Ratiometric bioassay and visualization of dopamine β-hydroxylase in brain cells utilizing a nanohybrid fluorescence probe.

Dopamine β-hydroxylase (DBH) is involved in various neuronal transmission processes in the brain. Due to the severe diseases caused by abnormity levels of such important enzyme in human serum, sensitive and rapid detection of DBH at early stages is crucial, particularly for clinical analysis. Herein, we developed optical sensors for DBH that include the following: (i) a ratiometric fluorescence sensor that hybridizes the bovine serum albumin (BSA)-gold nanoclusters (BSA-AuNCs) and nitrogen doped carbon dots (N-CDs). The sensor proved to be highly selective and sensitive, achieving a linear range of 0.02-0.16 μg mL and a limit of detection of 4.0 ng mL. In the presence of DBH, the fluorescence intensity of BSA-AuNCs (λ = 615 nm) was remarkably quenched by DBH serving as a reporter signal, whereas the N-CDs fluorescence intensity at 440 nm was almost kept unchanged serving as a reference signal. The developed ratiometric sensor is capable of demonstrating a color change from pink to violet and blue with a gradual increase in DBH concentration, which is discernible by the naked-eye. A test strip is prepared for semi-quantitative assay and convenient use. Intriguingly, by taking advantage of the inter-AuNCs aggregation in the presence of DBH, (ii) a resonance light scattering (RLS) sensor was also developed based on the nanohybrid probe (detection limit 95 ng mL). Fluorescence imaging in PC12 cell lines demonstrated that the BSA-AuNCs could be utilized in visualization assay towards intracellular DBH. Additionally, the sensors were tested in a real matrix by spiking serum samples with satisfactory recoveries.