Highly Sensitive and Wide-Range Detection of Thiabendazole via Surface-Enhanced Raman Scattering Using Bimetallic Nanoparticle-Functionalized Nanopillars.

Thiabendazole (TBZ) is a benzimidazole; owing to its potent antimicrobial properties, TBZ is extensively employed in agriculture as a fungicide and pesticide. However, TBZ poses environmental risks, and excessive exposure to TBZ through various leakage pathways can cause adverse effects in humans. Therefore, a method must be developed for early and sensitive detection of TBZ over a range of concentrations, considering both human and environmental perspectives. In this study, we used silver nanopillar structures (SNPis) and Au@Ag bimetallic nanoparticles (BNPs) to fabricate a BNP@SNPi substrate. This substrate exhibited a broad reaction surface with significantly enhanced surface-enhanced Raman scattering hotspots, demonstrating excellent Raman performance, along with high reproducibility, sensitivity, and selectivity for TBZ detection. Ultimately, the BNP@SNPi substrate successfully detected TBZ across a wide concentration range in samples of tap water, drinking water, juice, and human serum, with respective limits of detection of 146.5, 245.5, 195.6, and 219.4 pM. This study highlights BNP@SNPi as a promising sensor platform for TBZ detection in diverse environments and contributes to environmental monitoring and bioanalytical studies.

Imaging moiré excited states with photocurrent tunnelling microscopy.

Moiré superlattices provide a highly tuneable and versatile platform to explore novel quantum phases and exotic excited states ranging from correlated insulators to moiré excitons. Scanning tunnelling microscopy has played a key role in probing microscopic behaviours of the moiré correlated ground states at the atomic scale. However, imaging of quantum excited states in moiré heterostructures remains an outstanding challenge. Here we develop a photocurrent tunnelling microscopy technique that combines laser excitation and scanning tunnelling spectroscopy to directly visualize the electron and hole distribution within the photoexcited moiré exciton in twisted bilayer WS2. The tunnelling photocurrent alternates between positive and negative polarities at different locations within a single moiré unit cell. This alternating photocurrent originates from the in-plane charge transfer moiré exciton in twisted bilayer WS2, predicted by our GW-Bethe-Salpeter equation calculations, that emerges from the competition between the electron-hole Coulomb interaction and the moiré potential landscape. Our technique enables the exploration of photoexcited non-equilibrium moiré phenomena at the atomic scale.

Ultra-sensitive SERS detection of perfluorooctanoic acid based on self-assembled p-phenylenediamine nanoparticle complex.

PFOA is a representative perfluorinated compound that is used as a surfactant in various industrial fields. However, because PFOA has severe side effects due to its strong toxicity, such as carcinogenesis, liver damage, and immune system damage, it is crucial to enable PFOA detection with high sensitivity. Herein, we developed a perfluorooctanoic acid (PFOA) surface-enhanced Raman scattering (SERS) sensor using self-assembled p-phenylenediamine (SAp-PD) nanoparticles and an Ag SERS substrate. For the ultra-sensitive detection of PFOA, we synthesized and optimized SAp-PD, which shows a decrease in SERS intensities when reacting with PFOA. Using the Ag nanograss SERS substrate, the change in intensity that resulted from the SAp-PD and PFOA reaction was amplified. Consequently, we detected the 1.28 pM (detection limit) of PFOA in distilled water. Moreover, PFOA molecules were successfully detected in samples of the PFOA-coated frying pan and rice extraction at concentrations up to 1.69 nM and 10.3 µM, respectively.

Asterias forbesi-Inspired SERS Substrates for Wide-Range Detection of Uric Acid.

Uric acid (UA), the final metabolite of purine, is primarily excreted through urine to maintain an appropriate concentration in the bloodstream. However, any malfunction in this process can lead to complications due to either deficiency or excess amount of UA. Hence, the development of a sensor platform with a wide-range detection is crucial. To realize this, we fabricated a surface-enhanced Raman spectroscopy (SERS) substrate inspired by a type of starfish with numerous protrusions, Asterias forbesi. The Asterias forbesi-inspired SERS (AF-SERS) substrate utilized an Au@Ag nanostructure and gold nanoparticles to mimic the leg and protrusion morphology of the starfish. This substrate exhibited excellent Raman performance due to numerous hotspots, demonstrating outstanding stability, reproducibility, and repeatability. In laboratory settings, we successfully detected UA down to a concentration of 1.16 nM (limit of detection) and demonstrated selectivity against various metabolites. In the experiments designed for real-world application, the AF-SERS substrate detected a broad range of UA concentrations, covering deficiencies and excesses, in both serum and urine samples. These results underscore the potential of the developed AF-SERS substrate as a practical detection platform for UA in real-world applications.

Detection of Cd2+ and Pb2+ using amyloid oligomer-reduced graphene oxide composite.

Heavy metal ions are toxic to humans and can further interact with amyloid in the human body to produce amyloid plaques, which disrupt neurotransmitter function and are linked to Alzheimer's and Parkinson's diseases. In this study, we developed an amyloid oligomer-reduced graphene oxide composite (AOrGOC) electrochemical sensor for effective heavy metal ion detection based on square-wave anodic stripping voltammetry. The reactivity between amyloids and heavy metal ions was studied by analyzing the stripping current for different amyloids (lysozyme, bovine serum albumin, and ß-lactoglobulin) and amyloid growth types (monomers, oligomers, and fibrils). Reduced graphene oxide was used to improve the sensitivity of the sensor. The AOrGOC sensor exhibited the detection limits of 86.0 and 9.5 nM for Cd2+ and Pb2+, respectively, and selectively detected Cd2+ and Pb2+ over other heavy metal ions. The AOrGOC sensor also detected Cd2+ and Pb2+ in human plasma, thus exhibiting its potential as a biosensor. This study not only promoted our fundamental understanding of amyloids and the detection of heavy metal ions using amyloids, but also provided valuable insights into amyloid-based electrochemical sensors.

Enhanced thermoelectric performance of defect engineered monolayer graphene.

We propose a method of improving the thermoelectric properties of graphene using defect engineering through plasma irradiation and atomic layer deposition (ALD). We intentionally created atomic blemishes in graphene by oxygen plasma treatment and subsequently healed the atomistically defective places using Pt-ALD. After healing, the thermal conductivity of the initially defective graphene increased slightly, while the electrical conductivity and the square of the Seebeck coefficient increased pronouncedly. The thermoelectric figure of merit of the Pt-ALD treated graphene was measured to be over 4.8 times higher than the values reported in the literature. We expect that our study could provide a useful guideline for the development of graphene-based thermoelectric devices.

Bio-inspired Ag nanovilli-based sandwich-type SERS aptasensor for ultrasensitive and selective detection of 25-hydroxy vitamin D3.

Vitamin D has been identified as an essential biomarker for various diseases such as rheumatoid arthritis, cancer, and cardiovascular diseases. Recently, many reports have demonstrated a potential link between vitamin D and systemic infections, including coronavirus disease 2019. The villi of the small intestine increase the surface area of the intestinal walls, demonstrating exceptionally efficient absorption of nutrients in the lumen and adding digestive secretions. In this study, based on the villi structure, we developed a bio-inspired silver nanovilli-based sandwich-type surface enhanced Raman scattering aptasensor for the ultrasensitive and selective detection of 25-hydroxy vitamin D3. The densely packed nanovilli structure enhanced the Raman signal, forming hotspots owing to its large surface area. Using experiments and electromagnetic simulations, we optimized the nanovilli structure as a SERS sensor. The sandwich-type aptasensor was designed using an aptamer and 4-Phenyl-1,2,4-triazoline-3,5-dione-methylene blue complex. The nanovilli-based aptasensor could sensitively detect various concentrations of 25-hydroxy vitamin D3, ranging from those found in deficient to excess conditions. The detection limit of the nanovilli-based sandwich-type aptasensor for 25-hydroxy vitamin D3 was 0.001 ng/mL, which is much lower than the deficiency concentration, and was detectable even in the human serum. In addition, our proposed sensor exhibited good repeatability (17.76%) and reproducibility (7.47%). Moreover, the nanovilli-based sandwich-type SERS aptasensor could selectively distinguish 25-hydroxy vitamin D3 from other vitamins. The silver nanovilli-based sandwich-type surface enhanced Raman scattering aptasensor opens a new avenue for the development of a bio-inspired vitamin-sensing platform.

Wide-range direct detection of 25-hydroxyvitamin D3 using polyethylene-glycol-free gold nanorod based on LSPR aptasensor.

Vitamin D is associated with various diseases such as obesity, digestive problems, osteoporosis, depression, and infections, which has emerged as an interest in public healthcare. Recently, vitamin D has received more attention because of the potential implication with coronavirus disease 2019. In this study, we developed a localized surface plasmon resonance (LSPR) aptasensor based on polyethylene-glycol(PEG)-free gold nanorods (AuNRs) for the wide-range and direct detection of 25-hydroxyvitamin D3. The surfactant on AuNRs was removed by exchanging with polystyrene sulfonate (PSS) instead of PEG then the PSS was exchanged with citrate. By exchanging the stabilizer of AuNRs from PEG to PEG-free (i.e., citrate), the sensing efficiency of LSPR aptasensor was significantly improved. Additionally, LSPR aptasensor was functionalized with aptamer and blocking agent to enhance the sensing performance. The LSPR aptasensor achieved the direct, highly sensitive, and selective detection of 25-hydroxyvitamin D3 over a wide concentration range (0.1-105 ng/mL), with a limit of detection of 0.1 ng/mL. This detection range included the concentration of vitamin D from deficiency to excess. The PEG-free AuNR-based LSPR aptasensor affords a new avenue for the development of robust sensing technology for vitamins.

Innocuous, Highly Conductive, and Affordable Thermal Interface Material with Copper-Based Multi-Dimensional Filler Design.

Thermal interface materials (TIMs), typically composed of a polymer matrix with good wetting properties and thermally conductive fillers, are applied to the interfaces of mating components to reduce the interfacial thermal resistance. As a filler material, silver has been extensively studied because of its high intrinsic thermal conductivity. However, the high cost of silver and its toxicity has hindered the wide application of silver-based TIMs. Copper is an earth-abundant element and essential micronutrient for humans. In this paper, we present a copper-based multi-dimensional filler composed of three-dimensional microscale copper flakes, one-dimensional multi-walled carbon nanotubes (MWCNTs), and zero-dimensional copper nanoparticles (Cu NPs) to create a safe and low-cost TIM with a high thermal conductivity. Cu NPs synthesized by microwave irradiation of a precursor solution were bound to MWCNTs and mixed with copper flakes and polyimide matrix to obtain a TIM paste, which was stable even in a high-temperature environment. The cross-plane thermal conductivity of the copper-based TIM was 36 W/m/K. Owing to its high thermal conductivity and low cost, the copper-based TIM could be an industrially useful heat-dissipating material in the future.

Bioinspired Micro Glue Threads Fabricated by Liquid Bridge-to-Solidification as an Effective Sensing Platform.

Spiders synthesize their web using a liquid bridge-to-solidification mechanism at the end of their glands. Inspired by this process, in this work, we fabricated micro-glue threads (µGTs, polymer microwires) by a simple "pinch and spread" process using just two fingertips. The µGTs exhibited excellent tensile strength (∼50 GPa), comparable to those of spider silk and biological fibers. The chemical, physical, and mechanical properties of the µGTs were investigated, and it was confirmed that the thickness of the µGTs could be controlled by ethanol treatment in varying concentrations. Moreover, electrically conductive µGTs were easily fabricated by simply mixing them with various nanomaterials such as gold nanoparticles, zinc oxide nanowires, and reduced graphene oxide (rGO). Interestingly, the conductive µGTs, fabricated using rGO, exhibited remarkable electrical conductivity (0.45 µS) compared to those fabricated using other materials. The conductive µGTs are applicable not only to NO2 gas sensing but also as electrical fuselike materials that melt when the humidity increases. Collectively, the results present µGTs as cost-effective, simple, and versatile materials, which enables their application in a variety of sensors.

Formation of Interstitial Hot-Spots Using the Reduced Gap-Size between Plasmonic Microbeads Pattern for Surface-Enhanced Raman Scattering Analysis.

To achieve an effective surface-enhanced Raman scattering (SERS) sensor with periodically distributed "hot spots" on wafer-scale substrates, we propose a hybrid approach combining physical nano-imprint lithography and a chemical deposition method to form a silver microbead array. Nano-imprint lithography (NIL) can lead to mass-production and high throughput, but is not appropriate for generating strong "hot-spots." However, when we apply electrochemical deposition to an NIL substrate and the reaction time was increased to 45 s, periodical "hot-spots" between the microbeads were generated on the substrates. It contributed to increasing the enhancement factor (EF) and lowering the detection limit of the substrates to 4.40 × 106 and 1.0 × 10-11 M, respectively. In addition, this synthetic method exhibited good substrate-to-substrate reproducibility (RSD < 9.4%). Our research suggests a new opportunity for expanding the SERS application.