Fig. 2

Dopamine detection in physiological buffers with gMTAs. A Schematic illustration of aptamer structure reorientation close to an EG–gFET graphene channel upon dopamine binding. B Calibration curve for dopamine detection in 1 × PBS (data is mean ± sem, with 4th order polynomial line fit) (top). Representative transfer curve shifts as a function of increasing dopamine concentrations for the linear detection range of one EG–gFET in 1 × PBS. V_DIRAC moves towards positive gate voltages (V_GS) (black arrow indicates the direction of V_DIRAC shifts) (middle). Illustration of the hypothesized reorientation of the aptamer's backbone negative charges close to the gFETs upon dopamine binding in 1 × PBS, leading to electrostatic repulsion in the graphene channel (bottom). C Calibration curve for dopamine detection in 1 × aCSF (data is mean ± sem, with 4th order polynomial line fit) (top). Representative transfer curve shifts as a function of increasing dopamine concentrations for the linear detection range of one EG–gFET in 1 × aCSF, with V_DIRAC moving towards negative gate voltages (V_GS) (black arrow indicates the direction of V_DIRAC shifts) (middle). Illustration of the hypothesized reorientation of the aptamer's structure in aCSF upon dopamine binding, with the increased attraction of positive charges closer to the graphene channel, leading to negative shifts of V_DIRAC (bottom). D Calibration curves for dopamine detection in 1 × PBS at pH 6.4 (blue), 7.4 (red) and 8.4 (dark green) (data is mean ± sem, with 4th order polynomial line fit). E Comparative responses of gMTAs to 1 pM dopamine, 1 nM L-DOPA, 1 nM L-tyrosine and 1 nM ascorbic acid in 1 × PBS (normalized data is mean + sem; One-way ANOVA, *p < 0.0001)