Near-Infrared Ratiometric Two-Photon Probe for pH Measurement in Human Stomach Cancer Tissue

Abstract

Stomach cancer is a global health issue because of its incidence and mortality rates worldwide. We developed a near-infrared (NIR) emissive ratiometric two-photon (TP) probe (<b>HCC1</b>) for the quantitative analysis of pH in live cells and human stomach tissues. The probe design is based on a restrained hemicyanine core that controls the intramolecular charge transfer from 2-naphthol, with a suitable p<i>K</i>_a value (7.50) under physiological conditions. The probe exhibited improved quantum yield, stability, and TP activity under physiological conditions. In addition, intracellular pH titration (pH 4.0 to 10.0) of <b>HCC1</b> revealed an ideal intracellular p<i>K</i>_a of approximately 7.2, negligible cytotoxicity, and TP excited fluorescence in situ, thereby allowing direct imaging of the cellular pH in live cells and tissues. Ratiometric two-photon microscope imaging with <b>HCC1</b> of human stomach tissue revealed a clear intratissue pH variation among normal, adenoma, and cancer tissues. Our results demonstrate that <b>HCC1</b> is useful as an NIR imaging probe for in situ pH-related studies and in cancer research.