In this paper, a comprehensive theoretical framework for understanding surface-enhanced Raman scattering (SERS) measurements in both solution and thin-film setups, focusing on electromagnetic ...enhancement principles, was presented. Two prevalent types of SERS substrates found in the literature were investigated: plasmonic colloidal particles, including spherical and spheroid nanoparticles, nanoparticle diameters, and thin-film-based SERS substrates, like ultra-thin substrates, bundled nanorods, plasmonic thin films, and porous thin films. The investigation explored the impact of analyte adsorption, orientation, and the polarization of the excitation laser on effective SERS enhancement factors. Notably, it considered the impact of analyte size on the SERS spectrum by examining scenarios where the analyte was significantly smaller or larger than the hot spot dimensions. The analysis also incorporated optical attenuations arising from the optical properties of the analyte and the SERS substrates. The findings provide possible explanations for many observations made in SERS measurements, such as variations in relative peak intensities during SERS assessments, reductions in SERS intensity at high analyte concentrations, and the occurrence of significant baseline fluctuations. This study offers valuable guidance for optimizing SERS substrate design, enhancing SERS measurements, and improving the quantification of SERS detection.
A rapid, portable, and cost-effective method to detect the infection of SARS-CoV-2 is fundamental toward mitigating the current COVID-19 pandemic. Herein, a human angiotensin-converting enzyme 2 ...protein (ACE2) functionalized silver nanotriangle (AgNT) array localized surface plasmon resonance (LSPR) sensor is developed for rapid coronavirus detection, which is validated by SARS-CoV-2 spike RBD protein and CoV NL63 virus with high sensitivity and specificity. A linear shift of the LSPR wavelength versus the logarithm of the concentration of the spike RBD protein and CoV NL63 is observed. The limits of detection for the spike RBD protein, CoV NL63 in buffer and untreated saliva are determined to be 0.83 pM, 391 PFU/mL, and 625 PFU/mL, respectively, while the detection time is found to be less than 20 min. Thus, the AgNT array optical sensor could serve as a potential rapid point-of-care COVID-19 diagnostic platform.
Localized surface plasmon resonance (LSPR) virus sensor was developed based on human angiotensin-converting enzyme 2 protein (ACE2) functionalized silver nanotriangle (AgNT) arrays. The sensor has high sensitivity and specificity to the receptor binding domain (RBD) of SARS-CoV-2 as well as human coronavirus NL63. Display omitted
•ACE2 functionalized LSPR virus sensor has high sensitivity and specificity.•The limit of detection for human coronavirus NL63 is 625 PFU/mL in untreated saliva.•The detection time for coronavirus is determined to be less than 20 min.•This simple LSPR sensor can be performed using a handheld UV-Vis spectrometer.•Coronavirus detection model of LSPR sensor has been established.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Tissue plasminogen activator (tPA) is the only FDA approved thrombolytic drug for acute ischemic stroke but concerns regarding its limitations remain. Here, we developed a new strategy by ...incorporating tPA into porous magnetic iron oxide (Fe3O4)-microrods (tPA-MRs) for targeted thrombolytic therapy in ischemic stroke induced by distal middle cerebral artery occlusion. We showed that intra-arterial injection of tPA-MRs could target the cerebral blood clot in vivo under the guidance of an external magnet, where tPA was subsequently released at the site of embolism. When applied with an external rotating magnetic field, rotating tPA-MRs significantly improved not only the mass transport of the tPA-clot reaction, but also mechanically disrupted the clot network, which thus increased clot interaction and penetration of tPA. Importantly, intravenously injected MRs could be discharged from the kidney, and the function of liver and kidney were not damaged at different durations after administration of tPA-MRs. Our data suggest that tPA-MRs overcome the limitations of thrombolytic therapy with tPA alone, which may be not only just for the treatment of ischemic stroke but also have majorly impact on other thrombotic diseases.
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Combining conventional physical vapor deposition and wet chemical etching, nanoshell catalytic motors with catalyst coated inside the shell have been fabricated. Those motors are propelled by bubble ...ejection or burst mechanism due to small bubble nucleation energy, and they move much faster than the Janus catalytic motors of the same size. The speeds of the motors (∼100 μm s–1) are closely related to the bubble size and generation frequency. The experimental data show that the bubbles do not totally block the opening of the shell and, thus, achieve a fast mass transport and sustain continuous motion of the motors.
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The combination of colloidal lithography and glancing angle deposition facilitates a new powerful fabrication technique – shadow sphere lithography (SSL), which can greatly expand the variety and ...complexity of nanostructures fabricated using simple evaporation and colloidal monolayer templates. Their applications have been widely investigated in plasmonics and associated fields. Here, we present an overview of the principle of SSL, followed by different strategies of utilizing SSL to design various nanostructures by changing the nanosphere monolayer masks, deposition configurations, different ways to combine deposition and etching, etc. Typical nanostructures fabricated by SSL, including nanorods on nanospheres, patchy nanospheres, nanotriangles, nanoring, nanocrescents, etc., are introduced. Recent optical applications of these plasmonic nanostructures are also summarized. It is expected that this review will inspire more ingenious designs of plasmonic nanostructures by SSL for advanced and smart applications.
Ag/Ti composite nanohole arrays are fabricated by a simple combination of nanosphere lithography, reactive ion etching, and dual e-beam deposition techniques. Based on the X-ray diffraction, ...conductivity, and ellipsometry measurements, there exists a Ag composition threshold CAg = 80 at% above which Ag is percolated through the entire film. Significant extraordinary optical transmission (EOT) is observed in nanohole samples with composition larger than the threshold. The main EOT peak position, the (1,0) Ag/glass resonance peak, redshifts as the CAg value decreased, but its index sensitivity monotonically increased with CAg till a value of 300 RIU nm-1 for the CAg = 100 at% sample is achieved. However, the LSPR peak of the nanoholes can achieve a sensitivity of 390 nm RIU-1 when CAg decreases from 100 at% to 85 at%. This study demonstrates that besides the shape, size, and measurement configuration, the resonances and sensitivities of nanohole arrays can be effectively predicted and tuned by the composition of a plasmonic composite.
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•Silver nanorod array substrates with high reproducibility were fabricated by oblique angle deposition technique.•SERS enhancement effect of AgNR array substrates reached over ...108.•Sodium saccharin was detected with an excellent LOD and a broad linear range.•A one-step liquid-liquid extraction procedure was applied to the detection of sodium saccharin from soft drinks.
Sodium saccharin (SS) is a commonly used synthetic sweetener in carbonated soft drinks and beverages. Long-term consumption of SS could result in health problems. Here, a sensitive surface-enhanced Raman spectroscopy (SERS) method with silver nanorod (AgNR) array substrates was explored for quantification of SS in soft drinks. The AgNR array substrates fabricated by an oblique angle deposition technique exhibited an excellent SERS activity with an enhancement factor of ∼108. A good linear relationship was demonstrated between SERS peak intensity and SS concentration in the concentration range of 0.5–100mg/L, and a limit of detection was determined to be 0.3mg/L. The detection of SS in different soft drinks was further explored by combining SERS spectra with the partial least squares discriminant analysis. The results showed that the LODs of SS from Sprite, Cola, Fanta and Schweppes detected by SERS were 20, 5, 20 and 10mg/L, respectively, which was far below the national standard. This SERS-based method enables the rapid and highly sensitive detection of SS with minimal sample pretreatment, and holds great promise in this food safety application.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Photoelectrochemical cells based on traditional and nanostructured ZnO thin films are investigated for hydrogen generation from water splitting. The ZnO thin films are fabricated using three ...different deposition geometries: normal pulsed laser deposition, pulsed laser oblique‐angle deposition, and electron‐beam glancing‐angle deposition. The nanostructured films are characterized by scanning electron microscopy, X‐ray diffraction, UV‐vis spectroscopy and photoelectrochemical techniques. Normal pulsed laser deposition produces dense thin films with ca. 200 nm grain sizes, while oblique‐angle deposition produces nanoplatelets with a fishscale morphology and individual features measuring ca. 900 by 450 nm on average. In contrast, glancing‐angle deposition generates a highly porous, interconnected network of spherical nanoparticles of 15–40 nm diameter. Mott‐Schottky plots show the flat band potential of pulsed laser deposition, oblique‐angle deposition, and glancing‐angle deposition samples to be −0.29, −0.28 and +0.20 V, respectively. Generation of photocurrent is observed at anodic potentials and no limiting photocurrents were observed with applied potentials up to 1.3 V for all photoelectrochemical cells. The effective photon‐to‐hydrogen efficiency is found to be 0.1%, 0.2% and 0.6% for pulsed laser deposition, oblique‐angle deposition and glancing‐angle deposition samples, respectively. The photoelectrochemical properties of the three types of films are understood to be a function of porosity, crystal defect concentration, charge transport properties and space charge layer characteristics.
Three types of ZnO photoelectrochemical cell are examined and utilized for water splitting. Pulsed laser deposition, oblique angle deposition and glancing angle deposition techniques are found to drastically affect crystal growth, morphology and photoelectrochemical properties. Hydrogen generation efficiencies are 0.1, 0.2 and 0.6% for pulsed laser deposition, oblique angle deposition and glancing angle deposition photoelectrochemical cells, respectively.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
A large-area (over 1 cm2) nanoparticle-in-ring array (NPIRA) with strong Fano resonance is fabricated by a low-cost shadow sphere lithography (SSL) method. Controlled narrow nanogaps of 8–20 nm are ...formed between the nanoparticles (NPs) and rings. Quadrupole modes are excited in the nanogaps and interact with the dipole mode of the NPs and ring, resulting in two Fano resonances. The two Fano resonances are in the visible and near-infrared region, respectively, and show a maximum refractive index sensitivity of 425 nm/RIU and a figure of merit of 4.7–7.1 RIU–1. In addition, the NPIRAs show enhanced Raman intensity due to the strong electric fields confined in the nanogaps. The structure has great potential for the dual plasmonic sensor applications, i.e., surface-enhanced Raman scattering and refractive index sensing, and provides a robust sensing performance for each.
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The self-diffusiophoresis of Janus catalytic micromotors (JCMs) in confined environment is studied using direct numerical simulations. The simulations revealed that, on average, the translocation of ...a JCM through a short pore is moderately slowed down by the confinement. This slowdown is far weaker compared to the transport of particles through similar pores driven by forces induced by external means or passive diffusiophoresis. Pairing of two JCMs facilitates the translocation of the one JCM entering the pore first but slows down the second JCM. Depending on its initial orientation, a JCM near the entrance of a pore can exhibit different rotational motion, which determines whether it can enter the pore. Once a JCM enters a narrow pore, it can execute a self-alignment process after which it becomes fully aligned with the pore axis and moves to the center line of the pore. Analysis of these results showed that, in addition to hydrodynamic effect, the translation and rotation of JCM is also affected by the “chemical effects”, i.e., the modification of the chemical species concentration around a JCM by confining walls and neighboring JCMs. These chemical effects are unique to the self-diffusiophoresis of JCMs and should be considered in design and operations of JCMs in confined environment.
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