SU-8 based pyrolytic carbon for the electrochemical detection of dopamine

Here we investigated the electrochemical properties and dopamine (DA) detection capability of SU-8 photoresist based pyrolytic carbon (PyC) as well as its biocompatibility with neural cells. This approach is compatible with microfabrication techniques which is crucial for device development. X-ray photoelectron spectroscopy shows that PyC consists 98.5% of carbon, while oxygen plasma treatment (PyC-O₂) increases the amount of oxygen up to 27.1%. PyC showed nearly reversible (ΔE_p 63 mV) electron transfer kinetics towards outer sphere redox probe (Ru(NH₃)₆ ^2+/3+), while the reaction on PyC-O₂ was quasi-reversible (ΔE_p > 75 mV). DA showed both diffusion and adsorption-defined reaction kinetics with fast electron transfer with the ΔE_p values of 50 mV and 30 mV, for PyC and PyC-O₂, respectively. The strong interaction between the hydroxyl groups on the surface and DA, as confirmed by simulations, facilitates the redox reactions of DA. DA showed a linear response in the measured physiologically relevant range (50 nM-1 μM) and sensitivities were 1.2 A M^-1 cm^-2 for PyC and 2.7 A M^-1 cm^-2 for PyC-O₂. Plasma oxidation (PyC-O₂) improved cell adhesion even more than poly-l-lysine (PLL) coating on PyC, but best adhesion was achieved on PLL coated PyC-O₂. Glial cells, neuroblastoma cells and neural stem cells all showed similar behavior.