Ultrasensitive turn-on fluorescent detection of trace thiocyanate based on fluorescence resonance energy transfer

•A fluorescent off-on probe for trace thiocyanate (SCN−) was exploited.•The assay for SCN− is ultrasensitive with detection limit 0.09 nM.•The method cost is 0.2$ per sample with the aid of fluorescence spectrometer.•The operation is ultraselective and relatively fast response time within10 min.

Thiocyanate (SCN−) is a small anion byproduct of cyanide metabolism. Several methods have been reported to measure SCN− above the micromolar level. However, SCN− is derived from many sources such as cigarettes, waste water, food and even car exhaust and its effect is cumulative, which makes it necessary to develop methods for the detection of trace SCN−. In this paper, a simple and ultrasensitive turn-on fluorescence assay of trace SCN− is established based on the fluorescence resonance energy transfer (FRET) between gold nanoparticles (AuNPs) and fluorescein. The detection limit is 0.09 nM, to the best of our knowledge, which has been the lowest detection LOD ever without the aid of costly instrumentation. The fluorescence of fluorescein is significantly quenched when it is attached to the surface of AuNPs. Upon the addition of SCN−, the fluorescence is turned on due to the competition action between SCN− and fluorescein towards the surface of AuNPs. Under an optimum pH, AuNPs size and concentration, incubation time, the fluorescence enhancement efficiency [(IF−I0)/I0] displays a linear relationship with the concentration of SCN− in the range of 1.0 nM to 40.0 nM. The fluorescein–AuNP sensor shows absolutely high selectivity toward SCN− than other 16 anions. The common metal ions, amino acids and sugars have no obvious interference effects. The accuracy and precision were evaluated based on the recovery experiments. The cost effective sensing system is successfully applied for the determination of SCN− in milk products and saliva samples.

Graphical abstractA simple and ultrasensitive turn-on fluorescence assay of trace thiocyanate (SCN−) is established based on the fluorescence resonance energy transfer (FRET) between the gold nanoparticles (AuNPs) and fluorescein. The limit of detection is 0.09 nM which has been the lowest ever reported without the expensive instrumentation to our best of knowledge.Figure optionsDownload full-size imageDownload as PowerPoint slide