Fig. 2

Comparison between optical and redox-reactive nanowire FET measurements of bacteria’s metabolic activity. a Transmittance versus time, and b Glucose signal versus time, as measured by spectrophotometer (at 600 nm) and by redox-reactive SiNW, respectively, during the growth of E. coli bacteria. in minimal broth medium supplemented with glucose as the only carbon source, at pH 7.3. inset of b Demonstration of the calculation method used to extract plot b. Before each injection of a new sample (800 µL sample, rate = 100 µL/second), the devices were switched off (Vsd = 0 V). Each measurement lasted for 180 s, during which the source-drain voltage (Vsd) was 0.3 V and the gate voltage (Vg) was 0 V. The glucose signal-versus-time curve was constructed from the current values at 180 s from the beginning of each measurement, right before the devices were switched off (Vsd = 0). The sensing conditions were chosen based on previous studies [13]. The signal was calculated by subtracting the value of the current after the addition of oxidase from the value of the current before its addition. The black dashed line marks the baseline obtained by the addition of reductant (1 vol% DEHA in medium). The error in the current values (Y-axis in b) is estimated to be ± 0.100 nA, the error in the transmittance values (Y-axis in a) is calculated as a function of the absorption measurements, as described in Additional file 1: Section 15