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 SiO<sub>2</sub> surface is a robust, very straightforward, and inexpensive method for preparing biosensors.
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<sup>-1</sup> 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.