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Surfactants that are organized self-assembly to form micelles have been widely utilized for detection of several analytes. However, the surfactants only provide a hydrophobic space, which does not involve the molecular recognition process. Here, we report a surfactant-involved colorimetric assay for visual and sensitive detection of fentanyl (FTN), a third-generation new psychoactive substance. It is found that sodium dodecyl sulfate (SDS) simultaneously enhance the halogen-bonding interaction between Rose Bengal (RB) as the probe and FTN as well as stabilize the RB-FTN complex. This molecular recognition induces the intermolecular charge transfer, generating a significant redshift in the absorption band of RB and accompanying a distinct color change from red to purple. This assay possesses an ultrahigh response speed (within 1 min), and the limit of detection is calculated to be as low as 0.1 mg·L−1. It also shows good selectivity and application potential. The recovery rates of real samples are between 92.5% and 110%, suggesting that it is suitable for rapid and accurate analysis of food samples such as mineral water, orange juice and cocktail. The current strategy can be further exploited in surfactant enhanced detection applications for other substances. • A new surfactant-involved colorimetric detection strategy is proposed for visual detection of fentanyl (FTN). • The limit of detection of this assay for FTN is down to 0.1 mg·L−1. • This assay allows for accurate analysis of FTN in food samples within 1 min. [ABSTRACT FROM AUTHOR]

Okadaic acid (OA) is a major marine toxin that can cause diarrheic shellfish poisoning (DSP). Because of food safety concerns, simple and reliable field assays are in high demand. Herein, a highly sensitive fluorescent assay for OA in seafood was reported. For this purpose, a duplexed aptamer (DA) based on a conformational change upon binding OA was designed and immobilized on the surface of streptavidin-conjugated magnetic beads (SMBs). With the addition of OA, the DAs melted, and ss-aptamers were released into the solution. After magnetic separation, a terminal deoxynucleotidyl transferase (TdT)-mediated isothermal amplification system was formed via a free ss-aptamer acting as a template. This product with a poly(thymine) tail was directly added to a fluorescent copper nanoparticle (CuNP) formation system, and the ultralong consecutive T-rich sequence provided deposition sites for copper. Finally, the OA concentration was determined by recording fluorescence spectra and calculating the intensity change. This duplexed aptamer-isothermal amplification-based nucleic acid CuNP (DAIA-CuNP) sensor can achieve ultrahigh-sensitivity detection of OA compared to LC-MS and electrochemical methods. This DAIA-CuNP sensor can detect OA with a limit of detection (LOD) of 1.1 ng/L and a good linear range from 1.0 ng/L to 50.0 μg/L in shellfish extract. Additionally, this method is expected to be compatible with a handheld fluorescence reader and can meet field detection needs. • A simple, sensitive, and novel DAIA-CuNPs sensor was firstly proposed for specifically detecting OA in seafood. • A specific duplexed aptamer based on conformational change for OA was designed. • Single stranded T-rich nucleic acid CuNPs signal output system based on the TdT amplification to improve detection sensitivity. • DAIA-CuNPs sensor had a low LOD and wide linear range for OA. [ABSTRACT FROM AUTHOR]

Highlights • Electrostatic self-assembly of CDs@MnO 2 is used to develop a new fluorescent immunoassay. • The fluorescent immunoassay has significantly high sensitivity for the detection of amantadine in chicken.. • The alkaline phosphatase-dependent fluorescent immunoassay has a great potential in food analysis. Abstract Fluorescence immunoassays are rapid, convenient and cost-effective for the sensitive quantitation of chemical contaminants in foodstuff. In this study, a competitive fluorescence ELISA was developed for the sensitive detection of amantadine (AMD) based on the alkaline phosphatase (ALP)-triggered fluorescence "turn-on" signals. As a fluorescence substrate, carbon dots (CDs) were adsorbed onto the surface of the MnO 2 nanosheets (NSs) and formed a nanoassembly of p-CDs@MnO 2 NSs which results in the fluorescence quench of CDs. The ALP labelled on antibody could catalyze the hydrolysis of the 2-phosphoascorbic acid into ascorbic acid. The latter could then reduce and decompose the MnO 2 NSs, which was accompanied by the release of CDs from the surface of MnO 2 NSs and led to the fluorescence recovery of CDs. The change of the fluorescence intensity is related to the concentration of AMD in solution and thus could be applied to detect AMD in an ALP-based ELISA system. The fluorescent ELISA showed a linear detection for AMD in the range of 0.048 ng mL−1 to 1.1 ng mL−1 with a detection limit (LOD) of 0.035 ng mL−1. The novel fluorescent ELISA shows potential for the highly sensitive detection of AMD and other analytes in food analysis. [ABSTRACT FROM AUTHOR]

Swab sampling for the trace surface-enhanced Raman scattering (SERS) analysis of an aromatic dye (e.g., malachite green, MG) residue in fruits as well as fingerprints is promising due to its practical utility and efficiency in food security and forensic science. However, the durability and recyclability of the SERS substrates pose an enormous challenge. In this study, a novel flexible film was constructed by embedding a commercial Ag nanowire suspension into a polydimethylsiloxane film (Ag NWs@PDMS), which simultaneously exhibits SERS activity, durability and recyclability. High SERS performance was still maintained, even against 20 times stretchability, corrosion by HNO 3 , destruction by ultrasonication and a broad working temperature of −20 ℃ to 80 ℃. Excellent recyclability for MG sensing was achieved in ten cycles. Ag NWs@PDMS was successfully used for the quantitative detection of MG in juices of fruits (such as apple and pear) by drop dripping, with a limit of detection of 10 nM and good anti-interference. Meanwhile, the sensitive detection of the MG residue (only 3 ng/cm2) on fruits was enabled by the on-site surface swabbing by recycling for five cycles. Portable detection of the MG residue was further achieved from the 10th fingerprint after successively touching a dye drop onto the functional film combined with a portable Raman spectrometer. [Display omitted] • Ag nanowires were embedded into PDMS as a flexible and durable SERS substrate. • The prominent SERS performance included recyclability, stretchability and anti-corrosion. • The substrate was applied for surface swabbing detection of malachite green residue on fruit. • Portable SERS detection of MG residue was achieved in successive 10 fingerprints. [ABSTRACT FROM AUTHOR]