Visual and fluorescent detection of citalopram based on the inner filter effect of gold nanoparticles on the fluorescence of CdS quantum dots

Citalopram is a selective serotonin reuptake inhibitor that is used for the treatment of depression without the adverse effects commonly associated with classical antidepressants. Various analytical methodologies have been utilized for determination of citalopram in pharmaceutical and biological samples including HPLC with different detectors, GC-MS, electrophoretic methods and spectrofluorometry. Gold nanoparticles due to their unique properties are usually used in the colorimetric-based detections systems and recently fluorescent assays for construction of IFE-based visual sensors as quenching agents using modified QDs. In this way the fluorescence of modified QDs which was quenched by AuNPs due to inner filter effect, is recovered in the presence of analytes due to the induced aggregation of AuNPs which causes the red shift in their absorption spectra [1-4].In this work, we developed a low-cost, rapid, simple and sensitive analytical method for the visual and fluorescent detection of citalopram based on the inner filter effect (IFE) of gold nanoparticles (AuNPs) on the fluorescence of CdS quantum dots (QDs). The fluorescence of L-Cysteine capped CdS QDs was significantly quenched by citrate-stabilized AuNPs via IFE. Upon addition of citalopram the IFE of AuNPs on the fluorescence of CdS QDs was weakened and the fluorescence intensity was recovered, since citalopram could induce the aggregation of AuNPs accompanying color change from red to blue, which resulted in turn-on of the IFE-decreased fluorescence of CdS QDs. Under the optimum conditions, the fluorescence intensity of the CdS QDs/AuNPs system was proportional to the concentration of citalopram in the range of 0.5 – 200 µM, with a detection limit of 0.14 µM. The sensing platform had been used for citalopram detection in human serum and pharmaceutical samples with satisfactory results.