Superficial-Layer-Enhanced Raman Scattering (SLERS) for Depth Detection of Noncontact Molecules

Surface segregation of rigid polyarylene ether amidoxime on polyurethane nanofiber into hierarchical membranes as substrate of flexible SERS nanosensor for sulfamethoxazole detection

Electrospun polymeric nanofibrous membranes are emerging as the promising substrates for preparation of flexible SERS nanosensors due to their intrinsic nanoscale surface roughness, easy scalability as well as rich surface reactivity. Although the nanofiber membranes prepared from high performance thermoplastics exhibit good mechanical stability, the SERS nanosensors based on these substrates normally have lower signal-to-noise ratio because of the interference from background Raman signals of aromatic moieties. Herein, we synthesized an optically transparent polyurethane (PU) and rigid polyarylene ether amidoxime (PEA), which were electrospun into core-shell nanofibers membranes with a "beads-on-web" morphology. Furthermore, the PU-PEA membranes were coated with ultra-thin silver layer and thermally annealed to prepare the flexible SERS nanosensor without any background noises. In addition, the Raman enhancement of SERS nanosensor can be readily improved by tuning of PU-PEA composition, silver thickness as well as thermal annealing temperature. Finally, the optimized SERS nanosensor enables label-free detection of sulfamethoxazole as low as 0.1 nM with a good reproducibility and detection performance in real water sample. Meanwhile, the optimized SERS nanosensor shows long term anti-biofouling capacity. Thanks to its facile fabrication, competitive analytical performance and resistance to biofouling, the current work basically open new way for design of flexible SERS nanosensors for biomedical applications.

Surface-Enhanced Raman Scattering Imaging Assisted by Machine Learning Analysis: Unveiling Pesticide Molecule Permeation in Crop Tissues

Surface-enhanced Raman scattering (SERS) imaging technology faces significant technical bottlenecks in ensuring balanced spatial resolution, preventing image bias induced by substrate heterogeneity, accurate quantitative analysis, and substrate preparation that enhances Raman signal strength on a global scale. To systematically solve these problems, artificial intelligence techniques are applied to analyze the signals of pesticides based on 3D and dynamic SERS imaging. Utilizing perovskite/silver nanoparticles composites (CaTiO3/Ag@BONPs) as enhanced substrates, enabling it not only to cleanse pesticide residues from the surface to pulp of fruits and vegetables, but also to investigate the penetration dynamics of an array of pesticides (chlorpyrifos, thiabendazole, thiram, and acetamiprid). The findings challenge existing paradigms, unveiling a previously unnoticed weakening process during pesticide invasion and revealing the surprising permeability of non-systemic pesticides. Of particular note is easy to overlook that the combined application of pesticides can inadvertently intensify their invasive capacity due to pesticide interactions. The innovative study delves into the realm of pesticide penetration, propelling a paradigm shift in the understanding of food safety. Meanwhile, this strategy provides strong support for the cutting-edge application of SERS imaging technology and also brings valuable reference and enlightenment for researchers in related fields.

Chiral nanomaterials in tissue engineering

Addressing significant medical challenges arising from tissue damage and organ failure, the field of tissue engineering has evolved to provide revolutionary approaches for regenerating functional tissues and organs. This involves employing various techniques, including the development and application of novel nanomaterials. Among them, chiral nanomaterials comprising non-superimposable nanostructures with their mirror images have recently emerged as innovative biomaterial candidates to guide tissue regeneration due to their unique characteristics. Chiral nanomaterials including chiral fibre supramolecular hydrogels, polymer-based chiral materials, self-assembling peptides, chiral-patterned surfaces, and the recently developed intrinsically chiroptical nanoparticles have demonstrated remarkable ability to regulate biological processes through routes such as enantioselective catalysis and enhanced antibacterial activity. Despite several recent reviews on chiral nanomaterials, limited attention has been given to the specific potential of these materials in facilitating tissue regeneration processes. Thus, this timely review aims to fill this gap by exploring the fundamental characteristics of chiral nanomaterials, including their chiroptical activities and analytical techniques. Also, the recent advancements in incorporating these materials in tissue engineering applications are highlighted. The review concludes by critically discussing the outlook of utilizing chiral nanomaterials in guiding future strategies for tissue engineering design.

A SERS substrate based on perovskite quantum dots and graphene for the determination of cardiac troponin I

Noble metal has always been used as a preferred base for SERS substrate. However, the preparation cost of such materials is trully high. Therefore, many researchers have begun to search for succedanea which cost were lower. In this work, CsPbBr3@ZIF-8 was synthesized by in-situ reduction method and combined with graphene nanosheets to construct a SERS substrate. The SERS performance of this substrate could be further enhanced by the synergistic effect of perovskite quantum dots and graphene. Base on this material, a sensitive SERS strategy composed of CsPbBr3@ZIF-8@G, antibody, and Bradford method was developed for the quantitative determination of cardiac troponin I (cTnI) in human serum. It's worth noting that the sensitivity and accuracy of this method could approach the level of other SERS methods using noble metals. The "reverse"-SERS method could improve the uniformity and stability of detection platform obviously. The detection range of this method was 0.01-100 ng/mL, and the estimated detection of limit (LOD) was 4.7 pg/mL. The recovery rate of this method range was between 93.1 % and 104.8 %, and RSD range was between 4.47 % and 7.06 %.

SERS-active plasmonic metal NP-CsPbX3 films for multiple veterinary drug residues detection

Sensitive and multiple veterinary drug residues detection is of important for food safety. Herein, uniform plasmonic Au nanobipyramids@Ag nanorods (Au NBP@Ag NR)-CsPbX₃ films with strong surface-enhanced Raman scattering (SERS) activity were constructed. The effects of different CsPbX₃ (X = Cl, Br, I, or mixed halogens) quantum dots (QDs) on the SERS performances of plasmonic metal NP films were investigated. CsPbI₃ QDs with large dielectric constant could be served as the dielectric media to retard the attenuation of electromagnetic evanescent wave, inducing strong electromagnetic strength for SERS enhancement. Plasmon-induced metal-to-perovskite interfacial charge transfer transition also contributed to SERS enhancement. SERS-active plasmonic Au NBP@Ag NR-CsPbI₃ films had excellent sensitivity and high reproducibility for quantitative, accurate and multiple detection of chloramphenicol, diazepam and malachite green in food matrix. This work deepened the understanding of the SERS enhancement mechanisms of plasmonic metal NP-perovskite hybrid heterostructures, showing potential prospects in food safety monitoring.

Surface enhanced Raman scattering of adsorbates on Au-CsPbIBr2 perovskite-based nanocomposites: charge-transfer and electromagnetic enhancement

In this study, perovskite-based nanocomposites as surface enhanced Raman scattering substrates were designed by physically sputtering Au nanoparticles onto fabricated all-inorganic CsPbIBr₂ perovskite films, which provide much stronger SERS signals as compared to normal Au or perovskite substrates. Their synergism enhancement mechanisms and influence factors, including hybrid layer sequence, fabrication parameters and excitation source, are discussed. In addition, the prepared composite substrate exhibits excellent uniformity, reproducibility and time stability. This study promotes an easily prepared perovskite-based substrate for SERS-related applications and develops further understanding of molecule-semiconductor-noble metal nanostructure interfacial interactions.

Self-Assembled Supercrystals Enhance the Photothermal Conversion for Solar Evaporation and Water Purification

Photothermal materials can convert renewable solar energy into thermal energy and have great potential for solar water evaporation. Copper sulfide (Cu_{2- x} S) is an easily available and inexpensive plasmonic material with a high photothermal conversion efficiency and can be applied to solar evaporation and water purification. Monodispersed Cu₇ S₄ nanoparticles (NPs) and supercrystalline self-assembled superparticles are obtained via wet chemical synthesis and micelle self-assembly. The photothermal properties of the superstructures are investigated using the finite difference time domain method and laser radiation photothermography. The results show that the electromagnetic field intensity and photothermal efficiency of the self-assembly are significantly higher than those of isolated NPs, which is due to the plasmonic coupling of the NPs. The evaporation efficiency of the superstructure is significantly higher than that of isolated NPs, the metal salt ion and total organic carbon concentrations in the waterbody significantly decrease after evaporation, and the water polluted by high salt and organic dye concentrations is purified. The water quality significantly improves after the lake water from Fuxian Lake in the Yunnan-Guizhou Plateau of China is used for solar evaporation. The color changes from pale yellow to colorless and the ion and total organic carbon contents significantly decrease.

Combining printing and nanoparticle assembly: Methodology and application of nanoparticle patterning

Functional nanoparticles (NPs) with unique photoelectric, mechanical, magnetic, and chemical properties have attracted considerable attention. Aggregated NPs rather than individual NPs are generally required for sensing, electronics, and catalysis. However, the transformation of functional NP aggregates into scalable, controllable, and affordable functional devices remains challenging. Printing is a promising additive manufacturing technology for fabricating devices from NP building blocks because of its capabilities for rapid prototyping and versatile multifunctional manufacturing. This paper reviews recent advances in NP patterning based on the combination of self-assembly and printing technologies (including two-, three-, and four-dimensional printing), introduces the basic characteristics of these methods, and discusses various fields of NP patterning applications.

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Nanoparticles (NPs) printing assembly is a good solution for patterned devices

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NPs assembly can be combined with 2D, 3D, and 4D printing technologies

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A variety of ink-dispersed NPs are available for printing assembly

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NPs printing assembly technology is applied for nanosensing, energy storage, photodetector

SERS-Active Composites with Au-Ag Janus Nanoparticles/Perovskite in Immunoassays for Staphylococcus aureus Enterotoxins

The accurate detection of Staphylococcus aureus enterotoxins (SEs) is vital for food safety owing to their high pathogenicity, which may be performed with surface-enhanced Raman scattering (SERS) if SERS-active nanostructures are used. Herein, a Au-Ag Janus nanoparticle (NPs)/perovskite composite-engineered SERS immunoassay was developed for SEC detection. Plasmonic Au-Ag Janus NPs demonstrated inherent SERS activity from the 2-mercaptobenzoimidazole-5-carboxylic acid ligands. CsPbBr₃@mesoporous silica nanomaterials (MSNs) were prepared and transformed into CsPb₂Br₅@MSNs in the aqueous phase. Paired SEC antibody-antigen-driven plasmonic Au-Ag Janus NP-CsPb₂Br₅@MSN composites were prepared. They showed amplified SERS activity, attributed to the depressed plasmonic decay due to electromagnetic field enhancement and the electron transfer mechanism. A positive relationship was established between SERS signals of composites and the SEC concentration. An additive-free SERS immunoassay was developed for simple, sensitive, and reproducible SEC detection. This study will be extended to develop multiple additive-free SERS-active plasmonic NP/perovskite composites that will open up the possibility of exploring more SERS detection probes for food safety monitoring.

Plasmonic-perovskite solar cells, light emitters, and sensors

The field of plasmonics explores the interaction between light and metallic micro/nanostructures and films. The collective oscillation of free electrons on metallic surfaces enables subwavelength optical confinement and enhanced light-matter interactions. In optoelectronics, perovskite materials are particularly attractive due to their excellent absorption, emission, and carrier transport properties, which lead to the improved performance of solar cells, light-emitting diodes (LEDs), lasers, photodetectors, and sensors. When perovskite materials are coupled with plasmonic structures, the device performance significantly improves owing to strong near-field and far-field optical enhancements, as well as the plasmoelectric effect. Here, we review recent theoretical and experimental works on plasmonic perovskite solar cells, light emitters, and sensors. The underlying physical mechanisms, design routes, device performances, and optimization strategies are summarized. This review also lays out challenges and future directions for the plasmonic perovskite research field toward next-generation optoelectronic technologies.

Flexible Plasmonic Biosensors for Healthcare Monitoring: Progress and Prospects

The noble metal nanoparticle has been widely utilized as a plasmonic unit to enhance biosensors, by leveraging its electric and/or optical properties. Integrated with the "flexible" feature, it further enables opportunities in developing healthcare products in a conformal and adaptive fashion, such as wrist pulse tracers, body temperature trackers, blood glucose monitors, etc. In this work, we present a holistic review of the recent advance of flexible plasmonic biosensors for the healthcare sector. The technical spectrum broadly covers the design and selection of a flexible substrate, the process to integrate flexible and plasmonic units, the exploration of different types of flexible plasmonic biosensors to monitor human temperature, blood glucose, ions, gas, and motion indicators, as well as their applications for surface-enhanced Raman scattering (SERS) and colorimetric detections. Their fundamental working principles and structural innovations are scoped and summarized. The challenges and prospects are articulated regarding the critical importance for continued progress of flexible plasmonic biosensors to improve living quality.

Gold Nanorods: The Most Versatile Plasmonic Nanoparticles

Gold nanorods (NRs), pseudo-one-dimensional rod-shaped nanoparticles (NPs), have become one of the burgeoning materials in the recent years due to their anisotropic shape and adjustable plasmonic properties. With the continuous improvement in synthetic methods, a variety of materials have been attached around Au NRs to achieve unexpected or improved plasmonic properties and explore state-of-the-art technologies. In this review, we comprehensively summarize the latest progress on Au NRs, the most versatile anisotropic plasmonic NPs. We present a representative overview of the advances in the synthetic strategies and outline an extensive catalogue of Au-NR-based heterostructures with tailored architectures and special functionalities. The bottom-up assembly of Au NRs into preprogrammed metastructures is then discussed, as well as the design principles. We also provide a systematic elucidation of the different plasmonic properties associated with the Au-NR-based structures, followed by a discussion of the promising applications of Au NRs in various fields. We finally discuss the future research directions and challenges of Au NRs.

Surface-Enhanced Raman Scattering-Active Plasmonic Metal Nanoparticle-Persistent Luminescence Material Composite Films for Multiple Illegal Dye Detection

Uniform two-dimensional plasmonic nanoparticle (NP)-semiconductor composite films could retard the attenuation of electromagnetic evanescent wave and show intensive Raman activity for the multiplex monitoring of hazards in a practical food matrix. Here, an efficient Raman platform is developed by employing a plasmonic nanoparticle (NP)-persistent luminescence material (PLM) composite film. PLM show upconversion photoluminescence (UCPL) properties. The emitted photons are absorbed by plasmonic NPs, which further boost the surface plasmon resonance for the generation of high polarizability and induce strong electromagnetic strength for surface-enhanced Raman scattering (SERS) enhancement. A UCPL-assisted SERS-enhanced mechanism is proposed and verified. A plasmonic NP-PLM film with superior SERS activity and detection capability becomes an alternative candidate for the sensitive and multiple detection of illegal addition of dyes in a food matrix. The proposed UCPL-assisted SERS-enhanced mechanism provides promising future directions to this end to design a next-generation SERS-active plasmonic NP-PLM composite film for the specific detection in complex samples.

Nanoassembled Interface for Dynamics Tailoring

The properties and performance of solid nanomaterials in heterogeneous chemical reactions are significantly influenced by the interface between the nanomaterial and environment. Oriented tailoring of interfacial dynamics, that is, modifying the shared boundary for mass and energy exchange has become a common goal for scientists. Although researchers have designed and constructed an abundance of nanomaterials with excellent performances for the tailoring of reaction dynamics, a complete understanding of the mechanism of nanomaterial-environment interfacial interaction still remains elusive. To predictively understand the nanomaterial-environment relationship over a wide range of time scale, a deep and dynamic insight is required urgently. In this Account, our recent works including advances in the design and construction of nanoassembled interfaces and understanding the dynamic interaction mechanisms between different combinations of nanoparticle (NP) assembly environment interfaces for tailoring the reaction dynamics.NP assemblies with well-defined structures and compositions are inherently suitable for replacing bulk-type nanomaterials for the research on interfaces. We primarily introduced two most relevant nanoassembled surfaces that were fabricated in our laboratory, namely, ordered self-assembly interface and animate nanoassembled interface. The disordered nanoparticles can be arranged into an ordered superlattice based on the self-assembly method and patterned-assembly method. In addition, we used NPs with flexible properties to construct three-dimensional (3D) animate assemblies. On the basis of a thorough understanding of the structure-property correlation, a series of nanoassembled interfaces with various structures have been developed for practice. In comparison with traditional nanomaterial-environment interfaces, the nanoassembled interfaces can change the mode of contact between the nanomaterial and environment, thereby maximizing the number of active sites and driving interferent/product off the nanoassembled interface. The geometry, porosity, and deformable/motional properties in the nanoassembled interface can be applied to enhance the mass transfer dynamics in the chemical reaction. Moreover, the nanoassembled interface can be used to strengthen the affinity between the NP assemblies and targets, thereby enhancing the adsorption efficiency. As shown in these examples, the nanoassembled interface can effectively change the speed, intensity, and mode of interactions between the NP assemblies and environment in spatiotemporal scales.The overall performance of the interfacial dynamics can be improved by the nanoassembled interface, thereby facilitating practical application in flowing systems. We have extended the applications of nanoassembled interfaces from simple adsorption to complex reactions in flowing systems, including in vivo magnetic resonance imaging, electrocatalytic gas evolution reaction, bacterial capture, sensing of exhaled volatile organic compounds, and heterogeneous catalysis. Our current endeavors to explore the applicability of animate nanoassembled interfaces for dynamic tailoring have widened the scope of research, and attempts to construct intelligent interfaces for applications are underway.

In Situ Detection of Neurotransmitters from Stem Cell-Derived Neural Interface at the Single-Cell Level via Graphene-Hybrid SERS Nanobiosensing

In situ quantitative measurements of neurotransmitter activities can provide useful insights into the underlying mechanisms of stem cell differentiation, the formation of neuronal networks, and neurodegenerative diseases. Currently, neurotransmitter detection methods suffer from poor spatial resolution, nonspecific detection, and a lack of in situ analysis. To address this challenge, herein, we first developed a graphene oxide (GO)-hybrid nanosurface-enhanced Raman scattering (SERS) array to detect dopamine (DA) in a selective and sensitive manner. Using the GO-hybrid nano-SERS array, we successfully measured a wide range of DA concentrations (10^-4 to 10^-9 M) rapidly and reliably. Moreover, the measurement of DA from differentiating neural stem cells applies to the characterization of neuronal differentiation. Given the challenges of in situ detection of neurotransmitters at the single-cell level, our developed SERS-based detection method can represent a unique tool for investigating single-cell signaling pathways associated with DA, or other neurotransmitters, and their roles in neurological processes.

Understanding the Role of Metal-Organic Frameworks in Surface-Enhanced Raman Scattering Application

Metal-organic frameworks (MOFs), built from organic linkers and metal ions/clusters, have emerged as highly promising materials for wide applications. Combining highly porous crystalline MOFs with the surface-enhanced Raman scattering (SERS) technique can achieve unprecedented advantages of high selectivity, high sensitivity, and expedience in analysis and detection. In this critical review, the aim is to present a comprehensive review of recent advances in understanding of the roles of MOFs in MOF-SERS systems, particularly their structure-to-property correlation. Key examples are selected from representative literature to illustrate critical concepts and the MOF-based property-dependent applications are particularly emphasized. Finally, the barriers, future trends, and prospects for further advances in MOF-SERS platforms are also discussed.

DNA-Based Plasmonic Heterogeneous Nanostructures: Building, Optical Responses, and Bioapplications

The integration of multiple functional nanoparticles into a specific architecture allows the precise manipulation of light for coherent electron oscillations. Plasmonic metals-based heterogeneous nanostructures are fabricated by using DNA as templates. This comprehensive review provides an overview of the controllable synthesis and self-assembly of heterogeneous nanostructures, and analyzes the effects of structural parameters on the regulation of optical responses. The potential applications and challenges of heterogeneous nanostructures in the fields of biosensors and bioanalysis, in vivo monitoring, and phototheranostics are discussed.

Preparation of Monolayer Photonic Crystals from Ag Nanobulge-Deposited SiO2 Particles as Substrates for Reproducible SERS Assay of Trace Thiol Pesticide

Surface-enhanced Raman scattering (SERS) greatly increases the detection sensitivity of Raman scattering. However, its real applications are often degraded due to the unrepeatable preparation of SERS substrates. Herein presented is a very facile and cost-effective method to reproducibly produce a novel type of SERS substrate, a monolayer photonic crystal (PC). With a building block of laboratory-prepared monodisperse SiO₂ particles deposited with space-tunable silver nanobulges (SiO₂@nAg), a PC substrate was first assembled at the air-water interface through needle tip flowing, then transferred onto a silicon slide by a pulling technique. The transferred monolayer PCs were characterized by SEM and AFM to have a hexagonal close-packed lattice. They could increase Raman scattering intensity by up to 2.2 × 10⁷-fold, as tested with p-aminothiophenol. The relative standard deviations were all below 5% among different substrates or among different locations on the same substrate. The excellent reproducibility was ascribed to the highly ordered structure of PCs, while the very high sensitivity was attributed to the strong hotspot effect caused by the appropriately high density of nanobulges deposited on SiO₂ particles and by a closed lattice. The PC substrates were validated to be applicable to the SERS assay of trace thiol pesticides. Thiram pesticide is an example determined in apple juice samples at a concentration 10²-fold lower than the food safety standard of China. This method is extendable to the analysis of other Raman-active thiol chemicals in different samples, and the substrate preparation approach can be modified for the fabrication of more PC substrates from other metallic nanobulge-deposited particles rather than silica only.

Silver nanoparticle-assembled micro-bowl arrays for sensitive SERS detection of pesticide residue

It is of great significance to develop a simple and effective method for constructing large-scale high-quality surface-enhanced Raman scattering (SERS) substrate. Here, an Ag nanoparticle-assembled micro-bowl array was prepared by a close-packed polystyrene (PS) sphere monolayer templated electrodeposition approach. The fabricated Ag nanoparticle-assembled micro-bowl array shows high SERS sensitivity to rhodamine 6G (R6G) under an ultra-low concentration of 1 fM, and exhibits excellent SERS spectral uniformity with a small relative standard deviation (RSD) of 7.6% and good reproducibility (a RSD ∼8.2% for the average peak intensities from different batches of SERS substrates). The fabricated micro-bowl array SERS substrate was employed to detect pesticide residue (thiram and methyl parathion) on vegetables. The limit of detections (LODs) for the two pesticides are lower than the maximum residue limits (MRLs) set by the European Union respectively, showing promising application in rapid inspection of food safety.

Effect of structure: A new insight into nanoparticle assemblies from inanimate to animate

Nanoparticle (NP) assemblies are among the foremost achievements of nanoscience and nanotechnology because their interparticle interactions overcome the weaknesses displayed by individual NPs. However, previous studies have considered NP assemblies as inanimate, which had led to their dynamic properties being overlooked. Animate properties, i.e., those mimicking biological properties, endow NP ensembles with unique and unexpected functionalities for practical applications. In this critical review, we highlight recent advances in our understanding of the properties of NP assemblies, particularly their animate properties. Key examples are used to illustrate critical concepts, and special emphasis is placed on animate property-dependent applications. Last, we discuss the barriers to further advances in this field.

Recent advances in gold nanoparticles for biomedical applications: from hybrid structures to multi-functionality

Hybrid gold nanoparticles for biomedical applications are reviewed in the context of a novel classification framework and illustrated by recent examples.