A biocompatible hydrogel-coated fiber-optic probe for monitoring pH dynamics in brains of freely moving mice

The pH dynamics in the brain microenvironment is related to a variety of brain diseases, so it is critical to develop pH probes with great efficiency for in vivo detection of brain. Here, we report a biocompatible hydrogel-coated fiber optic probe (HCFOP) for monitoring pH dynamics in the brains of freely-moving mice. The novel pH probe was prepared by combining hydrogel coated silica multimode fiber with pH-sensitive microspheres embedded in hydrogel fiber, and the pH calibration is based on fluorescence ratio detection. The sensor has a dynamic range of pH from 3.0 to 9.0, and a resolution of 0.0014 pH units with good reproducibility, reversibility, and time stability. We tested the capability of our proposed sensor in dynamically detecting pH in the brains of free moving mice, and the biocompatibility for long-term implantation. We implanted the fiber-optic probes into the striatum and hippocampus of mouse brains. During cerebral ischemia, we detected a decrease in pH of about 0.5 after ~15 mins. During epilepsy induced by kanic acid (KA), we found that pH in the hippocampus decreased by about 0.2 after ~80 mins, in relation to the dynamical concentrations of adenosine. This biofriendly and easy-to-manufacture HCFOP provides a unique solution for assessing small changes in the pH of the brain microenvironment, thus holds great promises in neuroscience study.