Gold disk microelectrode-coupled label-free electrochemical aptasensor for dopamine assay

We fabricated a gold disk microelectrode (Au DME) and developed a label-free electrochemical aptasensor for highly sensitive and selective detection of dopamine (DA) in brain slices using an anti-DA specific aptamer as the molecular recognition element and DA oxidation signal as the analytical signal. Au DME with a disk-shaped geometry and a radius in the range of 1.25 to 4 μm was fabricated by fine-tuning the size of the gold microwire inside a borosilicate capillary using laser-assisted pulling and mechanical polishing methods for easily positioning the target object. A label-free electrochemical aptasensor was fabricated by self-assembling an anti-DA-specific aptamer on the surface of Au DME with a radius of 2 μm. The obtained aptasensor directly detected DA based on the oxidation current of DA as an analytical signal, in which the recognition of DA by the anti-DA specific aptamer immobilized on Au DME enabled DA to be close to the electrode surface and facilitated the electrochemical oxidation of DA. Benefitting from Au DME with a small capacitive current and anti-DA specific aptamer with good binding affinity to DA, the label-free electrochemical aptasensor not only sensitively detected DA with a wide linear range of 0.5 to 27 μM and a low detection limit of 0.11 μM but also selectively detected DA in the presence of other interfering neurochemicals. Moreover, the label-free electrochemical aptasensor was successfully applied in the recording of the dynamic increase in DA concentration in a striatal slice from mice upon electrical stimulation. This work provides a promising strategy for the preparation of label-free electrochemical aptasensor based on microelectrodes with high spatial resolution, sensitivity and selectivity to determine neurochemical dynamics in living systems.