A multiple amplified electrochemiluminescence immunosensor is described for the determination of the illicit β-adrenergic agonist brombuterol. Firstly, cystein-coated silver nanowires (SCNW) were modified with polyamidoamine dendrimers (PAMAM) and then immobilized on a glassy carbon electrode (GCE). Then, Ag@Au core/shell nanoparticles (NPs) were deposited on the surface of the modified GCE via gold-nitrogen bonds. The use of Cys-coated silver nanowires accelerates the electron transfer process and also prevents the aggregation of the Ag@Au NPs. The nanocomposites on the GCE have a large surface and outstanding electrical conductivity. It can carry a large amount of coating antigen to amplify the ECL signal. Moreover, PAMAM-Au-CdSe quantum dot bioprobes were prepared, and the unique dendrimer-encapsulated gold nanoparticles with numerous functional amino groups were employed to load abundant activated CdSe quantum dots for further enhancement of the ECL signal. On the basis of signal amplification of the SCNW-PAMAM-Ag@Au-based immunosensor and the PAMAM-Au-CdSe quantum dot bioprobes. The assay has a wide linear range that extends over the 0.001–1000 ng·mL−1 brombuterol concentration range and a lower detection limit of 37 fg·mL−1. The method is well reproducible, stable and specific. It was applied to the determination of brombuterol in spiked samples of pork and feed where it gave satisfactory recoveries.

The authors describe a dual signal amplification electrochemiluminescent (ECL) immunoassay for ultrasensitive determination of the β-adrenergic agonist salbutamol (SAL). It is based on the use of gold nanoparticles (AuNPs) and silica-coated quantum dots of the type CdSe@SiO2. The CdSe@SiO2 nanoparticles (NPs) were synthesized by water-in-oil reversed-phase microemulsion. Amino-modified NPs were then prepared and used as an ECL signal probe for detection of SAL in the presence of K2S2O8. The gold NPs with their large specific surface carry the antigen, facilitate electron transfer and improve the electrochemical reaction efficiency of QDs and K2S2O8. The ECL immunosensor was fabricated by coating the AuNPs with antigen, and then SAL competed with SAL antigen for the binding sites of the antibody on the CdSe@SiO2 NPs. Under optimized conditions, the ECL intensity is linearly related to the logarithm of the SAL concentration in the range from 0.001 to 1000 ng mL−1, with a lower detection limit of 0.17 pg mL−1 (at an S/N ratio of 3). The assay has good operational stability, is highly sensitive and selective. It is judged to possess a wider scope in that it may be applied to many other small molecule analytes for which adequate antibodies are available.

•Casein was firstly used as the sources of carbon, nitrogen and sulfur for the synthesis of NSCDs using a one-step pyrolysis strategy.•The NSCDs displayed a blue emission with quantum yield of 31.8%, good aqueous solubility, photostability and biocompatibility.•The NSCDs were used as a probe for rapid and sensitive detection of Hg2+ with the limit of detection (LOD) of 6.5 nM.•The NSCDs-Hg2+ system was employed as a fluorescent sensor for sensitive detection of biothiols.•The NSCDs were used as effective fluorescent probes in cellular imaging without noticeable cytotoxicity.Fluorescent nitrogen and sulfur co-doped carbon dots (NSCDs) were synthesized by a one-step pyrolysis strategy using casein as carbon, nitrogen and sulfur sources, and characterized by UV–vis spectrum, fluorescent spectrum, X-ray photoelectron spectroscopy (XPS) and FT-IR, etc. The synthesized NSCDs displayed a blue emission under ultraviolet illumination with a quantum yield of 31.8%, and a good aqueous solubility, photostability and biocompatibility. It was found that the fluorescence intensity of NSCDs could be selectively quenched by Hg2+, so NSCDs was used as an effective probe for the detection of Hg2+. The linear range and the limit of detection (LOD) of the fluorescent sensor based on NSCDs for the detection of Hg2+ were 0.01–0.25 μM and 6.5 nM, respectively. Spiked water samples were detected by the sensor with the recovery of 95.4–106.3% and relative standard deviation (RSD) of 3.6–8.6%. It was also observed that the quenched NSCDs-Hg2+ system could be restored by the addition of biothiols such as l-cysteine (Lcy), homocysteine (Hcy) and glutathione (GSH), thus NSCDs-Hg2+ system was employed as a fluorescent sensor for the detection of biothiols. The linear range and LOD of the NSCDs-Hg2+ system were 1–10 μM and 23.6 nM for Lcy, 0.2–2.5 μM and 12.3 nM for Hcy, and 0.1–2.0 μM and 16.8 nM for GSH, respectively. The NSCDs-Hg2+ system was applied for the detection of biothiols in serum samples with satisfied results. In addition, the study in vitro imaging HeLa cells revealed that the synthesized NSCDs could be used as effective fluorescent probes in cellular imaging without noticeable cytotoxicity.Download high-res image (174KB)Download full-size image

The use of salbutamol (SAL), a β-adrenergic receptor agonist (β-agonist) that could enhance the lean meat-to-fat ratio in livestock, has been prohibited as an additive in animal feeds for livestock production in many countries due to its harmful effect to the consumers. Herein, we present a sensitive and group-specific ELISA based on monoclonal antibodies (mAb) for the determination of SAL in swine meat and liver samples. The SAL derivative, containing the carboxylic group, was prepared by directly reacting SAL with succinic anhydride and then the derivative was linked to carrier proteins. Mice immunized with SAL–bovine serum albumin (BSA) conjugate were utilized for mAb generation. A hybridoma clone (1C3) specifically secreting mAb against SAL with higher sensitivity was successfully obtained. Under optimal conditions, the IC50 and LOD values of the mAb-based ELISA for SAL were calculated to be 0.47 ng mL−1 and 0.049 ng mL−1, respectively, indicating high sensitivity of the assay. The mAb displayed high cross-reactivity (CR) with four β-agonists, i.e., clenbuterol (55%), terbutaline (44%), brombuterol (33%) and cimbuterol (134%) because these compounds contain the same tert-butyl group on the nitrogen atom as does SAL. The CR of the mAb with other β-agonists, including cimaterol, clorprenaline, isoprenaline, neophryn, ractopamine and phenylethylamine A, was less than 2.2% due to relatively large structural differences compared to that of SAL. Swine meat and liver samples were spiked with different SAL content and detected by ELISA. The recovery rates were found in the range of 76.4–107.6% and 71.8–106.8%, respectively, with coefficients of variation less than 20%. Spiked samples were also analyzed by HPLC. A good correlation between both methods was obtained. These results demonstrated that the proposed ELISA is a feasible quantitative/screening method for SAL analysis in swine meat and liver samples. In addition, the recovery results of the β-agonists that displayed the high CR values with mAb in an additional spiking experiment revealed that the ELISA could also be an alternative method for multiple β-agonist detection.

The use of salbutamol (SAL), a β-adrenergic receptor agonist (β-agonist) that could enhance the lean meat-to-fat ratio in livestock, has been prohibited as an additive in animal feeds for livestock production in many countries due to its harmful effect to the consumers. Herein, we present a sensitive and group-specific ELISA based on monoclonal antibodies (mAb) for the determination of SAL in swine meat and liver samples. The SAL derivative, containing the carboxylic group, was prepared by directly reacting SAL with succinic anhydride and then the derivative was linked to carrier proteins. Mice immunized with SAL–bovine serum albumin (BSA) conjugate were utilized for mAb generation. A hybridoma clone (1C3) specifically secreting mAb against SAL with higher sensitivity was successfully obtained. Under optimal conditions, the IC50 and LOD values of the mAb-based ELISA for SAL were calculated to be 0.47 ng mL−1 and 0.049 ng mL−1, respectively, indicating high sensitivity of the assay. The mAb displayed high cross-reactivity (CR) with four β-agonists, i.e., clenbuterol (55%), terbutaline (44%), brombuterol (33%) and cimbuterol (134%) because these compounds contain the same tert-butyl group on the nitrogen atom as does SAL. The CR of the mAb with other β-agonists, including cimaterol, clorprenaline, isoprenaline, neophryn, ractopamine and phenylethylamine A, was less than 2.2% due to relatively large structural differences compared to that of SAL. Swine meat and liver samples were spiked with different SAL content and detected by ELISA. The recovery rates were found in the range of 76.4–107.6% and 71.8–106.8%, respectively, with coefficients of variation less than 20%. Spiked samples were also analyzed by HPLC. A good correlation between both methods was obtained. These results demonstrated that the proposed ELISA is a feasible quantitative/screening method for SAL analysis in swine meat and liver samples. In addition, the recovery results of the β-agonists that displayed the high CR values with mAb in an additional spiking experiment revealed that the ELISA could also be an alternative method for multiple β-agonist detection.

•An ultrasensitive QDs-based ECL immunosensor for detecting RAC is firstly developed.•Specific pAb was applied in ECL competitive immunoassay improving the selectivity.•Dual amplification was gained by using QDs/PDDA-GN/AuNPs probe and AuNPs as template.•A competitive ECL immunoassay is performed to detect small molecules of RAC.•The immunosensor will expand the usage of QDs, graphene and AuNPs in ECL biosensing.In this work, gold nanoparticals (AuNPs) and CdSe QDs decorated poly (diallyldimethylammonium chloride)-graphene (CdSe QDs/PDDA-GN/AuNPs) were prepared and applied as probe to assemble an electrochemiluminescence (ECL) immunosensor for detecting ractopamine (RAC) for the first time. The CdSe QDs/PDDA-GN/AuNPs composite showed good electronic conductivity, fast response and satisfactory stability which employed for fabricating ECL biosensors with high sensitivity. AuNPs and PDDA-GN were creatively applied in this sensor not only accelerate electron conduction to achieve dual signal amplification, but also provide large surface for coating antigen and antibody loading. A competitive immunoassay strategy was chosen for determining RAC, where RAC in the sample would compete with the coating antigen for the limited biomarkers. The well-prepared ECL immunosensor satisfied in samples detection of RAC with a wider linear range from 0.01 to 1000 ng mL−1 and a lower detection limit of 2.6 pg mL−1 (S/N = 3). The proposed ECL immunosensor displayed high sensitivity and stability, and provided an approach for determining other important biomarkers.An ultrasensitive competition-type electrochemiluminescent immunoassay for the ractopamine (RAC) is put forward. Dual-signal amplified strategy was proposed by using CdSe QDs/PDDA-GN/AuNPs-labeled antibody composite as probe and AuNPs-labeled coating antigen as substrates led to high sensitivity and wider detection range. It has been used in the detection of real samples with satisfactory results, indicating a promising method for tracing RAC and other small molecular compounds.

•The proposed ICT was able to directly detect Hg2+ without formation of Hg2+-ligand complex.•The proposed ICT exhibited high sensitivity, specificity, stability, precision and accuracy for Hg2+ detection.•The proposed ICT was applicable for the detection of trace amount of Hg2+ in water, human serum and urine samples.An immunochromatographic test (ICT) strip was developed for ultrasensitive competitive immunoassay of Hg2+. This strategy was achieved by combining the easy-operation and rapidity of ICT with the high sensitivity of surface-enhanced Raman scattering (SERS). Monoclonal antibody (mAb) against Hg2+ and Raman active substance 4-mercaptobenzoic acid (MBA) dual labelled gold nanoparticles (GNPs) were prepared as an immunoprobe. The Raman scattering intensity of MBA on the test line of the ICT strip was measured for quantitative determination of Hg2+. The ICT was able to directly detect Hg2+ without complexing due to the specific recognition of the mAb with Hg2+. The IC50 and limit of detection (LOD) of the assay for Hg2+ detection were 0.12 ng mL−1 and 0.45 pg mL−1, respectively. There was no cross-reactivity (CR) of the assay with other nineteen ions and the ICT strips could be kept for 5 weeks without loss of activity. The recoveries of the assay for water, human serum and urine samples spiked with Hg2+ were in range of 88.3–107.3% with the relative standard deviations (RSD) of 1.5–9.5% (n = 3). The proposed ICT was used for the detection of Hg2+ in urine samples collected from Occupational Disease Hospital and the results were confirmed by cold-vapor atomic fluorescence spectroscopy (CV-AFS). The assay exhibited high sensitivity, selectivity, stability, precision and accuracy, demonstrating a promising method for the detection of trace amount of Hg2+ in environmental water samples and biological serum and urine samples.

•A multiple signal amplification ECL immunosensor of eco-friendly CdSe QDs for brombuterol determination was developed.•Besides substrates, AuNPs and PAMAM-SNR were creatively used to accelerate the electron transport between electrode and QDs.•SNR-PAMAM with numerous amino groups also could be employed to bond abundant actived QDs to amplify ECL signal.•Competitive immunoassay was performed with ECL to detect small molecules of brombuterol.•It provided a method for detecting Brom and enlarged the usage of QDs, AuNPs and SNR-PAMAM in ECL biosensing.Electrochemiluminescent (ECL) immunosensor with multiple signal amplification was designed based on gold nanoparticles (AuNPs), polyamidoamine dendrimers (PAMAM) and silver-cysteine hybrid nanoribbon (SNR). Low toxic l-cysteine capped CdSe QDs was chosen as the ECL signal probe. To verify the proposed ultrasensitive ECL immunosensor for β-adrenergic agonists (β-AA), we detected Brombuterol (Brom) as a proof-of-principle analyte. Therein, AuNPs as the substrate can simplify the experiment process, accelerate the electron transfer rate, and carry more coating antigen (Ag-OVA) to enlarge ECL signal. On one hand, SNR on the surface of electrode can avoid the aggregation of AuNPs, and SNR-PAMAM-AuNPs also can be acted as a good accelerator for electron transfer. On the other hand, PAMAM (16 -NH2) functionalized SNR (SNR-PAMAM) with numerous amino groups could be employed to bond abundant actived QDs to further amplify ECL signal. The new immunosensor can offer a simple, reliable, rapid, and selective detection for Brom, which have a dynamic range of 0.005–700 ng mL−1 with a low detection limit at 1.5 pg mL−1. The proposed biosensor will extend the application of nanomaterials in ECL immunoassays and open a new road for the detection of Brom and other β-AA in the future.

Brombuterol, a new β-adrenergic agonist which can enhance the lean meat-to-fat ratio, is forbidden as an additive in animal feeds for livestock production due to its adverse effects on consumers. In this study, a highly sensitive and specific competitive enzyme-linked immunosorbent assay (ELISA) for the detection of brombuterol in tissue and feed samples was developed. The immunogen and coating antigen were prepared by directly linking brombuterol to carrier proteins using the diazobenzidine method. The antisera against brombuterol were obtained from immunized rabbits. The IC50 and limit of detection (LOD) values of the superior ELISA were 0.165 ng mL−1 and 0.007 ng mL−1, respectively. The cross-reactivity (CR) values of ELISA with clenbuterol, terbutaline and cimbuterol were less than 6.2%; there was no CR of ELISA with nine other compounds. To investigate the accuracy and precision of the assay, liver, meat and feed samples were spiked with brombuterol at different concentrations and analyzed by ELISA. Acceptable recovery rates of 91.9–115.4% and intra-assay coefficients of variation of 1.5–9.5% (n = 3) were achieved. The ELISA was also validated by HPLC. As revealed, both methods were highly correlated (R2 = 0.9927–0.9994, n = 6). The proposed ELISA was proven to be a feasible method for quantitative analysis of brombuterol in tissue and feed samples.

Immunoaffinity chromatography (IAC) for simultaneous determination of four fluoroquinolone antibiotics, e.g., norfloxacin (NOR), pefloxacin (PEF), lomefloxacin (LOM), and enrofloxacin (ENRO) from swine and chicken meat samples, was developed. The IAC column was constructed by covalently coupling polyclonal antibody (pAb) against NOR to cyanogen bromide (CNBr)-activated Sepharose 4B and packed into a common solid-phase extraction (SPE) cartridge. It was found that IAC column was able to separately capture NOR, PEF, LOM, and ENRO with a maximum capacity of 200, 336, 352, and 421 ng, respectively. The extraction conditions including loading, washing, and eluting solutions were carefully optimized. Under optimal conditions, the extraction recoveries of the IAC column for NOR, PEF, LOM, and ENRO at two different contents were within 85.8–105.9 %. The IAC column was also applied to real sample extraction. Swine and chicken meat samples were collected and spiked with NOR, PEF, LOM, and ENRO at the content of 20 and 35 ng g−1, respectively. The spiked and unspiked samples were extracted by IAC column and measured by high-performance liquid chromatography (HPLC). It was found that there was no detectable NOR, PEF, LOM, and ENRO in the blank samples, and the extraction recoveries of the IAC for NOR, PEF, LOM, and ENRO from the spiked samples were within 75.3–99.8 % with the relative standard deviation (RSD) of 4.3–12.1 %. The stability of the column was also tested. It was showed that after 30 times repeated usage, 65 % of the maximum capacity was still remained, indicating high reusability of the IAC column. The proposed IAC was proven to be an effectively selective extraction method for NOR, PEF, LOM, and ENRO from swine and chicken meat samples with the properties of high maximum capacity, extraction efficiency, and stability.

Salbutamol (SAL), a kind of β-agonist which can enhance the lean meat-to-fat ratio, has been inhibited as an additive used in animal feeds for livestock production in many countries due to its harmful effect to the consumers. In this study, an ultrasensitive and specific competitive immunochromatographic test (ICT) integrated with surface-enhanced Raman scattering (SERS) for the detection of SAL was described. The immunoprobe was prepared by immobilizing polyclonal antibody against SAL on the surface of Au@Ag nanoparticles in which the Raman reporter (4-mercaptobenzoic acid, MBA) had been sandwiched. After ICT procedures, the specific SERS signals generated from MBA on the test line of the ICT strip were measured for the quantitative determination of SAL. The assay was completed in 15 min. The IC50 and the limit of detection (LOD) values of the assay for SAL were 0.028 ng mL−1 and 3.0 pg mL−1, respectively. There was no cross-reactivity (CR) of the assay with other three β-agonists (clenbuterol, phenylethanolamine A, and ractopamine), showing high specificity of the assay. Spiking experiments indicated that the average recoveries (n = 3) of SAL from swine feed, meat, and urine samples were in ranges of 98.4–105.2 % with the relative standard deviations (RSDs) of 1.7–7.8 %. The results demonstrated that the proposed ICT was a feasible method for ultrasensitive and specific detection SAL in swine feed, meat and urine samples, and could be extended for the detection of other target analytes.

The article describes the preparation of chitosan-coated hemoglobin (Hb-CS) microcapsules by (a) preparing a CaCO3 precipitate containing Hb, (b) crosslinking Hb with glutaraldehye, (c) coating the particles with chitosan, and (d) preparing Hb-CS microcapsules by removing the CaCO3 template with a solution of disodium EDTA. The morphology and electrochemical properties of the Hb-CS microcapsules were investigated by scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. An oxygen sensor was obtained by immobilizing the Hb-CS microcapsules on the surface of a glassy carbon electrode (GCE) first modified with gold nanoparticles. The application of Hb-CS microcapsules facilitates electron transfer on the surface of GCE and warrants the integrity and biological activity of Hb. The oxygen sensor, operated best at a working voltage of −0.335  V (vs. SCE), displays a low limit of detection (30 nM). The Hb-CS microcapsules also are shown to release loaded oxygen to an anaerobic aqueous environment within 300 min.

A multiple signal amplification strategy was designed for an ultrasensitive competitive immunoassay for Hg2+. This strategy was achieved using graphene conjugated with a large number of CdSe quantum dots to enhance the basal signal and enormous horseradish peroxidase (HRP) labeled with gold nanoparticles (AuNPs) to consume the coreactant H2O2 generated in situ. The immunosensor was constructed by immobilization of coating antigen on poly(diallyldimethylammonium chloride)–graphene–CdSe composites (PDDA–GN–CdSe), and a strong electrochemiluminescence (ECL) signal was obtained. When the immunosensor was immersed in antibody–AuNPs–HRP composites, the ECL signal greatly decreased, which was ascribed to the bound enzyme on the electrode surface. The self-produced coreactant H2O2 was consumed by o-phenylenediamine in the presence of enzyme, effectively decreasing the ECL intensity from the quantum dots. The Hg2+ in solution and the corresponding coating antigen competed for the limited antibody, and thus, the ECL intensity was linearly dependent on the logarithm of the mercury(II) concentration from 0.2 to 1000 ng mL–1 with a detection limit of 0.06 ng mL–1. The immunoassay exhibited good stability and accuracy and acceptable reproducibility, indicating that it provides a promising approach for the detection of trace mercury and other small molecular compounds in environmental samples.

In the present work, a simple and sensitive flow injection chemiluminescent competitive immunoassay was developed for the determination of mercury(II) ion (Hg2+) based on carboxylic resin beads, a novel specific monoclonal antibody (McAb) and HRP enzyme-amplification. Resin beads with carboxyl groups were creatively employed as supports for immobilizing more coating antigen through acylamide bonds. With a competitive-type assay mode, the Hg2+ in solution competed with the immobilized coating antigen for the limited McAb. Then, the second antibody labeled with HRP was introduced, and an effectively increased CL was obtained, which was ascribed to the catalytic activity of HRP for the luminol–PIP–H2O2 reaction. With increasing concentration of Hg2+, the CL of this system decreases because less HRP is present in the CL reaction. At optimal conditions, the CL signal displayed a good linear relation toward Hg2+ in the range of 0.05–200 ng mL−1 with a detection limit (3σ) of 0.015 ng mL−1. The immunosensor possessed high specificity, acceptable accuracy and reproducibility, and was examined in real samples with favorable results. This immunoassay will have intriguing application prospects for the determination of other heavy metal ions and environmental contaminants.

This study describes a novel electrochemical immunosensor to amplify the electrochemiluminescence (ECL) signal for the ultrasensitive detection of salbutamol (SAL) using quantum dots (QDs) and gold nanoparticle (AuNP) conjugated horseradish peroxidase (HRP). The electrochemical detection was based on the HRP catalyzed consumption of self-produced H2O2, which has been extensively used as a co-reactant of QDs, by o-phenylenediamine (OPD). The enzymatic reaction rate is proportional to the amount of HRP bound to the electrode. In the presence of a SAL standard solution, the immobilized SAL coating antigens competed with the SAL solution for the Ab–AuNPs–HRP complexes. With an increase in the SAL concentration, the amount of immobilized HRP decreases, which leads to an increase in the ECL intensity. Under optimized conditions, the ECL intensity changes linearly with the logarithm of the SAL concentration in the range of 0.05–500 ng mL−1 with a detection limit of 0.017 ng mL−1 (S/N = 3). The ECL immunosensor possesses high sensitivity, satisfactory reproducibility and selectivity, and may provide a feasible route for practical application.

A simple, convenient and fast preparation for successful fabrication of water-soluble DL-homocysteine capped Au nanoclusters (hcy-AuNCs) was demonstrated. This preparation allowed the generation of water-soluble Au NCs within a short time of 15 min. The resulting hcy-AuNCs were characterized by photoluminescence, UV-Vis absorption, X-ray photoelectron spectroscopy, and transmission electron microscopy (TEM). The mean diameter of hcy-AuNCs was found to be 1.6 ± 0.2 nm. The Au NCs exhibited an orange-yellow fluorescence emission at 560 nm with a large Stokes shift of 120 nm, a quantum yield of 3.01% and a good stability over the physiologically relevant pH range and ionic strength. Furthermore, cytotoxicity studies showed that the Au NCs exhibited negligible effects in altering cell proliferation or triggering apoptosis. Cancer cell imaging of HeLa cell lines indicated that the obtained Au NCs could serve as a promising fluorescent bioprobe for bioimaging. This strategy, based on the one-step preparation using DL-homocysteine as a reducing/stabilizing reagent, may offer a novel approach to fabricate other water-soluble metal nanoclusters for application in biolabelling and bioimaging.

In this study, we present a novel immunochromatographic assay (ICA) based on surface-enhanced Raman scattering (SERS) for the sensitive and quantitative determination of clenbuterol in urine samples. The principle of this new ICA is similar to that based on colloidal gold particles, but using AuMBA@Ag–Ab [e.g. the polyclonal antibody of clenbuterol labelled Au@Ag core–shell nanoparticles (NPs) sandwiched with a Raman reporter (4-mercaptobenzoic acid, MBA)] as a probe. The clenbuterol in solution and the clenbuterol–ovalbumin conjugate previously coated on the test line of the ICA strip competed for limited antibody binding sites on the probe. The specific Raman scattering intensity of MBA on the test line was measured for the quantitative detection of clenbuterol. This proposed assay was completed within 15 min. The IC50 and limit of detection (LOD) values of the assay for clenbuterol were found to be 0.02 ng mL−1 and 0.24 pg mL−1, respectively. The relative standard deviations (RSD) of the signal obtained from 10 points along the middle part of the test line were within 4.3–8.7%. There was no cross-reactivity (CR) of the assay with ractopamine or phenylethanolamine A, and only 19% CR with salbutamol. The recoveries of clenbuterol from spiked swine urine samples were in the range of 93.8–112.4% with RSD values in range of 5.2–11.5% (n = 9). The proposed SERS-based ICA was demonstrated to be a rapid, simple and ultrasensitive analytical method for detecting clenbuterol in urine samples and could also be applied for the determination of other target analytes in different matrices.

We have designed an ultrasensitive electrochemiluminescence (ECL) immunoassay for the determination of the β-adrenergic agonist phenylethanolamine A (PA). It is based on the use of L-cysteine-capped CdSe quantum dots (QDs) immobilized on a glassy carbon electrode (GCE) with the help of chitosan. PA (the antigen) was linked to the surface of the GCE by using glutaraldehyde where it competes with the PA in the sample solution to bind to the antibody. Upon formation of the immunocomplex, a second antibody labeled with horseradish peroxidase was immobilized on the surface of the modified GCE. The ECL emission decreases due to steric hindrance by the immunocomplex which slows down the electron transfer rate of the reduction of dissolved oxygen, and this decrease can be strongly amplified by using an enzymatic cycle to consume the self-produced coreactant H2O2. Under optimal conditions, the ECL intensity measured in this competitive immunoassay is related to the concentration of PA over a range as wide as from 0.05 to 1,000 ng mL−1. The lower detection limit is 15 pg mL−1 at the S/N ratio of 3. This ECL immunoassay is rapid, sensitive, selective, acceptably precise, and extends the application of QDs-based ECL to immunoassays of β-agonists.

We have designed a rapid and ultrasensitive electrochemiluminescent (ECL) competitive immunoassay for the determination of mercury(II) ion. It is based on the use of CdSe quantum dots (QDs), methylmercury-6-mercaptonicotinic acid-ovalbumin as coating antigen and specific monoclonal antibodies (mAbs) against Hg(II). The latter is quite selective for Hg(II). The coating antigen was immobilized on the surface of a gold electrode via reaction between the functional groups of cysteamine and glutaraldehyde. The mercury(II) ions in a sample and the coating antigen compete for binding sites of QD-labeled monoclonal antibody which binds specifically to Hg(II) ions. The ECL of the system decreases with increasing concentration of Hg(II) because less QD-labeled mAbs are present on the surface of the electrode. Under optimal conditions, the decrease of ECL intensity is linearly related to the logarithm of the Hg(II) concentration in the range from 0.02 to 100 ng mL−1, with a detection limit of 6.2 pg mL−1. As far as we know, this is the first report on an ECL immunoassay for Hg(II) based on a specific monoclonal antibody. The favorable results obtained when this method was applied to real samples indicate that this detection scheme can widely enlarge the applicability of detecting heavy metal ions by exploiting the ECL of QDs for immunoassays.

A femtogram level and specific surface enhanced Raman spectroscopy (SERS) based competitive immunoassay was developed to detect Hg(II) in aqueous solution for the first time. This novel approach provides an alternative, ultrasensitive and specific analytical method for the detection of Hg(II).

This study reports the development of an electrochemiluminescent (ECL) immunosensor for ultrasensitive detection of phenylethanolamine A (PA) based on CdSe quantum dots (QDs) and gold nanoparticles (GNPs). The GNPs/ovalbumin–PA/anti-PA–QD immunosensor was fabricated layer by layer using GNPs as substrates and electron transport accelerators. The use of GNPs greatly enhanced the sensitivity for detecting PA due to the excellent electron transportation ability and the large surface area of GNP carriers allowing several binding events of ovalbumin–PA on each nanosphere. Transmission electron microscopy images (TEM), photoluminescence spectra, ultraviolet-visible absorption spectra and dynamic light scattering (DLS) were used to characterize the QDs and GNPs. The sensor was characterized with electrochemical impedance spectra (EIS), and a strong ECL emission of the modified electrode could be observed during the cathodic process of S2O82− and QDs in air-saturated PBS buffer containing 0.1 M K2S2O8 and 0.1 M KCl (pH 7.4). With a competitive immunoassay format, the ECL signal depended linearly on the logarithm of the phenylethanolamine A concentration within a range of 0.02 ng mL−1 to 50 ng mL−1, and the detection limit was 0.0047 ng mL−1, much lower than those reported in the literature. This ECL immunosensor is rapid, simple and sensitive with acceptable precision, and it will extend the application of QD ECL in immunoassays of β-agonists and open new avenues for the detection of food additive residues in the future.

Phenylethanolamine A (PA) is a new kind of β-agonist, which was illegally used as a feed additive for growth promotion in China. In this study, a novel immunochromatographic assay (ICA) based on surface-enhanced Raman scattering (SERS) for the ultrasensitive and quantitative detection of phenylethanolamine A is presented. The principle of this new ICA is similar to that based on colloidal gold particles, but using AuMBA@Ag-Ab [e.g., polyclonal antibody of PA labeled Au@Ag core–shell nanoparticles (NPs) sandwiched with a Raman reporter (4-mercaptobenzoic acid, MBA)] as a probe. After ICA procedures, the specific Raman scattering intensity of MBA on the test line was measured for quantitative detection of PA. This assay was completed within 15 min. The IC50 and limit of detection (LOD) values of the ICA for PA detection were 0.06 ng mL–1 and 0.32 pg mL–1, respectively, which were 1–3 orders of magnitude lower than those obtained by other immunoassays, indicating the ultrasensitivity of this ICA. There was no cross-reactivity (CR) of the assay with another three β-agonists (ractopamine, clenbuterol, and salbutamol), suggesting high specificity of the SERS-based ICA. A spiking experiment revealed that the recoveries of PA from pig urine samples were in range of 99.9– 101.2% with relative standard deviations (RSDs) of 3.6–5.8%. The results demonstrated that this SERS-based ICA was able to quantitatively detect PA in urine samples with high sensitivity, specificity, precision, and accuracy and might be a powerful method for the analysis of other target analytes in the food area.

In this paper, a flow-injection chemiluminescence (CL) immunoassay based on a transparent immunoaffinity reactor is reported for the detection of clenbuterol (CLB). The reactor prepared with coating-antigen immobilized on carboxylic resin beads was used as an immunosensor and was incorporated in a CL reaction system based on p-iodophenol–luminol–H2O2 in the presence of horse radish peroxidase (HRP) as an enzyme tracer. With a competitive immunoassay format, the decrease in CL intensity was proportional to the increase of clenbuterol concentration in the range of 0.40–120 ng mL−1 with a correlation coefficient of 0.999 (n = 9) and a limit of detection of 0.20 ng mL−1 at S/N of 3. The stability, specificity and reproducibility of the fabrication of the immunosensor system were good. The system was applied in the analysis of real samples with satisfactory results and has good potential for use in the screening of trace amounts of CLB residue.

•An IAC column for selective extraction of PA from feed, meat and liver was developed.•The IAC column was characterized in terms of maximum capacity, selectivity, etc.•The IAC extraction conditions for PA were carefully optimized.•PA in spiked real samples was extracted by IAC column and measured by HPLC.Phenylethanolamine A (PA) is a new emerged β-adrenergic agonist that has been illegally used as an animal feed additive for growth promotion in China. In this study, an immunoaffinity chromatography (IAC) column for selective extraction of PA from swine feed, meat and liver samples was developed. The IAC column was constructed by covalently coupling specific polyclonal antibody (Ab) against PA to CNBr-activated Sepharose 4B and packed into a common solid phase extraction (SPE) cartridge. The extraction conditions including loading, washing and eluting solutions were carefully optimized. Under optimal conditions, the IAC column was characterized in terms of maximum capacity, selectivity, extraction recovery and stability. The maximum capacity of the ICA for PA extraction was found to be 239.4 ng. For selectivity testing, 100 ng of other three β-adrenergic agonists (clenbuterol, ractopamine and salbutamol) was separately loaded onto the column, and it was observed that the tested compounds could not be captured on the column, e.g. the column could only selectively recognize PA. The recovery of the IAC for PA extraction was found within 96.47–101.98% when 10, 50 and 100 ng PA were separately loaded onto IAC column. The IAC column was also applied to real sample extraction. Swine feed, meat and liver samples were collected and spiked with PA in range of 1.0–20 ng g−1. The spiked and unspiked samples were extracted by IAC column and measured by high performance liquid chromatography (HPLC). It was found that there was no detectable PA in the blank samples, and the extraction recoveries of the IAC for PA from the spiked samples were within 89.48–104.89%. The stability of the column was also tested. It was showed that after 35 times repeated usage, 60% of the maximum capacity was still remained. The proposed IAC was proven to be a feasible extraction method for PA from different matrices with the properties of high maximum capacity, selectivity, extraction efficiency and stability.

•An ultrasensitive ECL immunosensor of CdSe QDs for clenbuterol determination is developed.•The CdSe QDs showed great biocompatibility and could be easier to make direct use of such QDs in the region of biological system.•Enzymatic amplification strategy was proposed by combining the coreactant and pAb/GaRIgG-HRP.•Enzymatic amplification increased ECL emission and extended the analyte in presence of substrate.•It provided a method for detecting clenbuterol and enlarged the usage of QDs in ECL biosensing.An ultrasensitive electrochemiluminescence (ECL) immunosensor based on CdSe quantum dots (QDs) has been designed for the detection of clenbuterol. The immunosensor was fabricated by layer by layer and characterized with atomic force microscopic images (AFM) and electrochemical impedance spectra (EIS). In oxygen-saturated pH = 9.0 Tris-HCl buffer, a strong ECL emission of QDs could be observed during the cathodic process due to the H2O2 product from electrochemical reduction of dissolved oxygen. Upon the formation of immunocomplex, the second antibody labeled with horseradish peroxidase was simply immobilized on the electrode surface. The ECL emission decreased since steric hindrance of the immunocomplex slowed down the electron-transfer speed of dissolved oxygen, and also could be greatly amplified by an enzymatic cycle to consume the self-produced coreactant. Using clenbuterol as model analyte, the ECL intensity was determined by the concentration of competitive immunoassay of clenbuterol with a wide calibration in the range of 0.05 ng mL−1 to 1000 ng mL−1, and a low detection limit was 0.02 ng mL−1. The immunosensor shows good stability and fabrication reproducibility. It was applied to detecting practical samples with the satisfactory results. This immunosensing strategy opens a new avenue for detection of residue and application of QDs in ECL biosensing.

Synthetic contraceptive levonorgestrel (LNG) and glucocorticoid methylprednisolone (MP) residues are eventually discarded to environmental water system and function as environmental hormones, displaying potential risk to humans and ecosystems, thus there is an urgent need for fast, sensitive and simultaneous detection of these compounds in water samples. In this study, a competitive immunochromatographic assay (ICA) using colloidal gold-labeled polyclonal antibodies as probes for rapid and simultaneous detection of LNG and MP in water samples was developed. The visual detection limits of LNG and MP in water samples were 10 ng/mL. The detection process could be completed within 10 min. There was no cross-reactivity of the ICA with other seven compounds. The strips could be stored at 4 °C for 10 weeks without significant loss of activity. The assay is a suitable tool for rapid and semi-quantitative detection of LNG and MP in water samples on site.A competitive immunochromatographic assay (ICA) using colloidal gold-labeled polyclonal antibodies as probes for rapid and simultaneous detection of contraceptive levonorgestrel (LNG) and glucocorticoid methylprednisolone (MP) in water samples were developed. The visual detection limits of LNG and MP in water samples were 10 ng/mL and the detection process could be completed within 10 min.

•PA derivative was synthesized and coupled to carrier proteins.•Polyclonal antibodies against PA were successfully produced.•Highly sensitive and specific ELISAs for PA were developed.•Acceptable recovery rates and intra-assay CV for PA detection were achieved.•There was a high correlation coefficient between the ELISA and LC–MS/MS for PA.Phenylethanolamine A (PA) is a new emerged β-adrenergic agonist illegally used as feed additives for growth promotion. In this study, a highly sensitive and specific indirect competitive enzyme-linked immunosorbent assay (ELISA) for the detection of PA in tissue and feed samples was developed and confirmed by liquid chromatography tandem mass spectrometry (LC–MS/MS). By reduction of nitryl group to amino group, the PA derivative was synthesized and coupled to carrier proteins with diazobenzidine method. The antisera obtained from four immunized rabbits were characterized in terms of sensitivity and specificity. All antisera displayed high sensitivity with IC50 values lower than 0.48 ng mL−1. The most sensitive ELISA was established with IC50 and limit of detection (LOD) values of 0.049 ng mL−1 and 0.003 ng mL−1, respectively. The cross-reactivity (CR) values of the antisera with three frequently used β-adrenergic agonists (clenbuterol, salbutamol and ractopamine) were lesser than 0.39%; there was no CR of the antisera with other six compounds including two structurally related substances (isoproterenol, phenylephrine). To investigate the accuracy and precision of the assay, swine kidney, liver, meat and feed samples were fortified with PA at different content and analyzed by ELISA. Acceptable recovery rates of 92.2–113.7% and intra-assay coefficients of variation of 3.8–10.9% (n=3) were achieved. Seven spiked samples were simultaneously analyzed by ELISA and LC–MS/MS. There was a high correlation coefficient of 0.9956 (n=7) between the two methods. The proposed ELISA proven to be a feasible quantitative/screening method for PA analysis in tissue and feed samples with the properties of high sensitivity and specificity, high sample throughput and low expensive.

We describe molecularly imprinted microspheres (MIMs) for the selective extraction of melamine from milk. The MIMs were made from melamine as the template molecule, methacrylic acid as the functional monomer, and ethylene glycol dimethacrylate as the linking agent. The MIMs were synthesized by suspension polymerization and characterized by rebinding experiments. They displayed high adsorption capacity, fast rebinding kinetics, and highly specific rebinding of melamine. The imprinting factor is 4.1. Scatchard analysis revealed a one-type rebinding behavior, the dissociation constant and maximum rebinding capacity being 37.59 g L−1 and 30.85 μmol g−1, respectively. The MIMs exhibited a 25% cross-reactivity towards atrazine, but less than 3.0% towards prometryn, clenbuterol and metronidazole. In addition, a MIM-based solid phase extraction (MISPE) column for melamine was prepared by packing MIMs into a common SPE cartridge. The MISPE extraction gave recoveries of 89.8 to 100.6% of melamine, with relative standard deviations of 5.9 to 7.5%. There was no significant loss of rebinding capacity after more than 60 repeated uses, thus demonstrating the high stability of the MISPE column. The MSPE column also was applied to the extraction of melamine from spiked liquid and powdered milk with satisfying accuracy and precision.

A femtogram level and specific surface enhanced Raman spectroscopy (SERS) based competitive immunoassay was developed to detect Hg(II) in aqueous solution for the first time. This novel approach provides an alternative, ultrasensitive and specific analytical method for the detection of Hg(II).

In this paper, a flow-injection chemiluminescence (CL) immunoassay based on a transparent immunoaffinity reactor is reported for the detection of clenbuterol (CLB). The reactor prepared with coating-antigen immobilized on carboxylic resin beads was used as an immunosensor and was incorporated in a CL reaction system based on p-iodophenol–luminol–H2O2 in the presence of horse radish peroxidase (HRP) as an enzyme tracer. With a competitive immunoassay format, the decrease in CL intensity was proportional to the increase of clenbuterol concentration in the range of 0.40–120 ng mL−1 with a correlation coefficient of 0.999 (n = 9) and a limit of detection of 0.20 ng mL−1 at S/N of 3. The stability, specificity and reproducibility of the fabrication of the immunosensor system were good. The system was applied in the analysis of real samples with satisfactory results and has good potential for use in the screening of trace amounts of CLB residue.