Selection and Functionalization of Germanium Nanowires for Bio-Sensing

Abstract

In this paper, we investigate the use of dielectrophoresis to align germanium nanowire arrays to realize nanowire-based diodes and their subsequent use for bio-sensing. After establishing that dielectrophoresis is a controllable and repeatable fabrication method to create devices from germanium nanowires, we use the optimum process conditions to form a series of diodes. These are subsequently functionalized with an aptamer, which is able to bind specifically to the spike protein of SARS-Cov2 and investigated as a potential sensor. We observe a linear increase in the source to drain current as the concentration of spike protein is increased from 100 fM/L to 1 nM/L.

Figure 1

(a) and (b) SEM images of typical as-grown Ge NWs, (c) overview schematic of DEP system (not to scale), (d) top view schematic of final device (not to scale), and (e) side profile of the final device with functionalization (not to scale).

Figure 2

(a) IV characteristics of as-fabricated Ge nanowire FETs at differing DEP frequencies with an ungrounded gate potential, (b) representation of contacted NWs, and (c) schematic of the resulting band alignment.

Figure 3

Forward IV characteristics of as-fabricated Ge NW devices fabricated at DEP frequencies of (a) 500 Hz, (b) 1 MHz, and (c) 10 MHz and reverse IV characteristics for devices fabricated at DEP frequencies of (d) 500 Hz, (e) 1 MHz, and (f) 10 MHz, all with a peak-to-peak DEP voltage of 8 V.

Figure 4

(a) Forward turn-on voltage, (b) asymmetry (at ±1.5 V) as a function of DEP frequency, and (c) (θμ) as extrapolated by fitting the Mott–Gurney law to IV curves as a function of DEP frequency.

Figure 5

IV characteristics of multiple Ge nanowire devices fabricated with a DEP frequency of 10 MHz and a peak-to-peak DEP voltage of 4 V.

Figure 6

Raman spectra for the Ge nanowire device after a complete functionalization process.

Figure 7

(a) IV characteristics of the as-fabricated Ge nanowire FETs; after functionalization and exposure to increasing concentrations of spike protein, all devices were fabricated with a DEP frequency of 10 MHz and (b) relative increase in the source–drain current, relative to a functionalized device at a bias ±2 V.

Figure 8

Relative increase in the source–drain current, relative to a functionalized device at a bias of ±2 V for exposure to increasing concentrations of BSA.