Multifunctional Ni(OH)2/Ag composites for ultrasensitive SERS detection and efficient photocatalytic degradation of ciprofloxacin and methylene blue

Stable metal-phase Nb-doped MoS2 nanoflowers for ultrasensitive SERS detection of food contaminants

In this work, we introduce a novel one-step hydrothermal method to synthesize Nb-doped 1T-MoS2 (NbMS), which stabilizes the metallic phase and significantly boosts its SERS activity. The NbMS, particularly the synthesized 0.8NbMS material, demonstrate a remarkable enhancement factor (EF) of 5.1 × 108 using methylene blue (MB) as the probe molecule. Additionally, these Nb-doped MoS2 exhibit excellent stability, with a metallic phase that can be maintained for more than four months, an important attribute for their practical application. We present a thorough evaluation of their performance, including a demonstrated limit of detection (LOD) for aspartame (APM) and thiabendazole (TBZ) at concentrations as low as 1.0 × 10-11 and 4.4 × 10-8 M, respectively. These features not only provide a powerful platform for detecting trace contaminant levels, but can also be used for real-world sample analysis, with great potential for application in food safety testing.

Ultrasensitive and light erasable surface-enhanced Raman scattering substrates based on Au-MoO2 heterostructures

Metal nanostructures are commonly utilized as surface-enhanced Raman scattering (SERS) substrates due to their strong localized surface plasmon resonance (LSPR) effects. However, these substrates are typically single-use because the analytes tend to remain on them. Molybdenum dioxide (MoO2), a metalloid oxide with excellent photothermal properties, allows for removal of residues through photothermolysis. Nevertheless, its inherent SERS performance is relatively limited, with a detection threshold around 10-7 M, approximately two orders of magnitude less sensitive than metal-based substrates. Here, we harnessed the synergistic interaction between Au and MoO2 to develop reusable and highly sensitive SERS substrates. Au nanoparticles (NPs) were selectively deposited onto MoO2 through a light-induced reduction method. The resulting Au-MoO2 heterostructures exhibit an excellent electric field at interstitial sites due to LSPR coupling and present remarkable SERS sensitivity towards rhodamine 6G (R6G), methyl blue (MB), rhodamine B (RhB), and crystal violet (CV). The limit of detection can be improved down to 10-9 M, achieving a maximum enhancement factor of 4.9 × 106. Additionally, when exposed to an 808 nm laser beam, the surface temperature of the Au-MoO2 nanocomposites can reach up to 529 °C, exceeding the decomposition temperatures of most organic compounds. Therefore, the residues can be entirely eliminated from the substrate under irradiation within 12 min, without sacrificing the SERS reproducibility and sensitivity. We expect our work to provide beneficial insights into the construction of ultrasensitive and recyclable SERS substrates.

A novel approach for the fabrication of SERS substrates based on 3D urchin-like TiO2@Gr-AuNPs architecture

3D urchin-like titanium dioxide@graphene-gold nanoparticles (UT@Gr-AuNPs) architectures with a core@shell structure of UT@Gr were successfully synthesized on silicon substrates via thermal chemical vapor deposition (CVD) technique using sodium deoxycholate surfactant (SDC) as a carbon source, followed by depositing AuNPs onto the surface of UT@Gr via a cold plasma (CP) process. The as-prepared samples were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman, X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), and ultraviolet-visible (UV-vis) spectroscopy. Thanks to the hot spots created by the AuNPs onto the surface of UT@Gr, the UT@Gr-AuNPs SERS substrates show significantly enhanced SERS sensitivity to detect hazardous pollutants and pesticide residue substances, e.g., rhodamine 6G (R6G) and malathion with a low detection limit (LOD) of about 5.86 × 10-11 M and 2.87 × 10-8 M, respectively. Moreover, these SERS substrates prepared in this study effectively enable in situ SERS monitoring of the R6G and rhodamine B (RhB) photodegradation reaction and self-cleaning performance under ultraviolet light (UV, 254 nm) irradiation.

Doping Detection Based on the Nanoscale: Biosensing Mechanisms and Applications of Two-Dimensional Materials

Doping undermines fairness in sports and threatens athlete health, while conventional detection methods like LC-MS and GC-MS face challenges such as complex procedures, matrix interferences, and lengthy processing times, limiting on-site applications. Two-dimensional (2D) materials, including graphene, MoS2, and metal-organic frameworks (MOFs), offer promising solutions due to their large surface areas, tunable electronic structures, and special interactions with doping agents, such as hydrogen bonding, π-π stacking, and electrostatic forces. These materials enable signal transduction through changes in conductivity or fluorescence quenching. This review highlights the use of 2D materials in doping detection. For example, reduced graphene oxide-MOF composites show high sensitivity for detecting anabolic steroids like testosterone, while NiO/NGO nanocomposites exhibit strong selectivity for stimulants like ephedrine. However, challenges such as environmental instability and high production costs hinder their widespread application. Future efforts should focus on improving material stability through chemical modifications, reducing production costs, and integrating these materials into advanced systems like machine learning. Such advancements could revolutionize doping detection, ensuring fairness in sports and protecting athlete health.

Synergizing PIERS and photocatalysis effects in a photo-responsive Ag/TiO2 nanostructure for an ultrasensitive and renewable PI-PC SERS technique

Surface-enhanced Raman spectroscopy (SERS) is a renowned analytical technique for non-invasive molecular identification. Advancements in SERS technology pivot on designing nano-structured substrates to enhance sensitivity and reliability. A key emerging trend involves integrating pre-treatment and post-treatment techniques on these substrates, leveraging advanced nanostructures to bring unique features, such as ultrasensitivity or reusability, to bridge the gap between laboratory and real-world applications of the SERS technique. Despite these advances, the synergistic application of pre- and post-treatment techniques on a single SERS substrate to fully exploit unique physicochemical effects remains underexplored. To address this, we introduce photo-induced-photo-catalytic SERS (PI-PC SERS), a novel technique that synergistically combines photo-induced enhanced Raman scattering (PIERS) and photocatalysis using a single Ag/TiO2 nanocomposite structure. This method aims to deliver ultrasensitive sensing capabilities and reusability. The PI-PC SERS technique involves pre-irradiating the SERS substrate with UV light to amplify the Raman signal and post-irradiating to remove fouled analytes. Pre-irradiation enhances the SERS signal by several orders of magnitude compared to normal SERS, attributed to the PIERS effect. Consequently, the detection sensitivity for methylene blue (MB) using PI-PC SERS reaches 1.02 × 10-14 M, significantly better than the 3.04 × 10-11 M achieved with normal SERS. Similar enhancements are observed for thiram, with a limit of detection (LOD) of 1.02 × 10-11 M for PI-PC SERS compared to 2.19 × 10-9 M for normal SERS. Additionally, post-irradiation facilitates the removal of analyte molecules via photocatalysis, restoring the substrate to its pristine state, as the byproducts - water and CO2 gas - are easily managed. Our findings demonstrate that PI-PC SERS creates ultrasensitive sensors and ensures substrate cleanliness and longevity. This method shows great promise for ultrasensitive, sustainable, and cost-effective applications in chemical sensing and molecular diagnostics.

Recyclable NiO/g-C3N4/ag hybrid substrates for sensitive SERS detection and photo-degradation of residual pesticides in beverages

In this research, we fabricated an innovative NiO/CN/Ag composite through the straightforward electrostatic assembly of Ag nanoparticles and g-C3N4 sheets onto NiO nanoflowers. This composite enables both surface enhanced Raman spectroscopy (SERS) detection and photo-degradation of pesticides. The results reveal NiO/CN/Ag can quantitatively detect thiram (TRM) and diquat dibromide (DQDB) in water, with a limit of detection (LOD) of 10-9 M, and also exhibit outstanding photo-degradation efficiency, exceeding 95 % for TRM and DQDB within 90 min under simulated sunlight. Significantly, after the organic reagent (citric acid) on NiO/CN/Ag was completely removed through simulated solar irradiation, the signal-to-noise ratios of SERS spectra on NiO/CN/Ag were enhanced, achieving LODs of 10-8 M for TRM and DQDB in different fruit juices and dried flower teas. Additionally, the composite demonstrate impressive recyclability, maintaining robust SERS signals and high degradation rates even after five cycles of "detection-degradation" processes.

Ultrasensitive detection of methylene blue by surface-enhanced Raman scattering (SERS) with Ag nanoparticle-decorated magnetic CoNi layered double hydroxides

The unreasonable use of organic dye leads to excessive residues in environmental water, which seriously threatens human health and the natural environment. In this paper, a spherical flower-like magnetic Fe3O4@CoNi layered double hydroxide@silver nanoparticle (Fe3O4@CoNi LDH@Ag NPs) SERS substrate was successfully fabricated via electrostatic self-assembly and applied for the sensitive detection of methylene blue (MB) in environmental water. The rapid concentration and separation of the SERS substrate from the water sample could be achieved using an external magnet. The Fe3O4@CoNi LDH@Ag NPs could not only rapidly enrich the trace analytes because of their outstanding absorptive capacity but also effectively enrich the cationic dye molecules to the "hot spots" through electrostatic interactions, resulting in higher SERS selectivity. Excellent SERS performance was observed, which exhibited a high enhancement factor (EF) of 5.81 × 108 and a low detection limit (LOD) of 1 × 10-11 mol L-1 with R6G as the probe molecule, and also possessed exceptional reproducibility and stability for at least 28 days. The Fe3O4@CoNi LDH@Ag NPs were used to detect MB, which displayed wide linearity (1 × 10-10 to 1 × 10-4 mol L-1) and high recoveries (89.68-103.72%). This Fe3O4@CoNi LDH@Ag NP substrate offers easy separation and selective detection of cationic dyes, providing potential application for the detection of environmental contaminants.

Facile synthesis of Ag NPs@MgO nanosheets for quantitative SERS-based detection and removal of hazardous organic pollutants

Surface-enhanced Raman spectroscopy (SERS) is a highly precise and non-invasive analytical method known for its ability to detect vibrational signatures of minute analytes with exceptional sensitivity. However, the efficacy of SERS is subject to substrate properties, and current methodologies face challenges in attaining consistent, replicable, and stable substrates to regulate plasma hot spots across a wide spectral range. This study introduces a straightforward and economical approach that incorporates monodispersed silver nanoparticles onto 2-D porous magnesium oxide nanosheets (Ag@MgO-NSs) through an in-situ process. The resulting nanocomposite, Ag@MgO-NSs, demonstrates substantial SERS enhancement owing to its distinctive plasmonic resonance. The effectiveness of this nanocomposite is exemplified by depositing diverse environmental pollutants as analytes, such as antibiotic ciprofloxacin (CIP), organic dyes like rhodamine 6G (R6G) and methylene blue (MB), and nitrogen-rich pollutant like melamine (MLN), onto the proposed substrate. The proposed nanocomposite features a 2-D porous structure, resulting in a larger surface area and consequently providing numerous adsorption sites for analytes. Moreover, engineering the active sites of the nanocomposite results in a higher number of hotspots, leading to an enhanced performance. The nanocomposite outperforms, exhibiting superior detection capabilities for R6G, MB, and MLN at concentrations of 10-6 M and CIP at concentration of 10-5 M, with impressive uniformity, reproducibility, stability, and analytical enhancement factors (EF) of 6.3 x 104, 2 x 104, 2.73 x 104 and 1.8 x 104 respectively. This approach provides a direct and cost-effective method for the detection of a broad spectrum of environmental pollutants and food additives, presenting potential applications across diverse domains. The detected environmental pollutants and food additives are removed through both catalytic degradation (R6G and MB) and adsorption (CIP and MLN).

Cascade internal electric field dominated carbon nitride decorated with gold nanoparticles as SERS substrate for thiram assay

The development of valid chemical enhancement strategy with charge transfer (CT) for semiconductors has great scientific significance in surface-enhanced Raman scattering (SERS) technology. Herein, a phosphorus doped crystalline/amorphous polymeric carbon nitride (PCPCN) is fabricated by a facile molten salt method, and is employed as a SERS substrate for the first time. Upon the synergies of phosphatization and molten salt etching, PCPCN owns a cascaded internal electric field (IEF) due to the formation of p-n homojunction (interface-IEF) and crystalline/amorphous homojunction (bulk-IEF). The interface-IEF and bulk-IEF could effectively suppress the recombination of charge carriers and promote electron transfer between PCPCN and target methylene blue (MB), respectively. The strong CT interaction endows PCPCN substrate with superior SERS activity with an enhancement factor (EF) of 5.53 × 105. Au nanoparticles (Au NPs) are subsequently decorated on PCPCN to introduce electromagnetic enhancement for a better SERS response. The Au/PCPCN substrate allows to reliably detect trace crystal violet, as well as the thiram residue on cherry tomato. This work offers an integrated solution to enhance CT efficiency based on collaborative homojunction and internal electric field, and may inspire the design of novel semiconductor-based SERS substrates.

Facile coupling of plasmonic Au-NPs on ZnS NFs as a robust SERS substrate for toluidine blue detection and degradation

BACKGROUND

The robustness and sensitivity of the surface-enhanced Raman spectroscopy (SERS) technique heavily relies on the development of SERS active materials. A hybrid of semiconductor and plasmonic metals is highly effective as a SERS substrate, which enables the trace level detection of various organic pollutants.

RESULTS

This approach demonstrates the photodeposition of plasmonic gold nanoparticles (Au-NPs) on the surface of semiconductor-zinc sulfide nanoflowers (ZnS NFs), grown via the hydrothermal route. The synergistic contribution of the charge-transfer phenomenon and localized surface plasmon resonance of the Au-NPs/ZnS NFs makes it an ideal SERS substrate for the detection of organic pollutants, toluidine blue (TB). The proposed material has a high SERS enhancement factor (109), low limit of detection (10-11 M), good reproducibility, selectivity and strong anti-interference ability. Furthermore, the practicability of the Au-NPs/ZnS NFs is explored in real-time water samples, which are obtained with the satisfactory recovery rates. Additionally, the UVC light illumination on the Au-NPs/ZnS NFs has efficiently degraded TB within a time period of 150 min.

SIGNIFICANCE AND NOVELTY

These finding demonstrate the significance of the proposed Au-NPs/ZnS NFs for SERS based detection and degradation of organic pollutants in real-time samples, highlighting their potential in monitoring and treating water pollutants in wastewater.

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.