Two-Photon Probe for Cu2+ with an Internal Reference: Quantitative Estimation of Cu2+ in Human Tissues by Two-Photon Microscopy

Copper ions play a crucial role in living systems as cofactors of numerous metalloenzymes. To quantitatively estimate the Cu2+ concentration in human tissue, we have developed a two-photon (TP) probe with an internal reference (ACCu2) that shows significant TP action cross-section and high selectivity for Cu2+ and can quantitatively estimate the Cu2+ concentration in human colon tissues by dual-color two-photon microscopy (TPM) imaging with minimum interference from other competing metal ions or pH and minimum cytotoxicity and photostability problems. The Cu2+ concentrations in human normal colon, polyp, and colon cancer tissues were found to be 8.3 +/- 0.3, 13 +/- 2, and 22 +/- 3 mu M, respectively. This result suggests that ACCu2 may be useful for the diagnosis of human colon cancer.