Theoretical investigation of size, shape, and aspect ratio effect on the LSPR sensitivity of hollow-gold nanoshells

Plasmonic Nanogap-Enhanced Tunable Three-Dimensional Nanoframes in Application to Clinical Diagnosis of Alzheimer's Disease

Advancements in nanotechnology led to significant improvements in synthesizing plasmon-enhanced nanoarchitectures for biosensor applications, and high-yield productivity at low cost is vital to step further into medical commerce. Metal nanoframes via wet chemistry are gaining attention for their homogeneous structure and outstanding catalytic and optical properties. However, nanoframe morphology should be considered delicately when brought to biosensors to utilize its superior characteristics thoroughly, and the need to prove its clinical applicability still remains. Herein, we controlled the frameworks of double-walled nanoframes (DWFs) precisely via wet chemistry to construct a homogeneous plasmon-enhanced nanotransducer for localized surface plasmon resonance biosensors. By tuning the physical properties considering the finite-difference time-domain simulation results, biomolecular interactions were feasible in the electromagnetic field-enhanced nanospace. As a result, DWF10 exhibited a 10-fold lower detection limit of 2.21 fM compared to DWF14 for tau detection. Further application into blood-based clinical and Alzheimer's disease (AD) diagnostics, notable improvement in classifying mild cognitive impairment patients against healthy controls and AD patients, was demonstrated along with impressive AUC values. Thus, in response to diverse detection methods, optimizing nanoframe dimensions such as nanogap and frame thickness to maximize sensor performance is critical to realize future POCT diagnosis.

Recent advances in the development of multiplexed nanophotonic biosensors

The field of nanophotonics has advanced and can be utilized as a method to detect different infectious diseases. The introduction of multiplex nanophotonic diagnostics has enabled the speedy and simultaneous detection of viral infections and specific biomarkers. The quick reaction times, high sensitivity, and specificity of multiplex nanophotonic diagnostics enable real-time identification of viruses without the need for nucleic acid amplification. This review presents an overview of nanophotonic tools used to identify diseases and particular biomarkers. The paper also examines possible research areas for the development of unique, cutting-edge multiplex nanophotonic diagnostics capable of concurrently detecting various diseases or biomarkers/biomolecules. Furthermore, it discusses barriers to further advancement and offers insight into anticipated trends.

Lysozyme-sensitive plasmonic hydrogel nanocomposite for colorimetric dry-eye inflammation biosensing

Detection of lysozyme levels in ocular fluids is considered crucial for diagnosing and monitoring various health and eye conditions, including dry-eye syndrome. Hydrogel-based nanocomposites have been demonstrated to be one of the most promising platforms for fast and accurate sensing of different biomolecules. In this work, hydrogel, electrospun nanofibers, and plasmonic nanoparticles are combined to fabricate a sensitive and easy-to-use biosensor for lysozyme. Poly(L-lactide-co-caprolactone) (PLCL) nanofibers were covered with silver nanoplates (AgNPls), providing a stable plasmonic platform, where a poly(N-isopropylacrylamide)-based (PNIPAAm) hydrogel layer allows mobility and good integration of the biomolecules. By integrating these components, the platform can also exhibit a colorimetric response to the concentration of lysozyme, allowing for easy and non-invasive monitoring. Quantitative biosensing operates on the principle of localized surface plasmon resonance (LSPR) induced by plasmonic nanoparticles. Chemical, structural, thermal, and optical characterizations were performed on each platform layer, and the platform's ability to detect lysozyme at concentrations relevant to those found in tears of patients with dry-eye syndrome and other related diseases was investigated by colorimetry and UV-Vis spectroscopy. This biosensor's sensitivity and rapid response time, alongside the easy detection by the naked eye, make it a promising tool for early diagnosis and treatment monitoring of eye diseases.

Plasmon resonances of GZO core-Ag shell nanospheres, nanorods, and nanodisks for biosensing and biomedical applications in near-infrared biological windows I and II

There is currently a great deal of interest in realizing localized surface plasmon resonances (LSPRs) in two distinct windows in the near-infrared (NIR) spectrum for in vivo biosensing and medical applications, the biological window (BW) I and II (BW I, 700-900 nm; BW II, 1000-1700 nm). This study aims to demonstrate that LSPRs of Ga-doped ZnO (GZO) core-silver (Ag) shell structures exhibit promising features for biological applications in the NIR BW I and II. Here, we study three different shapes for nanoshells: the core-shell nanosphere, nanorod, and nanodisk. In the calculation of the optical response of these nanoshells, an effective medium approach is first used to reduce the dielectric function of a nanoshell to that of an equivalent homogenous NP with an effective dielectric function. Then, the LSPR spectra of nanoshells are calculated using the modified long-wavelength approximation (MLWA), which corrects the polarizability of the equivalent NP as obtained by Gans theory. Through numerical investigations, we examine the impacts of the core and shell sizes of the proposed nanoshells as well as the medium refractive index on the position and line width of the plasmon resonance peaks. It is shown that the plasmon resonances of the three proposed nanoshells exhibit astonishing resonance tunability in the NIR region by varying their geometrical parameters. Specifically, the improved spectrum characteristics and tunability of its plasmon resonances make the GZO-Ag nanosphere a more viable platform for NIR applications than the spherical metal colloid. Furthermore, we demonstrate that the sensitivity and figure of merit (FOM) of the plasmon resonances may be significantly increased by using GZO-Ag nanorods and nanodisks in place of GZO-Ag nanospheres. It is found that the optical properties of the transverse plasmon resonance of the GZO-Ag nanodisk are superior to all plasmon resonances produced by the GZO-Ag nanorods and GZO-Ag nanospheres in terms of sensitivity and FOM. The FOM of the transverse plasmon mode of the GZO-Ag nanodisk is almost two orders of magnitude higher than that of the longitudinal and transverse plasmon modes of the GZO-Ag nanorod in BW I and BW II. And it is 1.5 and 2 times higher than the plasmon resonance FOM of GZO-Ag nanospheres in BW I and BW II, respectively.

Bonding states of gold/silver plasmonic nanostructures and sulfur-containing active biological ingredients in biomedical applications: a review

As one of the most instrumental components in the architecture of advanced nanomedicines, plasmonic nanostructures (mainly gold and silver nanomaterials) have been paid a lot of attention. This type of nanomaterial can absorb light photons with a specific wavelength and generate heat or excited electrons through surface resonance, which is a unique physical property. In innovative biomaterials, a significant number of theranostic (therapeutic and diagnostic) materials are produced through the conjugation of thiol-containing ingredients with gold and silver nanoparticles (Au and Ag NPs). Hence, it is essential to investigate Au/Ag-S interfaces precisely and determine the exact bonding states in the active nanobiomaterials. This study intends to provide useful insights into the interactions between Au/Ag NPs and thiol groups that exist in the structure of biomaterials. In this regard, the modeling of Au/Ag-S bonding in active biological ingredients is precisely reviewed. Then, the physiological stability of Au/Ag-based plasmonic nanobioconjugates in real physiological environments (pharmacokinetics) is discussed. Recent experimental validation and achievements of plasmonic theranostics and radiolabelled nanomaterials based on Au/Ag-S conjugation are also profoundly reviewed. This study will also help researchers working on biosensors in which plasmonic devices deal with the thiol-containing biomaterials (e.g., antibodies) inside blood serum and living cells.

Biomimetic SERS substrate with silicon-mediated internal standard: Improved sensing of environmental pollutants and nutrients

Biomimetic materials with fascinating natural micro-nano surface structures offer a good choice for the simple fabrication of surface-enhanced Raman scattering (SERS) substrate. This study presented a novel sodium carboxymethylcellulose (NaCMC)-Ag biomimetic substrate which was fabricated through the reverse replication of micro-nano structures from cantaloupe peel. Particularly, silicon nanoparticles (Si NPs) were doped into this flexible biomimetic substrate in its fabrication process. Abundant electromagnetic "hotspots" could be effectively excited in this Ag densely covered matrix which maintained numerous protrusions as well as vertical and horizontal grooves. Specifically, the doped Si NPs exhibited a robust intrinsic Raman peak, which could be employed as an internal standard to calibrate the target signal. In this regard, the biomimetic substrate with the optimal electromagnetic enhancement and the quantitative calibration capabilities exhibited a high enhancement factor and a remedied linear relationship in the detection. After a perfect uniformity of signal was proved by the corrected SERS mapping, the biomimetic SERS substrate was finally utilized in the practical analysis of methylene blue (MB) and β-carotene with ultra-low limit of detection, highlighting its importance in practical detection scenarios.

Bandwidth of quantized surface plasmons: competition between radiative and nonradiative damping effects

We investigate the damping effects of coherent electron oscillations on the bandwidth of a quantized nanoparticle plasmon resonance. The nanoparticle (NP) is treated as a two-level quantum system, and the total relaxation time involves both the population relaxation time associated with radiative processes and the collisional relaxation time associated with nonradiative processes that result in dephasing/decoherence of electron oscillations. We describe the optical response of NPs to an external electromagnetic field by the optical Bloch equations employing the density matrix formalism to capture the quantum description nature of dipolar plasmon resonance and suggest a generalized criterion for the validity of dipole approximation. Then we explore the competition between the radiative and nonradiative damping in determining the plasmon bandwidth of two typical NP models; metallic nanospheres and dielectric core-metal shell NPs (nanoshells). We show that the frequency of plasmon resonance, in addition to the NP size, plays an important role in the competition between the damping mechanisms. Consequently, the damping processes are significantly influenced by the factors that determine the resonance frequency, such as the core size, the dielectric constant of the medium, and the shell thickness (for nanoshells). For both models of NPs, we identify the optimum parameters that achieve a narrower plasmon bandwidth (minimal damping), which is a prerequisite for advanced sensing and medical applications. We demonstrate excellent agreement of the simulated spectral features of the plasmon resonance with previously reported experimental results for a single NP where the inhomogeneous broadening of the plasmon line is excluded. For NP ensembles where inhomogeneous broadenings and interface chemical effects are significant, our theoretical approach successfully predicts the overall trend of size-dependent damping rates.

Plasmonic Nanoparticle-Enhanced Optical Techniques for Cancer Biomarker Sensing

This review summarizes recent advances in leveraging localized surface plasmon resonance (LSPR) nanotechnology for sensitive cancer biomarker detection. LSPR arising from noble metal nanoparticles under light excitation enables the enhancement of various optical techniques, including surface-enhanced Raman spectroscopy (SERS), dark-field microscopy (DFM), photothermal imaging, and photoacoustic imaging. Nanoparticle engineering strategies are discussed to optimize LSPR for maximum signal amplification. SERS utilizes electromagnetic enhancement from plasmonic nanostructures to boost inherently weak Raman signals, enabling single-molecule sensitivity for detecting proteins, nucleic acids, and exosomes. DFM visualizes LSPR nanoparticles based on scattered light color, allowing for the ultrasensitive detection of cancer cells, microRNAs, and proteins. Photothermal imaging employs LSPR nanoparticles as contrast agents that convert light to heat, producing thermal images that highlight cancerous tissues. Photoacoustic imaging detects ultrasonic waves generated by LSPR nanoparticle photothermal expansion for deep-tissue imaging. The multiplexing capabilities of LSPR techniques and integration with microfluidics and point-of-care devices are reviewed. Remaining challenges, such as toxicity, standardization, and clinical sample analysis, are examined. Overall, LSPR nanotechnology shows tremendous potential for advancing cancer screening, diagnosis, and treatment monitoring through the integration of nanoparticle engineering, optical techniques, and microscale device platforms.

Enhancement and quenching of plasmon-enhanced spectroscopy of single molecule confined in metallic nanoparticle dimers

We present a theoretical analysis of plasmon-enhanced fluorescence (PEF) and Raman scattering (PERS) spectroscopy of a single molecule confined in the laser-irradiated metallic nanoparticles (NPs) dimer, focusing on the origin of the spectral enhancement and quenching effects. The theoretical method ofD-parameters has been used to calculate the dimer distance-dependent nonlocal dielectric effect in Ag and Au NPs. Meanwhile, other damping rates and electric field enhancements are quantitatively computed by finite element method. Moreover, PEF and PERS spectra of rhodamine 6G are obtained within the density-functional theory. Our calculated results show that the PERS mainly depend on the excitation and emission field enhancements, and thus it occurs at the narrower dimer gap due to the stronger localized plasmon coupling. The PEF is related to fluorescence rate caused by the competition between excitation electric field and quantum efficiency, and the increase of former may enhance the fluorescence intensity while the lower latter lead to reduce the intensity as decreasing the dimer distance. The contribution of nonlocal dielectric effect can significantly reduce the quantum efficiency at smaller distance so that it overcomes the excitation field enhancement, leading to the fluorescence quenching for Au NPs dimer. Furthermore, by optimizing the dimer distance and NPs size, the maximum PERS and PEF cross sections reach 10-14and 10-15under 2.45 eV laser excitation for Ag NPs dimer, and 10-18for Au NPs. Our study finely explains the experiment results showed either fluorescence enhancement or quenching with the change of molecule-NPs distance, and better guidance for optimizing the experiments.

A dual functional asymmetric plasmonic silver nanostructure for temperature and magnetic field sensing

Many diverse technological applications, such as soft robotics and flexible electronics, demand the development of intelligent sensors that can simultaneously detect different physical parameters. Taking advantage of plasmonic structures, which can experience minute variations in physical parameters upon close contact, herein, a dual channel based silver nanostructure of concentric square rings and disks on an SiO2 substrate is proposed for the synchronized detection of magnetic field (H) and temperature (T). The thermometric polydimethylsiloxane (PDMS) and ferromagnetic Fe3O4 were placed in two channels of the nanostructure, forming the sensor. The structure modeling and electromagnetic study were carried out using the finite element method (FEM). The simultaneous detection of H and T was realized through the sensing matrix, which solved the problem of cross-sensitivity caused by a variation in temperature. Furthermore, the impact of structural asymmetry on the performance of the sensor was studied by tuning its geometrical parameters, such as disk length and ring length, separately and together. Asymmetry and the channel size significantly enhanced the performance, where disk optimization increased the temperature and magnetic field sensitivity by about 760 and 8319 times using 70% and 80% asymmetric systems, respectively. Also, the smallest ΔW (5 nm) provided a sufficiently high channel separation factor of about 7.47 μm during multi-parameter sensing. In addition, asymmetric sensing toward a single parameter was tested by placing PDMS/Fe3O4 on both channels. Multiple peaks were displayed with high sensitivity and CH-factor, making the detection more specific. Thus, the system possessing a combination of narrow channels and unique channel asymmetry exhibited excellent multi- and single-sensing for the detection of temperature and magnetic field.

High Efficiency over 15% by Breaking the Theoretical Efficiency Limit of Fluorescent Organic Light-Emitting Diodes with Localized Surface Plasmon Resonance Effects

The theoretical efficiency limit of fluorescence organic light-emitting diodes (OLEDs) was successfully surpassed by utilizing the localized surface plasmon resonance (LSPR) effect with conventional emissive materials. The interaction between polaritons and plexcitons generated during the LSPR process was also analyzed experimentally. As a result, the external quantum efficiency (EQE) increased dramatically from 6.01 to 15.43%, significantly exceeding the theoretical efficiency limit of fluorescent OLEDs. Additionally, we introduced a new concept of the LSPR effect, called "LSPR sensitizer", which allowed for simultaneous improvement in color conversion and efficiency through cascade transfer of the LSPR effect. To the best of our knowledge, the EQE and the current efficiency of our LSPR-OLED are the highest among LSPR-based fluorescent OLEDs to date.

Detailed Investigation of Factors Affecting the Synthesis of SiO2@Au for the Enhancement of Raman Spectroscopy

The reaction time, temperature, ratio of precursors, and concentration of sodium citrate are known as the main factors that affect the direct synthesis process of SiO₂@Au based on the chemical reaction of HAuCl4 and sodium citrate. Hence, we investigated, in detail, and observed that these factors played a crucial role in determining the shape and size of synthesized nanoparticles. The significant enhancement of the SERS signal corresponding to the fabrication conditions is an existing challenge. Our study results show that the optimal reaction conditions for the fabrication of SiO₂@Au are a 1:21 ratio of HAuCl₄ to sodium citrate, with an initial concentration of sodium citrate of 4.2 mM, and a reaction time lasting longer than 6 h at a temperature of 80 °C. Under optimal conditions, our synthesis process result is SiO₂@Au nanoparticles with a diameter of approximately 350 nm. In particular, the considerable enhancement of Raman intensities of SiO₂@Au compared to SiO₂ particles was examined.

Review on LSPR assisted photocatalysis: effects of physical fields and opportunities in multifield decoupling

Since nano scale local surface plasmon resonance (LSPR) can broaden the visible absorption region, enhance the local electromagnetic field and produce a thermal effect simultaneously, the appropriate utilization of the LSPR effect is a noteworthy research direction towards visible light driven photocatalysts with high efficiency and low cost. In this study, the influence mechanism of the optical, electric, magnetic, and thermal physical fields on the photocatalytic efficiency of the LSPR system is for the first time reviewed, based on which the research bottlenecks of this method including the accurate predesign and regulation of the photocatalyst, the interpretation of electron movement and energy transfer mechanism, are specifically analyzed. Due to the micro-nano localization of LSPR, auxiliary methods are needed to reflect the micro electromagnetic and temperature field distribution which are otherwise formidable to measure experimentally. Alternatively, numerical methods with decoupling calculations of nano-scale physical fields are necessary to develop. Therefore, the development potential of different numerical simulation methods including mainstream FDTD, FEM and DDA is subsequently expounded, providing opportunities in resolving the bottleneck issues associated with photocatalysis. It is worth mentioning that although many important advances have been achieved in the preparation and application of LSPR assisted photocatalysts, the convincing function mechanism of LSPR is still lacking due to its multifield synergistic enhancement effect.

Latest Trends in Lateral Flow Immunoassay (LFIA) Detection Labels and Conjugation Process

LFIA is one of the most successful analytical methods for various target molecules detection. As a recent example, LFIA tests have played an important role in mitigating the effects of the global pandemic with SARS-COV-2, due to their ability to rapidly detect infected individuals and stop further spreading of the virus. For this reason, researchers around the world have done tremendous efforts to improve their sensibility and specificity. The development of LFIA has many sensitive steps, but some of the most important ones are choosing the proper labeling probes, the functionalization method and the conjugation process. There are a series of labeling probes described in the specialized literature, such as gold nanoparticles (GNP), latex particles (LP), magnetic nanoparticles (MNP), quantum dots (QDs) and more recently carbon, silica and europium nanoparticles. The current review aims to present some of the most recent and promising methods for the functionalization of the labeling probes and the conjugation with biomolecules, such as antibodies and antigens. The last chapter is dedicated to a selection of conjugation protocols, applicable to various types of nanoparticles (GNPs, QDs, magnetic nanoparticles, carbon nanoparticles, silica and europium nanoparticles).

Smartphone-based Surface Plasmon Resonance Sensors: a Review

The surface plasmon resonance (SPR) is a phenomenon based on the combination of quantum mechanics and electromagnetism, which leads to the creation of charge oscillations on a metal-dielectric interface. The SPR phenomenon creates a signal which measures refractive index change at the metal-dielectric interface. SPR-based sensors are being developed for real-time and label-free detection of water pollutants, toxins, disease biomarkers, etc., which are highly sensitive and selective. Smartphones provide hardware and software capability which can be incorporated into SPR sensors, enabling the possibility of economical and accurate on-site portable sensing. The camera, screen, and LED flashlight of the smartphone can be employed as components of the sensor. The current article explores the recent advances in smartphone-based SPR sensors by studying their principle, components, application, and signal processing. Furthermore, the general theoretical and practical aspects of SPR sensors are discussed.

Enhanced refractive index sensitivity of localized surface plasmon resonance inflection points in single hollow gold nanospheres with inner cavity

Hollow gold nanoparticles have great potential for localized surface plasmon resonance (LSPR) sensing. In this study, we investigated the refractive index (RI) sensitivities of single hollow gold nanosphere (HAuNS) with thin Au shell and inner cavity and single solid gold nanosphere (AuNS) in media with different RIs. The HAuNS exhibited a remarkable improvement in the RI sensitivity than the AuNS of similar size. The increased RI sensitivity of HAuNSs was ascribed to plasmon coupling between the inner and outer surface of the Au nanoshell. We then investigated the homogeneous LSPR scattering inflection points (IFs) to better understand the RI sensitivity of single HAuNS. The LSPR IF at the long wavelength side exhibited a better RI sensitivity compared to the wavelength shift of its counterpart LSPR maximum peak. Furthermore, the single HAuNS showed a remarkable improvement in the RI sensitivity at the LSPR IFs when compared to the AuNS of similar size. Therefore, we provided a new insight into the effect of inner cavity of HAuNS on the RI sensitivity of homogeneous LSPR IFs for use in LSPR-based biosensors.

Gold nanoparticle based plasmonic sensing for the detection of SARS-CoV-2 nucleocapsid proteins

An inexpensive virus detection scheme with high sensitivity and specificity is desirable for broad applications such as the COVID-19 virus. In this article, we introduce the localized surface plasmon resonance (LSPR) principle on the aggregation of antigen-coated gold nanoparticles (GNPs) to detect SARS-CoV-2 Nucleocapsid (N) proteins. Experiments show this technique can produce results observable by the naked eye in 5 min with a LOD (Limits of Detection) of 150 ng/ml for the N proteins. A comprehensive numerical model of the LSPR effect on the aggregation of GNPs has been developed to identify the key parameters in the reaction processes. The color-changing behaviors can be readily utilized to detect the existence of the virus while the quantitative concentration value is characterized with the assistance of an optical spectrometer. A parameter defined as the ratio of the light absorption intensity at the upper visible band region of 700 nm to the light absorption intensity at the peak optical absorption spectrum of the GNPs at 530 nm is found to have a linear relationship with respect to the N protein concentrations. As such, this scheme could be utilized as an inexpensive testing methodology for applications in POC (Point-of-Care) diagnostics to combat current and future virus-induced pandemics.

Selective controlling transverse plasmon spectrum of pentagonal gold nanotube: from visible to near-infrared region

In this paper, the optical properties and local electric field distribution of transverse plasmon mode of a single pentagonal gold nanotube are studied for the first time by the discrete dipole approximation (DDA). We find that the transverse plasmon peaks can nonlinearly red shift from visible to infrared region via controlling the inner diameter. In addition, the transverse plasmon peak firstly blue shifts and then red shifts in the visible region with the increase of outer diameter. Further analysis shows that the spectra red shift with the increase of outer diameters when scattering is dominant. Local electric field analysis reveals that transverse plasmon resonance peaks of gold nanotube mainly come from dipole resonance. When the tube wall is thin enough, multi-polar plasmon resonance mode will be generated, and the number of peaks will be increased. The surface charges of inner and outer tube walls are changed by tuning the inner diameter and outer diameter parameters of pentagonal gold nanotube. The selective controlling transverse plasmon spectra of gold nanotube are realized, which is of great significance to the study of optical properties of gold nanotube and the application of molecular detection and biological imaging.

Detection of the Chilli Leaf Curl Virus Using an Attenuated Total Reflection-Mediated Localized Surface-Plasmon-Resonance-Based Optical Platform

The development of a nanoparticle-based optical platform has been presented as a biosensor for detecting target-specific plant virus DNA. The binding dynamics of gold nanoparticles has been studied on the amine-functionalized surface by the attenuated total reflection (ATR)-based evanescent wave absorption method monitoring the localized surface plasmon resonance (LSPR). The developed surface was established as a refractive index sensor by monitoring the LSPR absorption peak of gold nanoparticles. This nanoparticle-immobilized surface was explored to establish as a biosensing platform with target-specific immunoglobulin (IgG) antibody-antigen interaction. The IgG concentration-dependent variation of absorbance was correlated with the refractive index change. After successfully establishing this ATR configuration as an LSPR-based biosensor, the single-stranded DNA of the chilli leaf curl virus was detected using its complementary DNA sequence as a receptor. The limit of detection of this sensor was determined to be 1.0 μg/mL for this target viral DNA. This ATR absorption technique has enormous potential as an LSPR based nano-biosensor for the detection of other begomoviruses.

Circular dichroism enhancement and dynamically adjustment in planar metal chiral split rings with graphene sheets arrays

Chiral plasmonic nanostructures have become a promising platform for polarization converters and molecular analysis. However, the circular dichroism (CD) of planar chiral plasmonic nanostructures is always weak and difficult for dynamic adjustment. In this work, graphene sheets (GSs) are introduced in planar metal chiral split rings (MCSRs) to enhance and dynamically adjust their CD effect. The chiral split rings consist of rotated big and small split rings. Simulation results show that the plasmonic coupling between MCSRs and GSs can enhance the absorption and CD spectra of MCSRs at two resonant wavelengths. The surface current distributions reveal that the CD signals are due to the localized surface plasmon resonances on the big and small split rings, respectively. The loss distributions illustrate that the increased loss mainly locates in GSs. In addition, the CD spectra of MCSRs/GSs can be dynamically adjusted and influenced by the Fermi energy of GSs, the geometric parameters of MCSRs and, the mediums in the environment. It can be used to detect the environmental temperature and concentration. The results help to design dynamically adjustable chiral nanostructures and promote their applications in environment detection.

M. M. de Almeida J, Pastoriza-Santos I, C. C. Coelho L. Advances in Plasmonic Sensing at the NIR-A Review

Surface plasmon resonance (SPR) and localized surface plasmon resonance (LSPR) are among the most common and powerful label-free refractive index-based biosensing techniques available nowadays. Focusing on LSPR sensors, their performance is highly dependent on the size, shape, and nature of the nanomaterial employed. Indeed, the tailoring of those parameters allows the development of LSPR sensors with a tunable wavelength range between the ultra-violet (UV) and near infra-red (NIR). Furthermore, dealing with LSPR along optical fiber technology, with their low attenuation coefficients at NIR, allow for the possibility to create ultra-sensitive and long-range sensing networks to be deployed in a variety of both biological and chemical sensors. This work provides a detailed review of the key science underpinning such systems as well as recent progress in the development of several LSPR-based biosensors in the NIR wavelengths, including an overview of the LSPR phenomena along recent developments in the field of nanomaterials and nanostructure development towards NIR sensing. The review ends with a consideration of key advances in terms of nanostructure characteristics for LSPR sensing and prospects for future research and advances in this field.

Laser-induced optothermal response of gold nanoparticles: From a physical viewpoint to cancer treatment application

Gold nanoparticles (GNPs)-based photothermal therapy (PTT) is a promising minimally invasive thermal therapy for the treatment of focal malignancies. Although GNPs-based PTT has been known for over two decades and GNPs possess unique properties as therapeutic agents, the delivery of a safe and effective therapy is still an open question. This review aims at providing relevant and recent information on the usage of GNPs in combination with the laser to treat cancers, pointing out the practical aspects that bear on the therapy outcome. Emphasis is given to the assessment of the GNPs' properties and the physical mechanisms underlying the laser-induced heat generation in GNPs-loaded tissues. The main techniques available for temperature measurement and the current theoretical simulation approaches predicting the therapeutic outcome are reviewed. Topical challenges in delivering safe thermal dosage are also presented with the aim to discuss the state-of-the-art and the future perspective in the field of GNPs-mediated PTT.

Structural control and biomedical applications of plasmonic hollow gold nanospheres: A mini review

Hollow gold nanospheres (HGNs) are core/shell structures with a dielectric material core, usually composed of solvent, and a gold metal shell. Such structures have two metal/dielectric interfaces to allow interaction between the gold metal with the interior and external dielectric environment. Upon illumination by light, HGNs exhibit unique surface plasmon resonance (SPR) properties compared to solid gold nanoparticles. Their SPR absorption/scattering can be tuned by changing their diameter, shell thicknesses, and surface morphologies. In addition to the low toxicity, easy functionalization, resistance to photobleaching, and sensitivity to changes in surrounding medium of gold, the enhanced surface-to-volume ratio and tunable SPR of HGNs make them highly attractive for different applications in the fields of sensing, therapy, and theranostics. In this article, we review recent progress on the synthesis and structural control of HGNs and applications of their SPR properties in biomedical sensing and theranostics. This article is categorized under: Diagnostic Tools > Biosensing Diagnostic Tools > in vitro Nanoparticle-Based Sensing Diagnostic Tools > in vivo Nanodiagnostics and Imaging.

Recent Developments in Plasmonic Nanostructures for Metal Enhanced Fluorescence-Based Biosensing

Metal-enhanced fluorescence (MEF) is a unique phenomenon of surface plasmons, where light interacts with the metallic nanostructures and produces electromagnetic fields to enhance the sensitivity of fluorescence-based detection. In particular, this enhancement in sensing capacity is of importance to many research areas, including medical diagnostics, forensic science, and biotechnology. The article covers the basic mechanism of MEF and recent developments in plasmonic nanostructures fabrication for efficient fluorescence signal enhancement that are critically reviewed. The implications of current fluorescence-based technologies for biosensors are summarized, which are in practice to detect different analytes relevant to food control, medical diagnostics, and forensic science. Furthermore, characteristics of existing fabrication methods have been compared on the basis of their resolution, design flexibility, and throughput. The future projections emphasize exploring the potential of non-conventional materials and hybrid fabrication techniques to further enhance the sensitivity of MEF-based biosensors.

Photopolarimetrical properties of coronavirus model particles: Spike proteins number influence

Coronavirus virions have spherical shape surrounded by spike proteins. The coronavirus spike proteins are very effective molecular mechanisms, which provide the coronavirus entrance to the host cell. The number of these spikes is different; it dramatically depends on external conditions and determines the degree of danger of the virus. A larger number of spike proteins makes the virus infectivity stronger. This paper describes a mathematical model of the shape of coronavirus virions. Based on this model, the characteristics of light scattered by the coronavirus virions were calculated. It was found two main features of coronavirus model particles in the spectral region near 200 nm: a minimum of intensity and a sharp leap of the linear polarization degree. The effect of the spike protein number on the intensity and polarization properties of the scattered light was studied. It was determined that when the number of spike proteins decreases, both the intensity minimum and the position of the linear polarization leap shift to shorter wavelengths. This allows us to better evaluate the shape of the coronavirus virion, and, therefore, the infectious danger of the virus. It was shown that the shorter the wavelength of scattered light, the more reliably one can distinguish viruses from non-viruses. The developed model and the light scattering simulations based on it can be applied not only to coronaviruses, but also to other objects of a similar structure, for example, pollen.

Bioinspired Brochosomes as Broadband and Omnidirectional Surface-Enhanced Raman Scattering Substrates

Surface-enhanced Raman scattering (SERS) substrates capable of working under laser excitation in a broad wavelength range are highly desirable in diverse application fields. Here, we demonstrate that the bioinspired Ag brochosomes, hollow microscale particles with submicroscale pits, have broadband and omnidirectional SERS performance. The SERS performance of the Ag brochosomes under near-infrared laser excitation makes them promising for applications in biosensing fields, such as the sensitive detection of Staphylococcus aureus bacteria and bovine hemoglobin protein. Additionally, the SERS intensity was insensitive to the incident angle of the laser beam, resulting from the spherical structure of the Ag brochosomes. The omnidirectional SERS performance makes the Ag brochosomes have application potential for in-the-field analysis using a hand-held Raman spectrometer for which it is difficult to accurately control the laser beam normal to the SERS substrates. Overall, the broadband and omnidirectional brochosome SERS substrates will find applications in diverse fields, particularly in biomedicine and in-the-field analysis.