Plasmonic Coupling of Au Nanoclusters on a Flexible MXene/Graphene Oxide Fiber for Ultrasensitive SERS Sensing

3D composite SERS substrates with COF spaced Au nanoparticles for enrichment and selective sensitive detection

The excellent performance of surface-enhanced Raman spectroscopy (SERS) is closely related to the intensity, density and uniformity of hotspots. In this study, we introduce a PET/Au NPs@COF Raman substrate featuring three-dimensional hotspots. The spacing between each layer of gold nanoparticles (NPs) is precisely controlled by adjusting the thickness of the COF via the interfacial synthesis technique, causing the strong coupling between gold particles across the layers. The porosity of the COF enables the substrate to adsorb numerous analyte molecules into the large-area uniform hotspots. Through simulations and adsorption detection on the substrate, Raman testing further demonstrated that the substrate with double-layer Au NPs@COF exhibited the most favorable SERS performance. Additionally, the substrate allows for selective detection based on the particle size of the target molecule. The flexibility of the substrate enables it to conform to irregular surfaces, effectively capturing analytes from a variety of real samples.

Trace detection of S. aureus cells in food samples via RCA-assisted SERS signal amplification with core-shell nanoprobe

Staphylococcus aureus (S. aureus) has been identified as a indicator of food contamination. In this study, a sensitive and accurate biosensor strategy for S. aureus through rolling circle amplification-assisted surface-enhanced Raman scattering (RCA-assisted-SERS), has been established. The work relies on the interaction between the aptamer and its partial complementary DNA strands fabricated on the surface of gold and silver-assisted magnetic microspheres and the subsequent detachment to trigger the activation of the RCA process. In RCA, template DNA, T4 DNA ligase, and Phi29 DNA polymerase were assembled to form long single-stranded DNA containing repetitive sequences. The gold core encapsulated with a layer of 4-nitrothiophenol and further covered with a silica shell was employed as the SERS nanoprobe (Au@NTP@SiO2). Subsequently, the output and amplification of SERS signal were performed by hybridizing ssDNA functionalized Au@NTP@SiO2 to realize the quantitative detection of S. aureus. Under the optimal conditions, S. aureus sensing was monitored (36.0-3.6 × 108 cfu/mL) with a limit of detection of 2.0 cfu/mL. This strategy was further validated for S. aureus recognition in spiked real samples with favorable recoveries (94.0-103.4 %) at p > 0.05. The suggested RCA-assisted SERS approach exhibits potential for multiple foodborne pathogens in both food safety and biomedical investigations.

Highly sensitive thin SERS substrate by sandwich nanoarchitecture using multiscale nanomaterials for pesticide detection on curved surface of fruit

Various flexible surface-enhanced Raman scattering (SERS) substrates have been developed for the Raman detection of environmental pollutants due to their high sensitivity, low cost, and rapid sampling capabilities. However, achieving high reproducibility, reliability, and sensitivity in large areas remains challenging. In this study, we present a simple fabrication method for a layered, sandwich-nanoarchitectured SERS substrate consisting of multiscale nanomaterials of (1) 0D, Au nanoparticles (AuNPs), (2) 1D, TEMPO-oxidized nanocellulose fibers (TC), and (3) 2D, MXene (Ti3C2Tx). The resulting MXene@AuNP@MXene@TC (MX@Au@MX@TC) film demonstrated enhanced SERS performance based on the synergistic effect of efficient charge transfer (CT) and the presence of numerous nanogaps. Vertical plasmonic coupling in the MX@Au@MX@TC film, combined with the uniform adsorption of the target molecules, led to an ultra-low limit of detection of 10-11 M and an enhancement factor of 9.9 × 109 for rhodamine 6 G (R6G). In addition, the substrate exhibited excellent reliability, providing uniform and stable signals across various spatial scales with a relative standard deviation of 2.29 %. Furthermore, the SERS substrate detected thiram (0.02 μg/cm²) via direct in-situ sampling on curved fruit surfaces, offering insights into the scalable, cost-effective production of flexible SERS substrates for practical use.

Bionic learning in MXene-based actuators: An emerging frontier

Bionics offers valuable insights into the design and application of MXene-based soft actuators, which have garnered significant attention in the fields of flexible electronics and smart materials owing to their exceptional electrical conductivity, tunable interlayer spacing, and responsiveness to diverse external stimuli. This review begins with a comprehensive summary of the main response mechanisms of MXene-based soft actuators under various external stimuli. It presents a detailed analysis of the advantages and limitations of different actuation modes and discusses strategies for composite modification with other materials to enhance MXene performance under multi-stimulus conditions. Inspired by the sensory capabilities of animals and plants in nature, this work explores the potential for biomimetic design and identifies four key challenges for advancing the field: (1) the development of efficient and controllable material synthesis techniques, (2) the electrochemical stability and environmental robustness of devices, (3) the overall performance optimization of actuators, and (4) the nascent exploration of biomimetic learning mechanisms. Finally, future research directions are outlined, offering novel perspectives to promote the broader application of MXene-based soft actuators in biomimetic systems.

Hollow Au nanoparticles for single-molecule Raman spectroscopy via a synergistic electromagnetic and chemical enhancement strategy

Raman spectroscopy has demonstrated significant potential in molecular detection, analysis, and identification, particularly when it adopts single-molecule surface-enhanced Raman scattering (SM-SERS) substrates. A recent SM-SERS scheme incorporates two-fold Raman enhancement mechanisms: the electromagnetic enhancement enabled by a plasmonic nanogap hotspot formed from gold sphere nanoparticles sitting on a gold mirror and the chemical enhancement enabled by a two-dimensional material, WS2, inserted into the nanogap. In this work we integrate multiple advanced concepts and techniques to achieve remarkable performance improvements of SM-SERS. We have used hollow gold nanoparticles to form plasmonic nanogaps, which better match the wavelength of near-infrared pump lasers, thus maximizing the electromagnetic field enhancement within the nanogap and creating a more effective hotspot. Notably, our strategy has achieved universal, robust, fast, and uniform SM-SERS detection of three dye molecules (Rhodamine B, Rhodamine 6G and Crystal Violet) with a detection limit of 10 mol L-1. This innovative approach opens up new possibilities for bringing state-of-the-art optical imaging, monitoring, and spectroscopy technologies into the single-molecule science arena for disclosing more unknown physical, chemical, and biological properties and principles.

Mechanically Flexible, Large-Area Fabrication of Three-Dimensional Dendritic Au Films for Reproducible Surface-Enhanced Raman Scattering Detection of Nanoplastics

The escalating crisis of nanoplastic pollution in water and food products demands the development of novel methodologies for detection and recycling. Despite various techniques available, surface-enhanced Raman scattering (SERS) is emerging as a highly efficient technique for the trace detection of micro/nanoplastics. However, the development of highly reproducible and stable, flexible SERS substrates that can be used for sensitive detection in environmental medium remains a challenge. Here, we report a fabrication of large-area, three-dimensional (3D), and highly flexible SERS substrate based on porous dendritic Au films onto a flexible indium tin oxide (ITO) substrate via facile, thermal evaporation of Au over the vacuum-compatible deep eutectic solvent (DES)-coated glass substrate and subsequent direct transfer process. The as-fabricated 3D dendritic Au/ITO flexible substrates can be used for ultrasensitive SERS detection of crystal violet (CV) as probe analyte molecules with the limit of detection (LOD) as low as 6.4 × 10-15 M, with good signal reproducibility (RSD of 11.3%). In addition, the substrate showed excellent sensitivity in detecting nanoplastics such as poly(ethylene terephthalate) (200 nm) and polystyrene (100 nm) with LODs reaching up to 0.051 and 8.2 μg/mL, respectively. This work provides a facile approach for the preparation of highly flexible plasmonic substrates, showing great potential for the SERS detection of a variety of environmental pollutants.

Uniformly aligned Ag NPs/graphene paper for enhanced SERS detection of pesticide residue

The surface-enhanced Raman scattering (SERS) technique provides a quick and reliable method for detecting pesticide residues. In this study, flexible substrates, composed of orderly arranged silver nanospheres (Ag NPs) films on graphene paper, were fabricated through a simple, low-cost Ag NP self-assembly process at a liquid-liquid interface, followed by transfer of the films onto the graphene paper. The SERS performance of the fabricated substrates was evaluated using a portable Raman spectrometer, with rhodamine 6G (R6G) serving as the probe molecule. The results indicate that the bilayer Ag NP films-covered graphene paper exhibits optimal overall performance, characterized by high sensitivity and high uniformity. The limit of detection (LOD) for the R6G molecule is as low as 8.73 × 10-9 M, demonstrating the strong signal amplification capability of the SERS substrate. Moreover, the relative standard deviation (RSD) of the Raman intensity at 1508 cm-1 for different selected points on the substrate is 5.018 %, indicating high uniformity of the SERS substrate. Finally, the performance of the SERS substrate was further evaluated by detecting thiram in fresh orange juice, demonstrating the capability to detect concentrations as low as 10-6 M. This result highlights the significant potential of the developed SERS substrate for practical applications in food safety and quality control.

Synergistic enhancement of the Ag/ZIF-67 cage@MXene 3D heterogeneous structure for ultrahigh SERS sensitivity and stability

There is an urgent need in the in situ field for rapid extraction and analysis of target molecules from irregular surfaces. The application of SERS technology is often limited by low adhesion between precious metal nanoparticles and the substrate and complex fabrication processes. In order to solve this problem, a carbon fiber cloth (CFC) loaded Ag/ZIF-67 cage@MXene 3D detection platform (AZMC) was constructed in this study. The platform takes advantage of the large surface area and defects of MXene flakes to host noble metals, the high carrier transport efficiency between flakes, and van der Waals forces to build highly sensitive and stable composite SERS substrates. The hydrophilicity and subsurface oxidation behavior of MXene make its optoelectronic performance unstable. In this study, the ZIF-67 cage was chemically bonded to MXene through the Co-O-Ti bond, and the ZIF 67@MXene heterojunction was successfully constructed to maintain the optimal photoelectric stability and excellence of MXene. The high performance of the substrate stems from the synergistic effects of charge transfer (CT) and surface plasmon resonance (SPR) of AgNPs and MXene flakes, while the 3D nanocage structure provides additional hotspot regions. Substrate sensitivity was analyzed using rhodamine 6G (R6G) as a probe molecule (detection limit as low as 10-11 M). Notably, the AZMC substrate is highly stable (SERS performance remains essentially unchanged after 45 days of exposure to air). Using this substrate, we also successfully analyzed methylene blue (MB) molecules and Sudan I molecules on apple epidermis, which were successfully detected at concentrations of 0.5 mg L-1 and 1 mg L-1, respectively.

Au nanoparticle-engineered Ti3C2Tx MXenes as a high-performance SERS platform for detection of organic pollutants

The detection of organic pollutants at ultra-low concentrations is crucial for environmental monitoring, yet existing surface-enhanced Raman scattering (SERS) platforms often suffer from limited sensitivity, poor stability, and inconsistent signal reproducibility. To address these challenges, this study presents a high-performance SERS platform based on in situ gold (Au) nanoparticle-engineered Ti3C2Tx MXenes. This novel approach enhances signal amplification and ensures long-term stability for pollutant detection. The platform achieves an exceptional limit of detection (LOD) of 10-11 M with an enhancement factor of 1010 for Methylene Blue (MB), demonstrating its superior sensitivity. Additionally, signal repeatability has been validated by calculating the relative standard deviation (RSD), and the SERS substrate retains 83% of its signal intensity after 5 months of storage, confirming its durability. Furthermore, the platform effectively detects polybrominated diphenyl ether (BDE-47), a persistent organic pollutant, at concentrations below the regulatory threshold of 10-6 M. These results highlight the potential of the proposed SERS platform for reliable and long-term environmental monitoring of hazardous substances.

Combining array-assisted SERS microfluidic chips and machine learning algorithms for clinical leukemia phenotyping

The disease progression and treatment options of leukemia between different subtypes vary considerably, emphasizing the importance of phenotyping. However, early typing of leukemia remains challenging due to the lack of highly sensitive and specific analytical tools. Herein, we propose a SERS-based platform for the classification of acute lymphoblastic T-cell leukemia (T-ALL) and chronic myeloid leukemia (CML) through the combination of machine learning and microfluidic chips. The ordered arrays in microfluidic channels reshape the microscopic flow field and contacting interfaces, facilitating the uniform and efficient capture of tumor cells. To enable phenotypic analysis, spectrally orthogonal SERS aptamer nanoprobes were applied, providing composite spectral signatures of individual cells in accordance with surface protein expression. Further, machine learning algorithms were employed to analyze the SERS signatures automatically, resulting in an accuracy of 98.6 % for 73 clinical blood samples. The results demonstrate that this platform holds promising potential for clinical leukemia diagnosis and precision medicine.

A flexible 3D ordered SERS sensor for rapid and reliable detection of pesticide residues in fruits

We fabricated flexible, three-dimensional (3D) ordered silicon nanowire (SiNW) arrays decorated with high-density silver nanoparticles (AgNPs) for the sensitive and reproducible detection of pesticide residues. These sensors demonstrated a detection limit of 10-9 M for methyl parathion (MPT) on curved surfaces.

A Three-Dimensional, Flexible Conductive Network Based on an MXene/Rubber Composite for Lithium Metal Anodes

Flexibility enhancement is a pressing issue in the current development of advanced lithium-metal battery applications. Many types of organic polymers are inherently flexible, which can form a composite structure enhancing electrode flexibility. However, organic polymers have a negative influence on the plating and stripping of lithium-metal anodes, and the large number of polymers block the pore of the material, reducing the utilization of the active site. Herein, we report a flexible porous substrate as an anode host based on a serine-modified three-dimensional structure of MXene and epoxidized natural rubber composite (3D/MXene-S-ENR), in which lithium ions can uniformly deposit in the interconnected pore structure. The 3D/MXene-S-ENR, having more nucleation sites, can effectively improve the uniformity of lithium metal, which effectively reduces the local current density and inhibits lithium dendrites. Compared with the serine-modified MXene and the epoxidized natural rubber electrode (MXene-S-ENR), the 3D/MXene-S-ENR electrode has lower overpotential and stable cycling. The lithium-sulfur batteries (Li-S) based on the 3D/MXene-S-ENR anode and sulfur cathode (3D/MXene-S-ENR@Li|S/C) deliver a stable discharge capacity of 316.2 mAh g-1 after 350 cycles, with a Coulombic efficiency of 98.05%. Finally, we assembled a flexible pack battery, which demonstrates the potential value of the 3D/MXene-S-ENR anode in high-performance flexible lithium-sulfur batteries.

Elevating electron transfer of recyclable SERS sensor using AuNPs/TiO2/Ti3C2 heterostructures for detection of malachite green in sunfish

Malachite green (MG)-contaminated aquatic products pose a serious threat to animal and human health. Hence, a novel recyclable surface-enhanced Raman scattering (SERS) substrate based on AuNPs/TiO2/Ti3C2 heterostructures was developed for the detection and degradation of MG in aquatic products. Specifically, AuNPs/TiO2/Ti3C2 heterostructures were synthesized by in situ oxidation and electrostatic adsorption based on Ti3C2 nanosheets. The excellent photocatalytic and SERS performance of the AuNPs/TiO2/Ti3C2 was demonstrated by Density functional theory (DFT) calculations and experimental results, which was attributed to the enhancement of charge transfer (CT) after the formation of heterostructures. The results demonstrate that AuNPs/TiO2/Ti3C2 is highly sensitive and recyclable. The detection limit of the sensor for MG is 8.91 × 10-5 mg/L. The sensor can be recycled for five times under the condition of light, and shows satisfactory self-cleaning performance in the food matrix, providing a possible alternative solution for the recyclable detection of MG.

Structurally-Modulated Substrate of MXene for Surface-Enhanced Raman Scattering Sensing

The distinctive structure of MXene offers exceptional electron transport properties, abundant surface chemistry, and robust mechanical attributes, thereby bestowing it with remarkable advantages and promising prospects in the realm of surface-enhanced Raman scattering (SERS). This review comprehensively outlines the evolution, synthesis methodologies, and characterization techniques employed for MXene-based SERS substrates. It delves into the intricacies of its SERS enhancement mechanism, substrate variants, and performance metrics, alongside showcasing its diverse applications spanning molecular detection, biosensing, and environmental monitoring. Furthermore, it endeavors to pinpoint the research bottlenecks and chart the future research trajectories for MXene-based SERS substrates.

In Situ Laser Direct Writing of Graphene-Based Layered Hybrid Materials with Superhydrophilicity

Laser-induced graphene (LIG) has attracted extensive attention as an electrode material. However, it usually exhibits limited electrochemical performance in many applications due to the limited electrical conductivity and charge storage properties. Herein, we proposed a simple and environmentally friendly strategy for in situ preparation of flexible Au/LIG/PI layered hybrid materials using laser direct writing. The transformation from hydrophobic to superhydrophilic of hybrid materials was successfully achieved. At a laser power of 6.0 W during laser reirradiation, the contact angle of the prepared Au/LIG/PI layered hybrid material was 0°. Characterizations confirmed a formed continuous Au layer covered on the porous LIG skeleton with a uniform distribution. The superhydrophilicity resulting from this unique microstructure greatly enhanced the electrochemical performance of the microsupercapacitors (MSCs) designed and fabricated based on Au/LIG/PI hybrid materials. Meanwhile, this MSC demonstrated excellent flexibility due to the PI substrate. The in situ preparation of superhydrophilic Au/LIG/PI layered hybrid materials provides a strategy for improving the performance of LIG-based MSCs, thereby enhancing their application potential.

MXene Bimetallic Coating Synergistic Enhanced Colorimetric-Raman Dual Signal-Based Immunochromatographic Assay for Advancing Detection Performance

Herein, a three-dimensional thin film-like multifunctional MXene bimetallic coating material (Ti3C2@Au-Ag) with strong color intensity, high surface-enhanced Raman scattering (SERS) activity, and strong antibody affinity (1.00 × 108 M-1) was prepared. It was the first time that Ti3C2@Au-Ag-based colorimetric-SERS dual-signal immunochromatographic assay (ICA) was developed for the detection of dexamethasone, achieving the limits of detection of 0.0089, 0.14, and 0.084 μg/kg for milk, beef, and pork in colorimetric mode and 0.0015, 0.060, and 0.075 μg/kg in SERS mode. It was up to 200-fold more sensitive than the reported ICAs. The recoveries were 82.0%-112.6%, and the coefficients of variation were 1.4%-13.7%. The Ti3C2@Au-Ag-ICA was verified by LC-MS/MS in the application on 30 real samples with a correlation coefficient greater than 0.98. This study can provide efficient theoretical and practical value for the development of a colorimetric-SERS dual-signal immunoassay platform.

Wet-spun Ag/PEDOT: PSS composite fibers for high-sensitive SERS sensing and high electrical conducting

Nanometal-based composite fibers have been widely explored in flexible sensors due to their outstanding optical and electrical properties. However, the weak binding force between metallic nanomaterial and fiber greatly limits the real application. In this work, nano silver (Ag) are strongly bonded with poly(3,4-ethylenedioxythiophene)-poly (styrene sulfonate) (PEDOT: PSS) fiber by the wet-spun process. Ag-S chemical bonds are formed by the interaction of Ag and PEDOT. The Ag/PEDOT: PSS composite fiber shows excellent surface-enhanced Raman scattering (SERS) sensitivity on Rhodamine 6G (R6G) molecules. The detection limit can reach 10-11 M and Raman enhancement factor (EF) is of 1.3 × 107. The high-sensitive SERS activity of Ag/PEDOT: PSS composite fiber mainly results from PEDOT: PSS, and the enhancement factor is 3 orders of magnitude better than that of other PEDOT: PSS based SERS substrates. Moreover, the composite fiber has metal-level conductivity of 1019 S/cm. This is 5 times higher than the conductivity of PEDOT: PSS fiber and a two-fold improvement over the reported values for nanometal/PEDOT: PSS based fabrics. The composite fiber has electric stability under bending test with bending speeds of 2 Hz indicating the composite fiber has good structural stability. In addition, the temperature of the composite fiber with 7 cm length can reach 76.5 °C at a voltage of 18 V. Additionally, the composite fiber shows anti-bacterial property and melting drop resistance, which pave the way for the integration of fiber-based optical and electrical sensors in the future multifunctional flexible devices.

2D Material-Based Surface-Enhanced Raman Spectroscopy Platforms (Either Alone or in Nanocomposite Form)-From a Chemical Enhancement Perspective

Surface-enhanced Raman spectroscopy (SERS) is a vibrational spectroscopic technique with molecular fingerprinting capability and high sensitivity, even down to the single-molecule level. As it is 50 years since the observation of the phenomenon, it has now become an important task to discuss the challenges in this field and determine the areas of development. Electromagnetic enhancement has a mature theoretical explanation, while a chemical mechanism which involves more complex interactions has been difficult to elucidate until recently. This article focuses on the 2D material-based platforms where chemical enhancement (CE) is a significant contributor to SERS. In the context of a diverse range (transition metal dichalcogenides, MXenes, etc.) and categories (insulating, semiconducting, semimetallic, and metallic) of 2D materials, the review aims to realize the influence of various factors on SERS response such as substrates (layer thickness, structural phase, etc.), analytes (energy levels, molecular orientation, etc.), excitation wavelengths, molecular resonances, charge-transfer transitions, dipole interactions, etc. Some examples of special treatments or approaches have been outlined for overcoming well-known limitations of SERS and include how CE benefits from the defect-induced physicochemical changes to 2D materials mostly via the charge-transport ability or surface interaction efficiency. The review may help readers understand different phenomena involved in CE and broaden the substrate-designing approaches based on a diverse set of 2D materials.

Cu-doped ZnO/Ag/CuO heterostructure: superior photocatalysis and charge transfer

Doped semiconductor heterostructures have superior properties compared to their components. In this study, we observed the synthesis of Cu-doped ZnO/Ag/CuO heterostructure with the presence of charge transfer and visible light-harvesting properties resulting from doping and heterojunction. The porous heterostructures were prepared using the bottom-up combustion (BUC) approach. This method generated porous heterostructures by eliminating gaseous by-products. X-ray diffraction (XRD) optimization revealed that the ideal conditions included 1.00 g of polyvinyl alcohol (PVA), a synthesis temperature of 50 °C, and a 1 hour calcination time. Introducing copper (Cu) into the zinc oxide (ZnO) lattice caused a high-angle shift in the XRD pattern peaks. High-resolution transmission electron microscopy (HRTEM) images and XRD patterns confirmed the formation of Cu-doped ZnO/Ag/CuO (c-zac) heterostructures. Elemental mapping analysis confirmed the even surface distribution of Ag metal. The c-zac heterostructures exhibited superior optoelectrical and charge transfer properties compared to single ZnO. The heterostructures demonstrated improved methylene blue (MB) dye degradation potential (k = 0.065 min-1) compared to single ZnO (k = 0.0041 min-1). This photocatalytic potential is attributed to enhanced light absorption and charge transfer properties. The extended visible light absorption resulted from CuO and Ag's surface plasmon resonance properties. The selected 15c-zac heterostructure also performed well in a reusability photocatalytic test, remaining effective until the 3rd cycle. Consequently, this heterostructure holds promise for scaling up as a catalyst for environmental remediation.

Jellyfish-like Gold Nanowires as FlexoSERS Sensors for Sweat Analysis

We introduce the FlexoSERS sensor, which is notable for its high stretchability, sensitivity, and patternability. Featuring a hierarchically oriented jellyfish-like architecture constructed from stretchable gold nanowires, this sensor provides an ultrasensitive SERS signal even under 50% strain, with an enhancement factor (EF) of 3.3 × 1010. Impressively, this heightened performance remains consistently robust across 2,500 stretch-release cycles. The integration of nanowires with 3D-printed hydrogel enables a customizable FlexoSERS sensor, facilitating localized sweat collection and detection. The FlexoSERS sensor successfully detects and quantifies uric acid (UA) in both artificial and human sweat and functions as a pH sensor with repeatability and sensitivity across a pH range of 4.2-7.8, enabling real-time sweat monitoring during exercise. In summary, the rational architectural design, scalable fabrication process, and hydrogel integration collectively position this nanowire-based FlexoSERS sensor as a highly promising platform for customizable wearable sweat diagnostics.

Functional structures assembled based on Au clusters with practical applications

The advancement of gold nanoclusters (Au NCs) has given rise to a new era in fabricating functional materials due to their controllable morphology, stable optical properties, and excellent biocompatibility. Assemblies based on Au NCs demonstrate significant potentiality in constructing multiple structures as acceptable agents in applications such as sensing, imaging technology, and drug delivery systems. In addition, the assembled strategies illustrate the integration mechanism between each component while facing material requirement. It is necessary to provide supplementary and comprehensive reviews on the assembled functional structures (based Au NCs), which hold promise for applications and could expand their functional range and potential applications. This review focuses on the assembled structures of Au NCs in combination with metals, metal oxides, and non-metal materials, which are intricately arranged through various interaction forces including covalent bonds and metal coordination, resulting in a diverse array of multifunctional Au NC assemblies. These assemblies have widespread applications in fields such as biological imaging, drug delivery, and optical devices. The review concludes by highlighting the challenges and future prospects of Au NC assemblies, emphasizing the importance of continued research to advance nanomaterial assembly innovation.

A Scalable Synthesis of Ag Nanoporous Film As an Efficient SERS-Substrates for Sensitive Detection of Nanoplastics

Nanoplastics pollution has led to a severe environmental crisis because of a large accumulation of these smaller nanoplastic particles in the aquatic environment and atmospheric conditions. Detection of these nanoplastics is crucial for food safety monitoring and human health. In this work, we report a simple and eco-friendly method to prepare a SERS-substrate-based nanoporous Ag nanoparticle (NP) film through vacuum thermal evaporation onto a vacuum-compatible deep eutectic solvent (DES) coated growth substrate for quantitative detection of nanoplastics in environmental samples. The nanoporous Ag NP films with controlled pores were achieved by the soft-templating role of DESs over the growth substrate, which enabled the self-assembly of deposited Ag NPs over the surface of DES. The optimized nanoporous Ag substrate provides high sensitivity in the detection of analyte molecules, crystal violet (CV), and rhodamine 6G (R6G) with a limit of detection (LOD) up to 1.5 × 10-13 M, excellent signal reproducibility, and storage stability. Moreover, we analyzed quantitative SERS detection of polyethene terephthalate (PET, size of 200 nm) and polystyrene (PS, size of 100 nm) nanoplastics with an LOD of 0.38 and 0.98 μg/mL, respectively. In addition, the SERS substrate efficiently detects PET and PS nanoplastics in real environmental samples, such as tap water, lake water, and diluted milk. The enhanced SERS sensing ability of the proposed nanoporous Ag NP film substrate holds immense potential for the sensitive detection of various nanoplastic contaminants present in environmental water.

Snowflake Cu2S@ZIF-67: A novel heterostructure substrate for enhanced adsorption and sensitive detection in BPA

Developing semiconductor substrates with superior stability and sensitivity is challenging in surface-enhanced Raman scattering (SERS) research. Here, a snowflake Cu2S@ZIF-67 heterostructure was fabricated using a straightforward method, exhibiting a notable enhancement factor of 9.0 × 109 and a limit of detection (LOD) of 10-14 M for methylene blue (MB). In addition, the Cu2S@ZIF-67 heterostructure substrate demonstrates outstanding homogeneity (relative standard deviation (RSD) = 9.2%) and stability (120 days). Employing Cu2S generates highly sensitive hotspots via an electromagnetic (EM) mechanism, and the growth of ZIF-67 on its surface augments the adsorption capacity and charge transfer capability (chemical mechanism, CM), thereby enhancing the SERS detection sensitivity. Furthermore, the Cu2S@ZIF-67 heterostructure, which was used as a SERS substrate, facilitated the detection of bisphenol A (BPA) with an LOD of 10-11 M. The Cu2S@ZIF-67 heterostructure substrate has excellent selectivity and anti-interference, which is very suitable for BPA detection in complex environment applications. The accuracy of the Cu2S@ZIF-67 heterostructure as a SERS substrate for detecting BPA in real water samples (water bottles, tap water, and pure milk) was confirmed by comparison with high-performance liquid chromatography (HPLC). These results demonstrate that through the rational design of heterostructures can achieve the quantitative and accurate detection of hazardous substances in food and the environment can be achieved.

3D-Bioprinted Hepar-on-a-Chip Implanted in Graphene-Based Plasmonic Sensors

Precise three-dimensional (3D) bioprinting designs enable the fabrication of unique structures for 3D-cell culture models. There is still an absence of real-time detection tools to effectively track in situ 3D-cell performance, hindering a comprehensive understanding of disease progression and drug efficacy assessment. While numerous bioinks have been developed, few are equipped with internal sensors capable of accurate detection. This study addresses these challenges by constructing a 3D-bioprinted hepar-on-a-chip embedded with graphene quantum dot-capped gold nanoparticle-based plasmonic sensors, featuring strong surface-enhanced Raman scattering (SERS) enhancement, biostability, and signal consistency. Such an integrated hepar-on-a-chip demonstrates excellent capability in the secretion of liver function-related proteins and the expression of drug metabolism and transport-related genes. Furthermore, the on-site detection of cell-secreted biomarker glutathione transferase α (GST-α) was successfully achieved using the plasmonic probe, with a dynamic linear detection range of 20-500 ng/mL, showcasing high anti-interference and specificity for GST-α. Ultimately, this integrated hepar-on-a-chip system offers a high-quality platform for monitoring liver injury.

Beyond the Charge Transfer Mechanism for 2D Materials-Assisted Surface Enhanced Raman Scattering

Two-dimensional (2D) materials have been extensively implemented as surface-enhanced Raman scattering (SERS) substrates, enabling trace-molecule detection for broad applications. However, the accurate understanding of the mechanism remains elusive because most theoretical explanations are still phenomenological or qualitative based on simplified models and rough assumptions. To advance the development of 2D material-assisted SERS, it is vital to attain a comprehensive understanding of the enhancement mechanism and a quantitative assessment of the enhancement performance. Here, the microscopic chemical mechanism of 2D material-assisted SERS is quantitatively investigated. The frequency-dependent Raman scattering cross sections suggest that the 2D materials' SERS performance is strongly dependent on the excitation wavelengths and the molecule types. By analysis of the microscopic Raman scattering processes, the comprehensive contributions of SERS can be revealed. Beyond the widely postulated charge transfer mechanisms, the quantitative results conclusively demonstrate that the resonant transitions within 2D materials alone are also capable of enhancing the molecular Raman scattering through the diffusive scattering of phonons. Furthermore, all of these scattering routines will interfere with each other and determine the final SERS performance. Our results not only provide a complete picture of the SERS mechanisms but also demonstrate a systematic and quantitative approach to theoretically understand, predict, and promote the 2D materials SERS toward analytical applications.

An Au bipyramids@CuZn MOF core-shell nanozyme enables universal SERS and a colorimetric dual-model bioassay

In this study, a new type of gold nano-bipyramids@CuZn bimetallic organic framework (AuNBPs@CuZn MOF) nanozyme with high peroxidase (POD)-like activity and surface enhanced Raman scattering (SERS) activity was constructed with a special core-shell structure, which can catalyze the oxidation of TMB (colourless and Raman-inactive) into ox-TMB (blue and Raman-active). An AuNBPs@CuZn MOF-enabling universal SERS and colorimetric dual-model bioassay was thus developed for biomolecules with excellent performance, and has promising application prospects in the biosensing fields.

Simple Synthesis of Cellulose-Based Nanocomposites as SERS Substrates for In Situ Detection of Thiram

There is a growing interest in the use of flexible substrates for label-free and in situ Surface-enhanced Raman Spectroscopy (SERS) applications. In this study, a flexible SERS substrate was prepared using self-assembled Au/Ti3C2 nanocomposites deposited on a cellulose (CS) paper. The Au/Ti3C2 nanocomposites uniformly wrapped around the cellulose fibers to provide a three-dimensional plasma SERS platform. The limit of detection (LOD) of CS/Au/Ti3C2 was as low as 10-9 M for 4-mercaptobenzoic acid(4-MBA) and crystal violet (CV), demonstrating good SERS sensitivity. CS/Au/Ti3C2 was used for in situ SERS detection of thiram on apple surfaces by simple swabbing, and a limit of detection of 0.05 ppm of thiram was achieved. The results showed that CS/Au/Ti3C2 is a flexible SERS substrate that can be used for the detection of thiram on apple surfaces. These results demonstrate that CS/Au/Ti3C2 can be used for the non-destructive, rapid and sensitive detection of pesticides on fruit surfaces.

Improved Surface-Enhanced Raman Scattering Performance of 2D Ti3C2Tx MXene Embedded in PVDF Film Enabled by Photoinduction and Electric Field Modulation

In this study, we introduce a synergistic approach to enhance the surface-enhanced Raman scattering (SERS) signal in two-dimensional (2D) MXene through photo-irradiation and electric field modulation. Our methodology involves the integration of 2D Ti3C2Tx MXene with piezoelectric polyvinylidene fluoride (PVDF) polymer, resulting in the creation of a free-standing, flexible composite film. On this composite film, a thin layer of Au was deposited. Our flexible substrate was able to sense methylene blue (MB), crystal violet (CV), 4-aminothiophenol (ATP), and melamine. The SERS substrate exhibits low detection limit of 10-8 M MB with a 6.7 × 106 enhancement factor (EF). The SERS substrate enables picomolar (pM) detection sensitivity for CV molecules with an EF of 9.2 × 109. Furthermore, the introduction of photo-irradiation leads to an additional ∼3.5-fold enhancement in the SERS signal, which is attributed to the altered work function and defects. The application of mechanical force to the piezoelectric PVDF/Ti3C2Tx film results in a ∼4.5-fold boost in SERS signal due to mechanical force-induced electrical energy. The fabrication strategy employed here for producing a flexible piezoelectric PVDF/Ti3C2Tx film holds significant promise for expanding the potential application of 2D MXene in rapid, on-site sensing scenarios.

Molecularly Imprinted Polymer Biosensor Based on Nitrogen-Doped Electrochemically Exfoliated Graphene/Ti3 CNTX MXene Nanocomposite for Metabolites Detection

Rapid and accurate quantification of metabolites in different bodily fluids is crucial for a precise health evaluation. However, conventional metabolite sensing methods, confined to centralized laboratory settings, suffer from time-consuming processes, complex procedures, and costly instrumentation. Introducing the MXene/nitrogen-doped electrochemically exfoliated graphene (MXene@N-EEG) nanocomposite as a novel biosensing platform in this work addresses the challenges associated with conventional methods, leveraging the concept of molecularly imprinted polymers (MIP) enables the highly sensitive, specific, and reliable detection of metabolites. To validate our biosensing technology, we utilize agmatine as a significant biologically active metabolite. The MIP biosensor incorporates electrodeposited Prussian blue nanoparticles as a redox probe, facilitating the direct electrical signaling of agmatine binding in the polymeric matrix. The MXene@N-EEG nanocomposite, with excellent metal conductivity and a large electroactive specific surface area, effectively stabilizes the electrodeposited Prussian blue nanoparticles. Furthermore, increasing the content of agmatine-imprinted cavities on the electrode enhances the sensitivity of the MIP biosensor. Evaluation of the designed MIP biosensor in buffer solution and plasma samples reveals a wide linear concentration range of 1.0 nM-100.0 μM (R2 = 0.9934) and a detection limit of 0.1 nM. Notably, the developed microfluidic biosensor offers low cost, rapid response time to the target molecule (10 min of sample incubation), good recovery results for detecting agmatine in plasma samples, and acceptable autonomous performance for on-chip detection. Moreover, its high reliability and sensitivity position this MIP-based biosensor as a promising candidate for miniaturized microfluidic devices with the potential for scalable production for point-of-care applications.

A critical mini-review on doping and heterojunction formation in ZnO-based catalysts

This mini-review on doping and heterojunctions for catalysis applications provides a comprehensive overview of key aspects. Doping, when carried out adequately with a uniform distribution, creates a new energy level that significantly enhances charge transfer and light absorption. This new level alters the material's morphology and enhances intrinsic defects. For instance, ZnO, despite its exceptional band edge concerning oxygen reduction and water oxidation redox potentials, faces the issue of electron-hole recombination. However, forming a heterojunction can effectively aid charge transfer and prolong electron-hole relaxation without recombination. This is where the role of doping and heterojunctions becomes crucial. Additionally, incorporating noble metals with S- and Z-scheme heterojunctions offers a promising mechanism for charge transfer and visible light harvesting, further amplifying the catalytic properties.

Hybrid plasmonic aerogel with tunable hierarchical pores for size-selective multiplexed detection of VOCs with ultrahigh sensitivity

Sensitive and rapid identification of volatile organic compounds (VOCs) at ppm level with complex composition is vital in various fields ranging from respiratory diagnosis to environmental safety. Herein, we demonstrate a SERS gas sensor with size-selective and multiplexed identification capabilities for VOCs by executing the pre-enrichment strategy. In particular, the macro-mesoporous structure of graphene aerogel and micropores of metal-organic frameworks (MOFs) significantly improved the enrichment capacity (1.68 mmol/g for toluene) of various VOCs near the plasmonic hotspots. On the other hand, molecular MOFs-based filters with different pore sizes could be realized by adjusting the ligands to exclude undesired interfering molecules in various detection environments. Combining these merits, graphene/AuNPs@ZIF-8 aerogel gas sensor exhibited outstanding label-free sensitivity (up to 0.1 ppm toluene) and high stability (RSD=14.8%, after 45 days storage at room temperature for 10 cycles) and allowed simultaneous identification of multiple VOCs in a single SERS measurement with high accuracy (error < 7.2%). We visualize that this work will tackle the dilemma between sensitivity and detection efficiency of gas sensors and will inspire the design of next-generation SERS technology for selective and multiplexed detection of VOCs.

Unusual Raman Enhancement Effect of Ultrathin Copper Sulfide

In surface-enhanced Raman spectroscopy (SERS), 2D materials are explored as substrates owing to their chemical stability and reproducibility. However, they exhibit lower enhancement factors (EFs) compared to noble metal-based SERS substrates. This study demonstrates the application of ultrathin covellite copper sulfide (CuS) as a cost-effective SERS substrate with a high EF value of 7.2 × 104 . The CuS substrate is readily synthesized by sulfurizing a Cu thin film at room temperature, exhibiting a Raman signal enhancement comparable to that of an Au noble metal substrate of similar thickness. Furthermore, computational simulations using the density functional theory are employed and time-resolved photoluminescence measurements are performed to investigate the enhancement mechanisms. The results indicate that polar covalent bonds (Cu─S) and strong interlayer interactions in the ultrathin CuS substrate increase the probability of charge transfer between the analyte molecules and the CuS surface, thereby producing enhanced SERS signals. The CuS SERS substrate demonstrates the selective detection of various dye molecules, including rhodamine 6G, methylene blue, and safranine O. Furthermore, the simplicity of CuS synthesis facilitates large-scale production of SERS substrates with high spatial uniformity, exhibiting a signal variation of less than 5% on a 4-inch wafer.

Charge transfer in TiO2-based photocatalysis: fundamental mechanisms to material strategies

Semiconductor-based photocatalysis has attracted significant interest due to its capacity to directly exploit solar energy and generate solar fuels, including water splitting, CO2 reduction, pollutant degradation, and bacterial inactivation. However, achieving the maximum efficiency in photocatalytic processes remains a challenge owing to the speedy recombination of electron-hole pairs and the limited use of light. Therefore, significant endeavours have been devoted to addressing these issues. Specifically, well-designed heterojunction photocatalysts have been demonstrated to exhibit enhanced photocatalytic activity through the physical distancing of electron-hole pairs generated during the photocatalytic process. In this review, we provide a systematic discussion ranging from fundamental mechanisms to material strategies, focusing on TiO2-based heterojunction photocatalysts. Current efforts are focused on developing heterojunction photocatalysts based on TiO2 for a variety of photocatalytic applications, and these projects are explained and assessed. Finally, we offer a concise summary of the main insights and challenges in the utilization of TiO2-based heterojunction photocatalysts for photocatalysis. We expect that this review will serve as a valuable resource to improve the efficiency of TiO2-based heterojunctions for energy generation and environmental remediation.

Unveiling the Dual-Enhancing Mechanisms of Kinetically Controlled Silver Nanoparticles on Piezoelectric PVDF Nanofibers for Optimized SERS Performance

Noble metal nanoparticle (NMP)-based composite substrates have garnered significant attention as a highly promising technique for surface-enhanced Raman scattering (SERS) in diverse scientific disciplines because their remarkable ability to amplify and functionalize Raman signals has positioned them as valuable tools for molecular detection. However, optimizing the size and distribution of NMPs has not received sufficient emphasis because of challenges associated with the precise control of deposition and the modulation of reducing rates during growth. In this research, we achieved the optimized size and spatial patterns of AgNWs on electrospun poly(vinylidene fluoride) (PVDF) nanofibers by utilizing a polydopamine (PDA) layer as a mild and controllable reduction mediator, by which the size and density of the AgNWs could be relatively precisely manipulated, achieving a dense distribution of effective "hot spots". On the other hand, harnessing the inherent piezoelectric properties of the electrospun PVDF nanofibers further boosted the LSPR effect during the SERS test, forming a flexible dual-enhancing composite SERS substrate with excellent sensitivity. In addition to addressing structural aspects, exploiting synergistic systems capable of transferring external energy or forces to enhance the SERS performances presents a compelling avenue to broaden the practical applications of SERS. The dual-enhanced substrate achieved an exceptional enhancement factor (EF) of 1.05 × 108 and a low detection limit (LOD) of 10-10 M during the SERS test. This study focuses on integrating NMPs with electrospun piezoelectric polymer nanofibers to develop a dual-enhancing SERS substrate with excellent sensitivity and practicality. The findings provide valuable insights into controllably depositing NMPs on electrospun polymer fibers and hold significant implications for the development of highly sensitive and practical SERS substrates across various applications.

Therapeutic drug monitoring mediated by the cooperative chemical and electromagnetic effects of Ti3C2TX modified with Ag nanocubes

It is pivotal for the credible utilization of surface-enhanced Raman scattering (SERS) technique in clinical drug monitoring to exploit versatile substrates with dependable quantitative detection and robust recognition abilities. Herein, a commendable electromagnetic-chemical dual-enhancement SERS substrate dependent on Ti3C2TX and Ag nanocubes (Ag NCs) was fabricated for the precise quantification of ritonavir and ibrutinib in serum. Specifically, it was revealed that numerous electromagnetic "hotspots" emerged nearby the extremely tiny nanogaps among the intimately clustered Ag NCs, which also acted as optimal channels to facilitate effective photo-induced charge transfer (PICT) between the two-dimensional Ti3C2TX matrix and target molecules. The cooperation between electromagnetic and chemical effects yielded a satisfactory enhancement factor (EF) of 4.77 × 107 for the composite substrate. Benefiting from the remarkable sensitivity of the Ti3C2TX/Ag NCs composite substrate, the low limit of detection (LOD) at 10-6 mg/mL was successfully attained, along with exceptional recoveries of exceeding 90% for ritonavir and ibrutinib in serum. Considering its reliability and simplicity, our strategy holds immense promise for its utilization in efficient monitoring and identification of clinical blood drug concentration.

Microfluidics-aided fabrication of 3D micro-nano hierarchical SERS substrate for rapid detection of dual hepatocellular carcinoma biomarkers

The simultaneous analysis of trace amounts of dual biomarkers is crucial in the early diagnosis, treatment, and prognosis of hepatocellular carcinoma (HCC). In this study, we prepared SERS-active hydrogel microparticles (SAHMs) with 3D hierarchical gold nanoparticles (AuNPs) micro-nanostructures by microdroplet technology and in situ synthesis, which demonstrated high reproducibility and sensitivity. Compared with traditional 2D SERS substrates, this newly prepared 3D SERS substrate provided a high density of nano-wrinkled structures and numerous AuNPs. Furthermore, a newly designed SERS-active substrate was proposed for the simultaneous microfluidic detection of AFP and AFU. The Raman signals of sandwich immunocomplexes on the surface of the SAHMs were measured for the trace analysis of these biomarkers. The proposed microfluidic platform achieved AFP and AFU detection in the range of 0.1-100 ng mL-1 and 0.01-100 ng mL-1, respectively, which represents a good response. Indeed, this platform is easy to fabricate, of low cost and has short detection time and comparable detection limits to other methods. As far as we know, this is the first study to achieve the simultaneous detection of AFP and AFU on a microfluidic platform. Therefore, we proposed a new simultaneous detection platform for dual HCC biomarkers that shows strong potential for the early diagnosis of HCC.

Wearable Plasmonic Sensors Engineered via Active-Site Maximization of TiVC MXene for Universal Physiological Monitoring at the Molecular Level

Two-dimensional transition metal carbon/nitrides (MXenes) are promising candidates to revolutionize next-generation wearable sensors as high-performance surface-enhanced Raman scattering (SERS) substrates. However, low sensitivity of pure MXene nanosheets and weak binding force or uncontrolled in situ growth of plasmonic nanoparticles on hybrid MXene composites limit their progress toward universal and reliable sensors. Herein, we designed and manufactured a highly sensitive, structurally stable wearable SERS sensor by in situ fabrication of plasmonic nanostructures on the flexible TiVC membranes via the maximization of chemically reducing sites using alkaline treatment. DFT calculations and experimental characterization demonstrated that the hydroxyl functional groups on the surface of MXenes can facilitate the reduction of metal precursors and the nucleation of gold nanoparticles (AuNPs) and can be covalently attached to AuNPs. Thus, the fabricated flexible TiVC-OH-Au sensor satisfied the rigorous mechanical requirements for wearable sensors. In addition, combining the electromagnetic (EM) enhancement from dense AuNPs formed by the activation of nucleation sites and charge transfer (CT) between target molecule and substrate induced by the abundant DOS near the Fermi level of TiVC, the fabricated sensor exhibits ultrasensitivity, long-term stability, good signal repeatability, and excellent mechanical durability. Moreover, the proof-of-concept application of the wearable SERS sensor in sweat sensing was demonstrated to monitor the content of nicotine, methotrexate, nikethamide, and 6-acetylmorphine in sweat at the molecular level, which was an important step toward the universality and practicality of the wearable sensing technology.

SERS-active immunoassay kit for SARS-CoV‑2 mediated by the cooperative chemical and electromagnetic effects of MXene modified with gold nanowires

Surface-enhanced Raman scattering (SERS) technique with high sensitivity, reliable specificity, and rapid recognition ability exhibits attractive promise for the effective fast-monitoring of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Herein, a novel SERS-active immunoassay kit for SARS-CoV-2 nucleocapsid (N) protein was prepared by in-situ growing gold (Au) nanowire forests (NFs) onto Ti3C2Tx, which was then modified onto polymethyl methacrylate (PMMA) matrix and encapsulated into kit. It was noted that the Au nanowires with fibrous structures which vertically anchored on Ti3C2Tx served as perfect channels to promote photo-induced charge transfer. The synergistic action of electromagnetic and chemical effects resulted in an enhancement factor (EF) of 1.27 × 107. Furthermore, the unreliable fluctuation of the enhanced signal was eliminated by using the intrinsic Raman signal of the flexible PMMA platform, achieving an improved correlation coefficient (R2) value from 0.950 to 0.990. Moreover, the as-designed immunoassay kit with both high sensitivity and remedied quantitative ability rendered by the Ti3C2Tx@Au NFs-PMMA composite exhibited a powerful performance in the practical detection of N-protein with concentration low to 5.0 × 10-8 mg/mL.

New Advances in Antenna Design toward Wearable Devices Based on Nanomaterials

Wearable antennas have recently garnered significant attention due to their attractive properties and potential for creating lightweight, compact, low-cost, and multifunctional wireless communication systems. With the breakthrough progress in nanomaterial research, the use of lightweight materials has paved the way for the widespread application of wearable antennas. Compared with traditional metallic materials like copper, aluminum, and nickel, nanoscale entities including zero-dimensional (0-D) nanoparticles, one-dimensional (1-D) nanofibers or nanotubes, and two-dimensional (2-D) nanosheets exhibit superior physical, electrochemical, and performance characteristics. These properties significantly enhance the potential for constructing durable electronic composites. Furthermore, the antenna exhibits compact size and high deformation stability, accompanied by greater portability and wear resistance, owing to the high surface-to-volume ratio and flexibility of nanomaterials. This paper systematically discusses the latest advancements in wearable antennas based on 0-D, 1-D, and 2-D nanomaterials, providing a comprehensive overview of their development and future prospects in the field.

Large-scale assembly of geometrically diverse metal nanoparticles-based 3D plasmonic DNA nanostructures for SERS detection of PNK in cancer cells

The organization of geometrically diverse metal nanoparticles into a core/satellite structure at a large scale is a promising strategy for improve SERS performance due to hot spots localized enrichment and signal increase. However, due to the lack of extensional frames and strong electrostatic repulsion between plasma NPs, the fabrication of such 3D architectures with a high-density periodic hotspot in the focus volume has proven exceedingly difficult. Herein, we demonstrate a facile large-scale assembly of geometrically diverse metal nanoparticles strategy for constructing spatially extended 3D plasmonic nanostructures resembling "signal towers" based on RCA-mediated periodic organization of gold nanospheres (GNS) surrounding gold nanorods (GNRs). Using cancer cell T4 PNK as a model, a padlock probe with 5'- hydroxyl (P-circle) was designed as the T4 PNK substrate. The center Au nanorod was coated with P1 and served as a "pedestal" to allow substantial loading of P-circle after target phosphorylation to initiate the rolling ring amplification reaction (RCA). The resultant DNA nanowire serves as an "antenna" to successively lock numerous Raman reporter P2 (Cy3-P2-SH) through base pairing at regular intervals. Finally, the 3D plasma DNA nanostructures that resemble "signal towers" could be obtained by placing a large number of GNS with a strong affinity for Au-S. The proposed 3D SERS sensor exhibited a sensitivity of LOD as low as 0.274 mU/mL, which was attributed to a substantial electromagnetic field enhancement at the inter-nanoparticle gaps between the adjacent pedestal and antenna. Moreover, by exploiting the synergistic effect of the periodically extended DNA scaffold generated by RCA amplification and the co-assembly of thiol ligand, the loaded GNS can be extended to three-dimensional space, forming a high-density periodic hotspot in the focal volume, thereby ensuring high enhancement and high reproducibility of Raman signals. In addition, this method can be used to quantify T4 PNK in HeLa cells, demonstrating its applicability in diagnosing and estimating PNK-related diseases in complex fluids.

Surface-Enhanced Raman Scattering in Silver-Coated Suspended-Core Fiber

In this paper, the silver-coated large-core suspended-core fiber (LSCF) probe was fabricated by the dynamic chemical liquid phase deposition method for surface-enhanced Raman scattering (SERS) sensing. The 4-mercaptophenylboronic acid (4-MPBA) monolayer was assembled in the LSCF as the recognition monolayer. Taking advantage of the appropriate core size of the LSCF, a custom-made Y-type optical fiber patch cable was utilized to connect the semiconductor laser, Raman spectrometer, and the proposed fiber SERS probe. The SERS signal is propagated in the silver-coated air channels, which can effectively reduce the Raman and fluorescence background of the silica core. Experiments were performed to measure the Raman scattering spectra of the 4-MPBA in the silver-coated LSCF in a non-enhanced and enhanced case. The experiment results showed that the Raman signal strength was enhanced more than 6 times by the surface plasmon resonance compared with the non-enhanced case. The proposed LSCF for SERS sensing technology provides huge research value for the fiber SERS probes in biomedicine and environmental science. The combination of SERS and microstructured optical fibers offers a potential approach for SERS detection.

Eu3+-Functionalized MOFs for the simple and rapid 5-Hydroxymethylfurfural determination in food

5-Hydroxymethylfurfural (5-HMF) is an important product of the Maillard reaction and can be used as a quality indicator of food. 5-HMF has been found in studies to be harmful to human health. In this study, a highly selective and anti-interference fluorescent sensor Eu@1 is constructed based on Eu3+-functionalized Hf-based MOF for monitoring 5-HMF in a variety of food products. Eu@1 shows high selectivity, low LOD (8.46 μM), fast response time, and repeatability for 5-HMF. More importantly, after adding 5-HMF to milk, honey and apple juice samples, the probe Eu@1 is proved to be successfully in sensing 5-HMF in the above food samples. Therefore, this study provides a dependable and efficient alternative for the detection of 5-HMF in food samples.

Room-temperature phosphorescence and fluorescence nanocomposites as a ratiometric chemosensor for high-contrast and selective detection of 2,4,6-trinitrotoluene

Reports on using complementary colours for high-contrast ratiometric assays are limited to date. In this work, graphitized carbon nitride (g-C3N4) nanosheets and mercaptoethylamine (MEA) capped Mn-doped ZnS QDs were fabricated by liquid exfoliation of bulk g-C3N4, and by a coprecipitation and postmodification strategies, respectively. Mn-doped ZnS quantum dots were deposited onto g-C3N4 nanosheets through an electrostatic self-assembly to form new nanocomposites (denoted as Mn-ZnS QDs@g-C3N4). Mn-ZnS QDs@g-C3N4 can emit a pair of complementary colour light, namely, orange room-temperature phosphorescence (RTP) at 582 nm and blue fluorescence at 450 nm. After 2,4,6-trinitrotoluene (TNT) dosing into Mn-ZnS QDs@g-C3N4 aqueous solution, and pairing with MEA to generate TNT anions capable of quenching the emission of Mn-doped ZnS QDs, the fluorescence colours of the solution changed from orange to blue across white, exhibiting unusual high-contrast fluorescence images. The developed ratiometric chemosensor showed very good linearity in the range of 0-12 μM TNT with a limit of detection of 0.56 μM and an RSD of 6.4 % (n = 5). Also, the ratiometric probe had an excellent selectivity for TNT over other nitroaromatic compounds, which was applied in the ratiometric test paper to image TNT in water, and TNT sensing under phosphorescence mode to efficiently avoid background interference. A high-contrast dual-emission platform for selective ratiometric detection of TNT was therefore established.

Tuning LSPR of Thermal Spike-Induced Shape-Engineered Au Nanoparticles Embedded in Si3N4 Thin-Film Matrix for SERS Applications

While gold nanoparticles (Au NPs) are widely used as surface-enhanced Raman spectroscopy (SERS) substrates, their agglomeration and dynamic movement under laser irradiation result in the major drawback in SERS applications, viz., the repeatability of SERS signals. We tune the optical and structural properties of size- and shape-modified Au NPs embedded in a thin silicon nitride (Si3N4) matrix by intense electronic excitation with swift heavy ion (SHI) irradiation with the aim of overcoming this classical SERS disadvantage. We demonstrate the shape evolution of a single layer of Au NPs inserted between amorphous Si3N4 thin films under fluences of 120 MeV Au9+ ions ranging between 1 × 1011 and 1 × 1013 ions cm-2. This shape modification results in the gradual blue shift of the localized surface plasmon resonance (LSPR) dip until 1 × 1012 ions/cm2 and then a sudden diminishment at 1 × 1013 ions/cm2. Finite domain time difference (FDTD) simulations further justify our experimental optical spectra. The dynamical NP aggregation and dissolution, in addition to NP elongation and deformation at different fluences, are noted from 2D grazing incidence small-angle X-ray scattering (GISAXS) profiles, as well as cross-sectional transmission electron microscopy (X-TEM). The systematic shape evolution of metal NPs embedded in the insulating matrix is shown to be due to thermal spike-induced localized melting and a localized pressure hike upon SHI irradiation. Utilizing this specific control over the characteristics of Au NPs, viz., shape, size, interparticle gap, and corresponding optical response via SHI irradiation, we demonstrate their applications as very stable SERS substrates, where the separation between NPs and analyte does not alter under laser illumination. Thus, these irradiated SERS active substrates with controlled NP size and gap provide the optimal conditions for creating localized electromagnetic hotspots that amplify the SERS signals, which do not alter with time or laser exposure. We found that the film irradiated with 1 × 1011 exhibits the highest SERS intensity due to its optimal NP size distribution and shape. Thus, not only our study provides a SERS substrate for stable and repeatable signals but also the understanding depicted here opens new research avenues in designing SERS substrates, photovoltaics, optoelectronic devices, etc. with ion beam irradiation.

Efficient interfacial self-assembled MXene/Ag NPs film nanocarriers for SERS-traceable drug delivery

Combining the unique advantages of two-dimensional transition metal carbon/nitrogen compounds (MXene) and the excellent surface-enhanced Raman scattering (SERS) performance of noble metal materials, MXene/Ag NPs films were proposed as nanocarriers for SERS-traceable drug delivery. The films were prepared by two-step self-assembly on positively charged silicon wafers using virtue of the high evaporation of ethyl acetate, the Marangoni effect, and an oil/water/oil three-phase system. With 4-mercaptobenzoic acid (4-MBA) as the probe molecule, the SERS detection limit was 10-8 M and had shown a good linear relationship in the range of 10-8-10-3 M. Simultaneously, the film had good uniformity, repeatability, and stability. When Ti3C2Tx/Ag NPs films were used as nanocarriers, the anticancer drug doxorubicin (DOX) was loaded onto the surface through 4-MBA, and the tracking and monitoring were realized by SERS. The addition of glutathione (GSH) triggered the thiol exchange reaction, resulting in the shedding of 4-MBA from the surface of the film, which indirectly achieved the efficient release of DOX. Furthermore, the loading of DOX and the drug release effect triggered by GSH maintained a certain stability in serum, which provided a potential possibility for the subsequent loading and release of drugs by films with three-dimensional structures as scaffolds in biological therapy. Self-assembled MXene/Ag NPs film nanocarriers for SERS-traceable drug delivery and GSH-triggered high-efficiency drug release.

High-efficient adsorption for versatile adsorbates by elastic reduced graphene oxide/Fe3O4 magnetic aerogels mediated by carbon nanotubes

Fabrication of highly elastic three-dimensional aerogel adsorbents with outstanding adsorption capacities is a long pursuit for the treatment of industrial contaminated water. In this work, a magnetic reduced graphene oxide (rGO)/Fe₃O₄/carbon nanotubes (CNTs) aerogel material was constructed by the electrostatic attraction between the negatively charged GO and positively charged CNTs following a one-pot water bath treatment. The as-synthesized aerogel demonstrated high compressive stress (28.4 kPa) and lower density (24.11 mg/cm³) with exceptional adsorption capacities for versatile adsorbates which are attributed to CNTs and magnetic Fe₃O₄ nanoparticles. The effect of pH, initial concentration of adsorbates (dyes, Cd (ІІ) ions, organic solvents, and pump oil), content of CNTs and cyclic times on the adsorption capacities of the aerogel were investigated in detail. Furthermore, from simulation, the adsorption kinetics, and thermodynamics of the aerogel for adsorbates were more satisfied by endothermic quasi-second-order kinetic model with characteristic physical adsorption. Thus, the optimized rGO/Fe₃O₄/CNTs-10 aerogel adsorbent can be used as a powerful and versatile tool to deal with contaminated industrial or domestic wastewater.

ReS2 Nanoflowers-Assisted Confined Growth of Gold Nanoparticles for Ultrasensitive and Reliable SERS Sensing

ReS₂, as a new member of transition metal dichalcogenides (TMDCs), has emerged as a promising substrate for semiconductor surface-enhanced Raman spectroscopy (SERS) due to its unique optoelectronic properties. Nevertheless, the sensitivity of the ReS₂ SERS substrate poses a significant challenge to its widespread application in trace detection. In this work, we present a reliable approach for constructing a novel ReS₂/AuNPs SERS composite substrate, enabling ultrasensitive detection of trace amounts of organic pesticides. We demonstrate that the porous structures of ReS₂ nanoflowers can effectively confine the growth of AuNPs. By precisely controlling the size and distribution of AuNPs, numerous efficient and densely packed "hot spots" were created on the surface of ReS₂ nanoflowers. As a result of the synergistic enhancement of the chemical and electromagnetic mechanisms, the ReS₂/AuNPs SERS substrate demonstrates high sensitivity, good reproducibility, and superior stability in detecting typical organic dyes such as rhodamine 6G and crystalline violet. The ReS₂/AuNPs SERS substrate shows an ultralow detection limit of 10^-10 M and a linear detection of organic pesticide molecules within 10^-6-10^-10 M, which is significantly lower than the EU Environmental Protection Agency regulation standards. The strategy of constructing ReS₂/AuNPs composites would contribute to the development of highly sensitive and reliable SERS sensing platforms for food safety monitoring.