Detection of analytes in extracted biofluids, such as urine for bladder cancer biomarkers, is challenging owing to sample dilution and instability outside the human body. Here we demonstrate an annular nanosensor array grafted onto a standard biomedical catheter, which enables three-dimensional chemical efflux imaging from within a tissue compartment or luminal space. This platform integrates near-infrared fluorescent single-walled carbon nanotubes with the catheter, leveraging a ball-lens scanning optical device for chemical signal mapping. We develop nanosensors based on a phospholipid copolymer that selectively detect nuclear matrix protein (NMP-22), a biomarker for bladder cancer. The results show differential sensor responses between apoptosis in six bladder cancer cell lines and healthy fibroblast cells. Nanosensor-functionalized catheters track gemcitabine-stimulated cell death and monitor protein efflux in vitro. We demonstrate spatial imaging of incident chemical flux using this platform, achieving localization of biomarker sources in complex tissues and organs with 182-fold signal enhancement compared with extracted biofluid sampling. As an application, the catheter equipped with a rotating ball lens chemically images porcine bladders, detecting biomarker efflux up to 2 cm away, highlighting its potential as a point-of-care diagnostic tool.