Fabrication of SERS substrate using nanoporous anodic alumina template decorated by silver nanoparticles

A Novel 3D Hierarchical Plasmonic Functional Cu@Co3O4@Ag Array as Intelligent SERS Sensing Platform with Trace Droplet Rapid Detection Ability for Pesticide Residue Detection on Fruits and Vegetables

Rapid and effective detection of pesticide residues from complex surfaces of fruits and vegetables has important significance. Herein, we report a novel three-dimensional (3D) hierarchical porous functional surface-enhanced Raman scattering (SERS) substrate, which is fabricated by successive two-step hydrothermal synthesis strategy of silver nanoparticles (Ag NPs) and cobalt oxide nanowires (Co₃O₄ NWs) on the 3D copper foam framework as Cu@Co₃O₄@Ag-H. The strategy offers a new avenue for localized plasmonic materials distribution and construction, which exhibits better morphology regulation ability and SERS activity (or hotspots engineering) than physical spurring obtained Cu@Co₃O₄@Ag-S. The developed Cu@Co₃O₄@Ag-H possesses large surface area and rich hotspots, which contributes to the excellent SERS performance, including homogeneity (RSD of 7.8%), sensitivity (enhancement factor, EF of 2.24 × 10⁸) and stability. The Cu@Co₃O₄@Ag-H not only provides plenty of Electromagnetic enhancement (EM) hotspots but also the trace detection capability for droplet rapid sensing within 2 s. Cu@Co₃O₄@Ag-H substrate is further developed as an effective SERS sensing platform for pesticide residues detection on the surfaces of fruits and vegetables with excellent LOD of 0.1 ppm, which is lower than the most similar reported works. This work offers new potential for bioassay, disease POCT diagnosis, national security, wearable flexible devices, energy storage and other related fields.

Fabrication of homogeneous waffle-like silver composite substrate for Raman determination of trace chloramphenicol

Waffle-like anodized aluminum oxide homogeneously immobilized with Ag nanoparticles (AAO/Ag) is rationally designed and fabricated as surface-enhanced Raman scattering (SERS) substrate. The as-prepared SERS substrate is characterized with transmission electron microscope (TEM), scanning electron microscopy (SEM), UV-Vis spectrophotometer, and Fourier transform infrared spectrometer (FT-IR). The AAO/Ag substrate shows good uniformity of the Raman signals (RSD = 7.02%) due to waffle-like AAO supporting the well-dispersed Ag nanoparticles. For real application, the AAO/Ag substrate is used for rapid determination of chloramphenicol (CAP) in honey with low detection limit (4.0 × 10^-9 mol L^-1) and good linearity from 1.0 × 10^-5 to 1.0 × 10^-8 mol L^-1 based on the SERS peak at 1348 cm^-1. The better accumulation in the short pore path of AAO improves the target molecule approaching into the vicinity of hot spots of Ag nanoparticles. The high selectivity for CAP is attributed to the strong interaction between -NO₂ group in CAP and the composite substrate. Schematic representation of the preparation of SERS substrate, AAO₁₅₀/Ag₁₀-5 composite nanoparticles, and antibiotic determination.

Surface-enhanced Raman spectroscopy: benefits, trade-offs and future developments

Surface-enhanced Raman spectroscopy (SERS) is a vibrational spectroscopy technique with sensitivity down to the single molecule level that provides fine molecular fingerprints, allowing for direct identification of target analytes. Extensive theoretical and experimental research, together with continuous development of nanotechnology, has significantly broadened the scope of SERS and made it a hot research field in chemistry, physics, materials, biomedicine, and so on. However, SERS has not been developed into a routine analytical technique, and continuous efforts have been made to address the problems preventing its real-world application. The present minireview focuses on analyzing current and potential strategies to tackle problems and realize the SERS performance necessary for translation to practical applications.

Synthesis and Deposition of Ag Nanoparticles by Combining Laser Ablation and Electrophoretic Deposition Techniques

Silver nanostructured thin films have been fabricated on silicon substrate by combining simultaneously pulsed laser ablation in liquid (PLAL) and electrophoretic deposition (ED) techniques. The composition, topography, crystalline structure, surface topography, and optical properties of the obtained films have been studied by energy dispersive X-ray spectroscopy (EDS), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and UV-visible spectrophotometry. The coatings were composed of Ag nanoparticles ranging from a few to hundred nm. The films exhibited homogenous morphology, uniform appearance, and a clear localized surface plasmon resonance (LSPR) around 400 nm.

SERS activity with tenfold detection limit optimization on a type of nanoporous AAO-based complex multilayer substrate

Most of SERS applications are constricted by heterogeneous hotspots and aggregates of nanostructure, which result in low sensitivity and poor reproducibility of characteristic signals. This work intends to introduce SERS properties of a type of SERS-active substrate, Au-CuCl2-AAO, which is innovatively developed on a porous anodic alumina oxide (AAO) template. Spectral measuring results of Rhodamine 6G (R6G) on this substrate optimized by controlling morphology and gold thickness showed that enhancement factor (2.30 × 10(7)) and detection limit (10(-10) M) were both improved and represented better performance than its template AAO. Homogenous hot spots across the region of interest were achieved by scanning SERS intensity distribution for the band at 1505 cm(-1) in 5 × 5 μm(2) area. Furthermore, the promising SERS activity of the flower-patterned substrate was theoretically explained through simulation of the electromagnetic field distribution. In addition, this SERS substrate is proposed for applications within the field of chemical and biochemical analyses.

Multifunctional substrates of thin porous alumina for cell biosensors

We have fabricated anodic porous alumina from thin films (100/500 nm) of aluminium deposited on technological substrates of silicon/glass, and investigated the feasibility of this material as a surface for the development of analytical biosensors aiming to assess the status of living cells. To this goal, porous alumina surfaces with fixed pitch and variable pore size were analyzed for various functionalities. Gold coated (about 25 nm) alumina revealed surface enhanced Raman scattering increasing with the decrease in wall thickness, with factor up to values of approximately 10(4) with respect to the flat gold surface. Bare porous alumina was employed for micro-patterning and observation via fluorescence images of dye molecules, which demonstrated the surface capability for a drug-loading device. NIH-3T3 fibroblast cells were cultured in vitro and examined after 2 days since seeding, and no significant (P > 0.05) differences in their proliferation were observed on porous and non-porous materials. The effect on cell cultures of pore size in the range of 50-130 nm--with pore pitch of about 250 nm--showed no significant differences in cell viability and similar levels in all cases as on a control substrate. Future work will address combination of all above capabilities into a single device.

Generalized green synthesis of diverse LnF3–Ag hybrid architectures and their shape-dependent SERS performances

Diverse LnF₃–Ag hybrid architectures as substrates exhibit superior SERS performance and excellent detection sensibility for analytes.

Plasmon based biosensor for distinguishing different peptides mutation states

Periodic and reproducible gold nanocuboids with various matrix dimensions and with different inter-particle gaps were fabricated by means of top-down technique. Rhodamine 6G was used as a probe molecule to optimize the design and the fabrication of the cuboid nanostructures. The electric field distribution for the nanocuboids with varying matrix dimensions/inter-particle gap was also investigated. These SERS devices were employed as biosensors through the investigation of both myoglobin and wild/mutated peptides. The results demonstrate the probing and the screening of wild/mutated BRCA1 peptides, thus opening a path for the fabrication of simple and cheap SERS device capable of early detection of several diseases.

Fabrication of large-area ordered and reproducible nanostructures for SERS biosensor application

We propose a large-area SERS device with efficient fluorescence quenching capability. The substrate is based on anodic porous alumina templates with various pore size and wall thickness as small as 15 and 36 nm, respectively. The nano-patterned SERS substrate, with excellent control and reproducibility of plasmon-polaritons generation, shows very efficient enhanced Raman signal in the presence of intrinsically fluorescent molecules such as cresyl violet, rhodamine, and green fluorescent protein. This work demonstrates that, when the nanostructures are properly designed and fabricated, Raman and fluorescence spectroscopy can be used in combination in order to obtain complementary molecular informations. Theoretical simulation shows excellent agreement with the experimental findings. The enhancement factor is found to be 10(3)-10(4), with respect to flat gold surface when the molecules are supposed to be closely packed, with considerable fluorescence suppression, showing a promising disposable biosensor.

SERS effects in silver-decorated cylindrical nanopores

Optimization of pore diameter, the placement of nanoparticles, and the transmission of surface-enhanced Raman scattering (SERS) substrates are found to be very critical for achieving high SERS activity in porous alumina-membrane-based substrates. SERS substrates with a pore diameter of 355 nm incorporating silver nanoparticles show very high SERS activity with enhancement factors of 10(10) .