Vamsy P. Chodavarapu

Bio: Vamsy P. Chodavarapu is an academic researcher from University of Dayton. The author has contributed to research in topics: CMOS & Capacitive sensing. The author has an hindex of 18, co-authored 118 publications receiving 1384 citations. Previous affiliations of Vamsy P. Chodavarapu include State University of New York System & McGill University.

NeuroMEMS: Neural Probe Microtechnologies

Abstract: Neural probe technologies have already had a significant positive effect on our understanding of the brain by revealing the functioning of networks of biological neurons. Probes are implanted in different areas of the brain to record and/or stimulate specific sites in the brain. Neural probes are currently used in many clinical settings for diagnosis of brain diseases such as seizers, epilepsy, migraine, Alzheimer's, and dementia. We find these devices assisting paralyzed patients by allowing them to operate computers or robots using their neural activity. In recent years, probe technologies were assisted by rapid advancements in microfabrication and microelectronic technologies and thus are enabling highly functional and robust neural probes which are opening new and exciting avenues in neural sciences and brain machine interfaces. With a wide variety of probes that have been designed, fabricated, and tested to date, this review aims to provide an overview of the advances and recent progress in the microfabrication techniques of neural probes. In addition, we aim to highlight the challenges faced in developing and implementing ultralong multi-site recording probes that are needed to monitor neural activity from deeper regions in the brain. Finally, we review techniques that can improve the biocompatibility of the neural probes to minimize the immune response and encourage neural growth around the electrodes for long term implantation studies.

Structured color humidity indicator from reversible pitch tuning in self-assembled nanocrystalline cellulose films

Abstract: Iridescence is an example of structured color that is widespread in the biosphere, exhibited by multilayer inorganic thin films for optical filters, photonic crystals and other materials in which the periodic patterning of matter interacts with an electromagnetic field. Nanocrystalline cellulose (NCC) can be cast in the form of thick iridescent films whose color originates in the multi-domain chiral nematic texture created by self-assembly of the rigid rod crystallites. Scanning electron microscopy confirms the periodic layer structure that arises from the helical twist axis of the chiral nematic mesophase film. In effect, the film comprises multi-domain Bragg reflectors. On exposure to liquid water, and high relative humidity (RH), a reversible shift in the film iridescence from dry state blue-green to wet state red-orange is observed. This color change, which requires no pigment, is quantified by reflectance spectroscopy. The color transition is attributed to sorption of water that causes the pitch of the Bragg reflector to enlarge, and this leads to a red shift in the iridescence. The subsequent expansion of the film thickness was observed using polarized optical microscopy. The effect resembles molecular dopant and electric field induced pitch tuning along the helicoid axis in one-dimensional photonic crystal-like chiral nematic molecular systems. The color shift for a 40 μm thick NCC film is slow, occurring on timescale of 1–3 min. Thinner films change color in less than 2 s.

Algal fluorescence sensor integrated into a microfluidic chip for water pollutant detection

Abstract: We report the first miniaturized fluorescent sensor based on algae, with an organic light emitting diode (OLED) and an organic photodetector (OPD) integrated into a microfluidic chip. The blue emission OLED was used as the excitation source, while a blend of PTB3/PC61BM was used for the fabrication of the organic photodetector. Excitation and emission color filters based on acid/base dyes and a metal complex were developed and assembled with the organic optoelectronic components in order to complete the fluorescent detection system. The detection system was then integrated in a microfluidic chip made from (poly)dimethylsiloxane (PDMS). The complete sensor is designed to detect algal fluorescence in the microfluidic chamber. Algal chlorophyll fluorescence enables evaluation of the toxicity of pollutants like herbicides and metals-ions from agricultural run-offs. The entirely organic bioassay here presented allowed detection of the toxic effects of the herbicide Diuron on Chlamydomonas reinhardtii green algae that gave 50% inhibition of the algae photochemistry (EC50) with a concentration as low as 11 nM.

Bacteria Growth Monitoring Through a Differential CMOS Capacitive Sensor

Abstract: In this paper, we present a bacteria growth monitoring technique using a complementary metal-oxide semiconductor capacitive sensor. The proposed platform features a differential capacitive readout architecture with two interdigitized reference and sensing electrodes. These electrodes are exposed to pure Luria-Bertani (LB) medium and Escherichia Coli (E. Coli) bacteria suspended in the LB medium, respectively. In order to direct the solutions toward the electrodes, two microfluidic channels are implemented atop the electrodes through a direct-write assembly technique. We thereafter demonstrate and discuss the experimental results by using two different bacteria concentrations in the order of 106 and 107 per 1 mL in the LB medium.

Nanocrystalline cellulose for covert optical encryption

Abstract: Nanocrystalline cellulose (NCC) solid films derived from spruce pulp exhibit iridescence when cast from chiral nematic aqueous phase suspensions of the nanocrystals. The iridescence has potential for overt encryption as an anti-counterfeiting measure and also offers an intrinsic level of covert encryption since films of NCC reflect left-circularly polarized light. Addition of TINOPAL, an optical brightening agent (OBA), adds a third level of (covert) encryption potential since the chromophore exhibits strong fluorescence when excited with ultraviolet (UV) light. The overall result is a selectively polarizing fluorescent iridescent film. We examined the impact of additions of OBA on NCC iridescence, optical activity, and physical structure variation with polarized optical microscopy, circular dichroism (CD) spectropolarimetry, and zeta potential analysis. Increasing OBA additions increase the chiral nematic pitch of NCC films and alter chiral nematic domain structure in the solid film. Under low-concentration conditions, OBA yields intense UV fluorescence without compromising the visible light iridescent properties of the film. The potential security offered by the NCC film can be authenticated using a UV light source, a circular polarizer in conjunction with an iridescent feature that can be verified by the eye or by chiral spectrometry.

American Society for Testing and Materials

Abstract: The American Society for Testing and Materials (ASTM) is an independent organization devoted to the development of standards.

Design Of Analog Cmos Integrated Circuits

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Wood-Derived Materials for Green Electronics, Biological Devices, and Energy Applications.

Abstract: With the arising of global climate change and resource shortage, in recent years, increased attention has been paid to environmentally friendly materials. Trees are sustainable and renewable materials, which give us shelter and oxygen and remove carbon dioxide from the atmosphere. Trees are a primary resource that human society depends upon every day, for example, homes, heating, furniture, and aircraft. Wood from trees gives us paper, cardboard, and medical supplies, thus impacting our homes, school, work, and play. All of the above-mentioned applications have been well developed over the past thousands of years. However, trees and wood have much more to offer us as advanced materials, impacting emerging high-tech fields, such as bioengineering, flexible electronics, and clean energy. Wood naturally has a hierarchical structure, composed of well-oriented microfibers and tracheids for water, ion, and oxygen transportation during metabolism. At higher magnification, the walls of fiber cells have an interes...

Methods and apparatus for measuring analytes using large scale fet arrays

Abstract: An apparatus may include a semiconductor chip and a fluidics assembly. The semiconductor chip has an array of wells and an array of sensors and each sensor of the array of sensors is in fluid communication with a well of the array of wells. The fluidics assembly is located on top of the semiconductor chip and is configured to deliver fluids to the semiconductor chip. The fluidics assembly includes a flow expansion chamber configured to introduce the fluids, an outlet portion configured to pipe out the fluids, and a flow chamber portion. The flow chamber portion is configured to allow the fluids to flow from the flow expansion chamber to the outlet portion and to allow the fluids to interact along the way with material in the array of wells. The flow expansion chamber has a curved wall at the top or bottom so that the height of the flow expansion chamber at the center is less than at the walls that restrict the fluids to the left and right.

Optical methods for sensing and imaging oxygen: materials, spectroscopies and applications

Abstract: We review the current state of optical methods for sensing oxygen. These have become powerful alternatives to electrochemical detection and in the process of replacing the Clark electrode in many fields. The article (with 694 references) is divided into main sections on direct spectroscopic sensing of oxygen, on absorptiometric and luminescent probes, on polymeric matrices and supports, on additives and related materials, on spectroscopic schemes for read-out and imaging, and on sensing formats (such as waveguide sensing, sensor arrays, multiple sensors and nanosensors). We finally discuss future trends and applications and summarize the properties of the most often used indicator probes and polymers. The ESI† (with 385 references) gives a selection of specific applications of such sensors in medicine, biology, marine and geosciences, intracellular sensing, aerodynamics, industry and biotechnology, among others.