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Dive into the research topics where Valber A. Pedrosa is active.

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Featured researches published by Valber A. Pedrosa.


Colloids and Surfaces B: Biointerfaces | 2010

Enhanced stability of enzyme organophosphate hydrolase interfaced on the carbon nanotubes.

Valber A. Pedrosa; Sheetal Paliwal; Shankar Balasubramanian; Dhriti Nepal; Virginia A. Davis; James R. Wild; Erlan Ramanculov; Aleksandr Simonian

In this paper we demonstrate that SWNTs and a covalent immobilization strategy enable very sensitive sensors with excellent long term stability. Organophosphorus hydrolase (OPH) functionalized single and multi-walled carbon nanotube (CNT) conjugates were exploited for direct amperometric detection of paraoxon, a model organophosphate. The catalytic hydrolysis of paraoxon produces equimoles of p-nitrophenol; oxidation was monitored amperometrically in real time under flow-injection (FIA) mode. OPH covalently immobilized on single-walled carbon nanotubes (SWNTs) demonstrated much higher activity than OPH conjugated to multi-walled carbon nanotubes (MWNTs). The dynamic concentration range for SWNT-OPH was 0.5-8.5 micromolL(-1) with a detection limit of 0.01 micromolL(-1) (S/N=3). In addition to this high sensitivity, the immobilized OPH retained a significant degree of enzymatic activity, and displayed remarkable stability with only 25% signal loss over 7 months. These results suggest that covalent immobilization of OPH on CNTs can be used for specific immobilization with advantages of long term stability, high sensitivity, and simplicity.


ACS Applied Materials & Interfaces | 2010

Immobilizing enzymes onto electrode arrays by hydrogel photolithography to fabricate multi-analyte electrochemical biosensors.

Jun Yan; Valber A. Pedrosa; Aleksandr Simonian; Alexander Revzin

This paper describes a biomaterial microfabrication approach for interfacing functional biomolecules (enzymes) with electrode arrays. Poly (ethylene glycol) (PEG) hydrogel photopatterning was employed to integrate gold electrode arrays with the enzymes glucose oxidase (GOX) and lactate oxidase (LOX). In this process, PEG diacrylate (DA)-based prepolymer containing enzyme molecules as well as redox species (vinylferrocene) was spin-coated, registered, and UV cross-linked on top of an array of gold electrodes. As a result, enzyme-carrying circular hydrogel structures (600 microm diameter) were fabricated on top of 300 microm diameter gold electrodes. Importantly, when used with multiple masks, hydrogel photolithography allowed us to immobilize GOX and LOX molecules on adjacent electrodes within the same electrode array. Cyclic voltammetry and amperometry were used to characterize biosensor electrode arrays. The response of the biosensor array was linear for up to 20 mM glucose with sensitivity of 0.9 microA cm(-2) mM(-1) and 10 mM lactate with sensitivity of 1.1 microA cm(-2) mM(-1). Importantly, simultaneous detection of glucose and lactate from the same electrode array was demonstrated. A novel strategy for integrating biological and electrical components of a biosensor described in this paper provides the flexibility to spatially resolve and register different biorecognition elements with individual members of a miniature electrode array. Of particular interest to us are future applications of these miniature electrodes for real-time monitoring of metabolite fluxes in the vicinity of living cells.


Biosensors and Bioelectronics | 2009

Enzymatic AND-gate based on electrode-immobilized glucose-6-phosphate dehydrogenase: Towards digital biosensors and biochemical logic systems with low noise

Vladimir Privman; Valber A. Pedrosa; Dmitriy V. Melnikov; Marcos Pita; Aleksandr Simonian; Evgeny Katz

Electrode-immobilized glucose-6-phosphate dehydrogenase is used to catalyze an enzymatic reaction which carries out the AND logic gate. This logic function is considered here in the context of biocatalytic processes utilized for the biocomputing applications for digital (threshold) sensing/actuation. We outline the response functions desirable for such applications and report the first experimental realization of a sigmoid-shape response in one of the inputs. A kinetic model is developed and utilized to evaluate the extent to which the experimentally realized gate is close to optimal.


Langmuir | 2010

Renewable nanocomposite layer-by-layer assembled catalytic interfaces for biosensing applications.

Saroja Mantha; Valber A. Pedrosa; Eric V. Olsen; Virginia A. Davis; Aleksandr Simonian

A novel, easily renewable nanocomposite interface based on layer-by-layer (LbL) assembled cationic/anionic layers of carbon nanotubes customized with biopolymers is reported. A simple approach is proposed to fabricate a nanoscale structure composed of alternating layers of oxidized multiwalled carbon nanotubes upon which is immobilized either the cationic enzyme organophosphorus hydrolase (OPH; MWNT-OPH) or the anionic DNA (MWNT-DNA). The presence of carbon nanotubes with large surface area, high aspect ratio and excellent conductivity provides reliable immobilization of enzyme at the interface and promotes better electron transfer rates. The oxidized MWNTs were characterized by thermogravimetric analysis and Raman spectroscopy. Fourier transform infrared spectroscopy showed the surface functionalization of the MWNTs and successful immobilization of OPH on the MWNTs. Scanning electron microscopy images revealed that MWNTs were shortened during sonication and that LbL of the MWNT/biopolymer conjugates resulted in a continuous surface with a layered structure. The catalytic activity of the biopolymer layers was characterized using absorption spectroscopy and electrochemical analysis. Experimental results show that this approach yields an easily fabricated catalytic multilayer with well-defined structures and properties for biosensing applications whose interface can be reactivated via a simple procedure. In addition, this approach results in a biosensor with excellent sensitivity, a reliable calibration profile, and stable electrochemical response.


Biomicrofluidics | 2011

Electrochemical biosensors for on-chip detection of oxidative stress from immune cells.

Jun Yan; Valber A. Pedrosa; James Enomoto; Aleksandr Simonian; Alexander Revzin

Seamless integration of biological components with electrochemical sensors is critical in the development of microdevices for cell analysis. The present paper describes the integration miniature Au electrodes next to immune cells (macrophages) in order to detect cell-secreted hydrogen peroxide (H(2)O(2)). Photopatterning of poly(ethylene glycol) (PEG) hydrogels was used to both immobilize horseradish peroxidase molecules onto electrodes and to define regions for cell attachment in the vicinity of sensing electrodes. Electrodes micropatterned in such a manner were enclosed inside poly(dimethylsiloxane) fluid conduits and incubated with macrophages. The cells attached onto the exposed glass regions in the vicinity of the electrodes and nowhere else on the non-fouling PEG hydrogel surface. A microfluidic device was converted into an electrochemical cell by placing flow-through Ag∕AgCl reference and Pt wire counter electrodes at the outlet and inlet, respectively. This microdevice with integrated H(2)O(2)-sensing electrodes had sensitivity of 27 μA∕cm(2) mM with a limit of detection of 2 μM. Importantly, this microdevice allowed controllable seeding of macrophages next to electrodes, activation of these cells and on-chip monitoring of H(2)O(2) release in real time. In the future, this biosensor platform may be utilized for monitoring of macrophage responses to pathogens or for the study of inflammatory signaling in micropatterned cell cultures.


Electrochimica Acta | 2010

Deposition of selenium thin layers on gold surfaces from sulphuric acid media: Studies using electrochemical quartz crystal microbalance, cyclic voltammetry and AFM

Murilo F. Cabral; Valber A. Pedrosa; Sergio Machado


Sensors and Actuators B-chemical | 2009

Copper nanoparticles and carbon nanotubes-based electrochemical sensing system for fast identification of tricresyl-phosphate in aqueous samples and air

Valber A. Pedrosa; Rigved Epur; Jessica Benton; Ruel A. Overfelt; Aleksandr Simonian


Electroanalysis | 2011

Micropatterned Nanocomposite Hydrogels for Biosensing Applications

Valber A. Pedrosa; Jun Yan; Aleksandr Simonian; Alexander Revzin


Sensors and Actuators B-chemical | 2011

Tethered DNA scaffolds on optical sensor platforms for detection of hipO gene from Campylobacter jejuni

Tony Jefferson Gnanaprakasa; Omar A. Oyarzabal; Eric V. Olsen; Valber A. Pedrosa; Aleksandr Simonian


International Journal of Unconventional Computing | 2010

Enzymatic Logic Gates with Noise-Reducing Sigmoid Response

Valber A. Pedrosa; Dmitriy V. Melnikov; Marcos Pita; Jan Halámek; Vladimir Privman; Aleksandr Simonian; Evgeny Katz

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Jun Yan

University of California

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Rigved Epur

University of Pittsburgh

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