Dual-Mode Graphene Field-Effect Transistor Biosensor with Isothermal Nucleic Acid Amplification

Abstract

Despite a substantial increase in testing facilities during the pandemic, access remains a major obstacle, particularly in low-resource and remote areas. This constraint emphasizes the need for high-throughput potential point-of-care diagnostic tools in environments with limited resources. Loop-mediated isothermal amplification (LAMP) is a promising technique, but improvements in sensitivity are needed for accurate detection, especially in scenarios where the virus is present in low quantities. To achieve this objective, we present a highly sensitive detection approach of a dual-mode graphene-based field-effect transistor (G-FET) biosensor with LAMP. The G-FET biosensor, which has a transparent graphene microelectrode array on a glass substrate, detects LAMP products in less than 30 min using both observable color changes and Dirac point voltage measurements, even in samples with low viral concentrations. This dual-mode G-FET biosensor emerges as a potential alternative to conventional RT-PCR for severe acute respiratory syndrome-associated coronavirus (SARS-CoV)-2 detection or point-of-care testing, particularly in resource-constrained scenarios such as developing countries. Moreover, its capacity for colorimetric detection with the naked eye enhances its applicability in diverse settings.

Keywords: SARS-CoV-2; colorimetric detection; graphene field-effect transistor; loop-mediated isothermal amplification; multi-array.

Figure 1

Schematic diagram and functional concept of the graphene field-effect transistor (G-FET) biosensor. (a) Chemical vapor deposition-grown graphene transfer accomplished using copper (Cu) as a sacrificial layer and polydimethylsiloxane (PDMS) as a supportive layer. (b) Design of the multi-electrode array featuring a graphene channel connecting the drain/source contacts, gate, and PDMS chamber. (c) Dual-mode monitoring illustrating the detection of amplicons through loop-mediated isothermal amplification (LAMP) via pH changes.

Figure 2

Detailed analysis of the transferred graphene sheet. (a) Raman spectra of the graphene sheet transferred to the multi-electrode array. (b) Ultraviolet–visible spectroscopy transmittance before and after transferring a single-layer graphene film to the glass substrate. (c) Transfer curves for the five-electrode array graphene field-effect transistor, with 1× phosphate buffer solution within the polydimethylsiloxane chambers. (d) Atomic force micrograph of the transferred graphene sheet.

Figure 3

Loop-mediated isothermal amplification assay with ten-fold serially diluted templates ranging from 1.48 × 10⁸ to 1.48 × 10¹ copies per reaction. Graphical representations of amplification plots, melting curves, and standard curves for the (a) E and (b) RdRP genes.

Figure 4

Dual-mode analysis of the loop-mediated isothermal amplification assay using the graphene field-effect transistor biosensor. (a) Colorimetric and (b) electrical analyses of the Envelope (E) and RNA-dependent RNA polymerase (RdRP) genes. (c) Dirac point voltage (ΔV_Dirac) values for the clinical samples. NTC = non-template control.