Proposed Surface-enhanced Raman Scattering Substrate Research Articles

Detection and analysis of rotavirus in clinical stool samples using silver nanoparticle functionalized paper as SERS substrate

Among the different analytical techniques, surface-enhanced Raman scattering (SERS) approach is a widely used technique for the detection and analysis of various chemicals and biological samples. Present study reports a low-cost, sensitive SERS substrate that has an ability to detect rotavirus in clinical stool samples. The proposed SERS substrate has been fabricated through drop-casting of silver nanoparticles (AgNPs) on a printing-grade paper. Rotavirus particles were extracted from clinical stool samples. The presence of rotavirus antigen in stool samples was confirmed using enzyme-linked immunosorbent assay (ELISA), polymerase chain reaction (PCR), and sequencing. The characteristic Raman peaks of rotavirus (RV) particles in solution were found to be significantly enhanced when Raman signals were recorded from the paper-based SERS substrates. Using the proposed SERS substrate, rotavirus samples with concentration as low as 1% could be reliably recorded by the Raman spectrometer. The paper SERS substrate reported herein is an extremely cost-efficient platform and may find applications in other research and clinical laboratories as well.

Quasi‐3D‐Structured Surface‐Enhanced Raman Scattering Substrates Based on Silver Nanoparticles/Mesoporous Silicon Hybrid

The surface‐enhanced Raman scattering (SERS) is a powerful spectroscopic technique for ultrasensitive and selective biochemical detection due to its capability of providing the “fingerprint” of information of molecular structures at low concentrations. Herein, mesoporous silicon (MPSi)‐based nanocomposites containing silver nanoparticles (AgNPs) provide novel efficient substrates for the detection of molecules. The quasi‐3D‐structured SERS substrate is formed by introducing Ag into the MPSi hollow column‐shaped nanostructure. This SERS substrate uniquely combines the ability of metal surfaces to amplify Raman scattering signals with an enlarged surface area and the increasing light–matter interaction duration that generates large SERS signals for the detection of chemicals. The proposed SERS substrate is verified by detecting orange methylene in solutions at ultralow concentration in the range of 10−11–10−6 m with a linear‐dependent coefficient of R2 = 0.99922 and the SERS enhancement factor is achieved up to 1010. Moreover, the proposed platform can detect diphenylamine with ultralow concentration of 10−10 m and reliable reproducibility with an average relative stand deviation of 6.3%. The ability for MPSi substrate to detect target molecules at low concentrations helps pave a way to develop the detection tool for integrated, on‐chip devices.

Facile Fabrication of Micro/Nano Hierarchical SERS Sensor via Anisotropic Etching and Electrochemical Treatment for Malachite Green Detection

We propose a facile method to produce micro/nano hierarchical surface-enhanced Raman scattering (SERS) active substrates using simple steps and inexpensive costs. The proposed SERS substrate is a silicon pyramid array covered by a nanostructured gold film (AuNS @ SiPA). Through finite element method (FEM) simulation, we showed that many strong local electric field enhancements (hot spots) were formed between the nano-gap of gold nanostructures. In addition, the micron-scale pyramid structure not only increases the sensing surface area of the sensor, but also helps trap light. By combining these micro and nano structures, the proposed micro/nano hierarchical SERS sensor exhibited high sensitivity. Experimental results confirmed that the AuNS @ SiPA substrate has high sensitivity. The SERS signal enhancement factor obtained from the Rhodamine 6G (R6G) probe molecules was as high as 1 × 107 and the SERS substrates were found to be able to detect a very low concentration of 0.01 nM malachite green (MG) solution. Therefore, this study provides a novel and practical method for fabricating SERS substrates that can facilitate the use of SERS in medicine, food safety, and biotechnology.

Nanotip-assisted photoreduction of silver nanostructures on chemically patterned ferroelectric crystals for surface enhanced Raman scattering

Nanotips made of metal and semiconductor have been widely utilized in versatile applications to strengthen the electric field through lightning rod effect and localized surface plasmon resonance (LSPR) effect. Here, we present the utilization of ferroelectric nanotips to assist photoreduction of silver nanostructures for surface enhanced Raman scattering (SERS). Ferroelectric nanotips with spontaneous polarization posses the unique feature of producing the permanent electrostatic field without requiring external excitation, which differs from the present nanotips requiring electrical and optical excitation. The enhanced electrostatic field promotes the formation of silver nanoparticles by reducing the effect of Stern layer and accelerating the movement of photoelectrons and silver ions to the template surface. Experimental results show that sharp ferroelectric nanotips facilitate the formation of large-diameter nanoparticles with strong LSPR action. Compared to the conventional ferroelectric templates, the SERS substrates using nanotip-equipped ferroelectric templates produce 5.51 times larger Raman intensity, which can be further increased by >10.76 times by increasing the reaction time. The proposed SERS substrate owns the limit of detection <10−8 M and the enhancement factor of 2.3 × 109. The presented ferroelectric nanotips with permanent electrostatic field would open promising applications in the versatile areas, such as nanomaterial fabrication and optoelectronic devices.

Gold-coated electrospun PVA nanofibers as SERS substrate for detection of pesticides

Owing to its ability to detect Raman signals from trace amount of Raman active samples, surface enhanced Raman scattering (SERS) substrate has emerged as an interesting field of research for different areas of applications. Herein, we demonstrate a large area with good degree of reproducibility SERS substrate using PVA nanofibers. Gold (Au) coated electrospun PVA nanofibers has been used as SERS substrate in the present study. Using the designed SERS substrate, Raman signal from malachite green (MG) with concentration as low as 10 nM has been measured reliably by the Raman spectrometer. The relative standard deviation (RSD) for signature peaks of this Raman active sample at 420 cm−1, 1188 cm−1, 1378 cm−1 and 1618 cm-1 were found to be 6.01%, 7.38%, 5.71% and 6.50% respectively. The usability of the designed SERS substrate for detection of three commonly used pesticides namely deltamethrin, quinalphos and thiacloprid has been successfully demonstrated. It has been observed that for concentration well below the maximum residue limit as set in the Global Agricultural Information Network (GAIN) report from United States department of agriculture (USDA) foreign agricultural service, with the proposed SERS substrate one can easily estimate the concentration of the pesticide samples well below the permissible limit.

Surface enhanced Raman scattering of gold nanoparticles aggregated by a gold-nanofilm-coated nanofiber

Aggregation of metal nanoparticles plays an important role in surface enhanced Raman scattering (SERS). Here, a strategy of dynamically aggregating/releasing gold nanoparticles is demonstrated using a gold-nanofilm-coated nanofiber, with the assistance of enhanced optical force and plasmonic photothermal effect. Strong SERS signals of rhodamine 6G are achieved at the hotspots formed in the inter-particle and film-particle nanogaps. The proposed SERS substrate was demonstrated to have a sensitivity of 10−12 M, reliable reproducibility, and good stability.

Experimental and theoretical investigation for a hierarchical SERS activated platform with 3D dense hot spots

Hot spots generated from the ultra-small nanogaps will tremendously contribute to the strong electromagnetic field. Therefore, the establishment and design of nanogaps are extremely significant. Here, a hierarchical structure, AgNPs/bilayer graphene/Au nanonet, was proposed to form the dense three-dimensional (3D) hot spots and demonstrated in experiment and theory. Numerous nanometer gaps in the complex Au nanonet structure (∼8.67 nm) and in AgNPs/Au nanonet isolated by bilayer graphene (0.64 nm) were achieved, which is much beneficial for the obtainment of the hot spots. Based on this surface enhanced Raman scattering (SERS) substrate, an excellent SERS activity (EF ∼ 9.1 × 109), high sensitivity (10−13 and 10−12 M respective for Rhodamine 6G (R6G) and crystal violet (CV)), and SERS signals homogeneity, outstanding reproducibility (maximum intensity deviation from substrate to substrate ∼10.43%) were obtained, which can be attributed to the abundant lateral and vertical hot spots introduced by the hierarchical structure. Moreover, the proposed SERS substrate was used to sensitively detect the harmful malachite green (MG), which exhibits a great prospect as a potential SERS sensor in food safety field and biochemical molecules.

Sensitive Surface-Enhanced Raman Scattering Detection Using On-Demand Postassembled Particle-on-Film Structure.

Highly sensitive and low-cost surface-enhanced Raman scattering (SERS) substrates are essential for practical applications of SERS. In this work, we report an extremely simple but effective approach to achieve sensitive SERS detection of molecules (down to 10-10 M) by using a particle/molecule/film sandwich configuration. Compared to conventional SERS substrates which are preprepared to absorb analyte molecules for detection, the proposed sandwich configuration is achieved by postassembling a flexible transparent gel tape embedded with plasmonic nanoparticles onto an Au film decorated with to-be-detected analyte molecules. In such a configuration, the individual plasmonic gel tape and Au film have low or no SERS activity but the final assembled sandwich structure shows strong SERS signal due to the formation of numerous hot spots at the particle-film interface, where the analyte molecules themselves serve as both spacer and signal probes. Because of its simple configuration, we demonstrate that the proposed SERS substrate can be obtained over a large area with extremely low cost. Particularly, because of the on-demand nature and the flexibility, such a postassembly strategy provides an ideal solution to detect the pesticide residue on fruit surfaces with significantly enhanced sensitivity.

Nanostructured SERS substrates produced by nanosphere lithography and plastic deformation through direct peel-off on soft matter

We present a novel fragmented-film surface-enhanced Raman scattering (SERS) substrate produced by nanosphere lithography and direct peel-off for SERS efficacy enhancement. The 2D hexagonally close-packed polystyrene nanospheres on the polydimethylsilozane (PDMS) substrate are covered with silver film and then directly peeled off using sticky tape. During the peel-off process, the pulling force induces the stretch and contraction of the PDMS substrate and causes fracture of the 2D triangular silver film. Under laser excitation, a stronger localized electric field is induced in the smaller cracks and enhances the SERS intensity. The origin of this SERS enhancement is confirmed by numerical simulation using the finite element method and substrate annealing to smoothen the cracks. For the case using nanospheres with a diameter of 740 nm, an enhancement factor 6.5 × 106 can be achieved. The proposed fragmented-film SERS substrate gains 1.8 and 2.6 times larger Raman intensity at the 1358 cm−1 SERS peak than those using pyramidal silver islands and silver nanoshell array. The proposed SERS substrate has the features of easy fabrication, low production cost, short fabrication time and high enhancement factor.

Robustness of surface-enhanced Raman scattering substrate with a mercaptosilane adhesive layer for in vivo sensing applications

A highly robust surface-enhanced Raman scattering (SERS) substrate for in vivo sensing applications is reported. In vivo sensing demands structurally robust substrates with good optical performance. SERS substrates containing gold nanostructures on SiO2 supports often suffer from a low adhesion strength of gold on SiO2. The proposed SERS substrate contains a mercaptosilane adhesive layer, which provides a high robustness without deteriorating the plasmon performance, in contrast to traditional titanium adhesive layers. The mercaptosilane-modified SERS substrate is sufficiently robust for in vivo sensing, as evidenced by its implantation in the animal skin for 2 months.

Focused-ion-beam-fabricated Au/Ag multilayered nanorod array as SERS-active substrate for virus strain detection

A surface-enhanced Raman scattering (SERS) substrate was fabricated as well ordered Au/Ag multilayered nanorod arrays (fibAu/Ag_Rn, n=0–4) via the focused ion beam technique for the detection of the influenza A virus strain. Since the shape, thickness, space between nanorods, and dimensions affect the performance of SERS, these factors were optimized before the fabrication of the substrate by varying the thickness of the Au layer (4 variables), Ag layer (3 variables), and their corresponding Ag/Au repeated layers. Au/Ag multilayers with the optimal thickness were used to fabricate the designed SERS substrate. The results indicate that Ag layer plays an important role in the improvement of SERS mechanism by inducing the electromagnetic effect at the Au surface. The as-prepared fibAu/Ag_Rn substrate serves as an excellent SERS substrate, even verified at a very low concentration using rhodamine 6G as a reference, e.g., it exhibited an enhancement factor ranging from 2.62×106 to 1.74×107 using the proposed SERS substrate. Furthermore, the influenza A virus strains (A/WSN/33 (H1N1), A/England/12/64 (H2N2), and A/Philippine/2/82 (H3N2)) could be well distinguished at a low concentration of 106PFU/ml.