Abstract: Aspects of the present disclosure relate to methods and compositions useful for in vivo and/or in vitro profiling of environmental triggers (e.g., enzyme activity, pH or temperature). In some embodiments, the disclosure provides methods of in vivo enzymatic processing of exogenous molecules followed by detection of nanocatalysts as representative of the presence of active enzymes (e.g., proteases) associated with a disease, for example, cancer or infection. In some embodiments, the disclosure provides compositions and methods for production of in vivo sensors comprising nanocatalysts.