Ionic liquids functionalized Fe3O4-based colorimetric biosensor for rapid determination of ochratoxin A.

A stainless steel mesh (SSM) with the feature of flexibility was employed as the colorimetric biosensor substrate, and aptamer was bond onto the surface of the SSM. Through the cross-linking of ionic liquids (ILs), AuPt nanoparticles were deposited  onto the surface of Fe3O4 material to obtain a magnetic nanozyme with high peroxidase catalytic activity and rapid color change. Through the competing interaction of OTA and cDNA with aptamer, AuPt@IL@Fe3O4 signal probe was separated to catalyze the 3,3',5,5'-tetramethylbenzidine/hydrogen peroxide (TMB/H2O2) system to observe the color by bare eye and record the absorbance at 652 nm using a UV-spectrophotometer. Through the study of the catalytic properties on the basis of the Michaelis equation, AuPt@IL@Fe3O4 nanozyme presented a Vmax of 3.85 × 10-8 M s-1 and Km of 0.01 mM. Under the optimized conditions, the linear range of the colorimetric biosensor towards OTA was 5-100 ng mL-1, and the detection limit was 0.078 ng mL-1. This biosensor was applied to beer and corn samples with recoveries of 70.4-102.6% and 93.3-104.7%, respectively. Results showed that this sensor is a portable, rapid, economical, sensitive visual sensing platform towards mycotoxin in real samples.

An aptamer and flower-shaped AuPtRh nanoenzyme-based colorimetric biosensor for the detection of profenofos.

In this work, a simple, sensitive and selective colorimetric method was established for the detection of profenofos. Firstly, novel flower-shaped AuPtRh trimetallic nanospheres were synthesized via a simple one-pot method, and had outstanding peroxidase catalytic activity. AuPtRh nanospheres with a great specific surface area were linked with an aptamer via Au-S and Pt-S bonds to specifically recognize profenofos. A graphene oxide grafted stainless-steel mesh (SSM-GO) was prepared to be a carrier and the aptamer-AuPtRh was nonspecifically adsorbed on the surface of SSM-GO, which was to be the capture probe for the detection of profenofos in real samples. They were characterized and confirmed by transmission electron microscopy, atomic force microscopy, etc. Through the investigation of the catalytic performance on the basis of the Michaelis equation, the Vmax of AuPtRh nanospheres was 22.27 × 10-8 M s-1, and Km was 0.6632 mM, which indicated that the affinity of AuPtRh nanospheres was relatively higher than that of horseradish peroxidase and Au NPs. In the presence of profenofos, the aptamer-AuPtRh would specifically combine with profenofos, which would further detach from SSM-GO. Then, it was introduced into the 3,3',5,5'-tetramethylbenzidine/H2O2 (TMB/H2O2) system to form blue oxTMB. The linear range of this colorimetric biosensor was 1-300 ng L-1 and the limit of detection was 0.725 ng L-1. It also had good recovery and anti-interference ability in real samples, which provided a new strategy for the rapid detection of pesticides.

Construction of an electrochemical sensor with graphene aerogel doped with ZrO2 nanoparticles and chitosan for the selective detection of luteolin.

A simple, fast and sensitive method for the detection of luteolin is proposed based on the chitosan/reduced graphene oxide aerogel with dispersed ZrO2 nanoparticles modified glassy carbon electrode (ZrO2/CS/rGOA-GCE) as an electrochemical sensor. The ZrO2/CS/rGOA composite was prepared by one pot synthesis from a mixture of GO, CS and zirconyl chloride octahydrate, and subsequently be freeze-dried. Scanning electron microscope images showed a typical thin, wrinkled and fluctuant morphology of graphene nanosheets and the polymerized CS and ZrO2 nanoparticles deposited on the surface of rGOA. Cyclic voltammetry and differential pulse voltammetry were used to measure the electrochemical response of ZrO2/CS/rGOA composite-based biosensor towards luteolin at the working potential window (-0.8-0.8 V). The improved performance of this biosensor was attributed to efficient electron transfer and large surface area of 3D rGOA, and high specific activity of Zr towards adjacent hydroxyl groups. Under optimized conditions, the analytical performance of this method towards luteolin was investigated with a detection limit of 1 nM and a linear range from 5 nM to 1000 nM.. Finally, the ZrO2/CS/rGOA-GCE electrochemical method coupled with solid phase extraction was used for the detection of luteolin in real samples. Recoveries of  spiked samples with different concentrations were in the range 78.6-103.3% with a relative RSD lower than 12.0%. Graphical abstract Schematic representation of the preparation of the ZrO2 nanoparticles and chitosan doped graphene aerogel modified electrode. The electrode was employed for the detection of luteolin coupled with the solid-phase extraction technique.

ß-Cyclodextrin-modified three-dimensional graphene oxide-wrapped melamine foam for the solid-phase extraction of flavonoids.

A new three-dimensional graphene oxide-wrapped melamine foam was prepared and used as a solid-phase extraction substrate. ß-Cyclodextrin was fabricated onto the surface of three-dimensional graphene oxide-wrapped melamine foam by a chemical covalent interaction. In view of a specific surface area and a large delocalized π electron system of graphene oxide, in combination with a hydrophobic interior cavity and a hydrophilic peripheral face of ß-cyclodextrin, the prepared extraction material was proposed for the determination of flavonoids. In order to demonstrate the extraction properties of the as-prepared material, the adsorption energies were theoretically calculated based on periodic density functional theory. Static-state and dynamic-state binding experiments were also investigated, which revealed the monolayer coverage of flavonoids onto the ß-cyclodextrin/graphene oxide-wrapped melamine foams through the chemical adsorption. 1 H NMR spectroscopy indicated the formation of flavonoids-ß-cyclodextrin inclusion complexes. Under the optimum conditions, the proposed method exhibited acceptable linear ranges (2-200 µg/L for rutin and quercetin-3-O-rhamnoside; 5-200 µg/L for quercetin) with correlation coefficients ranging from 0.9979 to 0.9994. The batch-to-batch reproducibility (n = 5) was 3.5-6.8%. Finally, the as-established method was satisfactorily applied for the determination of flavonoids in Lycium barbarum (Goji) samples with relative recoveries in the range of 77.9-102.6%.

A porous polyaniline nanotube sorbent for solid-phase extraction of the fluorescent reaction product of reactive oxygen species in cells, and its determination by HPLC.

A method is described for extracting and detecting the fluorescent reaction product (2',7'-dichlorofluorescein, DCF) that is formed by reaction of reactive oxygen species (ROS) with dichlorodihydrofluorescein diacetate (DCFH-DA). DCF is extracted by using porous polyaniline nanotubes (PPN) which have a large specific surface and pore volume which favor the adsorption capacity. Additional attractive features include an appropriate pore size distribution, hydrophobic surface, and electron-attracting groups which contribute to DCF adsorption. A variety of methods was applied to characterize the morphology of PPN. Under optimal conditions and by performing DCF in 0.08-1.0 µM concentrations, the correlation coefficient of the calibration plot is 0.999. The limits of detection for standard DCF solutions is 20 nM. Compared with commercial sorbents for solid-phase extraction (SPE) such as commercially available carbon or Welchrom® C18, the use of the new sorbent results in better retraction recovery (92%) and longer reuse times (30 times). Doxorubicin and X-ray radiation were used to externally stimulate the ROS production in HepG2 and Hela cells. ROS was stabled by DCFH-DA and quantified by DCF. Following SPE, DCF was detected by HPLC and the concentration ROS was calculated. Graphical abstract ᅟ.

Graphene oxide for solid-phase extraction of bioactive phenolic acids.

A solid-phase extraction (SPE) method for the efficient analysis of trace phenolic acids (PAs, caffeic acid, ferulic acid, protocatechuic acid, cinnamic acid) in urine was established. In this work, a graphene oxide (GO) coating was grafted onto pure silica to be investigated as SPE material. The prepared GO surface had a layered and wrinkled structure that was rough and well organized, which could provide more open adsorption sites. Owing to its hydrophilicity and polarity, GO showed higher extraction efficiency toward PAs than reduced GO did, in agreement with the theoretical calculation results performed by Gaussian 09 software. The adsorption mechanism of PAs on GO@Sil was also investigated through static state and kinetic state adsorption experiments, which showed a monolayer surface adsorption. Extraction capacity of the as-prepared material was optimized using the response surface methodology. Under the optimized conditions, the as-established method provided wide linearity range (2-50 µg L-1 for protocatechuic acid and 1-50 µg L-1 for caffeic acid, ferulic acid, and cinnamic acid) and low limits of detection (0.25-1 µg L-1). Finally, the established method was applied for the analysis of urine from two healthy volunteers. The results indicate that the prepared material is a practical, cost-effective medium for the extraction and determination of phenolic acids in complex matrices. Graphical Abstract A graphene oxide coating was grafted onto pure silica as the SPE material for the extraction of phenolic acids in urines and the extraction mechanism was also mainly investigated.

Zinc sulfide nanosheets as a novel solid-phase extraction material for flavonoids.

As a novel solid-phase extraction material, zinc sulfide nanosheets were prepared by a simple method and were used to extract flavonoids. We used scanning electron microscopy to show its nanosheet morphology and energy dispersive X-ray spectroscopy and powder X-ray diffraction to confirm its chemical and phase compositions. Coupled to a high-performance liquid chromatography, the zinc sulfide nanosheets were packed into a microcolumn and were used to extract four model flavonoids to examine their extraction ability. The parameters of sample loading and elution were investigated. Under optimized conditions, the analytical method for flavonoids was established. For the method, wide linearities from 1 to 250 µg/L and low limits of detection from 0.25 to 0.5 µg/L were obtained. The relative standard deviations for single column repeatability and column to column reproducibility were less than 7.7 and 10.4%, respectively. The established method was also used to analyze two real samples and the recoveries from 88.7 to 98.2% further proved the reliability of the method. Moreover, the zinc sulfide nanosheets have good stability and that in one column can be reused for more than 50 times. This work proves that the prepared zinc sulfide nanosheets are a good candidate as the flavonoids sorbent.

Application of a ß-cyclodextrin/graphene oxide-modified fiber for solid-phase microextraction of six fragrance allergens in personal products.

A new ß-cyclodextrin/graphene oxide hybrid material prepared via a chemical covalent interaction and layer-to-layer assembly was developed as a sorbent for the solid-phase microextraction of fragrance allergens. As a result of its ultra-large surface area, large delocalized π-electron system and abundant hydroxyls, the ß-cyclodextrin/graphene oxide-coated fiber could be used to extract particular compounds via strong π-π interactions, van der Waals forces and hydrogen bonding interactions. ß-Cyclodextrin with a hydrophobic interior cavity and hydrophilic peripheral face was conducive in extracting the fragrances with hydrophobic and hydrophilic groups. Under the optimized extraction and desorption conditions, the ß-cyclodextrin/graphene oxide-coated fiber showed acceptable extraction efficiency for hydrophilic and hydrogen-bonding-donating alcohols. Compared with other methods based on different coating fibers, the proposed fiber obtained wide linear ranges for fragrances with correlation coefficients ranging from 0.9921 to 0.9970, and low limits of detection in the range of 0.050-0.150 µg L(-1). The obtained results indicated that the newly developed fiber was a selective, feasible and cost-effective microextraction medium and could be successfully applied for the determination of several fragrances in personal products.

Graphene oxide decorated with silver nanoparticles as a coating on a stainless-steel fiber for solid-phase microextraction.

A novel graphene oxide decorated with silver nanoparticles coating on a stainless-steel fiber for solid-phase microextraction was prepared. Scanning electron microscopy and X-ray photoelectron spectroscopy were used to characterize the coating surface and showed that silver nanoparticles were dispersed on the wrinkled graphene oxide surface. Coupled to gas chromatography with flame ionization detection, the extraction abilities of the fiber for polycyclic aromatic hydrocarbons were examined in the headspace solid-phase microextraction mode. The extraction parameters including adsorption time, adsorption temperature, salt concentration, desorption time and desorption temperature were investigated. Under the optimized condition, wide linearity with low limits of detection from 2 to 10 ng/L was obtained. The relative standard deviations for single-fiber repeatability and fiber-to-fiber reproducibility were less than 10.6 and 17.5%, respectively. The enrichment factors were from 1712.5 to 4503.7, showing the fiber has good extraction abilities. Moreover, the fiber exhibited a good stability and could be reused for more than 120 times. The established method was also applied for determination of polycyclic aromatic hydrocarbons in two real water samples and the recoveries of analytes ranged from 84.4-116.3% with relative standard deviations less than 16.2%.

Polyethylene glycol/graphene oxide coated solid-phase microextraction fiber for analysis of phenols and phthalate esters coupled with gas chromatography.

A new polyethylene glycol/graphene oxide composite material bonded on the surface of a stainless-steel wire was used for solid-phase microextraction. The layer-by-layer structure increased the adsorption sites of the novel fiber, which could facilitate the extraction of trace compounds. The polyethylene glycol/graphene oxide was characterized by Fourier transform infrared spectroscopy and elemental analysis, which verified that polyethylene glycol was successfully grafted onto the surface of graphene oxide. The performance of the polyethylene glycol/graphene oxide coated fiber was investigated for phenols and phthalate esters coupled with gas chromatography with flame ionization detection under the optimal extraction and desorption conditions, and the proposed method exhibited an excellent extraction capacity and high thermal stability. Wide linear ranges were obtained for the analytes with good correlation coefficients in the range of 0.9966-0.9994, and the detection limits of model compounds ranged from 0.003 to 0.025 µg/L. Furthermore, the as-prepared fiber was used to determine the model compounds in the water and soil samples and satisfactory results were obtained.

Poly (ionic liquid) cross-linked hydrogel encapsulated with AuPt nanozymes for the smartphone-based colorimetric detection of zearalenone.

A poly (ionic liquid) enhanced poly(acrylamide-acrylic acid) (PIL-PAM/AA) hydrogel-based colorimetric sensor was designed to detect zearalenone (ZEN). Different AuxPty nanoparticles were synthesized via the on-pot method. Through the kinetic analysis and the theoretical calculation, Au0.4Pt0.6 possessed the relatively low energy barriers to adsorb and decompose H2O2 so that it exhibited relatively better catalytic activity (Km = 2.02 × 10-3, Vmax = 6.14 × 10-7). AuPt nanoparticles were encapsulated into PIL-PAM/AA hydrogel via the interaction between aptamer and cDNA. In the presence of ZEN, the embedded AuPt nanoparticles were released to complete the catalytic reaction. Coupled with the smartphone application, the established method provided the linear range of 1-250 ng mL-1, with a detection limit of 0.6979 ng mL-1 for ZEN. Meanwhile, it also possessed excellent selectivity and good anti-interference performance. In wheat and corn samples, spiked recoveries were ranging from 75% to 113.30%.

Ionic liquid-enhanced silica aerogels for the specific extraction and detection of aflatoxin B1 coupled with a smartphone-based colorimetric biosensor.

The polymer ionic liquid (1-allyl-3-butylimidazolium bromide) enhanced silica aerogel was modified onto the surface of stainless-steel mesh to immobilize aptamer-1 for the specific recognition of AFB1. The porous channels of silica aerogel could prevent the interference of macromolecules in food samples. Enzyme kinetic analysis showed that the MoS2/Au was an effective peroxidase mimic with a relatively low Michaelis constant (Km) value of 0.17 mM and a high catalytic rate of 3.87 × 10-8 mol (L·s)-1, which exhibited obvious superiority compared with horseradish peroxidase. The established "sandwich-structure" biosensor was coupled with the smartphone "Color Picker" application was used to detect AFB1 with a wide linear range (1-100 ng mL-1) and low detection limit (0.25 ng mL-1). The anti-interference ability of the established biosensor was evaluated by adding different concentrations of standards in corn, peanut, and wheat and matrix effects were 90.84-106.11 %. The results showed that this method demonstrated high specificity, sensitivity, rapidity and low interference in food samples.

A covalent-organic framework-based platform for simultaneous smartphone detection and degradation of aflatoxin B1.

This study developed a smartphone-based biosensor that could simultaneously detect and degrade aflatoxin B1 (AFB1). A donor-acceptor covalent organic framework (COF) was bound onto the surface of stainless-steel mesh (SSM) via the in-situ synthesis, which was used to immobilize the aptamer (Apt) to specifically capture AFB1 and was also as a photocatalyst to degrade AFB1. Au@Ir nanospheres were synthesized, which exhibited better peroxidase catalytic activity (Km=5.36 × 10-6 M, Vmax=3.48 × 10-7 Ms-1, Kcat=1.00 × 107 s-1) than Ir@Au nanospheres, so Au@Ir nanospheres were linked with Apt2 to be utilized as the signal probe. The density functional theory calculation also described that Au@Ir nanospheres possessed the lower energy barriers to decompose H2O2 than Ir@Au nanospheres. Coupled with the "Color Picker" application in the smartphone, the established "sandwich-structure" colorimetric method exhibited a linear range of 0.5-200 µg L-1 and a detection limit of 0.045 µg L-1. The photocatalytic capacity of SSM/COF towards AFB1 was investigated and the degradation rate researched 81.14 % within 120 min under the xenon lamp irradiation, and the degradation products were validated by ESI-MS. It was applied for the detection of AFB1 in peanuts, corn, and wheat samples. Recoveries were ranging from 77.90 % to 112.5 %, and the matrix effect was 75.10-111.6 %. Therefore, the smartphone-based biosensor provided a simple, fast, and sensitive platform for the detection of AFB1, and meanwhile could realize the efficient degradation of AFB1.

Integration of Metallic Nanomaterials and Recognition Elements for the Specifically Monitoring of Pesticides in Electrochemical Sensing.

Although all countries have been controlling the excessive use of pesticides, incidents of pesticide residues still existed. Electrochemical biosensors are extensively applied detection techniques to monitor pesticides with the help of different types of biorecognition components mainly including, antibodies, aptamers, enzymes (i.e., acetylcholinesterase, organophosphorus hydrolase, etc.), and synthetic molecularly imprinted polymers. Besides, the electrode materials mainly affected the sensitivity of electrochemical biosensors. Metallic nanomaterials with various structures and excellent electrical conductivity were desirable choice to construct electrochemical platforms to achieve the detection with high sensitivity and good specificity toward the target. This work reviewed the developed metallic materials including monometallic nanoparticles, bimetallic nanomaterials, metal atoms, metal oxides, metal molybdates, metal-organic frameworks, MXene, etc. Integration of recognition elements endowed the electrode materials with higher specificity toward the target pesticide. Besides, future challenges of metallic nanomaterials-based electrochemical biosensors for the detection of pesticides are also discussed and described.

Electrochemical (Bio)Sensors for the Detection of Organophosphorus Pesticides Based on Nanomaterial-Modified Electrodes: A Review.

Organophosphorus pesticides were easily remained in fruits and vegetables which would be harm to the environmental safety and human health. In recent years, due to the simple preparation process, fast response and high sensitivity, the electrochemical (bio)sensors have received increasing attention, which were extensively used as the sensing platform for the detection of OPPs. The mechanisms for the determination of OPPs mainly included redox of nitrophenyl OPPs, enzyme hydrolysis and inhibition, immunosensor, aptasensor. Nowadays, the mainly explored electrode material has focused on metal-organic frameworks, metal and metal derivatives, carbon materials (carbon nanotube, graphene, g-C3N4), MXene, etc. These nanomaterials played important roles in the electrochemical (bio)sensors, which included: (a) as an electrocatalyst to promote the redox reaction, (b) as a carrier to load the enzyme or aptamer, (c) as a recognizer to identify the targets. The nanomaterials-based electrochemical (bio)sensor was a rapid, cost-effective methods to detect OPPs with high sensitivity. Besides, this review compared the analytical performance of different nanomaterials-based electrochemical (bio)sensors, and also identified the key challenges in the future. It would provide new ideas and insights to the further development and application of electrochemical (bio)sensors and the detection of pesticides in real samples.

[Determination of organophosphorus pesticides based on graphene oxide aerogel solid phase extraction column].

A graphene oxide aerogel was prepared and directly filled in a solid phase extraction (SPE) column without the aid of silica or other substrates. The aerogel was used to extract and detect residual organophosphorus pesticides (phoxim, temephos, fenthion, and fenitrothion) in food, and exhibited good elasticity and high mechanical strength. The graphene oxide aerogel was prepared by freeze-drying. Its morphology and physical properties were characterized by scanning electron microscopy, infrared spectroscopy, and BET surface adsorption. Results proved the successful synthesis of the graphene oxide aerogel. Scanning electron micrographs of the aerogel exhibited a layered and fold structure, with a surface area of 740.51 m2/g. The effect of experimental conditions on the extraction recovery of organophosphorus pesticides was systematically studied through a series of single-factor experiments. Due to limited adsorption sites, sample volumes of 5-60 mL were investigated, and 15 mL was determined was the optimum sample volume. The rate of sample loading was investigated in the range of 0.8-3.0 mL/min. When the rate of sample loading was higher than 3.0 mL/min, the insufficient contact between the analytes and sorbent appeared to cause a decrease in the extraction recovery. A lower rate of sample loading would prolong the operation time due to the re-elution of organophosphorus pesticides. The sample pH was optimized from a pH range of 2-11. An acidic solution was found to be good for inducing electrostatic interactions between the graphene oxide aerogel and organophosphorus pesticides. The maximum extraction recoveries were obtained at pH 4. Three eluents (acetonitrile, methanol, and acetone) were explored for optimization, and results showed that acetonitrile was the most appropriate eluent. The eluent volume (0.6-1.2 mL) was also investigated, and the optimal value was found to be 1.0 mL. Compared with commercial extraction materials including C18 silica, the anion exchange column (SAX), amino (-NH2), and Florisil, the extraction recovery of this new material showed distinct improvement. The lifetime of the extraction column directly filled with the graphene oxide aerogel was investigated. The column could be repeatedly used for 15 times, which overcame the issue of blocking of the sieve plates of fragmented graphene nanosheets dispersed without any matrix support. The linearities of the four organophosphorus pesticides were 1-200 µg/L for phoxim, temephos, and fenthion, and 2-200 µg/L for fenitrothion. The linear correlation coefficients were all ≥0.9949, and limits of detection were in the range of 0.2-0.5 µg/L. An extraction column was used to extract the analytes continuously for five times, and the RSDs of the extraction recoveries were ≤6.5%. Subsequently, five extraction columns were used to extract the analytes under the same conditions, and the RSDs of the extraction recoveries were ≤11.3%. Finally, the established method was applied for the extraction and detection of a real sample (apple peel); no organophosphorus pesticide was detected in the apple peel. The recoveries for spiked standard solutions were between 70.5% and 93.6%, and RSDs were ≤10.4%.

Progress in Nanomaterials-Based Enzyme and Aptamer Biosensor for the Detection of Organophosphorus Pesticides.

With the improvement of people's safety awareness, the requirement of pesticide detection is gradually increasing, and many new detection methods toward Organophosphorus pesticide (OPs) has been further developed and applied. Nanomaterials-based biosensors have played an important role in the trace detection of OPs. This article mainly introduces the detection principle of enzymes and aptamers as the identification element of biosensors. Various nanomaterials (i.e., metals and metal oxides, carbon nanotubes, graphene and graphene oxide, quantum dots, metal organic frameworks, molecular imprinted polymers, etc.) possess their unique properties and play different roles in the enzyme and aptamer-based biosensors toward OPs: (a) to produce the optical or electrochemical signal; (b) as a carrier to load the enzyme or aptamer; (c) to enhance the signal response. Besides, the intelligent portable devices provide the possibility to realize the onsite and real-time detection. The limitations of some nanomaterials and the future development are discussed. Finally, the future of enzyme and aptamer-based biosensors has prospected.

Hydrophilic Covalent Organic Frameworks Coated Steel Sheet As a Mass Spectrometric Ionization Source for the Direct Determination of Zearalenone and Its Derivatives.

Zearalenone has attracted worldwide attention due to its toxic properties and threat to public health. A rapid determination method for zearalenone and its derivatives by hydrophilic covalent organic frameworks coated steel sheet (HCOFCS) combined with ambient mass spectrometry (AMS) was developed. The HCOFCS behaved as both a tip for solid-phase microextraction and a solid substrate for electrospray ionization mass spectrometry (ESI-MS). To evaluate the HCOFCS-ESI-MS method, five zearalenone and its derivatives in milk samples were determined, including zearalenone (ZEA), α-zearalenol (α-ZEL), ß-zearalenol (ß-ZEL), α-zearalanol (α-ZAL), and ß-zearalanol (ß-ZAL). After the extraction procedure, the HCOFCS was directly added with a high voltage for ESI-MS, and the analysis could be completed within 1 min. The developed method showed good linearity in the range 0.1-100 µg/L with a coefficient of determination (R2) > 0.9991. The limits of detection (LODs) and limits of quantitation (LOQs) ranged from 0.05 to 0.1 and 0.2 to 0.3 µg/L, respectively. The results demonstrated that the HCOFCS combined with ESI-MS can be used for the rapid and sensitive determination of trace ZEA and its derivatives in milk samples with satisfactory recoveries from 80.58% to 109.98% and reproducibility with relative standard deviations (RSDs) no more than 11.18%. Furthermore, HCOFCS showed good reusability, which could reuse at least 10 extraction cycles with satisfactory adsorption performance.

Chiral carbon quantum dots as fluorescent probe for rapid chiral recognition of isoleucine enantiomers.

Chiral recognition is always a significant and challenging work in analytical chemistry. A fluorescent chiral recognition method based on chiral carbon quantum dots (CCQDs) towards isoleucine (Ile) enantiomers was developed in this work. CCQDs were synthesized by one-step hydrothermal method using l-cysteine as chiral source. The fluorescence intensity of CCQDs enhanced obviously in the presence of L-Ile, but had no observable change in the presence of D-Ile. The response speed of this chiral sensing system is fast, Ile enantiomers can be discriminated by CCQDs within 5 min, the enantioselectivity (IL/ID) can reach up to 2.2. Good linearity for detecting L-Ile was obtained over the concentration range from 0 to 30 mM with a LOD of 0.29 mM. The fluorescence intensity also increased linearly with the enantiomeric percentages of L-Ile in the mixture of Ile enantiomers. Thus, the developed method not only can achieve quantitative detection of L-Ile but also can determine the enantiomeric percentage in racemates. The chiral recognition mechanism can be explained by the difference in binding energy and interaction types between D-Ile and L-Ile with CCQDs by molecular modeling. The current method was applied in detecting L-Ile in real samples of functional drinks, the detection results were in consistent with the results obtained from high performance liquid chromatography, and the recoveries of standard addition were also satisfactory, which verified the reliability of the developed method.

ZrO2 Nanoparticles and Poly(diallyldimethylammonium chloride)-Doped Graphene Oxide Aerogel-Coated Stainless-Steel Mesh for the Effective Adsorption of Organophosphorus Pesticides.

A novel sorbent based on the ZrO2 nanoparticles and poly(diallyldimethylammonium chloride)-modified graphene oxide aerogel-grafted stainless steel mesh (ZrO2/PDDA-GOA-SSM) was used for the extraction and detection of organophosphorus pesticides (OPPs). Firstly, the PDDA and GO composite was grafted onto the surface of SSM and then freeze-dried to obtain the aerogel, which efficiently reduced the accumulation of graphene nanosheets. It integrated the advanced properties of GOA with a thin coating and the three-dimensional structural geometry of SSM. The modification of ZrO2 nanoparticles brought a selective adsorption for OPPs due to the combination of the phosphate group as a Lewis base and ZrO2 nanoparticles with the Lewis acid site. The ZrO2/PDDA-GOA-SSM was packed into the solid-phase extraction (SPE) cartridge to extract OPPs. According to the investigation of different factors, the extraction recovery was mainly affected by the hydrophilic-hydrophobic properties of analytes. Effective extraction and elution parameters such as sample volume, sample pH, rate of sample loading, eluent, and eluent volume, were also investigated and discussed. Under the optimal conditions, the linearity of phoxim and fenitrothion was in the range of 1.0-200 µg L-1, and the linearity of temephos was in the range of 2.5-200 µg L-1. The limits of detection were ranged from 0.2 to 1.0 µg L-1. This established method was successfully applied to detect OPPs in two vegetables. There was no OPP detected in real samples, and results showed that the matrix effects were in the range of 46.5%-90.1%. This indicates that the ZrO2/PDDA-GOA-SSM-SPE-HPLC method could effectively extract and detect OPPs in vegetables.