Surface Enhanced Raman Spectroscopy Probe Research Articles

Innovative suspended ring core fiber for SERS application

Solid core photonic crystal fibers (SC-PCFs) have garnered attention as probes for surface-enhanced Raman spectroscopy (SERS) due to their potential as optofluidic devices, offering heightened sensitivity and reliability compared to traditional planar/colloidal nanoparticle-based SERS platforms. A smaller core allows for more light interaction but might compromise sensitivity and reliability due to reduced surface area for interaction. Here, we introduce an innovative SC-PCF design aimed at resolving the trade-off between increasing the evanescent field fraction and the core surface area. By substituting a suspended silica rod with a suspended thin-silica ring, we augment the surface area for attached nanoparticles by one order of magnitude while retaining a substantial amount of evanescent light interaction with the analyte. Experimental findings showcase an improved sensitivity in SERS signal compared to previously reported top-performing PCF sensor designs. Importantly, with necessary refinement and optimization, this innovative fiber design extends beyond SERS applications, potentially amplifying the sensitivity of various other fiber-based sensing platforms.

Detection of mercury in spiked cosmetics by surface enhanced Raman spectroscopy using silver shelled iron oxide nanoparticles

Heavy metal, such as lead (Pb), arsenic (As), and mercury (Hg), contamination is a grave global issue that has affected public health via drinking water, paints, and a wide range of personal consumer products such as cosmetics. Here, we have used Surface enhanced Raman spectroscopy (SERS) for the novel solution phase detection of Hg2+ ions in spiked cosmetic (skin whitening) samples by using 2,5-Dimercapto-1,3,4-thiadiazole (DMcT) functionalized silver shelled iron oxide (Fe3O4@Ag-DMcT) nanoparticles (NPs). Fe3O4@Ag NPs (12 ± 4 nm) are the magneto-plasmonic SERS enhancers, and DMcT work as the Hg2+ reporter. We have optimized 2 mg/mL of Fe3O4@Ag:DMcT with 10−4 M of DMcT to be the best for SERS based Hg2+ detection in spiked samples of commercial skin whitening product. The samples mixed with the SERS probe were sealed in a capillary tube and placed on a magnet under the Raman spectroscope. A calibration curve of the variation of the 1360 cm−1 band of DMcT as a function of Hg2+ concentration was first determined using a cream, and a liquid phase randomly chosen cosmetics. Unknown samples spiked with low (10−8 M), and high (10−4 M) concentrations of Hg2+ could be successfully detected with ∼ 35 %, and 14.6 % error in measured intensities, respectively, with respect to the calibrated data. We estimate a limit of detection (LoD) for Hg2+ in real cosmetic sample as 1 nM (∼0.2 ppb).

Surface Enhanced Raman Spectroscopy With Electrodeposited Copper Ultramicro-Wires With/Without Silver Nanostars Decoration.

The electrochemical preparation of arrays of copper ultramicrowires (CuUWs) by using porous membranes as templates is critically revisited, with the goal of obtaining cheap but efficient substrates for surface enhanced Raman spectroscopy (SERS). The role of the materials used for the electrodeposition is examined, comparing membranes of anodized aluminum oxide (AAO) vs. track-etched polycarbonate (PC) as well as copper vs. glassy carbon (GC) as electrode material. A voltammetric study performed on bare electrodes and potentiostatic tests on membrane coated electrodes allowed the optimization of the deposition parameters. The final arrays of CuUWs were obtained by chemical etching of the template, with NaOH for AAO and CH2Cl2 for PC. After total etching of the template, SERS spectra were recorded on CuUWs using benzenethiol as SERS probe with known spectral features. The CuUW substrates displayed good SERS properties, providing enhancement factor in the 103–104 range. Finally, it was demonstrated that higher Raman enhancement can be achieved when CuUWs are decorated with silver nanostars, supporting the formation of SERS active hot-spots at the bimetallic interface.

Optimization of gold nanorod arrays for surface enhanced Raman spectroscopy (SERS) detection of atrazine.

Recently, there has been increasing concern over the widespread use of the herbicide atrazine which has been reported to have problematic side effects on local ecosystems. This has highlighted the need for rapid and accurate point-of-need assessment tools for analytical determination of herbicides in ground and surface waters. Surface enhanced Raman spectroscopy (SERS) is a sensitive vibrational spectroscopy technique which has recently been employed for the analysis of a variety of analytes in water, ranging from pharmaceuticals to pesticides. In this work, SERS sensors constructed using gold nanorod (AuNR) arrays are optimized and then utilized for the rapid and sensitive detection of atrazine. In this study, the effect of relative humidity on the self-assembly of gold nanorods into arrays was explored, and the SERS performance was assessed using para-aminothiophenol as a SERS probe. Once the SERS performance of the substrates was deemed optimal, the detection of atrazine was highlighted. This work represents the first time that relative humidity has been explored as an optimization strategy for controlled alignment of gold nanorods for SERS analysis of atrazine.

Large-area surface-enhanced Raman spectroscopy substrate by hybrid porous GaN with Au/Ag for breast cancer miRNA detection

Surface Enhanced Raman Spectroscopy (SERS) method is widely used as a powerful undamaged tool to analysis low concentration of molecules, which gives great potential for bio-detection. In this work, large area SERS substrates were fabricated by hybrid large area porous GaN nanostructures with Au/Ag. By controlling porous GaN morphology, the Au/Ag layer thickness and morphology, the detection limit of 1.13 × 10-13 M and enhancement factor of 2.5 × 108 of t he large area SERS substrate were obtained with good uniformity and stability by using R6G as SERS probe. The high performance of the SERS substrate is attribute to the electromagnetic enhancement after hybrid GaN nanostructure with Au /Ag, which conformed by finite difference time domain method (FDTD) simulation. The potential application for the detection of miRNA (miR-K12-5-5p as breast cancer related biomarker) was evaluated with fluorescent molecular (FAM) as Raman target molecular and a sensitive miR-K12-5-5p detection with a limit down to 8.84 × 10-10 M was achieved, which confirming the potentialities of the Au/Ag/ porous GaN hybrid SERS substrate for early-cancer diagnosis, and giving great potential to develop ultrasensitive SERS biosensors for various biological and chemical analyses.

Development of a SERS Probe for Selective Detection of Healthy Prostate and Malignant Prostate Cancer Cells Using ZnII.

Even in the 21st century, prostate cancer remains the second leading cause of cancer-related death for men. Since a normal prostate gland has a high ZnII content and there are huge differences in ZnII content between healthy and malignant prostate cancer cells, mobile zinc can be used as a biomarker for prostate cancer prediction. A highly efficient surface enhanced Raman spectroscopy (SERS) probe using a p-(imidazole)azo)benzenethiol attached gold nanoparticle as a Raman reporter, which has the capability to identify prostate cancer cells based on ZnII sensing, has been designed. A facile synthesis, characterization and evaluation of a ZnII sensing Raman probe are described. Reported data indicate that after binding with ZnII , Raman reporter attached to a gold nanoparticle forms an assembly structure, which allows selective detection of ZnII even at 100 ppt concentration. Theoretical full-wave finite-difference time-domain (FDTD) simulations have been used to understand the enhancement of the SERS signal. The SERS probe is highly promising for in vivo sensing of cancer, where near-IR light can be easily used to avoid tissue autofluorescence and to enhance tissue penetration depth. Reported data show that the SERS probe can distinguish metastatic cancer cells from normal prostate cells very easily with a sensitivity as low as 5 cancer cells mL-1 . The probe can be used as a chemical toolkit for determining mobile ZnII concentrations in biological samples.

Amino‐methyl coumarin as a potential SERS@Ag probe for the evaluation of protease activity and inhibition

Proteases are found deregulated in many diseases including cancer and neurodegenerative diseases. They thus represent good therapeutical targets for the development of inhibitors mainly small organic molecules. Peptide substrates containing fluorogenic groups constitute central tools for the monitoring of protease activities and inhibitor screening platforms. Amino‐methyl coumarin (AMC) is a well‐known fluorogenic group that functionalized a huge number of peptide substrates used for kinetics in vitro but also in vivo. However, either autofluorescence or quenching of the AMC fluorescence could compromise selection and accurate evaluation of these inhibitors. It is thus needed to explore alternative spectroscopic tools to unravel these limitations. Here, we investigate whether AMC could constitute a valuable Surface Enhanced Raman Spectroscopy probe in the presence of Creighton' silver colloids under 532‐nm excitation to monitor protease activity and to evaluate inhibitors. The kallikrein‐related peptidase 8 was used as model of proteolytic enzyme. Band‐Target Entropy Minimization analysis was successfully used to validate the present Surface Enhanced Raman Spectroscopy approach. Copyright © 2016 John Wiley & Sons, Ltd.

Simple control of surface topography of gold nanoshells by a surfactant-less seeded-growth method.

We report the synthesis of branched gold nanoshells (BGNS) through a seeded-growth surfactant-less method. This was achieved by decorating chitosan-Pluronic F127 stabilized poly(lactic-co-gycolic) acid nanoparticles (NPs) with Au seeds (NP-seed), using chitosan as an electrostatic self-assembling agent. Branched shells with different degrees of anisotropy and optical response were obtained by modulating the ratios of HAuCl4/K2CO3 growth solution, ascorbic acid (AA) and NP-seed precursor. Chitosan and AA were crucial in determining the BGNS size and structure, acting both as coreductants and structure directing growth agents. Preliminary cytotoxicity experiments point to the biocompatibility of the obtained BGNS, allowing their potential use in biomedical applications. In particular, these nanostructures with "hybrid" compositions, which combine the features of gold nanoshells and nanostars showed a better performance as surface enhanced Raman spectroscopy probes in detecting intracellular cell components than classical smoother nanoshells.

Plasmonic DNA-origami nanoantennas for surface-enhanced Raman spectroscopy.

We report that plasmonic nanoantennas made by DNA origami can be used as reliable and efficient probes for surface-enhanced Raman spectroscopy (SERS). The nanoantenna is built up by two gold nanoparticles that are linked together by a three-layered DNA origami block at a separation distance of 6 nm in order to achieve plasmonic coupling and the formation of a plasmonic "hot spot". The plasmonic properties of the hybrid structure are optically characterized by dark-field imaging and polarization-dependent spectroscopy. SERS measurements on molecules that are embedded in the DNA origami that bridges the nanoantenna gap were performed in order to demonstrate the excellent performance of these structures for enhancing spectroscopic signals. A strong enhancement of the Raman signal was recorded from measurements on single hot spots compared to measurements in bulk. Finally, we show that the laser polarization with respect to the dimer orientation has a strong impact on the SERS performance.

Gold nanoparticles explore cells: Cellular uptake and their use as intracellular probes

Understanding uptake of nanomaterials by cells and their use for intracellular sensing is important for studying their interaction and toxicology as well as for obtaining new biological insight. Here, we investigate cellular uptake and intracellular dynamics of gold nanoparticles and demonstrate their use in reporting chemical information from the endocytotic pathway and cytoplasm. The intracellular gold nanoparticles serve as probes for surface-enhanced Raman spectroscopy (SERS) allowing for biochemical characterisation of their local environment. In particular, in this work we compare intracellular SERS using non-functionalised and functionalised nanoparticles in their ability to segregate different but closely related cell phenotypes. The results indicate that functionalised gold nanoparticles are more efficient in distinguishing between different types of cells. Our studies pave the way for understanding the uptake of gold nanoparticles and their utilisation for SERS to give rise to a greater biochemical understanding in cell-based therapies.

Optical fiber tip for field-enhanced second harmonic generation

We propose a simple optical fiber tip for field-enhanced second harmonic generation (SHG). The tip shows nonlinear phenomena of SHG over a wide range of sources, at least from 630 to 830nm. The optical field corresponding to the second harmonic appears as a nondiffracting bottle beam with voids due to the surface curvature of the tip. The field-enhanced second harmonic can also induce surface plasmons, converting the tip to a plasmonic probe with reduced background signal. The tip can be useful in nanophotonics characterization. As an example, we demonstrate the tip's response as a surface-enhanced Raman spectroscopy probe.

Growth of Ag, Au, Cu, and Pt nanostructures on surfaces by micropatterned laser-image formations

Silver, gold, copper and platinum nanoparticles (NPs) were grown on surfaces in the form of patterns by the exposure of laser radiation onto droplets of metal ion solutions and the aid of a reducing agent. The generation of patterns from metallic NPs was achieved by combining induced growth of NPs and nanostructures by laser incidence directly on surfaces and optical image formation techniques for transferring the patterns. Near-UV (363.8 nm) and visible (532 nm) laser wavelengths were used for the laser-induced growth of NPs into microstructures on glass, quartz, stainless steel, silicon, and gold-on-silicon substrates. The sizes of the patterns formed were on the micrometer scale and the sizes of the transferred patterns were on the millimeter scale. The patterns formed were generated by optical transference of image and interference of laser beams. Ag and Au substrates were highly active in surface enhanced Raman spectroscopy (SERS). The enhanced Raman activity was measured for SERS probe molecules: 9H-purin-6-amine (adenine) and 1,2-bis (4-pyridyl)-ethane analytes on Ag and Au substrates, respectively. The enhancement factors obtained were 1.8×10(5) and 6.2×10(6), respectively.