Elizabeth C. Tehan

Tools to Rapidly Produce and Screen Biodegradable Polymer and Sol-Gel-Derived Xerogel Formulations:

A new method to rapidly produce and screen biodegradable polymer- and xerogel-based formulations is described. The approach is based on a high-speed pin printer and imaging with an epi-fluorescence microscope/charge-coupled device detector. By using this approach we can produce and screen over 600 formulations/h and rapidly identify lead formulations and/or compositions that are the most useful for the development of biodegradable devices or (bio)sensors.

Chemical sensing systems using xerogel-based sensor elements and CMOS photodetectors

We present the first example of an integrated complementary metal-oxide-semiconductor (CMOS) photodetector coupled with a solid-state xerogel-based thin-film sensor to produce a compact chemical sensor system. We compare results using two different CMOS-based detector systems to results obtained by using a standard photomultiplier tube (PMT) or charge-coupled device (CCD) detector. Because the chemical sensor elements are governed by a Stern-Volmer relationship, the Stern-Volmer quenching constant is used as the primary comparator between the different detectors. All of the systems yielded Stern-Volmer constants from 0.042 to 0.049 O/sub 2/%/sup -1/. The results show that the CMOS detector system yields analytical data that are comparable to the CCD- and PMT-based systems. The disparity between the data obtained from each detector is primarily associated with the difference in how the signals are obtained by each detector as they presently exist. We have also observed satisfactory reversibility in the operation of the sensor system. The CMOS-based system exhibits a response time that is faster than the chemical sensor elements intrinsic response time, making the CMOS suitable for time-dependent measurements. The CMOS array detector also uses less than 0.1% the power in comparison to a standard PMT or CCD. The combined xerogel/CMOS system represents an important step toward the development of a portable, efficient sensor system.

CMOS integrated optical sensor using phase detection

In this paper, we present an integrated fiber optic sensor based on a phase detection technique. The operation principle of the sensor as a xerogel based oxygen sensor has been demonstrated The integrated device includes a light emitting diode, an oxygen sensing probe and a CMOS Integrated Circuit (IC). The CMOS IC combines the LED driver circuitry, optical detector and the phase detector circuitry on a single chip. The integrated sensor provides accurate, low cost and low power detection for quantifying oxygen and for recording excited-state lifetimes ranging from nanoseconds to milliseconds.

CMOS-based biosensor systems using integrated nanostructured recognition elements

Rapid advances in point-of-care devices for medical and biomedical diagnostic and therapeutic applications have increased the need for low cost, low power, high throughput, and miniaturized systems. To this end, we developed several optical sensor systems using CMOS detection and processing components and sol-gel derived xerogel recognition elements for monitoring various biochemical analytes. These sensors are based either on the measurement of the luminescence intensity or the excited-state lifetimes of luminophores embedded in the nanostructured xerogel matrices. Specifically, the design and development of CMOS detection and signal processing components and their system integration will be described in detail. Additionally, we will describe the factors that limit the performance of these sensor systems in terms of sensitivity, response time, and dynamic range. Finally, the results obtained for monitoring important biochemical analytes such as oxygen (O2) and glucose will be discussed.

Biomolecule-less sensors for biomolecules based on templated xerogel platforms

We report on a new strategy for producing self-contained sensor elements for protein detection. The method exploits molecular imprinting, sol-gel-derived xerogels, and selective installation of the fluorescent reporter molecule within the template site. There are no biological reagents used. We term these new xerogel-based sensor elements as Protein Imprinted Xerogels with Integrated Emission Sites (PIXIES). The analytical figures of merit are described.

Chemical sensor systems using xerogels and CMOS detectors

We have developed a chemical sensing platform based on xerogel thin film sensor elements coupled with CMOS detectors. We demonstrate the operation of the sensing platform as a simple oxygen sensor. The quenchometric operation of the oxygen sensor coupled with CMOS detectors is compared to standard laboratory detection systems (CCD and PMT). The Stern-Volmer quenching constant (k/sub SV/) is used as a comparative measure of the operation of each of these systems. In our initial experiments all three systems yielded a k/sub SV/ between 0.042 and 0.049 O/sub 2/%/sup -1/. The xerogel sensor elements have demonstrated satisfactory reusability and stability over a period of more than six months. The CMOS detectors consume less than 0.1% of the power required for the PMT or CCD detectors, and are an attractive platform for array processing and portable applications.

Creating diversified response profiles from a single quenchometric sensor element by using phase-resolved luminescence.

We report a new strategy for generating a continuum of response profiles from a single luminescence-based sensor element by using phase-resolved detection. This strategy yields reliable responses that depend in a predictable manner on changes in the luminescent reporter lifetime in the presence of the target analyte, the excitation modulation frequency, and the detector (lock-in amplifier) phase angle. In the traditional steady-state mode, the sensor that we evaluate exhibits a linear, positive going response to changes in the target analyte concentration. Under phase-resolved conditions the analyte-dependent response profiles: (i) can become highly non-linear; (ii) yield negative going responses; (iii) can be biphasic; and (iv) can exhibit super sensitivity (e.g., sensitivities up to 300 fold greater in comparison to steady-state conditions).