Strong Surface-enhanced Raman Scattering Intensity Research Articles

Polypeptide@AuNC probe catalytic amplification-tetramode molecular spectral biosensor for trace Al3+

Nanoclusters have strong catalytic effect, but their stability was poor. Biomolecule functionalized gold nanoclusters (AuNC) have attracted extensive attention due to their good biocompatibility, stable physicochemical properties and strong catalytic activity. In this study, the peptide (PT) was used as a template to synthesize the PTAuNC nanoprobe with recognition and catalysis. The results show that PTAuNC has a strong catalytic effect on the indicator reaction of 3,3′,5,5′-tetramethylbenzidine (TMB)–H2O2 to produce the oxidized TMB (TMBox). The TMBox had a strongest fluorescence (FL) peak at 410 nm and an absorption peak at 650 nm. Addition of nanosilver (AgNPs), it produced a strong surface enhanced Raman scattering (SERS) peak at 1616 cm−1 and a resonance Rayleigh scattering (RRS) peak at 370 nm. The new nanocatalytic indicator reaction was organically coupled with the PTAuNC-Al3+ recognition reaction, and a PTAuNC catalytic amplification SERS/RRS/FL/Abs tetramode biosensor platform for Al3+ was constructed. The Al3+ concentration in the range of 0.5–60 nmol/L had a good linear relationship with SERS intensity, with detection limit of 0.21 nmol/L. The method has been applied to the determination of Al3+ in water and food samples. The recovery and relative standard deviation (RSD) were 92.4–109.8% and 1.2–9.8%, respectively.

A new Fe/N doped carbon dot naocatalytic amplification-aptamer SERS/RRS/Abs trimode assay platform for ultratrace Pb2+

Nanocatalytic amplification of carbon dots is a new way to improve sensitivity. The preparation of the high catalytic activity and stable iron/nitrogen-doped carbon dot (CDBFe) sol and its application in aptamer (Apt) assay have not been reported yet. In this paper, a simple hydrothermal procedure for the preparation of CDBFe derived from Fe2+-2,2′-bipyridine complex has been developed. It is found that CDBFe has a strong catalytic effect on the indicator reaction of glyoxal (C2H2O2) reduction of HAuCl4 to produce gold nanoparticle (AuNP) probe with strong surface enhanced Raman scattering (SERS) at 1617 cm−1, resonance Rayleigh scattering (RRS) effect at 370 nm and absorption (Abs) at 550 nm. A rapid and sensitive CDBFe catalytic amplification Apt method for SERS/RRS/Abs trimode detecting ultratrace lead ions was established, based on the Apt reaction mediated the nanocatalytic indicator reaction. The results show that the SERS intensity and Pb(II) concentration have a good linear relationship in the range of 1.3–16 pM, and the detection limit is the lowest. In addition, Hg(II) and As(III) can also be measured by this naocatalytic amplification- Apt assay platform.

A simple gold nanoplasmonic SERS method for trace Hg2+ based on aptamer‐regulating graphene oxide catalysis

The as-prepared graphene oxide (GO) exhibited a strong catalytic effect on reduction of HAuCl4 by trisodium citrate to form gold nanoplasmons (AuNPs) with a strong surface-enhanced Raman scattering (SERS) effect at 1615cm-1 in the presence of molecular probe Victoria blue 4R (VB4r). SERS intensity increased with nanocatalyst GO concentration due to the formation of more AuNP substrates. The aptamer (Apt) of Hg2+ can bind to GO to form Apt-GO complexes, which can strongly inhibit nanocatalysis. When target Hg2+ is present, the formed stable Hg2+ -Apt complexes are separated from the GO surface, which leads to GO catalysis recovery. The enhanced SERS signal was linear to Hg2+ concentration in the range 0.25-10nmol/L, with a detection limit of 0.08nmol/L Hg2+ . Thus, a new gold nanoplasmon molecular spectral analysis platform was established for detecting Hg2+ , based on Apt regulation of GO nanocatalysis.

A Sensitive Gold Nanoplasmonic SERS Quantitative Analysis Method for Sulfate in Serum Using Fullerene as Catalyst

Fullerene exhibited strong catalysis of the redox reaction between HAuCl4 and trisodium citrate to form gold nanoplasmon with a strong surface-enhanced Raman scattering (SERS) effect at 1615 cm−1 in the presence of Vitoria blue B molecule probes. When fullerene increased, the SERS peak enhanced linearly due to formation of more AuNPs as substrate. Upon addition of Ba2+, Ba2+ ions adsorb on the fullerene surface to inhibit the catalysis of fullerene that caused the SERS peak decreasing. Analyte SO42− combined with Ba2+ to form stable BaSO4 precipitate to release free fullerene that the catalysis recovered, and the SERS intensity increased linearly. Thus, a new SERS quantitative analysis method was established for the detection of sulfate in serum samples, with a linear range of 0.03–3.4 μM.

SERS quantitative analysis of trace ferritin based on immunoreaction regulation of graphene oxide catalytic nanogold reaction

In 50 °C conditions, the gold nanoreaction of HAuCl4-H2O2 is very slow, graphene oxide (GO) exhibited strong catalysis on the nanoreaction to form gold nanoparticles (AuNPs) with strong surface-enhanced Raman scattering (SERS) activity at 1614 cm−1 in the presence of molecular probes of Victoria Blue (VB4r). The SERS intensity increased with the GO increasing due to formation of more AuNPs. The ferritin antibody (Ab) can bind to GO surface to form Ab-GO that can inhibit the nanocatalysis. When ferritin (Ag) existed, the produced immunocomplexes of Ab-Ag are separated from the GO surface, which led to the recovery of GO catalysis. The enhanced SERS signal △I1614cm-1 is linear to ferritin concentration in the range of 0.017–1.02 ng/mL. Accordingly, a new SERS quantitative analysis method was established for detection of ferritin, based on the regulating GO nanocatalysis.

Simple and sensitive SERS quantitative analysis of sorbic acid in highly active gold nanosol substrate

Abstract Gold nanosol with good stability and high SERS activity was prepared under the light wave irradiation, with triethanolamine as reducing agent. In the acid medium, the oxidized product of scorbic acid (SA) by H2O2, malondialdehyde, react with thiobarbituric acid (TBA) to produce 3,5,5-trimethyloxazole-2,4-dione (trimethadione, TMD) that exhibited strong surface-enhanced Raman scattering (SERS) effect at 1280 cm−1 in the as-prepared gold nanosol substrate containing enhancement reagent of AlCl3. Under the chosen conditions, the SERS intensity at 1280 cm−1was linear to the SA concentration in the linear range of 0.0066–1.59 μg/mL, with a detection limit of 3.2 ng/mL. This SERS method has been applied to the quantitative analysis of SA in real samples with advantages of high sensitivity, good selectivity and simple operation.

A novel nanocatalytic SERS detection of trace human chorionic gonadotropin using labeled-free Vitoria blue 4R as molecular probe

In pH 7.4 Na2HPO4-NaH2PO4 buffer solution containing the peptide probes for human chorionic gonadotropin (hCG), silver nanoparticles (AgNPs) were aggregated to big AgNPs clusters that exhibited very weak catalytic effect on the gold nanoparticle reaction of H2O2-HAuCl4. When hCG was present in the peptide probe solution, the AgNPs did not aggregate and it had strong catalytic effect on the gold nanoparticle reaction with a strong resonance Rayleigh scattering (RRS) peak at 370nm and a strong surface enhanced Raman scattering (SERS) peak at 1615cm−1 in the presence of molecular probe of Victoria blue 4R (VB4R). With the increase of the hCG concentration, the catalysis enhanced due to the nanocatalyst of AgNPs increasing, and the RRS intensity increased at 370nm. The increased RRS intensity was linear to the hCG concentration in 0.05–10ng/mL, with a linear regression equation of ΔI370nm=409.8C +294. And the SERS intensity at 1615cm−1 increased linearly with the hCG concentration in the range of 0.05–20ng/mL, with a linear regression equation of ΔI1615cm-1=142C+134. Based on this, two new methods of nanocatalytic SERS and RRS were proposed for the determination of trace hCG.

SERS quantitative detection of trace human chorionic gonadotropin using a label-free Victoria blue B as probe in the aggregated immunonanogold sol substrate.

Nanogold particles (NG) were modified by anti-rabbit antibody (RAb) against human chorionic gonadotropin to obtain an immunonanogold probe (ING). In pH 7.0 Na2HPO4-citrate buffer solution containing KCl, ING probes formed large aggregates in which Victoria blue B (VBB) molecules were adsorbed on the surface and which exhibited strong surface-enhanced Raman scattering (SERS) at a peak of 1612 cm(-1). After addition of human chorionic gonadotropin (hCG) an immune reaction with the ING probe occurred to form dispersive ING-hCG complexes with non-SERS activity that led to a decreased SERS peak at 1612 cm(-1). The decreased SERS intensity was linear to the concentration of hCG over 2.4-73.2 ng/mL. The ING reaction was studied in detail by SERS, scanning electron microscope (SEM), resonance Rayleigh scattering (RRS), surface plasmon resonance (SPR) absorption and laser scattering techniques. SERS quenching was observed and discussed.

SERS detection of trace nitrite ion in aqueous solution based on the nitrosation reaction of rhodamine 6G molecular probe

The stable reduced graphene oxide/triangular plate-type nanosilver aggregation/rhodamine 6G (rGO/TAgA/Rh6G) nanosensor exhibited a strong surface-enhanced Raman scattering (SERS) peak at 1505cm−1 that was used to monitor the Rh6G concentration changes in the nitrosation reaction between Rh6G and NO2−, in which NO2− increase results in the SERS intensity decrease due to the decreasing Rh6G. The decreased SERS intensity was linear to nitrite concentration in the range of 0.7–72nmol/L, with a detection limit of 0.2nmol/L. Nitrite in water samples was analyzed by this Rh6G SERS nanosensor, with recovery of 94.8%–108% and relative standard deviation of 4.4%–7.5%.

Synthesis of rGO–Ag nanoparticles for high-performance SERS and the adsorption geometry of 2-mercaptobenzimidazole on Ag surface

The sliver nanoparticles (AgNPs) with diameters of 30∼50 nm were self-assembled onto the surfaces of reduced graphene oxide (rGO) sheets simply by mixing AgNO3 aqueous solution and GO dispersion via a synchronous reduction process. Structure and morphology of the rGO–AgNPs hybrids were well characterized. More significantly, the surface-enhanced Raman scattering (SERS) spectrum of 2-mercaptobenzimidazole (MBI) adsorbed on the solid rGO–AgNPs surface shown that the rGO–AgNPs system gives a very strong SERS intensity at in-plane vibrational modes in comparison to the out-of-plane vibrational modes. This large enhancement effect is most likely a result of charge-transfer (CT) mechanism. Based on the surface selection rules and the information provided by the highly enhanced in-plane vibrational modes, it can be found that MBI molecule was adsorbed on AgNPs surface as a thiol form via the sulphur and nitrogen atoms with a slightly tilted geometric conformation.

Influence of Dopamine Concentration and Surface Coverage of Au Shell on the Optical Properties of Au, Ag, and AgcoreAushell Nanoparticles

Gold (Au), silver (Ag), and Ag(core)Au(shell) nanoparticles (NPs) were explored as optical sensing agents for the sensitive detection of dopamine (DA) neurotransmitters in surface-enhanced Raman scattering (SERS) measurements. In these colloidal systems, dopamine (DA) molecules played as a cross-linker between M NPs (Au or Ag NPs), allowing them to reside in the confined junctions (i.e., hot spots) between aggregated NPs. The progressive addition of DA molecules (from 1 × 10(-6) to 1 × 10(-3) M) consequently decreased a primary absorption peak attributed to the characteristic M NPs and generated a secondary absorption peak at longer wavelengths attributed to heavily aggregated M NPs formed by molecular bridging effects of DA molecules at high concentrations. The aggregation degree of M NPs was also dependent on the surface states of Au and Ag NPs, i.e., DA molecules with positive amine groups induced more aggregations of Au NPs in comparison to Ag NPs with less negative charges. As the final outcome, Au NPs demonstrated higher sensitivity in SERS detection of DA at low concentrations (1 × 10(-7) to 1 × 10(-5) M), whereas Ag NPs exhibited the stronger Raman signals of DA molecules at high concentrations (1 × 10(-4) to 1 × 10(-3) M). Besides, Ag(core)Au(shell) NPs with the lowest surface coverage of Au shell exhibited more sensitive and stronger SERS activity for DA molecules than that of singular Au NPs, probably due to the combined contribution by Ag core with strong SERS intensity and Au shell with high SERS sensitivity.

Growth and surface-enhanced Raman scattering of Ag nanoparticle assembly in agarose gel

Agarose gel loaded with silver nanoparticles has attracted a lot of attention recently due to its excellent molecular trapping capabilities and strong surface-enhanced Raman scattering (SERS). Despite its potential, the influence of the growth condition on the gel structure and resultant SERS intensity and reproducibility is not clear. In this work, we examine the effect of silver nitrate feed solution concentration, the precursor to neutral silver nanoparticles, on the resultant nanoparticle morphology, gel homogeneity, SERS signal intensity and reproducibility. SERS of trans-1,2-bis-(4-pyridyl) ethylene, a non-resonant molecule, was conducted. A substantial rise in SERS signal strength with increasing feed concentration was observed, accompanied by a modest increase in average particle size as disclosed by TEM analysis. At higher concentrations, gels possessed larger particles from broader size distributions which had a higher tendency to aggregate. This created a higher density of SERS ‘hotspots’, regions of intense electromagnetic field crucial for maximal enhancement of the Raman signal, but also led to increased spot-to-spot signal variation due to a marked change in nanoparticle morphology and gel homogeneity. Beyond an optimal feed concentration, no further increase in overall signal strength was evident, correlating with no appreciable rise in the number of larger particles.

A colorimetric and surface-enhanced Raman scattering dual-signal sensor for Hg2+ based on Bismuthiol II-capped gold nanoparticles

The addition of Bismuthiol II to the gold nanoparticles (AuNPs) solution led to the aggregation of AuNPs with a color change from red to blue. As a result, hot spots were formed and strong surface-enhanced Raman scattering (SERS) signal of Bismuthiol II was observed. However, the Bismuthiol II-induced aggregation of AuNPs could be reversed by Hg2+ in the system, accompanied by a remarkable color change from blue to red. As evidenced by UV–vis and SERS spectroscopy, the variation in absorption band and SERS intensity was strongly dependent on the concentration of Hg2+, suggesting a colorimetric and SERS dual-signal sensor for Hg2+. The sensor had a high sensitivity, low detection limits of 2nM and 30nM could be achieved by UV–vis spectroscopy and by SERS spectroscopy, respectively. Other environmentally relevant metal ions did not interfere with the detection of Hg2+. The method was successfully applied to detect Hg2+ in water samples. It was simple, rapid and cost-effective without any modifying or labeling procedure.

A Rapid Surface-Enhanced Raman Scattering Method for the Determination of Trace Hg2+ Using Rhodamine 6G-Aggregated Nanosilver as Probe

In pH 6.0 Na2HPO4-NaH2PO4 buffer solution and in the presence of cetyltrimethyl ammonium bromide, nanosilver particles were aggregated to a stable suspension. Therein, rhodamine 6G (Rh6G) exhibited three strong surface-enhanced Raman scattering (SERS) peaks at 613, 1,363, and 1,510 cm−1, and their SERS intensities were enhanced when the concentration of Rh6G increased. In the presence of Hg2+, the SERS intensity decreased greatly owing to formation of stable Rh6G-HgBr42− ternary association complex molecules as well as its particles. In the optimal condition, the decreased SERS intensity at 613 cm−1 responds linearly with the concentration of Hg2+ over 25–2,000 nmol/L. Thus, a new sensitive SERS method has been proposed for the determination of trace Hg2+ in the water sample, with satisfactory results.

Facile fabrication of large area of aggregated gold nanorods film for efficient surface-enhanced Raman scattering

An effective and facile method for fabrication of large area of aggregated gold nanorods (AuNRs) film was proposed by self-assembly of AuNRs at a toluene/water interface for the first time. It was found that large area of aggregated AuNRs film could be formed at the interface of toluene and water due to the interfacial tension between the two phases. The obtained large area of aggregated AuNRs film exhibits strong surface-enhanced Raman scattering (SERS) activity with 4-aminothiophenol (4-ATP) and 2-aminothiophenol (2-ATP) as the probe molecules based on the strong electromagnetic coupling effect between the very adjacent AuNRs. Enhancement factors (EF) were used to estimate the SERS activity of the aggregated AuNRs film, which is obtained to be 1.7 × 10 5 for 7a vibration of 4-ATP. SERS intensity is compared with AuNRs deposited directly on glass, indicating high SERS activity and reproducibility of the aggregated AuNRs film. In addition, SERS activity has also been successfully demonstrated for dye molecule (Rhodamin 6G (R6G)) and biological small molecule (adenine) on the aggregated AuNRs film, showing great potential of the aggregated AuNRs film as a convenient and powerful SERS substrate for biological tags and biological molecular detection.

Surface enhanced Raman scattering from transition metal nano-wire array and the theoretical consideration

Co, Ni, Pt and Pd nano-wire arrays with diameter of about 50 nm were fabricated by means of template synthesis. By alternating current (AC) electrodeposition these metals were filled into channels of anodic aluminum oxide (AAO) film respectively. Nano-electrode arrays having good electric contact with the substrate was also fabricated by employing combined electroless deposition and the AC electrodeposition. Strong surface enhanced Raman scattering (SERS) was observed from both metal nano-wire arrays and nano-electrode arrays after partial removal of the AAO film. The SERS intensity of probe molecules adsorbed at the arrays depends critically on the length of the nano-wire explored at the surface. The experimental results agree well with the corresponding theoretic calculations based on electromagnetic enhancement. The lightning rod effect may play an important role for the enhancement of the Ni nano-rod under the favorable length. It has been shown that metal nano-wire arrays can be developed to a new generation of substrate exhibiting very high SERS activity, especially for transition metals. These well-ordered surface nano-structures can also be served as a proper model for the SERS mechanism study.

A complementary study of surface-enhanced Raman scattering and metal nanorod arrays

Abstract The two-dimensional arrays of various metal nanowires with diameters ranging from 15 to 70 nm have been fabricated by electrodepositing metals of Cu, Ag, Au, Ni, and Co into the nanoholes of the anodic aluminum oxide (AAO) films, followed by partial removal of the film. The strong surface-enhanced Raman scattering (SERS) effects were observed from the metal nanowire arrays including Ni, Co metals that were normally considered to be non-SERS active substrates. It has been shown that metal nanowire arrays can serve as very good SERS active substrates, especially for transition metals. The SERS intensity of the probe molecule adsorbed at the nanowires depends critically on the length of the nanowires explored at the surface. And the band frequency is very sensitive to the diameter, which reflects the change in the electronic property of metal nanowires. Applying this probe molecule strategy, SERS could develop into a diagnostic tool of metal nanowires (nanorods).