Biosensors are important devices that can be used to obtain information from within a living organism. They can be implanted within living tissues in order to continuously monitor for changes. This allows for personalized, noninvasive medicine, since a baseline can be more accurately established and any deviations, even slight, can be detected. These devices have applications in the treatment of diseases such as diabetes and cancer, as well as the study of pathways of interest and tailored drug dosing. Proteases within the tumor microenvironment can be studied in vivo in order to indicate the effectiveness of treatments received. This unprecedented real-time information is extremely valuable as it can be used to alter the course of treatment accordingly.