Alkaline phosphatase (ALP) is distributed widely in living organisms and is an important biomarker closely related to many physiological and pathological processes. However, in vivo real-time detection of ALP remains a significant challenge. Herein, we developed a turnon molecular probe (denoted as LET-3) to visualize ALP activity in tumor tissues through near-infrared fluorescence (NIRF) and photoacoustic (PA) dual-modal imaging. LET-3, composed of NIR hemicyanine dye (LET-CyOH) and a phosphate moiety, showed a 23-fold NIRF enhancement at 730 nm and 27-fold PA enhancement at 710 nm upon activation by ALP. More importantly, both in vitro and in vivo diagnostic experiments indicated that LET-3 has a high sensitivity and good selectivity for ALP. These findings provide a promising strategy for in vivo ALP detection using NIRF and PA dual-channel turn-on probes.

The detection of Cu2+ in living plants and animals is of great importance for environment monitoring and disease diagnosis. Here, a near‐infrared (NIR) turn‐on photoacoustic (PA) probe (denoted as LET‐2) is developed for Cu2+ detection in living subjects, such as soybean sprouts and mice. The absorbance band of LET‐2 shifts from 625 to 715 nm after the interaction with Cu2+, thus producing strong PA signal output at 715 nm (PA715) as an indicator. The PA715 value is increased as a function of the concentration of Cu2+ (0 × 10−6–20 × 10−6m), with a calculated limit of detection of 10.8 × 10−9m. More importantly, both in vitro and in vivo studies in soybean sprouts and mice indicate that the as‐prepared LET‐2 PA probe is highly sensitive and selective for Cu2+ detection. These findings provide a solution for in vivo detection of metal ions by using chemoselective PA probes.

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In vivo real-time monitoring gastric acid is of great importance for diagnosis and treatment of gastrointestinal diseases. Herein, we synthesized a pH-responsive photoacoustic (PA) nanoprobe (denoted as LET-4) based on near-infrared (NIR) dye (IR1061) for in vivo photoacoustic imaging (PAI) of gastric acid in living subjects. In the acidic condition, the protonated LET-4 nanoprobe has a strong absorbance peak at 808 nm, followed by a strong PA signal output at 808 nm. The PA808 signal at pH 3 is 3.45-fold higher than the signal at pH 7. More importantly, the LET-4 nanoprobe could monitor in vivo gastric acid secretion assessment in animal model using PAI. This organic small molecule NIR dye-based probe with simple components, facile preparation, good biocompatibility, and rapid excretion has great potential for gastrointestinal disease diagnosis.