Title of Invention	A METHOD OF DETECTING THE CHANGE IN CONCENTRATION OF AN ORGANIC DYE IN A SAMPLE
Abstract	A METHOD OF DETECTING THE CHANGE IN CONCENTRATION OF AN ORGANIC DYE IN A SAMPLE A method of detecting the change in concentration of an organic dye in a sample characterised by the steps of determining the RRE (radiative rate enhancement) values which are related to the respective dye concentrations, the said RRE values being obtained by measuring the fluorescence lifetimes of the said dye doped in single microspherical polymer particles.

Title of Invention

A METHOD OF DETECTING THE CHANGE IN CONCENTRATION OF AN ORGANIC DYE IN A SAMPLE

Abstract

A METHOD OF DETECTING THE CHANGE IN CONCENTRATION OF AN ORGANIC DYE IN A SAMPLE A method of detecting the change in concentration of an organic dye in a sample characterised by the steps of determining the RRE (radiative rate enhancement) values which are related to the respective dye concentrations, the said RRE values being obtained by measuring the fluorescence lifetimes of the said dye doped in single microspherical polymer particles.

Full Text	This invention relates to a chemical concentration sensor for detecting the change in concentration of an organic dye or a chemical in a sample. The concentration sensor is based on concentration dependence of 'radiative-rate enhancement' (RRE). The RRE is obtained by measuring the fluorescence lifetimes of a dye doped in single microspherical polymer particles. In other words lifetime of the dye in the microsphere is a function of concentration which inn turn is a function of RRE. This invention makes use of the effect of Mie resonances, on the fluorescence lifetime. In the past, Mie resonances (or morphology dependent resonances, MDR) have been studied both, by spectral, as well as by fluorescence lifetime measurements. It is for the first time we have constructed a sensor based on a parameter (RRE) related to the measurement of fluorescence lifetime as a concentration sensor. The detection of concentration or change in concentration of an organic dye or a chemical in a sample is important as seen from the following points: For proper functioning of the ecosystem, concentration levels of harmful chemicals or pollutants in the environment have to be constantly kept under check. This requires sensing of the concentration of the chemicals. To the best of our knowledge, following are the existing techniques (based on spectral information) for sensing the concentration of chemicals by using microspheres: a. A microsphere whispering-gallery mode evanescent-wave sensor: This sensor has been used in the detection and identification of atoms or molecules In this sensor, the species to be detected is made to interact with the evanescent field of a resonant mode of the microsphere. The species to be detected absorbs a portion of the microsphere's evanescent light energy at compound-specific wavelengths. This portion of the absorption is then used to detect and identify the subject FLOMS technicals and Sandeep Abstract species. Its concentration may be determined from the absorption signal on the light in reflection or transmission, A sensor of electromagnetic microcavities: This sensor has been used for detection of chemical and/or biological compounds by detecting the probe beam at which the resonance of the microcavity is observed, which is indicative of a particular species being present An optical microsphere sensor: This sensor has been used for the detection of traces of chemical species by making the species absorb the light from the resonances of the microsphere. The detection is done by measuring the change in quality factor of the resonant mode of the microcavity A calibration of the change in quality factor renders information of the concentration of the absorbing species. Application of single microspheres for the detection of unlabelled macromolecules in a low concentration solution. Single silica microspheres were utilized for the detection of non-labeled biological macromolecules like proteins in solution. This sensor makes use of the shift in the position of the cavity resonance due to the increase in the radius of the microsphere by the adsorption of the macromolecules on to its surface. The drawbacks of the known sensors are: The sensitivity of the measurement of the quality factor or the shift in the position of the MDR is highly dependent on the high-resolution spectral measurement techniques of the order of 1.34 x 10'5 nm . In general, larger microspheres of diameter of- 300 μm to 400 μm are used for these techniques. A lowest limit of 40 μm has been estimated on the diameter of the single microsphere to be used as a concentration sensor, using the steady state spectral detection. Therefore the spatial resolution of the sensor cannot be less than 40 μm. c. The necessity of high quality factors also imposes the usage of high refractive index (m) materials like silica {m =1.55) or amorphous sapphire (m =1.7) for the microspheres. FLOMS technicals and Sandeep Abstract Measurement of fluorescence lifetime in known to be a more accurate way of characterizing a material in comparison to the spectral measurements. While spectral overlaps of various chemicals pose a serious hindrance in detection using spectral techniques, the fluorescence lifetime of chemicals are known to be unique. Hence, we have utilized the technique of fluorescence lifetime measurements for the detection of concentration of fluorescent dyes by embedding them in single microspheres. The advantages of this invention are: 1. Since our sensor uses cavity resonances of low quality factor (0, microspheres as small a 3 μm can be used for sensing purpose, which is >10 times smaller than the lower limit of the diameter imposed by other techniques . Thus detection is done at a much smaller volume than available till now. 2. In our sensor the sensitivity of concentration sensing is found to be the highest for the smallest diameter of the microsphere. 3. The sensitivity of detection of a change in concentration is found to be highest for the smallest concentration. 4. Our sensor uses polymethyl methacrylate (PMMA) single microspheres (m =1.49), which are commercially available 5. Our sensor does not require the use of high-resolution spectral measurement techniques, which are almost 10 times more expensive. It can be done even with a few nm resolution equipment available in any lab. The industrial applications of this invention are many and varied: Sensing of traces of chemicals in very small volumes is of immense commercial interest in the fields of: 1. Pharmaceutical Manufacturing 2. Environmental Monitoring 3. Process Control FLOMS technicals and Sandeep Abstract The salient points of difference between known concentration sensing and the present invention using single microspheres are: 1. The present invention uses fluorescence lifetime measurement while other sensors use steady-state spectral measurements. 2. With the present invention, single microspheres as small as 3 μm can be used as sensors (hence a resolution of space >10 times smaller than the smallest proposed for similar sensitivity of detection by other techniques). 3. The present invention is more sensitive for a change in concentration at smaller concentrations. 4. The present invention does not require the use of high-resolution spectral measurements, which is about 10 times more expensive The following is an Example of the measurement of fluorescence lifetimes of the dye doped single microspheres: A slide glass with the doped microspheres (doping is done by immersing microspheres in a dye solution) was mounted on the stage of a fluorescence microscope (Nikon, Eclipse E400). The fluorescence emission from the single microsphere was collected with a 40X objective lens using a >420 nm cut off emission filter and was fed to a photomultiplier tube (R928, Hamamatsu) through a monochromator (Oriel, 772501). A 40 ps diode laser at 408 nm (PILAS, Advanced Photonics Ltd) was used as the excitation source. The output from the photomultiplier tube was fed to a time correlated single photon counting card (Edinburgh Instruments, TC900) through an external delay unit. The full width at half maximum of the instrument response function (IRF) was ~ 0.36 ns. The fluorescence decay profiles were deconvolved with the IRF and fitted to Exponential functions (Edinburgh Instruments, T900) using least square fitting method. The quality of the fit was judged by %2 and the weighted residuals. We perform the fluorescence lifetime study of 9AAHH doped single microspheres. A single exponential fluorescence decay can be described by FLOMS technicals and Sandeep Abstract where Io is the peak intensity and I is the intensity at time t. r is the fluorescence lifetime. For a double exponential decay the function used is where B1 and B2 are the amplitudes of the lifetime constants t1 and t2 respectively. The experimental curves are fitted with eqn. 1 or 2 and the fitting is judged by the residuals and χ2. For the best fits the residuals were distributed evenly on both sides of the fitted curve and the values of the χ2 was near 1. Table 1 gives the observed fluorescence lifetimes of 9AAHH in single microspheres doped with a concentration of 5 x 10-4 M along with the fitting parameters. It was observed that the fluorescence decay of a ~ 20 μm-diameter microsphere fits well with a single exponential decay function with a decay time of 12.2 ns T. On reduction in the diameter of the microsphere till 12 μm the fluorescence decay fits well with the single exponential function without any considerable change in the fluorescence lifetime. Table 1. The fluorescence lifetimes (tj, x%) for 9AAHH along with the corresponding amplitudes (Bi, B2) and x for single microspheres of PMMA with a doping concentration of 5 x 10 M. FLOMS technicals and Sandeep Abstract However a further reduction in the diameter of the microsphere to 10 μm results in appearance of an additional faster component Tl in the fluorescence decay profile. The new component with a decay time of 7.56 ns has a smaller amplitude (20 %) relative to the former. A further decrease in the microsphere diameter is followed by a decrease of the decay time of the new component with concomitant increase in its amplitude (Table 1). For a microsphere of ~ 3 )μm diameter, the new component has a decay time of 0.78 ns with an amplitude of 84 %, whereas the slow component shows a decay time of 10.40 ns with an amplitude of 16 %. RRE is defined as the ratio of the lifetime of the dye observed from the bulk T to that obtained from a microsphere T1. Since there was a small reduction in the fluorescence lifetime of the slower component, the RRE was calculated for both the components as a function of the microsphere diameter. It is observed that the variation in the value of the slow component is very small and it maintains almost the same radiative rate with decrease in the diameter of the microsphere. On the other hand the fast component shows an RRE of as high as ~ 16 for a ~ 3 jim diameter microsphere (fig. 2). It is observed that the RRE shows a threshold like behavior for the diameter of the microsphere. The threshold diameter is found to be ~ 10 μm. Comparison of RRE obtained through fluorescence lifetime measurements of various concentrations of 9AAHH doped in single microspheres reveals the concentration sensing capability of the technique. For this study we took 3 concentrations (5 x 10-4 M, 1 x 10-3 M, 3.5 x 10-3 M). The threshold value of the diameter for the RRE does not change with a change in the doping concentration. However, it was observed that the magnitude of the RRE obtained for the fast component falls off rapidly on increasing the adsorbed concentration. This behavior is shown in Table 2. Thus, while for a - 3 μm diameter single microsphere an RRE is found to be 15.76 at a doping concentration of 5 x 10'4 M, it is reduced to 5.94 for doping concentration of 3.5 x 10~3 ML As mentioned earlier, the longer lifetime component does not show major changes with the concentration. FLOMS technicals and Sandeep Abstract Table 2. The calibration table of RRE of the faster component of 9AAHH in single microspheres for varying concentrations as a function of the microsphere diameter. In the case of another dye viz. Eosin-Y, we have observed the faster component to show RRE of 2.46 at a concentration of 5 x 10"4 M for a 3 μm diameter single microsphere. It was also seen that the trend of reduction of RRE with an increase in concentration was present in this case also. The RRE value reduced to 2.05 and 1.67 for doping concentrations of 7.5 x 10"4 M and 1 x 10"3 M, respectively. In the case of eosin-Y, it was observed that the slower component of the fluorescence lifetime also undergoes a radiative rate inhibition (RRI), in contrast to the case of 9AAHH. The RRI was also found to be sensitive to doping concentration and hence could be made use for sensing purpose as well. There is higher sensitivity for smaller diameter microspheres. As shown in table 2, for a ~ 3 jam diameter single microsphere the RRE is found to drop from 15.76 at a doping concentration of 5 x 10"4 M, to 8.43 for doping concentration of 1 x 103 M. On the other hand, RRE falls from 1.62 to 1.58 (a fall of only 0.04) for a 10 μm diameter microsphere for the same change in concentration. This shows that the single microsphere of smallest diameter is the most sensitive towards the change in the concentration of the adsorbed dye molecule. There is higher sensitivity at smaller concentrations Table 2 also shows that for a fixed diameter of 3 μn of the microsphere, a doubling of the concentration from an initial concentration of 5 x 10 M to 1 x 10" M FLOMS techniques and Sandeep Abstract yields a change in RRE of 7.33 (from 15.76 to 8.43). However, for the same 3 μm diameter microsphere, an increase of 3.5 times the concentration, from 1 x 10"3 M to 3.5 x 10"3 M yields only a change of 2.49 (from 8.43 to 5.94). This shows that the FLOMS technique is more sensitivity at smaller concentrations. In addition to 9AAHH, in eosin-y we have seen that the RRE goes from 2.46 at a concentration of 5 x 104 Mto 2.05 and 1.67 for doping concentrations of 7.5 x 10'4 M and 1x10" M, respectively. In addition to RRE, RRI was also observed in this case, which can also be used as a sensing parameter similar to RRE. Other molecules such as Pyrene in PMMA microspheres, and laser dyes like Rhodamine 6G, Rhodamine B and chelated Europium ions in microdroplets which have been shown to exhibit the RRE effect, are potential candidates for use as concentration sensors. The following points are noteworthy This invention shows that there is a decrease in the magnitude of the RRE with increase in the adsorbed dye concentration. Hence this invention can be used as a concentration sensor. In this invention, the sensitivity of the detection of the adsorbed concentration of dye molecules increases on decreasing the diameter of the microsphere. This invention can access spaces as small as 3 μm by using the diameter of the microsphere that is used as a sensor. In this invention, the sensitivity of detection of a change in concentration is found to be higher at smaller concentrations. We have explained the results on the basis of a change in refractive index of the single microsphere. FLOMS teehni$ag£kU hnd Sandeep Abstract End Product Concentration sensing with single microspheres using RRE variation RRE: Radiative rate enhancement New idea: RRE variation with concentration→ RR E based concentration sensor Schematic: FLOMS technique, Bisht and Sandeep 11:20:46 AM 4/13/2005 We Claim: 1. A method of detecting the change in concentration of an organic dye in a sample comprising the steps of determining the RRE (radiative rate enhancement) values which are related to the respective dye concentrations, the said RRE values being obtained by measuring the fluorescence lifetimes of the said dye doped in single microspherical polymer particles, the values of RRE and concentrations so obtained being plotted on a chart for determination of other values of concentration against related values of RRE. 2. A method of detecting the change in concentration of an organic dye in a sample substantially as herein described and illustrated with reaspect to the Examples and Tables Dated this the 19th May 2005

Full Text

This invention relates to a chemical concentration sensor for detecting the change in concentration of an organic dye or a chemical in a sample. The concentration sensor is based on concentration dependence of 'radiative-rate enhancement' (RRE). The RRE
is obtained by measuring the fluorescence lifetimes of a dye doped in single microspherical polymer particles. In other words lifetime of the dye in the microsphere is a function of concentration which inn turn is a function of RRE. This invention makes use of the effect of Mie resonances, on the fluorescence lifetime. In the past, Mie resonances (or morphology dependent resonances, MDR) have been studied both, by spectral, as well as by fluorescence lifetime measurements. It is for the first time we have constructed a sensor based on a parameter (RRE) related to the measurement of fluorescence lifetime as a concentration sensor.
The detection of concentration or change in concentration of an organic dye or a chemical in a sample is important as seen from the following points:
For proper functioning of the ecosystem, concentration levels of harmful chemicals or pollutants in the environment have to be constantly kept under check. This requires sensing of the concentration of the chemicals.
To the best of our knowledge, following are the existing techniques (based on spectral information) for sensing the concentration of chemicals by using microspheres:
a. A microsphere whispering-gallery mode evanescent-wave sensor: This sensor has been used in the detection and identification of atoms or molecules In this sensor, the species to be detected is made to interact with the evanescent field of a resonant mode of the microsphere. The species to be detected absorbs a portion of the microsphere's evanescent light energy at compound-specific wavelengths. This portion of the absorption is then used to detect and identify the subject
FLOMS technicals and Sandeep
Abstract

species. Its concentration may be determined from the absorption signal on the light in reflection or transmission,
A sensor of electromagnetic microcavities: This sensor has been used for detection of chemical and/or biological compounds by detecting the probe beam at which the resonance of the microcavity is observed, which is indicative of a particular species being present
An optical microsphere sensor: This sensor has been used for the detection of traces of chemical species by making the species absorb the light from the resonances of the microsphere. The detection is done by measuring the change in quality factor of the resonant mode of the microcavity A calibration of the change in quality factor renders information of the concentration of the absorbing species.
Application of single microspheres for the detection of unlabelled macromolecules in a low concentration solution. Single silica microspheres were utilized for the detection of non-labeled biological macromolecules like proteins in solution. This sensor makes use of the shift in the position of the cavity resonance due to the increase in the radius of the microsphere by the adsorption of the macromolecules on to its surface. The drawbacks of the known sensors are:
The sensitivity of the measurement of the quality factor or the shift in the position of the MDR is highly dependent on the high-resolution spectral measurement techniques of the order of 1.34 x 10'5 nm . In general, larger microspheres of diameter of- 300 μm to 400 μm are used for these techniques. A lowest limit of 40 μm has been estimated on the diameter of the single microsphere to be used as a concentration sensor, using the steady state spectral detection. Therefore the spatial resolution of the sensor cannot be less than 40 μm. c. The necessity of high quality factors also imposes the usage of high refractive index (m) materials like silica {m =1.55) or amorphous sapphire (m =1.7) for the microspheres.
FLOMS technicals and Sandeep Abstract

Measurement of fluorescence lifetime in known to be a more accurate way of characterizing a material in comparison to the spectral measurements. While spectral overlaps of various chemicals pose a serious hindrance in detection using spectral techniques, the fluorescence lifetime of chemicals are known to be unique. Hence, we have utilized the technique of fluorescence lifetime measurements for the detection of concentration of fluorescent dyes by embedding them in single microspheres.
The advantages of this invention are:
1. Since our sensor uses cavity resonances of low quality factor (0, microspheres as small a 3 μm can be used for sensing purpose, which is >10 times smaller than the lower limit of the diameter imposed by other techniques . Thus detection is done at a much smaller volume than available till now.
2. In our sensor the sensitivity of concentration sensing is found to be the highest for the smallest diameter of the microsphere.
3. The sensitivity of detection of a change in concentration is found to be highest for the smallest concentration.
4. Our sensor uses polymethyl methacrylate (PMMA) single microspheres (m =1.49), which are commercially available
5. Our sensor does not require the use of high-resolution spectral measurement techniques, which are almost 10 times more expensive. It can be done even with a few nm resolution equipment available in any lab.
The industrial applications of this invention are many and varied: Sensing of traces of chemicals in very small volumes is of immense commercial interest in the fields of:
1. Pharmaceutical Manufacturing
2. Environmental Monitoring
3. Process Control
FLOMS technicals and Sandeep Abstract

The salient points of difference between known concentration sensing and the present invention using single microspheres are:
1. The present invention uses fluorescence lifetime measurement while other sensors use steady-state spectral measurements.
2. With the present invention, single microspheres as small as 3 μm can be used as sensors (hence a resolution of space >10 times smaller than the smallest proposed for similar sensitivity of detection by other techniques).
3. The present invention is more sensitive for a change in concentration at smaller concentrations.
4. The present invention does not require the use of high-resolution spectral measurements, which is about 10 times more expensive
The following is an Example of the measurement of fluorescence lifetimes of the dye doped single microspheres:
A slide glass with the doped microspheres (doping is done by immersing microspheres in a dye solution) was mounted on the stage of a fluorescence microscope (Nikon, Eclipse E400). The fluorescence emission from the single microsphere was collected with a 40X objective lens using a >420 nm cut off emission filter and was fed to a photomultiplier tube (R928, Hamamatsu) through a monochromator (Oriel, 772501). A 40 ps diode laser at 408 nm (PILAS, Advanced Photonics Ltd) was used as the excitation source. The output from the photomultiplier tube was fed to a time correlated single photon counting card (Edinburgh Instruments, TC900) through an external delay unit. The full width at half maximum of the instrument response function (IRF) was ~ 0.36 ns. The fluorescence decay profiles were deconvolved with the IRF and fitted to Exponential functions (Edinburgh Instruments, T900) using least square fitting method. The quality of the fit was judged by %2 and the weighted residuals.
We perform the fluorescence lifetime study of 9AAHH doped single microspheres. A single exponential fluorescence decay can be described by
FLOMS technicals and Sandeep Abstract

where Io is the peak intensity and I is the intensity at time t. r is the fluorescence lifetime. For a double exponential decay the function used is
where B1 and B2 are the amplitudes of the lifetime constants t1 and t2 respectively. The experimental curves are fitted with eqn. 1 or 2 and the fitting is judged by the residuals and χ2. For the best fits the residuals were distributed evenly on both sides of the fitted curve and the values of the χ2 was near 1.
Table 1 gives the observed fluorescence lifetimes of 9AAHH in single microspheres doped with a concentration of 5 x 10-4 M along with the fitting parameters. It was observed that the fluorescence decay of a ~ 20 μm-diameter microsphere fits well with a single exponential decay function with a decay time of 12.2 ns T. On reduction in the diameter of the microsphere till 12 μm the fluorescence decay fits well with the single exponential function without any considerable change in the fluorescence lifetime.
Table 1.
The fluorescence lifetimes (tj, x%) for 9AAHH along with the corresponding amplitudes
(Bi, B2) and x for single microspheres of PMMA with a doping concentration of 5 x 10
M.

FLOMS technicals and Sandeep Abstract

However a further reduction in the diameter of the microsphere to 10 μm results in appearance of an additional faster component Tl in the fluorescence decay profile. The new component with a decay time of 7.56 ns has a smaller amplitude (20 %) relative to the former. A further decrease in the microsphere diameter is followed by a decrease of the decay time of the new component with concomitant increase in its amplitude (Table 1). For a microsphere of ~ 3 )μm diameter, the new component has a decay time of 0.78 ns with an amplitude of 84 %, whereas the slow component shows a decay time of 10.40 ns with an amplitude of 16 %.
RRE is defined as the ratio of the lifetime of the dye observed from the bulk T to that obtained from a microsphere T1.
Since there was a small reduction in the fluorescence lifetime of the slower component, the RRE was calculated for both the components as a function of the microsphere diameter. It is observed that the variation in the value of the slow component is very small and it maintains almost the same radiative rate with decrease in the diameter of the microsphere. On the other hand the fast component shows an RRE of as high as ~ 16 for a ~ 3 jim diameter microsphere (fig. 2). It is observed that the RRE shows a threshold like behavior for the diameter of the microsphere. The threshold diameter is found to be ~ 10 μm.
Comparison of RRE obtained through fluorescence lifetime measurements of various concentrations of 9AAHH doped in single microspheres reveals the concentration sensing capability of the technique. For this study we took 3 concentrations (5 x 10-4 M, 1 x 10-3 M, 3.5 x 10-3 M). The threshold value of the diameter for the RRE does not change with a change in the doping concentration. However, it was observed that the magnitude of the RRE obtained for the fast component falls off rapidly on increasing the adsorbed concentration. This behavior is shown in Table 2. Thus, while for a - 3 μm diameter single microsphere an RRE is found to be 15.76 at a doping concentration of 5 x 10'4 M, it is reduced to 5.94 for doping concentration of 3.5 x 10~3 ML As mentioned earlier, the longer lifetime component does not show major changes with the concentration.
FLOMS technicals and Sandeep Abstract

Table 2.
The calibration table of RRE of the faster component of 9AAHH in single microspheres
for varying concentrations as a function of the microsphere diameter.

In the case of another dye viz. Eosin-Y, we have observed the faster component to show RRE of 2.46 at a concentration of 5 x 10"4 M for a 3 μm diameter single microsphere. It was also seen that the trend of reduction of RRE with an increase in concentration was present in this case also. The RRE value reduced to 2.05 and 1.67 for doping concentrations of 7.5 x 10"4 M and 1 x 10"3 M, respectively. In the case of eosin-Y, it was observed that the slower component of the fluorescence lifetime also undergoes a radiative rate inhibition (RRI), in contrast to the case of 9AAHH. The RRI was also found to be sensitive to doping concentration and hence could be made use for sensing
purpose as well.
There is higher sensitivity for smaller diameter microspheres.
As shown in table 2, for a ~ 3 jam diameter single microsphere the RRE is found to drop from 15.76 at a doping concentration of 5 x 10"4 M, to 8.43 for doping concentration of 1 x 10*3 M. On the other hand, RRE falls from 1.62 to 1.58 (a fall of only 0.04) for a 10 μm diameter microsphere for the same change in concentration. This shows that the single microsphere of smallest diameter is the most sensitive towards the change in the concentration of the adsorbed dye molecule. There is higher sensitivity at smaller concentrations
Table 2 also shows that for a fixed diameter of 3 μn of the microsphere, a doubling of the concentration from an initial concentration of 5 x 10 M to 1 x 10" M
FLOMS techniques and Sandeep
Abstract

yields a change in RRE of 7.33 (from 15.76 to 8.43). However, for the same 3 μm diameter microsphere, an increase of 3.5 times the concentration, from 1 x 10"3 M to 3.5 x 10"3 M yields only a change of 2.49 (from 8.43 to 5.94). This shows that the FLOMS technique is more sensitivity at smaller concentrations.
In addition to 9AAHH, in eosin-y we have seen that the RRE goes from 2.46 at a concentration of 5 x 10*4 Mto 2.05 and 1.67 for doping concentrations of 7.5 x 10'4 M and 1x10" M, respectively. In addition to RRE, RRI was also observed in this case, which can also be used as a sensing parameter similar to RRE.
Other molecules such as Pyrene in PMMA microspheres, and laser dyes like Rhodamine 6G, Rhodamine B and chelated Europium ions in microdroplets which have been shown to exhibit the RRE effect, are potential candidates for use as concentration sensors.
The following points are noteworthy
This invention shows that there is a decrease in the magnitude of the RRE with increase
in the adsorbed dye concentration. Hence this invention can be used as a concentration
sensor.
In this invention, the sensitivity of the detection of the adsorbed concentration of dye
molecules increases on decreasing the diameter of the microsphere.
This invention can access spaces as small as 3 μm by using the diameter of the
microsphere that is used as a sensor.
In this invention, the sensitivity of detection of a change in concentration is found to be
higher at smaller concentrations.
We have explained the results on the basis of a change in refractive index of the single
microsphere.
FLOMS teehni$ag£kU hnd Sandeep Abstract

End Product
Concentration sensing with single microspheres using RRE variation
RRE: Radiative rate enhancement New idea:
RRE variation with concentration→ RR E based concentration sensor
Schematic:

FLOMS technique, Bisht and Sandeep
11:20:46 AM 4/13/2005

We Claim:
1. A method of detecting the change in concentration of an organic dye in a
sample comprising the steps of determining the RRE (radiative rate
enhancement) values which are related to the respective dye concentrations, the said RRE values being obtained by measuring the fluorescence lifetimes of the said dye doped in single microspherical polymer particles, the values of RRE and concentrations so obtained being plotted on a chart for determination of other values of concentration against related values of RRE.
2. A method of detecting the change in concentration of an organic dye in a
sample substantially as herein described and illustrated with reaspect to
the Examples and Tables
Dated this the 19th May 2005

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Patent Number

234769

Indian Patent Application Number

602/CHE/2005

PG Journal Number

29/2009

Publication Date

17-Jul-2009

Grant Date

15-Jun-2009

Date of Filing

19-May-2005

Name of Patentee

INDIAN INSTITUTE OF TECHNOLOGY

Applicant Address

IIT P.O. CHENNAI 600 036

Inventors:

#	Inventor's Name	Inventor's Address
1	PROF. PREM BALLABH BISHT	DEPARTMENT OF PHYSICS IIT CHENNAI 600 036
2	PALLIKKUTH SANDEEP	DEPARTMENT OF PHYSICS IIT CHENNAI 600 036

PCT International Classification Number

G01N21/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA