A Droplet‐Based High‐Throughput SERS Platform on a Droplet‐Guiding‐Track‐Engraved Superhydrophobic Substrate

A novel droplet‐based surface‐enhanced Raman scattering (SERS) sensor for high‐throughput real‐time SERS monitoring is presented. The developed sensors are based on a droplet‐guiding‐track‐engraved superhydrophobic substrate covered with hierarchical SERS‐active Ag dendrites. The droplet‐guiding track with a droplet stopper is designed to manipulate the movement of a droplet on the superhydrophobic substrate. The superhydrophobic Ag dendritic substrates are fabricated through a galvanic displacement reaction and subsequent self‐assembled monolayer coating. The optimal galvanic reaction time to fabricate a SERS‐active Ag dendritic substrate for effective SERS detection is determined, with the optimized substrate exhibiting an enhancement factor of 6.3 × 10⁵. The height of the droplet stopper is optimized to control droplet motion, including moving and stopping. Based on the manipulation of individual droplets, the optimized droplet‐based real‐time SERS sensor shows high resistance to surface contaminants, and droplets containing rhodamine 6G, Nile blue A, and malachite green are successively controlled and detected without spectral interference. This noble droplet‐based SERS sensor reduces sample preparation time to a few seconds and increased detection rate to 0.5 µ L s^?1 through the simple operation mechanism of the sensor. Accordingly, our sensor enables high‐throughput real‐time molecular detection of various target analytes for real‐time chemical and biological monitoring.     

An effective three-dimensional surface-enhanced Raman scattering substrate based on oblique Si nanowire arrays decorated with Ag nanoparticles

Silicon nanowire arrays (SiNWAs) decorated with metallic nanoparticle heterostructures feature promising applications in surface-enhanced Raman scattering (SERS). However, the densely arranged SiNWAs are usually inconvenient for the following decoration of metallic nanoparticles, and only the top area of silicon nanowires (SiNWs) contributes to the SERS detection. To improve the utilization of the heterostructure, herein, oblique SiNWAs were grown separately, and Ag nanoparticles (AgNPs) were uniformly deposited by magnetron sputtering to get the three-dimensional (3D) SiNWAs decorated with AgNPs (AgNPs-SiNWAs) SERS substrate. The large open surfaces of oblique SiNWs would create more surface area available for the formation of hotspots and improve the adsorption and excitation of analyte molecules on the wire. The optimized AgNPs-SiNWAs substrate exhibits high sensitivity in detecting chemical molecule Rhodamine 6G, and the detection limit can reach 1 × 10^?10 M. More importantly, the substrate also can be used as an effective DNA sensor for label-free DNA detection.     

Microfluidic Surface‐Enhanced Raman Scattering Sensors Based on Nanopillar Forests Realized by an Oxygen‐Plasma‐Stripping‐of‐Photoresist Technique

A novel surface‐enhanced Raman scattering (SERS) sensor is developed for real‐time and highly repeatable detection of trace chemical and biological indicators. The sensor consists of a polydimethylsiloxane (PDMS) microchannel cap and a nanopillar forest‐based open SERS‐active substrate. The nanopillar forests are fabricated based on a new oxygen‐plasma‐stripping‐of‐photoresist technique. The enhancement factor (EF) of the SERS‐active substrate reaches 6.06 × 10⁶, and the EF of the SERS sensor is about 4 times lower due to the influence of the PDMS cap. However, the sensor shows much higher measurement repeatability than the open substrate, and it reduces the sample preparation time from several hours to a few minutes, which makes the device more reliable and facile for trace chemical and biological analysis.     

A multifunctional Ag/PAOCG reusable substrate for <Emphasis Type="Italic">p</Emphasis>-nitrophenol reduction and SERS applications

We demonstrate a facile galvanic replacement reaction route to direct growth of silver nanoparticles (AgNPs) into porous alumina on conductive glass (PAOCG). Porous Al₂O₃ layer was prepared by using boehmite as precursor, deposited on conductive glass via spin coating, and followed by a heat treatment. PAOCG was attached firmly with a tiny sheet of steel and was then soaked in AgNO₃ solution. Ag⁺ ions in the nanopores of PAOCG adsorbed by capillarity were automatically reduced to metallic AgNPs, thus forming Ag/PAOCG. The catalytic property of Ag/PAOCG was investigated for p-nitrophenol (PNP) reduction using UV–Vis absorption spectroscopy, and the rate constant was evaluated using the pseudo-first-order kinetic model. This film catalyst could be readily regenerated and reused for up to ten times without significantly depreciate its efficiency. The SERS performance of Ag/PAOCG was investigated using aqueous crystal violet (CV) as a probe molecule. The optimum Ag/PAOCG substrate was capable of detecting as low as 10^?10 M aqueous CV. The reusability of Ag/PAOCG was achieved by heating the substrate at 400 °C for 5 min in air. This substrate could be reused for at least five cycles without significantly reduced SERS performance. Therefore, this powerful multifunctional surface can serve as a portable, durable and reusable substrate for PNP reduction and SERS applications.     

In vitro biomechanical properties,fluorescence imaging,surface-enhanced Raman spectroscopy,and photothermal therapy evaluation of luminescent functionalized CaMoO4:Eu@Au hybrid nanorods on human lung adenocarcinoma epithelial cells

Highly dispersible Eu³⁺-doped CaMoO₄@Au-nanorod hybrid nanoparticles (HNPs) exhibit optical properties, such as plasmon resonances in the near-infrared region at 790 nm and luminescence at 615 nm, offering multimodal capabilities: fluorescence imaging, surface-enhanced Raman spectroscopy (SERS) detection and photothermal therapy (PTT). HNPs were conjugated with a Raman reporter (4-mercaptobenzoic acid), showing a desired SERS signal (enhancement factor 5.0 × 10⁵). The HNPs have a heat conversion efficiency of 25.6%, and a hyperthermia temperature of 42°C could be achieved by adjusting either concentration of HNPs, or laser power, or irradiation time. HNPs were modified with antibody specific to cancer biomarker epidermal growth factor receptor, then applied to human lung cancer (A549) and mouse hepatocyte cells (AML12), and in vitro PTT effect was studied. In addition, the biomechanical properties of A549 cells were quantified using atomic force microscopy. This study shows the potential applications of these HNPs in fluorescence imaging, SERS detection, and PTT with good photostability and biocompatibility.     

Facile Synthesis of Bimetallic Ag/Ni Core/Sheath Nanowires and Their Magnetic and Electrical Properties

This paper describes a facile method for coating Ag nanowires with uniform, ferromagnetic sheaths made of polycrystalline Ni. A typical sample of these core/sheath nanowires had a saturation magnetization around 33 emu g^?1. We also demonstrated the use of this magnetic property to align the nanowires by simply placing a suspension of the nanowires on a substrate in a magnetic field and allowing the solvent to evaporate. The electrical conductivity of these core/sheath nanowires (2 × 10³ S cm^?1) was two orders of magnitude lower than that of bulk Ag (6.3 × 10⁵ S cm^?1) and Ni (1.4 × 10⁵ S cm^?1). This is likely caused by the transfer of electrons from the Ag core to the Ni sheath due to the difference in work function between the two metals. The electrons are expected to experience an increased resistance due to spin‐dependent scattering caused by the randomized magnetic domains in the polycrystalline, ferromagnetic Ni sheath. Studies on the structural changes to the Ni coating over time under different storage conditions show that storage of the nanowires on a substrate under ambient conditions leads to very little Ni oxidation after 6 months. These Ag/Ni core/sheath nanowires show promise in areas such as electronics, spintronics, and displays.     

Alumina-coated Ag nanocrystal monolayers as surfaceenhanced Raman spectroscopy platforms for the direct spectroscopic detection of water splitting reaction intermediates

A novel Ag-alumina hybrid surface-enhanced Raman spectroscopy （SERS） platform has been designed for the spectroscopic detection of surface reactions in the steady state. Single crystalline and faceted silver （Ag） nanoparticles with strong light scattering were prepared in large quantity, which enables their reproducible self-assembly into large scale monolayers of Raman sensor arrays by the Langrnuir-Blodgett technique. The close packed sensor film contains high density of sub-nm gaps between sharp edges of Ag nanoparticles, which created large local electromagnetic fields that serve as ＂hot spots＂ for SERS enhancement. The SERS substrate was then coated with a thin layer of alumina by atomic layer deposition to prevent charge transfer between Ag and the reaction system. The photocatalytic water splitting reaction on a monolayer of anatase TiO2 nanoplates decorated with Pt co-catalyst nanoparticles was employed as a model reaction system. Reaction intermediates of water photooxidation were observed at the TiO2/solution interface under UV irradiation. The surface-enhanced Raman vibrations corresponding to peroxo, hydroperoxo and hydroxo surface intermediate species were observed on the TiO2 surface, suggesting that the photo-oxidation of water on these anatase TiO2 nanosheets may be initiated by a nucleophilic attack mechanism.     

Dielectrophoresis‐Based Protein Enrichment for a Highly Sensitive Immunoassay Using Ag/SiO2 Nanorod Arrays

A nanoscale insulator‐based dielectrophoresis (iDEP) technique is developed for rapid enrichment of proteins and highly sensitive immunoassays. Dense arrays of nanorods (NDs) by oblique angle deposition create a super high electric field gradient of 2.6 × 10²⁴ V² m^?3 and the concomitant strong dielectrophoresis force successfully traps small proteins at a bias as low as 5 V. 1800‐fold enrichment of bovine serum albumin protein at a remarkable rate of up to 180‐fold s^?1 is achieved using oxide coated Ag nanorod arrays with pre‐patterned sawtooth electrodes. Based on this system, an ultrasensitive immunoassay of mouse immunoglobulin G is demonstrated with a reduction in the limit of detection from 5.8 ng mL^?1 (37.6 pM) down to 275.3 fg mL^?1 (1.8 f M), compared with identical assays performed on glass plates. This methodology is also applied to detect a cancer biomarker prostate‐specific antigen spiked in human serum with a detection limit of 2.6 ng mL^?1. This high sensitivity results from rapid biomarker enrichment and metal enhanced fluorescence through the integration of nanostructures. The concentrated proteins also accelerate binding kinetics and enable signal saturation within 1 min. Given the easy fabrication process, this nanoscale iDEP system provides a highly sensitive detection platform for point‐of‐care diagnostics.     

Multiplexed Molecular Imaging of Fresh Tissue Surfaces Enabled by Convection‐Enhanced Topical Staining with SERS‐Coded Nanoparticles

There is a need for intraoperative imaging technologies to guide breast‐conserving surgeries and to reduce the high rates of re‐excision for patients in which residual tumor is found at the surgical margins during postoperative pathology analyses. Feasibility studies have shown that utilizing topically applied surface‐enhanced Raman scattering (SERS) nanoparticles (NPs), in conjunction with the ratiometric imaging of targeted versus untargeted NPs, enables the rapid visualization of multiple cell‐surface biomarkers of cancer that are overexpressed at the surfaces of freshly excised breast tissues. In order to reliably and rapidly perform multiplexed Raman‐encoded molecular imaging of large numbers of biomarkers (with five or more NP flavors), an enhanced staining method has been developed in which tissue surfaces are cyclically dipped into an NP‐staining solution and subjected to high‐frequency mechanical vibration. This dipping and mechanical vibration (DMV) method promotes the convection of the SERS NPs at fresh tissue surfaces, which accelerates their binding to their respective biomarker targets. By utilizing a custom‐developed device for automated DMV staining, this study demonstrates the ability to simultaneously image four cell‐surface biomarkers of cancer at the surfaces of fresh human breast tissues with a mixture of five flavors of SERS NPs (four targeted and one untargeted control) topically applied for 5 min and imaged at a spatial resolution of 0.5 mm and a raster‐scanned imaging rate of >5 cm² min^?1.     

Ultrathin Molybdenum Dioxide Nanosheets as Uniform and Reusable Surface‐Enhanced Raman Spectroscopy Substrates with High Sensitivity

Metal oxides have advantages over the traditional noble metals to be used as substrate materials for surface‐enhanced Raman spectroscopy (SERS) with low cost, versatility, and biocompatibility, but their enhancement factors are generally quite low with a poor limit of detection. Here, ultrathin molybdenum dioxide (MoO₂) nanosheets synthesized by chemical vapor deposition demonstrated in large area are used as SERS substrates with superior signal uniformity in the whole area with a limit of detectable concentration down to 4 × 10^?8m and enhancement factor up to 2.1 × 10⁵, exceeding that of 2D materials and comparable to that of noble metal films. More practically important, the planar MoO₂ substrate is more robust than noble metals and shows excellent reusability and uniformity, which is usually prohibited for nanostructured or nanoparticle‐based metal oxide substrates. The enhancement is mainly attributed to the surface plasmon resonance effect as evidenced by the first principle calculations and UV–vis absorption spectroscopy characterization, which can be further increased by decreasing the thickness of the MoO₂ nanosheets. The overall superior performance makes the MoO₂ nanosheets an ideal substrate for practical SERS applications.     

SERS Active Surface in Two Steps,Patterning and Metallization

Robust and reproducible metallized nano/microstructured surfaces of polymeric surfaces have been successfully prepared by direct laser interference patterning (DLIP) of commercial polymeric films followed by sputtering of metallic thin films. The SERS spectra for 2‐thioaniline adsorbed on a structured polycarbonate surfaces covered with a gold or platinum film showed a ca. three order of magnitude enhancement over a flat surface with the same metal film. The method here reported is suitable for mass production of substrates for SERS since large areas (several cm²) can be structured in ca. 1–5 s.     

Novel flexible photoanode based on Ag nanowire/polymer composite electrode

A novel flexible photoanode based on a silver nanowire (AgNW)/polymer composite electrode was fabricated and used for dye-sensitized solar cells. The AgNW/polymer composite substrate comprised a thin percolation network of AgNWs embedded on the surface of polyacrylic ester. As titanium dioxide film formed on top of the composite substrate, the effect of compression was investigated. Drop-cast sensitization was then used for both pressed and nonpressed photoanode, and the nonpressed one performed better. A cell efficiency of 0.91% was achieved under 100 mW cm^?2 simulated solar irradiation. After a bending test on the flexible photoanode, the solar cell retained 0.71% efficiency.     

Facile synthesis of Ag dendrites on Al foil via galvanic replacement reaction with [Ag(NH3)2]Cl for ultrasensitive SERS detecting of biomolecules

Symmetric silver dendrites have been synthesized on commercial aluminum foil via galvanic replacement reaction with [Ag(NH₃)₂]Cl. This process is facile and environmentally friendly, without the use of any templates, surfactants or oxidants, and also avoiding the introduction of fluoride anions as a strong toxicity resulting in hypocalcemia. The products were characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM), high-resolution TEM (HRTEM) and X-ray diffraction (XRD). SEM characterizations and electrochemical measurements including an electrochemical direct current polarization method and OCP-t technique demonstrate that chloride has proven to be the key factor to the formation of well-defined dendritic shape. The as-prepared Ag dendrites are developed as a surface-enhanced Raman scattering (SERS)-active platform for detection of folic acid, DNA and RNA with well resolved bands and high Raman intensities. The detection concentration for the three biomolecules reaches the level of 10⁻¹² M, and thus the symmetric silver dendrites can potentially be employed as effective SERS sensors for label-free and ultrasensitive biomolecule detection.     

A High‐Sensitivity and Low‐Power Theranostic Nanosystem for Cell SERS Imaging and Selectively Photothermal Therapy Using Anti‐EGFR‐Conjugated Reduced Graphene Oxide/Mesoporous Silica/AuNPs Nanosheets

A high‐sensitivity and low‐power theranostic nanosystem that combines with synergistic photothermal therapy and surface‐enhanced Raman scattering (SERS) mapping is constructed by mesoporous silica self‐assembly on the reduced graphene oxide (rGO) nanosheets with nanogap‐aligned gold nanoparticles (AuNPs) encapsulated and arranged inside the nanochannels of the mesoporous silica layer. Rhodamine 6G (R6G) as a Raman reporter is then encapsulated into the nanochannels and anti‐epidermal growth factor receptor (EGFR) is conjugated on the nanocomposite surface, defined as anti‐EGFR‐PEG‐rGO@CPSS‐Au‐R6G, where PEG is polyethylene glycol and CPSS is carbon porous silica nanosheets. SERS spectra results show that rGO@CPSS‐Au‐R6G enhances 5 × 10⁶ magnification of the Raman signals and thus can be applied in the noninvasive cell tracking. Furthermore, it displays high sensitivity (detection limits: 10^?8m R6G solution) due to the “hot spots” effects by the arrangements of AuNPs in the nanochannels of mesoporous silica. The highly selective targeting of overexpressing EGFR lung cancer cells (A549) is observed in the anti‐EGFR‐PEG‐rGO@CPSS‐Au‐R6G, in contrast to normal cells (MRC‐5). High photothermal therapy efficiency with a low power density (0.5 W cm^?2) of near‐infrared laser can be achieved because of the synergistic effect by conjugated AuNPs and rGO nanosheets. These results demonstrate that the anti‐EGFR‐PEG‐rGO@CPSS‐Au‐R6G is an excellent new theranostic nanosystem with cell targeting, cell tracking, and photothermal therapy capabilities.     

Present Status of the SuperCDMS program

The expected final reach of the Weakly Interacting Massive Particle (WIMP) search experiment CDMS-II by the end of 2007 is a WIMP-nucleon cross-section sensitivity of 2.1×10⁻⁴⁴ cm². To proceed further in our search, we have proposed the SuperCDMS Phase A project that would deploy 42 1-inch thick Ge detectors, at a site deeper than the location of CDMS II, and reach a desired sensitivity goal of 1.3×10⁻⁴⁵ cm². These cross-sections are of interest and are complementary to Supersymmetry searches at the Large Hadron Collider (LHC) and future linear colliders. P.L. Brink for the SuperCDMS Collaboration.     

Focusing Plasmons in Nanoslits for Surface‐Enhanced Raman Scattering

The focusing of plasmons to obtain a strong and localized electromagnetic‐field enhancement for surface‐enhanced Raman scattering (SERS) is increasing the interest in using plasmonic devices as molecular sensors. In this Full Paper, we report the successful fabrication and demonstration of a solid‐state plasmonic nanoslit–cavity device equipped with nanoantennas on a freestanding thin silicon membrane as a substrate for SERS. Numerical calculations predict a strong and spatially localized enhancement of the optical field in the nanoslit (6 nm in width) upon irradiation. The predicted enhancement factor of SERS was 5.3 × 10⁵, localized in an area of just 6 × 1.5 nm². Raman spectroscopy and imaging confirm an enhancement factor of ≈10⁶ for SERS from molecules chemisorbed at the nanoslit, and demonstrate the electromagnetic‐field‐enhancing function of the plasmonic nanoantennas. The freestanding membrane is open on both sides of the nanoslit, offering the potential for through‐slit molecular translocation studies, and opening bright new perspectives for SERS applications in real‐time (bio)chemical analysis.     

A bifunctional electrocatalyst of PtNi nanoparticles immobilized on three-dimensional carbon nanofiber mats for efficient and stable water splitting in both acid and basic media

Inspired by the excellent activity of platinum in hydrogen evolution reaction (HER) and the good performance of Ni-based compounds in oxygen evolution reaction (OER), a bifunctional electrocatalyst PtNi carbon nanofiber (CNF) is designed and fabricated using electrospinning followed by carbonization. Ultra-small PtNi nanoparticles of several nanometers in size are densely dispersed on every CNF, along with a few larger nanoparticles with sizes of several decades of nanometers. The as-prepared catalysts can be directly used as an electrode and act as high-efficiency materials for water splitting, including HER and OER. For HER activity, the PtNi/CNFs reach 10 mA cm^?2 current density at low overpotentials of 34 mV and exhibit a small Tafel slope of 31 mV dec^?1 in acidic electrolytes of 0.5 M H₂SO₄, which is close to that of commercial Pt/C (20 wt%) electrocatalytic catalysts. In 1 M KOH solution, the PtNi/CNFs also exhibit excellent HER activity with a low overpotential of 82 mV to achieve a current density of 10 mA cm^?2 and a small Tafel slope of 34 mV dec^?1. Moreover, the PtNi/CNFs also show good activity for OER in alkaline electrolyte of 1 M KOH with a Tafel slope of 159 mV dec^?1 and a small overpotential of 151 mV to reach a current density of 10 mA cm^?2. In addition, the OER performance of the PtNi/CNFs in acid media is also favorable, with a 198 mV dec^?1 Tafel slope. The decent activity of the PtNi/CNFs for water splitting originates from the synergistic effects of using Pt and Ni, large amounts of ultra-small nanoparticles densely dispersed on the CNFs, high conductivity of the support materials and interconnected three-dimensional structures of the carbon nanofiber mats.     

Growth of In. 53Ga. 47as layers on InP substrates for I.R. detectors by MBE

The increasing interest in the 1.3–1.55 μm region for optical fibre communications assignes to In_{. 53}Ga_{. 47}As a prominent role for detectors operating at these wavelengths. In this contribute we mainly discuss the origin of several kinds of morphological defects on this material and the technical solutions used to reduce the defect density to less than 1×10⁴/cm². Using chemical etching techniques combined with transmission cathodoluminescence and optical microscope observations, we show that there is no relation between single dislocations in the substrate and morphological defects in the layer. Most of defects originate at the interface between the substrate and the layer, and are strongly dependent on the substrate cleaning procedures. Moreover we discuss the influence of growth conditions (growth rate, substrate temperatures and As pressure) on the evolution of these defects.Hall measurements on InGaAs single layers give a residual doping concentration as low as n = 1.10¹⁴cm^?3 and a mobility (at n = 2 10¹⁵cm^?3) as high as 10000 cm²·V^?1·sec^?1 at room temperature.InGaAs PIN detectors were fabbricated, and dark currents as low as 3 nA at 10V were obtained over 65 μm mesa diameter.     

Development of nanostructured CdS sensor for H2S recognition: structural and physical characterization

In the present work, we report on the performance of a nanostructured CdS gas sensor. The sensor was fabricated using spin coating technique on glass substrate. The CdS sensor was characterized for their, structural microstructural as well as optoelectronic and H₂S response was studied. The XRD analysis showed formation of nanocrystalline CdS. Morphological analysis using SEM revealed nanostructured morphology with average grain size in the range of 40–50nm. Optical investigations showed a high absorption coefficient (10⁴ cm⁻¹) with a direct band gap of 2.54 eV. Electrical transport studies revealed films shows n-type conduction mechanism with room temperature dc electrical conductivity 10⁻⁶ (Ω cm)⁻¹. The CdS sensors showed the maximum response of 13.2% upon exposure to 100 ppm H₂S at operating temperature 100 °C.     

A 1300 mm2 Ultrahigh‐Performance Digital Imaging Assembly using High‐Quality Perovskite Single Crystals

By fine‐tuning the crystal nucleation and growth process, a low‐temperature‐gradient crystallization method is developed to fabricate high‐quality perovskite CH₃NH₃PbBr₃ single crystals with high carrier mobility of 81 ± 5 cm² V^?1 s^?1 (>3 times larger than their thin film counterpart), long carrier lifetime of 899 ± 127 ns (>5 times larger than their thin film counterpart), and ultralow trap state density of 6.2 ± 2.7 × 10⁹ cm^?3 (even four orders of magnitude lower than that of single‐crystalline silicon wafers). In fact, they are better than perovskite single crystals reported in prior work: their application in photosensors gives superior detectivity as high as 6 × 10¹³ Jones, ≈10–100 times better than commercial sensors made of silicon and InGaAs. Meanwhile, the response speed is as fast as 40 µs, ≈3 orders of magnitude faster than their thin film devices. A large‐area (≈1300 mm²) imaging assembly composed of a 729‐pixel sensor array is further designed and constructed, showing excellent imaging capability thanks to its superior quality and uniformity. This opens a new possibility to use the high‐quality perovskite single‐crystal‐based devices for more advanced imaging sensors.