Microscale loop-mediated isothermal amplification of viral DNA with real-time monitoring on solution-gated graphene FET microchip

Rapid and reliable molecular analysis of DNA for disease diagnosis is highly sought-after. FET-based sensors fulfill the demands of future point-of-care devices due to its sensitive charge sensing and possibility of integration with electronic instruments. However, most of the FETs are unstable in aqueous conditions, less sensitive and requires conventional Ag/AgCl electrode for gating. In this work, we propose a solution-gated graphene FET (SG-FET) for real-time monitoring of microscale loop-mediated isothermal amplification of DNA. The SG-FET was fabricated effortlessly with graphene as an active layer, on-chip co-planar electrodes, and polydimethylsiloxane-based microfluidic reservoir. A linear response of about 0.23 V/pH was seen when the buffers from pH 5-9 were analyzed on the SG-FET. To evaluate the performance of SG-FET, we monitored the amplification of Lambda phage gene as a proof-of-concept. During amplification, protons are released, which gradually alters the Dirac point voltage (VDirac) of SG-FET. The resulting device was highly sensitive with a femto-level limit of detection. The SG-FET could easily produce a positive signal within 16.5 min of amplification. An amplification of 10 ng/μl DNA for 1 h produced a ∆VDirac of 0.27 V. The sensor was tested within a range of 2×102 copies/μl (10 fg/μl) to 2×108 copies/μl (10 ng/μl) of target DNA. Development of this sensing technology could significantly lower the time, cost, and complications of DNA detection.