A 3D spongy flexible nanosheet array for on-site recyclable swabbing extraction and subsequent SERS analysis of thiram

Rapid Detection of Malathion, Phoxim and Thiram on Orange Surfaces Using Ag Nanoparticle Modified PDMS as Surface-Enhanced Raman Spectroscopy Substrate

Malathion, phoxim, and thiram are organophosphates and organosulfur pesticides widely used in agricultural products. The residues of these pesticides present a direct threat to human health. Rapid and on-site detection is critical for minimizing such risks. In this work, a simple approach was introduced using a flexible surface-enhanced Raman spectroscopy (SERS) substrate. The prepared Ag nanoparticles-polydimethylsiloxane (AgNPs-PDMS) substrate showed high SERS activity, good precision (relative standard deviation = 5.33%), and stability (30 days) after optimization. For target pesticides, the linear relationship between characteristic SERS bands and concentrations were achieved in the range of 10~1000, 100~5000, and 50~5000 μg L^-1 with LODs down to 3.62, 41.46, and 15.69 μg L^-1 for thiram, malathion, and phoxim, respectively. Moreover, SERS spectra of mixed samples indicated that three pesticides can be identified simultaneously, with recovery rates between 96.5 ± 3.3% and 118.9 ± 2.4%, thus providing an ideal platform for detecting more than one target. Pesticide residues on orange surfaces can be simply determined through swabbing with the flexible substrate before acquiring the SERS signal. This study demonstrated that the prepared substrate can be used for the rapid detection of pesticides on real samples. Overall, this method greatly simplified the pre-treatment procedure, thus serving as a promising analytical tool for rapid and nondestructive screening of malathion, phoxim, and thiram on various agricultural products.

Enhancing the Activity of Silver Nanowire Membranes by Electrochemical Cyclic Voltammetry as Highly Sensitive Flexible SERS Substrate for On-Site Analysis

The development of high-quality flexible surface-enhanced Raman spectroscopy (SERS) substrates is crucial for developing rapid SERS analysis in situ. Silver nanowire membranes as novel flexible substrates could benefit from the high collection efficiency of analytes by wrapping complex surfaces or wiping the surfaces of samples. However, their low SERS performance impedes further applications of silver nanowire membranes in analyte detection. Herein, we report an ultra-high-sensitivity silver nanowire membrane synthesized by a simple and time-saving cyclic voltammetry (CV) method. After CV treatment, a part of the silver nanowires on the silver nanowire membrane turned into small nanoparticles and nanorods. This nanostructure’s reconstitution increased the analytical enhancement factor of silver nanowire membranes by 14.4 times. Scanning and transmission electron microscopy, UV-vis spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy were employed to investigate the transformation in the membrane nanostructure. The CV-treated substrates exhibited high surface-enhanced Raman activity and good temporal stability. The limits of detection (LODs) for p-aminothiophenol, crystal violet, tetramethylthiuram disulfide, sodium perchlorate, malachite green, fluoranthene, and potassium nitrate are 3.7 × 10⁻¹² M, 5.1 × 10⁻¹¹ M, 5.4 × 10⁻¹¹ M, 6.3 × 10⁻⁹ M, 0.00693 ng, 0.0810 ng, and 0.0273 ng on this substrate, respectively. Additionally, the developed substrate is feasible for the detection of crystal violet in real samples. These results certify that CV-treated substrates possess broad application prospects in on-site SERS analysis.

A Portable Smartphone Platform Using a Ratiometric Fluorescent Paper Strip for Visual Quantitative Sensing

Instrument-free, portable, and direct read-out mini-devices have wider application prospects in various fields, especially for real-time/on-site sensing. Herein, combined with a paper strip, a smartphone sensing platform integrated with a UV lamp and dark cavity by 3D-printing technology has been developed for the rapid, sensitive, instrument-free, and visual quantitative analysis in real-time/on-site conditions. The platform proved the feasibility for visual quantitative detection of pesticide via a fluorescence "on-off-on" response with a single dual-emissive ratiometric paper strip. Red-emitting CdTe quantum dots (rQDs) were embedded into the silica nanoparticles (SiO₂ NPs) as an internal reference, while blue-emitting carbon dots (bCDs) as a signal report unit were covalently linked to the outer surface of SiO₂ NPs. The blue fluorescence could be quenched by gold nanoparticles (Au NPs) and then recovered with pesticide. The red (R), green (G), and blue (B) channel values of the generated images were determined by a color recognizer application (APP) installed in the smartphone, and the R/B values could be used for pesticide quantification with a sensitive detection limit (LOD) of 59 nM. The smartphone sensing platform based on 3D printing might provide a general strategy for visual quantitative detection in a variety of fields including environments, diagnosis, and safety monitoring.

Fluorescent assay based on phenyl-modified g-C3N4 nanosheets for determination of thiram

Phenyl-modified graphitic carbon nitride nanosheets (Ph-g-C₃N₄ NSs) were synthesized by a thermal copolymerization and ultrasonic exfoliation method. The Ph-g-C₃N₄ NSs are used as a fluorescent assay for determination of thiram. The results of X-ray photoelectron spectroscopy, ¹³C solid-state nuclear magnetic resonance and Fourier transform infrared spectra confirm that phenyl group is integrated into the heptazine network of g-C₃N₄. Compared to the g-C₃N₄ NSs, the Ph-g-C₃N₄ NSs show bigger stokes shift about 185 nm and higher fluorescence intensity. The fluorescence of Ph-g-C₃N₄ NSs is quenched by Cu²⁺ via the photo-induced electron transfer mechanism, which then recovers in the presence of thiram. The fluorescence restoring of Ph-g-C₃N₄ NSs is correlated with the concentration of thiram. Under the optimized conditions, the fluorescent intensity of g-C₃N₄ NSs at excitation/emission wavelengths of 310/455 nm give a linear range of 33.0-670 nM with detection limit of 9.90 nM. While fluorescent assay based on the Ph-g-C₃N₄ NSs show the linear range of 6.70-1300 nM at excitation/emission wavelengths of 310/495 nm with detection limit of 2.01 nM. Graphical abstract Schematic representation of fluorescent "on-off-on" assay based on phenyl-modified graphitic carbon nitride nanosheets (Ph-g-C₃N₄ NSs) for determination of thiram.