Recent advances and challenges in monitoring chromium ions using fluorescent probes

Chromium is among the most strategic and critical transition metal elements and has extensive applications in both industrial and biological contexts. The most stable oxidation states of chromium are trivalent chromium (Cr(III)) and hexavalent chromium (Cr(VI)). Cr(III) is recognized as an effective trace nutrient, whereas Cr(VI) in its highest oxidation state poses a toxic threat to human health due to its potent oxidizing capacities. To mitigate the risk of poisoning, efficient detection methods have been developed to meet testing requirements. Comparing with traditional methods, colorimetric and fluorescent techniques have emerged as simple, time-efficient, highly selective and sensitive, cost-effective and particularly well-suited for biological applications. Furthermore, these methods excel in distinguishing between trivalent and hexavalent chromium, even in low-level concentrations and complex matrices. Since the scarcity of fluorescent probes for chromium, most existing reviews merely touch upon this topic without providing comprehensive coverage. Therefore, this review aims to consolidate information on small molecular fluorescent probes and fluorescent materials serve as fluorescent probes for monitoring Cr²⁺, Cr³⁺, Cr₂O₇^2- and CrO₄^2- in environmental settings and living cells. We anticipate that this review will promote the development of novel fluorescent probes for chromium detection, facilitating their applications in chemical, biological and medical domains.