No methodology has been built to distinguish intracellular SERS nanosensors from cell outer membrane bound-ones. Here we propose a "turning off" strategy by combining etchable SERS nanosensors with a non-permeable etchant. The SERS signals outside the living cells can be rapidly removed, leaving only the internalized nanosensors for imaging and thereby allowing accurate intracellular pH and H2O2 sensing.