Strong Surface-enhanced Raman Scattering Activity Research Articles

SERS-based boronate affinity biosensor with biomimetic specificity and versatility: Surface-imprinted magnetic polymers as recognition elements to detect glycoproteins

Glycoproteins are a class of proteins with significant biological functions and clinical implications. Due to glycoproteins’ reliability for the quantitative analysis, they have been used as biomarkers and therapeutic targets for disease diagnosis. We propose a sandwich structure-based boronate affinity biosensor that can separate and detect target glycoproteins by magnetic separation and Surface-enhanced Raman scattering (SERS) probes. The biosensor relies on boronic acid affinity magnetic molecularly imprinted polymer (MMIPs) with pH response as "capturing probe" for glycoproteins, and Au-MPBA@Ag modified with 4-mercaptophenylboronic acid (MPBA) as SERS probes, among which, MPBA has both strong SERS activity and can specifically recognize and bind to glycoproteins. MMIPs ensured specific and rapid analysis, and SERS detection provided high sensitivity. The proposed boronate affinity SERS strategy exhibited universal applicability and provided high sensitivity with limit of detection of 0.053 ng/mL and 0.078 ng/mL for horseradish peroxidase and acid phosphatase, respectively. Ultimately, the boronate affinity SERS strategy was successfully applied in detection of glycoprotein in spiked serum sample with recovery between 90.6% and 103.4%, respectively. In addition, this study used a portable Raman meter, which can meet the requirements of point-of-care testing. The biosensor presented here also has advantages in terms of cost-effectiveness, stability, and detection speed.

Enhance Raman scattering for probe methylene blue molecules adsorbed on ZnO microstructures due to charge transfer processes

It is generally understood that the chemical enhancement process is essential in surface-enhanced Raman scattering (SERS) of semiconductor-based substrates. Understanding the chemical enhancement mechanism is one of the most significant issues in improving the SERS activity of semiconductor substrates and designed hybrid substrates. Nevertheless, understanding the chemical enhancement process, on the other hand, remains controversial and elusive. In this study, ZnO semiconductor microstructures are prepared to investigate SERS activities in probing methylene blue (MB). The SERS mechanism is well elucidated based on the chemical enhancement mechanism related to both the formation of charge-transfer band and charge transfer from the second ionization of the oxygen vacancy defect (V o •• ) to lowest unoccupied molecular orbital (LUMO) of MB. Remarkably, the charge-transfer band was evidenced by examining the ground state absorption spectra with a large band centred at 600 nm. These explanations are consistent with the strong SERS substrate behaviour of ZnO microstructures, with the SERS enhancement factor (EF) of ZnO plate substrates being highest among four investigated samples (ZnO tube, hexagonal, plate and flory-rod) at 2.9 × 10 4 at a concentration of MB of 10 −4 M. To the best of our knowledge, this is the first investigation of detecting MB molecules using a pure semiconductor surface with a strong SERS activity. • We have successfully fabricated various morphologies of semiconductor ZnO microstructures by hydrothermal route, including tube, hexagonal, plate and flory-like structures. • These products were studied surface-enhanced Raman scattering (SERS) behaviour for probing methylene blue (MB) molecules with the enhancement factor (EF) achieving 2.9 × 10 4 (10 −4 M). • The charge-transfer band corresponding to the interaction between the ZnO surface and the MB molecule was evidenced by examining the ground state absorption spectra with a large band centred at 600 nm. • The SERS mechanism is well elucidated based on the chemical enhancement mechanism related to both the formation of charge-transfer band and charge transfer. • The combination of the existence of charge-transfer band and charge-transfer resonance leads to the large enhancement factor of using pure ZnO as SERS surface.

Facile fabrication of PS/Cu2S/Ag sandwich structure as SERS substrate for ultra-sensitive detection

In this work, a serials of PS(polystyrene)/Cu2S/Ag sandwich substrates were successfully constructed using the magnetic sputtering method by adjusting the Ag sputtering time (0 min, 2 min, 4 min, 6 min, 8 min and 10 min) and used as the surface-enhanced Raman scattering (SERS) substrates. When the Ag sputtering time was 6 min, the strongest SERS signal was observed. The optimized SERS substrate has strong SERS activity on 4-mercaptobenzoic acid (4-MBA), the minimum detection limit was 10−13 M and the enhancement factor was as high as 4.7 × 107. In addition, the SERS signals were highly reproducible with small standard deviation. The SERS enhancement mechanism of the PS/Cu2S/Ag system was attributed to the synergistic effect of the chemical mechanism and the electromagnetic enhancement mechanism. This strategy has find a new way for manufacturing SERS activity sensor with high sensitivity and reproducibility.

A Highly Sensitive and Stable SERS Sensor for Malachite Green Detection Based on Ag Nanoparticles In Situ Generated on 3D MoS2 Nanoflowers

AbstractThe hybrid plasmon composition based on MoS2 has been extensively studied as a higher disposition surface enhanced Raman scattering (SERS) substrate. In this paper, a novel silver nanoparticle based SERS substrate was developed via in situ microwave synthesis approach on a three dimensional (3D) MoS2 nanoflower (MoS2 NF/ Ag NPs). The prepared SERS sensor has strong SERS activity on malachite green (MG), the Raman enhancement factor (EF) is as high as 1.46×1012. The standard Raman signal peak of MG at 1618 cm−1 has a good linear relationship at 10−12 ‐ 10−2 mol⋅L−1. The limit of detection (LOD) was calculated as approximately 10−14 mol⋅L−1, which shows the good prospects for MG's microtests. In addition, the SERS sensor still shows good SERS performance stability after 112 days, which improves the shelf life of the SERS sensor and can be effectively applied to fishery water monitoring.

Porous silicon photonic crystal/silver composite produced by microwave-assisted reduction: Applications to surface-enhanced Raman scattering

A high enhancement activity is realized via reduction of silver nanoparticles on multilayered porous silicon assisted by microwave radiation. The as-prepared silver nanoparticles/porous silicon photonic crystals (Ag NPs/PSi PhCs) surface enhanced Raman scattering (SERS) active substrate shows outstanding performance in detecting Rhodamine 6G (R6G). A maximum enhancement factor (EF) of 7.8 × 1014 for R6G and a 9.38% relative standard deviation (RSD) of repeatability at a R6G concentration of 10−12 M are obtained, confirming the high sensitivity and excellent uniformity. The strong SERS activity is ascribed to the advantages of photonic crystal effect of PSi PhC and microwave radiation in regulating absorption and distribution of Ag NPs on PSi PhC, which results in a high density of hot spot regions to improve the SERS signals. In general, the Ag NPs/PSi PhCs SERS active substrates exhibit great potential applications the fields of environment, food and disease diagnosis.

Surface-Enhanced Raman Scattering Spectral Imaging for the Attomolar Range Detection of Crystal Violet in Contaminated Water.

A series of nanocomposites based on polyamide (NL16, PA) filter membranes containing metal nanoparticles (NPs) have been prepared by filtration under reduced pressure of the metal colloids. The ensuing materials were then investigated as substrates for surface-enhanced Raman scattering (SERS) imaging studies envisaging the spectroscopic detection of vestigial organic pollutants dissolved in contaminated water. The organic dye crystal violet (CV) was used here as a model pollutant because it is a hazardous compound present in certain effluent waters. Moreover this compound is well-known for its strong SERS activity, which is clearly advantageous in the context of material development for SERS. Indeed, several preparative strategies were employed to prepare PA-based composites, and the impact on SERS detection was investigated. These include the use of chemical and morphological distinct plasmonic NPs (Ag, Au), a variable metal load and changing the order of addition of the analytical specimens. These studies demonstrate that the parameters employed in the fabrication of the SERS substrates have a strong impact on the Raman signal enhancement. The use of Raman imaging during the fabrication process allows establishing improvements that translate to better performances of the substrates in the analyte detection. The results have been interpreted by considering an integrated set of operational parameters that include the affinity of CV molecules to the substrate, amount and dispersion of NPs in the PA membranes, and the detection method. Noteworthy the use of SERS analysis assisted with Raman imaging allowed achieving a detection limit for CV as low as 100 aM in ultrapure water and 10 fM in real samples.

Two-Step Centrifugation Method for Subpicomolar Surface-Enhanced Raman Scattering Detection.

The potentiality of surface-enhanced Raman scattering (SERS) to detect ultralow concentrations of analyte has attracted much attention in detection of trace components in both medicinal and environmental samples. However, detection at trace concentration usually requires sophisticated systems. Here, we present an ultrasensitive and facile SERS approach, a two-step centrifugation method, which achieved a detection limit of 500 fM with phenformin hydrochloride and risperidone as acidic and alkaline analyte, respectively. This method consists of two steps: (1) centrifuging colloidal silver to increase nanoparticles' concentration and to remove small-size nanoparticles, thus increasing the chance of analyte adsorption on large nanoparticles that have strong SERS activity; (2) centrifuging samples after the analytes were mixed with nanoparticles. After the first centrifugation and mixing with aqueous analyte, the colloidal silver is either flocculated (for high-concentration samples) or forms a nanoparticle-analyte complex (for low-concentration samples). Until the second centrifugation, the concentration of analyte and hot-spot formation is significantly increased, and thus a high SERS enhancement factor is obtained. In short, the two-step centrifugation method overcomes drawbacks of the traditional method, which demands not only sophisticated operation but also expensive instruments, to fully exploit the potential of SERS detection.

High surface enhanced Raman scattering activity of BN nanosheets–Ag nanoparticles hybrids

A facile liquid-phase reducing route was developed to modify boron nitride (BN) nanosheets with silver nanoparticles (AgNPs) in order to fabricate BN–AgNPs hybrids with high surface enhanced Raman scattering (SERS) activity. The layered structure and morphology of BN–AgNPs nanohybrids were characterized by transmission electron microscopy and atomic force microscopy, meanwhile, Fourier transform infrared spectroscopy and ultraviolet–visible were used for studying optical properties and surface plasmon resonance applied to the optical sensor. The SERS of adsorbed 2-mercaptobenzimidazole (MBI) molecule was investigated which shown that the BN–AgNPs substrate exhibited a very strong SERS activity, offering a great potential application in molecular probe sensor. On the basis of the analysis of SERS and the Raman surface selection rules, we could draw a conclusion that the MBI molecule was adsorbed upright on the AgNPs surface through the sulphur and nitrogen atoms. What is more, the cyclic voltammetry experiment indicated the electrochemically irreversible behavior of BN–AgNPs nanohybrids in KCl solution.

Detection of mercury ions using silver telluride nanoparticles as a substrate and recognition element through surface-enhanced Raman scattering.

In this paper we unveil a new sensing strategy for sensitive and selective detection of Hg2+ through surface-enhanced Raman scattering (SERS) using Ag2Te nanoparticles (NPs) as a substrate and recognition element and rhodamine 6G (R6G) as a reporter. Ag2Te NPs prepared from tellurium dioxide and silver nitrate and hydrazine in aqueous solution containing sodium dodecyl sulfate at 90°C with an average size of 26.8 ± 4.1 nm (100 counts) have strong SERS activity. The Ag2Te substrate provides strong SERS signals of R6G with an enhancement factor of 3.6 × 105 at 1360 cm−1, which is comparable to Ag NPs. After interaction of Ag2Te NPs with Hg2+, some HgTe NPs are formed, leading to decreases in the SERS signal of R6G, mainly because HgTe NPs relative to Ag2Te NPs have weaker SERS activity. Under optimum conditions, this SERS approach using Ag2Te as substrates is selective for the detection of Hg2+, with a limit of detection of 3 nM and linearity over 10–150 nM. The practicality of this approach has been validated for the determination of the concentrations of spiked Hg2+ in a pond water sample.

Silver–gold core-shell nanoparticles containing methylene blue as SERS labels for probing and imaging of live cells

We report on silver-gold core-shell nanostruc- tures that contain Methylene Blue (MB) at the gold-silver interface. They can be used as reporter molecules in surface- enhanced Raman scattering (SERS) labels. The labels are stable and have strong SERS activity. TEM imaging revealed that these nanoparticles display bright and dark stripe structures. In addition, these labels can act as probes that can be detected and imaged through the specific Raman signatures of the reporters. We show that such SERS probes can identify cellular structures due to enhanced Raman spectra of intrinsic cellular molecules measured in the local optical fields of the core-shell nanostructures. They also provide structural information on the cellular environment as demonstrated for these nanoparticles as new SERS-active and biocompatible substrates for imaging of live cells.

Synthesis of p-aminothiophenol-embedded gold/silver core-shell nanostructures as novel SERS tags for biosensing applications

We describe a novel surface-enhanced Raman scattering (SERS) tag that is based on Au/Ag core-shell nanostructures embedded with p-aminothiophenol. The Au/Ag core-shell sandwich nanostructures demonstrate bright and dark stripe structure and possess very strong SERS activity. Under optimum conditions, the maximum SERS signal was obtained with a 10 nm thick Ag nanoshell, and the enhancement factor is 3.4 × 104 at 1077 cm−1. After conjugation to the antibody of muramidase releasing protein (MRP), the Au/Ag core-shell nanostructures were successfully applied to an SERS-based detection scheme for MRP based on a sandwich type of immunoassay.

Preparation, Characterization, and Surface-Enhanced Raman Spectroscopy Activity of Spherical α-Fe<sub>2</sub>O<sub>3</sub>/Ag Core/Shell Nanoparticles

Spherical α-Fe2O3/Ag core/shell nanoparticles were prepared by reducing Ag(NH3)2+ with formaldehyde using the seeding method. 3- Aminopropyltriethoxysilane (APS) acts as a “bridge” to link between α-Fe2O3 core and Ag shell. The obtained nanoparticles were characterized by XRD, TEM, SEM, EDS, and Roman. The results show thatα-Fe2O3 cores are coated by Ag shell completely. The average size of α-Fe2O3/Ag nanoparticles is 95 nm and the thicknesses of Ag shell are 15nm in 3.7% HCHO and 1.0M AgNO3. The thickness of Ag shell can be tunable by changing reaction conditions, such as the concentration of AgNO3, reduction reaction rate. The surface-enhanced Raman scattering (SERS) effect of the core/shell particles are measured with Pyridine (Py) as molecule probe. SERS indicate that the Raman signals of Py adsorbed on α-Fe2O3/Ag nanoparticles exhibit large enhancement at 1010 and 1038 cm-1 respectively. And the intensity of signals is enhanced with the increase of the thickness of Ag shell. The uniform and rough surface of α-Fe2O3/Ag particles exhibits strong SERS activity in 3.7% HCHO and 1.0M AgNO3. The spherical α-Fe2O3/Ag core/shell nanoparticles exhibit SERS activity.