Sensitive, rapid, and simple detection methods for the screening of extensively used organophosphorus pesticides and highly toxic nerve agents are in urgent demand. A novel label-free silicon quantum dots (SiQDs)-based sensor was designed for ultrasensitive detection of pesticides. This sensing strategy involves the reaction of acetylcholine chloride (ACh) with acetylcholinesterase (AChE) to form choline that is in turn catalytically oxidized by choline oxidase (ChOx) to produce betaine and H2O2 which can quench the photoluminescence (PL) of SiQDs. Upon the addition of pesticides, the activity of AChE is inhibited, leading to the decrease of the generated H2O2, and hence the PL of SiQDs increases. By measuring the increase in SiQDs PL, the inhibition efficiency of pesticide to AChE activity was evaluated. It was found that the inhibition efficiency was linearly dependent on the logarithm of the pesticides concentration. Consequently, pesticides, such as carbaryl, parathion, diazinon, and phorate, were determined with the SiQDs PL sensing method. The lowest detectable concentrations for carbaryl, parathion, diazinon, and phorate reached 7.25 × 10(-9), 3.25 × 10(-8), 6.76 × 10(-8), and 1.9 × 10(-7) g/L, respectively, which were much lower than those previously reported. The detecting results of pesticide residues in food samples via this method agree well with those from high-performance liquid chromatography. The simple strategy reported here should be suitable for on-site pesticides detection, especially in combination with other portable platforms.

Si quantum dots have been demonstrated to be environmentally friendly photoluminescence probes and their fluorescence was quenched by H(2)O(2) that was produced from the glucose oxidase-catalyzed oxidation of glucose. This strategy could be used to detect glucose with high sensitivity and selectivity.

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For developing highly selective and sensitive electrochemical sensors for chiral recognition, taking advantage of the synthetical properties of β-cyclodextrin (β-CD, strong host−guest recognition) and carbon nanotubes wrapped with reduced graphene oxide (CNTs@rGO, excellent electrochemical property and large surface area), as well as the differences in binding affinity between β-CD and guest molecules, a dual signal electrochemical sensing strategy was proposed herein for the first time in chiral recognition based on the competitive host−guest interaction between probe and chiral isomers with β-CD/CNTs@rGO. As a model system, rhodamine B (RhB) and phenylalanine enantiomers (Dand L-Phe) were introduced as probe and target enantiomers, respectively. Due to the host−guest interactions, RhB can enter into the β-CD cavity, showing remarkable oxidation peak current of RhB. In the presence of L-Phe, competitive interaction with the β-CD cavity occurs and RhB are replaced by L-Phe owing to the stronger binding affinity between L-Phe and β-CD, which results in the peak current of RhB decreasing and the peak current of L-Phe appears, and interestingly, the changes of both signals linearly correlate with the concentration of L-Phe. As for D-Phe, it cannot replace RhB owing to the weaker binding affinity between D-Phe and β-CD. Based on this, a dual-signal electrochemical sensor was developed successfully for recognizing Phe. This dual-signal sensing strategy can provide highly selective and sensitive recognition compared to single-signal sensor and has important potential applications in chiral recognition.C hirality has an important impact on chemical/biological research, since most active substances possess chirality. Generally, the performance of chiral enantiomers show great differences in terms of biochemical activity, toxicity, transport processes, and metabolic pathways. 1−3 Typically, only one isomer exhibits perfect activity and the other has no desirable value and even causes serious side-effects. Thus, chiral recognition is always a popular topic in chemical and biological research. 4−6 For resolving this problem, many approaches, such as capillary electrophoresis, 7 high-performance liquid chromatography, 8 circular dichroism spectroscopy, 9,10 colorimetry 11,12 and fluorescence, 13,14 were developed to recognize electroactive chiral molecules, which are very important in chiral recognition. However, the most of reported approaches need complex sample pretreatment and expensive chiral columns and are time-consuming as well. 15,16 Recently, electrochemical chiral recognition has received considerable attention, due to the many advantages they offer, such as low cost, fast response, inexpensive instrument, and facile miniaturization. 17−22 For instance, Kong et al. 23

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