Rachel M. Bukowski

CMOS-Based Phase Fluorometric Oxygen Sensor System

The design and development of a phase fluorometric oxygen (O2 ) sensor system using single-chip CMOS detection and processing integrated circuit (DPIC) and sol-gel derived xerogel thin-film sensor elements is described. The sensor system determines analyte concentrations using the excited state lifetime measurements of an O2-sensitive luminophore (tris(4,7-diphenyl-1,10- phenathroline)ruthenium (II)) embedded in the xerogel matrix. A light emitting diode (LED) is used as the excitation source, and the fluorescence is detected by the DPIC using a 16times16 phototransistor array on-chip. The DPIC also consists of a current mirror, current-to-voltage converter, amplifier, bandpass filter, and phase detector. The DPIC output is a dc voltage that corresponds to the detected fluorescence phase shift. With a 14-kHz modulation frequency, the entire system including driving the LED consumes 80 mW of average power. The sensor system provides stable, reproducible, analytically reliable, and fast response (~20 s) to changes in the gaseous oxygen concentrations and establishes the viability for low cost, low power and miniaturized biochemical sensor systems

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.

O 2 -Responsive Chemical Sensors Based on Hybrid Xerogels that Contain Fluorinated Precursors

We report the development and analytical figures of merit associated with several new O2-responsive sensor materials. These new sensing materials are formed by sequestering the luminophore tris(4,7-diphenyl-1,10-phenanthroline)ruthenium(II) ([Ru(dpp)3]2+) within hybrid xerogels that are composed of two of the following methoxysilanes: tetramethoxysilane, n-propyl-trimethoxysilane, 3,3,3-trifluoropropyl-trimethoxysilane, phenethyl-trimethoxysilane, and pentafluorophenylpropyl-trimethoxysilane. Steady-state and time-resolved luminescence measurements are used to investigate these hybrid xerogel-based sensor materials and elucidate the underlying reasons for the observed performance. The results show that many of the [Ru(dpp)3]2+-doped composites form visually uniform, crack-free xerogel films that can be used to construct O2 sensors that have linear calibration curves and excellent long-term stability. To the best of our knowledge, the [Ru(dpp)3]2+-doped fluorinated hybrid xerogels also exhibit the highest O2 sensitivity of any reported [Ru(dpp)3]2+-based sensor platform.

CMOS mixed-signal phase detector for integrated chemical sensor systems

The development of a portable chemical sensor system based on the measurement of the excited-state lifetimes of luminophore doped xerogels in the frequency-domain is described. The prototype sensor system is demonstrated for oxygen (O2) monitoring and consists of a silicon photodiode as the detector followed by a current-to-voltage converter, an amplifier, a band-pass filter and a custom-designed CMOS phase detector. The variation in the lifetime, due a change in the analyte concentration, is measured as a phase shift between a sinusoidally modulated reference excitation and the fluorescence emission using the designed CMOS phase shift detector. The CMOS mixed-signal phase detector is fabricated using the AMI 1.5 mum process available through MOSIS. A highly accurate, low cost, and hand-held prototype oxygen sensor is demonstrated using this CMOS phase detector

Nanostructured porous polymeric photonic bandgap structures for sensing

A methodology for enabling biochemical sensing applications using porous polymer photonic bandgap structures is presented. Specifically, we demonstrate an approach to encapsulation of chemical and biological recognition elements within the pores of these structures. This sensing platform is built on our recently demonstrated nanofabrication technique using holographic interferometry of a photo-activated mixture that includes a volatile solvent as well as monomers, photoinitiators, and co-initiators. Evaporation of the solvent after polymerization yields nanoporous polymeric 1D photonic bandgap structures that can be directly integrated into optical sensor systems that we have previously developed. More importantly, these composite structures are simple to fabricate, chromatically tunable, highly versatile, and can be employed as a general template for the encapsulation of biochemical recognition elements. As a specific example of a prototype device, we demonstrate an oxygen (O2) sensor by encapsulating the fluorophore (tris(4,7-diphenyl-1,10-phenathroline)ruthenium(II) within these nanostructured materials. Finally, we report initial results of extending this technique to the development of a hydrophilic porous polymer photonic bandgap structure for sensing in aqueous environments. The ability to control the hydrophilic/hydrophobic nature of these materials has direct impact on chemical and biological sensing.

CMOS Microsystems for Phase Fluorometric Biochemical Monitoring

This article will present a review of our recent work on the development of Complementary Metal-Oxide Semiconductor (CMOS) detection and signal processing interfaces for fluorescence based biochemical sensors as well as the development of a new sensor. We will discuss a number of microsystems that integrate CMOS Application Specific Integrated Circuits (ASICs) with nanoporous sensor materials. Specifically, sol-gel derived xerogel thin films, a class of nanoporous materials, are employed for monitoring various biochemical analytes including oxygen (O2), glucose, and pH. We have also demonstrated a single-chip CMOS based phase fluorometric system for monitoring O2 using xerogel sensor materials. In this paper, we will present a new, versatile, CMOS based platform for real-time phase fluorometric analysis that is capable of functioning with fluorophores having excited-state lifetimes as short as 400 nanoseconds. In addition, we will describe the employment of novel nanomaterials (porous polymer photonic bandgap structures) as immobilization media for biochemical recognition elements that enhance the fluorescence detection efficiency. Finally, the development of integrated sensors using these materials will be described.

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.

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).