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Hypoxia is one of the key characteristics of solid tumors. The over-expression of azoreductase resulting from hypoxia can be used as a target to visualize hypoxic levels and a trigger of the drug release system in tumor treatment. In this work, we developed a near-infrared fluorescent probe YLOD, composed of a near-infrared fluorophore, an azo bond, and an analogue of the anti-tumor drug melphalan. In the presence of azoreductase, YLOD displayed a red emission at 620 nm and released the anti-tumor drug concomitantly, thus achieving the integrated effects of hypoxic imaging and tumor treatment. Furthermore, YLOD successfully inhibited the growth of solid tumors during the tumor suppression experiments in nude mice. Considering all the results, YLOD emerges as a new fluorescence tool that can quickly determine the location and the edges of a tumor, showing concrete potential in clinical cancer treatment.

We constructed a reaction-based near-infrared fluorescent probe (Niap) to specifically identify alkaline phosphatase (ALP) with fast red fluorescence enhancement. Based on the positive concentration-dependent manner between the fluorescent intensity of the Niap and ALP, probe Niap was used to study the ALP enrichment and variation in golden apple snails (Pomacea canaliculata) exposed to the molluscicide candidate PPU06. After treatment with different concentrations of PPU06 over various times, three organs of the surviving snails, liver, stomach and plantaris, were frozen and sectioned for fluorescent imaging experiments. With increased PPU06 concentration, red fluorescence substantially increased in the liver and reached a maximum within 24 h when the PPU06 concentration was 0.75 mg/L. No obvious changes in the stomach or foot plantaris were found. It showed PPU06 caused liver injury and stimulated the increase of ALP in the liver of P. canaliculata. This study demonstrates a rapid ALP fluorescent identification method that can be used to study the effects of PPU06 on P. canaliculata. It also provides optical evidence that may aid in the discovery of new chemistry for snail control.

Optical sensors are widely used in the field of analytical sensing and optical imaging because of their high sensitivity, fast response time, and technical simplicity. The advantages of sensors lay in their non-invasive approach within biological tissues and inherent reliability in fluorescence imaging tests. In recent years the development of optical sensors for the sensing of ions, neutral molecules and especially tumor micro-environment-related parameters has been an active research area. This review focuses on recent contributions concerning fluorescent or colorimetric sensors and is organized according to their target classifications.