Silicon dioxide surfaces are commonly used in photonic microsensors for bioreceptor attachment. Functionalization of
sensor surface with aptamer receptors provides the opportunity to develop low cost, robust, field deployable sensors.
Most aptamer sensors are constructed by covalently linking modified aptamers to a derivatized surface. There have been
reports of using UV crosslinking to directly immobilize DNA with sequences that end with poly(T)10-poly(C)10 on an
unmodified glass surface for hybridization. We have expanded this strategy using thrombin-binding aptamers (TBAs)
with three different tail modifications. TBA with PolyT20 tail showed the best performance in terms of sensitivity and
dynamic range. PolyTC tailed aptamers did not bind thrombin well, which may be due to that the interactions between
the C bases and G-quadruplex affect their target binding capability. When compared to biotinylated aptamer
immobilized on a streptavidin surface, polyT aptamer printed directly on plain glass showed comparable affinity. Direct
immobilization of TBA on nonfunctionalized silicon dioxide wafer and its binding towards thrombin has also been
demonstrated. Our results showed that using polyT-tagged aptamer probes directly immobilized on unmodified glass
and SiO2 surface is a robust, very straightforward, and inexpensive method for preparing biosensors.
Development of localized surface plasmon resonance (LSPR) sensors for label-free biodetection draws considerable
attention because of the potential of these sensors to provide simplified detection schemes, improved detection limits,
and high-density multiplexed array configurations. In this paper, we present our recent results on the theoretical and
experimental development of LSPR label-free biosensors based on nanohole and nanopillar arrays. First, we
theoretically compare the analytical performance metrics of wavelength modulated SPR and LSPR platforms for
biological recognition with surface-immobilized bioreceptors (e.g. antibodies and aptamers). Further, we discuss our
results on the application of a focused ion beam (FIB) technique to fabricate arrays of nanoholes and nanopillars in Au
films, investigate the origin and type of FIB-induced surface contamination, and demonstrate an efficient way for its
elimination. Next, we evaluate the refractive index (RI) response sensitivity of FIB-fabricated arrays of nanoholes (443
- 513 nm/RIU) and nanopillars (423 nm/RIU) in Au films. Further, we demonstrate the opportunities that are available
from the multivariate spectral analysis of plasmonic nanostructures for improvement of sensor system performance.
Finally, we present typical simulation results of predicting RI sensitivity of plasmonic nanostructures using finite-difference
time-domain technique (FDTD) and discuss the remaining challenges of simulation techniques for design of
LSPR sensors.
Raman detection of nitrogen gas is very difficult without a multi-pass arrangement and high laser power. Hollow-core
photonic bandgap fibers (HC-PBF) provide an excellent means of concentrating light energy in a very small volume and
long interaction path between gas and laser. One particular commercial fiber with a core diameter of 4.9 microns offers
losses of about 1dB/m for wavelengths between 510 and 610 nm. If 514nm laser is used for excitation, the entire Raman
spectrum up to above 3000 cm-1 will be contained within the transmission band of the fiber. A standard Raman
microscope launches mW level 514nm laser light into the PBF and collects backscattered Raman signal exiting the fiber.
The resulting spectra of nitrogen gas in air at ambient temperature and pressure exhibit a signal enhancement of about
several thousand over what is attainable with the objective in air and no fiber. The design and fabrication of a flow-through
cell to hold and align the fiber end allowed the instrument calibration for varying concentrations of nitrogen.
The enhancement was also found to be a function of fiber length. Due to the high achieved Raman signal, rotational
spectral of nitrogen and oxygen were observed in the PBF for the first time to the best of our knowledge.
Design, validation, and implementation of an optical spectroscopic system for high-throughput analysis of combinatorially developed protective organic coatings are reported. Our approach replaces labor-intensive coating evaluation steps with an automated system that rapidly analyzes 8x6 arrays of coating elements that are deposited on a plastic substrate. Each coating element of the library is 10 mm in diameter and 2 to 5 micrometers thick. Performance of coatings is evaluated with respect to their resistance to wear abrasion because this parameter is one of the primary considerations in end-use applications. Upon testing, the organic coatings undergo changes that are impossible to quantitatively predict using existing knowledge. Coatings are abraded using industry-accepted abrasion test methods at single-or multiple-abrasion conditions, followed by high- throughput analysis of abrasion-induced light scatter. The developed automated system is optimized for the analysis of diffusively scattered light that corresponds to 0 to 30% haze. System precision of 0.1 to 2.5% relative standard deviation provides capability for the reliable ranking of coatings performance. While the system was implemented for high-throughput screening of combinatorially developed organic protective coatings for automotive applications, it can be applied to a variety of other applications where materials ranking can be achieved using optical spectroscopic tools.
This paper summarizes our recent activities to develop analytical spectroscopic tools for high-throughput screening (HTS) of combinatorial chemistry libraries and the adaptation of the developed techniques to more traditional, i.e., laboratory and manufacturing, scales. It is shown that, for a broad variety of applications, optical spectroscopic detection methods have a suite of attractive features that make them almost ideal HTS tools. Strategies for the development of new high-throughput screening tools are presented, followed by analysis of requirements for development of multivariate data analysis methods for prediction of properties of combinatorial materials, determination of contributing factors to combinatorial-scale chemical reactions using evolving factor analysis and multivariate curve resolution chemometric methods, high- throughput optimization of process parameters, and applicability of the developed HTS tools for in-line monitoring of scaled-up reactions.
An instrument for in-situ monitoring of volatile organics in groundwater at pat-per-billion levels has been developed and field tested. The device is an acoustic wave thickness-shear mode sensor based on a 10-MHa AT-cut quartz resonator coated with a non-polar polymer film. The sensor demonstrates a detection limit of 8 and 12 parts per billion in water for trichloroethylene and toluene, respectively, and a rapid reversible response. This low detection limit is achieved by carefully minimizing the noise level in the electronic detection system, by optimizing the thickness of the sensing polymer film, and by performing measurements in the headspace. Preliminary field test demonstrated good correlation of sensor response with conventional laboratory purge-and-trap/GC analysis.
An array of four acoustic wave chemical sensors has been developed and tested for recognition and quantitation of six closely related chlorinated organic vapors at low part-per- million concentrations. These vapors include PCE, TCE, VC, and DCE, cis-1,2-DCE, trans-1,2-DCE, and 1,1-DCE. The developed sensor array can detect as little as 0.2 ppm of PCE, 0.8 ppm of TCE, 1.4 ppm of cis-1,2-DCE, 1.4 ppm of trans-1,2-DCE, 3 ppm of 1,1-DCE, and 3.5 ppm of VC in air. Quantitation of TCE and cis-1,2-DCE vapor mixtures was achieved using multivariate calibration techniques. The locally weighted regression analysis provides more accurate results over the partial least squares regression.
The evolution of approaches to simultaneous real-time acquisition of analytical data from multiple locations is analyzed. Greatest emphasis is placed on optical time-of- flight (OTOF) chemical detection when the measurements are taken along the length of a single continuous extended-length 'distributed' sensing element. The attractive features of such distributed sensing element fabricated by immobilization of chemically sensitive reagents directly into the original cladding of a conventional plastic-clad silica (PCS) optical fiber are demonstrated. Several signal generation and processing methods are devised to address the requirements for spatially resolved chemical sensing. These requirements include high signal levels, a fairly uniform detection limit over the length of the sensing fiber, measurements with dynamically quenched fluorophores, and high spatial resolution. Applications of OTOF distributed chemical sensors for spatially resolved analyte mapping for environmental and process applications are discussed.
Polymer dye films incorporating a pH indicator, immobilized on a polymer support, can be used for ammonia gas (NH3) sensing in fiber optic and portable instruments in the field operating conditions with changing temperature and humidity. Experimental results on the NH3 detection in the range 0 - 100 mg/m3 are reported for the range of temperature 25 - 45 degree(s)C and 60 - 80% relative humidity. A model of steady-state instrument response in the field has been developed with four adjustable parameters to describe the coupling of ambient NH3 concentration to absorbance change of the sensing element. Practical problems associated with the applications of such sensing chemistry for NH3 monitoring in the field are discussed.
The molecular absorption spectra of pH dyes, employed for ammonia sensing
are investigated. Differences of absorption spectra of Bromothymol Blue and
Bromocresol Purple dyes, dissolved in water and entrapped in
Polymethylphenylsiloxane film are discussed. Correspondence of dye-films
absorption bands shape to the Gauss distribution shape in the spectral region
of light source emission band was determined.
A portable device is described, which continuously measures
ammonia gas concentrations. The detection is based on reversible
changes in the optical transmittance of a dye-film coated on a glass
support. The design of the analyzer is presented and response
characteristics are discussed.
Fiber-optic sensor, based on the principle of reversible changes
in absorption spectrum of dye-film, containing pH-dye, entrapped in a
polymer matrix, has been developed for use in sensing of ammonia
vapors of variable temperature. Differences of absorption spectra of
pH-dye in water solution and in polymer matrix are investigated. The
design of the sensor is presented and experimental results are
discussed.
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