Utilizing polyethyleneimine-capped silver nanoclusters as a new fluorescence probe for Sudan I–IV sensing in ethanol based on fluorescence resonance energy transfer

A novel fluorescence quenching method to detect Sudan I–IV based on efficient fluorescence resonance energy transfer (FRET) from polyethyleneimine-capped silver nanoclusters to Sudan I–IV was proposed. •A simple, rapid, and cost-effective quantification of Sudan I–IV was developed.•The mechanism was supposed to be based on FRET from PEI-AgNCs to Sudan dyes.•A low detection limit (7.6–11nM) was obtained without any amplification.•Metal nanoclusters were first used as the probe to detect Sudan dyes.•This strategy may broaden potential ways to assay other dyes or food additives. In this work, fluorescence resonance energy transfer (FRET) between Sudan I–IV and polyethyleneimine-capped silver nanoclusters (PEI-AgNCs), which are smaller than the critical size for electronic energy quantization (∼2nm), is investigated and subsequently utilized for Sudan I–IV sensing in ethanol. The PEI-AgNCs exhibit strong blue fluorescence when excited at 375nm, and the fluorescence would be greatly enhanced when the nanoclusters are dissolved in given organic solvents, especially in n-propanol and ethanol. The characteristic emission peak of Ag nanoclusters is centered at 450nm in ethanol. Upon addition of Sudan dyes, the fluorescence of PEI-AgNCs can be efficiently quenched. The fluorescence quenching efficiency was proportional to the concentration of Sudan dyes. Thus, precise quantification of Sudan I–IV can be made. Under optimum conditions, this fluorescence method shows a wide linear range of 0.4–25μM Sudan I, 0.4–30μM Sudan II, 0.2–20μM Sudan III, and 0.2–25μM Sudan IV, with the corresponding detection limits (3σ/slope) of 11.0, 12.2, 8.0, and 7.6nM, respectively. Using commercial chilli powder as a model sample, detection of Sudan I–IV could be made with satisfactory results. Furthermore, the sensing mechanism for detection of Sudan dyes is discussed.