Fig. 4: Sensing of dopamine molecules.

a Chronoamperometric sensing curves for 2D Ag/rGO (0 × 0 array) sensor. The dopamine (dopamine hydrochloride) concentration is diluted from 1 pm to 1000 μm in pbs solution (pH 7.4) containing 1 mm concentration of ferro/ferricyanide. The measurements were conducted without any enzyme at a fixed sensing potential of −0.1 V for 1 min. Inset of (a) shows a schematic of dopamine molecules released from pre-synaptic neuron to target post-synaptic neuron. b Saturation currents of 2D Ag/rGO sensor plotted against varying dopamine concentrations. c, e Chronoamperometric sensing of multi-length-scale 3D Ag/rGO (4 × 4 array) and 3D Ag/rGO (10 × 10 array) sensors, respectively, at the same condition as that performed for 2D Ag/rGO sensor. A low concentration (10 fm) of dopamine was tested in addition to 1 pm to 1000 μm for 3D Ag/rGO (10 × 10 array) sensor. Inset of (c) shows the biochemical oxidation/reduction reaction of dopamine. d, f Current responses with varying dopamine concentration for multi-scale 3D Ag/rGO (4 × 4 array) and 3D Ag/rGO (10 × 10 array) configurations, respectively. The detection time for all the results in this figure are within 60 seconds. Error bars in Fig. 4b, d, f are the standard deviation of three repeated measurements (n = 3 biologically independent experiments). Error bars, mean ± SD.