Manganese-doped ZnS quantum dots as a phosphorescent probe for use in the bi-enzymatic determination of organophosphorus pesticides

A portable smartphone-assisted digital image fluorimetry for analysis of methiocarb pesticide in vegetables: Nitrogen-doped carbon quantum dots as a sensing probe

The increasing use of pesticides in the agriculture fields strengthen the crop production to meet the needs of increasing population. The residues in water and food materials cause several health hazards. Herein, nitrogen-doped carbon quantum dot (N-CQDs) is designed for determination of methiocarb pesticide in vegetables by fluorescent paper sensor and compared the results with fluorimetry. The fluorescent paper-based detection is performed by recording the change in fluorescence of N-CQDs with introduction of methiocarb using smartphone and ImageJ software. Good linear range was acquired for analysis of methiocarb from 10 to 1000 μgL^-1 with a low detection limit (LOD) of 3.5 μgL^-1 in fluorimetry; and 700-10,000 μgL^-1 with a LOD of 500 μgL^-1 in fluorescent paper sensor. A better recovery from 92.0 to 95.4% illustrating the selectivity of both methods for analysis of methiocarb in vegetables. Thus, the advantage of using N-CQDs as a fluorescent sensor for analysis of methiocarb in vegetables is instrument free, portable and user-friendly.

Design and Evaluation of a Competitive Phosphorescent Immunosensor for Aflatoxin M1 Quantification in Milk Samples Using Mn:ZnS Quantum Dots as Antibody Tags

Aflatoxin M1 (AFM1) is one of the most widespread aflatoxins that can be present in the milk of lactating mammals. It can cause carcinogenicity, mutagenesis, teratogenesis, genotoxicity and immunosuppression. The WHO recommends reducing the AFM1 concentration in food products, so the European Commission has set a maximum allowable limit of 0.05 µg L−1 in milk and its products. Thus, there is a need to develop new methodologies to satisfy the demand for reliable, cost-effective, robust and sensitive AFM1 routine controls. In the present work, a competitive phosphorescent immunosensor for AFM1 quantification in milk, based on antibody–antigen recognition and Mn:ZnS quantum dots (d-QDs) as photoluminescent labels, has been developed. Two different assay strategies based on the use of d-QDs as labels of secondary antibodies (direct assay), or of a derivative species of the antigen AFM1-Bovine Serum Albumin (indirect assay) were compared in terms of analytical performance for AFM1 quantification. The best analytical results were obtained with the immunoassay format that uses d-QDs as tags of secondary antibodies (direct assay), and said design was finally selected. The selected immunosensor provided a detection limit for AFM1 quantification of only 0.002 µg L−1, which greatly satisfied the maximum tolerable limit of AFM1 in milk of 0.05 µg L−1. The accuracy, calculated as recovery of AFM1 in fortified skimmed milk samples, ranged from 81 to 90%, with relative standard deviations from 3% to 14%. These results bring to light the good performance of such phosphorescent biosensors as simple and fast alternatives to conventional chromatographic analytical methods.

A BCNO QDs-MnO2 nanosheets based fluorescence "off-on-off" and colorimetric sensor with smartphone detector for the detection of organophosphorus pesticides

In this work, boron carbon oxynitride quantum dots (BCNO QDs) were prepared by a one-step hydrothermal process of ethanolamine and boric acid. BCNO QDs exhibited blue fluorescence with the optimal excitation/emission fluorescence peak at 335 and 420 nm, respectively. As an efficient fluorescence quencher, manganese dioxide (MnO₂) nanosheets can effectively quench the fluorescence of BCNO QDs via the inner filter effect (IFE). Acetylcholinesterase (AChE) catalyzes the hydrolysis of acetylcholine (ATCh) to produce thiocholine (TCh). TCh can reductively degrade MnO₂ nanosheets to generate Mn²⁺, thereby recovering the fluorescence of BCNO QDs. Organophosphorus pesticides (OPs) can inhibit the activity of AChE enzymes, thereby preventing the production of TCh and the decomposition of MnO₂ nanosheets, resulting in the fluorescence "turn-off". Therefore, the concentration of OPs can be detected by measuring the fluorescence intensity change of AChE-ATCh-MnO₂-BCNO-QDs system. Under optimal experimental conditions, the dynamic detection range of paraoxon is 0.1-250 ng mL^-1, and the detection limit is 0.03 ng mL^-1. Meanwhile, the reaction system also showed concentration-dependent visual color changes from colorless to brownish. Furthermore, we prepared a portable BCNO QDs test paper. By using a smartphone to identify the RGB values of the reaction solution and the corresponding test paper, we carried out the digital image chromaticity analysis, which can shorten the detection time and reduce the detection cost, and provide an effective solution for the rapid detection of OPs on site.

Recent Advances on Detection of Insecticides Using Optical Sensors

Insecticides are enormously important to industry requirements and market demands in agriculture. Despite their usefulness, these insecticides can pose a dangerous risk to the safety of food, environment and all living things through various mechanisms of action. Concern about the environmental impact of repeated use of insecticides has prompted many researchers to develop rapid, economical, uncomplicated and user-friendly analytical method for the detection of insecticides. In this regards, optical sensors are considered as favorable methods for insecticides analysis because of their special features including rapid detection time, low cost, easy to use and high selectivity and sensitivity. In this review, current progresses of incorporation between recognition elements and optical sensors for insecticide detection are discussed and evaluated well, by categorizing it based on insecticide chemical classes, including the range of detection and limit of detection. Additionally, this review aims to provide powerful insights to researchers for the future development of optical sensors in the detection of insecticides.

pH-Response Quantum Dots with Orange-Red Emission for Monitoring the Residue, Distribution, and Variation of an Organophosphorus Pesticide in an Agricultural Crop

Development of simple, sensitive, and reliable fluorescence sensors for monitoring the residue, distribution, and variation of organophosphorus pesticides (OPs) in agricultural crops is highly urgent but remains challenging, which is ascribed to deprivation of an ideal fluorophore and ingenious detection strategy. Herein, we report the fabrication of cadmium telluride quantum dots (CdTe QDs) with bright emission, good water dispersion, and long emission wavelength for OP screening based on the unique response of CdTe QDs to pH and the inhibition of OPs on acetylcholinesterase (AChE) activity. AChE catalyzed hydrolysis of acetylcholine (ACh) into CH₃COOH, which protonated CdTe QDs to decline the fluorescence, whereas target OP impeded AChE from catalyzing hydrolysis of ACh into CH₃COOH, making little influence in fluorescence of CdTe QDs. On the basis of the change in fluorescence, sensitive detection of OP was acquired, with the limit of detection at 0.027 ng/mL, which was comparable or lower than that of most known OP sensors. Furthermore, the CdTe-QD-based sensor was successfully applied for precisely monitoring the residue, distribution, and variation of methidathion in Chinese cabbage and cultivated soil. Therefore, the proposed sensor was anticipated to supply a promising alternative for food safety guarantee and was an valuable application for OP screening.

Development of enzymatic electrochemical biosensors for organophosphorus pesticide detection

The enzymatic electrochemical biosensor has the advantages of simple operation, speed, and integration in the detection of organophosphorus pesticide (OPs) residues. It has the potential to become the best alternative to the traditional OP detection technology. This article introduces the OP identification principle of different enzymes, the OP detection mechanism of several common sensors, and the enzyme assembly method. In addition, the article discusses application of nanomaterials in sensor preparation and sensor performance parameters in the past decade. The related content of early sensors is outside the scope of this article.

CdTe QD-based inhibition and reactivation assay of acetylcholinesterase for the detection of organophosphorus pesticides

An enzyme immobilized glutathione (GSH)-capped CdTe quantum dot (QD)-based fluorescence assay has been developed for monitoring organophosphate pesticides.

A novel fluorescence "turn off-on" nanosensor for sensitivity detection acid phosphatase and inhibitor based on glutathione-functionalized graphene quantum dots

In this paper, we developed a label-free and sensitive fluorescence sensor for acid phosphatase (ACP) and its inhibitor parathion-methyl (PM) detection based on glutathione-functionalized graphene quantum dots (GQDs@GSH). Upon addition of MnO₂ nanosheets, the fluorescence of GQDs@GSH could be efficiently quenched via a fluorescence resonance energy transfer. ACP could easily catalyze the hydrolysis of L-Ascorbic acid-2-phosphate (AAP) to ascorbic acid (AA), which could reduce MnO₂ nanosheets to Mn²⁺ in acidic environment, leading to dramatically increase of the fluorescence intensity of GQDs@GSH. Quantitative detection of ACP in a broad range from 0.1 to 9 mU mL^-1 with a detection limit of 0.027 mU mL^-1 could be achieved. The feasibility of the proposed sensor in real samples analysis was also studied and satisfactory results were obtained. Furthermore, the fluorescence assay strategy could also be used for the detection of parathion-methyl (PM) as ACP inhibitor.

Direct Detection of Potential Pyrethroids in Yangtze River via an Imprinted Multilayer Phosphorescence Probe

A novel tailored multilayer probe for monitoring potential pyrethroids in the Yangtze River was proposed. The room-temperature phosphorescence method was applied to realize a detection strategy that is superior to the fluorescence method. Efficient Mn-doped ZnS quantum dots with uniform size of 4.6 nm were firstly coated with a mesoporous silica to obtain a suitable intermediate transition layer, then an imprinted layer containing bifenthrin specific recognition sites was anchored. Characterizations verified the multilayer structure convincingly and the detection process relied on the electron transfer-induced fluorescence quenching mechanism. Optional detection time and standard detection curve were obtained within a concentration range from 5.0 to 50 μmol L^-1. The stability was verified to be good after 12 replicates. Feasibility of the probe was proved by monitoring water samples from the Zhenjiang reach of the Yangtze River. The probe offers promise for direct bifenthrin detection in unknown environmental water with an accurate and stable phosphorescence analysis strategy.

Quantum Dots Applied to Methodology on Detection of Pesticide and Veterinary Drug Residues

The pesticide and veterinary drug residues brought by large-scale agricultural production have become one of the issues in the fields of food safety and environmental ecological security. It is necessary to develop the rapid, sensitive, qualitative and quantitative methodology for the detection of pesticide and veterinary drug residues. As one of the achievements of nanoscience, quantum dots (QDs) have been widely used in the detection of pesticide and veterinary drug residues. In these methodology studies, the used QD-signal styles include fluorescence, chemiluminescence, electrochemical luminescence, photoelectrochemistry, etc. QDs can also be assembled into sensors with different materials, such as QD-enzyme, QD-antibody, QD-aptamer, and QD-molecularly imprinted polymer sensors, etc. Plenty of study achievements in the field of detection of pesticide and veterinary drug residues have been obtained from the different combinations among these signals and sensors. They are summarized in this paper to provide a reference for the QD application in the detection of pesticide and veterinary drug residues.

Sensitive and Selective Detection of Oxo-Form Organophosphorus Pesticides Based on CdSe/ZnS Quantum Dots

A rapid, sensitive and enzyme-based optical biosensor was applied for the determination of seven organophosphorus pesticides (OPPs), including the oxo forms (malaoxon, paraoxon, dibrom, and dichlorvos), the thio forms (malathion and parathion) and the mixed form (demeton) in Panax ginseng. The principal of the proposed method is that the fluorescence quenching effect of quantum dots (QDs) can be observed by enzyme-generated H₂O₂. The active centers of acetylcholinesterase (AChE) could be inhibited in the presence of pesticides, which caused decrease of the generated H₂O₂. Then, the inhibition efficiency of pesticide to AChE activity could be evaluated by measuring the fluorescence changes. Different from biosensors based on immobilized enzyme or self-assembling technique, the proposed biosensor demonstrated a good selectivity for the detection of oxo forms of OPPs. In the present study, the important experimental conditions of the proposed biosensor were investigated. Under the optimized conditions (incubation temperature, 35 °C; incubation time, 20 min; pH value, 8.0; detection time, 30 min; AChE concentration, 40.9 U/L; and choline oxidase (ChOx) concentration, 637.5 U/L), the limit of detection for the investigated oxo-form OPPs was no more than 0.05 μM, which suggested that the proposed method could be used for sensitive and selective determination of trace amounts of OPPs residues in real samples with complex matrices.

Sensitive prostate specific antigen quantification using dihydrolipoic acid surface-functionalized phosphorescent quantum dots

Herein, high-quality Mn-doped ZnS quantum dots (QDs) have been synthesized using a facile approach directly in aqueous media. The surface of the obtained QDs was further modified by cap-exchange of the native cysteine shell with dihydrolipoic acid (DHLA) ligands resulting in nanocrystals with high water-stability having an intense phosphorescent signal. Covalent bioconjugation of the DHLA-coated nanoparticles with an anti-IgG antibody was then carried out. Interestingly the QD immunoprobe (QD-labelled antibodies) maintained an intense phosphorescence emission, without any significant spectral-shift (as compared to the free QDs). Coupling of an asymmetric flow field flow fractionation technique to an elemental mass spectrometry detection enabled the accurate determination of the efficiency of the bioconjugation reaction. The obtained nanoparticle-antibody bioconjugate was then applied to develop a quantitative sandwich-type phosphorescent immunoassay for Prostate Specific Antigen (PSA), and a limit of detection (LOD) of 17 pg mL^-1 of PSA was achieved and allow to quantify such biomarker in samples within clinically relevant levels. Finally, the assay was validated for the quantification of PSA in the cellular media of prostate cancer cells. Obtained results proved the robustness of the proposed immunoassay based on long-lived phosphorescence measurements against eventual photoluminescent interferences significantly affecting the conventional short-lived fluorescence detection.

β-Cyclodextrin functionalised gold nanoclusters as luminescence probes for the ultrasensitive detection of dopamine

A novel luminescence probe based on mono-6-amino-β-cyclodextrin (NH₂-β-CD) functionalised gold nanoclusters (β-CD-AuNC) was designed for dopamine (DA) detection.