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Semiconductor materials have become a competitive candidate for surface-enhanced Raman scattering (SERS) substrate. However, powdered semiconductors are difficult to execute a fast in situ detection for trace analytes. Here, we developed a new flexible semiconductor SERS substrate by in situ densely growing anatase TiO2 nanoparticles on the surface of cotton fabric through a filtration-hydrothermal method, in which TiO2 exhibits excellent controllability in size and distribution by regulating the ratio of water to alcohol in synthesis and the number of filtration-hydrothermal repetitive cycle. Cotton fabric/TiO2 (Cot/TiO2) substrate exhibits a high SERS activity and excellent spectral repeatability. The developed substrate has an ultra-high stability that can withstand long-term preservation; it can even resist the corrosions of strong acid and alkali, as well as high temperature up to 100 °C and low temperature down to − 20 °C. The flexible substrate can be used to carry out a rapid in situ detection for quinolone antibiotic (enrofloxacin and enoxacin) residues on the fish body surface by using a simple swabbing method, with high quantitative detection potential (up to an order of magnitude of 10−7 M), and even for the simultaneous detection of both drug residues. The flexible substrate also exhibits an excellent recyclability up to 6 recycles in the actual SERS detection. [ABSTRACT FROM AUTHOR]

Enhancement of the light‐matter coupling is a promising approach to improve the sensitivity and universality of semiconductor‐based surface‐enhanced Raman scattering (SERS). Herein, it is demonstrated that hollow multi‐shelled V2O5 microstructure can be utilized as an active substrate to integrate multiple synergistic contributions. The experiments and numerical simulations clearly reveal that the excellent SERS activity originates from the unique double‐shelled hollow structures, which allow multiple reflections of electromagnetic waves. This light‐trapping effect provides an efficient resonance absorption for charge‐transfer (CT) and exciton enhancements. More importantly, the coupling of outer and inner shells remarkably generates high electric field contribution for SERS enhancement. Besides, the symmetry analysis of vibrational modes based on density functional theory well explains the origin of the CT coupling of Herzberg–Teller selection rules. The synergy of all factors contributes to a significant increase in the sensitivity and universality of semiconductor SERS. It is anticipated that the strategy demonstrated in this study will widen the scope of currently available methodologies for designing substrates with high semiconductor SERS activity. [ABSTRACT FROM AUTHOR]

This paper reports the fabrication of gold‐patterned microarray chips for fast and ultrasensitive surface enhanced Raman scattering (SERS) detection of trace samples. By micro‐nano machining based on electron‐beam lithography, magnetron sputtering, and chemical modification, gold‐patterned microarray chips with hydrophilic and hydrophobic periodic structures are fabricated, and a polyethylene glycol (PEG) layer is coated on the surface of the gold well, making the chips long‐term stable. The hydrophilic surface of each gold well is surrounded by a hydrophobic layer, which makes the ultratrace sample amount for SERS measurement only 0.3 μl. In the detection of malachite green (MG), 4‐mercaptopyridine (4‐MPY), rhodamine 6G (R6G), and melamine, great enhanced SERS signals with the detection limit reaching nM level can be achieved due to the enrichment effect of the periodic structures and the hot‐spots generated between the sandwich structure built on the gold wells. Such gold‐patterned microarray chip is promising in fast and ultrasensitive SERS detection of various chemical and biological species with trace amount. Gold‐patterned microarray chips for fast and ultrasensitive surface enhanced Raman scattering detection of trace samples are reported. The hydrophilic surface of each gold well is surrounded by a hydrophobic layer, which makes the ultratrace sample amount for SERS measurement only 0.3 μl. Such gold‐patterned microarray chip is promising in fast and ultrasensitive SERS detection of various chemical and biological species with trace amount. [ABSTRACT FROM AUTHOR]

A method for the investigation of photocatalytic degradation of organic molecules adsorbed on the surface of a compound nanostructure, silver nanoparticle (Ag NP) modified titania nanotubes (TiO 2 NTs), namely Ag/TiO 2 NTs, was proposed. The method was applied to the photocatalytic degradation of rhodamine 6G (R6G) dye molecules in order to determine its effectiveness. The surface-enhanced Raman scattering (SERS) technique was employed to monitor the photodegradation processes on these bifunctional nanostructures. The photocatalytic characteristic was attributed to the TiO 2 NTs; however, the SERS activity was caused by the Ag NPs. The Ag/TiO 2 NTs were able to detect R6G molecular probes with concentration down to 10 −8 M. The substrates could not only degrade the adsorbates, but also discard them off under ultraviolet irradiation owing to the high photocatalytic activity of TiO 2 . Thus, the substrates were able to self-clean and be reused for a new SERS detection cycle. The photodegradation and SERS results revealed that Ag/TiO 2 NTs acted as promising candidates for photocatalytic activity and SERS substrates; and exhibited high recyclability in the detection of organic molecules. The optimized SERS-active substrates were then employed to study the photodegradation of R6G. The photodegradation kinetics analysis was assessed by selecting the strongest SERS peaks which indicated that the kinetics of the photodegradation of R6G followed the pseudo-first order reaction. Finally, the results presented herein demonstrated that the fabricated Ag/TiO 2 NTs nanostructures were remarkably suitable as photocatalytically active SERS substrates. Further, the substrates could be effectively utilized for highly sensitive in situ monitoring of the surface photodegradation processes of organic molecules and could be recycled in a more environmentally sustainable manner. [ABSTRACT FROM AUTHOR]

Efficient and generic enantioselective discrimination of various chiral alcohols is achieved by using surface-enhanced Raman scattering (SERS) spectroscopy through charge-transfer (CT) contributions. The relative intensities of the peaks in the SERS spectra of a chiral selector are strongly dependent on the chirality of its surroundings. This highly distinct spectral discrepancy may be due to the tendency of chiral isomers to form intermolecular hydrogen-bonding complexes with the chiral selector in different molecular orientations, resulting in different CT states and SERS intensities of the adsorbates in the system. This study opens a new avenue leading to the development of novel enantiosensing strategies. A particular advantage of this approach is that it is label-free and does not employ any chiral reagents, including chiral light. [ABSTRACT FROM AUTHOR]

In this study, we present a method of achieving highly sensitive immunoassays based on surface-enhanced Raman scattering ( SERS). The biofunctional-nanoprobe-linked immunosorbent assay is a closely related technique with a good linear range and the ability to simultaneously detect antigens with high sensitivity. Herein, we report a novel method based on a sandwich structure composed of a silver monolayer and biocompatible Au-mercaptobenzoic acid ( MBA)@ SiO2 that was assembled through an immune recognition reaction. To induce a strong plasmonic contribution of the nanoprobes, two or more MBA-adsorbed gold nanoparticles were saturated and loaded into silica. Silica-protected gold nanoaggregates exhibit stable SERS activity and biocompatibility for proteins. The capabilities of the proposed sandwich structure for analytical applications were demonstrated through the use of the SERS technique to detect antigens at very low concentrations. These techniques may prove to be superior to current protocols for biomarker research and clinical diagnosis, which require high sensitivity and quantitation over an extended range. [ABSTRACT FROM AUTHOR]

[Display omitted] • The selective enhancement mechanism in SERS for two types of Au nanoparticles was elucidated. • SERS spectra of probe molecules demonstrated the importance of specific SERS tags in determining the main enhancement factors. • 2T2D-COS results showed the relationship between nanoparticle type and SERS enhancement. The selective enhancement mechanism in surface-enhanced Raman scattering (SERS) is demonstrated. Two different types of single nanoparticles (Au nanosphere and Au nanorod) were used to investigate the role of the localized surface plasmon resonance (LSPR) in SERS spectra by using the two-trace two-dimensional (2T2D) correlation spectroscopy. The SERS intensities of three probe molecules, 4-mercaptobenzoic acid (4-MBA), 4-aminothiophenol (4-ATP), and 4-bromobenzenethiol (4-BBT), respectively, were enhanced but slightly different when adsorbed on Au nanospheres and Au nanorods. 2T2D correlation SERS spectra clearly showed that even with the same shape of Au nanoparticles, the main factors influencing the SERS enhancement can vary depending on the specific type of SERS tags used. Such subtle difference could not be clearly identified by the conventional spectral analysis. This result sheds light on potential applications of 2T2D correlation spectroscopy. For 4-MBA molecules, the a 1 and b 2 modes are mainly affected by the Au nanospheres and Au nanorods. For 4-ATP molecules, the a 1 and b 2 modes related to C–S stretching combined with C–C stretching band are mainly affected by Au nanorods and Au nanospheres. For 4-BBT molecules, the a 1 and b 2 modes of C–C (aromatic ring) stretching band are mainly affected by Au nanorods and Au nanospheres. This study offers valuable insights into the relationship between nanoparticle shape and SERS enhancement. [ABSTRACT FROM AUTHOR]

In diagnosing prostate cancer and distinguishing it from other prostate diseases, the ratio of the concentration of free prostate-specific antigen (f-PSA) to total prostate-specific antigen (t-PSA), i.e., (f-PSA%) is more accurate than the concentration of t-PSA alone. Immunoassay based on surface-enhanced Raman scattering (SERS) frequency shift has been proven to be particularly suitable for detecting large biomolecules with high reproducibility. Along similar lines, the present study developed a SERS-based biosensor that simultaneously detects t-PSA and f-PSA. The 4-mercaptobenzoic acid (MBA) on the immunocapture substrate is coupled to the t-PSA antibody through the carboxyl group, and the combination of t-PSA induces the Raman frequency shifts of MBA. The immunocolloidal gold attached with f-PSA antibodies selectively capture the f-PSA that immobilized on the MBA-modified SERS substrates, allowing for f-PSA quantification according to the SERS intensities of the 5, 5′-Dithiobis (succinimidyl-2-nitrobenzoate) (DSNB) probe. The results show that f-PSA and t-PSA have good linear response in the concentration scale of 0.1–20 ng/mL, and 1–200 ng/mL, respectively. The biosensor combines Raman frequency shifts and intensities, which greatly simplifies traditional procedures for f-PSA% detection. All the results demonstrated the great potential of the proposed biosensor in highly reproducible and accurate diagnosis of prostate cancers. [Display omitted] • A SERS-based biosensor for simultaneous detection of t-PSA and f-PSA is developed. • This method combines the advantages of spectral reproducibility and sensitivity. • The feasibility of using the proposed biosensor for clinical samples was validated in human serum. [ABSTRACT FROM AUTHOR]

Abstract Norfloxacin (NFX) is an antibacterial agent belonging to the fluoroquinolone family of drugs, known to bind bovine serum albumin (BSA). Surface-enhanced Raman scattering (SERS) and fluorescence spectroscopy in combination with molecular docking were explored to investigate the binding interaction between NFX with Bovine serum albumin (BSA) at a physiological condition. This study focused on identifying the binding site and relevant interaction mechanisms between NFX and BSA. Spectrophotometric titration with molecular docking results demonstrated that the binding site of NFX on BSA was located in sub-domain IIA. The principle binding site was identified within a hydrophobic cavity which is surrounded by the residues Leu 197, Arg 198, Ser 201, Ala 209, Trp 213, Ser 343, Leu 346, Lys 350, Ser 453, Leu 480, Val 481, and the binding force was mainly hydrophobic interaction and hydrogen bond interaction. In addition, the absorptive orientation of the NFX molecule on the colloidal surface underwent a set of changes during the process of NFX binding to BSA. Graphical Abstract Unlabelled Image Highlights • The combination of SERS and molecular docking were explored to investigate the binding site of Norfloxacin on BSA. • The absorptive geometry of Norfloxacin with BSA on the self-assembled monolayer film was confirmed. • The detailed binding position and relevant interaction mechanism of Norfloxacin to BSA were obtained. [ABSTRACT FROM AUTHOR]

Mercuric ion (Hg 2+ ) is a toxic metal ion in the environment, which will seriously damage the people's health. Therefore, the simple sensitive detection of Hg 2+ is of great significance. In this work, Ag-CoFe 2 O 4 /reduced graphene oxide (rGO) nanocomposites were synthesized via a one-pot microwave-assisted reaction, which can directly oxidize 3, 3′, 5, 5′-tetramethylbenzidine (TMB) to produce a light blue. Then we have developed a dual colorimetric and SERS detection of Hg 2+ based on the stimulus of intrinsic oxidase-like catalytic activity of Ag-CoFe 2 O 4 /rGO nanocomposites. It is demonstrated that the interaction between Hg 2+ and Ag nanoparticles can occur in a short time, which includes the formation of Ag-Hg alloy due to the reduction of Hg 2+ . In addition, the formation of such alloy can enhance the oxide-like activity, which makes the detection of Hg 2+ more sensitive. By using the SERS detection approach, the assay can detect Hg 2+ as low as 0.67 nM. This detection ability is much better than previous reports based on the enzyme-like catalytic reaction, which is also lower than the maximum value of Hg 2+ permitted in drinking water by the World Health Organization (WHO) (30 nM) and United States Environmental Protection Agency (EPA) (10 nM). In addition, this detection system also shows an excellent selectivity toward Hg 2+ due to the affinity of Hg to Ag-CoFe 2 O 4 /rGO nanocomposites. Therefore, this approach is potentially applicable for the sensitive determination of Hg 2+ in real environmental conditions. [ABSTRACT FROM AUTHOR]

Given the strong hydration propensity of fluoride ions, it is difficult to detect fluoride, especially inorganic fluoride, in aqueous samples. Resolving the issue of fluoride detection in aqueous samples is a scientific undertaking of great practical significance. Herein, we propose a new method for the sensitive and selective detection of fluoride in aqueous samples without the addition of organic solvents. The method involves surface-enhanced Raman spectroscopy using 1,4-diketo-3,6-diphenylpyrrolo[3,4- c ]pyrrole (DPP) compounds and Ag nanoparticles. The method is based on a diketopyrrolopyrrole compound linked to 1-butyl iodide (DPP1), which can sense fluoride sensitively and selectively. When DPP1 was combined with Ag NPs and reacted with tetrabutylammonium fluoride or inorganic fluoride in aqueous samples, an obvious Raman enhancement was obtained at the excitation wavelength of 633 nm. This response arises because the introduction of fluoride anions into the system changes the molecular orientation of DPP1 on the Ag NP substrate from horizontal to vertical, inducing a signal enhancement in the Raman spectrum. This system can detect inorganic fluoride at concentrations as low as 1.0 μmol L −1 (0.018 ppm), which is far below the public health service recommended levels for drinking water (0.7–1.2 ppm). Furthermore, using the proposed method, a linear response for fluoride in the concentration range of 1.0 × 10 −3 –1.0 × 10 −6 mol L −1 was obtained, which makes fluoride detection possible in practical samples, such as fluoride-containing toothpaste. [ABSTRACT FROM AUTHOR]

[Display omitted] • A rapid and sensitive SERS strategy using a portable Raman spectrometer was described. • β-CD-AgNPs was synthesized as SERS substrate to determine Thiram (THI) and atrazine (ATZ). • LOD was 2.42 × 10-9 mol L-1 (0.58 ppb) for THI and 7.26 × 10-9 mol L-1 (1.56 ppb) for ATZ. • Determination via SERS of THI in apple and ATZ in apple and water Samples. In this work, a rapid and sensitive strategy was developed to determine thiram (THI) and atrazine (ATZ) by surface-enhanced Raman scattering (SERS) technology. β-cyclodextrin modified silver nanoparticles (β-CD-AgNPs) were synthesized using β-CD as a reducing agent and encapsulating agent under alkaline conditions and employed as SERS substrate. The existence of β-CD can capture the molecules to form host–guest complex and fix molecular orientation in its cavity, thus ensuring the enhanced SERS signal intensity of THI and ATZ. The linear response extends from 2.56 × 10-8 to 2.56 × 10-3 mol/L for THI and 3.08 × 10-8 to 3.08 × 10-3 mol/L for ATZ, with the limits of detection (LOD) of 2.42 × 10-9 mol/L for THI and 7.26 × 10-9 mol/L for ATZ, respectively. The application of the proposed method in real samples including apple and water were investigated, and the results would help promote the application of SERS technology as a powerful analytical tool for detecting other pesticide residues. It is expected that this SERS strategy will provide great value for rapid detecting pesticide residues in food products and environmental systems. [ABSTRACT FROM AUTHOR]

The silver nanowires (AgNWs) were prepared through the method of polyol. The prepared AgNWs were characterized by TEM image, UV–vis spectroscopy and X-ray diffraction (XRD). AgNWs were assembled onto silicon wafer through entropy-driven self-assembly method. The 521 cm −1 band of silicon was used as internal standard band. The SERS performance of AgNWs-Si substrate was characterized by using R6G as the probe molecule, and the SERS substrate is employed to detect 6-MP. The linear concentration range of 6-MP is 0.05–3.8 μmolL −1 and the corresponding correlation coefficient is 0.994. The method is satisfactory for detecting 6-MP in two kinds of commercial tablets. [ABSTRACT FROM AUTHOR]

In this paper, silver nanoparticles-coated silicon wafer (AgNPs@Si) was used as surface-enhanced Raman scattering (SERS) substrate for detection of 6-Thioguanine (6-TG). The influence of experimental parameters including pH value and soaking time on SERS performance were examined. The SERS characteristic peak of 6-TG at 1303 cm −1 was selected for quantity analysis. With the 521 cm −1 band of silicon as internal standard, band intensity ratio of 6-TG to silicon, that was I 1303 / I 521 , could be used for quantification. Under the optimum conditions, I 1303 / I 521 exhibited a linear relationship with the concentration of 6-TG in the range of 0.1–15.0 μmol L −1 and detection limit (S/N = 3) was 0.065 μmol L −1 . The corresponding correlation coefficient of the linear equation was 0.998. This method based on AgNPs@Si was successfully applied to the detection of 6-TG in two kinds of commercial tablets. [ABSTRACT FROM AUTHOR]

Surface-enhanced Raman scattering (SERS) and fluorescence spectroscopy were employed to probe the interaction of the pharmaceutical and natural product molecules, ginsenoside Rb1, Rd, Rg3 and compound K (CK), with human serum albumin (HSA). Normal Raman spectra of these four ginsenosides were obtained from solid powder on glass slide. Based on the unsplit peak at 1445 cm −1 , the stacking modes of ginsenoside Rb1, Rd, Rg3 and CK were quite similar, when the deconvolution of alkyl chain was not occurred. SERS spectra of ginsenoside Rb1, Rd, Rg3 and CK were obtained from a colloidal silver surface on a self-assembled SERS substrate, the most enhanced modes were those with certain motions perpendicular to the metal surface, such as C24 C25 stretch and C H out-of-plane bending from alkyl chain. The SERS spectra were used to predict similar perpendicular orientation of flexible alkyl chain and parallel orientation of carbocyclic rings on Ag colloid particles. Therefore, when combined with HSA, the transformations of four ginsenosides still exhibit similar, although in different binding cavities in subdomain IIA and IIIA by making the methyls at C26 and C27 perpendicular plugging into the hydrophobic site of HSA, while the aglycone and glucose nearby are perpendicularly exposed outside to fit other suitable active targeting sites. [ABSTRACT FROM AUTHOR]

[Display omitted] • A uniform and small-sized (ca. 10 nm) core–shell Ag/o-GQDs nanohybrid are successfully prepared. • The Ag/o-GQDs show unique structure with parallel-interlaced staking of o-GQDs. • The Ag/o-GQDs exhibit excellent SERS sensitivity, biocompatibility and nanozymatic activity. • The intracellular H 2 O 2 can be accurately in situ SERS monitoring at the subcellular level. The small-sized plasmonic nanoparticles are easily internalized by cells and organelles, but usually possess poor surface-enhanced Raman scattering (SERS) activity, restricting their promising applications for intracellular SERS analysis. To break the current bottleneck of intracellular SERS application, herein, a uniform and small-sized (ca. 10 nm) core–shell Ag/oxidized graphene quantum dots (o-GQDs) nanohybrids have been prepared. The Ag/o-GQDs inherit unique features with parallel-interlaced stacking of o-GQDs as capping agent, possess the increasing and broadening plasmon adsorption and display a unique edge state charge transfer (CT) resonance in the long-wavelength region of visible light, enabling the enhanced electromagnetic (EM) and CT effect for superior SERS sensitivity at lower energy. Further, the Ag/o-GQDs demonstrate excellent biocompatibility and highly efficient nanozymatically catalytic activity, which are first put forward to integrate efficient SERS with Ag/o-GQDs nanozyme to catalyze peroxidase-like reaction for accurate sensing of the intracellular H 2 O 2 at the subcellular level. Moreover, the Ag/o-GQDs nanozyme-catalyzed reactive oxygen species (ROS) generation and the cancer cell multisubcellular-targeting capability provide a promising strategy for the synergistically catalytic therapy specifically toward tumors. This study illustrates a significant route to design an efficient small-sized noble metal/carbon nanozymatic SERS substrate, and demonstrates an exciting potential for ultrasensitive SERS bioanalysis at the subcellular level. [ABSTRACT FROM AUTHOR]

Total removal of organic mercury in industrial wastewater is a crucially important task facing environmental pollution in the current world. Herein, we demonstrate the fabrication of Au-NiFe layered double hydroxide (LDH)/rGO nanocomposite as not only an efficient nanozyme with oxidase-like activity but also an efficient surface-enhanced Raman spectroscopy (SERS) substrate to determine organic mercury, with the minimum detection concentration as low as 1 × 10−8 M. According to the binding energy of X-Ray photoelectron spectrometer (XPS) and the free radicals of electron paramagnetic resonance (EPR) spectra, the mechanism of catalytic enhanced degradation is the production of Au-amalgam on Au surface, accelerating the electron transfer and the generation of O 2 •– radicals from oxygen molecules and •CH 3 radicals from the methyl group in MeHg to participate the oxidase-like reaction. Furthermore, the Au-NiFe LDH/rGO nanocomposite is able to degrade and remove 99.9% of organic mercury in two hours without the secondary pollution by Hg2+. In addition, the material can be used for the multiple degradation-regeneration cycles in actual applications, which is significant in terms of the environmental and economic point of view. This work may open a new horizon for both highly sensitive detection and thorough degradation of organic mercury in environmental science and technology. ga1 • Au/Ni-Fe LDH/rGO nanocomposite with an oxidase-like activity has been prepared. • Au/Ni-Fe LDH/rGO nanocomposite can be used as an efficient SERS substrate. • The oxidase-like reaction can detect MeHg with a concentration as low as 1 × 10−8 M. • Au/Ni-Fe LDH/rGO nanocomposite can degrade 99.9% of MeHg in 2 h. • This work provides the removal of MeHg without the secondary pollution by Hg2+. [ABSTRACT FROM AUTHOR]

Protein phosphorylation, a post-translational modification of proteins, is of vital importance in biological regulation. Highly sensitive and site-specific identification of phosphorylated proteins is a key requirement for unraveling crucial signal transduction pathways relevant to cancers and neurodegenerative disorders. Traditional detection methods, however, suffer from relying on antibodies, labels or fragmentation prior to analysis. Here, an antibody- and label-free in situ approach to fingerprint protein phosphorylation was developed based on intrinsic Raman vibrational information of phosphorylated tyrosine, serine, threonine, or histidine residues. Combining surface-enhanced Raman scattering (SERS) spectroscopy and an immobilized-metal affinity strategy, this method is ultrasensitive to discriminate a single-site phosphorylated S396 in a Tau410 protein, an important biomarker in Alzheimer's disease. The binding feasibility of phosphorylated proteins to the modified SERS-active materials is further evidenced by molecular dynamics simulations. This proof-of-concept study paves a new way for the evaluation of site-specific and intact protein phosphorylation in both fundamental mechanical investigation and clinical applications. • Fingerprinting phosphorylated proteins by SERS combined with an immobilized-metal affinity strategy. • In situ Identification without antibodies and Raman reporters. • Single-site discrimination of phosphorylated S214 or S396 in an intact Tau protein. [ABSTRACT FROM AUTHOR]

In this study, we present a method of achieving highly sensitive immunoassays based on surface-enhanced Raman scattering ( SERS). The biofunctional-nanoprobe-linked immunosorbent assay is a closely related technique with a good linear range and the ability to simultaneously detect antigens with high sensitivity. Herein, we report a novel method based on a sandwich structure composed of a silver monolayer and biocompatible Au-mercaptobenzoic acid ( MBA)@ SiO2 that was assembled through an immune recognition reaction. To induce a strong plasmonic contribution of the nanoprobes, two or more MBA-adsorbed gold nanoparticles were saturated and loaded into silica. Silica-protected gold nanoaggregates exhibit stable SERS activity and biocompatibility for proteins. The capabilities of the proposed sandwich structure for analytical applications were demonstrated through the use of the SERS technique to detect antigens at very low concentrations. These techniques may prove to be superior to current protocols for biomarker research and clinical diagnosis, which require high sensitivity and quantitation over an extended range. [ABSTRACT FROM AUTHOR]