3D silver metallized nanotrenches fabricated by nanoimprint lithography as flexible SERS detection platform

Oblique Deposited Ultra-Thin Silver Films on Polymer Gratings for Sensitive SERS Performance

A small amount of silver was obliquely deposited onto a polymer subwavelength grating to form a metasurface that comprised silver split-tubes. An ultra-thin silver film with a monitor-controlled thickness of 20 nm at the corner of each ridge of the grating provided the most sensitive surface-enhanced Raman scattering (SERS) measurements. An excitation laser beam that was incident from the substrate provided similar or better SERS enhancement than did the general configuration with the laser beam incident directly on the surface of the nanostructure. Near-field simulations were conducted to model the localized electric field enhancement and to quantify the SERS performance, demonstrating the effectiveness of this novel deposition method.

Surface-enhanced Raman scattering based on noble metal nanoassemblies for detecting harmful substances in food

Residues of harmful substances in food can severely damage human health. The content of these substances in food is generally low, making detection difficult. Surface-enhanced Raman scattering (SERS), based on noble metal nanomaterials, mainly gold (Au) and silver (Ag), has exhibited excellent capabilities for trace detection of various substances. Noble metal nanoassemblies, in particular, have extraordinary flexibility and tunable optical properties, which cannot be offered by single nanoparticles (NPs). These nanoassemblies, with their various morphologies synthesized using NPs through artificially induced self-assembly or template-driven preparation, can significantly enhance the local electric field and create "hot spots" due to the gaps between adjacent NPs. Consequently, the SERS properties of NPs become more prominent, leading to improved performance in the trace detection of various substances and detection limits that are considerably lower than the current relevant standards. Noble metal nanoassemblies show promising potential in ensuring food safety. This review discusses the synthesis methods and SERS properties of noble metal nanoassemblies and then concentrates on their application in detecting biotoxins, drug residues, illegal additives, and heavy metals. The study provides valuable references for further research into the application of nanoassemblies in food safety detection.

Nanoimprinted Plasmonic Crystals for Cost-Effective SERS Identification of Methylated DNAs

The development of a cost-effective and rapid assay technique for the identification of DNA methylation is one of the most crucial issues in the field of biomedical diagnosis because DNA methylation plays key roles in human health. The plasmonic crystal-based surface-enhanced Raman spectroscopy (SERS) technique is promising for the realization of such an assay method owing to its capability of generating uniformly enhanced electric fields to achieve high reproducibility and accuracy in SERS assays. However, the time and technical costs of fabricating plasmonic crystals are high, owing to the need for nanofabrication equipment. In this study, we developed nanoimprinted plasmonic crystals for cost-effective and rapid DNA methylation assays. Our plasmonic crystals identified methylated DNA with the 40-base pair adenomatous polyposis coli (APC) gene sequence, which is correlated with cell growth and cancer cells.

SERS-active substrates using DVD-R coated in silver thin films: A preliminary study for detection of commercial glyphosate

Glyphosate (GLP) is the herbicide with the highest level of global commercialization and historical use. Even though numerous studies have found this substance to be harmless, current research demonstrates that GLP might affect human health. For this reason, researcher efforts are concentrating on alternatives for analytical quantification, such as Surface Enhanced Raman Spectroscopy (SERS). In this work, a DVD-R@AgNPs SERS substrate was produced by the Cathodic Cage Plasma Deposition (CCPD) technique, which allowed a thin film layer deposition of silver nanoparticles (AgNPs) on the PC grating structure from Digital Video/Versatile Disc Recordable (DVD-R). Scanning Electron Microscopy with energy-dispersive X-ray spectroscopy was used to characterize the substrate and chemical changes on the surface after AgNPs deposition. The DVD-R@AgNPs substrate was used to detect standard crystal violet (CV), GLP, and RoundupTM GLP (GLP-RU) using Raman Spectroscopy. The CV was used as a control sample for SERS measurement, allowing the calculation of the substrate enhancement factor, which was in the order of ∼ 105. To evaluate the efficiency of the SERS substrate, the limit of detection was calculated and showed values of ∼ 10-10 mol/L for CV, 10-7 and 10-8 mol/L for GLP, and 10-6 mol/L for GLP-RU. Thus, the DVD-R@AgNPs SERS sensor is a low-cost substrate that analyzes traces of pesticides such as commercial GLP, demonstrating high SERS sensitivities and many applications.

Detection and Characterization of Nodularin by Using Label-Free Surface-Enhanced Spectroscopic Techniques

Nodularin (NOD) is a potent toxin produced by Nodularia spumigena cyanobacteria. Usually, NOD co-exists with other microcystins in environmental waters, a class of cyanotoxins secreted by certain cyanobacteria species, which makes identification difficult in the case of mixed toxins. Herein we report a complete theoretical DFT-vibrational Raman characterization of NOD along with the experimental drop-coating deposition Raman (DCDR) technique. In addition, we used the vibrational characterization to probe SERS analysis of NOD using colloidal silver nanoparticles (AgNPs), commercial nanopatterned substrates with periodic inverted pyramids (Klarite^TM substrate), hydrophobic Tienta^® SpecTrim^TM slides, and in-house fabricated periodic nanotrenches by nanoimprint lithography (NIL). The 532 nm excitation source provided more well-defined bands even at LOD levels, as well as the best performance in terms of SERS intensity. This was reflected by the results obtained with the Klarite^TM substrate and the silver-based colloidal system, which were the most promising detection approaches, providing the lowest limits of detection. A detection limit of 8.4 × 10^-8 M was achieved for NOD in solution by using AgNPs. Theoretical computation of the complex vibrational modes of NOD was used for the first time to unambiguously assign all the specific vibrational Raman bands.

Cheminformatics Study on Structural and Bactericidal Activity of Latest Generation β-Lactams on Widespread Pathogens

Raman spectra of oxacillin (OXN), carbenicillin (CBC), and azlocillin (AZL) are reported for the first time together with their full assignment of the normal modes, as calculated using Density Functional Theory (DFT) methods with the B3LYP exchange-correlation functional coupled to the 6-31G(d) and 6-311+G(2d,p) basis sets. Molecular docking studies were performed on five penicillins, including OXN, CBC, and AZL. Subsequently, their chemical reactivity and correlated efficiency towards specific pathogenic strains were revealed by combining frontier molecular orbital (FMO) data with molecular electrostatic potential (MEP) surfaces. Their bactericidal activity was tested and confirmed on a couple of species, both Gram-positive and Gram-negative, by using the disk diffusion method. Additionally, a surface-enhanced Raman spectroscopy (SERS)-principal component analysis (PCA)-based resistogram of A. hydrophila is proposed as a clinically relevant insight resulting from the synergistic cheminformatics and vibrational study on CBC and AZL.

Laser Fabrication of Highly Ordered Nanocomposite Subwavelength Gratings

Optical nanogratings are widely used for different optical, photovoltaic, and sensing devices. However, fabrication methods of highly ordered gratings with the period around optical wavelength range are usually rather expensive and time consuming. In this article, we present high speed single-step approach for fabrication of highly ordered nanocomposite gratings with a period of less than 355 nm. For the purpose, we used commercially available nanosecond-pulsed fiber laser system operating at the wavelength of 355 nm. One-dimensional and two-dimensional nanostructures can be formed by direct laser treatment with different scan speed and intensity. These structures exhibit not only dispersing, but also anisotropic properties. The obtained results open perspectives for easier mass production of polarization splitters and filters, planar optics, and also for security labeling.

Flexible surface-enhanced Raman scatting substrates: recent advances in their principles, design strategies, diversified material selections and applications

Surface-enhanced Raman scattering (SERS) is widely used as a powerful analytical technology in cutting-edge areas such as food safety, biology, chemistry, and medical diagnosis, providing ultra-fast, ultra-sensitive, nondestructive characterization and achieving ultra-high detection sensitivity even down to the single-molecule level. Development of Raman spectroscopy is strongly dependent on high-performance SERS substrates, which have long evolved from the early days of rough metal electrodes to periodic nanopatterned arrays building on solid supporting substrates. For rigid SERS substrates, however, their applications are restricted by sophisticated pretreatments for detecting solid samples with non-planar surfaces. It is therefore essential to reassert the principles in constructing flexible SERS substrates. Herein, we comprehensively review the state-of-the-art in understanding, preparing and using flexible SERS. The basic mechanisms behind the flexible SERS are briefly outlined, typical design strategies are highlighted and diversified selection of materials in preparing flexible SERS substrates are reviewed. Then the recent achievements of various interdisciplinary applications based on flexible SERS substrates are summarized. Finally, the challenges and perspectives for future evolution of flexible SERS and their applications are demonstrated. We propose new research directions focused on stimulating the real potential of SERS as an advanced analytical technique for commercialization.