Facile fabrication of multifunctional cotton fabric by AgNC@boronate polymer/crosslinked chitosan.

Multifunctional cotton fabrics (M-CF) have important application prospects in intelligent home decoration and material packaging. In this work, nanoparticles (AgNC@BP) were prepared by coating the surface of silver nanocubes (AgNCs) with borate polymer. Subsequently, M-CF with electromagnetic wave (EMW) absorption, mechanical enhancement, flame-retardancy and antibacterial performances were prepared by immersing cotton fabrics (CF) into AgNC@BP/crosslinked chitosan (CS) solution. Expectantly, AgNC@BP endows AgNC@BP/CS-CF with good flame retardancy and low combustion heat release. That is, the char length of AgNC@BP/CS-CF is 7.9 cm after the vertical burning test (UL-94 V) and the peak heat release rate (pHRR) of AgNC@BP/CS-CF is reduced by 21.4% compared to pure CF. Meanwhile, the tensile strength of AgNC@BP/CS-CF is 18.8% higher than that of CF. Synchronously, the introduction of AgNC@BP can also endow M-CF with better EMW absorption, mechanical and antibacterial properties. In conclusion, this work provides a tactic for fabricating M-CF.

Rapid and sensitive detection of Rhodamine B in food using the plasmonic silver nanocube-based sensor as SERS active substrate.

The use of dye in food is harmful to human health and is prohibited nowadays. However, it is still used because of the benefits, such as cheap prices and abundant resources. Rhodamine B is usually used as the colorant in food such as chili powder, chili oil, etc. It is colorless at very low concentration 10-7 M. The sensitive detection of RhB at ultra-low concentration help to prevent some risk for human. Surface-enhanced Raman scattering (SERS) is a great technique to detect the analytes at ultra-low concentration and provide the molecule's information as a fingerprint. In this study, silver nano-cube was facilely synthesized by reducing Ag+ in ethylene glycol and upgraded to thin-film as a SERS active substrate. RhB was detected at 10-10 M by a silver nano-cube sensor. The dynamic linear regression between the Raman intensity and RhB concentration over seven orders of magnitude (from 10-4 to 10-10 M) was excellent with high reliability (R2 = 0.99). Moreover, the substrate can be used after storing in a dark area for 60 days. This proposed nano-cube silver could serve as a potential substrate for detecting RhB in food at very low concentration.

Silver Nanocubes as Electrochemical Labels for Bioassays.

Here, we report on the use of 40 ± 4 nm silver nanocubes (AgNCs) as electrochemical labels in bioassays. The model metalloimmunoassay combines galvanic exchange (GE) and anodic stripping voltammetry (ASV). The results show that a lower limit of detection is achieved by simply changing the shape of the Ag label yielding improved GE with AgNCs when compared to GE with spherical silver nanoparticles (sAgNPs). Specifically, during GE between electrogenerated Au3+ and the Ag labels, a thin shell of Au forms on the surface of the NP. This shell is more porous when GE proceeds on AgNCs compared to sAgNPs, and therefore, more exchange occurs when using AgNCs. ASV results show that the Ag collection efficiency (AgCE%) is increased by up to ∼57% when using AgNCs. When the electrochemical system is fully optimized, the limit of detection is 0.1 pM AgNCs, which is an order of magnitude lower than that of sAgNP labels.

In situ investigating the size-dependent scattering signatures and sensing sensitivity of single silver nanocube through a multi-model approach.

Insightful understanding of size-dependent optical signatures and precise regularity of nanosensors is critical for developing applications of plasmonic sensing. This work presents a systematic study on localized surface plasmon resonance (LSPR)-based nanosensors of plasmonic silver nanocubes (AgNCs) with the edge lengths of 59.84 ± 7.97 nm (no. 1 AgNCs), 75.70 ± 9.05 nm (no. 2 AgNCs) and 110.32 ± 14.63 nm (no. 3 AgNCs), respectively. The effects of different sizes on the scattering signatures and refractive index (RI) sensitivities of AgNCs were in situ determined using the multi-model co-localization approach of single AgNC by dark-field microscope (DFM), LSPR spectroscopy and scanning electron microscopy (SEM). The scattering light colour of single AgNC took place bathochromic shift from monocolour to multicolour with the growth of edge length of single AgNC. The LSPR scattering spectra of no. 1 and 2 AgNCs exhibited singlet and singlet with the shoulder peak from quadrupolar resonance mode, respectively. Compared with the scattering signatures of no. 1 and 2 AgNCs, the interesting LSPR effect of plasmon line shape with two distinct peaks was observed on single no. 3 AgNC. In situ studies on the scattering spectral response of single AgNC to the ambient solvents and probing the small-molecule adsorbates on the surface of single silver nanocube reveal that no. 2 AgNC is more suitable as nanosensor due to strong regularity and higher sensitivity. The mechanism involved in optical signatures was elaborated clearly by combining with the experiments and theoretical simulation.

Silver Nanocubes Coated in Ceria: Core/Shell Size Effects on Light-Induced Charge Transfer.

Plasmonic sensitization of semiconductors is an attractive approach to increase light-induced photocatalytic performance; one method is to use plasmonic nanostructures in core@shell geometry. The occurrence and mechanism of synergetic effects in photocatalysis of such geometries are under intense debate and proposed to occur either through light-induced charge transfer (CT) or through thermal effects. This study focuses on the relation between the dimensions of Ag@CeO2 nanocubes, the wavelength-dependent efficiency, and the mechanism of light-induced direct CT. A 4-mercaptobenzoic acid (4-MBA) linker between core and shell acts as a Raman probe for CT. For all Ag@CeO2 nanocubes, CT increases with decreasing excitation wavelength, with notable increase at and below 514 nm. This is fully explainable by CT from silver to the 4-MBA LUMO, with the increase for excitation wavelengths that exceed the Ag/4-MBA LUMO gap of 2.28 eV (543 nm). A second general trend observed is an increase in CT yield with ceria shell thickness, which is assigned to relaxation of the excited electron further into the ceria conduction band, potentially producing defects.

Glucose Oxidase-Instructed Fluorescence Amplification Strategy for Intracellular Glucose Detection.

The accurate detection of glucose at cellular level remains a big challenge. In this study, a signal amplification strategy mediated by silver nanocube (AgNC), glucose oxidase (GOx), and silver ion fluorescence probe (denoted as AgNC-GOx/Ag+-FP) is proposed for amplified intracellular glucose detection. The AgNC is oxidized into Ag+ by H2O2 generated from GOx-catalyzed glucose oxidation reaction, and Ag+ remarkably enhances the red fluorescence of Ag+-FP. Our results show that AgNC-GOx/Ag+-FP is highly sensitive and specific to glucose and H2O2. Afterward, the feasibility of using AgNC-GOx/Ag+-FP to detect intracellular glucose is verified in five different cell lines. In summary, a sensitive and specific fluorescence amplification strategy has been developed for intracellular glucose detection.

Simultaneous determination of dopamine and uric acid in the presence of ascorbic acid using a gold electrode modified with carboxylated graphene and silver nanocube functionalized polydopamine nanospheres.

A voltammetric sensor is presented for the simultaneous determination of dopamine (DA) and uric acid (UA) in the presence of ascorbic acid (AA). It is based on a gold electrode (GE) modified with carboxyl-functionalized graphene (CFG) and silver nanocube functionalized DA nanospheres (AgNC@PDA-NS). The AgNC@PDA-NS nanocomposite was characterized by scanning electron microscopy and UV-Vis spectroscopy. The electrochemical behavior of the modified electrode was evaluated by electrochemical impedance spectroscopy, cyclic voltammetry and differential pulse voltammetry. The modified electrode displays good electrocatalytic activity towards DA (typically at 0.14 V vs. Ag/AgCl) and UA (typically at 0.29 V vs. Ag/AgCl) even in the presence of ascorbic acid. Response to DA is linear in the concentration range of 2.5 to 130 µM with a detection limit of 0.25 µM. Response to UA is linear in the concentration range of 10 to 130 µM with a detection limit of 1.9 µM. In addition, the sensitivity for DA and UA is 0.538 and 0.156 µA µM-1 cm-2, respectively. The modified electrode also displays good stability, selectivity and reproducibility. Graphical abstract The gold electrode modified with polydopamine nanospheres functionalized with silver nanocube and carboxylated graphene is used for simultaneous determination of DA and UA in the presence of AA, with wide linear range and low detection limit.

Detection of Dithiocarbamate Pesticides with a Spongelike Surface-Enhanced Raman Scattering Substrate Made of Reduced Graphene Oxide-Wrapped Silver Nanocubes.

Dithiocarbamate (DTC) pesticides are widely used for fruits, vegetables, and mature crops to control fungal diseases. Their residues in food could pose a threat to human health. Therefore, a surface-enhanced Raman scattering-based (SERS-based) sensor is developed to detect DTC pesticides because SERS can provide the characteristic spectrum of pesticides and avoid the use of a molecular recognition probe in the sensor. For the acquisition of high sensitivity, good anti-interference ability, and robustness of the SERS sensor, a silver nanocube-reduced graphene oxide (AgNC-rGO) sponge is devised. In the AgNC-rGO sponge, the rGO sheets form a porous scaffold that physically holds the AgNCs, which create narrow gaps between the neighboring AgNCs, leading to the formation of "hot spots" for SERS-signal amplification. When DTC pesticides coexist with aromatic pesticides in a sample matrix, the AgNC-rGO sponge can selectively detect DTC pesticides because of the preferential adsorption of DTC pesticides on the Ag surface and aromatic pesticides on the rGO surface, which can effectively eliminate the interference of the SERS signals of aromatic pesticides, and facilitate the qualitative and quantitative analysis of DTC pesticides. The AgNC-rGO sponge shows great potential as a SERS substrate for selective detection of DTC pesticides.

Efficiency Enhancement of PbS Quantum Dot/ZnO Nanowire Bulk-Heterojunction Solar Cells by Plasmonic Silver Nanocubes.

For improvement of solar cell performance, it is important to make efficient use of near-infrared light, which accounts for ∼40% of sunlight energy. Here we introduce plasmonic Ag nanocubes (NCs) to colloidal PbS quantum dot/ZnO nanowire (PbS QD/ZnO NW) bulk-heterojunction solar cells, which are characterized by high photocurrents, for further improvement in the photocurrent and power conversion efficiency (PCE) in the visible and near-infrared regions. The Ag NCs exhibit strong far field scattering and intense optical near field in the wavelength region where light absorption of PbS QDs is relatively weak. Photocurrents of the solar cells are enhanced by the Ag NCs particularly in the range 700-1200 nm because of plasmonic enhancement of light absorption and possible facilitation of exciton dissociation. As a result of the optimization of the position and amount of Ag NCs, the PCE of PbS QD/ZnO NW bulk-heterojunction solar cells is improved from 4.45% to 6.03% by 1.36 times.

Hierarchical 3D SERS substrates fabricated by integrating photolithographic microstructures and self-assembly of silver nanoparticles.

Most of the surface-enhanced Raman scattering (SERS) substrates are 2D planar systems, which limits the SERS active area to a single Cartesian plane. Here, we fabricate 3D SERS substrates with the aim to break the traditional 2D SERS active area limitation, and to extend the SERS hotspots into the third dimension along the z-axis. Our 3D SERS substrates are tailored with increased SERS hotspots in the z-direction from tens of nanometers to tens of micrometers, increasing the hotspots in the z-direction by at least an order of magnitude larger than the confocal volume (~1 µm) of most Raman spectrometers. Various hierarchical 3D SERS-active microstructures are fabricated by combining 3D laser photolithography with Langmuir-Blodgett nanoparticle assembly. 3D laser photolithography creates microstructured platforms required to extend the SERS-active area into 3D, and the self-assembly of Ag nanoparticles ensures homogeneous coating of SERS-active Ag nanoparticles over the entire microstructured platforms. Large-area 3D Raman imaging demonstrates that homogeneous signals can be collected throughout the entire 3D SERS substrates. We vary the morphology, height, and inclination angles of the 3D microstructures, where the inclination angle is found to exhibit strong influence on the SERS signals. We also demonstrate a potential application of this hierarchical 3D SERS substrate in information tagging, storage and encryption as SERS micro-barcodes, where multiple micro-barcodes can be created within a single set of microstructures.

Silver nanocube on gold microplate as a well-defined and highly active substrate for SERS detection.

Strong enhancement and good reproducibility in Raman signals are two major requirements for a surface-enhanced Raman scattering (SERS) substrate to be used for sensitive detection of an analyte. Here we report a new type of SERS substrate that was fabricated by depositing a Ag nanocube (AgNC) on the surface of a Au microplate (AuMP). Owing to the strong and reproducible hot spots formed at corner sites of the AgNC in proximity with the AuMP surface, the new substrate showed high sensitivity and reproducibility. Using 1,4-benzenedithiol as a probe, the SERS enhancement factor of a typical "AgNC on AuMP" substrate could reach a level as high as 4.7×107. In addition to the high sensitivity and reproducibility, the "AgNC on AuMP" substrate also displayed very good stability. Potential use of the "AgNC on AuMP" substrate was demonstrated by detecting crystal violet with high sensitivity.