Electrical graphene aptasensor for ultra-sensitive detection of anthrax toxin with amplified signal transduction

Detection of the anthrax toxin, the protective antigen (PA), at the attomolar (aM) level is demonstrated by an electrical aptamer sensor based on a chemically derived graphene field-effect transistor (FET) platform. Higher affinity of the aptamer probes to PA in the aptamer-immobilized FET enables significant improvements in the limit of detection (LOD), dynamic range, and sensitivity compared to the antibody-immobilized FET. Transduction signal enhancement in the aptamer FET due to an increase in captured PA molecules results in a larger 30 mV/decade shift in the charge neutrality point (V _g,min) as a sensitivity parameter, with the dynamic range of the PA concentration between 12 aM (LOD) and 120 fM. An additional signal enhancement is obtained by the secondary aptamer-conjugated gold nanoparticles (AuNPs-aptamer), which have a sandwich structure of aptamer/PA/aptamer-AuNPs, induce an increase in charge-doping in the graphene channel, resulting in a reduction of the LOD to 1.2 aM with a three-fold increase in the V _g,min shift. A chemically derived graphene field-effect transistor (FET) with aptamer recognition molecules shows ultra-sensitivity (12 aM∼120 fM) for anthrax toxin due to the higher affinity of the aptamer probe compared to that of an Ab probe. Detection capability with a limit of detection (LOD) at the attomolar level (1.2 aM) is achieved due to the amplification of signal transduction by the additional use of the secondary aptamer-conjugated gold nanoparticles (aptamer-AuNPs).