Department of Biochemistry & Biophysics, Kavli Institute for Fundamental Neuroscience , University of California, San Francisco , San Francisco , California 94143 , United States.
Acc Chem Res. 2018 May 15;51(5):1023-1032. doi: 10.1021/acs.accounts.7b00564. Epub 2018 Apr 13.
Fluorescent nanosensors and molecular probes are next-generation tools for imaging chemical signaling inside and between cells. Electrophysiology has long been considered the gold standard in elucidating neural dynamics with high temporal resolution and precision, particularly on the single-cell level. However, electrode-based techniques face challenges in illuminating the specific chemicals involved in neural cell activation with adequate spatial information. Measuring chemical dynamics is of fundamental importance to better understand synergistic interactions between neurons as well as interactions between neurons and non-neuronal cells. Over the past decade, significant technological advances in optical probes and imaging methods have enabled entirely new possibilities for studying neural cells and circuits at the chemical level. These optical imaging modalities have shown promise for combining chemical, temporal, and spatial information. This potential makes them ideal candidates to unravel the complex neural interactions at multiple scales in the brain, which could be complemented by traditional electrophysiological methods to obtain a full spatiotemporal picture of neurochemical dynamics. Despite the potential, only a handful of probe candidates have been utilized to provide detailed chemical information in the brain. To date, most live imaging and chemical mapping studies rely on fluorescent molecular indicators to report intracellular calcium (Ca) dynamics, which correlates with neuronal activity. Methodological advances for monitoring a full array of chemicals in the brain with improved spatial, temporal, and chemical resolution will thus enable mapping of neurochemical circuits with finer precision. On the basis of numerous studies in this exciting field, we review the current efforts to develop and apply a palette of optical probes and nanosensors for chemical sensing in the brain. There is a strong impetus to further develop technologies capable of probing entire neurobiological units with high spatiotemporal resolution. Thus, we introduce selected applications for ion and neurotransmitter detection to investigate both neurons and non-neuronal brain cells. We focus on families of optical probes because of their ability to sense a wide array of molecules and convey spatial information with minimal damage to tissue. We start with a discussion of currently available molecular probes, highlight recent advances in genetically modified fluorescent probes for ions and small molecules, and end with the latest research in nanosensors for biological imaging. Customizable, nanoscale optical sensors that accurately and dynamically monitor the local environment with high spatiotemporal resolution could lead to not only new insights into the function of all cell types but also a broader understanding of how diverse neural signaling systems act in conjunction with neighboring cells in a spatially relevant manner.
荧光纳米传感器和分子探针是用于对细胞内和细胞间化学信号进行成像的下一代工具。电生理学长期以来一直被认为是揭示神经动力学的金标准，具有高时间分辨率和精度，特别是在单细胞水平上。然而，基于电极的技术在以足够的空间信息照亮参与神经细胞激活的特定化学物质方面面临挑战。测量化学动力学对于更好地理解神经元之间以及神经元与非神经元细胞之间的协同相互作用至关重要。在过去的十年中，光学探针和成像方法的重大技术进步为在化学水平上研究神经细胞和电路提供了全新的可能性。这些光学成像模式有望结合化学、时间和空间信息。这种潜力使它们成为揭示大脑中多个尺度上复杂神经相互作用的理想候选者，可以与传统的电生理方法相结合，以获得神经化学动力学的完整时空图像。尽管有这种潜力，但只有少数探针候选物被用于提供大脑中的详细化学信息。迄今为止，大多数活体成像和化学映射研究依赖于荧光分子指示剂来报告细胞内钙（Ca）动力学，该动力学与神经元活动相关。因此，用于以更高的空间、时间和化学分辨率监测大脑中所有化学物质的方法进展将能够以更高的精度绘制神经化学回路图。基于该令人兴奋的领域中的众多研究，我们回顾了目前为开发和应用一系列用于大脑化学传感的光学探针和纳米传感器所做的努力。强烈需要进一步开发能够以高时空分辨率探测整个神经生物学单元的技术。因此，我们介绍了用于离子和神经递质检测的选定应用，以研究神经元和非神经元脑细胞。我们专注于光学探针家族，因为它们能够感知广泛的分子并以最小的组织损伤传递空间信息。我们从讨论当前可用的分子探针开始，重点介绍离子和小分子的遗传修饰荧光探针的最新进展，并以生物成像的纳米传感器的最新研究结束。具有定制化、纳米级的光学传感器可以以高精度和动态方式监测具有高时空分辨率的局部环境，不仅可以深入了解所有细胞类型的功能，还可以更深入地了解不同的神经信号系统如何以空间相关的方式与邻近细胞协同作用。
