Ratiometric detection of bilirubin at nanomolar concentration based on β-cyclodextrin-capped gold nanoclusters with intrinsic dual-emission.

As an important biomarker for liver and blood diseases, bilirubin quantification is vital for clinical diagnosis. Intrinsic dual-emitting gold nanoclusters (AuNCs) were synthesized in a one-pot hydrothermal method using mono-(6-mercapto-6-deoxy)-β-cyclodextrin as a reducing and protecting agent. The β-cyclodextrin-capped AuNCs possess dual emissions peaked at 530 nm and 730 nm respectively, allowing the construction of a ratiometric probe for biosensing. The weak fluorescence was effectively enhanced by assembling the clusters with polyelectrolytes through aggregate-enhanced emission (AEE). Cyclodextrins on the fluorescent assembly act as recognition units for bilirubin, and the host-guest interaction between bilirubin and cyclodextrin promotes the energy transfer between the dual emission peaks, resulting in fluorescence enhancement of the assembly emission at 530 nm and the intensity decrease at 730 nm. The intensity ratios of the two emissions changed linearly with bilirubin concentrations in the range 0.01 ~ 6.00 μmol∙L, with a detection limit of 5.36 ± 0.23 nmol∙L (3σ, n = 3). The sensing system has excellent anti-interference capability and the common coexisting components in the serum or urine did not interfere with the bilirubin detection. The probe showed a fast and highly sensitive response to bilirubin and could detect bilirubin in real samples with satisfactory results.