Porous g-C3N4 nanosheet (PCNS) photocatalyst with a thickness of 2.0 nm, pore volume of 0.61 cm3 g–1, and surface area of 190.1 m2 g–1 was prepared by a simple two-step template-free approach without the addition of extra reagents. Compared with the bulk g-C3N4 (BCN), PCNS possesses a greater number of surface reactive sites, improved efficiency of charge transfer, and accelerated separation of photogenerated electron–hole pairs. Accordingly, the visible-light-driven photocatalytic disinfection performance and organic pollutant degradation activity of PCNS are significantly enhanced. Escherichia coli (E. coli) cells can be killed completely by PCNS within 4 h, whereas only 77.1% of E. coli cells can be killed by BCN. The photodegradation rates of PCNS on methylene blue, Acid Red 27, and bisphenol A are almost 6.4, 4.0, and 1.9 times as fast as that of BCN, respectively. The photocurrent intensity of PCNS is about 3.7 times in comparison with that of BCN. Considering the easy preparation and excellent performance, PCNS could be a promising and competitive visible-light-driven photocatalyst in the field of environment remediation.Keywords: disinfection; g-C3N4; mesoporosity; nanosheets; photocatalysis; pollutant degradation; visible light;

Okadaic acid (OA) is a low molecular weight marine toxin from shellfish which causes diarrheic shellfish poisoning (DSP). Due to its frequent occurrence, OA has become a serious threat to human health and seafood industry. The authors describe a competitive fluorophore-linked aptamer assay for OA that is based on rolling circle amplification (RCA). It consists of the following steps: (a) The wells of a microplate are modified by fixing the OA aptamer on their surface; (b) The aptamer is hybridized with an aptamer-complementary sequence-primer complex; (c) the RCA reaction is performed; (d) the FAM labelled signal probe is added. OA competes with the detection probe for the immobilized aptamer. After the competitive reaction has occurred, the supernatants containing released detection probes are removed and then read with a microplate reader. This method, unlike in competitive assays where the signals negatively correlate with OA concentrations, has a positive correlation between fluorescence intensity and OA concentration. The optimized assay has a lower detection limit (1 pg·mL−1) and a wider linear range (from 1 pg·mL−1 to 100 ng·mL−1) owning to signal amplification via RCA. It also is highly specific, repeatable, has good recovery and can be used to detect OA in seafood.

•A colorimetric-based aptasensor was developed for bacteria detection.•ZnFe2O4-rGO nanostructures were synthesized as an effective peroxidase mimetics.•The method was sensitive and specific by using aptamers as recognition elements.•The method was successfully applied to milk samples.A new colorimetric aptasensor platform was fabricated to detect Salmonella enterica serovar typhimurium based on the peroxidase-like activity of ZnFe2O4-reduced graphene oxide (ZnFe2O4/rGO) nanostructures. The synthesized ZnFe2O4/rGO can catalytically oxidize 3,3′,5,5′-tetramethylbenzidine (TMB) by H2O2 and generate a typical blue product, which was detected by micro-reader at 652 nm. Therefore, ZnFe2O4/rGO was conjugated with aptamer to act as the signal probe. Biotin modified aptamer was immobilized onto the micro-plate to act as the capture probe. In the presence of target, a “sandwich-type” complex of aptamer (on micro-plate)-target-aptamer-ZnFe2O4/rGO complexes was formed through specific recognition of aptamers and corresponding target. The limit of detection was 11 cfu/mL and the detection range was 11 to 1.10 × 105 cfu/mL of S. typhimurium in buffer solution. Actual samples analysis indicated that this colorimetric aptasensor produced results consistent with plate-counting analysis. The developed method was simple and sensitive, which may pave the way for the detection of other pathogenic bacteria with suitable aptamers.

Clenbuterol hydrochloride (CLB) is often abused as additive feed for livestock to decrease adipose tissue deposition and to increase growth rate. It raises a potential risk to human health through the consumption of animal product. In this study, aptamers with higher affinity and specificity were screened through 16 selection rounds based on the ssDNA library immobilized systematic evolution of ligands by exponential enrichment (SELEX) technique. After cloning and sequencing, five aptamer candidates were picked out for affinity and specificity assays based on a graphene oxide (GO) adsorption method. The results showed that the aptamer CLB-2 binds specifically against CLB with a dissociation constant, Kd, value of 76.61 ± 12.70 nM. In addition, an aptamer-based fluorescence bioassay was established for CLB analysis. The correlation between the CLB concentration and fluorescent signal was found to be linear within the range of 0.10 to 50 ng/mL with a limit of detection of 0.07 ng/mL. It has been further applied for the determination of CLB in pork samples, showing its great potential for sensitive analysis in food safety control.Keywords: aptamer; clenbuterol hydrochloride; library immobilization; SELEX;

•A more universal Co2+/ABEI-AuNFs-cDNA complex that can significantly enhance the CL intensity was synthesized with easier operation.•Fe3O4 MNPs based solid-phase RCA strategy was fabricated and Co2+/ABEI-AuNFs was used as signal probes.•A steady-state chemiluminescent aptasensor was fabricated to detect S. typhimurium with high sensitivity and specificity.A sensitive steady-state chemiluminescent aptasensor based on rolling circle amplification (RCA) was fabricated for the detection of Salmonella typhimurium. The sensor utilized aptamer modified Fe3O4 magnetic nanoparticles (MNPs) as capture probes, aptamer as recognition molecules, and Co2+ enhanced N‑(aminobutyl)-N-(ethylisoluminol) (ABEI) functional flowerlike gold nanoparticles (AuNFs) and complementary strand (cDNA) complex (Co2+/ABEI-AuNFs-cDNA) as signal probes. And P-Iodophenol (PIP) was also added to form a typical ABEI- AuNFs-PIP-H2O2 steady-state CL system. By virtue of Fe3O4 MNPs based solid-phase RCA strategy, S. typhimurium can be first captured by the aptamer immobilized on the surface of Fe3O4 MNPs then complex with RCA products to form a sandwich complex. Co2+/ABEI-AuNFs-cDNA signal probes were then assembled on the RCA products to produce and enhance CL signals. Under optimal conditions, the logarithmic correlation between the concentration of S. typhimurium and the CL signal was found to be linear within the range of 32 cfu mL−1 to 3.2×106 cfu mL−1 (R2 =0.9921). The limits of detection of the developed method were found to be 10 cfu mL−1 for S. typhimurium. The method was also used to detect S. typhimurium in real pork samples. The results were compared with those obtained from the plate-counting methods and showed good consistency. Therefore, this detection aptasnesor can be a good candidate for sensitive and selective detection of S. typhimurium with simple and effective operations.

•The method can provide reliable detection of femtomolar level.•The Raman signal was enhanced in the hot spot between AuNPs.•The use of aptamer realized high specificity for target.This paper investigated a new detection method of oxytetracycline (OTC) in aquatic products with ultrasensitive detection limit. The method was constructed on the basis of raman hot spot between gold nanoparticles (AuNPs) (13 nm and 80 nm diameter respectively) linked by an DNA sequence. The DNA sequence combined with the OTC aptamer including its complementary sequence as well as a stem-loop structure. The raman signal molecule (4-MBA) was modified at the surface of 13 nm AuNPs. After the exposure of OTC, the aptamer sequence was preferentially combined with OTC and partially dehybridized with its complementary sequence which led the 13 nm AuNPs to get more closer to the 80 nm AuNPs. The raman intensity was thus increased for the more enhanced hot spot generated. Under the optimal experimental conditions, the SERS signal was positively related to the OTC concentration with a wide working range of 4.60×10−2–4.60×102 fg/mL and the limit of detection (LOD) was as low as 4.35×10−3 fg/mL. The recovery rates of fishmeal ranged from 91.29–110.98%. The specificity of this method was further examined, and the results showed that the AuNPs based aptasensor was highly selective. This developed ultrasensitive aptamer-based SERS detection platform suggested that it may be a promising strategy for a variety of sensing applications.

Foodborne ailments constitute a public health challenge and pose an incredible economic burden in healthcare system around the globe. This dilemma has urged authorities and other entities working in field of food quality control and supply chain to play a pivotal role in ensuring food safety. Analytical strategies have been developed using numerous systematic evolution of ligands by exponential enrichment (SELEX) methods to assure food safety. High-affinity and high-sensitivity ssDNA and RNA aptamers against pathogens have emerged as a novel strategy, as compared to the more resource-demanding and complicated biochemical test-based approaches. Thus, this review aims to focus on some methods used in the selection of specific bare, modified, and conjugated aptamers and on the further analysis of selected aptamers using flow cytometer or post-SELEX modifications for enhanced detection of frequently diagnosed foodborne bacteria such as Bacillus sp., Campylobacter jejuni, Escherichia sp., Salmonella sp., Staphylococcus aureus, Shigella sp., Listeria monocytogenes, and Streptococcus pyogenes and/or targeting their cell components towards attaining fast, sensitive, and selective methods for the detection of pathogens in food(s) or other sources.

•In this study, NaYF4:Yb, Tm@NaYF4:Yb nanoparticles with enhanced fluorescence were synthesized.•Upconversion nanoparticles and MoS2 was combined by aptamer to form a FAUM nanoplatform for MC-LR detection. To the best of our knowledge, this is the first time to detect MC-LR using energy transfer from enhanced fluorescence of CS-UCNPs to MoS2. The calibration curve for MC-LR detection with an excellent correlation (R2 of 0.9942) was achieved by fluorescence over the range of 0.01–50 ng/ml, and the LOD was calculated to be 0.002 ng/ml.•This aptamer-based platform might be a promising strategy for a variety of sensing applications.Water safety is one of the most pervasive problems afflicting people throughout the world. Microcystin-LR (MC-LR), a representative toxin released by cyanobacteria, poses an increasing and serious threat to water safety. In order to develop facile, specific and sensitive detection methods for MC-LR, we fabricated an ultrasensitive fluorescence aptasensor using the enhanced fluorescence of UCNP and the effective quenching ability, high affinity toward single strand DNA (ssDNA) of MoS2 (termed as FAUM). This assay specifically determined MC-LR in the linear range of 0.01–50 ng/ml with a limit of detection (LOD) of 0.002 ng/ml. The real water sample results indicated that this FAUM assay owns well enough reliability and feasibility to allow the determination of MC-LR. This aptamer-based method might be a promising strategy for a variety of sensing applications.

•A novel near-infrared magnetic aptasensor for Ochratoxin A was fabricated.•The result of the proposed method was compared with the ELISA method.•Highly sensitive detection of as low as 0.005 ng mL−1 OTA spiked into beer has been realized.A multiplexed, sensitive and specific detection method is highly desirable for the simultaneous detection of several pathogenic bacteria and bio-toxins. In our previous work, multicolor upconversion nanoparticles (UCNPs) via doping with various rare-earth ions to obtain well-separated emission peaks by means of a solvothermal method were synthesized and were successfully applied as luminescence labels in the detection of three pathogenic bacteria. One of the basic achievements of our group has been to establish that the key to increasing the number of simultaneous detection components is the preparation of more UCNPs, the emission peaks of which can be distinguished from each other. According to this vision, NaYF4:Yb0.2, Tm0.02 UCNPs were obtained via a thermal-decomposition protocol, which has a main near-infrared (NIR) UC emission at 804 nm under 980 nm excitation. The emission peak at 804 nm was well-separated from the emission peaks of UCNPs we have reported at 477 nm, 542 nm, and 660 nm. It means both the excitation and the emission of NaYF4:Yb0.2, Tm0.02 UCNPs are located in the NIR spectral range (NIR-to-NIR UC emission), the so-called biological window. This result establishes the basis of achieving simultaneous detection of four components. To confirm the analytical performance of this NaYF4:Yb0.2, Tm0.02 UCNPs, a novel near-infrared magnetic aptasensor for the detection of Ochratoxin A (OTA) was developed using the OTA aptamer-conjugated near-infrared upconversion nanoparticles (apt-UCNPs) and the complementary oligonucleotide-modified magnetic nanoparticles (cDNA-MNPs). The apt-UCNPs and cDNA-MNPs were hybridized to form a poly-network structure of MNP-UCNP nanocomposites. When the target OTA was introduced, the aptamer combined with the priority target and the cDNA-MNPs were replaced. The proposed method achieved a linear range between 0.01 and 100 ng mL−1, with a detection limit as low as 0.005 ng mL−1. Then, we successfully applied this method to measure Ochratoxin A (OTA) in beer samples and the results demonstrated that the method possessed a high sensitivity and good selectivity for the determination of OTA and thus is applicable to the determination of OTA in beer samples. This satisfying result shows that the NaYF4:Yb0.2, Tm0.02 UCNPs we synthesized has a great prospect in multiplexed simultaneous detection.Avidin-UCNPs are abbreviated for avidin modified upconversion nanoparticles.Avidin-MNPs are abbreviated for avidin modified magnetic nanoparticles.OTA is abbreviated for mycotoxin Ochratoxin A.Biotin-OTA Aptamer is 5′-biotin-labeled OTA aptamers.Biotin-cDNA is 5′-biotin-labeled OTA aptamers cDNA.

Microcystin-RR (MC-RR) is a highly acute hepatotoxin produced by cyanobacteria. It is harmful to both humans and the environment. A novel aptamer was identified by the systemic evolution of ligands by exponential enrichment (SELEX) method as a recognition element for determination of MC-RR in aquatic products. The graphene oxide (GO) SELEX strategy was adopted to generate aptamers with high affinity and specificity. Of the 50 aptamer candidates tested, sequence RR-33 was found to display high affinity and selectivity, with a dissociation constant of 45.7 ± 6.8 nM. Aptamer RR-33 therefore was used as the recognition element in a fluorometric assay that proceeds as follows: (1) Biotinylated aptamer RR-33 is immobilized on the streptavidinylated wells of a microtiterplate, and carboxyfluorescein (FAM) labelled complementary DNA is then allowed to hybridize. (2) After removal of excess (unbound) cDNA, sample containing MC-RR is added and incubated at 37 °C for 2 h. (3) Displaced free cDNA is washed away and fluorescence intensity measured at excitation/emission wavelengths of 490/515 nm. The calibration plot is linear in the 0.20 to 2.5 ng·mL−1 concentration range, and the limit of detection is 80 pg·mL−1. The results indicate that the GO-SELEX technology is appropriate for the screening of aptamers against small-molecule toxins. The detection scheme was applied to the determination of MC-RR in (spiked) water, mussel and fish and gave recoveries between 91 and 98 %. The method compares favorably to a known ELISA. Conceivably, this kind of assay is applicable to other toxins for which appropriate aptamers are available.

We report a method for trace detection of bisphenol A (BPA) based on fluorescence resonance energy transfer (FRET) between lanthanide-doped KGdF4 nanoparticles (KGdF4:Tb3+ NPs) as a donor, and gold nanoparticles (AuNPs) that act as an acceptor. The KGdF4:Tb3+ NPs were modified with an aptamer recognizing BPA, and AuNPs were modified with the complementary DNA (cDNA) of the aptamer. The donor–acceptor pair was fabricated by hybridizing the aptamers and their cDNA. Thus, fluorescence of the KGdF4:Tb3+ NPs could be quenched due to the good overlap between the KGdF4:Tb3+ NP fluorescence emission and the AuNP absorption spectrum. However, on addition of BPA, the aptamers preferentially bound to BPA, forming KGdF4:Tb3+ NP–aptamer–BPA complexes. As a result, the FRET was disrupted, and the fluorescence was restored. The recovered fluorescence of the KGdF4:Tb3+ NPs was linearly proportional to the concentration of BPA in the range of 0.5 to 100 ng mL−1, with detection limits as low as 0.16 ng mL−1. The assay was applied to real samples, and the results were consistent with the results obtained using high performance liquid chromatography (HPLC) methods. We presume that this strategy can be extended to the detection of other contaminants by simply substituting the aptamer.

Shigella sonnei is a highly contagious and harmful pathogenic type of entero bacteria that is a significant threat to public health around the world. In this study, aptamers with improved affinity and specificity were screened through twelve selection rounds based on whole-bacterium systematic evolution of ligands by exponential enrichment (SELEX). After cloning and sequencing, thirty sequences were obtained and nine aptamers were selected for affinity and specificity assays. According to the flow cytometric assessment, the dissociation constant (Kd) values for specific binding of the aptamers Sp1 and Sp20 to S. sonnei were 5.980 ± 0.835 nM and 14.32 ± 2.19 nM, respectively. A sensitive sandwich detection method using the dual aptamers Sp1 and Sp20 was developed to recognize S. sonnei. This method achieved a detection limit of 30 cfu mL−1. This study demonstrates that the selected dual aptamers have potential application for S. sonnei detection.

A novel sensitive aptasensor was developed for the quantification of oxytetracycline (OTC) in this study. Artificial aptamer-modified magnetic nanoparticles (aptamer-MNPs) were employed as capture probes, and complementary oligonucleotide-modified upconversion nanoparticles (cDNA-UCNPs) were used as signal probes. Then, the probes were hybridized to form poly-network structure MNPs-UCNPs signal probes. Finally, when the target was introduced, the aptamer combined with the priority target and the signal probe was replaced. The proposed method achieved a linear range between 0.05 and 100 ng mL−1, and the limit of detection (LOD) was as low as 0.036 ng mL−1, benefiting largely from labeling with UCNPs, aptamer affinity and magnetic separation. Then, we successfully applied the method to measure OTC in milk samples and validated it by a commercially available enzyme-linked immunosorbent assay (ELISA) method. The results demonstrated that the method possessed high sensitivity and good selectivity for the determination of OTC and is applicable to the determination of OTC in food samples.

•Aptamers were labeled by Ln3+-doped time-resolved fluorescence nano-probes.•Graphene oxide was used as a resonance energy acceptor of multiplex fluorescence.•Simultaneous detection of SEA, SEB and SEC1 was realized in a homogeneous solution.•The developed aptasensor was investigated in the undiluted milk sample analysis.Food safety is one of the most important public health issues worldwide. Foodborne illnesses caused by Staphylococcus aureus enterotoxins (SEs) commonly occur, affecting both developing and developed countries. In this study, multicolor lanthanide-doped time-resolved fluorescence nanoparticles labeled with aptamers were used as bioprobes, and graphene oxide (GO) was employed as a resonance energy acceptor. Based on the “turn down” strategy, the simultaneous detection of multiplex SEs was realized in a homogeneous solution. Under the optimal conditions, the developed method exhibited high sensitivity and selectivity to three serological types of enterotoxins, including type A, B, C1, with limits of detection below 1 ng mL−1. The application of this bioassay in milk analysis with no sample dilution was also investigated, and the results of recovery rates covered from 92.76% to 114.58%, revealing that the developed method was accurate. Therefore, this detection aptasnesor can be a good candidate for multiplex analysis and screening with simple and effective operations.

We are presenting an aptasensor for the sensitive determination of fumonisin B1 (FB-1) via electrochemical impedance spectroscopy (EIS) and applying aptamer-based biorecognition. A thiolated aptamer for FB-1 was anchored onto the surface of gold nanoparticles (AuNPs) on a glassy carbon electrode. A significant increase in resistance (Ret) is found on interaction with FB-1 in the 0.1 nM to 100 μM concentration range, and the detection limit is as low as 2 pM. The assay was applied to determine FB-1 in spiked maize samples and gave recovery rates ranging from 91 to 105 %. The results demonstrate this method to present new possibilities in the application of aptamers in food safety analysis.

A highly sensitive and specific multiplex method for the simultaneous detection of three pathogenic bacteria was fabricated using multicolor upconversion nanoparticles (UCNPs) as luminescence labels coupled with aptamers as the molecular recognition elements. Multicolor UCNPs were synthesized via doping with various rare-earth ions to obtain well-separated emission peaks. The aptamer sequences were selected using the systematic evolution of ligands by exponential enrichment (SELEX) strategy for Staphylococcus aureus, Vibrio parahemolyticus, and Salmonella typhimurium. When applied in this method, aptamers can be used for the specific recognition of the bacteria from complex mixtures, including those found in real food matrixes. Aptamers and multicolor UCNPs were employed to selectively capture and simultaneously quantify the three target bacteria on the basis of the independent peaks. Under optimal conditions, the correlation between the concentration of three bacteria and the luminescence signal was found to be linear from 50–106 cfu mL–1. Improved by the magnetic separation and concentration effect of Fe3O4 magnetic nanoparticles, the limits of detection of the developed method were found to be 25, 10, and 15 cfu mL–1 for S. aureus, V. parahemolyticus, and S. typhimurium, respectively. The capability of the bioassay in real food samples was also investigated, and the results were consistent with experimental results obtained from plate-counting methods. This proposed method for the detection of various pathogenic bacteria based on multicolor UCNPs has great potential in the application of food safety and multiplex nanosensors.

A high-affinity ssDNA aptamer that specifically binds to T-2 toxin was generated by the systemic evolution of ligands by exponential enrichment (SELEX) procedure assisted by graphene oxide (GO). After 10 rounds of selection against T-2 toxin, a highly enriched ssDNA pool was sequenced and the representative aptamers were subjected to binding assays to evaluate their affinity and specificity. Circular dichroism spectroscopy was also used to study the inherent interaction of T-2 toxin and the preferred aptamer Seq.16, which demonstrated a low dissociation constant (Kd) of 20.8 ± 3.1 nM and excellent selectivity for T-2 toxin. Using the selected aptamer Seq.16 as the recognition element, an aptamer-based fluorescent bioassay was developed for the measurement of T-2 in beer samples with a linear range from 0.5 to 37.5 μM (R2 = 0.988) and a limit of detection (LOD) of 0.4 μM. The results indicate that GO–SELEX technology is appropriate for the screening of aptamers against small-molecule toxins, offering a promising application for aptamer-based biosensors.

In recent years, staphylococcal food poisoning (SFP) caused by the ingestion of food contaminated with Staphylococcus aureus enterotoxins (SEs) has been one of the most common foodborne illnesses worldwide. As a result, rapid, sensitive and reliable detection methods are crucial for routine observations of SEs. However, current detection methods are primarily antibody-dependent, and the development of methods is limited by the preparation and instability of fresh antibodies during testing. In this study, aptamers that bind to Staphylococcus aureus enterotoxin A (SEA) with high affinity and selectivity were generated in vitro by a twelve-round selection process based on magnetic separation technology with a dissociation constant (Kd) value as low as 48.57 ± 6.52 nM. The optimal aptamer A15 was successfully used in the fluorescent bioassay to detect SEA in the food sample with a detection limit of 8.7 × 10−3 μg mL−1. Based on this study, the selected aptamers can be expected to be new molecular recognition elements that can be used in innovative biosensors for SEA detections.

•Nanocomposites of agarose gel embedded with gold nanoparticles were prepared.•Dynamic hot-spots were generated from the agarose gel contraction loss of water.•The nanocomposites were used successfully to detect Raman signal molecules.•Recycling of the nanocomposites could be achieved with washing solution.Agarose gel/gold nanoparticles hybrid was prepared by adding gold nanoparticles to preformed agarose gel. Nanocomposite structures and properties were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), and UV–Vis–NIR absorption spectroscopy. Based on the swelling–contraction characteristics of agarose gel and the adjustable localized surface plasmon resonance (LSPR) of the gold nanoparticles, the nanocomposites were used as surface enhanced Raman scattering (SERS) substrate to detect the Raman signal molecules (NBA, MBA, 1NAT). Results revealed that the porous structure of the agarose gel provided a good carrier for the enrichment of the gold nanoparticles. The gold nanoparticles dynamic hot-spot effect arising from the agarose gel contraction loss of water in the air greatly enhanced the Raman signal. Furthermore, the gel could be cleaned with washing solution and recycling could be achieved for Raman detection.Graphical abstract

Aflatoxins represent an important class of mycotoxins that are known to be mutagenic, carcinogenic, and teratogenic. Here, we report the use of the systematic evolution of ligands by exponential enrichment technology to screen for a DNA aptamer that recognizes Aflatoxin B1 (AFB1) with high affinity and specificity. AFB1 was first attached to magnetic nanoparticles and then incubated with an ssDNA library. After ten rounds of screening and amplification, 30 aptamer sequences were obtained following enrichment. Combined with a homological and structural analysis and affinity and specificity experiments, aptamer sequence 1, possessing the best affinity and specificity toward AFB1, was finally obtained. The dissociation constants value for aptamer sequence 1 was 11.39 nM. And, the specificity experiment results showed the binding between AFB1 aptamer with five other toxins was very week (did not exceed 15 % compared with AFB1). To demonstrate the potential use of this aptamer for quantitative analysis, a fluorescent bioassay with aptamer 1 was developed. The assay showed a wide linear range, with the AFB1 concentration ranging from 50 to 1,500 ng/L and a detection limit of 35 ng/L. Additionally, the spiked recovery experiment of AFB1 in peanut oil sample exhibited a recovery ratio between 94.2 and 101.2 % which showed good accuracy of the proposed aptamer-based bioassay. This fluorescent method represents a powerful tool for use in the detection of AFB1 without complex sample treatments.

•In this study, a gold nanoparticle-based colorimetric aptasensor for Staphylococcus aureus using tyramine signal amplification (TSA) technology was developed.•The detection limit of the developed method was observed to be 9 cfu mL−1.•This developed method could be applied in the detection of Staphylococcus aureus with high affinity and specificity.In this study, a gold nanoparticle-based colorimetric aptasensor for Staphylococcus aureus (S. aureus) using tyramine signal amplification (TSA) technology has been developed. First, the biotinylated aptamer specific for S. aureus was immobilized on the surface of the wells of the microtiter plate via biotin–avidin binding. Then, the target bacteria (S. aureus), biotinylated-aptamer–streptavidin-HRP conjugates, biotinylated tyramine, hydrogen peroxide and avidin–catalase were successively introduced into the wells of the microtiter plate. After that, the existing catalase consumed the hydrogen peroxide. Finally, the freshly prepared gold (III) chloride trihydrate was added, the color of the reaction production would be changed and the absorbance at 550 nm could be measured with a plate reader. Under optimized conditions, there was a linear relationship between the absorbance at 550 nm and the concentration of S. aureus over the range from 10 to 106 cfu mL−1 (with an R² of 0.9947). The limit of the developed method was determined to be 9 cfu mL−1.

•A novel dual fluorescence resonance energy transfer system was fabricated.•Matching the tunable UCNPs emission peaks and the controlled SPR peaks of AuNPs.•The dual FRET was used for simultaneous detection of Pb2+ and Hg2+ in foodstuff.•The detection limits of Pb2+ and Hg2+ were 50 pM and 150 pM, respectively.In this work, we presented a novel dual fluorescence resonance energy transfer (FRET) system for the simultaneous detection of Pb2+ and Hg2+. This system employed two color upconversion nanoparticles (UCNPs) as the donors, and controlled gold nanoparticles (AuNPs) as the acceptors. The two donor–acceptor pairs were fabricated by hybridizing the aptamers and their corresponding complementary DNA. Thus, the green and red upconversion fluorescence could be quenched because of a good overlap between the UCNPs fluorescence emission and the AuNPs absorption spectrum. In the presence of Pb2+ and Hg2+, the aptamers preferred to bind to their corresponding analytes and formed a G-quadruplexes structure for Pb2+ and the hairpin-like structure for Hg2+. As a result, the dual FRET was disrupted, and the green and red upconversion fluorescence was restored. Under optimized experimental conditions, the relative fluorescence intensity increased as the metal ion concentrations were increased, allowing for the quantification of Pb2+ and Hg2+. The relationships between the fluorescence intensity and plotting logarithms of ion concentrations were linear in the range from 0.1 to 100 nM for Pb2+ and 0.5 to 500 nM for Hg2+, and the detection limits of Pb2+ and Hg2+ were 50 pM and 150 pM, respectively. As a practical application, the aptasensor was used to monitor Pb2+ and Hg2+ levels in naturally contaminated samples and human serum samples. Ultimately, this type of dual FRET could be used to detect other metal ions or contaminants in food safety analysis and environment monitoring.

•Two bacteria were simultaneously detected using QD-apt as labels by flow cytometry.•QD-apt were used for recognition and fluorescence detection of two bacteria.•The method was applied successfully for bacteria detection in real samples.A sensitive, specific method for the collection and detection of pathogenic bacteria was demonstrated using quantum dots (QDs) as a fluorescence marker coupled with aptamers as the molecular recognition element by flow cytometry. The aptamer sequences were selected using a bacterium-based SELEX strategy in our laboratory for Vibrio parahaemolyticus and Salmonella typhimurium that, when applied in this method, allows for the specific recognition of the bacteria from complex mixtures including shrimp samples. Aptamer-modified QDs (QD-apt) were employed to selectively capture and simultaneously detect the target bacteria with high sensitivity using the fluorescence of the labeled QDs. The signal intensity is amplified due to the high photostability of QDs nanoparticles, resulting in improved sensitivity over methods using individual dye-labeled probes. This proposed method is promising for the sensitive detection of other pathogenic bacteria in food stuff if suitable aptamers are chosen. The method may also provide another potential platform for the application of aptamer-conjugated QDs in flow cytometry.

In this paper, a high-affinity ssDNA aptamer binding to Salmonella typhimurium was obtained by a whole-bacterium-based Systemic Evolution of Ligands by Exponential Enrichment (SELEX) procedure. After nine rounds of selection with S. typhimurium as the target, a highly enriched oligonucleotide pool was sequenced and then grouped into different families based on primary sequence homology and secondary structure similarity. Eleven sequences from different families were selected for further characterization via flow cytometry analysis. The results showed that the sequence ST2P demonstrates affinity for S. typhimurium much more strongly and specifically than other sequences tested. The estimated Kd value of this particularly promising aptamer was 6.33 ± 0.58 nM. To demonstrate the potential use of the aptamers in the quantitative determination of S. typhimurium, a fluorescent bioassay with the aptamer ST2P was prepared. Under optimal conditions, the correlation between the concentration of S. typhimurium and fluorescent signal was found to be linear within the range of 50–106 cfu/mL (R2 = 0.9957). The limit of detection (LOD) of the developed method was found to be 25 cfu/mL. This work demonstrates that this aptamer could potentially be used to improve the detection of S. typhimurium.

•A novel aptasensor was developed for determination FB1 based on FRET.•UCNPs as donors and AuNPs as quenchers both covalently conjugated with molecular beacons.•FB1 was recognised by FB1 aptamer with high affinity and specificity.•The proposed method was applied to measure FB1 in maize samples successfully.In this work, we presented a new aptasensor for fumonisin B1 (FB1) based on fluorescence resonance energy transfer (FRET) between NaYF4: Yb, Ho upconversion fluorescent nanoparticles (UCNPs) and gold nanoparticles (AuNPs). The quenchers (AuNPs) were attached to the 5′ end of the molecular beacon (MB), and the donors (UCNPs) were attached to the 3′ end of the MB. In the absence of target DNA (DNA complementary to FB1 aptamers), the energy donors and acceptors were placed in close proximity, leading to quenching of the fluorescence of the UCNPs. Due to the combination of FB1 and FB1-specific aptamers, this caused some complementary DNA dissociating from the magnetic nanoparticles (MNPs). In the presence of the complementary DNA, the MBs underwent spontaneous conformational change and caused the UCNPs and AuNPs to detach from each other, resulting in restoration of the upconversion fluorescence. Therefore, the fluorescence of UCNPs was restored in a FB1 concentration-dependent manner, which was the basis of the FB1 quantification. The aptasensors showed a linear relationship from 0.01 to 100 ng mL−1 for FB1 with a detection limit of 0.01 ng mL−1 in an aqueous buffer. As a practical application, the aptasensor was used to monitor FB1 levels in naturally contaminated maize samples. The results were consistent with that of a classic ELISA method, indicating that the UCNPs–FRET aptasensor, which benefited from the near infrared excitation of NaYF4: Yb, Ho UCNPs, was effective for directly sensing FB1 in foodstuff samples without optical interference. This work also created the opportunity to develop aptasensors for other targets using this FRET system.

We highlight a novel fluorescence analysis for sensitive and selective detection of EV-71 and CV-A16 by combining labelling technology based on dual-colour upconversion fluorescence nanoparticles (UCNPs) with magnetic bioseparation and concentration technology based on magnetite nanoparticles (MNPs).

We presented a new aptasensor for mycotoxins, which was based on multiplexed fluorescence resonance energy transfer (FRET) between multicolor upconversion fluorescent nanoparticles (UCNPs) as donors and graphene oxide (GO) as the entire and effective acceptor. BaY0.78F5:Yb0.2, Er0.02 and BaY0.78F5:Yb0.7, Tm0.02 upconversion nanoparticles were synthesized and functionalized, respectively, with immobilized ochratoxin A (OTA)-aptamers and fumonisin B1 (FB1)-aptamers. On the basis of the strong π–π stacking effect between the nucleobases of the aptamers and the sp2 atoms of GO, the aptamer modified-UCNPs can be brought in close proximity to the GO surface. The strong upconversion fluorescence both of BaY0.78F5:Yb0.2, Er0.02 and BaY0.78F5:Yb0.2, Tm0.02 can be completely quenched by the GO, because of a good overlap between the fluorescence emission of multicolor UCNPs and the absorption spectrum of GO. In contrast, in the presence of OTA and FB1, the aptamers preferred to bind to their corresponding mycotoxins, which led to changes in the formation of aptamers, and therefore, aptamer modified-UCNPs were far away from the GO surface. Our study results showed that the fluorescence intensity of BaYF5:Yb Er and BaYF5:Yb Tm were related to the concentration of OTA and FB1. We therefore developed a sensitive and simple platform for the simultaneous detection of OTA and FB1 with multicolor UCNPs and GO as the FRET pair. The aptasensor provided a linear range from 0.05 to 100 ng·mL–1 for OTA and 0.1 to 500 ng·mL–1 for FB1; the detection limit of OTA was 0.02 ng·mL–1 and FB1 was 0.1 ng·mL–1. As a practical application, the aptasensor was used to monitor OTA and FB1 level in naturally contaminated maize samples with the results consistent with that of a classic ELISA method. More importantly, the novel multiplexed FRET was established for the first time based on multiplexed energy donors to the entire energy acceptor; this work was expected to open up a new field of FRET system applications for various targets.

A sensitive luminescent bioassay for the simultaneous detection of Salmonella Typhimurium and Staphylococcus aureus was developed using aptamer-conjugated magnetic nanoparticles (MNPs) for both recognition and concentration elements and using upconversion nanoparticles (UCNPs) as highly sensitive dual-color labels. The bioassay system was fabricated by immobilizing aptamer 1 and aptamer 2 onto the surface of MNPs, which were employed to capture and concentrate S. Typhimurium and S. aureus. NaY0.78F4:Yb0.2,Tm0.02 UCNPs modified aptamer 1 and NaY0.28F4:Yb0.70,Er0.02 UCNPs modified aptamer 2 further were bond onto the captured bacteria surface to form sandwich-type complexes. Under optimal conditions, the correlation between the concentration of S. Typhimurium and the luminescent signal was found to be linear within the range of 101–105 cfu mL−1 (R2 = 0.9964), and the signal was in the range of 101–105 cfu mL−1 (R2 = 0.9936) for S. aureus. The limits of detection of the developed method were found to be 5 and 8 cfu mL−1 for S. Typhimurium and S. aureus, respectively. The ability of the bioassay to detect S. Typhimurium and S. aureus in real water samples was also investigated, and the results were compared to the experimental results from the plate-counting methods. Improved by the magnetic separation and concentration effect of MNPs, the high sensitivity of UCNPs, and the different emission lines of Yb/Er- and Yb/Tm-doped NaYF4 UCNPs excited by a 980 nm laser, the present method performs with both high sensitivity and selectivity for the two different types of bacteria.Graphical abstractFabrication process of biofunctionalized nanoparticles and principle of the performed bioassay. First, aptamer 1 and aptamer 2 were immobilized onto the surface of MNPs and the surface of NaY0.78F4:Yb0.2, Tm0.02 UCNPs, and NaY0.28F4:Yb0.70, Er0.02 UCNPs. Next, S. Typhimurium and S. aureus were added and, due to the highly affinity of aptamer to corresponding bacteria, the aptamer 1-MNPs-S. Typhimurium complex bind NaY0.78F4:Yb0.2, Tm0.02 UCNPs modified aptamer 1, and the aptamer 2-MNPs-S. aureus bind NaY0.28F4:Yb0.70, Er0.02 UCNPs modified aptamer 2. Finally, the luminescent signal was effectively amplified with the help of a magnetic field.Highlights► Simultaneous detection of two kind of bacteria. ► Bacteria-specific aptamer recognition. ► Dual-color upconversion luminescent nanoparticles labeling. ► Aptamer conjugated-magnetic nanoparticles-based separation and concentration.

A whole-bacterium systemic evolution of ligands by exponential enrichment (SELEX) method was applied to a combinatorial library of FAM-labeled single-stranded DNA molecules to identify DNA aptamers demonstrating specific binding to Vibrio parahemolyticus. FAM-labeled aptamer sequences with high binding affinity to V. parahemolyticus were identified by flow cytometric analysis. Aptamer A3P, which showed a particularly high binding affinity in preliminary studies, was chosen for further characterization. This aptamer displayed a dissociation constant (Kd) of 16.88 ± 1.92 nM. Binding assays to assess the specificity of aptamer A3P showed a high binding affinity (76%) for V. parahemolyticus and a low apparent binding affinity (4%) for other bacteria. Whole-bacterium SELEX is a promising technique for the design of aptamer-based molecular probes for microbial pathogens that does not require the labor-intensive steps of isolating and purifying complex markers or targets.

A novel magnetic nanobead-based immunoassay was developed for the quantification of carcinoembryonic antigen (CEA) in human serum in this study. Amine-functionalized Fe3O4 magnetic nanoparticles (MNPs) were conjugated with capture anti-CEA antibodies and amine-functionalized NaY0.78F4:Yb0.20, Ho0.02 upconversion nanoparticles (UCNPs) were synthesized and conjugated with detection anti-CEA antibodies, respectively. Based on a sandwich-type immunoassay format, the detection limit for CEA under optimal conditions was as low as 2.5 pg/mL, and the linear range of CEA detection was from 2.5 × 10−12 to 1 × 10−8 g/mL (I = 406.19 log X + 428.81) with a correlation coefficient equal to 0.9987. The established method was successfully applied to measure CEA in human serum samples and more sensitive than a commercially available chemiluminescence method. The precision expressed as the relative standard deviation of CEA detection was equal to 5.19% (1 ng/mL) or 4.36% (5 pg/mL), indicating that the developed method exhibited good reproducibility. The results demonstrate that the method offers potential advantages of sensitivity and good reproducibility for the determination of CEA, and is applicable to the determination of CEA in serum samples.

A sensitive luminescent bioassay for the detection of ochratoxin A (OTA), a small molecular mycotoxin, was developed using aptamer-conjugated magnetic nanoparticles (MNPs) as the recognition and concentration element and upconversion nanoparticles (UCNPs) as highly sensitive labels. The bioassay system was fabricated by immobilizing aptamer DNA 1 sequence onto the surface of Fe3O4 MNPs, which were implemented to capture and concentrate OTA from bulk samples. The aptamer DNA 1 sequence then hybridized with UCNPs modified with DNA 2 sequence, which could dissociate from DNA 1 and result in a decreased luminescent signal when aptamer DNA 1 recognized and bound to target OTA. Under the optimal conditions, the decreased luminescent intensity (ΔI) is proportional to the concentration of OTA in the range of 1 × 10−13 to 1 × 10−9 g mL−1 with a detection limit of 1 × 10−13 g mL−1. The proposed method then was successfully applied to measure OTA in naturally contaminated maize samples and validated by a commercially available enzyme-linked immunosorbent assay (ELISA) method. Benefiting from the magnetic separation and concentration effect of MNPs, the high sensitivity of UCNPs, as well as the selectivity and stability of the aptamer, the present upconversion luminescent bioassay offers a promising approach for the screening of small molecular mycotoxins because it is simple, rapid, highly sensitive, specific, does not require sample pre-concentration and lacks interference from autofluorescence of other biomolecules.

A sensitive and specific method for detecting foodborne pathogen, with Salmonella as model analyte, has been developed basing upon DNA hybridization and fluorescent bioconjugated nanoparticles probe. The indicator probe was designed through bioconjugating the Salmonella   sequence-specific oligonucleotide with the fluorescent Ru(bpy)32+-doped silica nanoparticles that were prepared by a microemulsion method. Through a sandwich-type DNA hybridization procedure, the target Salmonella DNA was captured and the indicator probe was assembled onto solid matrix so that the Salmonella DNA can be measured by the fluorescent signals of assembled indicator probes. Under optimal conditions, the calibration graph for detection of target Salmonella DNA is linear over the range of 10–10,000 fmol/L with a detection limit of 3 fmol/L. The proposed method was also applied to detect Salmonella in mixed bacteria sample. It gives the detection limit of 30 cfu/mL. The method offers a potential resolution for simple, rapid and sensitive detection of foodborne pathogens in food, clinical and environmental samples.

A novel analytical method for the detection of Ochratoxin A (OTA) is established based on the aptamer recognition and fluorescent probe technology. The present method is developed based on the fact that when the immobilized aptamer bonds to the target OTA, it can induce the conformation change of aptamer and result in the dissociation of the FAM-tagged complementary DNA chain from aptamer, finally leading to the fluorescent signal change. Based on it, OTA can be quantified. All the condition factors affecting the performance of the present method are investigated. The results show if the avidin concentration coated on the microplate is 25 mg L−1, the aptamer concentration is 50 nM, the FAM-tagged complementary DNA chain concentration is 150 nM, the binding buffer solution is chosen as 10 mM HEPES, pH 7.0 (contains 120 mM NaCl, 5 mM KCl, 20 mM MgCl2, and 20 mM CaCl2), and the binding reaction is conducted at 45°C for 40 min, the optimal analytical performance can be achieved for the present work. Under the optimal conditions, the linear range for the OTA concentration detection is 2.0 × 10−8-1.0 × 10−5 g L−1 with a detection limit of 1 × 10−8 g L−1. The RSD is 2.6% for 11 parallel measurements of 1 × 10−6 g L−1 OTA. Meanwhile, the present method is highly selective for OTA and easy to be operated. It has been successfully applied to measure OTA content in real samples.

•A DNA aptamer targeted against Shigella dysenteriae was selected and identified.•This aptamer bound to S. dysenteriae tightly with a Kd value of 23.47 ± 2.48 nM.•The selected aptamer could capture S. dysenteriae from complex sample matrices.•The selected aptamer could be applied to detection of S. dysenteriae in food.To identify DNA aptamers demonstrating binding specificity for Shigella dysenteriae, a whole-bacterium Systemic Evolution of Ligands by Exponential enrichment (SELEX) method was applied to a combinatorial library of single-stranded DNA (ssDNA) molecules. After several rounds of selection using S. dysenteriae as the target, the highly enriched oligonucleotide pool was sequenced and then grouped into different families based on primary sequence homologies and similarities in the secondary structures. Aptamer S 1, which showed particularly high binding affinity in preliminary studies, was chosen for further characterisation. This aptamer displayed a dissociation constant (Kd value) of 23.47 ± 2.48 nM. Binding assays to assess the specificity of aptamer S 1 showed high binding affinity for S. dysenteriae and low apparent binding affinity for other bacteria. The ssDNA aptamers generated may serve as a new type of molecular probe for microbial pathogens, as it has the potential to overcome the tedious isolation and purification requirements for complex targets.

•An aptamer-based electrochemical biosensor for Salmonella detection was constructed.•Graphene oxide and gold nanoparticles were modified on the glassy carbon electrode to enhance the electron transfer properties.•The biosensor method for Salmonella detection could be realized as low as 3 cfu/mL.Salmonella is one of the most common causes of food-associated disease. An electrochemical biosensor was developed for Salmonella detection using a Salmonella-specific recognition aptamer. The biosensor was based on a glassy carbon electrode modified with graphene oxide and gold nanoparticles. Then, the aptamer ssDNA sequence could be linked to the electrode. Each assembly step was accompanied by changes to the electrochemical parameters. After incubation of the modified electrode with Salmonella, the electrochemical properties between the electrode and the electrolyte changed accordingly. The electrochemical impedance spectrum was measured to quantify the Salmonella. The results revealed that, when more Salmonella were added to the reaction system, the current between the electrode and electrolyte decreased; in other words, the impendence gradually increased. A detection limit as low as 3 cfu/mL was obtained. This novel method is specific and fast, and it has the potential for real sample detection.Download full-size image

•Aptamers that recognize RAC were enriched using a target free immobilization -SELEX approach.•Aptamer RAC-6 with Kd value of 54.22 ± 8.02 nM was obtained.•A detection method for RAC was successfully developed based on the aptasensor.An improved SELEX technique was developed for selecting aptamers against ractopamine (RAC) by immobilizing ssDNA library on the magnetic beads. After sixteen selection rounds, a highly enriched ssDNA pool was sequenced and nine families were grouped according to their homology and secondary structures analysis. One representative aptamer candidate from each family was picked out for binding affinity identification by graphene oxide (GO) adsorption platform. The aptamer RAC-6 was demonstrated as the optimal aptamer with high specificity and dissociation constant (Kd) value of 54.22 ± 8.02 nM. To prove the potential application of aptamer RAC-6 in the quantitative determination of RAC, a fluorescent bioassay with aptamer RAC-6 was developed. The linear range for RAC was from 0.10 ng/mL to 100 ng/mL and the limit of detection was as low as 0.04 ng/mL. Furthermore, the method was validated for the analysis of RAC spiked real samples, and the recoveries were between 82.57% and 104.65%.

•Co2+ enhanced ABEI functional flowerlike gold nanoparticles (Co2+/ABEI-AuNFs) was first used as chemiluminescent donor.•Rolling circle amplification (RCA) technique was also applied in the WS2 nanosheet based CRET system for the first time.•The improved WS2 nanosheet based CRET platform can overcome the limitation that only DNA or RNA can be detected and expand the detection scope.•A steady-state CRET aptasensor based on P-Iodophenol (PIP) and RCA was fabricated to detect S. aureus with high sensitivity and specificity.A chemiluminescence resonance energy transfer aptasensor was fabricated for the detection of Staphylococcus aureus (S. aureus) with Co2+ enhanced N-(aminobutyl)-N-(ethylisoluminol) (ABEI) functional flowerlike gold nanoparticles (Co2+/ABEI-AuNFs) as donor and WS2 nanosheet as acceptor. In the presence of S. aureus, rolling circle amplification (RCA) can be started. Partially complementary sequence of RCA product functional ABEI-AuNFs (cDNA-ABEI-AuNFs) were then annealed to multiple sites of the RCA product to form duplex complex. This complex is less adsorbed onto the WS2 nanosheet, thus attenuating the quenching of ABEI-AuNFs chemiluminescence by WS2 nanosheet. In the absence of target S. aureus (and hence the absence of RCA and duplex formation), the free cDNA-ABEI-AuNFs is completely adsorbed onto the WS2 nanosheet and chemiluminescence quenching ensues. Under optimal conditions, the logarithmic correlation between the concentration of S. aureus and the CL signal was found to be linear within the range of 50 cfu/mL to 1.5 × 105 cfu/mL (R2 = 0.9913). The limits of detection of the developed method were found to be 15 cfu/mL for S. aureus. The selectivity and the capability of the biosensor in meat samples were also studied. Therefore, this simple and easy operation method can be used to detect S. aureus with high sensitivity and specificity.

•A colorimetric aptasensor was fabricated for the detection of S. typhimurium.•Aptamers play a role for the protection of GNPs from aggregation toward NaCl.•Aptamers preferably combined to S. typhimurium and broke the protection layer.•This method is simple, rapid and with a detection limit as low as 56 cfu/mL.A simple, fast and convenient colorimetric aptasensor was fabricated for the detection of Salmonella typhimurium (S. typhimurium) which was based on the color change effect of gold nanoparticles (GNPs). S. typhimurium is one of the most common causes of food-associated disease. Aptamers with specific recognition toward S. typhimurium was modified to the surface of prepared GNPs. They play a role for the protection of GNPs from aggregation toward high concentrations of NaCl. With the addition of S. typhimurium, aptamers preferably combined to S. typhimurium and the protection effect was broken. With more S. typhimurium, more aptamers detached from GNPs. In such a situation, the exposed GNPs would aggregated to some extent with the addition of NaCl. The color changed from red, purple to blue which could be characterized by UV–Vis spectrophotometer. The absorbance spectra of GNPs redshifted constantly and the intensity ratio of A700/A521 changed regularly. This could be calculated for the basis of quantitative detection of S. typhimurium from 102 cfu/mL to 107 cfu/mL. The obtained linear correlation equation was y = 0.1946x–0.2800 (R2 = 0.9939) with a detection limit as low as 56 cfu/mL. This method is simple and rapid, results in high sensitivity and specificity, and can be used to detect actual samples.

•NaYF4:Yb,Er@NaYF4 upconversion nanoparticles with enhanced luminescence as luminophores were synthesized.•To the best of our knowledge, this is the first time to detect OTA using energy transfer from enhanced luminescence of CS-UCNPs to GO.•This aptamer-based platform might be a promising strategy for a variety of sensing applications.We developed an ultrasensitive luminescence resonance energy transfer (LRET) aptasensor for Ochratoxin A (OTA) detection, using core/shell upconversion nanoparticles (CS-UCNPs) as luminophores. The OTA aptamer was tagged to CS-UCNPs as energy donor and graphene oxide (GO) acted as energy acceptor. The π-π stacking interaction between the aptamer and GO brought CS-UCNPs and GO in close proximity hence initiated the LRET process resulting in quenching of CS-UCNPs luminescence. A linear calibration was obtained between the luminescence intensity and the logarithm of OTA concentration in the range from 0.001 ng mL−1 to 250 ng mL−1, with a detection limit of 0.001 ng mL−1. The aptasensor showed good specificity towards OTA in beer samples. The ultrahigh sensitivity and pronounced robustness in beer sample matrix suggested promising prospect of the aptasensor inpractical applications.

We report a method for trace detection of bisphenol A (BPA) based on fluorescence resonance energy transfer (FRET) between lanthanide-doped KGdF4 nanoparticles (KGdF4:Tb3+ NPs) as a donor, and gold nanoparticles (AuNPs) that act as an acceptor. The KGdF4:Tb3+ NPs were modified with an aptamer recognizing BPA, and AuNPs were modified with the complementary DNA (cDNA) of the aptamer. The donor–acceptor pair was fabricated by hybridizing the aptamers and their cDNA. Thus, fluorescence of the KGdF4:Tb3+ NPs could be quenched due to the good overlap between the KGdF4:Tb3+ NP fluorescence emission and the AuNP absorption spectrum. However, on addition of BPA, the aptamers preferentially bound to BPA, forming KGdF4:Tb3+ NP–aptamer–BPA complexes. As a result, the FRET was disrupted, and the fluorescence was restored. The recovered fluorescence of the KGdF4:Tb3+ NPs was linearly proportional to the concentration of BPA in the range of 0.5 to 100 ng mL−1, with detection limits as low as 0.16 ng mL−1. The assay was applied to real samples, and the results were consistent with the results obtained using high performance liquid chromatography (HPLC) methods. We presume that this strategy can be extended to the detection of other contaminants by simply substituting the aptamer.

We highlight a novel fluorescence analysis for sensitive and selective detection of EV-71 and CV-A16 by combining labelling technology based on dual-colour upconversion fluorescence nanoparticles (UCNPs) with magnetic bioseparation and concentration technology based on magnetite nanoparticles (MNPs).

In recent years, staphylococcal food poisoning (SFP) caused by the ingestion of food contaminated with Staphylococcus aureus enterotoxins (SEs) has been one of the most common foodborne illnesses worldwide. As a result, rapid, sensitive and reliable detection methods are crucial for routine observations of SEs. However, current detection methods are primarily antibody-dependent, and the development of methods is limited by the preparation and instability of fresh antibodies during testing. In this study, aptamers that bind to Staphylococcus aureus enterotoxin A (SEA) with high affinity and selectivity were generated in vitro by a twelve-round selection process based on magnetic separation technology with a dissociation constant (Kd) value as low as 48.57 ± 6.52 nM. The optimal aptamer A15 was successfully used in the fluorescent bioassay to detect SEA in the food sample with a detection limit of 8.7 × 10−3 μg mL−1. Based on this study, the selected aptamers can be expected to be new molecular recognition elements that can be used in innovative biosensors for SEA detections.