Aluminum sheet induced flower-like carbon nitride anchored with silver nanowires for highly efficient SERS detection of trace malachite green

Recent Advances in Food Safety: Nanostructure-Sensitized Surface-Enhanced Raman Sensing

Food safety is directly related to human health and has attracted intense attention all over the world. Surface-enhanced Raman scattering (SERS), as a rapid and selective technique, has been widely applied in monitoring food safety. SERS substrates, as an essential factor for sensing design, greatly influence the analytical performance. Currently, nanostructure-based SERS substrates have garnered significant interest due to their excellent merits in improving the sensitivity, specificity, and stability, holding great potential for the rapid and accurate sensing of food contaminants in complex matrices. This review summarizes the fundamentals of Raman spectroscopy and the used nanostructures for designing the SERS platform, including precious metal nanoparticles, metal-organic frameworks, polymers, and semiconductors. Moreover, it introduces the mechanisms and applications of nanostructures for enhancing SERS signals for monitoring hazardous substances, such as foodborne bacteria, pesticide and veterinary drug residues, food additives, illegal adulterants, and packaging material contamination. Finally, with the continuous progress of nanostructure technology and the continuous improvement of SERS technology, its application prospect in food safety testing will be broader.

Gold nanoparticles decorated crystalline carbon nitride nano-walls as a SERS chip for rapid and sensitive detection of benzidine

Risk level of benzidine residue to the environment and food safety urges surface enhanced Raman scattering (SERS) substrates to develop with high sensitivity and rapid enrichment. Herein, a hybrid of Au NPs decorated crystalline carbon nitride nano-walls (Au/CCN NWs) is fabricated on Al sheet and employed as a SERS substrate for the first time. An electro-enhanced adsorption strategy is employed to endow as-prepared Au/CCN NWs/Al chip with rapid assay capability. Crystalline phase transition and nano-wall morphology respectively bestows high charge transfer efficiency and favorable enrichment activity upon Au/CCN NWs/Al chip, and the hybrid substrate owns a considerable enhancement factor of 1.76 × 106 under static adsorption mode. Moreover, Au/CCN NWs/Al substrate can achieve the saturation enrichment of benzidine in 120 s with the help of electro-enhanced adsorption, and gains a significantly enhanced signal response compared to static adsorption. Likewise, the highly sensitive response (1 μg L-1), superior reproducibility (RSD = 9.11 %, n = 100) and reliable accuracy (recovery rate of 95.55 %-109.46 %) jointly demonstrate that Au/CCN NWs/Al substrate may be applicable for detecting benzidine residue in actual application. This work offers an integrated solution to both enhance charge transfer efficiency and enrichment activity based on collaborative crystalline phase transition and electro-enhanced adsorption, and may inspire the design of novel noble metal/semiconductor hybrid SERS substrates.

A novel multifunctional SERS microfluidic sensor based on ZnO/Ag nanoflower arrays for label-free ultrasensitive detection of bacteria

This study proposes a microfluidic platform for rapid enrichment and ultrasensitive SERS detection of bacteria. The platform comprises ZnO nanoflower arrays decorated with silver nanoparticles to enhance the SERS sensitivity. The ZnO nanoflower array substrate with a 3D reticular columnar structure is prepared using the hydrothermal method. SEM analysis depicts the 3.05 μm gap distribution of the substrate array to intercept the most bacteria in the particle sizes range of 0.5 to 3 μm. Then, silver nanoparticles are deposited on the ZnO nano-array surface by liquid evaporation self-assembly. TEM and SEM analysis indicate nanosize of Ag particles, evenly distributed on the substrate, enhancing the SERS efficiency and improving sensing reproducibility. The probe molecules (R6G) are tested to demonstrate the high SERS activity of the proposed microfluidic sensor. Then, Escherichia coli, Staphylococcus aureus, Enterococcus faecalis, and Bacillus subtilis are selected, demonstrating the sensor's excellent bacterial capture and sensitive recognition capabilities, with a detection limit as low as 102 CFU mL-1. Additionally, the antibacterial properties of ZnO/Ag heterojunction nanostructures are studied, suggesting their ability to inactivate bacteria. Compared with the traditional Au-enhanced chip, the sensor preparation is easy, safe, reliable, and low-cost. Moreover, the ZnO nano-array exhibits a large specific surface area, high interception ability, stronger and uniform SERS performance, and effective and reliable detection of trace pathogens. This work provides potential future ZnO/Ag microfluidic SERS sensor applications for rapid, unlabeled, and trace pathogens detection in clinical and environmental applications, potentially achieving breakthroughs in early detection, prevention, and treatment.

Aramid nanofiber membrane decorated with monodispersed silver nanoparticles as robust and flexible SERS chips for trace detection of multiple toxic substances

Aramid nanofibers (ANFs) as an innovative nanoscale building block exhibit great potential for novel high-performance multifunctional membranes attributed to their extraordinary performance. However, the application of aramid nanofibers in the field of surface enhanced Raman scattering (SERS) sensing has been rarely reported. In this work, aramid nanofibers derived from commercial Kevlar fibers were synthesized by a facile dimethyl sulfoxide/potassium hydroxide (DMSO/KOH) solution treatment. The monodispersed silver nanoparticle-decorated aramid nanofiber (m-Ag@ANF) membranes were constructed by an efficient vacuum filtration technique. Taking advantages of unique intrinsic properties of ANF, the m-Ag@ANF substrates exhibit good flexibility, excellent mechanical properties and prominent thermal stability. Besides, due to the abundance of positively charged amino-group on the ANF substrates, the negatively charged m-AgNPs were uniformly and firmly deposited on the surface of ANF substrate through electrostatic interactions. As a result, the optimal flexible m-Ag-9@ANF SERS substrate exhibits high sensitivity of 10-9 M for methylene blue (MB) and excellent signal reproducibility (RSD = 6.37 %), as well as outstanding signal stability (up to 15 days). Besides, the 2D Raman mapping and FDTD simulations further reveal prominent signal homogeneity and strong electric field distribution for flexible m-Ag-9@ANF SERS substrate. Finally, it is demonstrated that the flexible m-Ag-9@ANF SERS substrate can also be used for detection of toxic molecules on irregular surfaces by a feasible paste-and-read process. The m-Ag@ANF paper exhibits potential applications as a flexible, low-cost, robust and stable SERS sensing platform for trace detection of toxic materials.

A portable architectonics of Al/carbon nitride/metal-organic frameworks anchored Ag nanoparticles for SERS detection and photocatalytic degradation of fungicide

In recent years, it is urgent to develop bi-functional materials for highly sensitive SERS detection and photocatalytic degradation of contaminants in water of fish pond. Herein, using 5-mercapto-1-methyltetrazole as the ligand, the tree-trunk like zeolitic imidazolate framework (ZIF-8) is induced and in-situ grown on the surface of aluminum/flower carbon nitride (Al/f-C₃N₄). Then, AgNPs are tightly anchored in ZIF-8 of Al/f-C₃N₄/ZIF-8 by strong Ag-N and Ag-S bonds, and a portable architecture of Al/f-C₃N₄/ZIF-8/Ag is successfully prepared. Results indicate that the Al/f-C₃N₄/ZIF-8/Ag architecture exhibits excellent SERS activity and the detection limit can as low as 2.15 × 10^-11 mol⋅L^-1 for crystal violet (CV, a typical fungicide). Also, the Al/f-C₃N₄/ZIF-8/Ag substrate presents good photocatalytic activity for CV molecule, and the degradation efficiency reaches 98.58% after illumination for 90 min. This is mainly due to the good adsorption capacity of ZIF-8 which can enrich more CV molecules and pull them to "hot spots" generated by Ag in Al/f-C₃N₄/ZIF-8/Ag, and thus SERS response are enhanced significantly. Besides, the strong synergistic effect of f-C₃N₄, ZIF-8 and AgNPs is also important which facilitates the separation of photogenerated electrons and holes. Thus, the designed portable and bi-functional substrate could be used as a potential material for the detection and removal of CV in practical application.

Toward High-Energy-Density Aqueous Lithium-Ion Batteries Using Silver Nanowires as Current Collectors

The lack of suitable lightweight current collectors is one of the primary obstacles preventing the energy density of aqueous lithium-ion batteries (ALIBs) from becoming competitive. Using silver nanowire (AgNW) films as current collectors and a molecular crowding electrolyte, we herein report the fabrication of ALIBs with relatively good energy densities. In the 2 m LiTFSI-94% PEG-6% H₂O solution, the AgNW films with a sheet resistance of less than 1.0 ohm/square exhibited an electrochemical stability window as broad as 3.8 V. The LiMn₂O₄//Li₄Ti₅O₁₂ ALIBs using AgNW films as the current collectors demonstrated an initial energy density of 70 Wh/kg weighed by the total mass of the cathode and anode, which retained 89.1% after 50 cycles.