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.

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.

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.

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.

Shape-Dependent Biodistribution of Biocompatible Silk Microcapsules.

Microcapsules are emerging as promising microsize drug carriers due to their remarkable deformability. Shape plays a dominant role in determining their vascular transportation. Herein, we explored the effect of the shape of the microcapsules on the in vivo biodistribution for rational design of microcapsules to achieve optimized targeting efficiency. Silk fibroin, a biocompatible, biodegradable, and abundant material, was utilized as a building block to construct biconcave discoidal and spherical microcapsules with diameter of 1.8 µm and wall thickness of 20 nm. We have compared the cytocompatibility, cellular uptake, and biodistribution of both microcapsules. Both biconcave and spherical microcapsules exhibited excellent cytocompatibility and internalization into cancer cells. During blood circulation in mice, both microcapsules showed retention in liver and kidney and most underwent renal clearance. However, we observed significantly higher accumulation of biconcave silk microcapsules in lung compared with spherical microcapsules, and the accumulation was found to be stable in lung even after 3 days. The higher concentration of biconcave discoidal microcapsules found in lung arises from pulmonary environment, margination dynamics, and enhanced deformation in bloodstream. Red blood cell (RBC)-mimicking silk microcapsules demonstrated here can potentially serve as a promising platform for delivering drugs for lung diseases.

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.

Towards an Integrated QR Code Biosensor: Light-Driven Sample Acquisition and Bacterial Cellulose Paper Substrate.

This paper addresses two key challenges toward an integrated forward error-correcting biosensor based on our previously reported self-assembled quick-response (QR) code. The first challenge involves the choice of the paper substrate for printing and self-assembling the QR code. We have compared four different substrates that includes regular printing paper, Whatman filter paper, nitrocellulose membrane and lab synthesized bacterial cellulose. We report that out of the four substrates bacterial cellulose outperforms the others in terms of probe (gold nanorods) and ink retention capability. The second challenge involves remote activation of the analyte sampling and the QR code self-assembly process. In this paper, we use light as a trigger signal and a graphite layer as a light-absorbing material. The resulting change in temperature due to infrared absorption leads to a temperature gradient that then exerts a diffusive force driving the analyte toward the regions of self-assembly. The working principle has been verified in this paper using assembled biosensor prototypes where we demonstrate higher sample flow rate due to light induced thermal gradients.

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.

Flexible solid-state supercapacitor based on tin oxide/reduced graphene oxide/bacterial nanocellulose.

We demonstrate a flexible and light-weight supercapacitor based on bacterial nanocellulose (BNC) incorporated with tin oxide (SnO2) nanoparticles, graphene oxide (GO) and poly(3,4-ethylenedioxyiophene)-poly(styrenesulfonate) (PEDOT:PSS). The SnO2 and GO flakes are introduced into the fibrous nanocellulose matrix during bacteria-mediated synthesis. The flexible PEDOT:PSS/SnO2/rGO/BNC electrodes exhibited excellent electrochemical performance with a capacitance of 445 F g-1 at 2 A g-1 and outstanding cycling stability with 84.1% capacitance retention over 2500 charge/discharge cycles. The flexible solid-state supercapacitors fabricated using PEDOT:PSS/SnO2/rGO/BNC electrodes and poly(vinyl alcohol) (PVA)-H2SO4 coated BNC as a separator exhibited excellent energy storage performance. The fabrication method demonstrated here is highly scalable and opens up new opportunities for the fabrication of flexible cellulose-based energy storage devices.

Add-on plasmonic patch as a universal fluorescence enhancer.

Fluorescence-based techniques are the cornerstone of modern biomedical optics, with applications ranging from bioimaging at various scales (organelle to organism) to detection and quantification of a wide variety of biological species of interest. However, the weakness of the fluorescence signal remains a persistent challenge in meeting the ever-increasing demand to image, detect, and quantify biological species with low abundance. Here, we report a simple and universal method based on a flexible and conformal elastomeric film with adsorbed plasmonic nanostructures, which we term a "plasmonic patch," that provides large (up to 100-fold) and uniform fluorescence enhancement on a variety of surfaces through simple transfer of the plasmonic patch to the surface. We demonstrate the applications of the plasmonic patch in improving the sensitivity and limit of detection (by more than 100 times) of fluorescence-based immunoassays implemented in microtiter plates and in microarray format. The novel fluorescence enhancement approach presented here represents a disease, biomarker, and application agnostic ubiquitously applicable fundamental and enabling technology to immediately improve the sensitivity of existing analytical methodologies in an easy-to-handle and cost-effective manner, without changing the original procedures of the existing techniques.

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.

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.

Wood-Graphene Oxide Composite for Highly Efficient Solar Steam Generation and Desalination.

Solar steam generation is a highly promising technology for harvesting solar energy, desalination and water purification. We introduce a novel bilayered structure composed of wood and graphene oxide (GO) for highly efficient solar steam generation. The GO layer deposited on the microporous wood provides broad optical absorption and high photothermal conversion resulting in rapid increase in the temperature at the liquid surface. On the other hand, wood serves as a thermal insulator to confine the photothermal heat to the evaporative surface and to facilitate the efficient transport of water from the bulk to the photothermally active space. Owing to the tailored bilayer structure and the optimal thermo-optical properties of the individual components, the wood-GO composite structure exhibited a solar thermal efficiency of ∼83% under simulated solar excitation at a power density of 12 kW/m2. The novel composite structure demonstrated here is highly scalable and cost-efficient, making it an attractive material for various applications involving large light absorption, photothermal conversion and heat localization.

Metal-Organic Framework as a Protective Coating for Biodiagnostic Chips.

Zeolitic imidazolate framework-8 (ZIF-8) grown around antibodies anchored to plasmonic nanostructures serves as a protective layer to preserve the biorecognition ability of antibodies stored at room and elevated temperatures for several days. The biofunctionality of the ZIF-8-protected biochip can be restored by a simple water-rinsing step, making it highly convenient for use in point-of-care and resource-limited settings.

PEGylated Artificial Antibodies: Plasmonic Biosensors with Improved Selectivity.

Molecular imprinting, which involves the formation of artificial recognition elements or cavities with complementary shape and chemical functionality to the target species, is a powerful method to overcome a number of limitations associated with natural antibodies. An important but often overlooked consideration in the design of artificial biorecognition elements based on molecular imprinting is the nonspecific binding of interfering species to noncavity regions of the imprinted polymer. Here, we demonstrate a universal method, namely, PEGylation of the noncavity regions of the imprinted polymer, to minimize the nonspecific binding and significantly enhance the selectivity of the molecular imprinted polymer for the target biomolecules. The nonspecific binding, as quantified by the localized surface plasmon resonance shift of imprinted plasmonic nanorattles upon exposure to common interfering proteins, was found to be more than 10 times lower compared to the non-PEGylated counterparts. The method demonstrated here can be broadly applied to a wide variety of functional monomers employed for molecular imprinting. The significantly higher selectivity of PEGylated molecular imprints takes biosensors based on these artificial biorecognition elements closer to real-world applications.

Silk-Encapsulated Plasmonic Biochips with Enhanced Thermal Stability.

Because of their high sensitivity, cost-efficiency, and great potential as point-of-care biodiagnostic devices, plasmonic biosensors based on localized surface plasmon resonance have gained immense attention. However, most plasmonic biosensors and conventional bioassays rely on natural antibodies, which are susceptible to elevated temperatures and nonaqueous media. Hence, an expensive and cumbersome "cold chain" system is necessary to preserve the labile antibodies by maintaining optimal cold temperatures during transport, storage, and handling. Herein, we introduce a facile approach to preserve the antibody activity on a biosensor surface even at elevated temperatures. We show that silk fibroin film could be used as a protective layer to preserve the activity of a model antibody (Rabbit IgG) and cardiac troponin antibody at both room temperature and 40 °C over several days. Furthermore, a simple aqueous rinsing process restores the biofunctionality of the biosensor. This energy-efficient and environmentally friendly method represents a novel approach to eliminate the cold chain and temperature-controlled packing of diagnostic reagents and materials, thereby extending the capability of antibody-based biosensors to different resource-limited circumstances such as developing countries, an ambulance, an intensive care unit emergency room, and battlefield.

Bilayered Biofoam for Highly Efficient Solar Steam Generation.

A novel bilayered hybrid biofoam composed of a bacterial nanocellulose (BNC) layer and a reduced graphene oxide (RGO)-filled BNC layer is introduced for highly efficient solar steam generation. The biofoam exhibits a solar thermal efficiency of ≈83% under simulated solar illumination (10 kW m-2 ). The fabrication method introduced here is highly scalable and cost-efficient.