The controllable synthesis of orange-red emissive Au nanoclusters and their use as a portable colorimetric fluorometric probe for dopamine

Facile and accurate detection of dopamine (DA) in biological samples is crucial for diagnostic needs. This study reports a portable colorimetric fluorescent probe for the tracing of DA based on orange-red emitting Au nanoclusters (AuNCs). The AuNCs were reduced and stabilized with L-methionine by strictly controlling the reaction conditions. The resultant L-methionine capped AuNCs (M-AuNCs) exhibit bright and stable orange-red emission with a quantum yield of 31.08%. The excitation/emission wavelength is located at 420 nm/610 nm, and the large Stoke's shift of 190 nm endows the M-AuNCs with great potential as a late-model sensing probe for life studies and environmental science. The M-AuNCs exhibit unique specificity and excellent sensitivity for tracing DA by an “on–off” strategy with a lower limit of detection (LOD) of 3.96 nM (S/N = 3) within a linear range of 10–100 nM. Notably, the colorimetric detection results can be explored as a visual sensor for sensitive, reliable and real-time/on-site detection of DA with the assistance of a smartphone. The LOD can be determined as 81.94 nM within a wide linear range of 0.1–1.0 μM by a smartphone. Furthermore, the M-AuNCs as a late-model potable probe allow simple and rapid discrimination of DA in serum, and the cellular imaging of the M-AuNCs indicated that the detection of DA can also be achieved in living cells, demonstrating their great feasibility for the tracing of DA in real samples.