Nanoparticles are widely used in medicine to deliver drugs, genes or imaging agents to specific parts of the body. Once a nanoparticle reaches a cell, however, many things can happen—it can reach its target, be degraded, interact with proteins that help transport it, or interact with proteins that hinder its transport.

A longstanding problem in designing nanomedicines has been understanding what happens to nanoparticles at the cellular level, but scientists have faced many challenges. For example, optical microscopy imaging techniques provide only a generalized view of nanomedicine localization.

On the other hand, proteomics approaches require cell lysis, which disrupts the natural distribution of proteins around the nanoparticle, making it difficult to understand how nanoparticles are transported within the cell. Another method—proximity labeling—enables in situ investigation of intracellular protein-protein interactions, but it relies on genetically engineered enzyme fusion, which limits its applicability across diverse systems.