Harsh Bais, PhD



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  • S. B. Warren, S. Vernick, E. Romano, and K. L. Shepard Complementary Metal-Oxide-Semiconductor Integrated Carbon Nanotube Arrays: Toward Wide-Bandwidth Single-Molecule Sensing Systems Nano Letters DOI: 10.1021/acs.nanolett.6b00319

    There is strong interest in realizing genomic molecular diagnostic platforms that are label-free, electronic, and single-molecule. One attractive transducer for such efforts is the single-molecule field-effect transistor (smFET), capable of detecting a single electronic charge and realized with a point-functionalized exposed-gate one-dimensional carbon nanotube field-effect device. In this work, smFETs are integrated directly onto a custom complementary metaloxide-semiconductor chip, which results in an array of up to 6000 devices delivering a measurement bandwidth of 1 MHz. In a first exploitation of these high-bandwidth measurement capabilities, point functionalization through electrochemical oxidation of the devices is observed with microsecond temporal resolution, which reveals complex reaction pathways with resolvable scattering signatures. High-rate random telegraph noise is detected in certain oxidized devices, further illustrating the measurement capabilities of the platform.

  • D. L. Bellin, H. Sakhtah, Y. Zhang, A. Price-Whelan, L. E.P. Dietrich & K. L. Shepard Electrochemical camera chip for simultaneous imaging of multiple metabolites in biofilms. Nat. Commun. 7:10535 doi: 10.1038/ncomms10535 (2016).

    Monitoring spatial distribution of metabolites in multicellular structures can enhance understanding of the biochemical processes and regulation involved in cellular community development. Here we report on an electrochemical camera chip capable of simultaneous spatial imaging of multiple redox-active phenazine metabolites produced by Pseudomonas aeruginosa PA14 colony biofilms. The chip features an 8mm8mm array of 1,824 electrodes multiplexed to 38 parallel output channels. Using this chip, we demonstrate potential-sweepbased electrochemical imaging of whole-biofilms at measurement rates in excess of 0.2 s per electrode. Analysis of mutants with various capacities for phenazine production reveals distribution of phenazine-1-carboxylic acid (PCA) throughout the colony, with 5-methylphenazine-1-carboxylic acid (5-MCA) and pyocyanin (PYO) localized to the colony edge. Anaerobic growth on nitrate confirms the O2-dependence of PYO production and indicates an effect of O2 availability on 5-MCA synthesis. This integrated-circuit-based technique promises wide applicability in detecting redox-active species from diverse biological samples.