We are designing a system for monitoring important physiological analytes such as sodium and glucose. Fluorescent nanosensors are one component of this system and have capabilities that range from single cell intracellular measurements to small animal in vivo tracking. The sensors will be injected into the epidermis of the skin and their fluorescence will be read using a handheld optical reader such as a modified camera on an iPhone. However, for the nanosensors to be used in human applications, it is advantageous from a regulatory perspective that they are biodegradable and break down into naturally occurring metabolic by-products over time. With this in mind, we have designed sodium nanosensors composed of popular FDA-approved biodegradable polymers and citrate-based plasticizers. These sensors have a dynamic and reversible fluorescence response to sodium and were tailored to respond within the physiological range. Sensor lifetime is at least 14 days and sensor degradation was accelerated in the presence of lipases. With the successful demonstration of biodegradable sodium nanosensors as our model, we will expand this new sensor platform to different sensing mechanisms for monitoring other analytes such as small molecules and enzymes.