Host-guest recognition-based fluorescent probe for ultrasensitive detection of free bilirubin using β-cyclodextrin-functionalized gold nanoclusters.

Bilirubin is a bile pigment widely present in the human body. At appropriate concentrations, it functions as an antioxidant, reduces obesity risk, and helps prevent cardiovascular diseases. However, excessive levels of unconjugated bilirubin (UCB) in the bloodstream can cross the blood-brain barrier, potentially causing kernicterus and irreversible neurological damage. Therefore, the accurate detection of bilirubin concentrations in human blood is of great significance for evaluating liver function and metabolic health status. Herein, we synthesized fluorescent gold nanocluster (AuNCs) probes using thiolated-cyclic β-cyclodextrin (β-CD) as the ligand. The as-synthesized β-CD-AuNCs exhibit intense fluorescence emission at 760 nm in the near-infrared (NIR) region. Notably, the fluorescence emission intensity of β-CD-AuNCs decreases significantly with the increase of bilirubin concentration, which is mainly attributed to the host-guest recognition interaction between β-cyclodextrin and bilirubin, as well as the inner filter effect (IFE). Within the linear range of 0-50 μM, the sensor shows a distinct concentration-dependent fluorescence response to bilirubin, achieving a detection limit (LOD) of 0.32 μM. This sensitivity is considerably lower than the normal concentration range of free bilirubin in human serum. Finally, the fluorescent sensor was applied to the detection of UCB in a murine hemolytic hyperbilirubinemia model, and the detection results were consistent with those obtained by the commercial kit. Hence the reported UCB sensing probe can serve as a powerful diagnostic tool to research UCB functions and to investigate UCB related diseases.