•We proposed a simple and fast fluorescence method to detect proteins by loop DNA.•The DNA can form a self-complementary structure with two stem-loop structures.•The target protein can bind to biotin protecting DNA from cleavage by exonuclease.•The DNA sequence could be randomly coded with part self-hybridization.•This method is a signal off-on fluorescent strategy.A novel label-free turn-on fluorescence biosensor for the determination of streptavidin (SA) was proposed. Using terminal protection of small molecule-linked DNA chimeras, which can protect DNA from degradation by various exonucleases when the small molecule moieties are bound to their protein target, we designed a loop probe, where the 3′-end was modified with biotin to resist digestion by exonucleases in the presence of target SA. Coupled with an intercalating dye, SYBR Green I, strong enhancement of the fluorescence signals was obtained compared with that in the absence of SA. A linear correlation equation was obtained for SA from 0 to 200 nM with a limit detection of 0.4 nM. This strategy holds great promise for practical applications with good specificity and sensitivity.

By coupling thin-film microextraction (TFME) with surface-enhanced Raman scattering (SERS), a facile method was developed for the determination of sulfur dioxide (SO2), the most effective food additive in winemaking technology. The TFME substrate was made by free settling of sea urchin-like ZnO nanomaterials on a glass sheet. The headspace sampling (HS) procedure for SO2 was performed in a simple homemade device, and then the SO2 was determined using SERS after uniformly dropping or spraying a SERS-active substrate (gold nanoparticles, AuNPs) onto the surface of the TFME substrate. A reproducible and strong SERS response of the SO2 absorbed onto the ZnO substrate was obtained. After condition optimization, the SERS signal intensity at a shift of 600 cm–1 and the SO2 concentration showed a good linearity in the range of 1–200 μg/mL, and the linear correlation coefficient was 0.992. The detection limit for SO2 was found to be 0.1 μg/mL. The HS–TFME–SERS method was applied for the determination of SO2 in wine, and the results obtained agreed very well with those obtained using the traditional distillation and titration method. Analysis of variance and Student t test show that there is no significant difference between the two methods, indicating that the newly developed method is fast, convenient, sensitive and has selective characteristics in the determination of SO2 in wine.

A novel technique combining solid-phase extraction and surface-enhanced Raman spectroscopy has been developed using a home-made test strip as the solid phase apparatus and detecting platform for surface-enhanced Raman spectroscopy. Single wall carbon nanotubes (SWCNTs) were functionalized with oxidizing acid and deposited on a filter membrane to fabricate the SWCNTs-oxide test strip for one-step solid-phase extraction. After spraying the surface of the SWCNTs-oxide test strip with gold colloids, surface-enhanced Raman scattering signals were greatly increased owing to the clean detection background of the matrix and the concentrated target molecules in the probed volume. A facile approach was recommended here to rapidly monitor simetryn residues in lake water samples using one-step solid-phase extraction with the SWCNTs-oxide test strip and subsequent direct detection on a portable Inspector Raman. The detection limit of this method was found to be 2 μg L−1, and the recovery was between 70 and 80%. In addition, the linearity was in the range 10 to 300 μg L−1 with a correlation coefficient of 0.9878. The method provides a promising approach for the fast analysis of triazine compounds in complex matrix samples.

•g-C3N4 can be used as a coating material for SPME applications.•g-C3N4 fiber can be applied to extract both low- and high- polarity analytes.•g-C3N4 fiber reveals excellent extraction ability and durability.In this study, graphitic carbon nitride (g-C3N4) was used as a coating material for solid-phase microextraction (SPME) applications. Coupled to gas chromatography (GC), the extraction ability of the SPME fiber was investigated and compared with the commercial fibers of 100 μm PDMS and 85 μm CAR/PDMS using six target analytes including deltamethrin, nerolidol, amphetamine, dodecane, ametryn and acrylamide. The g-C3N4 coating revealed excellent extraction ability and durability comparing with those of the commercial fibers due to its loose structure and unique physicochemical properties. The repeatability for each single fiber was found to be 3.46% and reproducibility for fiber to fiber was 8.53%. The g-C3N4 SPME fiber was applied to the determination of acrylamide in potato chips, the linearity and detection limit was 0.5-250 μg g−1 and 0.018 μg g−1, respectively.

We report on a preconcentration disk for the determination of trace amounts of heterocyclic aromatic amines (HAAs) in the groups of quinoline and quinoxaline congeners as possible human carcinogens. The disk is based on nanocomposite (NC) prepared from graphene oxide as the precursor and from gold nanoparticles that act as building blocks to form a three-dimensional NC. If deposited in the sampling valve of a HPLC system, the material displays excellent extraction capability for HAAs owing to its large surface and π-π stacking interaction. Following an optimization of the extraction parameters, the method was successfully applied to the simultaneous determination of polar HAAs in meat samples with detection limit of 0.09 to 0.16 ng g−1 and recoveries of 69.5 to 122.7 %. The disk was used in more than 150 subsequent preconcentration cycles without obvious loss of the absorption capability. The results reveal that this new NC represents an excellent sorbent for purposes of preconcentration.