Sensitive and Stable Detection of Pesticide Residues Using Flexible 3D Nanocellulose-Based SERS Substrates

Surface-enhanced Raman spectroscopy (SERS) has gained attention as a sensitive technique for the detection of pesticide residues. However, constructing homogeneous, stable, and large-volume "hot spots" is a challenge. In this study, D-T-CNFs@Ag SERS substrates were fabricated by decorating a flexible dialdehyde TEMPO-oxidized cellulose nanofibril (D-T-CNF) film with silver nanoparticles (AgNPs). Carboxylate groups and aldehyde groups on cellulose nanofibrils were used as the growth sites for AgNPs and the main reducing agents for forming three-dimensional "hot spots", respectively. D-T-CNFs provided protection and immobilization for the AgNPs, allowing SERS substrates to withstand intense ultrasonic treatment, and had a shelf life of over 60 days. In addition, thiram and thiabendazole could be detected at a concentration as low as 10-9 M. The D-T-CNFs@Ag SERS substrate could be used to test thiram on the surface of apples, with a limit of detection (LOD) of 0.047 ng/cm2, realizing the integration of collection and detection.

Gold-grafted melamine sponge as surface-enhanced Raman spectroscopy substrate for enzyme-linked immunoassay of mycotoxins in cereal samples

Gold-grafted melamine sponge (AuSp) was fabricated and applied as surface-enhanced Raman spectroscopy (SERS) substrate for enzyme-linked immunoassay of 2 typical mycotoxins, zearalenone (ZEN) and T-2 toxin. The gold nanoparticles were in situ grown on the sponge, and the product showed good effect in enhancing Raman signal and good stability. COMSOL and Gaussian simulations were used to analyze the enhancing effect. Some of the experimental conditions that may affect the determination results were studied in order to meet the maximum response to mycotoxins. At optimized conditions, the limits of detection of the method were 1 μg·kg-1 and 0.05 μg·kg-1 for ZEN and T-2 toxin, with linear ranges of 5-100 μg·kg-1 and 0.1-20 μg·kg-1, respectively, and relative standard deviations lower than 7.0%. The established method was used to determine ZEN and T-2 toxin in six kinds of cereal samples, the recoveries were 85-120%, and relative errors were less than 13.0%. These results indicated the accuracy of the established method. After 1-year storage, signal strength of AuSp for mycotoxins determination decreased by less than 10%, showing stability over a long time. Our work provided a new method for SERS determination of mycotoxins, which reduces the complexity of substrate preparation and the sample consumption compared with traditional methods, and thus has potential for on-line SERS determination.

Scalable Superhydrophilic Solar Evaporators for Long-Term Stable Desalination, Fresh Water Collection and Salt Collection by Vertical Salt Deposition

Solar-driven interfacial evaporation (SIE) is very promising to solve the issue of fresh water shortage, however, poor salt resistance severely hinders long-term stable SIE and fresh water collection. Here, we report design of superhydrophilic solar evaporators for long-term stable desalination, fresh water collection and salt collection by vertical salt deposition. The evaporators are prepared by sequentially deposition of silicone nanofilaments, polypyrrole and Au nanoparticles on a polyester fabric composed of microfibers. The evaporators feature excellent photothermal effect and ultrafast water transport, due to their unique micro-/nanostructure and superhydrophilicity. As a result, during SIE the salt gradually deposits vertically rather than occupies larger area on the evaporators. Consequently, long-term stable SIE with high evaporation rates of 2.4-2.1 kg m-2 h-1 for 3.5-20 wt % brine in continuous 10 h is achieved under 1 sun illumination. Meanwhile, the loosely deposited salt can be easily collected, realizing zero brine discharge. Moreover, scalable preparation of the evaporator is achieved, which exhibits efficient collection of high quality fresh water (10.08 kg m-2 in 8 h) via SIE desalination under weak natural sunlight (0.46~0.66 sun). This strategy sheds a new light on the design of high-performance solar evaporators and their real-world fresh water collection.

Surface-enhanced Raman scattering of a gold core-silver shell-sponge substrate for detection of thiram and diquat

Aiming at the difficulty of traditional pesticide sampling, a low-cost and convenient flexible surface enhanced Raman scattering (SERS) gold core-silver shell-sponge (Au-Ag-sponge) substrate was synthesized by chemical reduction. The SERS substrate consisted of Au-AgNPs and a melamine sponge. The sponge had a rich open pore structure, which could well "capture" Au-AgNPs, generating a large number of "hot spots". The SERS enhancement activity of the flexible substrate was characterized with rhodamine 6G (R6G) Raman probe molecules. The substrate showed good activity to 10-12 M rhodamine 6G with an enhancement factor (EF) of 7.72 × 106. Applying this substrate to the qualitative and quantitative detection of pesticide residues, the results showed that the Raman intensity was well related to the concentration of pesticide solution with the range of 0.1-10 mg L-1 of thiram and 1-10 mg L-1 of diquat. Furthermore, the substrate was analyzed by finite difference time domain (FDTD) simulation and the results were in good agreement with the experimental results. The reason for the difference in Raman signals of pesticide molecules on the same substrate was the different binding modes of Au-AgNPs on the sponge. Finally, we pointed out the advantages of flexible substrates in the field of pesticide residues, as well as future opportunities and challenges.

Highly Salt-Resistant interfacial solar evaporators based on Melamine@Silicone nanoparticles for stable Long-Term desalination and water harvesting

Interfacial solar-driven evaporation (ISE) is one of the most promising solutions for collecting fresh water, however, poor salt-resistance severely limits the long-term stability of solar evaporators. Here, highly salt-resistant solar evaporators for stable long-term desalination and water harvesting were fabricated by depositing silicone nanoparticles onto melamine sponge, and then modifying the hybrid sponge sequentially with polypyrrole and Au nanoparticles. The solar evaporators have a superhydrophilic hull for water transport and solar desalination, and a superhydrophobic nucleus for reducing heat loss. Spontaneous rapid salt exchange and reduction in salt concentration gradient were achieved due to ultrafast water transport and replenishment in the superhydrophilic hull with a hierachical micro-/nanostructure, which effectively prevents salt deposition during ISE. Consequently, the solar evaporators have long-term stable evaporation performance of 1.65 kg m^-2h^-1 for 3.5 wt% NaCl solution under 1 sun illumination. Moreover, 12.87 kg m^-2 fresh water was collected during consecutive 10 h ISE of 20 wt% brine under 1 sun without any salt precipitation. We believe that this strategy will shed a new light on the design of long-term stable solar evaporators for fresh water harvesting.

Simultaneous SERS detection of illegal food additives rhodamine B and basic orange II based on Au nanorod-incorporated melamine foam

In food safety assessment, surface-enhanced Raman spectroscopy (SERS) is a novel detection method with the advantages of being fast, easy, and of high sensitivity. However, many SERS substrate synthesis methods are complex, and there are only a few studies on the simultaneous detection of multiple substances. In this study, a new, simple, low-cost SERS substrate was synthesised for the first time to simultaneously detect illegal food additives rhodamine B and basic orange II in chilli products. A lightweight, porous, and low-cost material of melamine foam (MF) was employed as the SERS synthesis template. The substrate's SERS effect on, and sensitivity to, rhodamine B and basic orange II were demonstrated. The molecular vibration and SERS enhancement mechanisms of the two target molecules were analysed by density functional theory (DFT) calculations. The results reveal that this fabricated substrate has great application potential for the supervision and testing industry.

Fluorescence enhancement novel green analytical method for paraquat herbicide quantification based on immobilization on clay

Fluorescence emission enhancement by adsorption as a promising tool for the development of future green sensors.

Dual functional PDMS sponge SERS substrate for the on-site detection of pesticides both on fruit surfaces and in juice

A versatile dual-functional polydimethylsiloxane (PDMS) sponge Surface Enhanced Raman Scattering (SERS) substrate has been fabricated for the on-site detection of pesticide residues both on the surface and in solution with minimum or no sample pretreatment.