•An ultrasensitive colorimetric aptasensor for streptomycin detection has developed.•This probe was fabricated through porous silica (P-SiO2-SSB) labeled aptamer-nano gold -powervision as signal tags.•The strategy can achieve multiplex signal amplification based on the P-SiO2, PV and Exo I-assisted target recycling.•The aptasensor is easy to operate, rapid and sensitive for POCT detection of antibiotics.A point of care testing (POCT) colorimetric aptasensor was developed to detect streptomycin (STR) using porous SiO2 micro beads (pore size of 200 nm) −enzyme linked polymer (PowerVision™, PV) probes and exonuclease-assisted target recycling for signal amplification. The probe was fabricated by single- stranded DNA binding protein labelled SiO2 micro particles (P-SiO2-SSB) as capture probes and Au NPs & aptamer (Apt) co-immobilized on PV (Apt-Au-PV) as nanotracer. In the presence of STR and exonuclease I (Exo I), the nanotracer would combine with STR to form the complex (STR/Apt-Au-PV). Hereafter, Exo I further digest the aptamer on STR/Apt-Au-PV, then STR was released again to participate new cycling, the approach lead to generate more nanotracers into supernatant to improve the sensitivity. Moreover, the dendrimer PV which contains large quantities of HRPs can efficiently catalyzed H2O2-TMB (3,3′,5,5′- tetramethylbenzidine) system for color development and the results can observed by the naked eye. Due to the excellent multiple signal amplification effects for porous SiO2 micro particles to label more nanotracer, PV and exonuclease-assisted target recycling, the aptasensor exhibit a low detection limit with 1 pg mL−1 (S/N = 3). In addition, the developed method might provide a prospect assay for food tests at point of care.Download high-res image (116KB)Download full-size image

•A novel MoS2/RGO coating for efficiently extraction and determination of PCBs was developed via a saponification-HS-SPME.•Alkali solution was employed to help release PCBs from food, thus no organic solvents are needed for extraction.•The method exhibited high sensitivity, wide linearity and good precision for PCBs than commercial SPME.In this work, the molybdenum disulfide/reduced graphene oxide (MoS2/RGO) composite material was synthesized as a fiber coating to extract seven indicator polychlorinated biphenyls (PCBs; PCB28, PCB52, PCB101, PCB118, PCB138, PCB153, and PCB180) present in food via a saponification-headspace solid-phase microextraction assay (saponification-HS-SPME). The MoS2/RGO coating was prepared and deposited on a stainless steel wire with the help of a silicone sealant and used as an SPME fiber. The alkali solution dissolved the fat and helped in releasing the PCBs present in milk to the headspace for extraction under 100 °C. Following desorption in the inlet, the targets were quantified by gas chromatography-mass spectrometry. The effects of sorbent dosage, extraction time, added salts, and stirring rate on the extraction efficiency were investigated. The new coating was able to adsorb a higher amount of analytes, which was about 1.1–2.9 times in comparison with the commercially available SPME fiber (coated with divinylbenzene/carboxen/polydimethylsiloxane). It also showed the highest adsorption capability toward PCBs, which was 1.5–2.7 times that of the prepared RGO modified fiber. Moreover, MoS2 also showed a strong affinity toward PCBs in a manner similar to its affinity for graphene. The developed method is simple and environmentally friendly as it does not require any organic solvents. Furthermore, it exhibits good sensitivity with detection limits less than 0.1 ng mL−1, linearity (0.25–100 ng mL−1), and reproducibility (relative standard deviation below 10% for n = 3). The novel SPME fibers are inexpensive, reusable, and can be easily prepared and manipulated. In addition, the saponification-HS-SPME assay was also found to be suitable for screening persistent organic pollutants in dairy products.

•Homogeneous and “off–on” fluorescence aptamer-based assay was developed to detect chloramphenicol (CAP) residues in food.•This probe was fabricated based on a vesicle QDs signal tracer (SSB/L-QD) combining with Au-Aptamer.•The detection mechanism was based on FRET with high specificity.•The results for CAP detection in the milk samples agreed well with those from ELISA, while detection limit down to 0.3 pM.In this work, a novel homogeneous and signal “off–on” aptamer based fluorescence assay was successfully developed to detect chloramphenicol (CAP) residues in food based on the fluorescence resonance energy transfer (FRET). The vesicle nanotracer was prepared through labeling single stranded DNA binding protein (SSB) on limposome-CdSe/ZnS quantum dot (SSB/L-QD) complexes. It was worth mentioning that the signal tracer (SSB/L-QD) with vesicle shape, which was fabricated being encapsulated with a number of quantum dots and SSB. The nanotracer has excellent signal amplification effects. The vesicle composite probe was formed by combining aptamer labeled nano-gold (Au-Apt) and SSB/L-QD. Which based on SSB's specific affinity towards aptamer. This probe can't emit fluoresce which is in “off” state because the signal from SSB/L-QD as donor can be quenched by the Au-aptas acceptor. When CAP was added in the composite probe solution, the aptamer on the Au-Apt can be preferentially bounded with CAP then release from the composite probe, which can turn the “off” signal of SSB/L-QD tracer into “on” state. The assay indicates excellent linear response to CAP from 0.001 nM to 10 nM and detection limit down to 0.3 pM. The vesicle probes with size of 88 nm have strong signal amplification. Because a larger number of QDs can be labeled inside the double phosphorus lipid membrane. Besides, it was employed to detect CAP residues in the milk samples with results being agreed well with those from ELISA, verifying its accuracy and reliability.

•Aptamer-functionalized UiO-66-NH2 was applied to selectively extract PCBs.•UiO-66-NH2 used as the substrate to increase adsorption capacity.•Fe3O4@PDA@UiO-66-NH2was prepared without seeding by using PDA as covalent linker.In this paper, a novel dispersive solid phase extraction (dSPE) adsorbent based on aptamer-functionalized magnetic metal-organic framework material was developed for selective enrichment of the trace polychlorinated biphenyls (PCBs) from soil sample. Firstly, we developed a simple, versatile synthetic strategy to prepare highly reproducible magnetic amino-functionalized UiO-66 (Fe3O4@PDA@UiO-66-NH2) by using polydopamine (PDA) as covalent linker. Then amino-functionalized aptamers which can recognize 2,3′,5,5′-tetrachlorobiphenyl (PCB72), 2′,3′,4′,5,5′-pentachlorobiphenyl (PCB106) were covalent immobilized on UiO-66-NH2 through coupling reagent of glutaraldehyde. Aptamer-functionalized adsorbent (Fe3O4@PDA@UiO-66-Apt) can specifically capture PCBs from complex matrix with high adsorption capacity based on the specific affinity of aptamer towards target. Moreover, the adsorbent can be easily isolated from the solution through magnetic separation after extraction. Afterwards, the detection was carried out with gas chromatography tandem mass spectrometry (GC–MS). The selective dSPE pretreatment coupled with GC–MS possessed high selectivity, good binding capacity, stability, repeatability and reproducibility for the extraction of PCBs. Furthermore, the adsorbent possessed good mechanical stability which can be applied in replicate at least for 60 extraction cycles with recovery over 80%. It provided a linear range of 0.02–400 ng mL−1 with a good correlation coefficient (R2 = 0.9994–0.9996), and the limit of detection was found to be 0.010–0.015 ng mL−1. The method was successfully utilized for the determination of PCBs in soil samples.

•A sensitive aptasensor was achieved for multiplex detection of antibiotics.•Different metal ions encoded MHPs were fabricated for signals amplification.•Exonuclease-assisted target recycling were employed for signal amplification.•The dual amplification strategy present a 12-fold-amplified of silica nanotracer.A multiplex electrochemical aptasensor was developed for simultaneous detection of two antibiotics such as chloramphenicol (CAP) and oxytetracycline (OTC), and high-capacity magnetic hollow porous nanotracers coupling exonuclease-assisted target recycling was used to improve sensitivity. The cascade amplification process consists of the exonuclease-assisted target recycling amplification and metal ions encoded magnetic hollow porous nanoparticles (MHPs) to produce voltammetry signals. Upon the specific recognition of aptamers to targets (CAP and OTC), exonuclease I (Exo I) selectively digested the aptamers which were bound with CAP and OTC, then the released CAP and OTC participated new cycling to produce more single DNA, which can act as trigger strands to hybrid with nanotracers to generate further signal amplification. MHPs were used as carriers to load more amounts of metal ions and coupling with Exo I assisted cascade target recycling can amplify the signal for about 12 folds compared with silica based nanotracers. Owing to the dual signal amplification, the linear range between signals and the concentrations of CAP and OTC were obtained in the range of 0.0005–50 ng mL−1. The detection limits of CAP and OTC were 0.15 and 0.10 ng mL−1 (S/N=3) which is more than 2 orders lower than commercial enzyme-linked immunosorbent immunoassay (ELISA) method, respectively. The proposed method was successfully applied to simultaneously detection of CAP and OTC in milk samples. Besides, this aptasensor can be applied to other antibiotics detection by changing the corresponding aptamer. The whole scheme is facile, selective and sensitive enough for antibiotics screening in food safety.

•A novel fluorescence aptasensor was successfully developed to detect chloramphenicol (CAP).•This probe can be fabricated though magnetic vesicle probes.•The vesicle probes can effective amplified signal.•This method for CAP detection in the fish samples agreed well with those from ELISA.A novel fluorescence aptasensor was successfully developed to respond to chloramphenicol (CAP) in food based on magnetic aptamer-liposome vesicle probe. In order to fabricate it, aptamer labeled on functionalized magnetic beads (MB) was firstly employed as capture adsorbent (MB-Apt), then SSB (single-stranded DNA binding protein) and DIL (1,1′-dioctadecyl-3,3,3′,3′-tetramethyl-indocarbocyanineperchlorate) coimmobilized liposomes (SSB/DIL-Lip) was employed as vesicle signal tracer. The composite vesicle probe is formed between SSB/DIL-Lip and MB-Apt based on SSB's specific recognition towards aptamer on vesicle signal tracer. Upon the vesicle probe solution reacted with CAP, the aptamer on the magnetic beads preferentially bounded with CAP, and then released SSB/DIL-Lip vesicle signal tracer in the supernatant after magnetic separation. The released tracer can emit fluorescence which was correspondence with the concentration of the analyte. At the optimum conditions, the aptasensor exhibited a good linear response for CAP detection in the range of 0.003–10 nM with a detection limit of 1 pM. Importantly, the methodology was further validated for analyzing CAP in fish samples with consistent results obtained by ELISA kit, thus providing a promising approach for quantitative monitoring of CAP and significant anti-interference ability in food safety.

•A “signal-on’’ aptasensor for simultaneous detection of CAP and PCB72 was built.•Nanospherical branched PEI brushes as signal loader for signal amplification.•The detection was simplified by one-step competitive-type displacement reaction.A “signal-on’’ aptasensor was developed for simultaneous detection of chloramphenicols (CAP) and polychlorinated biphenyl-72 (PCB72) with a novel multi-metal ions encoded nanospherical brushes as nanotracers. To construct the assay, the respective aptamer of CAP and PCB72 labeled magnetic gold nanoparticles as capture probes (aptamer-MGPs), and their complementary single strand DNA (s-DNA) encoded metal ions (Cd2+ and Pb2+) on nanospherical branched polyethylene imine brushes as tracers (s-DNA-MSPEIs), were simultaneously synthesized. After that, the capture probe and tracers were connected through a hybridization reaction between s-DNA and aptamers. In the presence of CAP and PCB72, the analytes could react with the aptamers on capture probes and release the tracers into supernatant after magnetic separation. The released tracers with metal ions (Cd2+ and Pb2+) could be simultaneously detected through the square wave voltammetry (SWV) without acid dissolution, which can switch the signals of the biosensor to “on’’ state. Under optimal conditions, the assay could detect CAP and PCB72 as low as 0.3 pg mL−1 with the dynamitic range from 0.001 to 100 ng mL−1 and exhibited excellent selectivity. More importantly, the strategy can be extended easily to other targets after changing the corresponding aptamers and other metal ions tracers, which provides a promising and facile approach in multiplex detection of ultra-trace level of pollutants in food safety without more complex separation and washing steps.

•A dual-template MIPs modified electrochemiluminescence immunosensor array was fabricated.•The molecular imprinted films was employed instead of expensive antibody as capture probe.•A novel Ru(bpy)32+-Silica@Poly-L-lysine-Au nanocomposites were employed to connect with antibody as labels.•The labels can dual amplify the signal and display high ECL intensity.•The sensor can near-simultaneously detect two tumor markers in pg mL−1 and U mL−1 order of magnitude in serums.A novel electrochemiluminescence (ECL) immunosensor array was fabricated on a screen-printed electrode (SPE) to perform multiplexed immunoassay of tumor markers (TMs), such as carcinoembryonic antigen (CEA) and carbohydrate antigen-199 (CA199). The SPE substrate consisted of a common Ag/AgCl reference electrode, a common carbon counter electrode and two gold nanoparticles modified carbon working electrodes. Firstly, dopamine (DA) as the functional monomer along with the corresponding TMs (CEA or CA199) as template molecules was electro-polymerized on the surface of different working electrodes. Then, the dual-template molecularly imprinted polydopamine (MIP-PDA) film was formed as the capture probe to recognize CEA and CA199. Secondly, a novel label was fabricated by conjugating the antibodies of TMs with Ru(bpy)32+-Silica@Poly-L-lysine-Au (Ru-Si@PLL-Au) nanocomposites, in which gold colloids (Au NPs) were doped on the surface of Ru-Silica (Ru(bpy)32+-doped Silica) using poly-L-lysine (PLL) as a bridging agent. PLL was also employed as a co-reactant of the luminophore. Based on a sandwich-type immunoassay, the MIP-PDA film, the corresponding antigen and labels were conjugated to produce the immunocomplex. The signals from the ECL immunosensor array were near-simultaneously detected by a photomultiplier tube (PMT) using a homemade single-pore-two-throw switch, which could avoid crosstalk between adjacent working electrodes. The obtained concentrations were 0.05-100 pg mL−1 for CEA and 0.03-80 U L−1 for CA199, with detection limits of 0.02 pg mL−1 and 0.01 U L−1, respectively. This novel ECL strategy provides a simple, economical, fast and sensitive approach for multiplexed immunoassay of CEA and CA199, and has significant potential for protein detection in a clinical laboratory setting.

•A clean-up absorbent was fabricated to eliminate the matrix interference in soils during the detecton of PCBs.•The magneitic β-CD grafted absorbent has stronger absorption towards DDT, DDE, and DDD than highly chlorinated PCBs.•A simple and rapid analytical method for highly chlorinated PCBs in soil samples by dSPE–GC–MS was developed.In this study, we developed a magnetically multifunctional purifying material for efficient removal of matrix interferences, especially certain organochlorine pesticide (DDT, DDE, and DDD), during the determination of toxic highly chlorinated polychlorinated biphenyls (PCBs) at trace levels in soil samples. The multifunctional adsorbent (CMCD-NH2-MNPs) was prepared by grafting carboxymethyl-β-cyclodextrin on the surface of amino-functionalized magnetite (Fe3O4) nanoparticles. CMCD-NH2-MNPs has stronger host–guest complexation with DDT, DDE, and DDD, but the same adsorbent shows weaker adsorption ability toward highly chlorinated PCBs (from tetra- to octa-chlorinated PCBs) owing to their steric hindrance effect. Based on this principle, a simple and rapid gas chromatography–mass spectrometry (GC–MS) method was developed for six indicator PCBs (PCB28, PCB52, PCB101, PCB138, PCB153, and PCB180) in soil. Comparative studies were conducted to determine the clean-up efficiency of the following three techniques: (i) Oasis-HLB, (ii) multi-layer silica column, and (iii) dSPE employing CMCD-NH2-MNPs. The results indicate that CMCD-NH2-MNPs as the purification material can easily and effectively remove DDT, DDE, and DDD in soil samples within a short duration of time. The recoveries for highly chlorinated PCBs were in the range of 85.4–102.2%, with RSDs varying between1.0 and 6.5%. The proposed method was verified as one of the most effective clean-up procedures for the analysis of highly chlorinated PCBs in real soil samples