Sensing device with sol-gel derived film on the light source

Details Sensing device with sol-gel derived film on the light source Sensing device with sol-gel derived film on the light source

1998-05-20

2001-06-05

Warden, Sr., Robert J. (Department: 1744)

Chemical apparatus and process disinfecting, deodorizing, preser

Analyzer, structured indicator, or manipulative laboratory...

Means for analyzing liquid or solid sample

C422S082080, C356S436000, C356S437000, C257S098000

Reexamination Certificate

active

06241948

ABSTRACT:

FIELD OF THE INVENTION
This invention relates generally to a sensor and, more particularly, to a sensor for the quantification of an analyte in a sample.
Throughout this application, references are cited by reference to endnotes which appear after the detailed description. The respective disclosure of each of these references is incorporated in its entirety by reference.
BACKGROUND OF THE INVENTION
The ability to quantify gaseous species, such as O
2
and NH
3
, and analytes in solution, such as pH, PO
2
, PCO
2
, glucose, cholesterol, antigens, haptens, amino acids, and organic molecules, is important in industry, biomedicine, and the analytical sciences.
Traditionally, molecular oxygen, O
2
, has been sensed using a device known as the Clark electrode. Although this electrode works, it has limitations including consumption of the O
2
, relatively long response times, and the tendency of the electrode to become poisoned by contaminants, such as proteins and organics. As a result, other solutions, which rely upon optical sensing schemes for quantifying O
2
, have been developed.
1-21
Most optical sensing schemes are based on the quenching of a luminescent species by a gas, such as molecular oxygen.
1-11,22-24
In this approach, the O
2
dependence, or the dependence of any other quencher like Cl-, Br-, J-, Cu
2+
, Ni
2+
, Cr
2+
, Fe
2+
, Fe
3+
, or acrylamide, on the emission intensity is described by the Stern-Volmer expression:
25,26
I
0
I
=
1
+
K
SV
⁡
[
O
2
]
=
1
+
k
q
⁢
τ
0
⁡
[
O
2
]
where I
0
is the intensity in the absence of O
2
, I is the intensity in the presence of O
2
at concentration [O
2
], K
SV
is the Stern-Volmer quenching constant, k
q
is the bimolecular quenching constant, and &tgr;
0
is the excited-state luminescence lifetime of the emissive species in the absence of O
2
. Accordingly, by monitoring the luminescence intensity, the amount of O
2
present in a given sample can be determined.
Early optical sensing schemes used O
2
sensors which were based on the fluorescence from polycyclic aromatic hydrocarbons (PAHs) with long excited-state lifetimes, such as pyrene, benzo[a]pyrene, pyrenebutyric acid, and decacyclene.
1-5,11,12
Since these fluorophores have reasonably long excited-state lifetimes (to 400 ns), they are susceptible to O
2
quenching. Unfortunately, they also exhibit absorbance maxima in the ultraviolet or blue spectral region. As a result, the light sources in these optical sensing schemes consume significant electrical power and/or are expensive. Additionally, the detectors needed for these optical sensing schemes (e.g., photomultiplier tubes) are costly and require high voltage power supplies.
Other luminescent species that are susceptible to O
2
quenching include platinum and palladium porphyrin complexes
6-7
, and ruthenium poly(pyridyl) complexes 8-10,14-15,17-21 Tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II), which is commonly referred to as [Ru(dpp)
3
]
2+
, is particularly attractive for O
2
sensing because it exhibits a high luminescent quantum yield, long excited-state lifetime, large Stokes shift, and strong absorption in the blue-green spectral region.
22-24, 27
These luminescent species have shown promise as luminescence quantum counters, as singlet oxygen generators
25,26
for synthetic applications, and as sensors and molecular probes.
29
However, simple, small, and inexpensive optical sensing systems with these luminescent species have not yet been developed. The principal difficulties associated with constructing these sensing systems are with the immobilization of the O
2
responsive species and the relatively high cost of the excitation and detection system.
One approach to overcome these difficulties involves an optical O
2
sensor that uses a light emitting diode and a silica optical fiber with a sol-gel-derived film deposited on one surface.
17-21
The use of the sol-gel-derived film to entrap species provides a number of advantages including: (1) ambient processing conditions; (2) tunable film porosity; (3) good thermal stability; (4) optical transparency; and (5) simple dopant entrapment procedures.30-32 However, the use of the optical fiber adds to complexity and cost of the system and requires careful, precise, and costly manufacture to properly couple the light from the light emitting diode into the fiber and optically filter the fluorescence.
An alternative approach was recently described in U.S. Pat. No. 5,517,313 to Colvin, Jr., which is herein incorporated by reference. In this approach [(Ru(dpp)
3
]
2+
is immobilized within a silicone:naptha membrane (1:2, vol:vol), and a light emitting diode is embedded directly into the membrane. In this configuration, the housing for the light emitting diode acts essentially as a waveguide to couple the light into the film. This configuration is optically simpler than the aforementioned optical fiber design,
17-21
but still requires complicated flow cell and waveguide construction techniques for proper operation.
SUMMARY OF THE INVENTION
A sensing system for quantifying an analyte in a sample in accordance with one embodiment of the present invention includes a light source and a detector. The light source is coupled to a power source, and at least a portion of the light source is coated with a sol-gel-derived film doped with a doping material, such as a ruthenium complex. The detector is substantially across from and is separated by an open space from the portion of the light source coated with the sol-gel-derived film. The system may further include a filter which is located between the light source and the detector and a processing system which is coupled to the detector for quantifying the amount of analyte that is present in the sample based on data from the detector.
A sensing apparatus in accordance with another embodiment of the present invention includes a housing, a light source, a sol-gel-derived film, and a detector. The housing has an inlet for receiving a sample and an outlet for discharging the sample. The light source is coupled to a power source and is positioned in the housing between the inlet and the outlet. A sol-gel-derived film doped with a doping agent is deposited on at least a portion of the light source. The detector is spaced from and located substantially across from the portion of the light source coated with the sol-gel-derived film. The sensing apparatus may include a processing system which is coupled to the detector for processing data detected by the detector.
The present invention also relates to a method for quantifying an analyte in a sample. The method includes providing a light source which is coupled to a power source and on at least a portion of which is coated a sol-gel-derived film doped with a doping material. The sol-gel-derived film doped with the doping material is contacted with the analyte that is present in the sample. Light from the light source coated with the sol-gel-derived film doped with the doping material is transmitted through the sample towards the detector where it is detected.
One of the advantages of the present invention is the simplicity of its design when compared to prior designs. As discussed above, the sensing system can be easily constructed with an inexpensive light emitting diode, a low cost filter, and a low cost photodiode.
Another advantage of the present invention is that it consumes smaller amounts of electrical power than prior systems. As a result, the sensing system can be battery operated which makes it much more portable and also less expensive to operate.
Yet another advantage of one of the embodiments of the invention is the fast response times, good reversibility, and detection limits of 0.02% and 110 ppb, respectively, for O
2
in gaseous and aqueous samples that the sensing system can provide when ruthenium complex of tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) ([Ru(dpp
3
]
2+
) is immobilized within a porous sol-gel-derived film and cast directly onto the sur

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