378980 Photoacoustic Imaging of Nanosensors – in Vivo, Continuous Measurement of Lithium
In recent years the incredible versatility and utility of polymeric optode-based nanosensors has been demonstrated. Sensors for a wide variety of ionic analytes (e.g. sodium, potassium, pH) and nonionic analytics (e.g. glucose, histamine) have been applied in a wide range of applications. The application of sensors has yielded new knowledge on cellular metabolism and function. These sensors can be applied in vivo, through implantation in or under the skin in animals and using fluorescence imaging to measure sensor response. These nanosensors show potential as a research tool for continuous monitoring of analyte concentrations without the need for direct samples to be taken from the animal.
A key limitation of these nanosensors for in vivo application is the poor imaging depth afforded by fluorescence interrogation. In this work we overcame this limitation by coupling optode-based nanosensors with photoacoustic imaging. Photoacoustic imaging has superior imaging depth when compared with fluorescence, and enables imaging of nanosensors at locations deeper in tissue. We applied this technology to continuous monitoring of lithium administration. Both fluorescent and photoacoustic imaging gave similar results for nanosensors embedded in the skin of mice, demonstrating that the interrogation method does not affect sensor function, but does yield additional information. Photoacoustic imaging is able to probe the three-dimensional nature of nanosensors injections in vivo rather than the surface projection measurements in fluorescent imaging. This research serves as a proof of concept toward future work at continuous tracking analyte concentrations in deep tissue with superior spatial and temporal resolution.