A Programmable DNA-Silicification-Based Nanocavity for Single-Molecule Plasmonic Sensing

A novel controllable nanocyclic plasma coupled array in SERS trace detection of multi-component pollutants

The development and design of a novel, uniform and highly active local electromagnetic field enhanced structure is crucial for expanding Surface-enhanced Raman Scattering (SERS) applications. In this study, we developed Ag ring-coupled nanoarrays (Ag RCNAs) with controllable nanogaps using a substrate rotary evaporation coating technique with self-assembled polystyrene (PS) microspheres as templates. This straightforward and cost-effective method efficiently prepares plasma-coupled nanoarrays. Ag RCNAs demonstrated high sensitivity in detecting organic dyes, our prepared Ag RCNAs showed high sensitivity (with the limit of detection of 10-8 M), high signal reproducibility (with the relative standard deviation of 6.73 %). Furthermore, Ag RCNAs showed remarkable sensitivity to a broad spectrum of dyes in river water, indicating the large-area uniform and highly active circular-ring-shaped nanogaps can realize highly sensitive detection of various pollutants. This approach offers advantages in electromagnetic field enhancement, tunable nanogaps, uniformity, reproducibility, and recyclability, making it promising for applications in environmental monitoring, bioassays, food safety, and medical diagnostics.

Self-Adhesive, Biocompatible, Wearable Microfluidics with Erasable Liquid Metal Plasmonic Hotspots for Glucose Detection in Sweat

Sweat is a noninvasive metabolite that can provide clinically meaningful information about physical conditions without harming the body. Glucose, a vital component in sweat, is closely related to blood glucose levels, and changes in its concentration can reflect the health status of diabetics. We introduce a self-adhesive, wearable microfluidic chip with erasable liquid metal plasmonic hotspots for the precise detection of glucose concentration in sweat. The self-adhesive, wearable microfluidic chip is made from modified polydimethylsiloxane (PDMS) with enhanced stickiness, enabling conformal contact with the skin, and can collect, deliver, and store sweat. The plasmonic hotspots are located inside the microfluidic channel, are generated by synthesizing silver nanostructures on liquid metal, and can be removed in the alkaline solution. It indicates the erasable and reproducible nature of the plasmonic hotspots. The detection method is based on surface-enhanced Raman spectroscopy (SERS), which allows for accurate detection of the glucose concentration. To enhance the sensitive detection of glucose, the SERS substrate is modified by 4-mercaptophenylboronic acid to achieve the limit of detection of 1 ng/L glucose, which is much lower than the physiological conditions (7.2-25.2 μg/L). The developed microfluidic chip is soft, stretchable, and nontoxic, bringing new possibilities to wearable sweat-sensing devices.

Microfluidics and Nanofluidics in Strong Light-Matter Coupling Systems

The combination of micro- or nanofluidics and strong light-matter coupling has gained much interest in the past decade, which has led to the development of advanced systems and devices with numerous potential applications in different fields, such as chemistry, biosensing, and material science. Strong light-matter coupling is achieved by placing a dipole (e.g., an atom or a molecule) into a confined electromagnetic field, with molecular transitions being in resonance with the field and the coupling strength exceeding the average dissipation rate. Despite intense research and encouraging results in this field, some challenges still need to be overcome, related to the fabrication of nano- and microscale optical cavities, stability, scaling up and production, sensitivity, signal-to-noise ratio, and real-time control and monitoring. The goal of this paper is to summarize recent developments in micro- and nanofluidic systems employing strong light-matter coupling. An overview of various methods and techniques used to achieve strong light-matter coupling in micro- or nanofluidic systems is presented, preceded by a brief outline of the fundamentals of strong light-matter coupling and optofluidics operating in the strong coupling regime. The potential applications of these integrated systems in sensing, optofluidics, and quantum technologies are explored. The challenges and prospects in this rapidly developing field are discussed.

Comparison of Gap-Enhanced Raman Tags and Nanoparticle Aggregates with Polarization Dependent Super-Resolution Spectral SERS Imaging

Strongly confined electric fields resulting from nanogaps within nanoparticle aggregates give rise to significant enhancement of surface-enhanced Raman scattering (SERS). Nanometer differences in gap sizes lead to drastically different confined field strengths; so much attention has been focused on the development and understanding of nanostructures with controlled gap sizes. In this work, we report a novel petal gap-enhanced Raman tag (GERT) consisting of a bipyramid core and a nitrothiophenol (NTP) spacer to support the growth of hundreds of small petals and compare its SERS emission and localization to a traditional bipyramid aggregate. To do this, we use super resolution spectral SERS imaging that simultaneously captures the SERS images and spectra while varying the incident laser polarization. Intensity fluctuations inherent of SERS enabled super resolution algorithms to be applied, which revealed subdiffraction limited differences in the localization with respect to polarization direction for both particles. Interestingly, however, only the traditional bipyramid aggregates experienced a strong polarization dependence in their SERS intensity and in the plasmon-induced conversion of NTP to dimercaptoazobenzene (DMAB), which was localized with nanometer precision to regions of intense electromagnetic fields. The lack of polarization dependence (validated through electromagnetic simulations) and surface reactions from the bipyramid-GERTs suggests that the emissions arising from the bipyramid-GERTs are less influenced by confined fields.

Biominerals and Bioinspired Materials in Biosensing: Recent Advancements and Applications

Inspired by nature's remarkable ability to form intricate minerals, researchers have unlocked transformative strategies for creating next-generation biosensors with exceptional sensitivity, selectivity, and biocompatibility. By mimicking how organisms orchestrate mineral growth, biomimetic and bioinspired materials are significantly impacting biosensor design. Engineered bioinspired materials offer distinct advantages over their natural counterparts, boasting superior tunability, precise controllability, and the ability to integrate specific functionalities for enhanced sensing capabilities. This remarkable versatility enables the construction of various biosensing platforms, including optical sensors, electrochemical sensors, magnetic biosensors, and nucleic acid detection platforms, for diverse applications. Additionally, bioinspired materials facilitate the development of smartphone-assisted biosensing platforms, offering user-friendly and portable diagnostic tools for point-of-care applications. This review comprehensively explores the utilization of naturally occurring and engineered biominerals and materials for diverse biosensing applications. We highlight the fabrication and design strategies that tailor their functionalities to address specific biosensing needs. This in-depth exploration underscores the transformative potential of biominerals and materials in revolutionizing biosensing, paving the way for advancements in healthcare, environmental monitoring, and other critical fields.

Silicon-containing nanomedicine and biomaterials: materials chemistry, multi-dimensional design, and biomedical application

The invention of silica-based bioactive glass in the late 1960s has sparked significant interest in exploring a wide range of silicon-containing biomaterials from the macroscale to the nanoscale. Over the past few decades, these biomaterials have been extensively explored for their potential in diverse biomedical applications, considering their remarkable bioactivity, excellent biocompatibility, facile surface functionalization, controllable synthesis, etc. However, to expedite the clinical translation and the unexpected utilization of silicon-composed nanomedicine and biomaterials, it is highly desirable to achieve a thorough comprehension of their characteristics and biological effects from an overall perspective. In this review, we provide a comprehensive discussion on the state-of-the-art progress of silicon-composed biomaterials, including their classification, characteristics, fabrication methods, and versatile biomedical applications. Additionally, we highlight the multi-dimensional design of both pure and hybrid silicon-composed nanomedicine and biomaterials and their intrinsic biological effects and interactions with biological systems. Their extensive biomedical applications span from drug delivery and bioimaging to therapeutic interventions and regenerative medicine, showcasing the significance of their rational design and fabrication to meet specific requirements and optimize their theranostic performance. Additionally, we offer insights into the future prospects and potential challenges regarding silicon-composed nanomedicine and biomaterials. By shedding light on these exciting research advances, we aspire to foster further progress in the biomedical field and drive the development of innovative silicon-composed nanomedicine and biomaterials with transformative applications in biomedicine.

DNA-Based Gold Nanoparticle Assemblies: From Structure Constructions to Sensing Applications

Gold nanoparticles (Au NPs) have become one of the building blocks for superior assembly and device fabrication due to the intrinsic, tunable physical properties of nanoparticles. With the development of DNA nanotechnology, gold nanoparticles are organized in a highly precise and controllable way under the mediation of DNA, achieving programmability and specificity unmatched by other ligands. The successful construction of abundant gold nanoparticle assembly structures has also given rise to the fabrication of a wide range of sensors, which has greatly contributed to the development of the sensing field. In this review, we focus on the progress in the DNA-mediated assembly of Au NPs and their application in sensing in the past five years. Firstly, we highlight the strategies used for the orderly organization of Au NPs with DNA. Then, we describe the DNA-based assembly of Au NPs for sensing applications and representative research therein. Finally, we summarize the advantages of DNA nanotechnology in assembling complex Au NPs and outline the challenges and limitations in constructing complex gold nanoparticle assembly structures with tailored functionalities.

DNA-mediated regioselective encoding of colloids for programmable self-assembly

How far we can push chemical self-assembly is one of the most important scientific questions of the century. Colloidal self-assembly is a bottom-up technique for the rational design of functional materials with desirable collective properties. Due to the programmability of DNA base pairing, surface modification of colloidal particles with DNA has become fundamental for programmable material self-assembly. However, there remains an ever-lasting demand for surface regioselective encoding to realize assemblies that require specific, directional, and orthogonal interactions. Recent advances in surface chemistry have enabled regioselective control over the formation of DNA bonds on the particle surface. In particular, the structural DNA nanotechnology provides a simple yet powerful design strategy with unique regioselective addressability, bringing the complexity of colloidal self-assembly to an unprecedented level. In this review, we summarize the state-of-art advances in DNA-mediated regioselective surface encoding of colloids, with a focus on how the regioselective encoding is introduced and how the regioselective DNA recognition plays a crucial role in the self-assembly of colloidal structures. This review highlights the advantages of DNA-based regioselective modification in improving the complexity of colloidal assembly, and outlines the challenges and opportunities for the construction of more complex architectures with tailored functionalities.

Plasmonic Nanodiamonds

While nitrogen-vacancy (NV) centers in diamonds have emerged as promising solid-state quantum emitters for sensing applications, the tantalizing possibility of coupling them with photonic or broadband plasmonic nanostructures to create ultrasensitive biolabels has not been fully realized. Indeed, it remains technologically challenging to create free-standing hybrid diamond-based imaging nanoprobes with enhanced brightness and high temporal resolution. Herein, we leverage the bottom-up DNA self-assembly to develop hybrid free-standing plasmonic nanodiamonds, which feature a closed plasmonic nanocavity completely encapsulating a single nanodiamond. Correlated single nanoparticle spectroscopical characterizations suggest that the plasmonic nanodiamond displays dramatically and simultaneously enhanced brightness and emission rate. We believe that they hold huge potential to serve as a stable solid-state single-photon source and could serve as a versatile platform to study nontrivial quantum effects in biological systems with enhanced spatial and temporal resolution.

Current strategies of plasmonic nanoparticles assisted surface-enhanced Raman scattering toward biosensor studies

With the progressive nanofabrication technology, plasmonic nanoparticles (PNPs) have been increasingly deployed in the field of biosensing. PNPs have favorable biocompatibility, conductivity, and tunable optical properties. In addition, the localized surface plasmon resonance (LSPR) of PNPs plays a vital role in surface-enhanced Raman scattering (SERS). PNPs-based SERS biosensing enables wide-ranging applications for sensitive detection and high spatial and temporal resolution imaging. Numerous reviews of PNPs in the field of SERS biosensing highlight the fabrication or applications in one or more fields. However, the specific strategies for the SERS biosensor construction had not been summarized systematically. Thus, this work offers a comprehensive overview of SERS enhancement strategies based on PNPs, with a focus on SERS label-free detection along with label detection sensing construction, as well as its challenges and future trends.

DNA-Patched Nanoparticles for the Self-Assembly of Colloidal Metamaterials

Colloidal metamaterials are highly desired artificial materials that recapitulate the structure of simple molecules. They exhibit exceptional functionalities conferred by the organization of and specific interaction among constituent elements. Harvesting such exquisite attributes for potential applications necessitates establishing precise control over their structural configuration with high precision. Yet, creating molecule-like small clusters of colloidal metamaterials remains profoundly challenging, as a lack of regioselectively encoded surface chemical heterogeneity prevents specific recognition interactions. Herein, we report a new strategy by harnessing magnetic-bead-assisted DNA cluster transferring to create discretely DNA cluster-patched nanoparticles for the self-assembly of colloidal metamaterials. This strategy affords broad generalizability and scalability for robustly patching DNA clusters on nanoparticles unconstrained by geometrical, dimensional, and compositional complexities commonly encountered in colloidal materials at the nano- and microscale. We direct judiciously patched nanoparticles into a wide variety of nanoassemblies and present a case study demonstrating the distinct metamaterial properties in enhancing the spontaneous emission of diamond nanoparticles. This newly invented strategy is readily implementable and extendable to construct a palette of structurally sophisticated and functionality-explicit architecture, paving the way for nanoscale manipulation of colloidal material functionalities with wide-ranging applications for biological sensing, optical engineering, and catalytic chemistry.

On-chip ultrasensitive and rapid hydrogen sensing based on plasmon-induced hot electron-molecule interaction

Hydrogen energy is a zero-carbon replacement for fossil fuels. However, hydrogen is highly flammable and explosive hence timely sensitive leak detection is crucial. Existing optical sensing techniques rely on complex instruments, while electrical sensing techniques usually operate at high temperatures and biasing condition. In this paper an on-chip plasmonic-catalytic hydrogen sensing concept with a concentration detection limit down to 1 ppm is presented that is based on a metal-insulator-semiconductor (MIS) nanojunction operating at room temperature and zero bias. The sensing signal of the device was enhanced by three orders of magnitude at a one-order of magnitude higher response speed compared to alternative non-plasmonic devices. The excellent performance is attributed to the hydrogen induced interfacial dipole charge layer and the associated plasmonic hot electron modulated photoelectric response. Excellent agreements were achieved between experiment and theoretical calculations based on a quantum tunneling model. Such an on-chip combination of plasmonic optics, photoelectric detection and photocatalysis offers promising strategies for next-generation optical gas sensors that require high sensitivity, low time delay, low cost, high portability and flexibility.

Raman spectroscopy of optical-trapped single particle using bull's eye nanostructure

Surface-enhanced Raman spectroscopy (SERS) has enabled single nanoparticle Raman sensing with abundant applications in analytical chemistry, biomaterials, and environmental monitoring. Genuine single particle Raman sensing requires a cumbersome technique, such as atomic force microscopy (AFM) based tip-enhanced Raman spectroscopy; SERS-based single particle Raman sensing still collects an ensemble signal that samples, in principle, a number of particles. Here, we develop in situ Raman-coupled optical tweezers, based on a hybrid nanostructure consisting of a single bowtie aperture surrounded by bull's eye rings, to trap and excite a rhodamine-6G-dye-doped polystyrene sphere. We simulated a platform to ensure sufficient enhancement capability for both optical trapping and SERS of a single nanoparticle. Experiments with well-designed controls clearly attribute the Raman signal origin to a single 15-nm particle trapped at the center of a nanohole, and they also clarified the trapping and Raman enhancement role of the bull's eye rings. We claim Raman sensing of a smallest optically trapped particle.

Revealing the role of tunable amino acid residues in elastin-like polypeptides (ELPs)-mediated biomimetic silicification

Elastin-like polypeptides (ELPs) are attractive materials for the green preparation of silica nanoparticles via biomimetic silicification. However, the critical factors affecting the ELP-mediated silicification remain unclear. Herein, the role of tunable amino acid residues of ELPs in silicification was studied using three ELPs (ELPs[V9F-40], ELPs[KV8F-40], and ELPs[K5V4F-40]) and their fusion proteins (ELPs[V9F-40]-SpyCatcher, ELPs[KV8F-40]-SpyCatcher, and ELPs[K5V4F-40]-SpyCatcher) with different contents of lysine residues. Bioinformatics methods were employed for the first time to reveal the key physicochemical parameters correlated with silicification. The specific activity of ELPs was increased with the promotion of lysine content with a high correlation coefficient (R = 0.899). Furthermore, exogenous acidic protein SpyCatcher would hinder the interactions between the silica precursors and ELPs, leading to the significantly decrease in specific activity. The isoelectric point (pI) of ELPs presented the highest correlation to silicification with a coefficient of 0.963. The charges of the ELPs [K5V4F-40] at different pH were calculated based on the sequence or structure. Interestingly, the excellent correlation between charges based on structure and specific activity was obtained. Collectively, the novel methods developed here may pave a new way for rational design of ELPs or other peptides for efficient and green preparation of silica nanomaterials for biomedicine, biocatalysis, and biosensor.

Plasmonic/magnetic nanoarchitectures: From controllable design to biosensing and bioelectronic interfaces

Controllable design of the nanocrystal-assembled plasmonic/magnetic nanoarchitectures (P/MNAs) inspires abundant methodologies to enhance light-matter interactions and control magnetic-induced effects by means of fine-tuning the morphology and ordered packing of noble metallic or magnetic building blocks. The burgeoning development of multifunctional nanoarchitectures has opened up broad range of interdisciplinary applications including biosensing, in vitro diagnostic devices, point-of-care (POC) platforms, and soft bioelectronics. By taking advantage of their customizability and efficient conjugation with capping biomolecules, various nanoarchitectures have been integrated into high-performance biosensors with remarkable sensitivity and versatility, enabling key features that combined multiplexed detection, ease-of-use and miniaturization. In this review, we provide an overview of the representative developments of nanoarchitectures that being built by plasmonic and magnetic nanoparticles over recent decades. The design principles and key mechanisms for signal amplification and quantitative sensitivity have been explored. We highlight the structure-function programmability and prospects of addressing the main limitations for conventional biosensing strategies in terms of accurate selectivity, sensitivity, throughput, and optoelectronic integration. State-of-the-art strategies to achieve affordable and field-deployable POC devices for early multiplexed detection of infectious diseases such as COVID-19 has been covered in this review. Finally, we discuss the urgent yet challenging issues in nanoarchitectures design and related biosensing application, such as large-scale fabrication and integration with portable devices, and provide perspectives and suggestions on developing smart biosensors that connecting the materials science and biomedical engineering for personal health monitoring.

Ultrasensitive Automatic Detection of Small Molecules by Membrane Imaging of Single Molecule Assays

Determination of trace amounts of targets or even a single molecule target has always been a challenge in the detection field. Digital measurement methods established for single molecule counting of proteins, such as single molecule arrays (Simoa) or dropcast single molecule assays (dSimoa), are not suitable for detecting small molecule, because of the limited category of small molecule antibodies and the weak signal that can be captured. To address this issue, we have developed a strategy for single molecule detection of small molecules, called small molecule detection with single molecule assays (smSimoa). In this strategy, an aptamer is used as a recognition element, and an addressable DNA Nanoflower (DNF) attached on the magnetic beads surface, which exhibit fluorescence imaging, is employed as the output signal. Accompanied by digital imaging and automated counting analysis, E2 at the attomolar level can be measured. The smSimoa breaks the barrier of small molecule detection concentration and provides a basis for high throughput detection of multiple substances with fluorescence encoded magnetic beads.

A Wide-Field Imaging Approach for Simultaneous Super-Resolution Surface-Enhanced Raman Scattering Bioimaging and Spectroscopy

High spatial resolution imaging and chemical-specific detection in living organisms is important in a wide range of fields from medicine to catalysis. In this work, we characterize a wide-field surface-enhanced Raman scattering (SERS) imaging approach capable of simultaneously capturing images and SERS spectra from nanoparticle SERS tags in cancer cells. By passing the image through a transmission diffraction grating before it reaches an array detector, we record the image and wavelength dispersed signal simultaneously on the camera sensor. Optimization of the experiment provides an approach with better spectral resolution and more rapid acquisition than liquid crystal tunable filters commonly used for wide-field SERS imaging. Intensity fluctuations inherent to SERS enabled localization algorithms to be applied to both the spatial and spectral domain, providing super-resolution SERS images that are correlated with improved peak positions identified in the spectrum of the SERS tag. The detected Raman signal is shown to be sensitive to the focal plane, providing three-dimensional (3D) sectioning abilities for the detected nanoparticles. Our work demonstrates spectrally resolved super-resolution SERS imaging that has the potential to be applied to complex physical and biological imaging applications.

Wearable SERS Sensor Based on Omnidirectional Plasmonic Nanovoids Array with Ultra-High Sensitivity and Stability

Surface-enhanced Raman spectroscopy (SERS) is a promising technology for wearable sensors due to its fingerprint spectrum and high detection sensitivity. However, since SERS-activity is sensitive to both the distribution of "hotspots" and excitation angle, it is profoundly challenging to develop a wearable SERS sensor with high stability under various deformations during movements. Herein, inspired by omnidirectional light-harvesting of the compound eye of Xenos Peckii, a wearable SERS sensor is developed using omnidirectional plasmonic nanovoids array (OPNA), which is prepared by assembling a monolayer of metal nanoparticles into the artificial plasmonic compound-eye (APC). Specifically, APC is an interconnected frame containing omnidirectional "pockets" and acts as an "armour", not only rendering a broadband and omnidirectional enhancement of "hotspots" in the delicate nanoparticles array, but also maintaining an integrity of the "hotspots" against external mechanical deformations. Furthermore, an asymmetry super-hydrophilic pattern is fabricated on the surface of OPNA, endowing the hydrophobic OPNA with the ability to spontaneously extract and concentrate the analytes from sweat. Such an armored SERS sensor can enable the wearable and in situ analysis with high sensitivity and stability, exhibiting great potential in point-of-care analysis.

Surface-enhanced Raman scattering: An emerging tool for sensing cellular function

Continuous long-term intracellular imaging and multiplexed monitoring of biomolecular changes associated with key cellular processes remains a challenge for the scientific community. Recently, surface-enhanced Raman scattering (SERS) has been demonstrated as a powerful spectroscopic tool in the field of biology owing to its significant advantages. Some of these include the ability to provide molecule-specific information with exquisite sensitivity, working with small volumes of precious samples, real-time monitoring, and optimal optical contrast. More importantly, the availability of a large number of novel Raman reporters with narrower full width at half maximum (FWHM) of spectral peaks/vibrational modes than conventional fluorophores has created a versatile palette of SERS-based probes that allow targeted multiplex sensing surpassing the detection sensitivity of even fluorescent probes. Due to its nondestructive nature, its applicability has been recognized for biological sensing, molecular imaging, and dynamic monitoring of complex intracellular processes. We critically discuss recent developments in this area with a focus on different applications where SERS has been used for obtaining information that remains elusive for conventional imaging methods. Current reports indicate that SERS has made significant inroads in the field of biology and has the potential to be used for in vivo human applications. This article is categorized under: Diagnostic Tools > In Vitro Nanoparticle-Based Sensing Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Diagnostic Tools > Biosensing Diagnostic Tools > In Vivo Nanodiagnostics and Imaging.

Wearable plasmonic paper-based microfluidics for continuous sweat analysis

Wearable sweat sensors have the potential to provide clinically meaningful information associated with the health and disease states of individuals. Current sensors mainly rely on enzymes and antibodies as biorecognition elements to achieve specific quantification of metabolite and stress biomarkers in sweat. However, enzymes and antibodies are prone to degrade over time, compromising the sensor performance. Here, we introduce a wearable plasmonic paper-based microfluidic system for continuous and simultaneous quantitative analysis of sweat loss, sweat rate, and metabolites in sweat. Plasmonic sensors based on label-free surface-enhanced Raman spectroscopy (SERS) can provide chemical "fingerprint" information for analyte identification. We demonstrate the sensitive detection and quantification of uric acid in sweat at physiological and pathological concentrations. The well-defined flow characteristics of paper microfluidic devices enable accurate quantification of sweat loss and sweat rate. The wearable plasmonic device is soft, flexible, and stretchable, which can robustly interface with the skin without inducing chemical or physical irritation.

Three-dimensional surface-enhanced Raman scattering substrates constructed by integrating template-assisted electrodeposition and post-growth of silver nanoparticles

Three-dimensional (3D) plasmonic nano-arrays can provide high surface-enhanced Raman scattering (SERS) sensitivity, good spectral uniformity and excellent reproducibility. However, it is still a challenge to develop a simple and efficient method for fabrication of 3D plasmonic nano-arrays with high SERS performance. Here we report a facile approach to construct ordered arrays of silver (Ag) nanoparticles-assembled spherical micro-cavities using polystyrene (PS) sphere template-assisted electrodeposition and post-growth. The electrodeposited small Ag nanoparticles grow into bigger stable nanoparticles during the post-growth process, which could significantly improve the SERS sensitivity. The Ag nanoparticles-assembled 3D micro-cavity array provides much more hotspots in the excitation laser beam-covered volume than the two-dimensional counterpart. The relative standard deviation (RSD) of 612 cm^-1 peak of rhodamine 6G (R6G) was calculated to be 8%, and the RSD of the characteristic peak taken from substrates of different batches was less than 10%. The detectable lower concentration as low as 1 fM was achieved for an aqueous solution of R6G. Such SERS substrate also showed high sensitivity to thiram (fungicide) and paraquat (herbicide) in water with limits of detection of 0.067 nM and 2.5 nM respectively. Furthermore, it also demonstrated that SERS detection of pesticide residues on fruits can be realized, showing a potential application in rapid monitoring food safety.

A Super-Boosted Hybrid Plasmonic Upconversion Process for Photodetection at 1550 nm Wavelength

A super-boosted hybrid plasmonic upconversion (UC) architecture comprising a hierarchical plasmonic upconversion (HPU) film and a polymeric microlens array (MLA) film is proposed for efficient photodetection at a wavelength of 1550 nm. Plasmonic metasurfaces and Au core-satellite nanoassembly (CSNA) films can strongly induce a more effective plasmonic effect by providing numerous hot spots in an intense local electromagnetic field up to wavelengths exceeding 1550 nm. Hence, significant UC emission enhancement is realized via the amplified plasmonic coupling of an HPU film comprising an Au CSNA and UC nanoparticles. Furthermore, an MLA polymer film is synergistically coupled with the HPU film, thereby focusing the incident near-infrared light in the micrometer region, including the plasmonic nanostructure area. Consequently, the plasmonic effect super-boosted by microfocusing the incident light, significantly lowers the detectable power limit of a device, resulting in superior sensitivity and responsivity at weak excitation powers. Finally, a triple-cation perovskite-based photodetector coupled with the hybrid plasmonic UC film exhibits the excellent values of responsivity and detectivity of 9.80 A W^-1 and 8.22 × 10¹² Jones at a weak power density of ≈0.03 mW cm^-2 , respectively, demonstrating that the device performance is enhanced by more than 10⁴ magnitudes over a reference sample.

Large-Area Nanosphere Self-Assembly Monolayers for Periodic Surface Nanostructures with Ultrasensitive and Spatially Uniform SERS Sensing

Colloidal lithography provides a rapid and low-cost approach to construct 2D periodic surface nanostructures. However, an impressive demonstration to prepare large-area colloidal template is still missing. Here, a high-efficient and flexible technique is proposed to fabricate self-assembly monolayers consisting of orderly-packed polystyrene spheres at air/water interface via ultrasonic spray. This "non-contact" technique exhibits great advantages in terms of scalability and adaptability due to its renitent interface dynamic balance. More importantly, this technique is not only competent for self-assembly of single-sized polystyrene spheres, but also for binary polystyrene spheres, completely reversing the current hard situation of preparing large-area self-assembly monolayers. As a representative application, hexagonal-packed silver-coated silicon nanorods array (Si-NRs@Ag) is developed as an ultrasensitive surface-enhanced Raman scattering (SERS) substrate with very low limit-of-detection for selective detection of explosive 2,4,6-trinitrotoluene down to femtomolar (10^-14 m) range. The periodicity and orderliness of the array allow hot spots to be designed and constructed in a homogeneous fashion, resulting in an incomparable uniformity and reproducibility of Raman signals. All these excellent properties come from the Si-NRs@Ag substrate based on the ordered structure, open surface, and wide-range electric field, providing a robust, consistent, and tunable platform for molecule trapping and SERS sensing for a wide range of organic molecules.

Effect of the Duty Cycle of Flower-like Silver Nanostructures Fabricated with a Lyotropic Liquid Crystal on the SERS Spectrum

Surface-enhanced Raman scattering (SERS) has been widely reported to improve the sensitivity of Raman spectra. Ordinarily, the laser is focused on the sample to measure the Raman spectrum. The size of the focused light spot is comparable with that of micro-nano structures, and the number of micro-nano structures contained in the light spot area (defined as duty cycle) will severely affect the spectrum intensity. In this study, flower-like silver nanostructures were fabricated with a soft lyotropic liquid crystal template in order to investigate the effect of duty cycle. They were observed under a scanning electron microscope, and their spectrum enhancement factor was computed with the obtained Raman spectrum. Then, their duty cycles were measured using a SERS substrate at different locations. A formula was derived to represent the relation between the duty cycle of the nanoflowers and the Raman spectral intensity. This work could promote the actual applications of SERS in high-sensitivity spectrum testing.

Au Nanorings with Intertwined Triple Rings

We designed complex Au nanorings with intertwined triple rings (ANITs) in a single entity to amplify the efficacy of near-field focusing. Such a complex and unprecedented morphology at the nanoscale was realized through on-demand multistepwise reactions. Triangular nanoprisms were first sculpted into circular nanorings, followed by a series of chemical etching and deposition reactions eventually leading to ANITs wherein thin metal bridges hold the structure together without any linker molecules. In the multistepwise reaction, the well-faceted growth pattern of Au, which induces the growth of two distinctive flat facets in a lateral direction, is important to evolve the morphology from single to multiple nanorings. Although our synthesis proceeds through multiple steps in one batch without purification steps, it shows a remarkably high yield (>∼90%) at the final stage. The obtained high degree of homogeneity (in both shape and size) of the resulting ANITs allowed us to systematically investigate the corresponding localized surface plasmon resonance (LSPR) coupling with varying nanoring arrangements and observe their single-particle surface enhanced Raman scattering (SERS). Surprisingly, individual ANITs exhibited an enormously large enhancement factor (∼10⁹), which confirms their superior near-field focusing relative to other reported nanoparticles.