Brian L. Hassler

Amperometric Electrochemical Microsystem for a Miniaturized Protein Biosensor Array

Protein-based bioelectrochemical interfaces offer great potential for rapid detection, continuous use, and miniaturized sensor arrays. This paper introduces a microsystem platform that enables multiple bioelectrochemical interfaces to be interrogated simultaneously by an onchip amperometric readout system. A post-complementary metal-oxide semiconductor (CMOS) fabrication procedure is described that permits the formation of planar electrode arrays and self assembly of biosensor interfaces on the electrodes. The onchip, 0.5-mum CMOS readout electronics include a compact potentiostat that supports a very broad range of input currents-6 pA to 10 muA-to accommodate diverse biosensor interfaces. The 2.3 times 2.2-mm chip operates from a 5-V supply at 0.6 mA. A prototype electrochemical sensor platform, including an onchip potentiostat and miniaturized biosensor array, was characterized by using cyclic voltammetry. The linear relationship between the oxidization peak values and the concentrations of target analytes in the solution verifies functionality of the system and demonstrates the potential for future implementations of this platform in high sensitivity, low cost, and onchip protein-based sensor arrays.

A Protein-Based Electrochemical Biosensor Array Platform for Integrated Microsystems

This paper elucidates challenges in integrating different classes of proteins into a microsystem and presents an electrochemical array strategy for heterogeneous protein-based biosensors. The overlapping requirements and limitations imposed by biointerface formation, electrochemical characterization, and microsystem fabrication are identified. A planar electrode array is presented that synergistically resolves these requirements using thin film Au and Ag/AgCl electrodes on a dielectric substrate. Using molecular self-assembly, electrodes were modified by nano-structures of two diverse proteins, alkali ion-channel protein and alcohol dehydrogenase enzyme. Electrochemical impedance spectroscopy and cyclic voltammetry measurements were performed to characterize sensor response to alkali ion and alcohol, respectively. This work demonstrates the viability of the electrochemical microsystem platform for heterogeneous protein-based biosensor interfaces.

An electrochemical interface for integrated biosensors

This paper presents an integrated, protein-based, biosensor that can be scaled to form high-density, multi-analyte sensor arrays physically integrated on a signal conditioning circuit die. A fully scalable, post-CMOS-compatible, three-electrode interface to biochemical sensors has been developed. A silicon substrate electrode system, consisting of Ti/Au working and auxiliary electrodes and a Ti/Au/Ag/AgCl reference electrode has been adapted to biomimetic sensors. The functional Ag/AgCl reference electrode is isolated from the environment using a Nafion cation-exchange membrane to extend operation lifetime. To complete the sensor structure, lipid bilayers have been deposited in passivation layer openings formed over individual working electrodes using a special tethering molecule. Total internal reflection microscopy (TIRFM) studies were done to confirm that a wide range of proteins, such as dehydrogenase enzymes and ion channels, can then be embedded into the lipid bilayers. These results verify the potential to form highly selective recognition elements with direct physical connection to readout electronics on the supporting silicon substrate.

Versatile bioelectronic interfaces on flexible non-conductive substrates.

Bioelectronic interfaces that establish electrical communication between redox enzymes and electrodes have potential applications as biosensors, biocatalytic reactors, and biological fuel cells. These interfaces are commonly formed on gold films deposited using physical vapor deposition (PVD) or chemical vapor deposition (CVD). PVD and CVD require deposition of a primer layer, such as titanium or chromium, and require the use of expensive equipment and cannot be used on a wide range of substrates. This paper describes a versatile new bench-top method to form bioelectronic interfaces containing a gold film, electron mediator, cofactor, and dehydrogenase enzyme (secondary alcohol dehydrogenase, and sorbitol dehydrogenase) on nonconductive substrates such as polystyrene and glass. The method combines layer-by-layer deposition of polyelectrolytes, electroless metal deposition, and directed molecular self-assembly. Cyclic voltammetry, chronoamperometry, field emission X-ray dispersive spectroscopy, scanning electron microscopy, and atomic force microscopy were used to characterize the bioelectronic interfaces. Interfaces formed on flexible polystyrene slides were shown to retain their activity after bending to a radius of curvature of 18mm, confirming that the approach can be applied on cheap and flexible substrates for applications where traditional wafer-scale electronics is not suitable, such as personal or structural health monitors and rolled microtube biosensors.

Biomimetic interfaces for a multifunctional biosensor array microsystem

Bioelectronic interfaces that allow dehydrogenase enzymes to electrically communicate with electrodes have potential applications in the development of biosensors and biocatalytic reactors. A fully scalable, post-CMOS-compatible, three-electrode interface to biochemical sensors, consisting of Ti/Au working and auxiliary electrodes and a Ti/Au/Ag/AgCl reference electrode, has been developed. Also described is a tri-functional linking molecule that binds the mediator and cofactor to the electrode in a unique spatial arrangement in which the dehydrogenase enzyme can bind to cofactor and multistep electron transfer between the electrode and enzyme is achieved. This approach provides greater flexibility in assembling complex bioelectronic interfaces than is possible with previously reported, linear linking molecules. A cysteine molecule was self-assembled on a gold electrode via a thiol bond. The electron mediator toluidine blue O (TBO) and the cofactor, /spl beta/-nicotinamide adenine dinucleotide phosphate (NADP/sup +/) were chemically attached to cysteine via the formation of amide bonds. Cyclic voltammetry, was used to demonstrate the electrical activity, and enzymatic activity of the resulting bioelectronic interface.