The development of intelligent miniaturized biochemical sensors has been an area of active research over the past several
years. These microsensors and sensor microarrays are finding niche applications in point-of-care diagnostics, personal
care, food safety, and environmental monitoring. Among these sensors, optical (luminescence) sensing holds a great
promise towards implementing simple, specific, and highly sensitive biochemical sensors. It is generally understood that
biochemical recognition elements that respond specifically to the target analytes play a critical role in the overall sensor
operation. Aside from the recognition elements, signal detection and processing components are important to collect the
information provided by recognition elements and output an easily understandable response. The signal processing
component provides the best opportunity to incorporate intelligence to achieve low-power, adaptive, accurate, and
reliable sensors. We deal with sensors that use sol-gel derived xerogels as recognition materials and Complementary
Metal-Oxide Semiconductor (CMOS) integrated circuits for signal detection and processing. Xerogels are
nano/microporous glasses that can be used to encapsulate luminophores, enzymes, and nanoparticles in their pores. In
this Article, we will describe some of the emerging integrated sensor platforms that are based on monitoring the excited-state
luminescence intensity and lifetimes of the luminophores housed in the xerogels. Specifically, we describe a CMOS
imaging system for simultaneously monitoring xerogels sensor arrays. Next, we describe a non-linear phase
luminometric system with enhanced and dynamically tunable sensitivity and improved signal-to-noise performance.
Finally, we will describe time-based signal processing that could enable the direct measurement of excited state
fluorescence lifetimes. This time-to-digital converter requires simple circuit implementation and can be used to measure
lifetimes that are on the order of several hundred nanoseconds. The time based signal processing could ultimately allow
the development of low-cost lifetime imaging system wherein one could take the lifetimes' image of an array of
recognition elements rather than collecting an image of their fluorescence intensities.
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.
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.
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.
Over the past several years our group has been ex;poring the potential of sol-gel-derived glasses as platforms for advanced sensors and biosensors. In this paper we will outline the challenges that are associated with using these xerogels. Toward this end, we discuss recent results from our laboratories on the performance of polyclonal anti- dansyl antibodies sequestered within a series of xerogels. We assess antibody performance by determining the hapten/antibody association constant, the static excitation and emission for the dansyl hapten bound to the antibody combing site, and the excited-state fluorescence anisotropy and intensity decay kinetics for the dansyl/anti-dansyl system within a series of xerogels.
We report on the development, characterization, and photophysics of a new fiber-optic-based sensor which uses a sol-gel entrapped recognition element. The recognition element is modified (beta) -cyclodextrin to which we have added a short tether (glycine) and a fluorophore (dansyl). This recognition element forms an intramolecular complex, and the dansyl group can include within the cyclodextrin cavity. Non-fluorescent analytes, that bind to the cyclodextrin cavity, can effectively displace the included dansyl group and result in a measurable change in signal. We report on the detection limits, dynamic range, and photophysics (i.e., transduction mechanism) of this new sensor.