Gold Disk Microelectrode Coupled Label-free Electrochemical Aptasensor for Dopamine Assay

We fabricate gold disk microelectrode (Au DME) and develop a label-free electrochemical aptasensor for highly sensitive and selective detection of dopamine (DA) in a brain slice by using anti-DA specific aptamer as molecular recognition element and DA oxidation signal as analytical signal. The Au DME with a disk-shaped geometry and a radius in range from 1.25 to 4 μm is fabricated by fine tuning of the size of gold microwire inside a borosilicate capillary with laser-assisted pulling and mechanical polishing method for easily positioning the target object. A label-free electrochemical aptasensor is fabricated by self-assembling an anti-DA specific aptamer on the surface of Au DME with a radius of 2 μm. The obtained aptasensor can directly detect DA based on the oxidation current of DA as analytical signal, in which the recognition of DA by the anti-DA specific aptamer immobilized on Au DME allow DA close to the electrode surface and facilitate the electrochemical oxidation of DA. Taking advantage of 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 can sensitively detect DA with a wide linear range of 0.5 to 27 μM and a low detection limit of 0.11 μM, but also can selectively detect DA in the presence of other interference neurochemicals. Moreover, the label-free electrochemical aptasensor is successfully applied in the recording of the dynamic increase of DA in a brain slice from mice upon electrical stimulation. This work provides a promising strategy for the preparation of label-free electrochemical aptasensor based on microelectrode with high spatial resolution, sensitivity and selectivity to determinate neurochemicals dynamics in living systems.