One-Step Fabrication of Doped-Graphene Flexible Biosensors for Electrochemical Detection of Neurotransmitters with Nanomolar Sensitivity

A key challenge in graphene-based neural interfaces is fabricating functional graphene-based patterns on polymeric substrates, especially for microelectrode arrays in flexible devices that penetrate the brain. Moreover, both chemical and morphological control of graphene for optimizing electrochemical detection of neurotransmitters is exceedingly challenging for polymer-based devices that cannot withstand the typically extreme environments necessary for synthesis and doping of high-quality graphene. In this talk, we will present a new one-step patterning approach to directly grow three-dimensional porous graphene with controlled heteroatom content on polymer films. This process is based on localized laser irradiation of molecularly controlled polyimides for patterning graphene and doping it in situ during laser scanning, wherein the polyimide itself acts as the precursor. We use a two-step polycondensation of 4,4'-oxydianiline with three different tetracarboxylic dianhydrides for fabricating fully aromatic polyimides with various internal linkages such as phenylene, trifluoromethyl or sulfone groups. Our laser-induced doped graphene produced exhibit electrical resistivity lower than 12 ohm.sq^-1. Among the three different variants we fabricate (N-doped, F-doped, and S-doped), our results show that our F-doped graphene microelectrodes exhibit a superior performance of electrochemical detection of dopamine, which is one of the most important neurotransmitters in the brain. Specifically, the sensitivity of our high-surface area graphene-based microelectrodes is three orders of magnitude higher than carbon fiber electrodes that are currently considered the gold standard for electrochemical dopamine sensors. Furthermore, they can consistently detect 10 nM dopamine concentration with clear discrimination of the oxidation and reduction peaks. Hence, our findings pave the way for facile fabrication of functional graphene microelectrodes on polymers for various flexible device applications such as neural probes for highly sensitive neurochemical detection, stimulation and recording.