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Shiga toxin type II (Stx2), the major virulence component of enterohemorrhagic Escherichia coli, is strongly associated with the life-threatening hemolytic uremic syndrome thus posing a substantial risk to food safety and human health. In this work, a dual-mode aptasensor with colorimetric and surface-enhanced Raman scattering was developed for Stx2 specific detection based on noble metal nanoparticles and Raman reporter loaded metal-organic framework (Mn/Fe-MIL(53)@AuNSs-MBA). The Mn/Fe-MIL(53)@AuNSs could catalyze the H 2 O 2 -mediated oxidation of 3,3',5,5'-tetramethylbenzidine (TMB), thereby enabling visual detection. Meanwhile, the SERS signal from MBA can be enhanced by the decorated AuNSs. Under optimal conditions, a linear range of 0.05-500 ng/mL with limit of detection (LOD) of 26 pg/mL was achieved in colorimetric mode and a linear range of 5-1000 ng/mL with LOD of 0.82 ng/mL in SERS mode, in which the dual-mode results complement each other, widening the linear range, increasing the accuracy and reliability of the detection. The method was further applied to the detection of Stx2 in milk with average recovery of 101.1 %, demonstrating its superior potential for bacterial toxin monitoring., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

Herein, a SiO 2 @Ag NPs core/shell nanoparticles were synthesized to fabricate a surface-enhanced Raman spectroscopy (SERS) sensor for the simultaneous determination of histamine (HIS) and tyramine (TYR) based on specific aptamer recognition and ratiometric strategy. SiO 2 @Ag NPs with 4-thiosaminophenol (4-ATP) and Nile blue A (NBA) molecules were used as an internal standard (IS) and labeled with aptamers corresponding to HIS and TYR, respectively. Raman reporter molecules ROX and Cy5 labeled complementary DNA (cDNA) were then hybridized with aptamers to form rigid double-stranded DNA. After the HIS and TYR were captured by their aptamers, resulting in the dissociation of cDNA and separated from the SERS substrate. Therefore, the SERS signal intensity at 1503 cm -1 of ROX and 1358 cm -1 of Cy5 tagged on the terminal of cDNA decreased with the concentration of HIS and TYR increasing, while the SERS signal intensity at 1079 cm -1 of 4-APT and 592 cm -1 of NBA on the substrate remain stable. Thus, the concentrations of HIS and TYR can be determined by the I 1503 /I 1079 and I 1358 /I 592 values, respectively. This sensing strategy achieves a lower detection limit of 0.2 ng/mL for HIS and 0.05 ng/mL for TYR, respectively, demonstrating promising applications in sensitive detection of BAs in animal-derived foodstuff., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier B.V. All rights reserved.)

Chlorpromazine is a phenothiazine representative drug that can be used to anesthetize and calm animals. However, chlorpromazine excess may lead to residual persistence in edible tissues, which is potentially harmful to human health and animal production. In this work, high affinity and specificity aptamers against chlorpromazine were screened out based on Capture-SELEX. After ten rounds of screening, the candidate aptamers were obtained. The optimal aptamer of CHL-3 was obtained by isothermal titration calorimetry (ITC) and SYBR Green I (SGI) fluorescence-competition methods. The Kd value of CHL-3 was 69.8 ± 9.81 nM. Subsequently, the Uio-66-NH 2 material was prepared, filled with rhodamine 6G (Rho 6G) dye into the pore, and sealed with CHL-3, and fluorescence probes were obtained. The ratiometric fluorescence detection method was established to detect the concentration of chlorpromazine. A linear relationship was obtained in a range of 1-100 nM, with a lower detection limit of 0.67 nM. Meanwhile, a good recovery was shown in spiked food samples, such as eggs and milk. These results indicate that the constructed ratiometric fluorescence strategy can be successfully applied in food detection., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Levamisole (LEV) is a veterinary drug that often remains in animal food. Consuming products containing high levels of LEV will cause a series of harmful reactions to human health. This work describes the Capture-SELEX (Capture-systematic evolution of ligands by exponential enrichment) screening strategy of LEV aptamers, using streptavidin modified agarose beads as a solid phase medium to separate target-bound and unbound ssDNA. The affinity and specificity of candidate aptamers were determined by SYBR Green I (SGI) dye and isothermal titration calorimetry (ITC), in which LEV-5 showed good binding affinity and specificity, and the dissociation constant was 66.15 ± 11.86 nM. Circular dichroism (CD) was used to characterize aptamer conformational changes before and after target binding, including increased helicity and enhanced base stacking. To evaluate whether this aptamer can be used for LEV detection, a colorimetric-surface-enhanced Raman spectroscopy (colorimetric-SERS) dual-mode aptasensor was constructed based on the peroxidase-like activity and SERS effect of AuNPs/Cu-TCPP(Fe) nanosheets. The detection limits of this dual-mode aptasensor for LEV were 5 nM and 1.12 nM, respectively. This aptamer-based method was further successfully used to detect LEV in milk, with recoveries ranging from 94.95% to 111.2%, providing a potential application for the detection of harmful substances in food., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Weissella viridescens is a spoilage bacterium commonly found in low-temperature meat products. In this work, after fifteen rounds including three counter selection rounds of whole-cell systemic evolution of ligands by exponential enrichment (SELEX) in vitro, a novel aptamer L3 that can specifically recognize W. viridescens was obtained with a dissociation constant (K d ) value of 68.25 ± 5.32 nM. The sequence of aptamer L3 was optimized by truncation and a new aptamer sequence TL43 was obtained with a lower K d value of 32.11 ± 3.01 nM. Finally, a simple and rapid fluorescence polarization (FP) platform was constructed to detect W. viridescens, in which FAM-labeled complementary sequence (FAM-cDNA) was employed to generate FP signal and streptavidin was used to amplify FP signal. In the presence of target bacteria, FP value decreased owning to the dissociation of FAM-cDNA from streptavidin/biotin-TL43/FAM-cDNA complex. Under optimal conditions, the concentration of W. viridescens and FP value displayed a good linear relationship with the detection range from 10 2 to 10 6  cfu/mL. Moreover, the designed detection system had a good recovery rate of 90.6%-107.7% in smoked ham samples compared with classical plate counting method, indicating the great potential of the selected and truncated aptamer in practical biosensing applications., (Copyright © 2022 Elsevier B.V. All rights reserved.)

We designed a SERS-based method to detect β-lactoglobulin (β-Lg), a major allergen of milk, utilizing aptamers to specifically anchor β-Lg. The Au-Ag nanourchins with excellent Raman enhancement effects were prepared and modified with a β-Lg aptamer as the capture substrate. By taking advantage of the hybridization of aptamer and Raman reporter molecule (6-Carboxyl-X-Rhodamine: ROX)-labeled complementary DNA (cDNA), when ROX is close to Au-Ag nanourchins, the SERS signal is enhanced. In the presence of β-Lg, aptamer binding to β-Lg induces the dissociation of ROX-cDNA from Au-Ag nanourchins, thereby decreasing the SERS signal. Under optimal conditions, the present bioassay provides a wide detection range of 10 ng/mL to 1000 ng/mL with a detection limit of 0.07 ng/mL. In addition, the established SERS sensor can selectively and accurately identify β-Lg with recovery rates of 93.25-107.0% in milk samples. It provides great potential as a sensitive and reliable detection method against the growing threat of allergens., (Copyright © 2022 Elsevier B.V. All rights reserved.)

In this study, the original chloramphenicol aptamer containing 80 bases was truncated to 30 bases with high affinity by the SYBR Green I assay. It was found that the ionic strength and type affect the recognition of aptamers, especially magnesium ion played a vital role in the binding process. Furthermore, the binding performance of aptamer, including binding mode, key binding sites and conformational changes were further investigated by circular dichroism spectroscopy, UV-vis absorption spectrum and molecular docking. Based on these research data, we inferred that chloramphenicol bound to the minor groove region in the aptamer double helix. Finally, the optimized aptamer LLR10 was used to develop a novel label free fluorescence polarization assay to detect chloramphenicol within SYBR Green I as the source of fluorescence polarization signal. Under optimal conditions, the designed method showed a linear detection range of 0.1-10 nM with a detection limit of 0.06 nM. Additionally, the aptasensor exhibited a high accuracy to the detection of chloramphenicol in milk samples with a recovery rate from 93.7% to 98.4%. Therefore, the developed label free fluorescence polarization aptasensor provides a new idea for the rapid, reliable and sensitive detection of chloramphenicol, which can be applied to food safety control., (Copyright © 2021. Published by Elsevier B.V.)

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) (13nm and 80nm 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 13nm AuNPs. After the exposure of OTC, the aptamer sequence was preferentially combined with OTC and partially dehybridized with its complementary sequence which led the 13nm AuNPs to get more closer to the 80nm 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 -4.60×10 2 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., (Copyright © 2017 Elsevier B.V. All rights reserved.)

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 Fe 3 O 4 magnetic nanoparticles (MNPs) as capture probes, aptamer as recognition molecules, and Co 2+ enhanced N‑(aminobutyl)-N-(ethylisoluminol) (ABEI) functional flowerlike gold nanoparticles (AuNFs) and complementary strand (cDNA) complex (Co 2+ /ABEI-AuNFs-cDNA) as signal probes. And P-Iodophenol (PIP) was also added to form a typical ABEI- AuNFs-PIP-H 2 O 2 steady-state CL system. By virtue of Fe 3 O 4 MNPs based solid-phase RCA strategy, S. typhimurium can be first captured by the aptamer immobilized on the surface of Fe 3 O 4 MNPs then complex with RCA products to form a sandwich complex. Co 2+ /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 32cfumL -1 to 3.2×10 6 cfumL -1 (R 2 =0.9921). The limits of detection of the developed method were found to be 10cfumL -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., (Copyright © 2016 Elsevier B.V. All rights reserved.)

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 804nm under 980nm excitation. The emission peak at 804nm was well-separated from the emission peaks of UCNPs we have reported at 477nm, 542nm, and 660nm. 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 100ngmL(-1), with a detection limit as low as 0.005ngmL(-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., (Copyright © 2016 Elsevier B.V. All rights reserved.)

In this work, we presented a novel dual fluorescence resonance energy transfer (FRET) system for the simultaneous detection of Pb(2+) and Hg(2+). 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 Pb(2+) and Hg(2+), the aptamers preferred to bind to their corresponding analytes and formed a G-quadruplexes structure for Pb(2+) and the hairpin-like structure for Hg(2+). 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 Pb(2+) and Hg(2+). The relationships between the fluorescence intensity and plotting logarithms of ion concentrations were linear in the range from 0.1 to 100 nM for Pb(2+) and 0.5 to 500 nM for Hg(2+), and the detection limits of Pb(2+) and Hg(2+) were 50 pM and 150 pM, respectively. As a practical application, the aptasensor was used to monitor Pb(2+) and Hg(2+) 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., (Copyright © 2014 Elsevier B.V. All rights reserved.)

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 10(6) cfu mL(-1) (with an R² of 0.9947). The limit of the developed method was determined to be 9 cfu mL(-1)., (Copyright © 2014 Elsevier B.V. All rights reserved.)

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., (Copyright © 2013 Elsevier B.V. All rights reserved.)