Passivation of electrodes caused by nonspecific adsorption of protein can dramatically reduce sensing sensitivity and accuracy, which is a great challenge for in vivo neurochemical monitoring. However, most antipassivation strategies are not suitable to carbon fiber microelectrodes (CFMEs) for in vivo measurement, and these methods also do not work on electrochemical biosensors that fix biometric elements. In this study, we demonstrate that chitosan hydrogel-coated microelectrodes can avoid the current passivation caused by protein adsorption on the surface of carbon fiber because the chitosan hydrogel prepared by local pH gradient caused by hydrogen evolution reaction has three-dimensional networks containing large amounts of water. The highly hydrophilic three-dimensional structure of hydrogel not only forms a biocompatible interface to confine enzymes but also keeps the fast mass transfer of analytes, such as dopamine, ascorbic acid, and glucose. The consistency of the precalibration and postcalibration of the prepared sensor enables in vivo amperometric detection of both electroactive species based on their redox property and electroinactive species based on the enzyme. This study provides a simple and versatile strategy to constitute an amperometric sensor interface to resist passivation of protein adsorption in a complex biological environment such as the brain.

In vivo electrochemical analysis is of great significance in understanding the dynamics of various physiological and pathological activities. However, the conventional microelectrodes for electrochemical analysis are rigid and permanent, which comes with increased risks for long-term implantation and secondary surgery. Here, we develop one biodegradable microelectrode for monitoring the dynamics of extracellular Ca 2+ in rat brain. The biodegradable microelectrode is prepared by sputtering gold nanoparticles (AuNPs) on a wet-spun flexible poly(L-lactic acid) (PLLA) fiber for conduction and transduction and coating a Ca 2+ ion-selective membrane (ISM) with a PLLA matrix on the PLLA/AuNPs fiber, forming PLLA/AuNPs/Ca 2+ ISME (ISME = ion-selective microelectrode). The prepared microelectrode shows excellent analytical properties including a near-Nernst linear response toward Ca 2+ over the concentration range from 10 μM to 50 mM, good selectivity, and long-term stability for weeks as well as biocompatibility and biodegradability. The PLLA/AuNPs/ Ca 2+ ISME can monitor the dynamics of extracellular Ca 2+ following spreading depression induced by high potassium even if in the fourth day. This study provides a new design strategy for the biodegradable ISME and promotes the development of biodegradable microelectrodes for long-term monitoring of chemical signals in brain.

One potentiometric nanosensor for monitoring intracellular hydrogen sulfide (H2S) with fast potential response, high selectivity and excellent antifouling property was developed. This study constructs a powerful tool to real-time track...