Using a simple two step fabrication process substrates with a large and uniform Raman enhancement, based on flexible free standing nanopillars can be manufactured over large areas using readily ...available silicon processing equipment.
Centrifugal microfluidics has attracted much interest from academia as well as industry, since it potentially offers solutions for affordable, user-friendly and portable biosensing. A wide range of ...so-called fluidic unit operations, e.g. mixing, metering, liquid routing, and particle separation, have been developed and allow automation and integration of complex assay protocols in lab-on-a-disc systems. Besides liquid handling, the detection strategy for reading out the assay is crucial for developing a fully integrated system. In this review, we focus on biosensors and readout methods for the centrifugal microfluidics platform and cover optical as well as mechanical and electrical detection principles.
There is an increasing demand for rapid, sensitive, and low cost analytical methods to routinely screen antibiotic residues in food products. Conventional detection of antibiotics involves sample ...preparation by liquid–liquid or solid-phase extraction, followed by analysis using liquid chromatography–mass spectrometry (LC-MS), capillary electrophoresis (CE), or gas chromatography (GC). The process is labor-intensive, time-consuming, and expensive. In this study, we developed a new analytical method that combines magnetic molecularly imprinted polymer (MMIP)-based sample preparation with surface-enhanced Raman spectroscopy (SERS)-based detection for quantitative analysis of cloxacillin in pig serum. MMIP microspheres were synthesized using a core–shell technique. The large loading capacity and high selectivity of the MMIP microspheres enabled efficient extraction of cloxacillin, while the magnetically susceptible characteristics greatly simplified sample handling procedures. Low cost and robust SERS substrates consisting of vertical gold capped silicon nanopillars were fabricated and employed for the detection of cloxacillin. Quantitative SERS was achieved by normalizing signal intensities using an internal standard. By coherently combining MMIP extraction and silicon nanopillar-based SERS biosensor, good sensitivity toward cloxacillin was achieved. The detection limit was 7.8 pmol. Cloxacillin recoveries from spiked pig plasma samples were found to be more than 80%.
Robust, macroscopically uniform, and highly sensitive substrates for surface‐enhanced Raman spectroscopy (SERS) are fabricated using wafer‐scale block copolymer lithography. The substrate consists of ...gold nanoparticles that can slide and aggregate on dense and recyclable alumina/silicon nanohoodoos. Hot‐spot engineering is conducted to maximize the SERS performance of the substrate. The substrate demonstrates remarkably large surface‐averaged SERS enhancements, greater than 107 (>108 in hot spots), with unrivalled macroscopic signal uniformity as characterized by a coefficient of variation of only 6% across 4 cm. After SERS analyses, the nanohoodoos can be recycled by complete removal of gold via a one‐step, simple, and robust wet etching process without compromising performance. After eight times of recycling, the substrate still exhibits identical SERS performance in comparison to a new substrate. The macroscopic uniformity combined with recyclability at conserved high performance is expected to contribute significantly on the overall competitivity of the substrates. These findings show that the gold nanoparticles sliding on recyclable nanohoodoo substrate is a very strong candidate for obtaining cost‐effective, high‐quality, and reliable SERS spectra, facilitating a wide and simple use of SERS for both laboratorial and commercial applications.
Cheap, robust, macroscopically uniform, and highly efficient substrates for surface‐enhanced Raman spectroscopy (SERS) are fabricated using block copolymer lithography. A nanohoodoo template in the substrate is recyclable after SERS analyses via a simple wet chemistry process. The renovated substrate exhibits reproducibly low SERS backgrounds and identical SERS performance, in comparison to a new substrate.
Reusability of sensors is relevant when aiming to decrease variation between measurements, as well as cost and time of analysis. We present an electrochemically assisted surface-enhanced Raman ...spectroscopy (SERS) platform with the capability to reverse the analyte–surface interaction, without damaging the SERS substrate, allowing for efficient sensor reuse. The platform was used in combination with a sample pretreatment step, when detecting melamine from milk. We found that the electrochemically enhanced analyte–surface interaction results in significant improvement in detection sensitivity, with detection limits (0.01 ppm in PBS and 0.3 ppm in milk) below the maximum allowed levels in food samples. The reversibility of interaction enabled continuous measurement in aqueous solution and a complete quantitative assay on a single SERS substrate.
The combination of graphene with noble-metal nanostructures is currently being explored for strong light–graphene interactions enhanced by plasmons. We introduce a novel hybrid graphene–metal system ...for studying light–matter interactions with gold-void nanostructures exhibiting resonances in the visible range. Enhanced coupling of graphene to the plasmon modes of the nanovoid arrays results in significant frequency shifts of the underlying plasmon resonances, enabling 30% enhanced absolute light absorption by adding a monolayer graphene and up to 700-fold enhancement of the Raman response of the graphene. These new perspectives enable us to verify the presence of graphene on gold-void arrays, and the enhancement even allows us to accurately quantify the number of layers. Experimental observations are further supported by numerical simulations and perturbation-theory analysis. The graphene gold-void platform is beneficial for sensing of molecules and placing Rhodamine 6G (R6G) dye molecules on top of the graphene; we observe a strong enhancement of the R6G Raman fingerprints. These results pave the way toward advanced substrates for surface-enhanced Raman scattering (SERS) with potential for unambiguous single-molecule detection on the atomically well-defined layer of graphene.
Non-destructive orientation mapping is an important characterization tool in materials science and geoscience for understanding and/or improving material properties based on their grain structure. ...Confocal Raman microscopy is a powerful non-destructive technique for chemical mapping of organic and inorganic materials. Here we demonstrate orientation mapping by means of Polarized Raman Microscopy (PRM). While the concept that PRM is sensitive to orientation changes is known, to our knowledge, an actual quantitative orientation mapping has never been presented before. Using a concept of ambiguity-free orientation determination analysis, we present fast and quantitative single-acquisition Raman-based orientation mapping by simultaneous registration of multiple Raman scattering spectra obtained at different polarizations. We demonstrate applications of this approach for two- and three-dimensional orientation mapping of a multigrain semiconductor, a pharmaceutical tablet formulation and a polycrystalline sapphire sample. This technique can potentially move traditional X-ray and electron diffraction type experiments into conventional optical laboratories.
Ultra-sensitive in-field measurements of most forensic substances still today remain a challenge for first responders and forensic investigators. Handheld Raman spectroscopy equipment is getting more ...and more routinely used in the field for evidence collection, however, restricted to measurements of pure or high concentration samples. Here, surface-enhanced Raman scattering (SERS) sensing of common forensic substances with commercially available SERS substrates and handheld spectrometers, have been investigated. 3D Finite Element Method (FEM) and Density Functional Theory (DFT) simulations were used to interpret the high SERS enhancement of the Ag nanopillar substrate and the detection of the substances, respectively. The forensic generality and high performance of the analytical method were demonstrated by explicit detection of close to unprecedented amounts, down to femtograms, of Cyclosarin, RDX, Amphetamine and Picric acid. Implications are ultra-sensitive in-field SERS detection of these substances with commercial equipment.
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•Close to unprecedented detection of nerve gases, explosives and narcotics are presented.•Simulations are performed to support and interpret results.•Comprehensive peak-assignment tables are included in the supplementary material.•Implications are ultra-sensitive in-field SERS detection of these substances with commercial equipment.
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