Plasmonic nanomaterials-based flexible strips for the SERS detection of gouty arthritis.

Flexible biochips that enable sensitive detection and simultaneous quantification of biomarkers are of great importance in the field of point-of-care testing. Recently, surface-enhanced Raman scattering (SERS)-based flexible biochips have attracted a great deal of research attention for disease detection due to their rapid, sensitive, and noninvasive sensing abilities. Phenomenal progress in the synthesis of structure-controlled plasmonic nanomaterials has made SERS a powerful sensing platform for disease diagnosis and trace detection. Here, we demonstrate flexible plasmonic biochips for the SERS-based detection of uric acid (UA). Flexible strips exhibited excellent sensing performance with a detection limit of around 10 µM of UA, which is lower than the average level of UA in tears. This rapid and sensitive detection method enables the noninvasive diagnosis of gouty arthritis.

Photothermally Active Reduced Graphene Oxide/Bacterial Nanocellulose Composites as Biofouling-Resistant Ultrafiltration Membranes.

Biofouling poses one of the most serious challenges to membrane technologies by severely decreasing water flux and driving up operational costs. Here, we introduce a novel anti-biofouling ultrafiltration membrane based on reduced graphene oxide (RGO) and bacterial nanocellulose (BNC), which incoporates GO flakes into BNC in situ during its growth. In contrast to previously reported GO-based membranes for water treatment, the RGO/BNC membrane exhibited excellent aqueous stability under environmentally relevant pH conditions, vigorous mechanical agitation/sonication, and even high pressure. Importantly, due to its excellent photothermal property, under light illumination, the membrane exhibited effective bactericidal activity, obviating the need for any treatment of the feedwater or external energy. The novel design and in situ incorporation of the membranes developed in this study present a proof-of-concept for realizing new, highly efficient, and environmental-friendly anti-biofouling membranes for water purification.

Catalytically Active Bacterial Nanocellulose-Based Ultrafiltration Membrane.

Large quantities of highly toxic organic dyes in industrial wastewater is a persistent challenge in wastewater treatment processes. Here, for highly efficient wastewater treatment, a novel membrane based on bacterial nanocellulose (BNC) loaded with graphene oxide (GO) and palladium (Pd) nanoparticles is demonstrated. This Pd/GO/BNC membrane is realized through the in situ incorporation of GO flakes into BNC matrix during its growth followed by the in situ formation of palladium nanoparticles. The Pd/GO/BNC membrane exhibits highly efficient methylene orange (MO) degradation during filtration (up to 99.3% over a wide range of MO concentrations, pH, and multiple cycles of reuse). Multiple contaminants (a cocktail of 4-nitrophenol, methylene blue, and rhodamine 6G) can also be effectively treated by Pd/GO/BNC membrane simultaneously during filtration. Furthermore, the Pd/GO/BNC membrane demonstrates stable flux (33.1 L m-2 h-1 ) under 58 psi over long duration. The novel and robust membrane demonstrated here is highly scalable and holds a great promise for wastewater treatment.

Nanoantenna-Microcavity Hybrids with Highly Cooperative Plasmonic-Photonic Coupling.

Nanoantennas offer the ultimate spatial control over light by concentrating optical energy well below the diffraction limit, whereas their quality factor (Q) is constrained by large radiative and dissipative losses. Dielectric microcavities, on the other hand, are capable of generating a high Q-factor through an extended photon storage time but have a diffraction-limited optical mode volume. Here we bridge the two worlds, by studying an exemplary hybrid system integrating plasmonic gold nanorods acting as nanoantennas with an on-resonance dielectric photonic crystal (PC) slab acting as a low-loss microcavity and, more importantly, by synergistically combining their advantages to produce a much stronger local field enhancement than that of the separate entities. To achieve this synergy between the two polar opposite types of nanophotonic resonant elements, we show that it is crucial to coordinate both the dissipative loss of the nanoantenna and the Q-factor of the low-loss cavity. In comparison to the antenna-cavity coupling approach using a Fabry-Perot resonator, which has proved successful for resonant amplification of the antenna's local field intensity, we theoretically and experimentally show that coupling to a modest-Q PC guided resonance can produce a greater amplification by at least an order of magnitude. The synergistic nanoantenna-microcavity hybrid strategy opens new opportunities for further enhancing nanoscale light-matter interactions to benefit numerous areas such as nonlinear optics, nanolasers, plasmonic hot carrier technology, and surface-enhanced Raman and infrared absorption spectroscopies.

Influence of Surface Charge of the Nanostructures on the Biocatalytic Activity.

The physicochemical properties of abiotic nanostructures determine the structure and function of biological counterparts in biotic-abiotic nanohybrids. A comprehensive understanding of the interfacial interactions and the predictive capability of their structure and function is paramount for virtually all fields of bionanotechnology. In this study, using plasmonic nanostructures as a model abiotic system, we investigate the effect of the surface charge of nanostructures on the biocatalytic reaction kinetics of a bound enzyme. We found that the surface charge of nanostructures profoundly influences the structure, orientation, and activity of the bound enzyme. Furthermore, the interactions of the enzyme with nanoparticles result in stable conjugates that retain their functionality at elevated temperatures, unlike their free counterparts that lose their secondary structure and biocatalytic activity.

Structure-dependent SERS activity of plasmonic nanorattles with built-in electromagnetic hotspots.

Hollow plasmonic nanostructures with built-in and accessible electromagnetic hotspots such as nanorattles, obtained through a galvanic replacement reaction, have received wide attention in chemical and biological sensing and targeted drug delivery. In this study, we investigate the surface enhanced Raman scattering (SERS) activity of plasmonic nanorattles obtained through different degrees of galvanic replacement of Au@Ag nanocubes. We found that the SERS efficacy of the nanorattles is governed by the plasmon extinction intensity, localized surface plasmon resonance (LSPR) wavelength of the nanostructures with respect to the excitation source and intensity of the electromagnetic field at the hotspot, with the latter playing a determining role. Finite-difference time-domain (FDTD) simulations showed excellent agreement with the experimental findings that an optimal degree of galvanic replacement is critical for maximum SERS enhancement. The rational design and synthesis of the plasmonic nanorattles based on these findings can make these nanostructures highly attractive for SERS-based chemical and biological sensing and bioimaging.

Plasmonic Biofoam: A Versatile Optically Active Material.

Owing to their ability to confine and manipulate light at the nanoscale, plasmonic nanostructures are highly attractive for a broad range of applications. While tremendous progress has been made in the synthesis of size- and shape-controlled plasmonic nanostructures, their integration with other materials and application in solid-state is primarily through their assembly on rigid two-dimensional (2D) substrates, which limits the plasmonically active space to a few nanometers above the substrate. In this work, we demonstrate a simple method to create plasmonically active three-dimensional biofoams by integrating plasmonic nanostructures with highly porous biomaterial aerogels. We demonstrate that plasmonic biofoam is a versatile optically active platform that can be harnessed for numerous applications including (i) ultrasensitive chemical detection using surface-enhanced Raman scattering; (ii) highly efficient energy harvesting and steam generation through plasmonic photothermal heating; and (iii) optical control of enzymatic activity by triggered release of biomolecules encapsulated within the aerogel. Our results demonstrate that 3D plasmonic biofoam exhibits significantly higher sensing, photothermal, and loading efficiency compared to conventional 2D counterparts. The design principles and processing methodology of plasmonic aerogels demonstrated here can be broadly applied in the fabrication of other functional foams.

Plasmonic nanorattles with intrinsic electromagnetic hot-spots for surface enhanced Raman scattering.

The synthesis of plasmonic nanorattles with accessible electromagnetic hotspots that facilitate highly sensitive detection of chemical analytes using surface enhanced Raman scattering (SERS) is demonstrated. Raman spectra obtained from individual nanorattles demonstrate the significantly higher SERS activity compared to solid plasmonic nanostructures.

ZnO Nanocages Decorated with Au@AgAu Yolk-Shell Nanomaterials for SERS-Based Detection of Hyperuricemia.

Surface-enhanced Raman scattering (SERS) is widely recognized as a highly sensitive technology for chemical detection and biological sensing. In SERS-based biomedical applications, developing highly efficient sensing platforms based on SERS plays a pivotal role in monitoring disease biomarker levels and facilitating the early detection of cancer biomarkers. Hyperuricemia, characterized by abnormally high concentrations of uric acid (UA) in the blood, was associated with a range of diseases, such as gouty arthritis, heart disease, and acute kidney injury. Recent reports have demonstrated the correlation between UA concentrations in blood and tears. In this work, we report the fabrication of SERS substrates utilizing ZnO nanocages and yolk-shell-structured plasmonic nanomaterials for the noninvasive detection of UA in tears. This innovative SERS substrate enables noninvasive and sensitive detection of UA to prevent hyperuricemia-related diseases.

Plasmonic biochips with enhanced stability in harsh environments for the sensitive detection of prostate-specific antigen.

Hollow and porous plasmonic nanomaterials have been demonstrated for highly sensitive biosensing applications due to their distinctive optical properties. Immunosensors, which rely on antibody-antigen interactions, are essential constituents of diverse biosensing platforms owing to their exceptional binding affinity and selectivity. The majority of immunosensors and conventional bioassays needs special storage conditions and cold chain systems for transportation. Prostate-specific antigen (PSA), a serine protease, is widely employed in the diagnosis of prostate cancer. In this study, we present the successful utilization of a biopolymer-preserved plasmonic biosensor with improved environmental stability for the sensitive detection of PSA. The preserved plasmonic biosensors exhibited sustained sensitivity in the detection of PSA, achieving a limit of detection of 10 pg mL-1. Furthermore, these biosensors exhibited remarkable stability at elevated temperatures for one week.

Highly flexible MoS2 thin-film transistors with ion gel dielectrics.

Molybdenum disulfide (MoS(2)) thin-film transistors were fabricated with ion gel gate dielectrics. These thin-film transistors exhibited excellent band transport with a low threshold voltage (<1 V), high mobility (12.5 cm(2)/(V·s)) and a high on/off current ratio (10(5)). Furthermore, the MoS(2) transistors exhibited remarkably high mechanical flexibility, and no degradation in the electrical characteristics was observed when they were significantly bent to a curvature radius of 0.75 mm. The superior electrical performance and excellent pliability of MoS(2) films make them suitable for use in large-area flexible electronics.

Growth of large-area and highly crystalline MoS2 thin layers on insulating substrates.

The two-dimensional layer of molybdenum disulfide (MoS(2)) has recently attracted much interest due to its direct-gap property and potential applications in optoelectronics and energy harvesting. However, the synthetic approach to obtain high-quality and large-area MoS(2) atomic thin layers is still rare. Here we report that the high-temperature annealing of a thermally decomposed ammonium thiomolybdate layer in the presence of sulfur can produce large-area MoS(2) thin layers with superior electrical performance on insulating substrates. Spectroscopic and microscopic results reveal that the synthesized MoS(2) sheets are highly crystalline. The electron mobility of the bottom-gate transistor devices made of the synthesized MoS(2) layer is comparable with those of the micromechanically exfoliated thin sheets from MoS(2) crystals. This synthetic approach is simple, scalable, and applicable to other transition metal dichalcogenides. Meanwhile, the obtained MoS(2) films are transferable to arbitrary substrates, providing great opportunities to make layered composites by stacking various atomically thin layers.

Graphene-based high-efficiency surface-enhanced Raman scattering-active platform for sensitive and multiplex DNA detection.

We have developed a surface-enhanced Raman scattering (SERS)-active substrate based on gold nanoparticle-decorated chemical vapor deposition (CVD)-growth graphene and used it for multiplexing detection of DNA. Due to the combination of gold nanoparticles and graphene, the Raman signals of dye were dramatically enhanced by this novel substrate. With the gold nanoparticles, DNA capture probes could be easily assembled on the surface of graphene films which have a drawback to directly immobilize DNA. This platform exhibits extraordinarily high sensitivity and excellent specificity for DNA detection. A detection limit as low as 10 pM is obtained. Importantly, two different DNA targets could be detected simultaneously on the same substrate just using one light source.

Electrical probing of submicroliter liquid using graphene strip transistors built on a nanopipette.

Graphene sheets made by chemical vapor deposition are transferred onto a glass nanopipette to form graphene strips. Two strips are connected at the nanopipette tip end to form a transistor channel. This graphene-based transistor can be operated in a liquid-gating condition, thereby allowing the electrical detection of the pH value of a droplet with submicroliter volume.

Efficient reduction of graphene oxide catalyzed by copper.

We report that copper thin films deposited on top of graphene oxide (GO) serve as an effective catalyst to reduce GO sheets in a diluted hydrogen environment at high temperature. The reduced GO (rGO) sheets exhibit higher effective field-effect hole mobility, up to 80 cm(2) V(-1) s(-1), and lower sheet resistance (13 kΩ â–¡(-1)) compared with those reduced by reported methods such as hydrazine and thermal annealing. Raman and XPS characterizations are addressed to study the reduction mechanism on graphene oxide underneath copper thin films. The level of reduction in rGO sheets is examined by Raman spectroscopy and it is well correlated with hole mobility values. The conductivity enhancement is attributed to the growth of the graphitic domain size. This method is not only suitable for reduction of single GO sheets but also applicable to lower the sheet resistance of Langmuir-Blodgett assembled GO films.

Direct formation of wafer scale graphene thin layers on insulating substrates by chemical vapor deposition.

Direct formation of high-quality and wafer scale graphene thin layers on insulating gate dielectrics such as SiO(2) is emergent for graphene electronics using Si-wafer compatible fabrication. Here, we report that in a chemical vapor deposition process the carbon species dissociated on Cu surfaces not only result in graphene layers on top of the catalytic Cu thin films but also diffuse through Cu grain boundaries to the interface between Cu and underlying dielectrics. Optimization of the process parameters leads to a continuous and large-area graphene thin layers directly formed on top of the dielectrics. The bottom-gated transistor characteristics for the graphene films have shown quite comparable carrier mobility compared to the top-layer graphene. The proposed method allows us to achieve wafer-sized graphene on versatile insulating substrates without the need of graphene transfer.

Au@Ag nanostructures for the sensitive detection of hydrogen peroxide.

Hydrogen peroxide (H2O2) is an important molecule in biological and environmental systems. In living systems, H2O2 plays essential functions in physical signaling pathways, cell growth, differentiation, and proliferation. Plasmonic nanostructures have attracted significant research attention in the fields of catalysis, imaging, and sensing applications because of their unique properties. Owing to the difference in the reduction potential, silver nanostructures have been proposed for the detection of H2O2. In this work, we demonstrate the Au@Ag nanocubes for the label- and enzyme-free detection of H2O2. Seed-mediated synthesis method was employed to realize the Au@Ag nanocubes with high uniformity. The Au@Ag nanocubes were demonstrated to exhibit the ability to monitor the H2O2 at concentration levels lower than 200 µM with r2 = 0.904 of the calibration curve and the limit of detection (LOD) of 1.11 µM. In the relatively narrow range of the H2O2 at concentration levels lower than 40 µM, the LOD was calculated to be 0.60 µM with r2 = 0.941 of the calibration curve of the H2O2 sensor. This facile fabrication strategy of the Au@Ag nanocubes would provide inspiring insights for the label- and enzyme-free detection of H2O2.

Plasmonic Nanostructures-Decorated ZIF-8-Derived Nanoporous Carbon for Surface-Enhanced Raman Scattering.

Surface-enhanced Raman scattering (SERS) is considered to be a highly sensitive platform for chemical and biological sensing. Recently, owing to their high porosity and large surface area, metal-organic frameworks (MOFs) have attracted considerable attention in sensing applications. Porous carbon nanostructures are promising SERS substrates due to their strong broadband charge-transfer resonance and reproducible fabrication. Furthermore, an extraordinarily large enhancement of the electromagnetic field enables plasmonic nanomaterials to be ideal SERS substrates. Here, we demonstrate the porous Au@Ag nanostructure-decorated MOF-derived nanoporous carbon (NPC) for highly efficient SERS sensing. Specifically, this plasmonic nanomaterial-NPC composite offers high Raman signal enhancement with the ability to detect the model Raman reporter 2-naphthalenethiol (2-NT) at picomolar concentration levels.

Transfer printing of graphene strip from the graphene grown on copper wires.

A simple, cost-effective and lithography-free fabrication of graphene strips for device applications is demonstrated. The graphene thin layers were directly grown on Cu wires, followed by Cu etching and transfer printing to arbitrary substrates by a PDMS stamp. The Cu wires can be arranged on the PDMS stamp in a desired pattern; hence, the substrates can receive graphene strips with the same pattern. Moreover, the preparation of graphene strips does not involve conventional lithography; therefore, the surface of the graphene strip is free of residual photoresists, which may be useful for studies requiring clean graphene surfaces.

Gold Nanorod Size-Dependent Fluorescence Enhancement for Ultrasensitive Fluoroimmunoassays.

Plasmon-enhanced fluorescence (PEF) is a simple and highly effective approach for improving the signal-to-noise ratio and sensitivity of various fluorescence-based bioanalytical techniques. Here, we show that the fluorescence enhancement efficacy of gold nanorods (AuNRs), which are widely employed for PEF, is highly dependent on their absolute dimensions (i.e., length and diameter). Notably, an increase in the dimensions (length × diameter) of the AuNRs from 46 × 14 to 120 × 38 nm2 while holding the aspect ratio constant leads to nearly 300% improvement in fluorescence enhancement efficiency. Further increase in the AuNR size leads to a decrease of the fluorescence enhancement efficiency. Through finite-difference time-domain (FDTD) simulation, we reveal that the size-dependent fluorescence enhancement efficiency of AuNR stems from the size-dependent electromagnetic field around the plasmonic nanostructures. AuNRs with optimal dimensions resulted in a nearly 120-fold enhancement in the ensemble fluorescence emission from molecular fluorophores bound to the surface. These plasmonic nanostructures with optimal dimensions also resulted in a nearly 30-fold improvement in the limit of detection of human interleukin-6 (IL-6) compared to AuNRs with smaller size, which are routinely employed in PEF.