Individually-addressable composite microneedle electrode array by mold-and-place method for glucose detection

Microneedle (MN)-based electrochemical biosensors enable minimally invasive and in situ monitoring of biomolecules from interstitial fluid (ISF) that is strongly correlated to their concentrations in the blood. When an array of MNs is used as either working or counter electrodes for electrochemical sensing, it is often difficult to have narrow spacing between them and this can lead to poor measurement accuracy due to increased resistance, low sensitivity, and slow response time. This study aims to develop a method to fabricate independently functioning MN electrodes with narrow intervals between them for high precision electrochemical sensing. A mixture of photocurable polymer (SU-8) and single-wall carbon nanotubes (SWCNTs) was optimized for pressure-assisted transfer (PAT) molding and electrical conductivity. Single composite MNs were molded by PAT molding, and then attached on pre-patterned electrodes. After the ‘mold-and-place’ of the composite MN structures, plasma etching and electropolymerization of PEDOT:PSS were performed to enhance the electrochemical activity. Prussian blue (PB) and glucose oxidase (GOx) were electrodeposited on surface-treated MNs to enable glucose detection. MN electrodes showed limit of detection (LOD) at 1.02 mM and linearity up to 20 mM. Finally, MN electrodes were constructed on a flexible polyimide film and demonstrated the feasibility of detecting glucose in an in vivo mouse study.