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Designing probes to monitor blood flow is challenging because of the environment; the high protein levels in plasma and the high red blood cell concentrations are detrimental to optical imaging. Conventional techniques rely on staining red blood cells, using organic dyes with short-lived usage due to photobleaching, as the tracking motif. The relatively large size of the red blood cells (7-8 micrometres), which are effectively the probes, limits the resolution in imaging and analysis of flow dynamics of the smallest vessels which are of a similar width. Therefore, to have more detailed resolution and information about the blood flow in the microvasculature, even smaller probes are required.
Scientists at the University of Birmingham have designed gold nanoparticles, no bigger than 100 nanometres, which can be coated in iridium and used as luminescent probes to track blood flow in the smallest blood vessels in the body. The team was able to stabilize water-soluble gold nanoparticles, coated with the iridium luminescent probes – at up to 100 nanometres in size using a surfactant coating. The size of 100 nanometres is ideal for not disturbing blood flow, yet still be detectable by high resolution imaging using conventional microscopes. These nanoparticles can be used as trackers for detection in sub-millimetre channels of dimensions similar to many microvessels with higher resolution than fluorescently-stained blood cells.