Cerebral blood flow (CBF) is a key metric that provides critical information on physiological and pathological processes within the central nervous system (CNS). Understanding blood flow dynamics with high spatiotemporal resolution is fundamental for understanding pathological processes caused by vascular dysfunction. One method for measuring blood flow includes multiphoton laser-scanning microscopy (MPLSM), but this method lacks spatial and temporal resolution available for other multiphoton imaging methods. Fluorescence correlation spectroscopy (FCS) used in microfluidic devices also has been used to model vascular flow systems in vitro. These systems carry the advantage of providing detailed information on nanoparticle properties within flow systems, including flow rate, particle degradation, and concentration. However, neither FCS nor multiphoton excitation alone can provide high spatiotemporal resolution measurements of blood flow rates within live animals.
In a recent publication in Nano Letters, Fu et al. have developed a novel method that combines multiphoton excitation with FCS to overcome current limitations for measuring nanoparticles in vivo. To determine the capability of this method, the authors intravenously injected nanoparticles labeled with CF®488-dextran and rhodamine B-dextran into mice with thinned skull preparation. By tracking photon arrival events from a single location, the authors were able to detect spikes in fluorescence intensity that correspond to FCS tracked nanoparticles flowing through the focal volume, allowing monitoring of nanoparticle degradation, concentration, and half-life in vivo. The method was also capable of accurately monitoring flow velocity across vessels of varying diameter. With this high spatial resolution, the authors were able to construct subvessel resolution measurements and provide a map of the velocity within a vessel. Finally, the authors applied this method toward monitoring physiological dependent dynamic changes in blood flow rates during anesthesia. Overall, this method presents the capability of monitoring flow profiles with high spatial and temporal resolution in vivo.
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Full Citation:
Fu, X., Sompol, P., Brandon, J., Norris, C., Wilkop, T., Johnson, L., & Richards, C. (2020). In Vivo Single-Molecule Detection of Nanoparticles for Multiphoton Fluorescence Correlation Spectroscopy to Quantify Cerebral Blood Flow. Nano Letters. https://doi.org/10.1021/acs.nanolett.0c02280