Biodegradable optode-based nanosensors for in vivo monitoring

Optode-based fluorescent nanosensors are being developed for monitoring important disease states such as hyponatremia and diabetes. However, traditional optode-based sensors are composed of nonbiodegradable polymers such as poly(vinyl chloride) (PVC) raising toxicity concerns for long-term in vivo use. Here, we report the development of the first biodegradable optode-based nanosensors that maintain sensing characteristics similar to those of traditional optode sensors. The polymer matrix of these sensors is composed of polycaprolactone (PCL) and a citric acid ester plasticizer. The PCL-based nanosensors yielded a dynamic and reversible response to sodium, were tuned to respond to extracellular sodium concentrations, and had a lifetime of at least 14 days at physiological temperature. When in the presence of lipase, the nanosensors degraded within 4 h at lipase concentrations found in the liver but were present after 3 days at lipase concentrations found in serum. The development of biodegradable nanosensors is not only a positive step towards their future use in in vivo applications, but they also represent a new sensor platform that can be extended to other sensing mechanisms.