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Surface-enhanced Raman scattering (SERS) has gained a reputation as one of the most sensitive spectroscopic methods for biosensing. However, to design a SERS-based biosensor, almost all currently used methods involve the time-consuming and complicated modification of the metallic nanoparticles, which restricts their wide spread applications. Herein, a facile and sensitive SERS-based aptasensor for colorimetric detection of acetamiprid (AC) was demonstrated. The prepared crystal violet (CV)-aptamer decorated gold nanoparticles (GNPs) tended to aggregate in a solution with high concentrations of salt, and displayed a purple color. In the presence of AC, the specific binding of the target with the aptamer generated conformation changes of aptamer (confirmed by the circular dichroism spectrum), which made the stable GNPs aggregation in the salt solution, thus resulting the SERS signal enhanced. Sequel, the SERS intensity was increased linearly with the concentration of AC ranging from 3.0 × 10−8to 4.0 × 10−6M, with a relatively low limit of 1.76 × 10−8M. The detection ability of AC by this biosensor was also confirmed with different adulterated tea. This approach is not only straightforward in fabrication but also cost-effective in operation, and can be used for diverse bio-molecules detection by changing the aptamer.

In this study, a turn-on nanosensor for detecting Hg2+was developed based on the fluorescence resonance energy transfer (FRET) between long-strand aptamers-functionalized upconversion nanoparticles (UCNPs) and short-strand aptamers-functionalized gold nanoparticles (GNPs). In the absence of Hg2+, FRET between UCNPs and GNPs occurred because of the specific matching between two aptamers, resulting in the fluorescence quenching of UCNPs. In the presence of Hg2+, long-stranded aptamers fold back into a hairpin structure due to the stable binding interactions between Hg2+and thymine, leading to the release of GNPs from UCNPs, resulting in the quenched fluorescence restoration. Under the optimized conditions, the nanosensor achieved a linear detection range of 0.2–20 μM and a low detection limit (LOD) of 60 nM. Meanwhile, it showed good selectivity and has been applied to detecting Hg2+in tap water and milk samples with good precision.

This paper describes a novel ratiometric fluorescence-based sensor for the detection of fluoride ion. Yb3+, Er3+, and Tm3+codoped NaYF4upconversion nanoparticles (UCNPs), which can emit fluorescence at 546, 657, 758, and 812 nm under the 980 nm single wavelength excitation, were synthesized, amino-modified and applied as the fluorescent signal indicator. The natural chemical curcumin served as specific recognition element and mixed with UCNPs to make a nanosystem. In this nanosystem, the absorption peak of curcumin shows a bathochromic shift when F–was added, causing an upconversion fluorescence quenching at 546 and 657 nm through inner filter effects (IFE), whereas the upconversion emission at 758 and 812 nm remained unchanged. Thus, the fluorescence ratio I546/I758was inversely proportional to F–concentration. Meanwhile, the large absorption bathochromic shift also lead to a color change, based on the colorimetric analysis of F–by the naked eye. Under the optimized conditions, the developed UCNPs–curcumin mixed system achieved the colorimetric and ratiometric fluorescence sensing toward F–in the linear range of 25–200 μM and 5–200 μM, with the detection limits as low as 25 μM (ca. 0.48 ppm) and 5 μM (ca. 0.10 ppm), respectively. The developed nanosystem also has high selectivity and antijamming ability. Furthermore, this method showed promising practical applications in spiked real samples (ex., tap water and milk) with recoveries of 79.58% to 134.02% and RSD values in the range of 0.94% to 22.11%, which confirmed its great potential in harmful substance detection.

A symposium entitled “Chemistry, Flavor, and Health Effects of Tea” was held at the 256th American Chemical Society (ACS) Meeting in August 2018 in Boston, MA, U.S.A., and was sponsored by the ACS Division of Agricultural and Food Chemistry and the International Joint Laboratory on Tea Chemistry and Health Effects, Anhui Agricultural University, China. The purpose of the symposium was to bring together the leading tea researchers throughout the world to discuss the current state of knowledge as well as research needs with respect to chemistry and health beneficial properties of tea. Speakers from North America, Europe, and Asia delivered a total of 35 oral presentations. The presentations covered such diverse topics as polyphenol chemistry and flavor chemistry of tea, metabolomics application to identify the changes of phytochemical composition during processing, and health beneficial effects of drinking tea. This paper is intended to provide a brief summary of the presentations.