Flexible and Transparent Composite Electrode with 3D Freestanding Architecture for Dopamine Monitoring

Development of a flexible, transparent, and air-permeable dopamine (DA) sensor is highly desirable for fully integrated optoelectrochemical probes, which can provide a useful tool for closed-loop control and monitoring neural activities. Herein, a 3D freestanding architecture, which integrates a flexible and transparent metallic micromesh as the “core” with DA sensitive poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) as the “shell,” has been developed for DA monitoring. The freestanding micromesh electrode shows not only high mechanical flexibility (without apparent performance variation after 100 bending times), high optical transparency (≈85% at 550 nm), and air permeability (≈2600 mm s⁻¹ at 10 Pa), but also excellent DA sensing performance such as a sensitivity up to 1650 µAcm⁻² mM⁻¹, wide linear range from 1 × 10⁻⁶ to 1000 × 10⁻⁶ m, a low limit of detection (LOD) of 0.27 × 10⁻⁶ m, high selectivity and high stability. The outstanding performance may arise from the core-shell micromesh configuration, which combines high electrical conductivity of the Ni micromesh and high electrocatalytic activity of the PEDOT:PSS layer for DA oxidation. Such 3D freestanding architecture offers a simple and effective methodology to construct implantable biosensors for monitoring of DA and other neurotransmitters in the brain.