Gold Arrays Research Articles

Accurate and fast modeling of scattering from random arrays of nanoparticles using the discrete dipole approximation and angular spectrum method.

Lens-free microscopes can utilize holographic reconstruction techniques to recover the image of an object from the digitally recorded superposition of an unperturbed plane wave and a wave scattered by the object. Image reconstruction most commonly relies on the scalar angular spectrum method (ASM). While fast, the scalar ASM can be inaccurate for nanoscale objects, either because of the scalar approximation, or more generally, because it only models field propagation and not light-matter interaction, including inter-particle coupling. Here we evaluate the accuracy of the scalar ASM when combined with three different light-matter interaction models for computing the far-field light scattered by random arrays of gold and polystyrene nanoparticles. Among the three models-a dipole-matched transmission model, an optical path length model, and a binary amplitude model-we find that which model is most accurate depends on the nanoparticle material and packing density. For polystyrene particles at any packing density, there is always at least one model with error below 20%, while for gold nanoparticles with 40% or 50% surface coverage, there are no models that can provide errors better than 30%. The ASM error is determined in comparison to a discrete dipole approximation model, which is more computationally efficient than other full-wave modeling techniques. The knowledge of when and how the ASM fails can serve as a first step toward improved resolution in lens-free reconstruction and can also be applied to other random nanoparticle array applications such as lens-based super-resolution imaging, sub-diffraction beam focusing, and biomolecular sensing.

Robust Photoelectric Biomolecular Switch at a Microcavity-Supported Lipid Bilayer.

Biomolecular devices based on photo-responsive proteins have been widely proposed for medical, electrical, and energy storage and production applications. Also, bacteriorhodopsin (bR) has been extensively applied in such prospective devices as a robust photo addressable proton pump. As it is a membrane protein, in principle, it should function most efficiently when reconstituted into a fully fluid lipid bilayer, but in many model membranes, lateral fluidity of the membrane and protein is sacrificed for electrochemical addressability because of the need for an electroactive surface. Here, we reported a biomolecular photoactive device based on light-activated proton pump, bR, reconstituted into highly fluidic microcavity-supported lipid bilayers (MSLBs) on functionalized gold and polydimethylsiloxane cavity array substrates. The integrity of reconstituted bR at the MSLBs along with the lipid bilayer formation was evaluated by fluorescence lifetime correlation spectroscopy, yielding a protein lateral diffusion coefficient that was dependent on the bR concentration and consistent with the Saffman–Delbrück model. The photoelectrical properties of bR-MSLBs were evaluated from the photocurrent signal generated by bR under continuous and transient light illumination. The optimal conditions for a self-sustaining photoelectrical switch were determined in terms of protein concentration, pH, and light switch frequency of activation. Overall, a significant increase in the transient current was observed for lipid bilayers containing approximately 0.3 mol % bR with a measured photo-current of 250 nA/cm2. These results demonstrate that the platforms provide an appropriate lipid environment to support the proton pump, enabling its efficient operation. The bR-reconstituted MSLB model serves both as a platform to study the protein in a highly addressable biomimetic environment and as a demonstration of reconstitution of seven-helix receptors into MSLBs, opening the prospect of reconstitution of related membrane proteins including G-protein-coupled receptors on these versatile biomimetic substrates.

Laser-Scanning-Guided Assembly of Quasi-3D Patterned Arrays of Plasmonic Dimers for Information Encryption.

The application of plasmonic dimeric nanostructures in color displays, data storage, and especially metamaterials necessitates the patterning of dimers into ordered arrays, but controllable assembly of plasmonic nanoparticles into patterned dimer arrays on substrates still remains a challenge. Here, a facile laser-scanning-based strategy to fabricate quasi-3D patterned arrays of plasmonic nanoparticle dimers with controlled orientation for plasmonic information encryption is reported. Laser scanning of polymer-covered plasmonic nanoparticle (e.g., gold) arrays selectively exposes the surface of irradiated nanoparticle via localized photothermal heating, guiding the assembly of another type of nanoparticles onto the exposure nanoparticle surface to form dimers on substrates. This combined top-down/bottom-up approach is highly flexible in forming high-resolution patterns of plasmonic dimers from nanoparticles of different sizes and shapes. The z-axis orientation, interparticle spacing, and nanoparticle size and shape of plasmonic dimers can be precisely tuned, enabling the modulation of the coupled resonances of the dimer arrays. Moreover, it is demonstrated that the patterned dimer arrays can be used in information encryption where their plasmonic color can be repeatedly displayed and erased. This work provides an important addition to tools for the fabrication of patterned complex plasmonic nanostructures from as-synthesized nanoparticles with broad applications.

Streptavidin-functionalized terahertz metamaterials for attomolar exosomal microRNA assay in pancreatic cancer based on duplex-specific nuclease-triggered rolling circle amplification

Exosomal microRNA (miRNA) is a promising non-invasive biomarker for liquid biopsies. Herein, we fabricated a terahertz (THz) metamaterial biosensor that comprises an array of gold (Au) discs surrounded by annular grooves for exosomal miRNA assays based on duplex-specific nuclease (DSN)-triggered rolling circle amplification (RCA). In this strategy, the target miRNA is captured by a probe P0 immobilized on magnetic beads (MBs); it then repeatedly releases a primer P1 under the action of DSN, which acts as a highly specific initiator of the subsequent RCA step utilizing biotin-dUTP. After target recycling and nucleic acid amplification, the biotinylated amplification products were captured by the streptavidin (SA)-functionalized THz metamaterials, and further conjugated to SA-modified AuNPs that permit formation of a trimeric complex of SA-biotinylated RCA products-AuNP. The complex population scales with the starting concentration of the target miR-21, resulting in a red shift of the resonance peak of the THz metamaterials. This biosensor can lead to highly specific and sensitive detection with one-base mismatch discrimination and a limit of detection (LOD) down to 84 aM. Significant distinctions are seen in the frequency shifts for exosomal miR-21 quantitation in clinical plasma samples between pancreatic cancer patients and healthy controls. The frequency shifts of the THz metamaterials are consistent versus the reverse transcription-polymerase chain reaction (RT-PCR) results, illustrating the applicability and accuracy of our assay in real clinical samples.

Gold Nanoframe Array Electrode for Straightforward Detection of Hydrogen Peroxide

The nanostructuring of a sensing membrane is performed through colloidal nanosphere lithography (NSL) techniques with a tiny polystyrene nanobead template 100 nm in size. The solvent ratio adjustment has been proven to be effective in assisting the monolayer deposition of small templating particles with minimal defects. Two distinct structures, namely, a billowy gold nanostructure (BGN) where the nanobead template is left unetched and a gold nanoframe array (GNA) with a regular ring-like structure after template removal, are used for the extended-gate field-effect transistor (EGFET) electrodes. The GNA structure generates an electroactive surface area significantly (~20%) larger than its geometrical area as well as a greater surface roughness than the BGN. When integrated with the portable constant voltage–constant current (CVCC) FET circuitry for pH screening to determine the optimized measurement conditions for H2O2 sensing, the GNA sensing membrane also shows more improved Nernstian sensitivity at ~50 mV/pH than the BGN electrode. The more optimized sensitivity is then proven using the GNA in the detection of H2O2, the most common representative reactive oxygen species (ROS) involved in the environment, food, and neurodegenerative diseases, such as Parkinson´s and Alzheimer´s diseases. The GNA electrode has a sensitivity of 70.42 mV/log µM [H2O2] and a limit of detection (LoD) of 1.183 µM H2O2. The integrated ion sensing system employing unique, highly ordered gold array gate electrodes and a portable CVCC circuit system has shown a stable real-time output voltage signal, representing an alternative to bulky conventional FET devices for potential on-site H2O2 detection.

A dual-band photodetector induced by hybrid surface plasmon resonance

In this letter, we proposed an advanced dual-band detector based on the plasmonic response of patterned graphene integrated on a gold array. The photodetector shows ultra-high photoresponse performance in both visible light (0.4–0.7 μm) and mid-infrared (4–14 μm) light. The highest achievable responsivity of 2.7 A W−1 is comparable with typical visible and mid-infrared photodetectors. The working wavelength can be tuned by changing the external gate voltage bias, the dimension of graphene, and the architecture of the gold array. The demonstration of a surface plasmon resonance enhanced detector brings us a step closer to high sensitivity room-temperature multiband devices.

Enhancement of cardiac contractility using gold-coated SU-8 cantilevers and their application to drug-induced cardiac toxicity tests.

Herein, we propose an array of gold (Au)-coated SU-8 cantilevers with microgrooves for improved maturation of cardiomyocytes and describe its applications to drug-induced cardiac toxicity tests. Firstly, we evaluated the effect of cell culture substrates such as polydimethylsiloxane (PDMS), polyimide (PI), and SU-8 on the cardiomyocyte's maturation. Among these, the SU-8 with microgroove structures exhibits improved cardiomyocyte maturation. Further, thin layers of graphene and Au are coated on SU-8 substrates and the effects of these materials on cardiomyocyte maturation are evaluated by analyzing the expression of proteins such as alpha-actinin, Connexin 43 (Cx43), and Vinculin. While both conductive materials enhanced protein expression when compared to bare SU-8, the Au-coated SU-8 substrates demonstrated superior cardiomyocyte maturation. The cantilever structure is constructed using microgroove patterned SU-8 with and without an Au coating. The Au-coated SU-8 cantilever showed maximum displacement of 17.6 ± 0.3 μm on day 21 compared to bare SU-8 (14.2 ± 0.4 μm) owing to improved cardiomyocytes maturation. Verapamil and quinidine are used to characterize drug-induced changes in the contraction characteristics of cardiomyocytes on bare and Au-coated SU-8 cantilevers. The relative contraction forces and beat rates changed according to the calcium and sodium channel related drugs. Matured cardiomyocytes are less influenced by the drugs compared to immature cardiomyocytes and showed reliable IC50 values. These results indicate that the proposed Au-coated SU-8 cantilever array could help improve the accuracy of toxicity screening results by allowing for the use of cardiomyocytes that have been matured on the drug screening platform.

Simultaneous Evaluation of Electrochemical Impedance and Cell Membrane Damage to Understand Antibacterial Mechanism on Nanostructured Surface

In recent years, biomimetics or biomimicry have been paid attention which focus on biotic micro and nano structures. These structures show excellent and multiple functions. It is reported that the wings of cicada and dragonfly have countless nanostructures which exhibit antibacterial and bactericidal activities. These structures kill bacteria physically1-3). One of acceptable mechanism of bactericidal effect is proposed as below: the cell membrane is stretched by the interaction between the structure and bacteria, which induce the cell membrane to be deformed. Then the intracellular fluid leaks which make the cell death4). However, the detailed mechanism has not been cleared. In this study, electrochemical impedance spectroscopy (EIS) measurement and fluorescence microscopy were performed simultaneously to analyze the mechanism of cell adhesion and deformation on the nanostructure surface. The experimental method is described as below. A working electrode (WE) with the diameter of 100 µm was fabricated on a Si substrate. The WE had gold nanostructure arrays which were fabricated by using electron beam lithography and pulse deposition. In order to observe the surface of the WE by a fluorescent microscope, a counter electrode (CE) composed of Au thin film and a reference electrode (RE) were formed on a glass substrate by using photolithography and sputtering. Here, Ag/AgCl paste was solidified and used for the RE. These substrates were opposed to each other as shown in Fig. 1-a, and silicon rubber with a sample chamber with a thickness of 500 µm was sandwiched between these substrates and fixed with screws. An electrolyte solution (PBS (pH = 7.4) containing NaCl (0.15 M) and Fe(CN)6 3- / 4- (1 mM)) was injected through a hole provided on the glass substrate. Escherichia coli (E. coli) was used as a model bacteria and concentration of E. coli was adjusted to OD600 = 0.2. We used DNA staining reagent of SYTO 9 and PI. SYTO 9 diffuses into the cell cytoplasm through the cell membrane and stains DNA green. In contrast, PI enters the cell cytoplasm and stains DNA red when the cell membrane is damaged. Therefore, adhered cells without membrane damage were colored green. After mixing the bacterial broth and the electrolyte solution, the mixture was injected through a hole Then, AC impedance measurement and time-lapse observation using the fluorescence microscope were simultaneously performed every 5 minutes to evaluate changes over time. The obtained fluorescence images are summarized in Table 1, and Fig. 1-b shows the change rate of Rct over time. From Table 1, the number of E. coli stained red increased with the lapse of time on the pillared electrode. E. coli stained green was hardly observed. On the other hand, microscopic observation showed adsorption and desorption of E. coli which stained green on the flat electrode, Here, E. coli stained red could not be observed. According to Fig. 1-b, it was found that the change rate of Rct on the pillared electrode increased gradually and was much larger comparing with that on the flat electrode. In the case of the flat electrode, it is considered that the increase and decrease of impedance was due to adsorption and desorption of E. coli, respectively. In the case of the pillared electrode, the cell membrane was damaged and died after E. coli attached on the WE. The impedance continued to rise because E. coli died and remained on the electrode. At this time, only the attachment process of E. coli could be analyzed. In the future, we will aim for single-cell level analysis by reducing the electrode diameter. We plan to make measurements closer to real time and report more detailed analysis results. 【 References】1) E. P. Ivanova, et al.：Small 8, p. 2489-2494 (2012)2) E. P. Ivanova, et al.：Nature Communications 4, p. 1-7 (2013)3) A. Tripathy, et al.：Advances in Colloid and Interface Science, 248, p. 85-104 (2017)4) K. Nakade, et al.：ACS Applied Nano Materials, p. 5736-5741 (2018) Figure 1

Surface plasmon resonance imaging-based biosensor for multiplex and ultrasensitive detection of NSCLC-associated exosomal miRNAs using DNA programmed heterostructure of Au-on-Ag

Exosomal miRNAs are potential tumor biomarkers for early diagnosis of non-small cell lung cancer (NSCLC). Herein, a surface plasmon resonance imaging (SPRi)-based biosensor was developed for simultaneous detection of multiplex NSCLC-associated exosomal miRNAs in a clinical sample using Au-on-Ag heterostructure and DNA tetrahedral framework (DTF). Exosomal miRNAs are captured by various DTF probes immobilized on the gold array chip. Subsequently, single-stranded DNA (ssDNA) functionalized silver nanocube (AgNC) hybridizes with the captured exosomal miRNAs and then the ssDNA-coated Au nanoparticles assembled on the surface of AgNC, forming Au-on-Ag heterostructures as essential labels to realize amplified SPR response. With the aid of DNA programmed Au-on-Ag heterostructure and DTF, the SPRi-based biosensor exhibits wide detection range from 2 fM to 20 nM, ultralow limit of detection of 1.68 fM, enhanced capture efficiency, and improved antifouling capability. Furthermore, the biosensor enables accurate discrimination of NSCLC patients based on detection results of exosomal miRNAs. Overall, this developed biosensor is a promising tool for multiplex exosomal miRNAs detection, providing a new possibility for early diagnosis of NSCLC.

Gold Nanorod-Based Bio-Barcode Sensor Array for Enzymatic Detection in Biomedical Applications

Early diagnosis of disease onset requires sensor systems that detect multiple disease-related processes within the body. However, major obstacles must be surmounted for in vivo sensor use, includin...

Thermal tracing of a highly reconfigurable and wideband infrared heat sensor based on vanadium dioxide

In this paper, we investigate the thermodynamic properties of a highly reconfigurable and broadband perfect metamaterial absorber in the near-infrared region. Our model is a periodic nanostructure composed of an array of L-shaped hybrid gold and vanadium dioxide nanostructures on gold and glass substrates. The reconfigurability of the nanostructure is based on the metal–insulator transition of vanadium dioxide. The degree of reconfigurability depends on the temperature of the vanadium dioxide nanostructure. In order to study the photo-thermal effect on the reconfigurability of the nanostructure, we irradiate it with a time-dependent Gaussian pulse laser with a 1.5 ns pulse width. Our main purpose is twofold. On the one hand, we aim to investigate how the laser increases the temperature of the nanostructure, and on the other hand, we intend to explore whether the temperature modifies the absorption and reflection of the array. Our results reveal that the VO2 fully transitions to its metallic phase when the fluence of the incident laser is adjusted to 17.8 mJ/cm2.

Reflectance in AFM-IR: Implications for Interpretation and Remote Analysis of the Buried Interface

AFM-IR combines the chemical sensitivity of infrared spectroscopy with the lateral resolution of scanning probe microscopy, allowing nanoscale chemical analysis of almost any organic material under ambient conditions. As a result, this versatile technique is rapidly gaining popularity among materials scientists. Here, we report a previously overlooked source of data and artifacts in AFM-IR analysis; reflection from the buried interface. Periodic arrays of gold on glass are used to show that the overall signal in AFM-IR is affected by the wavelength-dependent reflectivity and thermal response of the underlying substrate. Excitingly, this demonstrates that remote analysis of heterogeneities at the buried interface is possible alongside that of an overlying organic film. On the other hand, AFM-IR users should carefully consider the composition and topography of underlying substrates when interpreting nanoscale infrared data. The common practice of generating ratio images, or indeed the normalization of AFM-IR spectra, should be approached with caution in the presence of substrate heterogeneity or variable sample thickness.

Sensors Based on Nanoantennas: Fundamentals

Nanoscience and nanotechnology are emerging fields where some phenomena were recently discovered, allowing the design of some new devices. One of these phenomena is extraordinary optical transmission - EOT -, which was discovered in 1998 by Ebbesen. He reported that light can be amplified in certain conditions, due to a resonant behaviour, using metallic arrays. Even more, he associated this behaviour to surface plasmon polaritons and suggested that devices, as optical sensors, can be designed based on this phenomenon. To understand the surface plasmon polaritons theory, classical theories will be studied and compared with it. Also, the composite diffracted evanescent waves - CDEW -, model, which is not the most accurate model in comparison with the surface plasmon polaritons, will be presented, in order to cover an important topic on the theoretical foundations. After it, the application of nanoantennas as a sensor is going to be analysed. Finally, stationary simulations for a 16-slit gold array were performed using COMSOL Multiphysics and they are going to be presented in order to observe the occurrence of EOT.

Resonant Optical Phenomena in Heterogeneous Plasmon Nanostructures of Noble Metals: A Review

The interaction of electromagnetic radiation with ordered and disordered arrays of noble metal nanoparticles, leading to the excitation of various modes of surface plasmon states in them, is analyzed. The dipole localized surface plasmon resonance in isolated nanoparticles and the influence of various size effects on its optical response are considered. The effect of dipole-dipole interaction between gold and silver nanoparticles on the optical properties of various nanosized and nanostructured objects is discussed. It is shown that both localized and delocalized (propagated) surface plasmon modes can be excited in composite gold and silver nanosystems, in particular, in porous films. The prospects for the practical application of nanostructures with arrays of gold and silver nanoparticles in sensor technology, surface-enhanced Raman spectroscopy, and modern optoelectronics are examined.

Using Chemiresistor Sensor Arrays to Test Petrol Station Groundwater Samples for Hydrocarbon Pollutants

Groundwater monitoring is a cumbersome and expensive process. Typically, once every three to six months a technician visits a site, collects water samples, and transports them to an analytical laboratory for testing. Not only is the testing expensive, but potentially catastrophic events could remain undetected for several months. A plausible alternative could be gold nanoparticle chemiresistors sensor arrays [1]. We have previously demonstrated that gold nanoparticle chemiresistors can operate in water irrespective of the salinity of the aqueous solution [2], and an array of these chemiresistors could discriminate between different complex mixtures of hydrocarbons such as gasoline, diesel, kerosene or crude oil dissolved in artificial seawater [3]. In addition, we have demonstrated that an array can identify BTEXN in the presence of 15 other structurally relevant hydrocarbons in laboratory-grade water. In the current study we investigate how feasible is it for these chemiresistor sensors to function in real groundwater samples.Using standard photolithography techniques, we fabricate our own interdigitated electrodes. (a) in the figure depicts the glass substrate and electrodes on which an array of 16 gold nanoparticle chemiresistor sensors are deposited on. Gold nanoparticle sensors can be very small, they consist of interdigitated microelectrodes just 0.3 mm wide as shown in (b) of the figure. The sensors can be given different affinities for different analytes by changing the chemistry of the molecules that coat the gold nanoparticles, (c) in the figure demonstrates a gold nanoparticle that is functionalised with 1-hexanethiol. This work focused on eight different sensor chemistries that impart chemical sensitivity and selectivity. Depending on the chemicals present in a water sample, each sensor in the array will change their electrical resistance to a different extent, providing a pattern of response or fingerprint.Groundwater samples were collected from 14 sites across western, central, and northern Sydney, Australia. From these sites, 48 samples were tested. Supplementary laboratory testing showed there was a variety of hydrocarbon contamination in the different samples. Though the testing order was randomised, generally the samples were tested in increasing order of known hydrocarbon contamination. Experiments were performed to determine the limit of detection in one groundwater sample, and the effect of the 48 different groundwater samples on the sensitivity of chemiresistor sensors.The limit of detection for benzene in a real groundwater sample was 70 µg/L. The sensor’s performance was determined to be even better for the other analytes: toluene was 30 µg/L, ethylbenzene was 11 µg/L, p-xylene was 13 µg/L, and naphthalene was 6 µg/L. BTEXN Limits of detection in groundwater are equivalent to the limits of detection previously determined when operating in laboratory-grade water.One type of chemiresistor sensor functionalised with 1-heptanethiol was especially resilient to 90% of the groundwater samples provided from across Sydney. On average, this sensor type experienced a negligible loss in sensitivity; it demonstrated an average normalised sensitivity decrease to the internal standard of only 6% after exposure to 48 different groundwater samples. For the remaining six other chemiresistor sensor types there was a range of normalised sensitivity losses between 15% – 58%.Gold nanoparticle chemiresistor sensors have been demonstrated to maintain their limits of detection to BTEXN analytes in real groundwater samples. Exposure to a variety of different groundwater samples from numerous sites across Sydney afforded valuable information on the performance of different chemiresistor sensor types. This feasibility study has laid a strong foundation for the next stage of work; developing a remotely deployed device that monitors the hydrocarbon ‘health’ of groundwater in a well, remotely and in real-time. 1. Ho, C.K., Robinson, A., Miller, D.R., Davis, M.J., Overview of sensors and needs for environmental monitoring, Sensors, 5 (2005) 4-37.2. Raguse, B., Chow, E., Barton, C.S., Wieczorek, L., Gold nanoparticle chemiresistor sensors: Direct sensing of organics in aqueous electrolyte solution, Analytical Chemistry, 79 (2007) 7333-7339.3. Cooper, J.S., Raguse, B., Chow, E., Hubble, L., Müller, K.H., Wieczorek, L., Gold nanoparticle chemiresistor sensor array that differentiates between hydrocarbon fuels dissolved in artificial seawater, Analytical Chemistry, 82 (2010) 3788-3795. Figure 1

Patterned Molecular Films of Alkanethiol and PLL-PEG on Gold-Silicate Interfaces: How to Add Functionalities while Retaining Effective Antifouling.

Spatial control of surface functionalization and interactions is essential for microarray-based analysis. This study reports the fabrication of two-dimensional molecular films with site-specific functionalities, forming microarrays at discrete locations. Arrays of microsized gold disks were produced on a silicate membrane using microfabrication. On these arrays, orthogonal self-assembly of molecules was performed that can specifically bind to gold or silicate. The gold array elements were functionalized with a range of alkanethiols and the silicate with polymeric poly-l-lysine-grafted-poly(ethylene glycol) (PLL-PEG). The surface functionalization on the gold disk array and the surrounding substrate was characterized at each step using X-ray photoelectron spectroscopy (XPS) to show that alkanethiols are specifically attached to the gold. PLL-PEG was used to provide resistance against nonspecific protein and cell adsorption and attached exclusively to the silicate. The effectiveness of the surface chemistry was validated by the selective self-assembly of a gold nanoparticle monolayer array on the gold regions. In a more sophisticated example, selective adhesion of MCF-7 cells to anti-EpCAM antibody modified gold areas of the gold-silicate surface was demonstrated to give a cell microarray. This study provides a general approach to fabricate chemical patterns on silicon-based devices with the convergence of microfabrication and material-specific surface modification, which may be useful to expand the functionalities and potential applications for patterned biomolecular films. Importantly, the ability to pattern surfaces with different surface chemistries is not limited to planar surfaces using this orthogonal surface-coupling approach.

Colorimetric aggregation assay based on array of gold and silver nanoparticles for simultaneous analysis of aflatoxins, ochratoxin and zearalenone by using chemometric analysis and paper based analytical devices.

A paper based sensor array ispresented to discriminate and determine five mycotoxins classified into three categories, namely aflatoxins, ochratoxins and zearalenone. The gold and silver nanoparticles, synthesized by three different reducing or capping agents, were employed as sensing elements of thefabricated device. These nanoparticles were poured onto hydrophilic circular zones embedded on the hydrophobic substrate. The response of the assay is dependent on the aggregation of nanoparticles for interaction with mycotoxins. Due to aggregation, the gold and silver nanoparticles changed to purple and brown, respectively. Color changes provide unique colorimetric signatures conducive to recognizing the type of mycotoxin, identifying its chemical structure, and finding the fungi that produce it. The discrimination ability of the assay was investigated by both supervised (linear discriminate analysis) and unsupervised (principle component analysis and hierarchical cluster analysis) pattern recognition methods. The assay was applied to the point of need determination of aflatoxin B1, aflatoxin G1, aflatoxin M1, ochratoxin A and zearalenone with a detection limit of 2.7, 7.3, 2.1, 3.3 and 7.0ng.mL-1, respectively. The fabricated device has highpotential of simultaneously determining the mycotoxins in pistachio, wheat, coffee and milk with the help of partial least square method. The root mean square errors for prediction of PLS model were 5.7, 5.2, 1.5, 7.2 and 2.9 for aflatoxin B1, aflatoxin G1, aflatoxin M1, ochratoxin A and zearalenone, respectively. Graphical abstractSchematic representation of paper based colorimetric sensor array based on gold and silver nanoparticles for both qualitative and quantitative analysis of aflatoxins, ochratoxin and zearalenone.

Gold alloy-based nanozyme sensor arrays for biothiol detection.

Biothiols play an important role in living cells and are associated with many diseases. Thus, it is necessary to develop a facile, cost-effective, and convenient analytical method for the detection of biothiols. Nanozymes are functional nanomaterials with enzymatic activities. Due to their unique advantages (e.g., low cost, high stability, and multifunctionality), nanozymes have been extensively used to construct sensing systems. Previous studies demonstrated colorimetric assays for biothiol detection because they could competitively inhibit the peroxidase-like activities of nanozymes. However, few studies were able to differentiate biothiols from each other. To address these challenges, herein, we first synthesized Au alloy nanozymes with better peroxidase-like activities than gold nanoparticles (AuNPs). Then, cross-reactive sensor arrays were constructed with three alloy nanozymes. Six typical biothiols (i.e., glutathione, cysteine, dithiothreitol, mercaptoacetic acid, mercaptoethanol, and mercaptosuccinic acid) were successfully detected and discriminated by the as-prepared nanozyme sensor arrays. Moreover, the practical application of the nanozyme sensor arrays was demonstrated by discriminating biothiols in serum successfully.

Correction: Gold alloy-based nanozyme sensor arrays for biothiol detection.

Correction for 'Gold alloy-based nanozyme sensor arrays for biothiol detection' by Junshu Lin et al., Analyst, 2020, .

Formation and optical response of self-assembled gold nanoparticle lattices on oxidized silicon synthesized using block copolymers

The authors report here on the optical response and extraction of the morphological properties of three sizes of self-assembled nearly hexagonal arrays of gold (Au) nanoparticles (NPs), deposited on the native oxide on c-Si. The arrays were prepared by templating gold NP growth with self-assembled cylindrically organized block copolymer thin films, with consecutive removal of the polymer matrix by plasma etching. The particle sizes were controlled by using block copolymers of different molecular weights when assembling the templates. The resulting gold nanostructures were characterized by scanning probe microscopy. Spectroscopic ellipsometry was used to record the optical response of the samples, and the modeling of the spectra and the extraction of morphological parameters were performed using a modification of the Bedeaux–Vlieger formalism implemented in GranFilm. The modeling issues upon the introduction of a thin intermediate (oxide) layer between the particle and the substrate are discussed in detail, and a solution to the model procedure is proposed. The particles were modeled as truncated oblate Au spheroids in a hexagonal lattice on the native oxide on c-Si. The model fit converged to a solution indicating that the particles present a low wetting of the native oxide substrate, with parameters describing the particles and lattice in good correspondence with AFM. The extended GranFilm model simulations are also supported by finite element modeling.