Integrating carbon dots and gold/silver core-shell nanoparticles to achieve sensitive detection of dopamine with fluorometric/colorimetric dual signal.

Dopamine (DA) is a potent neuromodulator in the brain that affects a wide range of motivated behaviors. Abnormal concentration of DA is related to a variety of diseases. Hence, it is imperative to establish a rapid and precise method for quantifying DA. In this work, we integrate orange-yellow emissive carbon dots (CDs) with target-induced silver deposition on gold nanoparticles (Au NPs), forming gold/silver core-shell nanoparticles (Au@Ag NPs), to construct a fluorometric and colorimetric dual-signal sensor for sensitive detection of DA. Au NPs and silver ions (Ag) have minimal effect on the fluorescence of CDs. DA can reduce the silver ions to Ag(0) on the surface of the Au NPs to form a silver shell, resulting in the blue-shift of the absorbance peak from 520 to 416 nm, which overlaps with the excitation spectrum of CDs. As a result, the system color turns from pink to orange-yellow, and the fluorescence of CDs is quenched due to the strong inner filter effect. The linear range of the colorimetry is 0.5-18 μM with a limit of detection (LOD) of 0.41 μM, while the linear range for the fluorometry method is 0.5-14 μM with a LOD of 0.021 μM. This method demonstrates notable advantages including a low detection limit, rapid response time, and straightforward operation in practical samples, showing great potential in biomedical analysis.