New two-dimensional nanocomposites combined with target-induced strategy in an electrochemical aptasensor for sensitive determination of sulfadimethoxine.

Ni-Zn bimetallic organic framework nanosheets (NiZn-MOF NSs) were modified onto PEI-functionalized MXene for the first time. The combination of the two kinds of nanosheets forms a sensing platform with superior conductivity and biocompatibility. On this basis, a highly sensitive biosensor was developed for the determination of sulfadimethoxine (SDM). Furthermore, Au and Mn nanoparticles decorated reduced graphene oxide (Au-Mn/rGO) was introduced as a signal hindering molecule under the target-induced amplification strategy. When the Au-Mn/rGO-labelled SDM-binding aptamer (Au-Mn/rGO-SBA) specifically bound to target SDM, it detached from the electrode, thereby further amplifying the electrochemical signal of [Fe(CN)6]3-/4-. The developed aptasensor for SDM showed excellent response signals in the range 1 pg mL-1 to 100 ng mL-1, with a limit of detection (LOD) as low as 0.22 pg mL-1. Significantly, the proposed sensor also showed satisfactory results in milk samples with recoveries ranging from 87.0 to 96.4% and RSD from 1.5 to 5.1%, which is believed to be useful in food safety assays.

Electrochemical aptasensor for ultrasensitive detection of lipopolysaccharide using silver nanoparticles decorated titanium dioxide nanotube/functionalized reduced graphene oxide as a new redox nanoprobe.

A novel and relatively simple signal-off electrochemical aptasensor was constructed for highly sensitive detection of lipopolysaccharide (LPS). For the first time, silver nanoparticles (AgNPs) decorated titanium dioxide nanotube (TNT) was conjugated with polydiallyldimethylammonium chloride (PDDA) functionalized reduced graphene oxide (rGO) to form a new nanohybrid of Ag-TNT/P-rGO. This nanohybrid with a large specific surface area exhibited excellent electrochemical activity, which not only served as the sensing platform to immobilize LPS binding aptamer (LBA) but was also employed as the redox probe to monitor the change of the electrochemical signal. The electrochemical signal responses were measured by cyclic voltammetry (CV) in the potential range -0.3 to 0.5 V at a scan rate of 0.1 V/s. The proposed aptasensor exhibited acceptable stability, reproducibility, and specificity for LPS detection with a wide linear range from 17 fg/mL to 100 ng/mL. The limit of detection (LOD) was 5 fg/mL. Furthermore, the prepared aptasensor showed acceptable recovery ranging from 96% to 103%, and the RSD varied between 1.4% and 8.5% for determining LPS in real samples.Graphical abstract.

An electrochemical aptasensor for Mycobacterium tuberculosis ESAT-6 antigen detection using bimetallic organic framework.

A label-free electrochemical aptasensor is reported for sensitive detection of the 6-kDa early secreted antigenic target (ESAT-6). For the first time, the bimetallic organic framework (b-MOF) of Zr-MOF-on-Ce-MOF was decorated with nitrogen-doped graphene (NG) and applied as the matrix for electroactive toluidine blue (Tb) to form the NG@Zr-MOF-on-Ce-MOF@Tb nanohybrid. The prepared nanohybrid with excellent hydrophilicity, dispersibility, and large specific surface exhibited significant electrochemical response. This nanohybrid could be directly used for anchoring ESAT-6 binding aptamers (EBA) through the interaction between the 5'-phosphate group (PO43-) of EBA and Zr4+ of Zr-MOF. The signal response before and after incubating the ESAT-6 antigen has been evaluated by cyclic voltammetry at a scan rate of 100 mV s-1 from - 0.7 to 0.3 V (vs. SCE). Under optimal conditions, the proposed aptasensor displayed a wide linear range from 100 fg mL-1 to 10 ng mL-1 with a limit of detection (LOD) of 12 fg mL-1. The developed method showed good reproducibility with a relative standard deviation (RSD) of 2.27%. The aptasensor showed favorable results in the analysis of the real samples. With these merits, the aptasensor has exceptional potential as a diagnostic tool for tuberculosis in clinical practice.

Voltammetric aptasensor for sulfadimethoxine using a nanohybrid composed of multifunctional fullerene, reduced graphene oxide and Pt@Au nanoparticles, and based on direct electron transfer to the active site of glucose oxidase.

This work describes a voltammetric and ultrasensitive aptasensor for sulfadimethoxine (SDM). It is based on signal amplification by making use of a multifunctional fullerene-doped reduced graphene oxide nanohybrid. The nanohybrid was coated with poly(diallyldimethylammonium chloride) to obtain a material (P-C60-rGO) with large specific surface area and a unique adsorption ability for loading it with glucose oxidase (GOx). The coating also facilitates the direct electron transfer between the active site of GOx and the glassy carbon electrode (GCE). The P-C60-rGO were then modified with Pt@Au nanoparticles, and the thiolated SDM-binding aptamer was immobilized on the nanoparticles. On exposure of the modified GCE to a solution containing SDM, it binds to the aptamer. The results were recorded through the signal responses generated from the redox center of GOx (FAD/FADH2) by cyclic voltammetry at a scan rate of 100 mV·s-1 from -0.25 to -0.65 V. Accordingly, The sensor has good specificity and stability, and response is linear in the 10 fg·mL-1 to 50 ng·mL-1 SDM concentration range with a detection limit of 8.7 fg·mL-1. Graphical abstract Schematic presentation of an electrochemical aptasensor for sulfadimethoxine (SDM) using multifunctional fullerene-doped graphene (C60-rGO) nanohybrids for amplification. The limit of detection for SDM is as low as 8.7 fg·mL-1.

A sandwich-type electrochemical immunosensor for sensitive detection of HER2 based on dual signal amplification of La-MOF-PbO2 and PEI-MoS2NFs composites.

In recent decades, the incidence of breast cancer has increased year by year, posing a serious threat to human health and quality of life, and about 30% of breast cancer patients have human epidermal growth factor receptor 2 (HER2) overexpression. Therefore, HER2 has become an important biomarker and indicator for the clinical evaluation of breast cancer in diagnosis, prognosis and recurrence. In this work, polyethyleneimine functionalized MoS2 nanoflowers (PEI-MoS2NFs) with good electrical conductivity and abundant active binding sites were designed and employed as a sensing platform for immobilizing the primary antibody of HER2 (Ab1). In addition, a La-MOF-PbO2 composite with a large specific surface area and good conductivity was used to load lots of electroactive toluidine blue (TB) and the secondary antibody of HER2 (Ab2) via gold nanoparticles (AuNPs) as the linker. Thus, the constructed sandwich-type electrochemical immunosensor was applied for sensitive detection of HER2, which showed a wide linear range from 100 fg mL-1 to 10 µg mL-1 with a lower limit of detection of 15.64 fg mL-1. Therefore, the resulting immunosensor in this study would have a potential application in clinical bioanalysis.

An enzymatic activity regulation-based clusterzyme sensor array for high-throughput identification of heavy metal ions.

The accurate identification and sensitive quantification of heavy metal ions are of great significance, considering that pose a serious threat to environment and human health. Most array-based sensing platforms, to date, utilize nanozymes as sensing elements, but few studies have explored the application of the peroxidase-like activity of clusterzymes in identification of multiple analytes. Herein, for the first time, we developed a clusterzyme sensor array utilizing gold nanoclusters (AuNCs) as sensing elements for five heavy metal ions identification including Hg2+, Pb2+, Cu2+, Cd2+ and Co2+. The heavy metal ions can differentially regulate the peroxidase-like activity of AuNCs, and that can be converted into colorimetric signals with 3,3',5,5'-tetramethylbenzidine (TMB) as the chromogenic substrate. Subsequently, the generated composite responses can be interpreted by combining pattern recognition algorithms. The developed clusterzyme sensor array can identify five heavy metal ions at concentrations as low as 0.5 µM and their multi-component mixtures. Especially, we demonstrated the successful identification of multiple heavy metal ions in tap water and traditional Chinese medicine, with an accuracy of 100% in blind test. This study provided a simple and effective method for identification and quantification of heavy metal ions, rendering a promising technique for environmental monitoring and drug safety assurance.

"Gold-plated" PCN-222(Fe) and superconductive carbon black-based sandwich-type immunosensor for detecting CYFRA21-1.

Cytokeratin 19 fragment antigen 21-1 (CYFRA21-1) is a protein fragment dissolved in the blood after apoptosis of lung epithelial cells, which is a predictive biomarker for the diagnosis of non-small cell lung cancer (NSCLC). Detection of serum CYFRA21-1 has a significant clinical value in diagnosis, monitoring and prognosis of NSCLC. Herein, a novel electrochemical immunosensor was constructed for the sensitive detection of CYFRA21-1. First, superconductive carbon black (KB) functionalized polyethyleneimine (PEI)-gold nanoparticles (AuNPs) were covered on the surface of methylene blue (MB) and used as substrate materials to immobilize the CYFRA21-1 antibody. Then, target CYFRA21-1 was successfully detected using an electrochemical immunosensor through specific recognition of antigen and antibody. The zirconium-based metal organic framework of PCN-222(Fe) with a large pore size and three-dimensional (3D) structure can absorb abundant AuNPs through strong electrostatic interaction, which enhances the conductive properties of PCN-222(Fe) and prevents the self-aggregation of AuNPs. However, PCN-222(Fe) with peroxidase-like activity can catalyze the generation of hydroxyl free radicals (˙OH) from H2O2, which oxidized MB, leading to a decrease in the current signal. The signal response to the degradation of MB was recorded using differential pulse voltammetry (DPV). This indirect method of immunosensor offered a new strategy to address the limitations imposed by the poor conductivity of PCN-222(Fe), further enabling the amplification of the signal through the oxidative degradation of MB. Compared with traditional electrochemical immunosensors, this method has the advantages of a stable current signal and good reproducibility, providing a promising reference for the broad application of PCN-222(Fe) in electrochemical biosensors.

A Novel Signal-On Electrochemiluminescence Immunosensor for the Detection of NSCLC Antigen Biomarker Based on New Co-Reaction Accelerators.

Non-small cell lung cancer (NSCLC) is the most common type of lung cancer with substantial morbidity and mortality. Herein, a new signal-on electrochemiluminescence (ECL) immunosensor based on multiple amplification strategies is constructed for ultrasensitive detection of cytokeratin 19 fragment antigen 21-1 (CYFRA21-1) biomarker related to NSCLC. Polyethyleneimine (PEI) functionalized MXene is decorated with NiMn layer double hydroxide (NiMn LDH) to form MXene-PEI-NiMn LDH composite. Specially, the La-MOF@ZIF-67 bimetallic organic framework (named as LZBM) and MXene-PEI-NiMn LDH both served as coreaction accelerators to improve the ECL emission of the luminol-H2 O2 system. To be specific, Au nanoparticles (AuNPs) coated MXene-PEI-NiMn LDH is applied to immobilize primary CYFRA21-1 antibody (Ab1 ), while AuNPs decorated LZBM was used for the loading of luminol and secondary CYFRA21-1 antibody (Ab2 ) to form tracer label. Therefore, the ECL signal of the sandwich-type immunosensor is significantly enhanced due to the high loading capability for luminol and the synergistic catalytic ability for the decomposition of H2 O2 into reactive oxygen species (ROS). Under the optimal experimental conditions, the ECL immunosensor exhibited good analytical performances for CYFRA21-1 detection with a wide linear range (100 fg mL-1 -100 ng mL-1 ) and a low limit of detection (85.20 fg mL-1 ), providing a promising method for early diagnosis of NSCLC.

A target-induced amperometic aptasensor for sensitive zearalenone detection by CS@AB-MWCNTs nanocomposite as enhancers.

In this research, a novel signal-on aptasensor for highly sensitive detection of zearalenone (ZEN) was reported based on target-induced amplification strategy. Specifically, chitosan functionalized acetylene black and multi-walled carbon nanotubes (CS@AB-MWCNTs) nanocomposite with large specific surface area and excellent conductivity was synthesized and served as the sensing platform. In addition, carboxylated graphene oxide-labeled ZEN binding aptamer (CGO-ZBA) would specifically recognized with ZEN to detach from the electrode, allowing the electrochemical signal of [Fe(CN)6]3-/4- increased more obviously. Under the optimal conditions, the proposed aptasensor exhibited exceptional detection performances for ZEN with a linear range from 10 fg mL-1 to 1 ng mL-1 and a low limit of detection of 3.64 fg mL-1. Given its great sensitivity, excellent selectivity, satisfactory stability and reproducibility, this method would provide a promising application for ZEN and other biomolecules by replacing the corresponding nucleicacidsequences.

An electrochemical aptasensor for highly sensitive detection of zearalenone based on PEI-MoS2-MWCNTs nanocomposite for signal enhancement.

In this work, an electrochemical aptasensor with a high signal response was constructed for zearalenone (ZEN) detection. Firstly, the polyethyleneimine (PEI) functionalized molybdenum disulfide (MoS2) doped multi-walled carbon nanotubes (PEI-MoS2-MWCNTs) nanohybrid was designed and prepared as sensing platform and the bioactive molecule of toluidine blue (Tb) as the signal probe. Then the synthesized platinum/gold core/shell (Pt@Au) nanoparticle was dropped on the modified electrodes to load a large amount of ZEN binding aptamer (ZBA). The variation of the electrochemical signal responses which originated from Tb was measured by cyclic voltammetry (CV) after ZEN binding to ZBA with high affinity. Scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDS) were employed to characterize the nanomaterial. Upon the optimal conditions, the proposed aptasensor showed excellent detection performances for ZEN with a wide concentration range from 0.5 pg mL-1 to 50 ng mL-1 and the limit of detection (LOD) of 0.17 pg mL-1. Furthermore, this presented method could be feasible for determining ZEN in the real beer samples.

An amperometric aptasensor for ultrasensitive detection of sulfadimethoxine based on exonuclease-assisted target recycling and new signal tracer for amplification.

The risks caused by veterinary drug residues in animal foodstuffs are of great concern to the public. Accordingly, this work reported an amperometric aptasensor for highly sensitive detection of sulfadimethoxine (SDM). Functionalised fullerene (C60)-doped graphene (C60-rGO) nanohybrid was designed and prepared to load electroactive toluidine blue (Tb) through the π-π stacking, forming a C60-rGO-Tb nanocomposite. Furthermore, the as-prepared nanocomposite was decorated with gold nanoparticles and used for the immobilization of signal probes to form a new signal tracer, which was coupled with exonuclease-catalyzed target recycling for amplification. To construct the aptasensor, a thiolated double-stranded DNA (dsDNA) of aptamer-capture probe complex was immobilised on a gold electrode surface through strong Au-S bond. In the presence of SDM, the aptamer preferred to form an aptamer-SDM complex, which led to the dissociation of dsDNA. Then aptamer could be selectively digested by RecJf exonuclease, resulting in liberated SDM molecules to participate in the next reaction cycling and achieve signal amplification. Then, capture probes released from the cyclic processes were hybridized with the signal tracer, which could further enhance electrochemical signal responses. On the basis of cascade signal amplification strategies, the proposed aptasensor exhibited a wide linear range from 10 fg/mL to 10 ng/mL for SDM with high sensitivity, good selectivity and satisfactory stability.

Simultaneous detection of 15 antibiotic growth promoters in bovine muscle, blood and urine by UPLC-MS/MS.

An analytical method was established for the rapid detection of antibiotic growth promoters (AGPs) in bovine muscle, and bovine blood and bovine urine, using ultra high performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS). After the addition of an aqueous solution of EDTA-Na2, the pH of bovine urine samples was directly adjusted to 5.2 by acetic acid-ammonium acetate and purified by HLB solid-phase extraction cartridge; bovine muscle and bovine blood samples processing were extracted with acetonitrile (ACN) and ACNwater (90:10; v/v) without any purification step. The samples were then centrifuged, concentrated and analysed by UPLC-MS/MS on an ACQUITY UPLC® BEH C18 column using gradient elution. The developed method was validated and mean recovery percentages at three spiked levels were 74-119%, 76-115% and 76-119%, respectively, in bovine muscle, bovine blood, and bovine urine. The relative standard deviation (RSD) ranged from 1.0% to 14.7% in spiked bovine muscle, bovine blood and bovine urine. The limits of detection (LOD) of all analytes were in the ranges 0.11-3.82 µg kg-1, 0.10-2.49 µg kg-1 and 0.06-4.53 µg kg-1 in bovine muscle, bovine blood, and bovine urine, respectively. The method was sensitive, accurate and was applied to monitor real samples. To the best of our knowledge, this is first method available for simultaneous determination of several classes of APGs in bovine muscle, and bovine blood and bovine urine.

[Determination of 21 illegally added chemical drugs in health foods using ultra performance liquid chromatography-tandem mass spectrometry coupled with QuEChERS].

A method for the simultaneous determination of 21 illegally added chemical drugs in improving sleep and immunity health foods using ultra performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was developed. Oral liquid and health wine samples were shaken with acetonitrile and acetonitrile-water-formic acid (60:39:1, v/v/v), respectively, then purified by QuEChERS method. The extracts were separated on an Acquity UPLCTM BEH C18 column (50 mm×2.1 mm, 1.7 µm) with gradient elution of acetonitrile and 2 mmol/L ammonium acetate solution containing 0.1% (v/v) formic acid as mobile phases. The electrospray ionization in positive ion mode was used for analysis in multiple reaction monitoring (MRM) mode. The results showed that the target drugs had a good linear relationship in the range of 1-100 µg/L with the correlation coefficients (R2) ≥ 0.992. The limits of detection (LODs) and limits of quantification (LOQs) were 0.07-3.41 µg/kg and 0.22-11.36 µg/kg, respectively. The average recoveries of the 21 chemical drugs in oral liquid and health wine were in the range of 61.4%-116.5% and 67.4%-98.4% with the relative standard deviations (RSDs) of 0.2%-13.4% and 0.2%-11.8%, respectively. The developed method is sensitive and reliable. It has been successfully used for the detection of illegally added chemical drugs in real samples.

[Pharmacokinetics of hylotelephin in Beagle dogs].

AIM: To investigate the pharmacokinetics of hylotelephin in Beagle dogs and obtain the main pharmacokinetic parameters. METHODS: An HPLC method with UV detection was developed to study the pharmacokinetics of hylotelephin in dogs by joining an internal standard (anthracene). Benzoyl chloride was used to the pre-column derivatization of hylotelephin and methanol-water (64:36) was used as the mobile phase. According to the 3P97 pharmacokinetic program, the main parameters were calculated. RESULTS: The hylotelephin pharmacokinetics conforms to a two-compartment open model after a single iv dose of hylotelephin 10.6 or 21.3 mg x kg(-1) in Beagle dogs. The parameters of two groups were as follows: T(1/2) alpha were 2.3 and 2.1 min, T(1/2) beta were 1.9 and 2.0 h, K12 were 0. 12 and 0.11 min, K21 were 0.17 and 0.21 min, K10 were 0.011 and 0.0094 min, Vc were 0.54 and 0.54 L x kg(-1), AUC were 1.8 and 4.1 g x min x L(-1), CL were 0.0048 and 0.0056 L x kg(-1) x min(-1), MRT were 2.10 and 2.4 h, respectively. CONCLUSION: The pharmacokinetics of hylotelephin after iv administration showed a rapid distribution and elimination process in Beagle dogs and was of first order kinetics.

Determination of the potential illegal addition of ß-blockers to function foods by QuEChERS sample preparation and UPLC-MS/MS analysis.

A novel method was established for the determination of 11 ß-blockers in sedative functional foods using QuEchERS sample preparation coupled with UPLC-MS/MS. The analytes were extracted twice with acetic acid-acetonitrile-methanol (0.1:3:7, v/v/v), and the extracts were purified with mixed QuEchERS adsorbents. Separation was performed on a C18 column, and detection using electrospray ionisation in positive-ion mode. The linear range for the 11 analytes was from 1 to 500 µg l(-1), and the correlation coefficients were above 0.9990. The limits of detection and quantification were 0.02-0.16 and 0.07-0.54 µg kg(-1), respectively. The average recovery for 11 analytes at the three spiking levels varied from 71.8% to 121.9%, and the relative standard deviation was 2.4-12.6%. The method was applied to the analysis of ß-blockers in 22 real samples, but none of the analytes was detected. The proposed method is sensitive, efficient, reliable and applicable to real samples.

Simultaneous determination of 30 hormones illegally added to anti-ageing functional foods using UPLC-MS/MS coupled with SPE clean-up.

A novel analytical method employing solid-phase extraction (SPE) coupled with ultra-high-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) was developed for the simultaneous determination of 30 hormones in anti-ageing functional foods (capsules, powders and tablets). The analytes were extracted with acetic acid-acetonitrile (1-99 v/v), methanol and acetone, respectively. The extract was purified using a combined column, followed by analyte detection with electrospray ionisation in positive- or negative-ion modes. The results indicated that the 30 compounds had good linear correlations in the range of 1-1000 µg kg⁻¹, and the correlation coefficients were above 0.99. The limits of detection (LOD) and limits of quantification (LOQ) were 0.03-2 and 0.1-5 µg kg⁻¹, respectively. The average recovery of 30 compounds at the three spiked levels varied from 74.7% to 124.1%, and the relative standard deviation (RSD) was 2.4-15.0%. This method was applied to the analysis of hormones in 14 real samples of which seven hormones (such as estrone, dienestrol) were detected in four samples, but the remainder of the hormones were not detected. The developed method is sensitive, efficient, reliable and applicable to real samples.

[Determination of biurea in flour and its products by liquid chromatography-tandem mass spectrometry].

A novel method was established for the determination and identification of biurea in flour and its products using liquid chromatography-tandem mass spectrometry (LC-MS/MS). The biurea was extracted with water and oxidized to azodicarbonamide by potassium permanganate. The azodicarbonamide was then derivatized using sodium p-toluene sulfinate solution. The separation was performed on a Shimpak XR-ODS II column (150 mm x 2.0 mm, 2.2 microm) using the mobile phase composed of acetonitrile and 2 mmol/L ammonium acetate aqueous solution (containing 0.2% (v/v) formic acid) with a gradient elution program. Tandem mass spectrometric detection was performed in multiple reaction monitoring (MRM) scan mode with a positive electrospray ionization (ESI(+)) source. The method used stable isotope internal standard quantitation. The calibration curve showed good linearity over the range of 1-20 000 microg/kg (R2 = 0.999 9). The limit of quantification was 5 microg/kg for biurea spiked in flour and its products. At the spiking levels of 5.0, 10.0 and 50.0 microg/kg in different matrices, the average recovery o biurea was 78.3%-108.0% with the relative standard deviations (RSDs) < or = 5.73%. The method developed is novel, reliable and sensitive with wide linear range, and can be used to determine the biurea in flour and its products.