Bradford J. Taft

Nanostructuring of Patterned Microelectrodes To Enhance the Sensitivity of Electrochemical Nucleic Acids Detection

Disease diagnosis on the basis of biomolecular analysis requires sensitive, cost-effective, and multiplexed assays. Biomarker analysis based on electronic readout has long been cited as a promising approach that would enable the creation of a new family of chip-based devices with appropriate cost and sensitivity for medical testing. The sensitivity of electronic readout, and specifically electrochemical analysis, is in principle sufficient to enable direct detection of small numbers of analyte molecules with simple instrumentation. Over the last several years, very high sensitivities have been demonstrated for nanomaterial-based electrochemical assays in particular, whereby nanowireand nanotube-based electrodes have shown some of the highest sensitivities to date. Whether these assays can be made practical and multiplexed remains to be seen, however, as the materials used have not been readily amenable to arrayed and straightforward fabrication. Herein, we present a new system that enables nanostructured materials to be produced and used as nucleic acids sensors in an arrayed format. By using lithographically defined apertures as a template, we grew microelectrodes on a silicon chip by metal electrodeposition (Figure 1). Drawing upon the numerous studies of nanostructures with diverse morphologies generated as dispersions in solution, we sought to manipulate precisely the surface morphology of these electrodes to control the level of nanostructuring present. We show that the production of nanostructured features on electrode surfaces is essential for the performance of the microelectrodes as ultrasensitive electrochemical detectors. A variety of studies have suggested that nanostructures are highly beneficial for biosensing applications because of the increased surface area, enhanced delivery of amplification agents, or precise biomolecule–electrode connections that are possible; however, the role of nano-

DNA-directed synthesis of zinc oxide nanowires on carbon nanotube tips

This paper describes a class of three component hybrid nanowires templated by DNA directed self-assembly. Through the modification of carbon nanotube (CNT) termini with synthetic DNA oligonucleotides, gold nanoparticles are delivered, via DNA hybridization, to CNT tips that then serve as growth sites for zinc oxide (ZnO) nanowires. The structures we have generated using DNA templating represent an advance toward building higher order sequenced one dimensional nanostructures with rational control.

Optoelectrical characteristics of individual zinc oxide nanorods grown by DNA directed assembly on vertically aligned carbon nanotube tips

The authors describe the properties of electronically active nanowires that can be assembled via DNA directed growth on a nanostructured array. DNA-modified nanoparticles are used to site-specifically address the tips of vertically aligned carbon nanotubes (CNTs) that serve as catalysts for the growth of zinc oxide (ZnO) nanorods. Using conductive probe atomic force microscopy, they measured the conductance characteristics of single ZnO-CNT structures under various force and illumination conditions and at different sites in a large array, thereby establishing that DNA directed formation of multimaterial, optically active nanostructures can yield devices that are electronically functional at the nanometer scale. The inherent ability of DNA to carry and convey encoded information provides the basis for targeted synthesis of nanostructured devices.