(a) Sequence of steps for BSA–streptavidin surface functionalization (I, II), non-electrophoretic probe DNA immobilization (III) and hybridization or control experiments (IV). (b) Measured VREF−IDS curves (five forward VREF sweeps; device 6) right before and after 100-fM target DNA hybridization. VS=−0.03 V and VD=+0.03 V. (c) V0 values extrapolated from the data of b. ΔV0 is the shift from the average of the pre-hybridization V0 values to that of the post-hybridization V0 values. (d) ΔV0 data for 100 fM hybridization and control for all 8 graphene FETs. Statistics are based on five VREF–IDS curve measurements right before and after the phase IV. Results from both forward and reverse VREF sweeps are shown. ΔV0 averaged across all eight graphene FETs, subsuming both forward and reverse sweeps, is also shown for hybridization and control. For all data here: *P<0.05; **P<0.01; no *, not significant; and the error bars represent ±1 s.d.