Recent Advances in In Vivo Neurochemical Monitoring

Abstract

The brain is a complex network that accounts for only 5% of human mass but consumes 20% of our energy. Uncovering the mysteries of the brain’s functions in motion, memory, learning, behavior, and mental health remains a hot but challenging topic. Neurochemicals in the brain, such as neurotransmitters, neuromodulators, gliotransmitters, hormones, and metabolism substrates and products, play vital roles in mediating and modulating normal brain function, and their abnormal release or imbalanced concentrations can cause various diseases, such as epilepsy, Alzheimer’s disease, and Parkinson’s disease. A wide range of techniques have been used to probe the concentrations of neurochemicals under normal, stimulated, diseased, and drug-induced conditions in order to understand the neurochemistry of drug mechanisms and develop diagnostic tools or therapies. Recent advancements in detection methods, device fabrication, and new materials have resulted in the development of neurochemical sensors with improved performance. However, direct in vivo measurements require a robust sensor that is highly sensitive and selective with minimal fouling and reduced inflammatory foreign body responses. Here, we review recent advances in neurochemical sensor development for in vivo studies, with a focus on electrochemical and optical probes. Other alternative methods are also compared. We discuss in detail the in vivo challenges for these methods and provide an outlook for future directions.

Electrically Controlled Neurochemical Delivery from Microelectrodes for Focal and Transient Modulation of Cellular Behavior

“…Miniaturized microelectrodes are favorable in neuroscience due to the reduced invasiveness, increased spatial resolution and selectivity. Microelectrodes have been extensively used in electrophysiology [ 1 ], electrical microstimulations [ 2 ], in vivo imaging [ 3 ], and chemical sensors [ 4 ]. Microelectrodes can also be used to study neurochemical interplay and neural circuitry dynamics when coupled to drug delivery tools.…”

Carbon Nanotube Fibers Decorated with MnO2 for Wire-Shaped Supercapacitor

“…The outstanding potential of CNT fibers for various fiber-based devices has been demonstrated, including for e.g., supercapacitors [ 10 ], solar cells [ 11 ], actuators [ 12 ], and biosensors [ 13 ]. CNT fiber electrodes have also been applied for biocompatible implantable supercapacitors [ 14 ], as well as for neurochemical monitoring [ 15 ]. However, the electrical double-layer capacitance of CNT fiber alone is rather limited (~10–20 F/g) [ 16 ] and is insufficient for commercial devices.…”

Wireless, battery-free push-pull microsystem for membrane-free neurochemical sampling in freely moving animals

“…However, in many neural circuits in the brain, we have a limited understand ing of how, where, and when the release of neuropeptides/other pro teins modulate diverse behavioral outputs of the brain, at the cellular or circuit level. This is, in part, because current measurement tech nologies, such as microdialysis or fastscan cyclic voltammetry (FSCV), have limited spatial and temporal precision or molecular specificity to detect these larger molecules (6)(7)(8). FSCV, a widely used electrochemical method, can measure redoxactive neurochemicals with high spatiotemporal precision (9,10).…”

“…n = 4. The time point when the droplet reached the maximum size was set as 0 s. (C) Normalized droplet size as a function of time under various PtNP concentrations(40,8,6,4, and 2 mg/ml). (D) The dynamics of fluid sampling as a function of PtNP concentrations.…”