Abstract

Nanomaterial-based field-effect transistors (FETs) have been proposed for real-time, label-free detection of various biological species. However, screening of the analyte charge by electrolyte ions (Debye screening) has so far limited their use in physiological samples. Here, this challenge is overcome by combining FETs based on single-walled semiconducting carbon nanotube networks (SWCNTs) with a novel surface functionalization comprising: (1) short nanobody receptors, and (2) a polyethylene glycol layer (PEG). Nanobodies are stable, easy-to-produce, short biological receptors (~2–4 nm) that enable analyte binding closer to the sensor surface. The addition of PEG enhances the signal in high ionic strength environment. Using green fluorescent protein (GFP) as a model antigen, high selectivity and sub-picomolar detection limit with a dynamic range exceeding 4 orders of magnitude is demonstrated in physiological solutions. The presented immunoassay is fast, label-free, does not require any sample pre-treatment or washing steps.

Highlights

  • Nanoelectronic biosensors based on field-effect transistors (FET) have received significant attention as highly sensitive transducers with potential applications in compact and inexpensive biosensing devices for diagnostics, environmental monitoring or screening

  • To study the effect of polyethylene glycol layer (PEG) on the signal due to green fluorescent protein (GFP) binding, VHH was immobilized on both the pyrene butyric acid (PBA) + PEG coated surface (Figure 1D) and on the control single-walled semiconducting carbon nanotube networks (SWCNTs) samples modified with PBA only (Figure 1A)

  • The transfer curves shift to more positive values in response to increasing GFP concentration, with the PEGylated surface reacting more strongly (Figure 1B,E)

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Summary

Introduction

Nanoelectronic biosensors based on field-effect transistors (FET) have received significant attention as highly sensitive transducers with potential applications in compact and inexpensive biosensing devices for diagnostics, environmental monitoring or screening. Debye screening is severe as the effective distance for charge detection in physiological conditions (100–200 mM ionic strength) is on the order of 1 nm. The nanobodies are produced and stable in a range of different conditions [7] Despite these advantageous properties, nanobodies have not been used yet as receptors for FET-based sensing. On the other hand, using short receptors alone may not be sufficient to achieve appropriate detection limits, as a large part of the analyte may be still screened by the electrolyte ions due to very short Debye length in high ionic strength solutions (

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