Starch-regulated copper-terephthalic acid as a pH/hydrogen peroxide simultaneous-responsive fluorescent probe for lysosome imaging.

Lysosome visualization is very important for accurate diagnosis of human diseases. However, currently developed lysosome imaging probes usually have poor specificity and are easily quenched, leading to a low signal to noise ratio in lysosome labeling. To resolve this problem, herein, metal-organic framework-based probes of copper-terephthalic acid (CuBDC) are investigated, which show sensitivity to pH and hydrogen peroxide (H ₂ O ₂ ), simultaneously. By self-assembling under the template effect of soluble starch, the particle size of CuBDC can be well controlled for entering into cells and locating lysosomes. Based on the Fenton-like reaction, CuBDC can catalyze the decomposition of H ₂ O ₂ into ˙OH, which in turn reacts with CuBDC to generate a stable fluorescent substance. Meanwhile, Cu ²⁺ can be released from CuBDC under acidic conditions for reacting with H ₂ O ₂ more thoroughly. And the synthesized CuBDC has a similar attraction to the electrophilic ˙OH at different pH values owing to the residual soluble starch in the particles. The above properties cause CuBDC to have a stable fluorescence signal with low pH values and high H ₂ O ₂ concentration, simultaneously. The fluorescence imaging experiments in HeLa cells demonstrate that CuBDC acting as a pH/H ₂ O ₂ responsive fluorescent probe holds great promise for lysosome-specific imaging.