A surface‐enhanced Raman scattering‐based mapping technique is reported for the highly sensitive and reproducible analysis of multiple mycotoxins. Raman images of three mycotoxins, ochratoxin A ...(OTA), fumonisin B (FUMB), and aflatoxin B1 (AFB1) are obtained by rapidly scanning the surface‐enhanced Raman scattering (SERS) nanotags‐anchoring mycotoxins captured on a nanopillar plasmonic substrate. In this system, the decreased gap distance between nanopillars by their leaning effects as well as the multiple hot spots between SERS nanotags and nanopillars greatly enhances the coupling of local plasmonic fields. This strong enhancement effect makes it possible to perform a highly sensitive detection of multiple mycotoxins. In addition, the high uniformity of the densely packed nanopillar substrate minimizes the spot‐to‐spot fluctuations of the Raman peak intensity in the scanned area when Raman mapping is performed. Consequently, this makes it possible to gain a highly reproducible quantitative analysis of mycotoxins. The limit of detections (LODs) are determined to be 5.09, 5.11, and 6.07 pg mL−1 for OTA, FUMB, and AFB1, and these values are approximately two orders of magnitude more sensitive than those determined by the enzyme‐linked immunosorbent assays. It is believed that this SERS‐based mapping technique provides a facile tool for the sensitive and reproducible quantification of various biotarget molecules.
Surface‐enhanced Raman scattering‐based mapping technique on 3D nanopillar substrates can be used for the highly sensitive and reproducible detection of multiple mycotoxins. Decreased gap distance between adjacent nanopillars by their leaning effects toward the nearest neighbors enhances the coupling of local plasmonic fields. The high uniformity of the densely packed nanopillars improves the reproducibility of the Raman signal intensity in the scanning area.
Electromagnetic enhancement effects through localized surface plasmon resonance considerably amplify the intensity of incident light when molecules are positioned in the vicinity of miniscule ...nanogaps. The aggregation of plasmonic nanoparticles synthesized using bottom‐up methods has been extensively used to generate hot spots in solutions. These methods assist in obtaining non‐periodic plasmonic signals, because the realization of uniform nanogaps through particle aggregation is difficult. Nanostructured substrates with gaps of 20–100 nm have also been fabricated using the top‐down approach. However, the fabrication of smaller nanogap templates using these methods is difficult owing to high costs and low throughput. Therefore, a nanodimple array internalized with AuNPs is developed in this study to mitigate the challenges encountered in the bottom‐up and top‐down approaches. Precise nanogaps are generated by regularly internalizing AuNPs in the cavities of nanodimples through DNA hybridization. Simulations of the electric field distribution indicate that the incorporation of 80 nm‐sized AuNPs into a curved nanodimpled Au substrate generate high‐density volumetric hot spots within a detection volume, and result in a high plasmonic enhancement factor of 8.25 × 107. The tremendous potential of the proposed plasmonic platform as an SERS‐based biomedical diagnostic device is also verified.
Development of a sensitive surface‐enhanced Raman scattering detection platform, in which 80 nm‐sized gold nanoparticles are uniformly distributed in curved cavities of a nanodimpled Au substrate through DNA hybridization is presented.
Positioning probe molecules at electromagnetic hot spots with nanometer precision is required to achieve highly sensitive and reproducible surface‐enhanced Raman spectroscopy (SERS) analysis. In this ...article, molecular positioning at plasmonic nanogaps is reported using a high aspect ratio (HAR) plasmonic nanopillar array with a controlled surface energy. A large‐area HAR plasmonic nanopillar array is generated using a nanolithography‐free simple process involving Ar plasma treatment applied to a smooth polymer surface and the subsequent evaporation of metal onto the polymer nanopillars. The surface energy can be precisely controlled through the selective removal of an adsorbed self‐assembled monolayer of low surface‐energy molecules prepared on the plasmonic nanopillars. This process can be used to tune the surface energy and provide a superhydrophobic surface with a water contact angle of 165.8° on the one hand or a hydrophilic surface with a water contact angle of 40.0° on the other. The highly tunable surface wettability is employed to systematically investigate the effects of the surface energy on the capillary‐force‐induced clustering among the HAR plasmonic nanopillars as well as on molecular concentration at the collapsed nanogaps present at the tops of the clustered nanopillars.
Molecular concentration at the electromagnetic hot spots is achieved using surface‐enhanced Raman spectroscopy (SERS) substrates with controlled surface energies. The surface energies of the high aspect ratio plasmonic nanostructures are precisely controlled via the selective removal of low‐surface energy chemicals that is chemisorbed onto the structures.
Plasmonic biosensors have demonstrated superior performance in detecting various biomolecules with high sensitivity through simple assays. Scaled‐up, reproducible chip production with a high density ...of hotspots in a large area has been technically challenging, limiting the commercialization and clinical translation of these biosensors. A new fabrication method for 3D plasmonic nanostructures with a high density, large volume of hotspots and therefore inherently improved detection capabilities is developed. Specifically, Au nanoparticle‐spiked Au nanopillar arrays are prepared by utilizing enhanced surface diffusion of adsorbed Au atoms on a slippery Au nanopillar arrays through a simple vacuum process. This process enables the direct formation of a high density of spherical Au nanoparticles on the 1 nm‐thick dielectric coated Au nanopillar arrays without high‐temperature annealing, which results in multiple plasmonic coupling, and thereby large effective volume of hotspots in 3D spaces. The plasmonic nanostructures show signal enhancements over 8.3 × 108‐fold for surface‐enhanced Raman spectroscopy and over 2.7 × 102‐fold for plasmon‐enhanced fluorescence. The 3D plasmonic chip is used to detect avian influenza‐associated antibodies at 100 times higher sensitivity compared with unstructured Au substrates for plasmon‐enhanced fluorescence detection. Such a simple and scalable fabrication of highly sensitive 3D plasmonic nanostructures provides new opportunities to broaden plasmon‐enhanced sensing applications.
New 3D plasmonic nanostructures composed of spherical Au nanoparticles on Au nanopillars with a 1 nm‐thick uniform spacer layer are developed. Direct self‐assembly of plasmonic nanoparticle‐spiked nanopillar arrays is enabled by enhanced surface diffusion of adsorbed Au atoms, and selective nucleation and growth of Au atoms on the 3D plasmonic surface with a low surface energy.
Abstract
Microplastics (MPs) are present not only in the environment but also in drinking water, food, and consumer products. These MPs being toxic, carcinogenic, endocrine disrupting, and genetic ...risk creators cause several diseases. Despite various approaches, the development of onsite applicable, facile, and quick MP detection methods is still challenging. Here, 3D‐plasmonic gold nanopocket (3D‐PGNP) nanoarchitecture is formed on a paper substrate for simultaneous MP filtration and detection. The paper‐based 3D‐PGNP is integrated with a syringe filter device, and then, MP‐containing solutions are injected through the syringe. Subsequent detection of the MPs using the surface‐enhanced Raman scattering (SERS) successfully identifies the MPs without pretreatment. The interface and volumetric hotspot generation of 3D‐PGNP around the captured MPs significantly improves the sensitivity, which is confirmed by finite‐difference time‐domain simulation. Then, the SERS mapping images obtained from a portable Raman spectrometer are transformed into digital signals via machine learning (ML) technique to identify and quantify the MP distribution. The developed SERS‐ML‐based MP detection method is applied for mixture MPs and for real matrix samples, demonstrating that the method provides improved accuracy. This system is expected to be used for various MPs detection and for environmentally hazardous substances, such as bacteria, viruses, and fungi.
We report the production of a two-dimensional (2D) heterostructured gas sensor. The gas-sensing characteristics of exfoliated molybdenum disulfide (MoS2) connected to interdigitated metal electrodes ...were investigated. The MoS2 flake-based sensor detected a NO2 concentration as low as 1.2 ppm and exhibited excellent gas-sensing stability. Instead of metal electrodes, patterned graphene was used for charge collection in the MoS2-based sensing devices. An equation based on variable resistance terms was used to describe the sensing mechanism of the graphene/MoS2 device. Furthermore, the gas response characteristics of the heterostructured device on a flexible substrate were retained without serious performance degradation, even under mechanical deformation. This novel sensing structure based on a 2D heterostructure promises to provide a simple route to an essential sensing platform for wearable electronics.
The reverse transcription-polymerase chain reaction (RT-PCR) method has been adopted worldwide to diagnose severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Although this method has good ...sensitivity and specificity, there is a need to develop a more rapid diagnostic technology, given the virus’s rapid spread. However, the RT-PCR method takes a long time to diagnose SARS-CoV-2 because of the required thermocycling steps. Therefore, we developed a surface-enhanced Raman scattering (SERS)-PCR detection method using an AuNP-internalized Au nanodimple substrate (AuNDS) to shorten the diagnosis time by reducing the number of thermocycling steps needed to amplify the DNA. For the representative target markers, namely, the envelope protein (E) and RNA-dependent RNA polymerase (RdRp) genes of SARS-CoV-2, 25 RT-PCR thermocycles are required to reach a detectable threshold value, while 15 cycles are needed for magnetic bead-based SERS-PCR when the initial DNA concentration was 1.00× 105 copies/μL. However, only 8 cycles are needed for the AuNDS-based SERS-PCR. The corresponding detectable target DNA concentrations were 3.36 × 1012, 3.28 × 109, and 2.56 × 107 copies/μL, respectively. Therefore, AuNDS-based SERS-PCR is seen as being a new molecular diagnostic platform that can shorten the time required for the thermocycling steps relative to the conventional RT-PCR.
•A SERS-PCR assay platform using an Au nanodimple substrate was developed.•This platform can notably shorten diagnosis time for SARS-CoV-2 using RT-PCR.•SERS-PCR is regarded as a new molecular diagnostic platform for SARS-CoV-2.
A wearable surface-enhanced Raman scattering (SERS) sensor has been developed as a patch type to utilize as a molecular sweat sensor. Here, the SERS patch sensor is designed to comprise a ...sweat-absorbing layer, which is an interface to the human skin, an SERS active layer, and a dermal protecting layer that prevents damage and contaminations. A silk fibroin protein film (SFF) is a basement layer that absorbs aqueous solutions and filtrates molecules larger than the nanopores created in the β-sheet matrix of the SFF. On the SFF layer, a plasmonic silver nanowire (AgNW) layer is formed to enhance the Raman signal of the molecules that penetrated through the SERS patch in a label-free method. A transparent dermal protecting layer (DP) allows laser penetration to the AgNW layer enabling Raman measurement through the SERS patch without its detachment from the surface. The molecular detection capability and time-dependent absorption properties of the SERS patch are investigated, and then, the feasibility of its use as a wearable drug detection sweat sensor is demonstrated using 2-fluoro-methamphetamine (2-FMA) on the human cadaver skin. It is believed that the developed SERS patch can be utilized as various flexible and wearable biosensors for healthcare monitoring.
Surface‐enhanced Raman scattering (SERS) is one of the most promising methods to detect small molecules for point‐of‐care analysis as it is rapid, nondestructive, label‐free, and applicable for ...aqueous samples. Here, microgels containing highly concentrated yet evenly dispersed gold nanoparticles are designed to provide SERS substrates that simultaneously achieve contamination‐free metal surfaces and high signal enhancement and reproducibility. With capillary microfluidic devices, water‐in‐oil‐in‐water (W/O/W) double‐emulsion drops are prepared to contain gold nanoparticles and hydrogel precursors in innermost drop. Under hypertonic condition, water is selectively pumped out from the innermost drops. Therefore, gold nanoparticles are gently concentrated without forming aggregates, which are then captured by hydrogel matrix. The resulting microgels have a concentration of gold nanoparticles ≈30 times higher and show Raman intensity two orders of magnitude higher than those with no enrichment. In addition, even distribution of gold nanoparticles results in uniform Raman intensity, providing high signal reproducibility. Moreover, as the matrix of the microgel serves as a molecular filter, large adhesive proteins are rejected, which enables the direct detection of small molecules dissolved in the protein solution. It is believed that this advanced SERS platform is useful for in situ detection of toxic molecules in complex mixtures such as biological fluids, foods, and cosmetics.
Surface‐enhanced Raman scattering (SERS)‐active microgels are designed by uniformly loading highly concentrated gold nanoparticles in microgel using microfluidic technology. High density and uniform distribution of gold nanoparticles enhance SERS activity and secure signal reproducibility. Moreover, the hydrogel matrix enables the direct detection of small target molecules without interruption from large adhesives. This class of SERS substrates is promising for point‐of‐care analysis of complex samples.
Background and Aim
This study aimed to investigate the relationship between hepatic steatosis (HS) evaluated by biopsy and visceral adiposity assessed by computed tomography in lean living liver ...donor candidates and to determine the risk factors for lean non‐alcoholic fatty liver disease (NAFLD).
Methods
This retrospective study included 250 lean (body mass index, < 23 kg/m2) potential living liver donors (mean age, 31.1 ± 8.6 years; 141 men) who had undergone liver biopsy and abdominal computed tomography between 2017 and 2018. Anthropometry, laboratory parameters, body composition, and the degree of HS were evaluated. Logistic regression was used to identify independent predictors of lean NAFLD.
Results
The visceral fat area (VFA) was significantly correlated with the degree of HS in men (r = 0.408; P < 0.001) and women (r = 0.360; P < 0.001). The subcutaneous fat area was significantly correlated with the degree of HS in men (r = 0.398; P < 0.001), but not in women. The skeletal muscle area did not correlate with the degree of HS in either men or women. In the multivariable logistic regression analysis, the VFA (odds ratio OR, 1.028; 95% confidence interval CI, 1.013–1.044; P < 0.001) and subcutaneous fat area (OR, 1.016; 95% CI, 1.004–1.028; P = 0.009) were independent risk factors for lean NAFLD in men, and the VFA (OR, 1.036; 95% CI, 1.013–1.059; P = 0.002) was an independent risk factor for lean NAFLD in women.
Conclusions
The severity of non‐alcoholic fatty liver was positively correlated with visceral fat accumulation in a lean Asian population. Visceral adiposity may be a risk factor for lean NAFLD in potential living liver donors.
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