A ratiometric fluorescence sensor based on the inner filtration effect of gold nanoparticles on quantum dots for monitoring dopamine.

In this study, a smart phone assisted ratiometric fluorescence sensor was designed for detecting dopamine (DA). The ratiometric fluorescence sensor was prepared by simple physical mixing green quantum dots (GQDS) and red quantum dots (RQDS). DA could induce gold nanoparticles (AuNPs) aggregate via hydrogen-bonding interactions, and further changed the absorption spectrum of gold nanoparticles to overlap with a certain emission spectrum of ratiometric fluorescence sensor. AuNPs had inner filtration effect (IFE) on the ratiometric fluorescence sensor. Due to the IFE, the dispersive AuNPs could quench GQDS, whereas the clustered AuNPs could quench RQDS. With the addition of DA, the color of ratiometric fluorescence changed from orange red to green. To simplify the detection process, a smartphone was employed to detecting DA in human urine by measuring RGB value of fluorescence color changes with a detection limit of 86 nM. This proposed method has the advantages of low cost, easy prevalence and simple operation, thus provides a great promise for rapid detection of biomarker in biological samples.