Field Effect Transistors Based on Semiconductive Microbially Synthesized Chalcogenide Nanofibers

Abstract

Microbial redox activity offers a potentially transformative approach to the low-temperature synthesis of nanostructured inorganic materials. Diverse strains of the dissimilatory metal-reducing bacteria Shewanella are known to produce photoactive filamentous arsenic sulfide nanomaterials by reducing arsenate and thiosulfate in anaerobic culture conditions. We present in situ microscopic observations and measure the thermally activated (79 kJ/mol) precipitation kinetics of high yield (504 mg per liter of culture, 82% of theoretical maximum) extracellular As2S3 nanofibers produced by Shewanella sp. strain ANA-3, and demonstrate their potential in functional devices by constructing field effect transistors (FETs) based on individual nanofibers and photoelectrochemical cells based on macroscopic mats. The use of strain ANA-3, which possesses both respiratory and detoxification arsenic reductases, result in significantly faster nanofiber synthesis than other strains previously tested, mutants of ANA-3 deficient in arsenic reduction, and when compared to abiotic arsenic sulfide precipitation from As(III) and S2-. Detailed characterization by electron microscopy, energy-dispersive X-ray spectroscopy, electron probe micro-analysis, and Tauc analysis of UV-Vis spectrophotometry show the biogenic precipitate to consist primarily of amorphous As2S3 nanofibers with an indirect optical band gap of 2.37 eV. X-ray diffraction also reveal the presence of crystalline As8S9-x minerals that, until recently, were thought to form only at higher temperatures and hydrothermal conditions. The nanoscale FETs enable a detailed characterization of the charge mobility (∼10−5 cm2/V s) and gating behavior of the heterogeneously doped nanofibers. We also present a characterization of detected photocurrent. These studies indicate that the biotransformation of metalloids and chalcogens by bacteria enables fast, efficient, sustainable synthesis of technologically relevant chalcogenides for potential electronic and optoelectronic applications.