A stable colorimetric biosensor for highly selective detection of malathion residue in food based on aptamer-regulated laccase-mimic activity.

Malathion causes a serious threat to human health due to its widespread use in the environment. Herein, a novel and stable smartphone-integrated colorimetric biosensor for malathion detection is firstly established based on aptamer-enhanced laccase-mimicking activity. The results indicate that the M17-F aptamer can increase the affinity of Ag2O nanoparticles to the substrate 2,4-dichlorophenol and enhance their laccase-mimicking activity. Thus, abundant semiquinone radicals are produced in the catalytic system, which are combined with chromogenic agent to generate dark red products. The corresponding RGB values for the colour change of the solution can be easily obtained using smartphones, which is used for the rapid detection of malathion. The established biosensor for malathion has a limit of detection as low as 5.85 nmol·L-1, and displays good selectivity for other competitive pesticides. Moreover, further studies have verified the applicability of the biosensor in actual samples, indicating that it may have the potential for application in malathion detection in food.

Facile colorimetric sensor using oxidase-like activity of octahedral Ag2O particles for highly selective detection of Pb(II) in water.

Pb(II) is a prevalent heavy metal ion classified as a 2B carcinogen. Excessive intake of Pb(II) in the human body can damage the central nervous system, kidneys, liver, and immune system, leading to permanent brain damage, anemia, and cancer. Colorimetry can be applied to rapidly determine Pb(II) residues, but there are still many challenges in the accuracy and sensitivity of detection. Based on the inhibitory impact of Pb(II) on the oxidase-like activity of octahedral silver oxide (Ag2O), a colorimetric sensor with smartphone-assisted analysis for the Pb(II) detection was first developed. Herein, it has been found that Pb(II) can adsorb onto the surface of octahedral Ag2O, hindering the production of O2- in the reaction system. This ultimately results in the suppression of oxidase-like activity, leading to a lighter purple appearance of the colorimetric reaction solution. The sensor exhibits a high degree of sensitivity and a limit of detection (LOD) for Pb(II) was calculated as 2.2 µg L-1. Hence, the developed colorimetric sensor with high sensitivity, excellent specificity, and high tolerance to sodium ions is hopeful to have practical applications in Pb(II) detection in environmental water samples. Moreover, the sensor will provide a novel strategy for heavy metal ion detection and other substances.

Enhancement of pyranoanthocyanin formation in blueberry wine with non-Saccharomyces yeasts.

The development of blueberry wine provides an alternative method for maintaining the nutritional value and extending the shelf life of blueberries. However, anthocyanin loss and off-flavor compound generation during fermentation impair blueberry wine color and quality. Hydroxycinnamate decarboxylase from yeast can catalyze the conversion of hydroxycinnamic acids to vinylphenols, which later may condense with anthocyanins to form more stable vinylphenolic pyranoanthocyanins. In this study, 10 non-Saccharomyces yeasts from Daqu that showed hydroxycinnamate decarboxylase activity were screened. Among the 10 strains, Wickerhamomyces anomalus Y5 showed the highest consumption (34.59%) of the total tested phenolic acids and almost no H2S production. Furthermore, Y5 seemed to produce four vinylphenol pyranoanthocyanins (cyanidin-3-O-galactoside/glucoside-4-vinylcatechol, cyanidin-3-O-galactoside/glucoside-4-vinylsyringol, malvidin-4-vinylguaiacol, and malvidin-4-vinylcatechol) during blueberry wine fermentation, which may improve the color stability of blueberry wine. These findings provide new insights for improving the quality of blueberry wine using non-Saccharomyces yeasts.

Airborne microorganisms and key environmental factors shaping their community patterns in the core production area of the Maotai-flavor Baijiu.

Airborne microorganisms are important parts of the Moutai-flavor Baijiu brewing microbial community, which directly affects the quality of Baijiu. However, environmental factors usually shape airborne microbiomes in different distilleries, even in the different production areas of the same distillery. Unfortunately, current understanding of environmental factors shaping airborne microbiomes in distilleries is very limited. To bridge this gap, we compared airborne microbiomes in the Moutai-flavor Baijiu core production areas of different distilleries in the Chishui River Basin and systematically investigated the key environmental factors that shape the airborne microbiomes. The top abundant bacterial communities are mainly affiliated to the phyla Actinobacteriota, Firmicutes, and Proteobacteri, whereas Ascomycota and Basidiomycota are the predominant fungal communities. The Random Forest analysis indicated that the biomarkers in three distilleries are Saccharomonospora and Bacillus, Thermoactinomyces, Oceanobacillus, and Methylobacterium, which are the core functional flora contributing to the production of Daqu. The correlation and network analyses showed that the distillery age and environmental temperature have a strong regulatory effect on airborne microbiomes, suggesting that the fermentation environment has a domesticating effect on air microbiomes. Our findings will greatly help us understand the relationship between airborne microbiomes and environmental factors in distilleries and support the production of the high-quality Moutai-flavor Baijiu.

Rapid colorimetric sensor for ultrasensitive and highly selective detection of Fumonisin B1 in cereal based on laccase-mimicking activity of silver phosphate nanoparticles.

Ag3PO4 nanoparticles (NPs) was prepared through a facile coprecipitation method, and was first found to have excellent laccase-mimicking catalytic activity. The study confirms that Fumonisin B1 (FB1) can effectively hinder the production of superoxide anion (O2-) between Ag3PO4 NPs and dissolved oxygen, and further inhibit laccase-mimicking activity of Ag3PO4 NPs. Thus, a novel rapid colorimetric sensor for FB1 analysis in cereal was first established using laccase-mimicking activity as sensing signal. The absorbance variation of sensing solution is directly related to the amount of FB1, and the color change is further combined with smartphone for quantitively analysis of FB1. The limit of detection (LOD) of the sensor is determined as low as 1.73 µg·L-1, which is far lower than the maximum residue limits (MRLs) of FB1 set by European Commission and US Food and Drug Administration (FDA). The average recovery of 87.8-104.5% for FB1 detection was obtained in cereal.

Smartphone-assisted colorimetric aptasensor for rapid detection of carbendazim residue in agriculture products based on the oxidase-mimicking activity of octahedral Ag2O nanoparticles.

Carbendazim (CBZ) is a widely used pesticides, and its excessive intake is serious damage to humans and animals. Herein, a stable and sensitive colorimetric aptasensor for rapid detection of CBZ residue has been established based on the enhancement of CBZ-specific aptamer (CZ-13) on oxidase-mimicking activity of octahedral Ag2O nanoparticles (NPs). The CZ-13 aptamer can significantly increase the catalytic activity by promoting the production of superoxide anion (·O2-) on the surface of Ag2O NPs and enhancing the affinity of octahedral Ag2O NPs to 3,3',5,5'-tetramethylbenzidine (TMB) molecules. In the presence of CBZ, the quantity of CZ-13 aptamer will be exhausted due to the specific binding to CBZ pesticide. Thus, the rest CZ-13 aptamer no longer enhanced the catalytic activity of octahedral Ag2O NPs, which leads to the change in color of sensing solution. The color change of sensing solution can be easily converted to the corresponding RGB value by a smartphone for quantitative and rapid detection of CBZ. The designed aptasensor has excellent sensitivity and specificity, and the limit of detection was determined as low as 7.35 µg L-1 for CBZ assay. Besides, the aptasensor exhibited good recoveries in the spiked cabbage, apple and cucumber, showing that it may have broad application prospects for detecting CBZ residues in agriculture products.

Screening and identification of a DNA aptamer to construct the label-free fluorescent aptasensor for ultrasensitive and selective detection of clothianidin residue in agricultural products.

Clothianidin pesticide not only pollutes the ecological environment, but also poses a potential threat to human health. Thus, it is of great importance to develop efficient and accurate methods to recognize and detect clothianidin residues in agricultural products. Aptamer has the advantages of easy modification, high affinity and good stability, which is particularly suitable as a recognition biomolecule for pesticide detection. However, the aptamer against clothianidin has not been reported. Herein, the aptamer (named CLO-1) had good selectivity and strong affinity (Kd = 40.66 ± 3.47 nM) to clothianidin pesticide, which was screened for the first time by Capture-SELEX strategy. The binding effect of CLO-1 aptamer to clothianidin was further studied by circular dichroism (CD) spectroscopy and molecular docking technique. Finally, the CLO-1 aptamer was used as the recognition molecule to construct a label-free fluorescent aptasensor using GeneGreen dye as sensing signal for the highly sensitive detection of clothianidin pesticide. The constructed fluorescent aptasensor had the limit of detection (LOD) as low as 5.527 µg L-1 for clothianidin, and displayed good selectivity against other competitive pesticides. The aptasensor was applied to detect the clothianidin spiked in tomatoes, pears and cabbages, and the recovery rate was good in the range of 81.99%-106.64%. This study provides a good application prospect for the recognition and detection of clothianidin.

Facile colorimetric smartphone-based biosensor for rapid detection of organophosphorus pesticides residues in environment using the aptamer-enhanced oxidase activity of octahedral Ag2O particles.

The long-term and excessive use of organophosphorus pesticides (OPs) leads to hazardous residues in the environment, which threatens human health to a considerable extent. Colorimetric methods can quickly and readily identify pesticide residue, but they still have various challenges in accuracy and stability. Herein, a smartphone-assisted and non-enzymatic colorimetric biosensor was constructed for rapid monitoring of multiple OPs based on the enhanced effect of aptamer on the catalytic ability of octahedral Ag2O. It was demonstrated that the aptamer sequence could enhance the affinity of colloidal Ag2O to chromogenic substrates, and accelerate the generation of oxygen radicals such as superoxide radical (·O2-) and singlet oxygen (1O2) from dissolved oxygen, thereby significantly increasing the oxidase activity of octahedral Ag2O. The color change of the solution can be easily converted to the corresponding RGB values by a smartphone for quantitative and rapid detection of multiple OPs. Hence, the smartphone-based and visual biosensor of multiple OPs was acquired with limit of detection of 10 µg L-1, 28 µg L-1 and 40 µg L-1 for isocarbophos, profenofos and omethoate, respectively. The colorimetric biosensor also exhibited good recoveries in several environmental and biological samples, showing that it may have broad application prospects for detecting OPs residues.

Porous-nanozyme-based colorimetric sensor for rapid detection of kanamycin in foods under neutral condition.

Most colorimetric methods based on nanozymes need to have excellent performance under acidic condition, so they are currently facing some challenges in the field of food hazard detection. Herein, a facile and rapid colorimetric sensor for kanamycin (KAN) detection in foods under neutral condition has been designed using the peroxidase-mimic activity of porous nanozyme like Co3 O4 nanodisk. Further investigations showed that the interaction mechanism between porous Co3 O4 nanodisk and substrates belongs to a ping-pong model, and the inhibition type of KAN on the peroxidase-mimic activity is noncompetitive inhibition. The constructed sensor has good sensitivity for KAN with the limit of 57 nM, and the color changes can be discerned visually when KAN exceeds 0.5 µM. Besides, the colorimetric sensor obtains excellent recovery results in chicken serum, milk, honey, and pork, which shows that the proposed sensing strategy can provide a rapid and convenient detection method for KAN in foods under neutral condition. PRACTICAL APPLICATION: The established sensing strategy can rapidly distinguish whether KAN residue exceeds the permissible level within 10 min, which meets the requirement for on-site monitoring of antibiotics in foods, and also open up a new idea for other hazards detection under neutral condition.

An ultrasensitive label-free electrochemical aptasensing platform for thiamethoxam detection based on ZIF-67 derived Co-N doped porous carbon.

Herein, a new electrochemical aptasensor was developed for the highly selective and sensitive detection of thiamethoxam (TMX). Co-N doped porous carbon (CoNC) was first modified on the glassy carbon electrode (GCE) as a conductive substrate. Then, nickel hexacyanoferrate nanoparticles (NiHCFNPs) were drop-coated on CoNC as signal probes to generate measurable redox peaks. Benefiting from the superior structural features and catalytic activity, CoNC not only facilitated the immobilization of NiHCFNPs, but also exhibited good catalytic activity for the redox of NiHCFNPs, thus clearly amplifying the sensing signal. Subsequently, gold nanoparticles (AuNPs) were deposited on NiHCFNPs/CoNC/GCE to anchor the aptamer of TMX. When TMX was captured onto the sensor via specific affinity of the aptamer, the formed TMX-Apt complex impeded electron transfer, resulting in a decrease in the peak current. Thus, TMX can be easily detected by measuring the change in peak current. The label-free aptasensor displays high sensitivity to TMX with a quite low LOD of 3.65 × 10-3 µg/L. The acceptable recoveries of environmental water and potato samples varied from 94.05 % to 105.20 %, demonstrating the proposed aptasensor will be a promising tool for the highly sensitive, specific and reliable detection of TMX in both environmental and food matrices.

Screening and identification of an aptamer as novel recognition molecule in the test strip and its application for visual detection of ethyl carbamate in liquor.

There is still a great challenge of on-site and rapid detection for ethyl carbamate (EC) in liquor. Herein, the aptamer (EC1) against EC was firstly screened by Capture-SELEX strategy, and its affinity and binding sites for EC were further investigated by fluorescence assay and molecular docking. Under the premise of retaining the structural features, the obtained aptamer was further truncated into a short sequence (named EC1-34), which has the dissociation constant of 17.97 ± 0.98 nM for EC. Subsequently, a visible, rapid, and cost-effective test strip was firstly designed for EC detection in liquor, in which the cationic polymer was used to efficiently capture the recognition probe conjugated with EC1-34 aptamer and gold nanoparticles (AuNPs). The minimum detection limit of the test strip is calculated as 2.14 µg⋅L-1. The rapid test strip can be widely used for EC detection in liquor due to the advantages of high stability, convenience and selectivity.

Distribution and Quantification of Lactic Acid Enantiomers in Baijiu.

Enantiomers of lactic acid were investigated in Baijiu, including soy sauce aroma-type Baijiu (SSB), strong aroma-type Baijiu (STB), and light aroma-type Baijiu (LTB), via high-performance liquid chromatography with a chiral separation column. The natural concentration and enantiomeric distribution of lactic acid were studied, and their contribution to the flavor of Chinese Baijiu was evaluated based on recognition threshold. The results showed that there were significant differences in the content of lactic acid and the ratio of enantiomeric isomers among different aroma types and storage year. In SSB, the concentrations of D-lactic acid and L-lactic acid were higher, with the highest concentrations of 1985.58 ± 11.34 mg/L and 975.31 ± 14.03 mg/L, respectively. In STB, the highest concentrations of D-lactic acid and L-lactic acid were 1048.00 ± 11.46 mg/L and 939.83 ± 0.23 mg/L, respectively. In LTB, the highest concentrations of D-lactic acid and L-lactic acid were 760.90 ± 9.45 mg/L and 558.33 ± 3.06 mg/L, respectively. The average D/L enantiomeric ratios were 78:22 ± 16.16 and 80:20 ± 9.72 in the Commercial Baijiu products of SSB and STB, respectively. The average D/L enantiomeric ratio in LTB was 90:10 ± 6.08. D-lactic acid in JSHS vintage Baijiu showed a wave variation with aging, while L-lactic acid gradually increased during aging, and the average D/L enantiomeric ratio was 76:24 ± 4.26. The concentration of D-lactic acid in XJCT vintage Baijiu also showed a wave variation with aging, and the concentration of L-lactic acid tended to be stable during aging, with an average D/L enantiomeric ratio of 88:12 ± 2.80. The content of the two configurations of lactic acid in the LZLJ vintage Baijiu showed a decreasing trend during aging, with an average D/L enantiomeric ratio of 60:40 ± 11.99. The recognition threshold of D-lactic acid in 46% ethanol solution was 194.18 mg/L with sour taste; while the L-lactic acid was 98.19 mg/L with sour taste. The recognition threshold of L-lactic acid was about half that of D-lactic acid, indicating that L-lactic acid has a stronger sour taste. The taste activity values (TAVs) of D-lactic acid and L-lactic acid were greater than 1 in most of the Baijiu samples, and the TAV of D-lactic acid was greater than that of L-lactic acid. The study showed that the lactic acid enantiomers contributed to the taste perception of Baijiu in most of the samples, and D-lactic acid contributed more to the Baijiu taste than L-lactic acid.

A Label-Free Electrochemical Aptasensor Based on Zn/Fe Bimetallic MOF Derived Nanoporous Carbon for Ultra-Sensitive and Selective Determination of Paraquat in Vegetables.

Paraquat (PQ) has high acute toxicity, even at low concentrations. For most people, the main pathway of exposure to PQ is through the diet. Therefore, the development of simple and efficient methods for PQ testing is critical for ensuring food safety. In this study, a new electrochemical detection strategy for paraquat is proposed based on the specific binding of PQ to its nucleic acid aptamer. Firstly, the Zn/Fe bimetallic ZIF derived nanoporous carbon (Zn/Fe-ZIF-NPC) and nickel hexacyanoferrate nanoparticles (NiHCF-NPs) were sequentially modified onto the glassy carbon electrode (GCE). NiHCF-NPs served as the signal probes, while Zn/Fe-ZIF-NPC facilitated electron transfer and effectively enhanced the sensing signal of NiHCF-NPs. Au nanoparticles (AuNPs) were then electrodeposited on the NiHCF-NPs/Zn/Fe-ZIF-NPC/GCE and then the thiolated aptamer was assembled on the AuNPs/NiHCF-NPs/Zn/Fe-ZIF-NPC/GCE via Au-S bonding. When incubated with PQ, the formation of PQ-aptamer complexes delayed the interfacial electron transport reaction of NiHCF-NPs, which caused a decrease in the current signals. As a result, simple and highly sensitive detection of PQ can be readily achieved by detecting the signal changes. A linear range was obtained from 0.001 to 100 mg/L with a detection limit as low as 0.34 µg/L. Due to the recognition specificity of the aptamer to its target molecule, the proposed method has excellent anti-interference ability. The prepared electrochemical aptasensor was successfully used for PQ assay in lettuce, cabbage and agriculture irrigation water samples with recoveries ranging from 96.20% to 104.02%, demonstrating the validity and practicality of the proposed method for PQ detection in real samples.

Aptamer-enhanced the Ag(I) ion-3,3',5,5'-tetramethylbenzdine catalytic system as a novel colorimetric biosensor for ultrasensitive and selective detection of paraquat.

A facile and simple colorimetric biosensor was first established for paraquat (PQ) detection based on the aptamer-enhanced oxidation process of 3,3',5,5'-tetramethylbenzidine (TMB) by Ag+. The study confirmed that the interaction of PQ-15 aptamer with Ag+ accelerates the electron transfer from the aptamer-Ag+ complex to dissolved oxygen, which enhances the release of superoxide anion radicals (O2̇-) and facilitates the catalytic oxidation of the chromogenic substrate. PQ-15 aptamer will preferentially bind to PQ molecules, resulting in no further enhancement of the catalytic activity of Ag+. Molecular docking results revealed that the PQ molecules are attached to the stem-loop region of the PQ-15 aptamer through σ-π conjugation interactions. The proposed method is simple that only contains Ag+ and corresponding aptamer. The limit of detection (LOD) of the constructed colorimetric biosensor for PQ detection was determined to be 16.5 µg·L-1, belowing the maximum residue limit in fruits and vegetables set by the EU. Moreover, the colorimetric biosensor showed excellent selectivity and anti-interference properties, which was validated for detecting PQ residues in several typical agricultural and water samples.

A novel electrochemical sensing platform based on the esterase extracted from kidney bean for high-sensitivity determination of organophosphorus pesticides.

Similar to acetylcholinesterase, the activity of plant-derived esterase can also be inhibited by organophosphorus pesticides. Therefore, an electrochemical sensing platform using kidney bean esterase as a new detection enzyme was proposed for the highly sensitive determination of organophosphorus pesticides. Purified kidney bean esterase was obtained by an efficient and economical aqueous two-phase extraction method. Carboxylated graphene/carbon nanotube composites (cCNTs-cGR) and Au nanoparticles were used to provide a biocompatible environment to immobilize kidney bean esterase and also accelerate electron transport between the analyte and the electrode surface. Due to the good synergistic electrocatalytic effects of these nanomaterials, the biosensor exhibited an amplified electrocatalytic response to the oxidation of α-naphthalenol, which makes the sensor more sensitive. Based on the inhibitory effect of trichlorfon on kidney bean esterase activity, high sensitivity and low-cost detection of trichlorfon was achieved. Under optimum conditions, the inhibition of trichlorfon is proportional to its concentration in the range of 5 to 150 ng L-1 and 150 ng L-1 to 700 ng L-1 with an ultra-low detection limit of 3 ng L-1. Moreover, the validity of the prepared biosensor was verified by analyzing several actual agricultural products (cabbage and rice) with satisfactory recoveries ranging from 94.05% to 106.76%, indicating that kidney bean esterase is a promising enzyme source for the analysis of organophosphorus pesticides in food samples.

A liquid colorimetric chemosensor for ultrasensitive detection of glyphosate residues in vegetables using a metal oxide with intrinsic peroxidase catalytic activity.

The control of pesticide residues in food is of increasing importance nowadays due to the over-use and misapplication of herbicides in agricultural production. However, the current colorimetric method for rapid detection of glyphosate still faces many challenges like the low sensitivity and stability. Herein, a simple and ultrasensitive liquid colorimetric chemosensor for glyphosate detection was successfully constructed. Glyphosate pesticide can interact with metallic oxidelike porous Co3O4 nanodisc, and inhibit its inherent peroxidase-mimicking activity, making the colour of the solution change from blue to light blue or even colourless. The colour variation of the colorimetric chemosensor enables us to easily distinguish in less than 20 min even by the naked eye whether glyphosate exceeds the allowable level. The limit of detection (LOD) of the chemosensor for glyphosate was calculated as low as 2.37 µg·L-1, and the chemosensor displays excellent selectivity against other competitive pesticides and metal ions. Further studies have also validated the applicability of the colorimetric chemosensor in actual samples like tomato, cucumber and cabbage, indicating that the proposed strategy may have promising application prospects for detecting glyphosate residues in agricultural products.

A simple sensing platform based on a 1T@2H-MoS2/cMWCNTs composite modified electrode for ultrasensitive detection of illegal Sudan I dye in food samples.

The work presented here describes a highly sensitive and simple electrochemical sensor for the detection of Sudan I dye based on a nanocomposite made of MoS2 heterogeneous nanosheets (1T@2H-MoS2) and carboxylated carbon nanotubes (cMWCNTs) (1T@2H-MoS2/cMWCNTs). XPS results indicate that the content of 1T phase MoS2 was estimated to be 72% in 1T@2H-MoS2. Electron microscopy results show that the tubular cMWCNTs are uniformly interwoven in MoS2 nanosheets to form a three-dimensional network structure. Due to the synergistic electrocatalytic ability and high electroactive surface area, the 1T@2H-MoS2/cMWCNTs modified electrode demonstrated excellent analytical performance for Sudan I, including simple operation, good stability and a wide linear range from 5.00 × 10-9 to 2.00 × 10-6 mol L-1 and 2.00 × 10-6 to 1.00 × 10-4 mol L-1 with an ultra-low detection limit of 1.56 × 10-9 mol L-1. The recoveries of Sudan I from spiked real samples (chilli powder and ketchup) were in the range of 95.60% to 106.10% with low RSD (<5%), indicating that the 1T@2H-MoS2/cMWCNTs modified electrode is a promising tool for the analysis of illegal Sudan I in food samples.

G-quadruplex DNAzyme as peroxidase mimetic in a colorimetric biosensor for ultrasensitive and selective detection of trace tetracyclines in foods.

The colorimetric method can determine the initial results even by the naked eyes, but its main challenge for antibiotics detection in food at present is the relatively low sensitivity. Herein, an ultrasensitive colorimetric biosensor based on G-quadruplex DNAzyme was firstly proposed for the rapid detection of trace tetracycline antibiotics like tetracycline, oxytetracycline, chlortetracycline and doxycycline. DNAzyme composed of hemin and G-quadruplex has peroxidase-like activity, and tetracyclines can combine with hemin to form a stable complex and reduce catalytic activity, making the color of solution changes from yellow to green. The limits of detection (LOD) of the proposed colorimetric biosensor for tetracyclines is determined as low as 3.1 nM, which is lower than most of the other colorimetric methods for antibiotics detection. Moreover, the average recovery range of tetracyclines in actual samples is from 89% to 99%, indicating that such strategy may has bright application prospects for tetracyclines detection in foods.

Selection and identification of a DNA aptamer for ultrasensitive and selective detection of λ-cyhalothrin residue in food.

Pyrethroid pesticides residues will not only pollute the environment, but also cause high toxicity to the human body. It is significant to establish an efficient and accurate method for pyrethroid detection in food. Considering that the common biomolecules like antibody is complicated and easy to inactivate, it is urgent to find a new type of biomolecule to specifically recognize pyrethroid pesticides. This study proposed the Capture-SELEX strategy to firstly select λ-cyhalothrin aptamer by immobilizing random ssDNA library. High-throughput sequencing was performed on the enriched ssDNA library through multiple Capture-SELEX rounds. Comprehensively inspecting structural similarity and homology, six sequences were chosen from five families for further analysis. The results showed that the aptamer (named LCT-1) could specifically recognize λ-cyhalothrin with the strongest affinity (Kd = 50.64 ± 4.33 nmol L-1). Molecular docking results revealed that the binding sites between λ-cyhalothrin and LCT-1 aptamer are mainly related to the bases A-5, C-6, C-28, A-29, C-30, G-31 and G-32. The LCT-1 aptamer was truncated to a shorter sequence (named as LCT-1-39) by removing other irrelevant bases, and its Kd value was determined as (10.27 ± 1.33) nmol·L-1 by Microscale Thermophoresis (MST). Both LCT-1 and LCT-1-39 aptamers were employed as recognition molecules to establish the colorimetric aptasensors for λ-cyhalothrin detection, which displayed good repeatability and reproducibility. The detection limit of the aptasensors were individually calculated as 0.0197 µg ml-1 and 0.0186 µg ml-1, and their recovery rate of λ-cyhalothrin in pear and cucumber samples was in the range of 82.93-95.50%. This article provides a promising application for the detection of λ-cyhalothrin.

Porous Co3O4 nanodisks as robust peroxidase mimetics in an ultrasensitive colorimetric sensor for the rapid detection of multiple heavy metal residues in environmental water samples.

The current method for rapid and ultrasensitive detection of multiple heavy metals in environmental water still face challenge. Herein, the porous Co3O4 nanodisks with robust peroxidase-mimicking activity were prepared, and its catalytic activity can be significantly inhibited by the heavy metals like Cd(II), Hg(II), Pb(II) and As, which makes us to establish an ultrasensitive and rapid colorimetric sensor for the detection of multiple heavy metals. Further investigation reveals the anticompetitive inhibition effect of heavy metals on peroxidase-mimicking activity. The colorimetric sensor displays excellent sensitivity and selectivity, and the limits of detection (LOD) for Cd(II), Hg(II), Pb(II) and As are 0.085 µg·L-1, 0.19 µg·L-1, 0.2 µg·L-1 and 0.156 µg·L-1, respectively. Notably, the absorbance variation will be greater than 0.5 as the concentration of heavy metals exceeds 5 µg·L-1, which can be clearly discriminated by the naked eyes. Moreover, the average recovery range of heavy metals in actual water samples is from 86.9% to 98.3%. The above results indicate that the proposed sensor exhibits excellent practical applicability for the rapid and ultrasensitive detection of multiple harmful heavy metals in several environmental water samples, which has potential bright application in protecting the environment and human health.