A Robust Au−C≡C Functionalized Surface: Toward Real‐Time Mapping and Accurate Quantification of Fe 2+ in the Brains of Live AD Mouse Models

Implantable Electrochemical Sensors for Brain Research

Implantable electrochemical sensors provide reliable tools for in vivo brain research. Recent advances in electrode surface design and high-precision fabrication of devices led to significant developments in selectivity, reversibility, quantitative detection, stability, and compatibility of other methods, which enabled electrochemical sensors to provide molecular-scale research tools for dissecting the mechanisms of the brain. In this Perspective, we summarize the contribution of these advances to brain research and provide an outlook on the development of the next generation of electrochemical sensors for the brain.

Real-Time Monitoring of Neurotransmitters in the Brain of Living Animals

Neurotransmitters, as important chemical small molecules, perform the function of neural signal transmission from cell to cell. Excess concentrations of neurotransmitters are often closely associated with brain diseases, such as Alzheimer's disease, depression, schizophrenia, and Parkinson's disease. On the other hand, the release of neurotransmitters under the induced stimulation indicates the occurrence of reward-related behaviors, including food and drug addiction. Therefore, to understand the physiological and pathological functions of neurotransmitters, especially in complex environments of the living brain, it is urgent to develop effective tools to monitor their dynamics with high sensitivity and specificity. Over the past 30 years, significant advances in electrochemical sensors and optical probes have brought new possibilities for studying neurons and neural circuits by monitoring the changes in neurotransmitters. This Review focuses on the progress in the construction of sensors for in vivo analysis of neurotransmitters in the brain and summarizes current attempts to address key issues in the development of sensors with high selectivity, sensitivity, and stability. Combined with the latest advances in technologies and methods, several strategies for sensor construction are provided for recording chemical signal changes in the complex environment of the brain.

Nano- and Microsensors for In Vivo Real-Time Electrochemical Analysis: Present and Future Perspectives

Electrochemical nano- and microsensors have been a useful tool for measuring different analytes because of their small size, sensitivity, and favorable electrochemical properties. Using such sensors, it is possible to study physiological mechanisms at the cellular, tissue, and organ levels and determine the state of health and diseases. In this review, we highlight recent advances in the application of electrochemical sensors for measuring neurotransmitters, oxygen, ascorbate, drugs, pH values, and other analytes in vivo. The evolution of electrochemical sensors is discussed, with a particular focus on the development of significant fabrication schemes. Finally, we highlight the extensive applications of electrochemical sensors in medicine and biological science.

Raman Fiber Photometry for Understanding Mitochondrial Superoxide Burst and Extracellular Calcium Ion Influx upon Acute Hypoxia in the Brain of Freely Moving Animals

Developing a novel tool capable of real-time monitoring and simultaneous quantitation of multiple molecules in mitochondria across the whole brain of freely moving animals is the key bottleneck for understanding the physiological and pathological roles that mitochondria play in the brain events. Here we built a Raman fiber photometry, and created a highly selective non-metallic Raman probe based on the triple-recognition strategies of chemical reaction, charge transfer, and characteristic fingerprint peaks, for tracking and simultaneous quantitation of mitochondrial O₂ ^.- , Ca²⁺ and pH at the same location in six brain regions of free-moving animal upon hypoxia. It was found that mitochondrial O₂ ^.- , Ca²⁺ and pH changed from superficial to deep brain regions upon hypoxia. It was discovered that hypoxia-induced mitochondrial O₂ ^.- burst was regulated by ASIC1a, leading to mitochondrial Ca²⁺ overload and acidification. Furthermore, we found the overload of mitochondrial Ca²⁺ was mostly attributed to the influx of extracellular Ca²⁺ .

Long-Term Tracking and Dynamically Quantifying of Reversible Changes of Extracellular Ca2+ in Multiple Brain Regions of Freely Moving Animals

Understanding physiological and pathological processes in the brain requires tracking the reversible changes in chemical signals with long-term stability. We developed a new anti-biofouling microfiber array to real-time quantify extracellular Ca²⁺ concentrations together with neuron activity across many regions in the mammalian brain for 60 days, in which the signal degradation was < ca. 8 %. The microarray with high tempo-spatial resolution (ca. 10 μm, ca. 1.3 s) was implanted into 7 brain regions of free-moving mice to monitor reversible changes of extracellular Ca²⁺ upon ischemia-reperfusion processes. The changing sequence and rate of Ca²⁺ in 7 brain regions were different during the stroke. ROS scavenger could protect Ca²⁺ influx and neuronal activity after stroke, suggesting the significant influence of ROS on Ca²⁺ overload and neuron death. We demonstrated this microarray is a versatile tool for investigating brain dynamic during pathological processes and drug treatment.