J. M. Taguenang

Detection of residual traces of explosives by surface enhanced Raman scattering using gold coated substrates produced by nanospheres imprint technique

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 individuals 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.

Photopatterning of polybutadiene substrates by interferometric ultraviolet lithography: fabrication of phospholipid microarrays.

Gratings are written holographically with low power (10 mW/cm(2)) 244 nm UV light on thin films of polybutadiene rubber polymer. The increase of hydrophilicity-wettability of polybutadiene films is measured over UV-exposed regions. Sequential fabrication of two orthogonal gratings results in hydrophilic microarrays having applications as functionalized substrates for immobilizing biomolecules. This is demonstrated by immobilizing a phospholipid in a microarray pattern.

Fabrication and characterization of a diffraction-grating transducer in thin polybutadiene rubber film for sensing dynamical strain

Surface relief gratings are holographically fabricated in thin polybutadiene rubber films produced by both spin coating and dip coating on glass and metal substrates. These thin-film gratings are characterized for their application as efficient transducers for detecting dynamic strain in solids. The performance of these rubber-grating transducers is compared to surface-mounted fiber Bragg gratings for a range of frequencies between 50 Hz and 30 kHz. Dynamic-strain sensitivity around 1 nepsilon/radicalHz is recorded for thin rubber-film grating transducers.

UV Lithographic Patterning on Spin-coated DNA Thin-films

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.

Photochemically deposited surface relief gratings of an azo-dye-labeled phospholipid from the aqueous phase

Surface relief holographic gratings are fabricated on the polybutadiene-coated walls of a cell filled with an aqueous solution of an azo-dye-labeled phospholipid. A low power (2 mW) 488 nm argon ion laser wavelength is used. Laser-excited azo dye reacts to produce a permanent surface-relief pattern on the polybutadiene substrate. Gratings are recorded for varying concentrations of the phospholipid solution as well as laser intensity. Lithographic masks are used to show that the photochemical pattern on the substrate is an exact replica of the light intensity distribution, and so the technique can be used for holographic recording as well as for biomolecular applications.

Surface enhanced Raman spectroscopy on the tip of a plastic optical fiber

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.

UV lithographic patterning on spin-coated DNA thin-films

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.

Nano-scale patterning of phospholipid thin films by interferometric UV lithography

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.

Chemical sensing through multiple light taps in plastic optical fiber

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.