One-step Constructed Biosensing Interfaces Towards In Vivo Detection Research

One of the main focuses underlying research community of brain chemistry lies in revealing and understanding of chemical processes behind in physiological and pathological events and such focus has been of a particularly great concern over a recent few years. Quantitative monitoring of neurochemicals in the extracellular brain environment would pave a straightforward avenue to the research into brain chemistry and is, therefore, of great importance in understanding the molecular basis of brain functions. Among the methods employed for neurochemical measurements, in vivo electrochemical methods are particularly useful due to the combined advantages of high sensitivity, low cost and high temporal and spatial resolution. However, the complexity of the cerebral environments substantially enables the effective monitoring of neurochemicals under pathological conditions a challenge for most kinds of the electrochemical biosensors reported so far. By taking advantage of the basic principle of electrochemical, biological technology and in vivo microdialysis, we have developed on-line electrochemical methods through integrating selective electrochemical detection with in vivo microdialysis for continuous measurements of neurochemicals including glucose, lactic acid, ascorbic acid. The main work can be summarized as follows:First, a new strategy was desmonstrated to develop in vivo electrochemical biosensors through rational design and simple formation of bioelectrochemically multifunctional film (BMF). The BMF is rationally designed by first efficiently incorporating oxidase, ferrocene mediator, and graphene oxide into polymaleimidostyrene/polystyrene (PMS/PS) matrix to form a homogenous mixture and then simply formed by drop-coating the mixture onto solid conducting substrate. By using the as-formed BMF, electrochemical biosensors could be constructed with a technical simplicity and reproducibility. To illustrate the BMF-based biosensors for in vivo applications, we directly couple the biosensors to in vivo microdialysis to establish an online electrochemical system (OECS) for in vivo monitoring of glucose in rat auditory cortex during salicylate-induced tinnitus model. Additionally, the OECS is stable and does not suffer from the interference from the electroactive species endogenously coexisting in the brain microdialysate. This vales is observed to remarkably increase following salicylate-induced tinnitus. This study essentially offers a new. technically simple and reproducible approach to development of in vivo electrochemical biosensors, which is envisaged to be relatively useful for understanding of the molecular basis of brain functions.Second, we demonstrate the fabrication, characterization, and the evaluation of in vivo performance of aminated carbon fibers microelectrodes (Am-CFMEs) obtained by electrooxidation of carbon fibers in ammonium carbamate aqueous solution at a relative mild potential (1.1 V vs. Ag/AgCl) for real-time in vivo monitoring the dynamic change of cerebral ascorbate (AA) upon direct cortical electrical stimulation of a living rat brain striatum. The mechanistic investigation supported by XPS characterization concludes that the pretreatment only renders the introduction of nitrogen-containing groups, avoiding the generation of surface oxides, which significantly minimizes the adsorption of cationic neurotransmitters and thus leads to enhanced sensitivity toward the oxidation of anionic AA. The simple single-step electrochemical pretreatment facilitates the oxidation of AA at a relative negative potential (-0.05 V vs. Ag/AgCl), forming the basis of selective measurement of AA. The electrical stimulation elicits an abrupt decrease in AA concentration, followed by a subsequent return to its initial level ? 150 s post-stimulation, reflecting the tight coupling between the AA contents in the brain upon direct electrical stimulation. With the facile and practical nature in procedure and the enhanced robustness and reproducibility in analytical performance, the Am-CFME demonstrated here could be reasonably envisaged to be a suitable analytical platform for the reliable real-time monitoring of AA in vivo and might enable novel applications in the investigations on the fundamental understanding of the functional significance of brain AA in neurochemical processes.