SERS and FDTD simulation of gold nanoparticles grafted on germanium wafer via galvanic displacement

Thermal Annealing Effect on Surface-Enhanced Raman Scattering of Gold Films Deposited on Liquid Substrates

We prepare metal films with various thicknesses on liquid substrates by thermal evaporation and investigate the annealing effect on these films. Gold films deposited on a silicone oil surface consist of a large number of branched aggregates, which contains plenty of gold nanoparticles. This characteristic morphology is mainly attributed to the isotropic and free-sustained liquid substrate. Thermal annealing results in the reintegration of nanoparticles; thus, the surface morphology and microstructure of gold films change significantly. The dependence of annealing conditions on the surface-enhanced Raman scattering performance of gold films is studied, in which gold films show favorable Raman activity when annealed at certain annealing temperature and the experimental results are verified by simulation analysis. The study on the optimal annealing temperature of surface-enhanced Raman scattering substrate will pave the way for the potential application of films deposited on liquid surfaces in microfluidics and enhanced Raman detection.

Wafer-scale Silver Nanodendrites with Homogeneous Distribution of Gold Nanoparticles for Biomolecules Detection

We report the fabrication and demonstrate the superior performance of robust, cost-effective, and biocompatible hierarchical Au nanoparticles (AuNPs) decorated Ag nanodendrites (AgNDs) on a Silicon platform for the trace-level detection of antibiotics (penicillin, kanamycin, and ampicillin) and DNA bases (adenine, cytosine). The hot-spot density dependence studies were explored by varying the AuNPs deposition time. These substrates’ potential and versatility were explored further through the detection of crystal violet, ammonium nitrate, and thiram. The calculated limits of detection for CV, adenine, cytosine, penicillin G, kanamycin, ampicillin, AN, and thiram were 348 pM, 2, 28, 2, 56, 4, 5, and 2 nM, respectively. The analytical enhancement factors were estimated to be ∼10⁷ for CV, ∼10⁶ for the biomolecules, ∼10⁶ for the explosive molecule, and ∼10⁶ for thiram. Furthermore, the stability of these substrates at different time intervals is being reported here with surface-enhanced Raman spectroscopy/scattering (SERS) data obtained over 120 days.

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Wafer-scale surface-enhanced Raman spectroscopy/scattering (SERS) substrate of Ag nanodendrites decorated with Au nanoparticles prepared

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Trace level detection of antibiotics achieved

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Versatility of these substrates demonstrated by detecting explosive, dye molecules

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Typical enhancement factors achieved were 10⁵–10⁷

SERS using two-photon polymerized nanostructures for mycotoxin detection

Improved chemical- and bio-sensing with Surface Enhanced Raman Spectroscopy (SERS) requires nanostuctures that can be flexibly designed and fabricated with different physical and optical properties. Here, we present nano-pillar arrays ranging from 200 nm to 600 nm as SERS substrates for mycotoxin detection that are fabricated by means of two-photon polymerization. We built a nominal shape and a voxel-based model for simulating the enhancement of the electric field of the nano-pillar arrays using the Finite-Difference Time-Domain (FDTD) method. A new model was built based on the Atomic Force Microscopy (AFM) data obtained from the fabricated nanostructures and introduced into a FDTD model. We demonstrated the enhancement behavior by measuring the Raman spectrum of Rhodamine B solutions. Both the simulations and experimental results suggest that the 200 nm nano-pillar array has the highest Enhancement Factor (EF). Besides, we determined the limit of detection of the 200 nm pillar array by performing Raman measurements on Rhodamine B solutions with different concentrations. The detection limit of our 200 nm nano-pillar array is 0.55 μM. Finally we discriminated 1 ppm deoxynivalenol and 1.25 ppm fumonisin b1 in acetonitrile solutions by our SERS substrate in combination with principal component analysis. This versatile approach for SERS substrates fabrication gives new opportunities for material characterization in chemical and biological applications.

Nano-pillar arrays are presented ranging from 200 nm to 600 nm as SERS substrates for mycotoxin detection, fabricated by two-photon polymerization. This versatile approach gives new opportunities for material characterization in chemical and biological applications.

Discrimination of Nosiheptide Sources with Plasmonic Filters

Bacteria identification plays a vital role in the field of clinical diagnosis, food industry, and environmental monitoring, which is in great demand of point of care detection methods. In this paper, in order to discriminate the source of nosiheptide product, a plasmonic filter was fabricated to filtrate, capture and identify Streptomycete spores with Surface enhanced Raman Scattering (SERS). Since the plasmonic filter was derived from self-assembled photonic crystal coated with silver, the plasmonic "hot spots" on the filter surface was distributed evenly in a fare good density and the SERS enhancement factor was 7.49 × 10⁷. With this filter, a stain- and PCR-free detection was realized with only 5 μL sample solution and 5 min in a manner of "filtration and measure". Comparison to traditional Gram stain method and silver-plated nylon filter membrane, the plasmonic filter showed good sensitivity and efficiency in the discrimination of nosiheptide prepared with chemical and biological methods. It is anticipated that this simple SERS detection method with plasmonic filter has promising potentials in food safety, environmental, or clinical applications.