Fig. 5. TPM images of tumor tissue slices with thickness of 500 μm at different depths. Control images of tissue slices treated without the nanoprobe at pH 7.4 (a) and pH 6.5 (c). The tissue slice was incubated with the nanoprobe in medium of pH 7.4 (b) or pH 6.5 (d) for 4 h, and then treated with H₂O₂ for another 1 h. Scale bar: 50 μm.