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We have investigated a nanopillar-based surface enhanced Raman scattering (SERS) for future multiplexed nanofluidic SERS (nanoSERS) arrays. Without using e-beam or focus ion beam method, we have accomplished this simple and batch processed nanoSERS arrays on a chip, which is economical and mass producible. The polysilicon nanopillar structures are fabricated on top of a silicon wafer using optical lithography, reactive ion etching and passivation steps. High aspect ratio pillar-like nanostructures and spacing are controlled by the reactive ion etching gas and passivation steps. The heights of nanopillars ranged from 0.1 μm to 0.3 mm and their diameters ranged from 20 nm to 100 nm. A thin gold (10-20 nm) layer is evaporated on top of the nanopillar surfaces for further surface enhancements. The Raman shifts were measured for 10-3 M of 4, 6-diamidino-2-phenylindole dihydrochloride dye in solution using a 500 mW near infrared laser (785 nm). A direct correlation between the density of nanopillars and the intensity of Raman enhancement is observed. The SERS spectra through thin PyrexTM glass and polydimethylsiloxane (PDMS) are characterized to find the optimized nanofluidic materials for an autonomous multiplexing biomolecular detection schemes.
We present a new method of increasing the effective electrode surface for improved neural recording. To optimize the electrode, the impedance can be decreased by introducing surface roughness or nanostructures on the electrode. High aspect ratio pillar-like polysilicon nanostructures are created in a reactive ion etch. Nanostructure robustness in cell culture is examined.
Microfabricated patch clamping devices comprising planar arrays of individually addressable nozzles, fluidic channels and electrodes have been developed. Patch clamp based electrophysiological techniques are among the most widespread methods in neurophysiology and are used to address a broad range of cellular physiology and quantitative biological questions. Among the limitations of the technique are the difficulty of obtaining multiple patches on connected cells or on the same cell, limited stability of patches, and constraints on chemical and optical access to the patched membrane. The parallel array device will enable the formation of multiple seals simultaneously. The structure facilitates visualization of the interior of the patched membrane during electrical recording, as well as delivery of chemicals. The microfabrication technique gives precise control over the capacitive and resistive characteristics of the electrode channels, as well as the flow resistance, which are important factors in patch clamp recording. The device is fabricated using an SOI wafer and Deep Reactive Ion Etching to create an array of cylindrical nozzles, each of which has a core of silicon dioxide and interior walls of silicon nitride. Vertical channel segments and plumbing holes are fabricated by deep reactive ion etching through the wafer. Important electrical properties of the device were characterized, and patch clamping was attempted.
Nanogap capacitors are fabricated for DNA hybridization detection. Without labeling, the nanogap capacitors on a chip can function as DNA microarray sensors. The difference in dielectric properties between single-stranded DNA and double-stranded DNA permits use of capacitance measurements to detect hybridization. To obtain high detection sensitivity, a 50 nm gap capacitor was fabricated using a Si-nanotechnology. To ensure proper measurement of DNA's dielectrical properties, the probe ssDNA was first immobilized onto the electrode surface using self-assembly monolayers and allowed to hybridize with the target ssDNA. The capacitance changes were measured for 35-mer homonucleotides. The self-assembly monolayer and DNA immobilization events were verified independently by contact angle measurement and FTIR. Capacitance values are measured at frequencies ranging from 75 kHz to 5 MHz, using 0 VDC bias and 25 mVAC signals. Approximately 9% change in capacitance was observed after DNA hybridization at 75 kHz.
Cell separation and sorting in micro-assay devices must be performed using minimal sample sizes and few processing steps. To meet these requirements, a biomimetic approach to cell sorting is proposed based on adhesive rolling of cells along surfaces. This type of interaction is mediated by a special class of adhesion proteins on cell membranes and is responsible for localizing cells to particular tissues in vivo. To perform cell capture in a microdevce, raw sample can be flowed through microstructured fluidic channels, which serve as chromatographic “separation columns” and whose surfaces are coated with adhesion proteins. Targeted cells are captured by the flow structures and are permitted to roll slowly under shear from passing fluid. Among captured cells, differences in rolling speed provide the basis for segregating different populations. In this study, two prospective designs for microstructured fluidic channels were coated with E-selectin IgG chimera. The capture and enrichment of HL-60 and U-937 cells from flowing samples were demonstrated. Additionally, the difference in transit speed through one of the fluidic channels indicates that separation of enriched populations of these cells is feasible.
In this talk, the development of key elements for BioPOEMS (Biomedical Polymer-based Opto Electro Mechanical Systems) will be discussed as a new generation of microscopic and microanalysis biochips. Current BioMEMS (Biomedical Microelectromechanical Systems) technology is in its infancy stage. Just as silicon-based microelectronics technology went through many stages since the late ‘60's, BioMEMS technology will have to overcome many obstacles before becoming a mature industry. The IC industry was made possible by the development of fabrication processes, integration technologies, and design tools. Similarly, the field of BioMEMS must prepare new components with biomaterials and tools for the development of new microsystems, enabling the combination of biological sensors and actuators with the rapidly growing capabilities of bioinformatics.
Polymers are not only used in macroscopic systems, but are now increasingly finding use in the microscopic realm such as microfluidic devices. Among the many different classes of polymers, it is the fluoropolymers that provide the most unique material characteristics.
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