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Herein, a competitive-type electrochemiluminescence immunosensor for ultrasensitive detection of 5-fluorouracil (5-FU) was fabricated.

Electric field-induced high strain with small hysteresis and good temperature stability is necessary for piezoactuators devices. Most of previous works focus on the giant strain achieved in Bi0.5Na0.5TiO3 (BNT)-based ceramics through electric field-induced transition from nonergodic relaxor to ferroelectric state, while the high remnant strain or/and large hysteresis are always accompanying. In this work, through enhancing the local polarization by rare earth ions doping (e.g., La3+), we propose to improve the strain properties of BNT-based lead-free ceramics with ergodic relaxor state which displays the near zero remnant strain, small hysteresis, high temperature stability but the low strain value. The addition of La3+ would not change the ergodic relaxor state, but can improve the short-range correlation of local polar nanoregions, cut down the critical electric field of transition between relaxor and ferroelectric states, and elevate the electrostrictive effect of ceramics. Finally, high strain of ∼0.3 % with low hysteresis of ∼8−30 % was obtained in the broad temperature range from room temperature to 100 °C, which is superior to previous BNT-based ceramics and other lead-based/lead-free ceramics. This work affords a paradigm to regulate the ergodic relaxor state to optimize the strain properties, which give the significant guide for strain developments.

A surface-enhanced Raman scattering (SERS)/electrochemical dual-signal readout immunosensor was developed for simultaneous detection of β-adrenergic agonists salbutamol (SAL), ractopamine (RAC) and phenylethanolamine A (PA). The highly-ordered gold/silver bimetallic cavity array (BMCA) was prepared by electrodepositing Au/Ag nanoparticles to the interstice of highly ordered close-packed polystyrene templates. After electrochemical and SERS characterization, the BMCA was used as the substrate for constructing SERS/electrochemical dual-signal readout immunosensor. 3,3',5,5'-tetramethylbenzidine (TMB), methylene blue (MB) and Nile blue (NB) were selected as the dual-signal reporters, and hybridization chain reaction (HCR) was used as the signal amplifier. The immunoprobe was prepared by absorption of the antibody (Ab) and constructing HCR system embedded with electro/SERS reporter on Au nanoparticles (NPs). After competitive immuno-reaction between coating antigen and analyte for limited Ab on immunoprobe, the SERS/electrochemical dual-signals on BMCA were measured for quantitatively detecting SAL, RAC and PA simultaneously. SAL, RAC and PA were detected in concentration range of 1 pg mL

Amphenicol antibiotics including chloramphenicol (CAP), florfenicol (FF) and thiamphenicol (TAP) have been widely used in aquaculture and veterinary to treat various infections. Because of their high toxicity, it is important to detect these amphenicol antibiotics simultaneously. Using the monoclonal antibody against CAP (mAbCAP) binding CAP only and the mAbFF recognizing both FF and TAP, the two antibodies were covalently coupled to CNBr-activated Sepharose-4B for the simultaneous extraction of CAP, FF and TAP from samples. The bound CAP, FF and TAP were eluted from the Sepharose-4B and measured by LC–MS/MS. The extraction conditions of the two-antibodies-immobilized immunoaffinity clean-up (IAC) for CAP, FF and TAP were optimized and the maximum capacity was investigated. The extraction efficiency of IAC for CAP, FF and TAP was 1.1–2.1 times higher than that of SPE. The LC–MS/MS coupled with IAC was a powerful analytical method for the detection of CAP, FF and TAP simultaneously.

In this work, a novel sensitive electrochemiluminescence immunosensor based on Ru@SiO2–Au NPs and Co(OH)2 two-dimensional nanosheets (2D Co(OH)2) is constructed for the detection of enrofloxacin (ENR). Ruthenium bipyridine silica spheres and modified gold nanoparticles were synthesized as immune probe materials, which were combined with ENR antibodies (Abs) to form the immune probe part. 2D Co(OH)2 with a large specific surface area and good catalytic effect was firstly used as an immune substrate material, and at the same time, it was conjugated with the coating antigen (Ae) of ENR to form an immune substrate. Based on the principle of competitive immunity, ENR and ENR coated antigen could jointly compete for the specific binding sites on the ENR antibody, so as to achieve efficient detection of ENR. Under optimal conditions, the prepared immunosensor exhibited high sensitivity with a wide linear range from 0.0001 to 1000 ng mL−1 and a low detection limit (LOD) of 0.063 pg mL−1. The proposed immunosensor has been successfully applied to the detection of ENR residues in poultry, aquatic products and lake water.

Brombuterol is a new emerging β-adrenergic agonist that has been used as an additive in animal feed to enhance the lean meat-to-fat ratio. Due to its potential harm to consumers, it is urgent to develop sensitive, simple and rapid analytical methods to monitor brombuterol residue. In this study, a competitive lateral flow immunochromatographic assay (FLIA) based on surface-enhanced Raman scattering (SERS) was developed for ultrasensitive quantitative determination of brombuterol in swine liver, pork and feed samples. Ag@Au core–shell bimetallic nanoparticles with the highest SERS enhancement were synthesized, characterized and used as the substrate for preparation of the immunoprobe AgMBA@Au–Ab, in which the Raman reporter mercaptobenzoic acid (MBA) was embedded between the core–shell layers and monoclonal antibodies against brombuterol were immobilized on the surfaces of nanoparticles. The presence of brombuterol was identified through a color change on testing lines. In addition, quantitative detection of brombuterol was achieved by measuring the characteristic Raman peak intensity of MBA in the immunoprobes captured by the coating antigen. The IC50 and limit of detection (LOD) of the SERS-based FLIA for brombuterol were 45 pg mL−1 and 0.11 pg mL−1, respectively. The recoveries of brombuterol from spiked samples were in the range of 87.27–100.16% with relative standard deviations of 1.29%–6.99% (n = 3). The proposed SERS-based LFIA was proven to be a feasible method for ultrasensitive and rapid detection of brombuterol and might be a platform for sensitive and rapid detection of a broad range of analytes in clinical, environmental and food analyses.

The emergence and progress of metal-organic frameworks (MOFs) with high stability, large surface area, and abundant unsaturated active sites, once again promote the development of nanozymes, making nanozymes more advantageous to replace natural enzymes and will increase the applications of chemiluminescence immunoassay. In this study, a flow injection chemiluminescence immunoassay based on Ni/Co metal-organic framework (Ni/Co-MOF) nanozymes was developed, which can quickly and highly sensitively detect florfenicol (FF) in animal-derived food residues. Ni/Co-MOF

5-Fluorouracil (5-FU) is an effective anticancer drug widely used in cancer treatment. In this study, two 5-FU derivatives containing a spacer arm with the carboxylic group at the end were synthesized, which were linked to the carrier proteins to form 5-FU-protein conjugates used as the immunogens for the production of monoclonal antibody (mAb). Based on the produced mAb, the highly sensitive and specific enzyme-linked immunosorbent assay (ELISA) for 5-FU detection was established. The IC

In this work, a novel sensitive electrochemiluminescence immunosensor based on Ru@SiO

In the last years, surface-enhanced Raman scattering based immunochromatographic assay (SERS-ICA) has been getting great attention and been applied for the detection of different target analytes. In this study, a novel SERS-ICA using AgMBA@SiO2-Ab as an immunoprobe has been developed for rapid, quantitative and ultrasensitive detection of a pharmaceutical diclofenac (DCF) residue in water samples. Ag, Ag@SiO2 and AgMBA@SiO2 nanoparticles (NPs) were synthesized and characterized. The immunoprobe was prepared by sandwiching the Raman reporter mercaptobenzoic acid (MBA) between the core-shell layers and immobilizing the monoclonal antibody (mAb) against DCF on the surface of the Ag@SiO2 NPs. Under optimal conditions, the sensitivity and limit of detection (LOD) of the SERS-ICA for DCF were found to be 9 pg mL−1 and 0.07 pg mL-1, respectively. The detection of the SERS-ICA for DCF was completed within 15 min. AgMBA@SiO2-Ab was stable within four months without significant loss of SERS intensity. The key to success of the SERS-ICA was the employment of the Ag@SiO2 NPs as the SERS substrate, which possessed gorgeous SERS enhancement capability, predominant biocompatibility and excellent stability. This SERS-ICA is potential as an ultrasensitive analytical method in point-of-care testing, clinical diagnosis, food inspecting and environmental monitoring.

Human telomerase RNA (hTR), an important biomarker for cancer diagnosis, is the template for the synthesis of telomeric DNA repeats and is found to be 7-fold overexpressed in tumor cells. Herein, we present a photoelectrochemical (PEC) biosensor for hTR detection coupled with a novel amplification strategy based on cascades of catalytic hairpin assembly (CHA) and hyperbranched hybridization chain reaction (HB-HCR). At the electrode surface, thiolated hairpin 1 probes were immobilized on deposited CdS nanoparticles via a Cd-S bond. In the presence of target hTR, a CHA reaction was triggered and the exposing of trigger1 could further initiate an HB-HCR reaction to form abundant hemin/G-quadruplex DNAzymes containing dendritic DNA structure. The DNAzymes' catalytic precipitation of 4-chloro-1-naphthol (4-CN) by H2O2 subsequently took place on the surface of the PEC electrode and efficiently suppressed the photocurrent output. Therefore, the change of photocurrent response had a positive linear relationship with logarithmic value of hTR concentration varying from 200 fM to 20.0 nM with a limit of detection (LOD) of 17.0 fM. The LOD for CHA/HB-HCR was about 8.8-fold lower than that of CHA/linear-branched HCR (CHA/LB-HCR) and 547-fold lower than that of CHA. By coupling the feature of high signal amplification capacity for DNA nanotechnology, a prominently stable, reproducible, and selective PEC biosensor was successfully constructed and applied in hTR detection.

Herein, we describe a competitive-type electrochemiluminescence (ECL) strategy for Hg2+ determination based on the peroxydisulfate/oxygen (S2O82-/O2) system that uses Pt/Pd nanodendrites (Pt/Pd NDs)-thiosemicarbazide/norfloxacin (TN)-covered gold nanoparticles (Pt/Pd-TNG50) as a signal enhancer. The Pt/Pd NDs, a dense array of Pt branches on a Pd core, possessed excellent catalytic properties to enhance ECL intensity by accelerating electron transfer. In addition, the binary intramolecular synergy of TN, which had cooperative interactions of powerful π-π stacking with a larger conjugated surface, could extremely enhance the ECL signal of the S2O82-/O2 system. Furthermore, we designed a competitive immunoassay method using a structured sensor where a monoclonal antibody (mAb) against Hg2+ exhibited high specificity and recognition of Hg2+, which greatly improved the specificity and sensitivity of the immunosensor. As a result, the proposed immunosensor gave Hg2+ detection with a low detection limit (16 pg mL-1) and displayed high sensitivity and stability. Importantly, this work not only, for the first time to our knowledge, utilized Pt/Pd NDs as promising ECL emitters for bioprobe construction but also opened an efficient way for the detection of Hg2+ in environmental monitoring.

In this study, a monoclonal antibody (mAb)-based enzyme-linked immunosorbent assay (ELISA) for the determination of chloramphenicol (CAP) in shrimp, feed and milk samples was developed and validated by LC-MS/MS coupled with immunoaffinity clean-up (LC-MS/MS-IAC). Three immunogens were synthesized and used to immunize mice. Spleen cells from the immunized mice with the highest titer were selected for cell fusion. Two lines of hybridoma cells (1B1 and 2D2) secreting specific antibodies against CAP were successfully screened. Under optimal conditions, the values of the 50% inhibitory concentration (IC50) and limit of detection (LOD) of the ELISA in phosphate-buffered saline (PBS) based on 2D2 mAb for the detection of CAP were 0.46 ng mL−1 and 0.06 ng mL−1, respectively. There was no cross-reactivity (CR) of the ELISA with other antibiotics (florfenicol, thiamphenicol, etc.). Shrimp, feed and milk samples were spiked with different contents of CAP and detected by ELISA. The recoveries and coefficients of variation (CVs) of the ELISA for CAP from three spiked samples were 80.6–116.0% and 5.5–15.4% (n = 3), 96.2–111.0% and 7.0–13.5% (n = 3), and 79.7–109.8% and 5.8–13.3% (n = 3), respectively. As the CAP concentrations in spiked samples measured by LC-MS/MS coupled with solid phase extraction (LC-MS/MS-SPE) were significantly lower than those measured by ELISA, we established an immunoaffinity clean-up (IAC) for CAP by covalently immobilizing our mAb against CAP on the CNBr-activated Sepharose-4B gel and directly mixing the mAb-immobilized gel with the spiked samples sufficiently. The recoveries of CAP from the spiked samples measured by LC-MS/MS-IAC were 78.6–106.7% with the CV less than 11.1% (n = 3).

The emergence and development of low-cost and high-efficiency nanozymes are promising to replace natural enzymes promoting the application of chemiluminescence immunoassays. Herein, a rapid and highly sensitive flow injection chemiluminescence immunoassay based on cobalt hydroxide (Co(OH)2) nanozyme was established to detect enrofloxacin (ENR) residues in food. In this system, Co(OH)2 nanosheets act as nanozymes to catalyze and amplify the chemiluminescence signal of the luminol-PIP-H2O2 system, as well as a carrier for immobilizing antibodies to form stable immunoprobes. In addition, carboxyl resin beads with good stability and biocompatibility were used as the base of the immunosensor to carry more coating antigens, based on the principle of competitive immunity and to achieve the rapid detection of ENR. Under optimal conditions, the linear working range is 0.0001 ~ 1000 ng/mL, and the limit of detection (LOD) is 0.041 pg/mL (S/N = 3). The method has been successfully applied to the analysis of aquatic products and poultry food.

Brombuterol is a new emerging β-adrenergic agonist that has been used as an additive in animal feed to enhance the lean meat-to-fat ratio. Due to its potential harm to consumers, it is urgent to develop sensitive, simple and rapid analytical methods to monitor brombuterol residue. In this study, a competitive lateral flow immunochromatographic assay (FLIA) based on surface-enhanced Raman scattering (SERS) was developed for ultrasensitive quantitative determination of brombuterol in swine liver, pork and feed samples. Ag@Au core-shell bimetallic nanoparticles with the highest SERS enhancement were synthesized, characterized and used as the substrate for preparation of the immunoprobe AgMBA@Au-Ab, in which the Raman reporter mercaptobenzoic acid (MBA) was embedded between the core-shell layers and monoclonal antibodies against brombuterol were immobilized on the surfaces of nanoparticles. The presence of brombuterol was identified through a color change on testing lines. In addition, quantitative detection of brombuterol was achieved by measuring the characteristic Raman peak intensity of MBA in the immunoprobes captured by the coating antigen. The IC50 and limit of detection (LOD) of the SERS-based FLIA for brombuterol were 45 pg mL-1 and 0.11 pg mL-1, respectively. The recoveries of brombuterol from spiked samples were in the range of 87.27-100.16% with relative standard deviations of 1.29%-6.99% (n = 3). The proposed SERS-based LFIA was proven to be a feasible method for ultrasensitive and rapid detection of brombuterol and might be a platform for sensitive and rapid detection of a broad range of analytes in clinical, environmental and food analyses.

A rapid and highly sensitive flow injection chemiluminescence immunoassay was developed to detect ractopamine residues in pork products. Palladium nanocubes with excellent catalytic performance for a traditional luminol–PIP–H2O2 chemiluminescence system were used as effective carriers to connect a ractopamine antibody and horseradish peroxidase (HRP). Double amplification of a chemiluminescence signal was realized because of palladium nanocubes and HRP. Carboxyl-modified resin beads were used as suitable materials to load ractopamine-coating antigens due to their good biocompatibility and large specific surface area. Based on the principle of competitive immunity, ractopamine standard solution would compete with antigen loaded on carboxyl resin beads for limited binding sites on a ractopamine antibody. Thus, the chemiluminescence intensity of an immunosensor has a linear negative correlation with the logarithm value of ractopamine concentration. Under optimal experimental conditions, the detection range of ractopamine was 0.005–1000 ng mL−1, and the limit of detection (LOD) was 1.7 pg mL−1 (S/N = 3). The proposed immunoassay possessed acceptable accuracy, high specificity and reproducibility and RAC was examined in pork and pig feed with satisfactory results, which would provide a better prospect for the detection of small molecules in food and environment analysis.

Methyl jasmonate (MeJA) and its free-acid form, jasmonic acid (JA), collectively referred to as jasmonates (JAs), are natural plant growth regulators that are widely present in higher plants. Simultaneous detection of JA and MeJA in plant samples is of significance and is a great challenging issue. In this study, coupling with two extraction methods, a sensitive monoclonal antibody (mAb) based enzyme-linked immunosorbent assay (ELISA) for simultaneous detection of JA and MeJA in plant samples was developed. The JA-bovine serum albumin (BSA) conjugate was used as an immunogen for the production of mAb. As the produced mAb exhibited higher recognition ability towards MeJA than towards JA, ELISA was established using MeJA as the standard. Under optimal experimental conditions, the IC50 and LOD values of ELISA for MeJA were 2.02 ng mL-1 and 0.20 ng mL-1, respectively. In the first extraction method, MeJA in plant samples was evaporated and only JA was extracted. In the second extraction method, both JA and MeJA were extracted. After methylation, JA in the extracts was converted into MeJA, and the whole MeJA in the extracts was measured by ELISA. Plant samples including the leaves of Salvia splendens, the flowers of Salvia splendens and the fruit of grapes were collected. JA and MeJA in these samples were detected by the proposed ELISA. It was found that the concentrations of JA in these three plant samples were about 3-5 times higher than those of MeJA in those samples. ELISA was also confirmed by HPLC. There was a good correlation between ELISA and HPLC.

A simple and ultrasensitive flow injection chemiluminescence competitive immunoassay based on gold nanoparticle-loaded enzyme for the detection of chloramphenicol (CAP) residues in shrimp and honey has been developed. Due to their good biocompatibility and large specific surface area, carboxylic resin beads can be used as solid phase carriers to immobilize more coating antigens (Ag). In addition, gold nanoparticles could provide an effective matrix for loading more CAP antibody and horseradish peroxidase, which would effectively catalyze the system of luminol-p-iodophenol (PIP)-H2 O2 . A competitive immunoassay strategy was used for detection of CAP, in which CAP in the sample would compete with the coating Ag for the limited antibodies, leading to a chemiluminescence (CL) signal decrease with increase in CAP concentration. A wide linear range 0.001-10 ng ml-1 (R2 = 0.9961) was obtained under optimized conditions, and the detection limit (3σ) was calculated to be 0.33 pg ml-1 . This method was also been successfully applied to determine CAP in shrimp and honey samples. The immunosensor proposed in this study not only has the advantages of high sensitivity, wider linear range, and satisfactory stability, but also expands the application of flow injection CL immunoassay in antibiotic detection.

Herein, Pd nanoparticles (PdNPs) and CdSe@CdS QDs decorated poly(etherimide) (PEI)-graphene oxide (GO) (PdNPs/PEI-GO-QDs) and ceria-zinc oxide were prepared and severally applied as probe and substrate to assemble an electrochemiluminescence (ECL) immunosensor for detecting diclofenac (DCF). The carboxyl groups (−COOH) covered Ce:ZnO and PEI-GO were creatively applied in this sensor not only load more CdSe@CdS QDs and accelerate electron conduction to obtain sensitive ECL signal, but also provide large surface for coating antigen and antibody loading. Furthermore, it is worth noting that the rapid Ce4+ ↔ Ce3+ reaction in this Ce:ZnO and PdNPs/PEI-GO can increase the rate of electron transfer to achieve multiple signal amplification. A competitive immunoassay strategy was used for determining DCF, where DCF in the sample would compete with the coating antigen for the limited antibodies. The proposed ECL immunoassay had exhibited high sensitivity for DCF detection with a wide linear range from 0.001 to 1000 ng mL−1 and an ultralow detection limit of 0.3 pg mL−1. This ECL immunosensor had good stability, acceptable fabrication reproducibility and accuracy for detecting DCF in environmental samples, and provided an approach for determining other important small molecules.

Herein, a novel ultrasensitive competition-type electrochemiluminescent (ECL) immunosensor for detecting Sudan I was constructed using palladium/aurum core-shell nanocrystallines (Pd/Au CSNs) and CdSe@CdS QDs as signal bioprobe. The Pd/Au CSNs as outstanding nanocarrier equipped with superior performance like highly catalytic activity, good biocompatibility and large specific surface area, which enhanced ECL intensity significantly. The surface of electrode was coated with gold nanorods functionalized graphene oxide (GNRs/GO) nanocomposite film as the substrate, which provided an effective matrix to immobilize more coating antigen but also facilitated the electronic transmission to increase the ECL signal. The proposed immunoassay based on the synergistic effect of Pd/Au CSNs and GNRs/GO for determining Sudan I exhibited good stability, high sensitivity and wide linearity with a lower detection limit of 0.3 pg mL−1 (S/N = 3) and the wide range from 0.001 to 500 ng mL−1. Furthermore, the developed immunosensor was successfully applied in determination of real samples with acceptable accuracy, and initiated a new route for detecting other small molecule in the future.

A novel competitive electrochemiluminescence (ECL) immunosensor based on CdSe quantum dots was developed for the detection of enrofloxacin (Enro). Fullerene (C60) as a substrate is chemically surface modified using L-cysteine to obtain better water solubility and abundant amino and thiol groups that can load Au nanoparticles. The loading of Au can not only anchor the antigen, but also accelerate the electron transfer at the electrode surface. Since flower-like Au@BSA nanoparticles have abundant amino groups and a large specific surface area, they can act as a probe carrier. In other words, they can immobilize a large number of CdSe QDs via an amidation reaction to amplify the ECL signal. The Enro antigens as well as Enro analytes can connect with Enro antibodies that bind to Au@BSA through gold–nitrogen bonds. As the concentration of analytes increase, their ability to compete with antigens increases. So the number of antibodies bound to the antigens on the electrode decreases. This means that the number of CdSe QDs connected to the antibodies also decreases, resulting in a relatively low ECL response. The ECL intensity is linearly related to the Enro concentration in the range of 0.001–20 ng mL−1 with a detection limit of 0.33 pg mL−1.

A novel competitive mechanism electrochemiluminescence (ECL) immunoassay based on resonance energy transfer was used to detect florfenicol for the first time. In this work, CeO2@TiO2 nanocomposite, which was used as a donor, was prepared in sol-gel method and the effective band gap of TiO2 could be reduced by CeO2, which promoted the ECL emission of TiO2 and made the ECL performance of the donor more outstanding. The absorption spectrum of Cu2S and the ECL emission spectrum of the donor could be highly matched, which ensured the occurrence of electrochemiluminescence resonance energy transfer (ECL-RET). In addition, the snowflake-like structure of cuprous sulfide could load more antibodies. It is worth mentioning that as far as we know, there have been no reports of this material as an ECL receptor before. Furthermore, the ECL-RET system based on this has shown excellent performance in the detection of florfenicol. The proposed immunoassay showed satisfactory sensitivity with a wide linear range from 0.001 to 1000 ng mL−1 and a low detection limit (0.3 pg mL−1). Due to the remarkable quenching effect and simple assembly process, the immunoassay is of great practical significance and has reference value for the detection of florfenicol or other biological small molecules.

A surface-enhanced Raman scattering (SERS)-based competitive immunoassay for detecting β-adrenergic agonists (salbutamol, SAL; brombuterol, BRO) was developed. Highly ordered gold cavity arrays (GCA) with adjustable localized surface plasmon resonance and great Raman enhancement were prepared by electrodepositing gold nanoparticles (NPS) to the interstices of polystyrene sphere templates, and then covered by a pre-punched sticker with many holes as detection areas in the assay. The immuno-probe was prepared by immobilizing antibody against SAL (or BRO) and DNA concatamers labelled with SERS reporter on gold NPS. After immunoreaction, the characteristic bands of SERS reporters captured on GCA were measured for quantification of SAL and BRO. The sensitivity was improved by introduction of long DNA concatamers and silver staining due to DNA amplification and strong plasmon coupling between Au and Ag NPS. The LODs for SAL and BRO were 2.0 pg mL−1 and 1.0 pg mL−1, respectively. The recoveries of the assay for SAL and BRO in spiked samples were 96.7∼105.3 % with RSD of 4.9–8.7 %. The results demonstrated that this approach was a sensitive, specific and high-throughput method for simultaneous detection of SAL and BRO, and might be a new platform for the detection of multiple compounds in food and biological fields.

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.

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.

Background The substitution of hazardous analytical reagents such as Cd with benign alternatives for chemical determination is one of the principles of green chemistry. An eco-friendly Zn reduction method for nitrate determination was developed to achieve this end. Methods Online zinc reduction-sequential injection analysis (ZnR-SIA) protocol was developed for the determination of nitrogen (N) species in the Lagos Lagoon sediments by modification of some standard methods. Results The novel application of boric acid-borate buffer employed in borate-buffered granular Zn reduction suppressed gas evolution from the Zn micro-column, making the Zn reduction adaptable to online use, unlike the frequently used ammonia-ammonium buffer. Further results showed that the sampling rate for the two-zone stack was 65 h−1. The boric acid-borate buffer offered 5.9-fold and 1.3-fold of the instrument response given by the ammonia-ammonium buffer at 0.50 and 5.0 mg N L−1 respectively. The method detection limits of the ZnR-SIA for the three matrices studied were 24.6 μg N L−1 for reagent water, 0.383 mg N kg−1 for KCl-extractable nitrate, and 3.18 mg N kg−1 for total nitrogen. The average recovery of nitrate-N in matrix samples was 94.7%, and its precision was 4.52%. The average recoveries of total N in blanks and matrix samples were 97.9 and 93.2% respectively. Conclusions The method accuracies demonstrated the suitability of the ZnR-SIA for sediment N determination. Zn reduction is recommended where sustainable development is desired and is a potential substitute for the standard Cd reduction owing to Cd toxicity.

The β-adrenergic agonist brombuterol (BB) is illicitly used as an additive in animal feed to enhance the lean meat-to-fat ratio. The authors describe an ultrasensitive lateral flow immunochromatographic assay (LFIA) based on the use of surface enhanced Raman scattering (SERS) for the determination of brombuterol in swine meat and urine samples. Flower-like gold-silver core-shell bimetallic nanoparticles (referred to as AuNF@Ag) displaying strong SERS enhancement were synthesized, characterized and used as the substrate for the preparation of the LFIA. Polyclonal antibody against brombuterol was immobilized on the surface of the AuNF@Ag particles carrying the Raman reporter 4-mercaptobenzoic acid (MBA). After performing an LFIA, the Raman scattering intensity of MBA on the test line was measured and used for quantitation of brombuterol. Figures of merit of this assay procedure include (a) duration of LFIA process of 15 min; (b) an IC50 value (e.g. the concentration of brombuterol producing 50% of signal inhibition in standard curve) of 380 pg mL-1; and (c) a limit of detection as low as 0.5 pg mL-1. The LFIA is selective over the molecules salbutamol, ractopamine, phenylethanolamine A, isoproterenol and phenylephrine, but shows a 8.5% cross-reactivity to clenbuterol, probably due to the high structural similarity. Swine meat and urine samples spiked with different amounts of brombuterol were analyzed by this method and gave recoveries between 95.8 and 108.0%, and relative standard deviations between 2.0 and 6.3% (for n = 3).

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.