address
1 COLVIN JR. ARTHUR E 4155 BALTIMORE NATIONAL PIKE, MT. AIRY, MD 21771
2 LYNN ROBERT W 17034 BARN RIDGE DRIVE, SILVER SPRING, MD 20906
PCT International Classification Number G01N 21/77
PCT International Application Number PCT/US2002/13734
PCT International Filing date 2002-05-03
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 60/288,498 2001-05-04 U.S.A.