A Three-Dimensional Electrochemical Biosensor Integrated with Hydrogel Enables Real-Time Monitoring of Cells under Their In Vivo-like Microenvironment

Three-dimensional (3D) cell culture can better reproduce the in vivo cell environment and has been extensively used in fields such as tissue engineering, drug screening, and pathological research. Despite the tremendous advancement of 3D cultures, an analysis technique that could collect real-time information of the biological processes therein is sorely lacking. Electrochemical sensing with fast response and high sensitivity has played a vital role in real-time monitoring of living cells, but most current sensors are based on planar electrodes and fail to perfectly match the 3D cell culture matrix. Herein, we developed a robust 3D electrochemical sensor based on functionalized graphene foam (GF), which could be integrated with hydrogels for the 3D culture and in situ monitoring of cells for the first time. Specifically, platinum nanoparticles (Pt NPs) electrodeposited on GF (GF/Pt NPs) conferred the prominent electrochemical sensing performance, and the anti-fouling coating of poly(3,4-ethylenedioxythiophene) (PEDOT) endowed the GF/Pt NPs electrode with greatly improved stability. As a proof of concept, collagen hydrogel with microglia seeded in was filled into the interspace of the 3D GF/Pt NPs/PEDOT sensor to establish an integrated platform, which allowed the successful real-time monitoring of reactive oxygen species released from microglia in the collagen matrix. Given the versatility, our proposed biosensor in conjunction with various 3D culture models will serve as an excellent tool to provide biochemical information of cells under their in vivo-like microenvironment.