Photopatterning with 266 nm UV light was accomplished on spin-coated DNA thin films using two different techniques.
Lithographic masks were used to create 10-100 micron-sized arrays of enhanced hydrophilicity. Two such masks were
used: (1) Polka Dot Filter having opaque squares and a transparent grid and (2) A metal wire-mesh having transparent
squares and opaque grid. UV light selectively photodissociates the DNA film where it is exposed into smaller more
hydrophilic fragments. UV-exposed films are then coated with a solution of a protein. The protein appears to selectively
coat over areas exposed to UV light. We have also used interferometric lithography with UV light to accomplish
patterning on the scale of 1 micron on DNA thin films. This technique has the potential to generate micro/nano arrays
and vary the array-size. This paper describes the fabrication of these microarrays and a plausible application for
fabricating antibody arrays for protein sensing applications.
Surface relief gratings produced on planar substrates have been widely investigated for their application as a
holographic recording medium. Much of this work has concentrated on gratings made in polymer thin films with an
azo-benzene group. We describe a novel phenomenon involving surface relief gratings which are formed by deposition
of Rhodamine 6G dye on polybutadiene thin film. This deposition as a grating pattern is photo-induced in a dye-solution
by holographic interference of low power 488 nm light from an argon-ion laser. Dynamics of this aqueousphase
grating deposition is investigated for various concentrations of the dye. A plausible mechanism of grating
formation involves photochemical reaction of polybutadiene substrate with the laser-excited dye. Surface relief
structure of the grating is characterized with an atomic force microscope.
Phospholipid, which is a building block of biological membranes, plays an important role in compartmentalization of cellular reaction environment and control of the physicochemical conditions inside the reaction environment. Phospholipid bilayer membrane has been proposed as a natural biocompatible platform for attaching biological
molecules like proteins for biosensing related application. Due to the enormous potential applications of biomimetic model biomembranes, various techniques for depositions and patterning of these membranes onto solid supports and their possible biotechnological applications have been reported by different groups. In this work, patterning of
phospholipid thin-films is accomplished by interferometric lithography as well as using lithographic masks in liquid phase. Surface Enhanced Raman Spectroscopy and Atomic Force microscopy are used to characterize the model phospholipid membrane and the patterning technique. We describe an easy and reproducible technique for direct patterning of azo-dye (NBD)-labeled phospholipid (phosphatidylcholine) in aqueous medium using a low-intensity
488 nm Ar<sup>+</sup> laser and various kinds of lithographic masks.
Explosives detection for national and aviation security has been an area of concern for many years. In order to
improve the security in risk areas, much effort has been focused on direct detection of explosive materials in vapor
and bulk form. New techniques and highly sensitive detectors have been extensively investigated and developed
to detect and identify residual traces that may indicate an individual's recent contact with explosive materials.
This paper reports on the use and results of Surface Enhanced Raman Scattering (SERS) technique, to analyze
residual traces of explosives in highly diluted solutions by using low-resolution Raman spectroscopy (LRRS). An
evaluation of the detection sensitivity of this technique has been accomplished using samples of explosives such
as Trinitrotoluene(TNT), Cyclotrimethylenetrinitramine (RDX) and HMX evaluated at different concentrations.
Additionally, different SERS substrates have been studied in order to achieve the best enhancement of the Raman
spectrum for residual amounts of materials. New substrates produced by gold-coated polystyrene nanospheres
have been investigated. Two different sizes of polystyrene nanospheres, 625nm and 992nm, have been used to
produce nanopatterns and nanocavities on the surface of a glass slide which has been coated with sputtered
gold. Results from homemade substrates have been compared to a commercial gold-coated substrate consisting
of an array of resonant cavities that gives the SERS effect. Sample concentration, starting from 1000ppm
was gradually diluted to the smallest detectable amount. Raman spectrum was obtained using a portable
spectrometer operating at a wavelength of 780nm.
Surface Enhanced Raman Spectroscopy is a powerful analytical technique capable of single molecule detection
sensitivity. We have detected SERS on the tip of a 3 mm-core diameter PMMA plastic optical fiber. The technique
involves deposition of 30 nm gold nanoparticles followed by deposition of sample of interest to be analyzed. SERS
enhancement has been demonstrated for several chemicals like glycerin and dye Rhodamine 6G as well biological
molecules like Acetaminophen, aspirin and Streptavidin and poly-L-Lysine. It is shown that interfering spectrum of
PMMA can be subtracted to reveal the SERS spectrum of molecule of interest. The technique can simplify SERS
detection by connecting the other end of fiber directly to a spectrometer. SERS was recorded for various concentrations
of analytes. Using a focused 633 nm laser, a detection sensitivity of 0.1picogram was established.
Interferometric lithography is one of the techniques used to produce micro and nano-scale periodic patterns like gratings
in polymers and other substrates of interest. In this work, holographic surface relief gratings are optically inscribed on
spin coated azo-dye (NBD)-labeled phospholipid (phosphatidylcholine) thin films using a low-intensity (10 mW) 244
nm frequency-doubled Ar+ laser. A systematic study of growth and decay of phospholipid grating is reported.
Multiple light taps in a plastic optical fiber provides a possibility of chemical sensing along its entire length. Unlike some point-by-point measurement techniques like fluorescence endoscopy, the technique described here makes it possible to sense large areas simultaneously and should be useful as an environmental chemical sensor.