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One of the biggest challenges in relation to the modernistic vision of smart city technology is to provide confident autonomous energy, notably in terms of power storage. If you want to change an existing lifestyle, you cannot ignore the basic concepts collected from basic physics. The subject of Metamaterials stands for an important research area that can be explored and used to come up with unparalleled ideas about the properties and functions that are completely absent from natural materials. In contrast to other bold technologies, combining a simple layered surface with appropriate material selection makes it possible to pattern and manufacture new types of solar cells that work in a wide frequency range. In this article, we propose a simple method to boost the coupling interaction between metallic gold nanowires with multiple MoS2 layers. The innovation of this work is that the thickness layer changes have great stability in the influence of the absorption performance and electric field distribution in the visible light and near-infrared spectra. Therefore, this new design can be seen as very important in many fields from sensing to solar cell applications. [ABSTRACT FROM AUTHOR]

In the realm of immune response, pro‐inflammatory cytokines play a crucial role in regulating various physiological functions. Accurate measurement of these low‐molecular‐weight proteins is essential for understanding immune function, predicting diseases, and monitoring treatment effects. Optical aptasensors with advanced nanostructures, which utilize aptamers as bio‐probes, have emerged as a promising technology for cytokine detection, offering advantages over traditional antibody‐based nanobiosensors. Aptamers, single‐stranded nucleic acids with high specificity and affinity, enable cost‐effective mass production and consistent quality. Optical biosensors incorporating aptamers exhibit stability, resistance to environmental factors, and prolonged functionality. This review explores the current methodologies and advancements in optical aptasensors for cytokine detection, highlighting their potential as robust tools in diagnostics and therapeutics. Specifically, the applications of surface plasmon resonance and fluorescence techniques in aptasensors are discussed, focusing on the innovative approaches used to enhance sensitivity and specificity in cytokine detection. Notable examples of aptasensor designs utilizing nanoparticles, Förster resonance energy transfer, and amplification strategies are presented. These designs demonstrate high affinity, specificity, and improved sensitivity in detecting pro‐inflammatory cytokines such as interferon gamma. Overall, optical aptasensors show great promise in advancing the understanding of cytokine‐related disorders and enabling effective interventions. [ABSTRACT FROM AUTHOR]

Highlights: A zero-reflection-induced phase singularity is achieved through precisely controlling the resonance characteristics using two-dimensional nanomaterials. An atomically thin nano-layer having a high absorption coefficient is exploited to enhance the zero-reflection dip, which has led to the subsequent phase singularity and thus a giant lateral position shift. We have improved the detection limit of low molecular weight molecules by more than three orders of magnitude compared to current state-of-art nanomaterial-enhanced plasmonic sensors. Detection of small cancer biomarkers with low molecular weight and a low concentration range has always been challenging yet urgent in many clinical applications such as diagnosing early-stage cancer, monitoring treatment and detecting relapse. Here, a highly enhanced plasmonic biosensor that can overcome this challenge is developed using atomically thin two-dimensional phase change nanomaterial. By precisely engineering the configuration with atomically thin materials, the phase singularity has been successfully achieved with a significantly enhanced lateral position shift effect. Based on our knowledge, it is the first experimental demonstration of a lateral position signal change > 340 μm at a sensing interface from all optical techniques. With this enhanced plasmonic effect, the detection limit has been experimentally demonstrated to be 10–15 mol L−1 for TNF-α cancer marker, which has been found in various human diseases including inflammatory diseases and different kinds of cancer. The as-reported novel integration of atomically thin Ge2Sb2Te5 with plasmonic substrate, which results in a phase singularity and thus a giant lateral position shift, enables the detection of cancer markers with low molecular weight at femtomolar level. These results will definitely hold promising potential in biomedical application and clinical diagnostics. [ABSTRACT FROM AUTHOR]

Whispering gallery mode (WGM) resonators have been exploited as a highly sensitive and efficient sensing technique in the past few years. They offer the advantages of ultrahigh sensitivity, compact size, and label‐free sensing capability. More recently, with the rapid development of microfluidic technologies, many integrated WGM sensors, by combining the portability of lab‐on‐chip devices and the high sensitivity of WGM resonators, have emerged. The capabilities of efficient sample handling and multiplexed analyte detection offered by these systems have led to many biological and chemical sensing applications, especially for the detection of single particle or biomolecule. In this review, different sensing mechanisms based on integrated whispering gallery mode resonators are introduced. Various geometries of WGM cavities including solid, liquid, and hollow resonators and a detailed discussion on their integration with microfluidic devices are also covered. Different types of packaging schemes and integration methods are compared in terms of ease of fabrication and device performance. Finally, recent applications of microfluidic‐based WGM sensors for detecting biological and chemical target molecules are discussed, with a prospect on future challenges and trends of development in microfluidics for multiplexed detection. [ABSTRACT FROM AUTHOR]

In this work, a plasmonic metasurface for ultra-sensitive biosensing based on graphene-transition metal dichalcogenide (TMDC)-graphene hybrid nanostructures are designed. The coating of the two-dimensional nanosheets plays an important role for the sensitivity enhancement of the biosensors at the atomic scale. To achieve the maximum plasmon resonance energy transfer, different parameters of the hybrid nanostructures are systematically investigated including the material types and the number of TMDC layers. The important characteristics of plasmonic biosensors such as dark minimum reflectivity, sharp differential phase change, high sensitivity and narrow full width at half maximum (FWHM) are carefully studied in this work to demonstrate the improved surface plasmon resonance sensing performances of the TMDC-based metasurfaces. The graphene-TMDC-graphene configurations with four different types of materials including MoS2/WS2/MoSe2/WSe2 are optimized respectively for potential sensing applications. Based on our theoretical analysis, the enhanced maximum sensitivity of graphene-TMDC-graphene hybrid nanostructure is three orders of magnitude higher than that of the conventional bare metallic substrate. [ABSTRACT FROM AUTHOR]

Biofunctionalized quantum dots (QDs), especially protein-coated QDs, are known to be useful targeted fluorescent labels for cellular and deep-tissue imaging. These nanoparticles can also serve as efficient energy donors in fluorescence resonance energy transfer (FRET) binding assays for the multiplexed sensing of tumor markers. However, current preparation processes for protein-functionalized QDs are laborious and require multiple synthesis steps (e.g. preparing them in high temperature, making them dispersible in water, and functionalizing them with surface ligands) to obtain a high quality and quantity of QD formulations, significantly impeding the progress of employing QDs for clinical diagnostics use such as a QD-based immunohistofluorescence assay. Herein, we demonstrate a one-step synthesis approach for preparing protein-functionalized QDs using a microfluidic (MF) chip setup. Using bovine serum albumin (BSA) molecules as the surface ligand model, we first studied and optimized the MF reaction synthesis parameters (e.g. reaction temperature, and channel width and length) for making protein-functionalized QDs using COMSOL simulation modeling, followed by experimental verification. Moreover, in comparison with the BSA-functionalized QDs synthesized using the conventional bench-top method, BSA–QDs prepared using the MF approach exhibit a significantly higher protein-functionalization efficiency, photostability and colloidal stability. The proposed one-step MF synthesis approach provides a rapid, cost effective, and a small-scale production of nanocrystals platform for developing new QD formulations in applications ranging from cell labeling to biomolecular sensing. Most importantly, this approach will considerably reduce the amount of chemical waste generated during the trial-and-error stage of developing and perfecting the desired physical and optical properties of new QD materials. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we propose and analytically demonstrate a biosensor configuration based on the excitation of surface electromagnetic waves in a graphene-based one-dimensional photonic crystal (1D PC). The proposed graphene-based 1D photonic crystal consists of alternating layers of high (graphene) and low (PMMA) refractive index materials, which gives a narrow angular reflectivity resonance and high surface fields due to low loss in PC. A differential phase-sensitive method has been used to calculate the sensitivity of the configuration. Our results show that the sensitivity of the proposed configuration is 14.8 times higher compared to those of conventional surface plasmon resonance (SPR) biosensors using gold thin films. This novel and effective graphene-based 1D PC will serve as a promising replacement of metallic thin film as a sensor head for future biosensing applications. [Copyright &y& Elsevier]

Abstract: The impact of spherical gold nanoparticles (Au NPs) with diameters of 40–80nm for the enhancement of surface plasmon resonance (SPR) sensing signals is presented. Numerical analysis is given to simulate the perturbation of evanescent field in the presence of Au NPs. The results indicate that Au NPs with 40nm possess the highest coupling effect when the separation of Au NP and SPR sensing film is fixed at 5nm. For experimental demonstrations, colloidal Au NPs with different sizes but unified extinction coefficient (optical density) are immobilized onto SPR sensing films respectively through a spacer, dithiothreitol (DTT). Phase changes of the reflected SPR signals, which are associated with the plasmonic coupling between the NPs and sensing film, are monitored using a differential phase SPR sensor. Results obtained from the experiments show good agreement with the theoretical studies. This work can considerably serve as a solid guidance for future development of Au NPs-enhanced SPR sensors. [Copyright &y& Elsevier]

This study provided a theoretical insight for designing novel plasmonic biosensors using bismuth selenide (Bi2Se3)-Graphene heterostructures. It was a van der Waals (vdWs) stacked configuration composed of gold (Au) film, few quintuple layer (QL) Bi2Se3 and few-layered graphene. In particular, the proposed biosensor was created by Goos-Hänchen (GH) shift rather than phase, resulting in a more sensitive biosensing response. Under the excitation of 632.8 nm, significant sensitivity enhancement performance was obtained via varying the thickness of Bi2Se3-Graphene heterostructures. The best configuration was 32 nm Au film−2-QL Bi2Se3-3-layer graphene, generating the largest GH shift, as high as −1.0202 × 104 µm. Moreover, the highest detection sensitivity was determined to be 8.5017 × 106 µm/RIU, responding to a tiny refractive index (RI) change of 0.0012 RIU (RIU, refractive index unit). More importantly, our proposed biosensor has shown a theoretical feasibility of monitoring virus samples. For example, there was an efficient linear detection range for severe acute respiratory syndrome coronavirus 2 (SARS-CoV−2, 0~13.44 nanomole (nM)) and its Spike (S) glycoprotein (0~59.74 nM), respectively. It is expected that our proposed plasmonic biosensor has a potential application in performing sensitive detection of SARS-CoV−2. [ABSTRACT FROM AUTHOR]

Abstract: Anisotropic growth of PbO with symmetrical hexagonal-shape nanosheet morphology was demonstrated for the first time via solution phase synthesis in the presence of Au nanoparticles at room temperature. Au NPs play a critical role in the formation of PbO nanosheets. No nanosheets were formed in absence of Au NPs. The effect of Au NPs appears to result from their ability to provide nucleation sites to seed anisotropic growth of the PbO nanocrystals and later the nanocrystals aggregated to form nanosheet structure. The method demonstrated here provides a facile room temperature colloidal method of producing high-quality and yield of high-symmetrical hexagonal-shape PbO nanosheets with controlled edge length. [Copyright &y& Elsevier]

The recent outbreak of coronavirus disease 2019 (COVID‐19) highlights the critical need for rapid, sensitive, and accurate virus detection methods to prevent and manage pandemics. Among the available sensing methods, photonic biosensors have emerged as a forefront technology, characterized by their high sensitivity, minimal analyte requirements, and suitability for miniaturization, making them ideal for point‐of‐care applications in virus detection. This review comprehensively summarizes the recent progress of photonic biosensor technologies, focusing on wavelength shift and luminescence‐based mechanisms. Their operational principles, general configurations, and the challenges associated with these technologies are looked into. An overview of the material developments used in photonic biosensors, encompassing organic, inorganic, and hybrid composite‐based materials is further presented. The discussion extends to surface functionalization using biorecognition elements, including DNA/RNA, aptamers, and antibodies, to craft the specificity of the photonic biosensors for viruses. Ultimately, the importance of a multidisciplinary approach is emphasized in developing new materials architecture, biological receptors, and modifications to photonic methods, aiming to realize better biosensors for virus detection with ultra‐high sensitivity, rapid response, and excellent selectivity. [ABSTRACT FROM AUTHOR]

Tumor necrosis factor-alpha (TNF-α) serves as a crucial biomarker in various diseases, necessitating sensitive detection methodologies. This study introduces an innovative approach utilizing an aptamer-functionalized surface plasmon resonance (SPR) substrate together with an ultrasensitive measure, the Goos–Hänchen (GH) shift, to achieve sensitive detection of TNF-α. The developed GH-aptasensing platform has shown a commendable figure-of-merit of 1.5 × 104 μm per RIU, showcasing a maximum detectable lateral position shift of 184.7 ± 1.2 μm, as characterized by the glycerol measurement. Employing aptamers as the recognition unit, the system exhibits remarkable biomolecule detection capabilities, including the experimentally obtained detection limit of 1 aM for the model protein bovine serum albumin (BSA), spanning wide dynamic ranges. Furthermore, the system successfully detects TNF-α, a small cytokine, with an experimental detection limit of 1 fM, comparable to conventional SPR immunoassays. This achievement represents one of the lowest experimentally derived detection limits for cytokines in aptamer-based SPR sensing. Additionally, the application of the GH shift marks a ground breaking advancement in aptamer-based biosensing, holding significant promise for pushing detection limits further, especially for small cytokine targets. [ABSTRACT FROM AUTHOR]

Tumor necrosis factor-alpha (TNF-α) serves as a crucial biomarker in various diseases, necessitating sensitive detection methodologies. This study introduces an innovative approach utilizing an aptamer-functionalized surface plasmon resonance (SPR) substrate together with an ultrasensitive measure, the Goos–Hänchen (GH) shift, to achieve sensitive detection of TNF-α. The developed GH-aptasensing platform has shown a commendable figure-of-merit of 1.5 × 104 μm per RIU, showcasing a maximum detectable lateral position shift of 184.7 ± 1.2 μm, as characterized by the glycerol measurement. Employing aptamers as the recognition unit, the system exhibits remarkable biomolecule detection capabilities, including the experimentally obtained detection limit of 1 aM for the model protein bovine serum albumin (BSA), spanning wide dynamic ranges. Furthermore, the system successfully detects TNF-α, a small cytokine, with an experimental detection limit of 1 fM, comparable to conventional SPR immunoassays. This achievement represents one of the lowest experimentally derived detection limits for cytokines in aptamer-based SPR sensing. Additionally, the application of the GH shift marks a ground breaking advancement in aptamer-based biosensing, holding significant promise for pushing detection limits further, especially for small cytokine targets. [ABSTRACT FROM AUTHOR]

In this work, we have designed highly sensitive plasmonic metasensors based on atomically thin perovskite nanomaterials with a detection limit up to 10−10 refractive index units (RIU) for the target sample solutions. More importantly, we have improved phase singularity detection with the Goos–Hänchen (GH) effect. The GH shift is known to be closely related to optical phase signal changes; it is much more sensitive and sharp than the phase signal in the plasmonic condition, while the experimental measurement setup is much more compact than that of the commonly used interferometer scheme to exact the phase signals. Here, we have demonstrated that plasmonic sensitivity can reach a record-high value of 1.2862 × 109 µm/RIU with the optimum configurations for the plasmonic metasensors. The phase singularity-induced GH shift is more than three orders of magnitude larger than those achievable in other metamaterial schemes, including Ag/TiO2 hyperbolic multilayer metamaterials (HMMs), metal–insulator–metal (MIM) multilayer waveguides with plasmon-induced transparency (PIT), and metasurface devices with a large phase gradient. GH sensitivity has been improved by more than 106 times with the atomically thin perovskite metasurfaces (1.2862 × 109 µm/RIU) than those without (918.9167 µm/RIU). The atomically thin perovskite nanomaterials with high absorption rates enable precise tuning of the depth of the plasmonic resonance dip. As such, one can optimize the structure to reach near zero-reflection at the resonance angle and the associated sharp phase singularity, which leads to a strongly enhanced GH lateral shift at the sensor interface. By integrating the 2D perovskite nanolayer into a metasurface structure, a strong localized electric field enhancement can be realized and GH sensitivity was further improved to 1.5458 × 109 µm/RIU. We believe that this enhanced electric field together with the significantly improved GH shift would enable single molecular or even submolecular detection for hard-to-identify chemical and biological markers, including single nucleotide mismatch in the DNA sequence, toxic heavy metal ions, and tumor necrosis factor-α (TNFα). [ABSTRACT FROM AUTHOR]

This paper introduces a highly sensitive biosensor based on a plasmonic nanostructure-enhanced resonance effect. The sensor exploits a hexagonal photonic crystal composed of plasmonic nano-cylinders, including a graphene nano-cylinder as a defect, which can considerably increase the concentration of electric fields. This amplification enables the detection of tiny variations in refractive indices linked to a laser source for plasmonic excitation. Each defect consists of a hollow metallic cylinder surrounded by graphene, all within a metallic matrix. During the sensing process, surface plasmon polaritons interact with the core-guided modes of the patterns, which are subsequently filled with the analytes to be measured. The nano-cylinders’ width is optimized to take advantage of their unique optical properties in nanoscale confinement, resulting in high sensitivity. The sensor achieves an impressive sensitivity of 17,750 nm/RIU (refractive index unit) and a FoM of 2218 (RIU−1) for n = 1.456 at the optimum value of ΔR = (Rout − Rin) = 200 nm. These metallic cylindrical channels exhibit distinct responses to different analytes across a wide range of ΔR, enabling simultaneous detection of various types of biomolecules. These exceptional properties make the sensor suitable for a broad range of applications, including real-time chemical and biological sensing. Furthermore, it offers the potential to create compact devices for measuring different refractive indices. [ABSTRACT FROM AUTHOR]

Metasurfaces are artificial two-dimensional (2D) planar surfaces that consist of subwavelength 'meta-atoms' (i.e. metallic or dielectric nanostructures). They are known for their capability to achieve better and more efficient light control in comparison to their traditional optical counterparts. Abrupt and sharp changes in the electromagnetic properties can be induced by the metasurfaces rather than the conventional gradual accumulation that requires greater propagation distances. Based on this feature, planar optical components like mirrors, lenses, waveplates, isolators and even holograms with ultrasmall thicknesses have been developed. Most of the current metasurface studies have focused on tailoring the linear optical effects for applications such as cloaking, lens imaging and 3D holography. Recently, the use of metasurfaces to enhance nonlinear optical effects has attracted significant attention from the research community. Benefiting from the resulting efficient nonlinear optical processes, the fabrication of integrated all-optical nano-devices with peculiar functionalities including broadband frequency conversions and ultrafast optical switching will become achievable. Plasmonic excitation is one of the most effective approaches to increase nonlinear optical responses due to its induced strong local electromagnetic field enhancement. For instance, continuous phase control on the effective nonlinear polarizability of plasmonic metasurfaces has been demonstrated through spin-rotation light coupling. The phase of the nonlinear polarization can be continuously tuned by spatially changing the meta-atoms' orientations during second and third harmonic generation processes, while the nonlinear metasurfaces also exhibit homogeneous linear properties. In addition, an ultrahigh second-order nonlinear susceptibility of up to 104 pm V−1 has recently been reported by coupling the plasmonic modes of patterned metallic arrays with intersubband transition of multi-quantum-well layered substrate. In order to develop ultra-planar nonlinear plasmonic metasurfaces, 2D materials such as graphene and transition metal dichalcogenides (TMDCs) have been extensively studied based on their unique nonlinear optical properties. The third-order nonlinear coefficient of graphene is five times that of gold substrate, while TMDC materials also exhibit a strong second-order magnetic susceptibility. In this review, we first focus on the main principles of planar nonlinear plasmonics based on metasurfaces and 2D nonlinear materials. The advantages and challenges of incorporating 2D nonlinear materials into metasurfaces are discussed, followed by their potential applications including orbital angular momentum manipulating and quantum optics. [ABSTRACT FROM AUTHOR]

Biofunctionalized quantum dots (QDs) are effective target fluorescent labels for bioimaging. However, conventional synthesis of biofunctionalized I–III–VI core–shell CuInS2/ZnS QDs requires complex bench-top operations, resulting in limited product performance and variety, and is not amenable to a 'one-step' approach. In this work, we have successfully demonstrated a fully automated method for preparing denatured bovine serum albumin (dBSA)-CuInS2/ZnS QDs by introducing microfluidic (MF) chips to synthesize biofunctionalized QDs, hence establishing a 'one-step' procedure. We have also studied and optimized the reaction synthesis parameters. The emission wavelength of the dBSA-CuInS2/ZnS QDs is located in the near-infrared range and can be tuned from 650 to 750 nm by simply varying the reaction parameters. In addition, the 'one-step'-synthesized dBSA-CuInS2/ZnS QDs have a long average fluorescence lifetime of 153.76 ns and a small particle size of 5 ± 2 nm. To demonstrate the applicability of the 'one-step'-synthesized dBSA-CuInS2/ZnS QDs in bioimaging studies, we modified the QDs with folic acid and hyaluronic acid, and then performed target bioimaging and cytotoxicity tests on macrophages, liver cancer cells and pancreatic cancer cells. The cell images show that the red emission signals originate from the QDs, which indicates that the dBSA-CuInS2/ZnS QDs prepared by the MF approach are suitable optical contrast agents for target bioimaging. This 'one-step' MF-based QD synthesis approach could serve as a rapid, cost-effective, and small-scale nanocrystal production platform for complex QD formulations for a wide range of bioapplications. [ABSTRACT FROM AUTHOR]

Surface plasmon resonance (SPR) sensor based on reflectivity measurement has been widely studied for its convenient detection, high sensitivity, and real-time functions. However, the resonance curves of SPR reflectivity spectrum are broad that lead to a low detection limit (DL) and low detection resolution. In this work, Fano resonance (FR), which has an asymmetrical sharp and narrow resonance peak, is demonstrated here to improve the DL and resolution of the plasmonic sensor. More importantly, a three-point method is employed here to analyzed and extract the polarization information of the reflected light by replacing the conventional intensity interrogation method. The sharp signal change of the Fano resonance realized by the designed configuration together with the three-point method led to a significantly enhancement on the DL and the resolution of the FR-based sensor up to one order of magnitude comparing to conventional scheme commonly used with the commercial products. Thus, the proposed sensor is of great potential for biochemical sensing such as DNA detection in terms of measuring the refractive index change at the sensing interface. [ABSTRACT FROM AUTHOR]

Hydrogen evolution from biomass via photocatalytic processes is possible but still challenging in the chemical industry. Herein, we report an enhanced photoreforming of biomass achieved by loading a graphitic carbon layer on TiO2/NiOx nanoparticles. Glucose and polyethylene glycol were used as renewable precursors to prepare a graphitic carbon layer on the NiOx nanoparticles. Enhanced hydrogen production yields of ∼270 μmol h−1 g−1 and ∼4000 μmol h−1 g−1 were obtained at room temperature and 80 °C, respectively, for photoreforming of a cellulose aqueous solution (∼2 wt%) over TiO2/NiOx@Cg. An interface between NiOx and the graphitic overlayer plays a key role in enhancing biomass photoreforming due to carbon modification for the nickel catalyst. This work demonstrates the feasibility of producing hydrogen directly from biomass by a single photocatalytic process, even over a non-precious metal co-catalyst with a fine-tuned structure of the carbon layer. [ABSTRACT FROM AUTHOR]

The exploration of the propensity of engineered materials to bring forward innovations predicated on their periodic nanostructured tailoring rather than the features of their individual compounds is a continuous pursuit that has propelled optical sensors to the forefront of ultra-sensitive bio-identification. Herein, a numerical analysis based on the Finite Element Method (FEM) was used to investigate and optimize the optical properties of a unidirectional asymmetric dimer photonic crystal (PhC). The proposed device has many advantages from a nanofabrication standpoint compared to conventional PhCs sensors, where integrating defects within the periodic array is imperative. The eigenvalue and transmission analysis performed indicate the presence of a protected, confined mode within the structure, resulting in a Fano-like response in the prohibited states. The optical sensor demonstrated a promising prospect for monitoring the DNA hybridization process, with a quality factor (QF) of roughly 1.53 × 10 5 and a detection limit (DL) of 4.4 × 10 − 5 RIU. Moreover, this approach is easily scalable in size while keeping the same attributes, which may potentially enable gaze monitoring. [ABSTRACT FROM AUTHOR]

To achieve a wide range and high accuracy detection of the vacuum level, for example, in an encapsulated vacuum microcavity, a composite-type MEMS Pirani gauge has been designed and fabricated. The Pirani gauge consists of two gauges of different sizes connected in series, with one gauge having a larger heat-sensitive area and a larger air gap for extending the lower measurable limit of pressure (i.e., the high vacuum end) and the other gauge having a smaller heat-sensitive area and a smaller air gap for extending the upper measurable limit. The high-resistivity titanium metal was chosen as the thermistor; SiNx was chosen as the dielectric layer, considering the factors relevant to simulation and manufacturing. By simulation using COMSOL Multiphysics and NI Multisim, a range of measurement of 2 × 10−2 to 2 × 105 Pa and a sensitivity of 52.4 mV/lgPa were obtained in an N2 environment. The performance of the fabricated Pirani gauge was evaluated by using an in-house made vacuum test system. In the test, the actual points of measurement range from 6.6 × 10−2 to 1.12 × 105 Pa, and the highest sensitivity is up to 457.6 mV/lgPa. The experimental results are better in the range of measurement, sensitivity, and accuracy than the simulation results. The Pirani gauge proposed in this study is simple in structure, easy to manufacture, and suitable for integration with other MEMS devices in a microcavity to monitor the vacuum level therein. [ABSTRACT FROM AUTHOR]

[Display omitted] • A non-noble-metal based novel SERS substrate-porous carbon film/WO 3-x nanosheets was developed; • Detection limit of 10-7 M with the Raman enhancement factor of 106 was achieved on the optical substrate. • A deep leaning method was used to accurately analyze the Raman spectra of flavonoids of quercetin, 3-hydroxyflavone and flavone. • Quercetin can be accurately detected by the fully convolutional network, and lowest detectable concentration of 10-5 M was achieved. The Surface-enhanced Raman scattering (SERS) is an attractive optical detecting method with high sensitivity and detectivity, however challenges on large-area signal uniformity and complex spectra analysis methods always retards its wide application. Herein, a highly sensitive and uniform SERS detection strategy supported by porous carbon film/WO 3-x nanosheets (PorC/WO 3-x) based noble-metal-free SERS substrate and deep learning algorithm are reported. Experimentally, the PorC/WO 3-x substrate was prepared by high-temperature annealing the PorC/WO 3 films under the argon atmosphere. The defect density of the WO 3 was controlled by tuning the reducing reaction time during the annealing process. The SERS performance was evaluated by using R6G as the Raman reporter, it showed that the SERS intensity obtained on the substrate with the optimal annealing time of 3 h was about 8 times as high as that obtained on the PorC/WO 3 substrate without annealing treatment. And detection limit of 10-7 M and Raman enhancement factor of 106 could be achieved. Moreover, the above optimal SERS substrate was utilized to detect flavonoids of quercetin, 3-hydroxyflavone and flavone, and a deep learning algorithms was incorporated to identify the quercetin. It revealed that quercetin can be accurately detected within the above flavonoids, and lowest detectable concentration of 10-5 M can be achieved. [ABSTRACT FROM AUTHOR]

Surface Plasmon Resonance (SPR) sensors are a useful tool for biomolecule detection, offering label-free and real-time monitoring characteristics. However, traditional SPR sensors still face the challenges of limited detection sensitivity, especially for sensing small molecules with a low concentration level (less than 1 pM (10−12 mol/L)). To overcome this challenge, in this paper, we designed a Kretschmann configuration which uses a plasmonic waveguide to generate a powerful Fano resonance through the coupling of the surface plasmon polariton (SPP) mode and photonic waveguide (PWG) mode at the sensing interface. By optimizing the thickness of the layers of the metamaterial structure, it is also possible to adjust the resonance angle, the reflectivity, the quality factor (Q factor), the intensity sensitivity, the angular sensitivity and the detection range. In our designed subwavelength grating waveguides (SWG) structure sensor, the intensity sensitivity reached 1.808 × 104 RIU−1, which surpassed the intensity sensitivity of uniform Si layers by 5.14 times. This approach provides a framework for physicists and biologists to develop the future generation of medical diagnostic devices. [ABSTRACT FROM AUTHOR]

By introducing the sub-wavelength grating (SWG) waveguide in the long-range surface phonon resonance (LRSPhR) device, a mid-infrared Fano resonance is formed due to the coupling between surface phonon polariton and Bloch mode. By taking advantage of strong light-matter interaction in the SWG, such Fano resonance is expected to offer improved sensing performance. Based on the rigorous coupled-wave analysis (RCWA) method, the index sensitivity and figure of merit of such a sensor reach 7496 RIU−1 and 46,432, respectively, which is 6 times compared with the conventional waveguide-coupled LRSPhR. The proposed SWG-coupled Fano resonance can be a promising platform for mid-infrared biochemical sensing. [ABSTRACT FROM AUTHOR]

Surface‐enhanced Raman scattering (SERS) technology is a cutting‐edge analytical tool for molecule detection. Attractive SERS performance has been achieved on noble metal nanostructures; however these substrates usually suffer from difficulties of direct adjusting of the physical structures to achieve tunable SERS performance. Studies on semiconductor oxides have revealed that attractive SERS performance can be obtained on them, but strategies of engineering material properties for SERS performance improvement still pose a challenge. Here, an electrically programmable SERS substrate is prepared by depositing hydrothermally synthesized MoOx/Ag hybrids within electrodes as the SERS active region. In the experiment, an electrical field is applied on the electrodes to regulate Ag+ ion migration and redeposition in the MoOx solid electrolyte. Through adjusting the leakage current level, the size of the Ag nanoparticles in the MoOx/Ag hybrids is electrically controlled. The SERS performance of the substrate is evaluated using rhodamine 6G as the Raman reporter. The results evidence that Raman enhancement factors of 1.13 × 105, 4.75 × 105, and 1.04 × 106 can be obtained by programming the leakage current level to 10−7, 10−5, and 10−3 A, respectively. A maximum detection limit of 10−8 m is achieved on the 10−3 A substrate. [ABSTRACT FROM AUTHOR]

[Display omitted] • Immunoassay kit was constructed by MXene, gold nanowire forests, and PMMA for implementing straightforward virus detection. • The unreliable fluctuation of the enhanced signal was eliminated by using the intrinsic Raman signal of the flexible PMMA platform. • Highly sensitive and remedially quantifiable detection of SARS-CoV-2 with LOD of 9.52 × 10−9 mg/mL was achieved by immunoassay kit. Surface-enhanced Raman scattering (SERS) technique with high sensitivity, reliable specificity, and rapid recognition ability exhibits attractive promise for the effective fast-monitoring of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Herein, a novel SERS-active immunoassay kit for SARS-CoV-2 nucleocapsid (N) protein was prepared by in-situ growing gold (Au) nanowire forests (NFs) onto Ti 3 C 2 T x , which was then modified onto polymethyl methacrylate (PMMA) matrix and encapsulated into kit. It was noted that the Au nanowires with fibrous structures which vertically anchored on Ti 3 C 2 T x served as perfect channels to promote photo-induced charge transfer. The synergistic action of electromagnetic and chemical effects resulted in an enhancement factor (EF) of 1.27 × 107. Furthermore, the unreliable fluctuation of the enhanced signal was eliminated by using the intrinsic Raman signal of the flexible PMMA platform, achieving an improved correlation coefficient (R2) value from 0.950 to 0.990. Moreover, the as-designed immunoassay kit with both high sensitivity and remedied quantitative ability rendered by the Ti 3 C 2 T x @Au NFs-PMMA composite exhibited a powerful performance in the practical detection of N-protein with concentration low to 5.0 × 10−8 mg/mL. [ABSTRACT FROM AUTHOR]

Exosome is a recently emerging cancer-associated biomarker for early diagnostic and prognostic owing to their noninvasive, intrinsic stability, and representativeness of primitive cell state. However, the development of convenient and quantitative methods for exosome analysis remains technically challenging. Here, we proposed a cost-effective assay for the direct capture and rapid monitoring of exosomes utilizing the multifunctional surface enhanced Raman scattering (SERS) substrate, which consisted of Cu 2 O–CuO nanowires prepared by a simple thermo-oxidative growth method and subsequently sputtered with Ag NPs. This reticulate substrate made up of interlaced one-dimensional nanowires that highly favored for exosome recognition and collection. Particularly, the electromagnetic hotspots with high density were uniformly distributed on the nanowires due to uniform physical deposition, facilitating robust SERS property with an enhancement factor (EF) of 3.3 × 108 and signal reproducibility with a relative standard deviation (RSD) of 13%. In addition, the presence of Cu 2 O–CuO heterojunction enabled further elevation of the SERS performance attributed to the effective charge transfer, triggering a significant chemical enhancement effect. Finally, clinical validation with the serum specimens of prostate cancer patients indicated that the proposed immunosensor possessed great potential for application in rapid cancer screening and diagnosis. [ABSTRACT FROM AUTHOR]

Both increasing demand for ultrasensitive detection in the scientific community and significant new breakthroughs in materials science field have inspired and promoted the development of new-generation multifunctional plasmonic sensing platforms by adopting promising plasmonic nanomaterials. Recently, high-quality surface plasmon resonance (SPR) sensors, assisted by two dimensional (2D) nanomaterials including 2D van der Waals (vdWs) materials (such as graphene/graphene oxide, transition metal dichalcogenides (TMDs), phosphorene, antimonene, tellurene, MXenes, and metal oxides), 2D metal−organic frameworks (MOFs), 2D hyperbolic metamaterials (HMMs), and 2D optical metasurfaces, have emerged as a class of novel plasmonic sensing platforms that show unprecedented detection sensitivity and impressive performance. This review of recent progress in 2D nanomaterials-enhanced SPR platforms will highlight their compelling plasmonic enhancement features, working mechanisms, and design methodologies, as well as discuss illustrative practical applications. Hence, it is of great importance to describe the latest research progress in 2D nanomaterials-enhanced SPR sensing cases. In this review, we present some concepts of SPR enhanced by 2D nanomaterials, including the basic principles of SPR, signal modulation approaches, and working enhancement mechanisms for various 2D materials-enhanced SPR systems. In addition, we also demonstrate a detailed categorization of 2D nanomaterials-enhanced SPR sensing platforms and comment on their ability to realize ultrasensitive SPR detection. Finally, we conclude with future perspectives for exploring a new generation of 2D nanomaterials-based sensors. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman scattering (SERS) technique is a powerful spectrum analysis technique for the ultra-low molecular trace detection. Conventionally, noble metals like silver (Ag) and gold (Au) are used to prepare the SERS substrates; however, limitations of complicated experimental designs and sophisticated process steps impede their wide applications in practice. Recently, metal oxides arise as a promising material for SERS application, but relatively weak Raman signal enhancement and poor material stability still pose as a challenge. Here, a UV-light-assisted fabrication of MoO3−x/silver nanoparticles (MoO3−x/Ag NPs) film is proposed. In the experiment, the sub-transition-metal-oxide of MoO3−x was used as the Raman chemical enhancement substrate as well as the reducing agent. Through the spin-coating of MoO3−x layer on the silicon substrate and UV-light-assisted reduction of silver nitride (AgNO3) on the MoO3−x layer, a novel MoO3−x/Ag NPs one-layer film was fabricated. Using the Rhodamine B (RhB) as the Raman reporter, SERS measurement shows that enhancement factor (EF) of 1.195 × 106 could be achieved. Moreover, a Raman signal amplifying strategy is further demonstrated by constructing MoO3−x/Ag NPs multi-layer films. And result evidences that maximum gain of 2.07 for the RhB Raman peak at 1280 cm−1 can be obtained on the MoO3−x/Ag NPs three-layer film when referred to that on the MoO3−x/Ag NPs one-layer film. Meanwhile, the EF of the MoO3−x/Ag NPs three-layer film is also improved to 2.985 × 106, giving the minimum detectable concentration of 10−9 M. [ABSTRACT FROM AUTHOR]

Integration of functional nanomaterials with optical micro/nanofibers (OMNFs) can bring about novel optical properties and provide a versatile platform for various sensing applications. OMNFs as the key element, however, have seldom been investigated. Here, we focus on the optimization of fiber diameter by taking micro/nanofiber-based localized surface plasmon resonance sensors as a model. We systematically study the dependence of fiber diameter on the sensing performance of such sensors. Both theoretical and experimental results show that, by reducing fiber diameter, the refractive index sensitivity can be significantly increased. Then, we demonstrate the biosensing capability of the optimized sensor for streptavidin detection and achieve a detection limit of 1 pg/mL. Furthermore, the proposed theoretical model is applicable to other nanomaterials and OMNF-based sensing schemes for performance optimization. [ABSTRACT FROM AUTHOR]

Ultrasensitive detection of chemicals and biological analytes in trace or single molecular level is highly desirable in both scientific and technological fields, e.g. , analytical chemistry, life science, materials science, biomedical diagnostics, and forensic science, etc . With high sensitivity, high specificity, narrow line-widths, and multiplexed non-destructive testing capabilities, surface enhanced Raman scattering (SERS)-based sensing is the most promising approach to monitor targeted analytes in the vicinity of nanostructured surface. An insight into the recent advances of SERS-based ultrasensitive sensing platform can provide an effective reference guideline to develop an optimal detection approach for arising real-world applications. Many SERS-based review articles mainly focus on the fundamental theory of SERS, nanostructured plasmonic SERS sensors, and single molecule SERS detection. However, no comprehensive review article targeting SERS-based ultrasensitive detection strategies, their working mechanisms and illustrative practical applications has been reported yet. Hence, it is important to project the latest SERS-based ultrasensitive detection research in a review, which will present a reference guideline to develop an optimal detection approach for specific detection or monitoring of analytes in highly diluted solutions. We present a systematic classification and discussion on the recent multiple strategies to achieve ultra-high SERS detection sensitivity. We also outline a detailed analysis on the up-to-date applications in vitro and in vivo . Finally, we also discuss a new trend in SERS-based ultrasensitive sensing applications. [ABSTRACT FROM AUTHOR]

We report the synthesis of silver nanodecahedrons (NDs) for extending the localized surface plasmon resonance (LSPR) of silver nanostructures from blue to green-orange (~590 nm), which will enable much wider application opportunities using common laser light sources. In our photo-assisted method, we use a light-emitting-diode (LED) to control regrowth of silver ND from precursor seeds. Highly uniform silver NDs are synthesized when the LED emission peak coincides with the LSPR peak of the seeds. A two-step process involving precursor self-transformation into silver nanoprisms and nanoplates, and subsequent photo-activated regrowth of silver NDs has been proposed. Surface-enhanced Raman scattering of silver NDs in different sizes has been studied, and the average enhancement factor for each size is estimated to be in the order of ~10. [ABSTRACT FROM AUTHOR]

Hyperbolic metamaterials (HMMs) have emerged as a burgeoning field of research over the past few years as their dispersion can be easily engineered in different spectral regions using various material combinations. Even though HMMs have comparatively low optical loss due to a single resonance, the noble‐metal‐based HMMs are limited by their strong energy dissipation in metallic layers at visible frequencies. Here, the fabrication of noble‐metal‐free reconfigurable HMMs for visible photonic applications is experimentally demonstrated. The low‐loss and active HMMs are realized by combining titanium nitride (TiN) and stibnite (Sb2S3) as the phase change material. A reconfigurable plasmonic biosensor platform based on active Sb2S3–TiN HMMs is proposed, and it is shown that significant improvement in sensitivity is possible for small molecule detection at low concentrations. In addition, a plasmonic apta‐biosensor based on a hybrid platform of graphene and Sb2S3–TiN HMM is developed and the detection and real‐time binding of thrombin concentration as low as 1 × 10−15m are demonstrated. A biosensor operating in the visible range has several advantages including the availability of sources and detectors in this region, and ease of operation particularly for point‐of‐care applications. [ABSTRACT FROM AUTHOR]