Centrifugation-induced assembly of dense hotspots based SERS substrate for enhanced Raman scattering and quenched fluorescence

Thermal-Assisted Multiscale Patterning of Nonplanar Colloidal Nanostructures for Multi-Modal Anti-Counterfeiting

Nanotransfer printing of colloidal nanoparticles is a promising technique for the fabrication of functional materials and devices. However, patterning nonplanar nanostructures pose a challenge due to weak adhesion from the extremely small nanostructure-substrate contact area. Here, the study proposes a thermal-assisted nonplanar nanostructure transfer printing (NP-NTP) strategy for multiscale patterning of polystyrene (PS) nanospheres. The printing efficiency is significantly improved from ≈3.1% at low temperatures to ≈97.2% under the glass transition temperature of PS. Additionally, the arrangement of PS nanospheres transitioned from disorder to long-range order. The mechanism of printing efficiency enhancement is the drastic drop of Young's modulus of nanospheres, giving rise to an increased contact area, self-adhesive effect, and inter-particle necking. To demonstrate the versatility of the NP-NTP strategy, it is combined with the intaglio transfer printing technique, and multiple patterns are created at both micro and macro scales at a 4-inch scale with a resolution of ≈2757 pixels per inch (PPI). Furthermore, a multi-modal anti-counterfeiting concept based on structural patterns at hierarchical length scales is proposed, providing a new paradigm of imparting multiscale nanostructure patterning into macroscale functional devices.

Graphene nanospacer layer modulated multilayer composite structures of precious metals and their SERS performance

Graphene(G)-noble metal-ZnO hybrid systems were developed as highly sensitive and recyclable surface enhanced Raman scattering (SERS) platforms, in which ultrathin graphene of varying thickness was embedded between two metallic layers on top of a ZnO layer. Due to the multi-dimensional plasmonic coupling effect, the Au/G/Ag@ZnO multilayer structure possessed ultrahigh sensitivity with the detection limit of Rhodamine 6 G (R6G) as low as 1.0×10-13 mol/L and a high enhancement factor of 5.68×107. Both experimental and simulation results showed that graphene films could significantly regulate the interlayer plasmon resonance coupling strength, and single-layer graphene had the best interlayer regulation effect. Additionally, the SERS substrate structure prepared through physical methods exhibited high uniformity, the graphene component of the substrate possessed excellent molecular enrichment ability and silver oxidation inhibition characteristics, resulting in a substrate with high stability and exceptional reproducibility. The signal change was less than 15%. Simultaneously, due to the excellent photocatalytic performance of the low-cost and wide-band-gap semiconductor material ZnO, the SERS substrate exhibited exceptional reusability. Even after five cycles of adsorption-desorption, the SERS performance remained stable and maintained a reliable detection limit. The study introduced a novel approach to creating multilayer composite SERS substrates that exhibited exceptional performance, offering a new analytical tool with high sensitivity, stability, and reusability.

Electric field-induced assembly of Au-Ag alloy nanoparticles into nano-reticulation for ultrasensitive SERS

This paper discusses a method for assembling Au-Ag alloy nanoparticles (NPs) using direct current (DC) electric field to fabricate highly active SERS substrates. Different nanostructures could be obtained by regulating the intensity and action time of DC electric field. Under the condition of 5mA*10 min, we obtained Au-Ag alloy nano-reticulation (ANR) substrate with excellent SERS activity (Enhancement factor on order of magnitude of 10⁶). ANR substrate has excellent SERS performance due to the resonance matching between its LSPR mode and excitation wavelength. The uniformity of the Raman signal on ANR is greatly improved than bare ITO glass. ANR substrate also has the ability to detect multiple molecules: ANR substrate can respectively detect Rh6G and CV molecules with a concentration as low as 10^-10 M and 10^-9 M and the Raman spectral intensity of the probe molecules on the surface of the ANR substrate has good linear correlation with the molecular concentration (R²> 0.95). In addition, ANR substrate can detect both thiram and aspartame (APM) molecules far below (thiram for 0.0024 ppm and APM for 0.0625 g/L) the safety standard, which demonstrate its practical application potential.

Hybrid Wetting Surface with Plasmonic Alloy Nanocomposites for Sensitive SERS Detection

In this paper, a hybrid wetting surface (HWS) with Au/Ag alloy nanocomposites was proposed for rapid, cost-effective, stable and sensitive SERS application. This surface was fabricated in a large area by facile electrospinning, plasma etching and photomask-assisted sputtering processes. The high-density 'hot spots' and rough surface from plasmonic alloy nanocomposites promoted the significant enhancement of the electromagnetic field. Meanwhile, the condensation effects induced by HWS further improved the density of target analytes at the SERS active area. Thus, the SERS signals increased ~4 orders of magnitude compared to the normal SERS substrate. In addition, the reproducibility, uniformity, as well as thermal performance of HWS were also examined by comparative experiments, indicating their high reliability, portability and practicability for on-site tests. The efficient results suggested that this smart surface had great potential to evolve as a platform for advanced sensor-based applications.

Solution Processed Photodetectors with PVK-WS2 Nanotube/Nanofullerene Organic-Inorganic Hybrid Films

Organic-inorganic hybrid photodetectors have attracted increased interest due to their exceptional properties, such as flexibility, transparency, and low cost for many promising applications. Low-dimensional tungsten disulfide (WS₂) nanostructures have outstanding electrical and optical properties, making them ideal candidates for ultrasensitive photodetector devices. In this paper, photodetectors were fabricated with hybrid thin films containing two different WS₂ nanomaterials, one-dimensional (1D) WS₂ nanotubes (WS₂-NTs) and a zero-dimensional (0D) WS₂ nanofullerene (WS₂-FLs) hybrid with poly(N-vinyl carbazole) (PVK). The electrical responses of the devices under visible-light illuminations were studied. The photodetector devices with 0D WS₂-FLs/PVK hybrid thin films have relatively higher sensitivity and stable voltage responses to visible light. Besides, the hybrid film shows a strong surface-enhanced Raman effect (SERS). These materials and new strategies enable the creation of a new class of processed photodetectors for practical applications.