Revealing the elevated sulfite levels in acute kidney injury using a promising ratiometric fluorescent probe.

The development of novel biomarkers for the early diagnosis of acute kidney injury (AKI) is critical for enabling timely protective interventions and predicting potential drug toxicity. Recent studies have highlighted metabolic abnormalities in sulfur-containing compounds during AKI progression. A ratiometric fluorescent probe, BP-BT-OH, has been designed for sulfite detection, featuring a covalent bond between benzothiazole and benzopyran-oxonium. The probe's ratio intensity is highly sensitive to sulfite concentration with an almost 80-fold increase. BP-BT-OH showed a rapid response of 50 s, an excellent detection limit of 0.21 μM, and a high selectivity and anti-interference capabilities. The probe can efficiently detects fluctuations in intracellular sulfite, both exogenous and endogenous. In cisplatin-treated cells, the ratio intensity between the two channels was significantly higher compared to untreated cells. More promisingly, BP-BT-OH was successfully used for imaging cisplatin-induced AKI in mice, revealing elevated sulfite levels in the kidneys. These findings validate sulfite as a potential biomarker for AKI. Further analysis of specific kidney proteins indicated that the increased sulfite concentration may be linked to downregulation of sulfur-containing compound metabolic enzymes. This approach offers a novel perspective on using molecular imaging tools for diagnosing early-stage diseases that lack obvious symptoms.