Electrically Controllable Single-Point Covalent Functionalization of Spin-Cast Carbon-Nanotube Field-Effect Transistor Arrays

Abstract

Carbon-nanotube field-effect transistors (CNTFETs) have been used to sense conformational changes and binding events in protein and nucleic acid structures from the intrinsic molecular charge. The key to utilizing these CNT devices as single-molecule sensors is the ability to attach a single probe molecule to an individual device. In contrast with noncovalent attachment approaches such as those based on van der Waals interactions, covalent attachment approaches generally deliver higher stability but have traditionally been more difficult to control, resulting in low yield. Here we present a single-point-functionalization method for CNTFET arrays based on electrochemical control of a diazonium reaction to create sp3 defects, combined with a scalable spin-casting method for large arrays of devices on arbitrary substrates. Attachment of probe DNA to the functionalized device verifies correct single molecule detection of DNA hybridization with the complementary target. This method enables rapid single-point defect generation with 80% yield, rendering it adaptable to fabricating large arrays of CNTFET devices.

Characterizing the conformational free-energy landscape of RNA stem-loops using single-molecule field-effect transistors

“…Observation of these transitions and states depended on a stem-loop having been tethered to the smFET (compare Figure S2 to Figure S3) and, once a stem-loop had been tethered, the observed transition frequencies were clearly temperature dependent (Figure S2b-c). A parsimonious analysis of these trajectories using a previously described two-state, drift-corrected, thresholding algorithm [31][32]40 separated the observed states into a cluster of high current states (blue portion of the idealized path depicted in Figure 1c) and a cluster of low current states (red portion). Previous studies utilizing the smFET platform for biomolecular sensing have shown that the naturally occurring, electrostatically charged chemical groups of a single biomolecule tethered to the SWCNT surface of an smFET device locally gate the current transduction through the SWCNT.…”

“…Previous efforts have focused on utilizing covalent tethering approaches and controlling this covalent chemistry to achieve single-molecule tethering. [31][32]34 Here, we focus on utilizing a non-covalent tethering approach 38,49 and developing a method to identify single nucleic acid molecules tethered to SWCNTs without perturbing the structural and/or electronic properties of the SWCNT. To characterize the number of nucleic acid molecules tethered to single smFETs and optimize our tethering protocol so as to ensure that only one molecule was tethered to each individual device, we developed a robust, AFM-based method for visualizing smFET-tethered nucleic acid constructs with single-molecule resolution.…”

“…smFETs enable high-time-resolution, single-molecule studies of biomolecular dynamics that, uniquely, do not rely on fluorophore reporters of conformational changes nor on the application of mechanical force using an optical trapping instrument or atomic force microscope (AFM). [30][31][32][33][34][35][36][37][38][39] Using this approach, we report the direct observation of conformational transitions in single RNA molecules across the microseconds-to-minutes timescales that are relevant for studies of RNA (un)folding and conformational dynamics. This includes transitions across the 1-200 ms timescales that would be exceedingly difficult, if not impossible, to simultaneously monitor at single-molecule resolution and in a fluorophore-and force-free manner.…”

“…(c) A representative, 400-ms current versus time trajectory recorded for the C4MM construct, with an 80-ms subsection magnified below.These trajectories were collected at 200 µs time resolution. An idealized current state versus time trajectory (blue and red), obtained by applying a previously described two-state, drift-corrected, thresholding algorithm[31][32]40 is overlaid on the current versus time trajectory. Details of the data analysis procedures are described in the Supporting Information.…”

Chemical-free and scalable process for the fabrication of a uniform array of liquid-gated CNTFET, evaluated by KCl electrolyte

“…In Table 1 , we compare our shadow mask-based s-SWNTs patterning approach with the reported fabrication methods for the realization of similar LG-CNTFET array of devices 49 , 51 – 55 . In most of the cases, for such semiconductor device array fabrication, the use of mixture (s-/m-) SWNTs results in variation in device-to-device characteristics and degradation of device performance especially due to m-SWNTs.…”