Room temperature preparation of water-soluble polydopamine-polyethyleneimine copolymer dots for selective detection of copper ions.

Polydopamine-polyethyleneimine (PDA-PEI) copolymer dots were prepared under mild conditions via the self-polymerization of dopamine and cross-linking with branched PEI (BPEI). The molecular weight of BPEI, mass ratio of dopamine to BPEI, and pH of reaction medium had significant influences on the quantum yield of PDA-PEI copolymer dots. Under the optimized conditions, the synthesized PDA-PEI copolymer dots have an average size of 9.4 ± 2.2 nm in diameter with good water dispersibility. The quantum yield is 12.5%. More importantly, they are very stable against extreme pH and high ionic strength. The PDA-PEI copolymer dots were employed as a fluorescent probe for sensitive and selective Cu2+ detection with a detection limit as low as 1.6 nM and a linear range from 0.0016 to 80 μM. The feasibility of the PDA-PEI copolymer dots-based method was verified by the successful determination of Cu2+ in water and oyster samples, demonstrating its potential for analysis of environmental water and food samples.