Quantum Dot-Based Headspace Single-Drop Microextraction Technique for Optical Sensing of Volatile Species

Core-shell CdSe/ZnS quantum dots (QDs) dispersed in a droplet of organic solvent have been applied for the first time as luminescent probes for the selective detection of volatile species. Luminescence quenching caused by volatile species was examined after their trapping onto a drop using the headspace single-drop microextraction (HS-SDME) approach along with microvolume fluorospectrometry. The novel method is characterized by low reagent and sample consumption, especially regarding QDs, a reduction about 500-fold for each analysis being attained in comparison with luminescent probing in aqueous phase using conventional luminescence spectrometers with 1 cm quartz cells for measurement. To assess QDs as luminescent probes along with HS-SDME, 14 volatile species were tried. Strong luminescence quenching (i.e., I(0)/I > 2.5) was observed for species such as CH(3)Hg(+) and Se(IV) after hydridation with NaBH(4). Moderate luminescent quenching (I(0)/I ≈ 2) was observed for species such as Hg(II) after its conversion into Hg(0), H(2)S, and methylcyclopentadienyl-manganese tricarbonyl (MMT). Small luminescence quenching effects (i.e., 1< I(0)/I <2) were caused by other hydride forming species such as As(III), Sb(III), Te(IV), and Bi(III), as well as SnBu(4), volatile amines, and endosulfan. Detection limits of 6.3 × 10(-9) and 1.6 × 10(-7) M were obtained for Se(IV) and CH(3)Hg(+), respectively. Repeatability expressed as relative standard deviation (N = 7) was about 5%. QD-HS-SDME-μvolume-fluorospectrometry allows one to carry out matrix separation, preconcentration, and confinement of QDs, hence achieving a selective, sensitive, fast, environmentally friendly, and miniaturized luminescence assay.