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

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 (similar to 2 nm), is investigated and subsequently utilized for Sudan I-IV sensing in ethanol. The PEI-AgNCs exhibit strong blue fluorescence when excited at 375 nm, 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 450 nm 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 0.4-25 mu M Sudan I, 0.4-30 mu M Sudan II, 0.2-20 mu M Sudan III, and 0.2-25 mu M Sudan IV, with the corresponding detection limits (3 sigma-/slope) of 11.0, 12.2, 8.0, and 7.6 nM, 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. (C) 2013 Elsevier B.V. All rights reserved.