Cost Effective Silver Nanowire-Decorated Graphene Paper for Drop-On SERS Biodetection.
ABSTRACT: The use of SERS for real-world bioanalytical applications represents a concrete opportunity, which, however, is being largely delayed by the inadequacy of existing substrates used to collect SERS spectra. In particular, the main bottleneck is their poor usability, as in the case of unsupported noble metal colloidal nanoparticles or because of the need for complex or highly specialized fabrication procedures, especially in view of a large-scale commercial diffusion. In this work, we introduce a graphene paper-supported plasmonic substrate for biodetection as obtained by a simple and rapid aerosol deposition patterning of silver nanowires. This substrate is compatible with the analysis of small (2 μL) analyte drops, providing stable SERS signals at sub-millimolar concentration and a detection limit down to the nanogram level in the case of hemoglobin. The presence of a graphene underlayer assures an even surface distribution of SERS hotspots with improved stability of the SERS signal, the collection of well-resolved and intense SERS spectra, and an ultra-flat and photostable SERS background in comparison with other popular disposable supports.
Project description:Graphene and its derivatives have been demonstrated to be good surface-enhanced Raman scattering (SERS) substrates. However, the literature offers some contrasting views on the SERS effect of graphene-based materials. Thus, understanding the mechanism of the SERS enhancement of graphene is essential for exploring its application as a SERS substrate. In this study, graphene oxide (GO) and chemically reduced graphene oxide (CRGO) films with different morphologies and structures were prepared and applied as SERS substrates to detect Raman dye molecules. The observed enhancement factors can be as large as 10~10³. The mechanism of SERS enhancement is discussed. It is shown that the SERS effect was independent of the adsorption of dye molecules and the surface morphologies of graphene-based films. Raman shifts are observed and are almost the same on different graphene-based films, indicating the existence of charge transfer between dye molecules and substrates. The Raman enhancement factors and sensitivities of dye molecules on different films are consistently within the <i>I<sub>G</sub></i>/<i>I<sub>D</sub></i> ratios of graphene-based substrates, indicating that the dramatically enhanced Raman spectra on graphene-based films are strongly dependent on the average size of <i>sp</i>² carbon domain.
Project description:Nanohybrids of graphene and two-dimensional (2D) layered transition metal dichalcogenides (TMD) nanostructures can provide a promising substrate for extraordinary surface-enhanced Raman spectroscopy (SERS) due to the combined electromagnetic enhancement on TMD nanostructures via localized surface plasmonic resonance (LSPR) and chemical enhancement on graphene. In these nanohybrid SERS substrates, the LSPR on TMD nanostructures is affected by the TMD morphology. Herein, we report the first successful growth of MoS<sub>2</sub> nanodonuts (N-donuts) on graphene using a vapor transport process on graphene. Using Rhodamine 6G (R6G) as a probe, SERS spectra were compared on MoS<sub>2</sub> N-donuts/graphene nanohybrids substrates. A remarkably high R6G SERS sensitivity up to 2 × 10<sup>-12</sup> M has been obtained, which can be attributed to the more robust LSPR effect than in other TMD nanostructures such as nanodiscs as suggested by the finite-difference time-domain simulation. This result demonstrates that non-metallic TMD/graphene nanohybrids substrates can have SERS sensitivity up to one order of magnitude higher than that reported on the plasmonic metal nanostructures/2D materials SERS substrates, providing a promising scheme for high-sensitivity, low-cost applications for biosensing.
Project description:Deep-ultraviolet surface-enhanced Raman scattering (UV-SERS) is a promising technique for bioimaging and detection because many biological molecules possess UV absorption lines leading to strongly resonant Raman scattering. Here, Al nanovoid substrates are developed by combining nanoimprint lithography of etched polymer/silica opal films with electron beam evaporation, to give a high-performance sensing platform for UV-SERS. Enhancement by more than 3 orders of magnitude in the UV-SERS performance was obtained from the DNA base adenine, matching well the UV plasmonic optical signatures and simulations, demonstrating its suitability for biodetection.
Project description:We registered surface enhanced Raman scattering (SERS) spectra of the human lactoferrin molecules adsorbed on a silvered porous silicon (por-Si) from 10-6?10-18 M solutions. It was found that the por-Si template causes a negative surface potential of silver particles and their chemical resistivity to oxidation. These properties provided to attract positively charged lactoferrin molecules and prevent their interaction with metallic particles upon 473 nm laser excitation. The SERS spectra of lactoferrin adsorbed from 10-6 M solution were rather weak but a decrease of the concentration to 10-10 M led to an enormous growth of the SERS signal. This effect took place as oligomers of lactoferrin were broken down to monomeric units while its concentration was reduced. Oligomers are too large for a uniform overlap with electromagnetic field from silver particles. They cannot provide an intensive SERS signal from the top part of the molecules in contrast to monomers that can be completely covered by the electromagnetic field. The SERS spectra of lactoferrin at the 10-14 and 10-16 M concentrations were less intensive and started to change due to increasing contribution from the laser burned molecules. To prevent overheating the analyte molecules on the silvered por-Si were protected with graphene, which allowed the detection of lactoferrin adsorbed from the 10-18 M solution.
Project description:Printable multi-marker biochips that enable simultaneous quantitative detection of multiple target biomarkers in point-of-care and resource-limited settings are a holy grail in the field of biodiagnostics. However, preserving the functionality of biomolecules, which are routinely employed as recognition elements, during conventional printing approaches remains challenging. In this article, we introduce a simple yet powerful approach, namely plasmonic calligraphy, for realizing multiplexed label-free bioassays. Plasmonic calligraphy involves a regular ballpoint pen filled with biofunctionalized gold nanorods as plasmonic ink for creating isolated test domains on paper substrates. Biofriendly plasmonic calligraphy approach serves as a facile method to miniaturize the test domain size to few mm(2), which significantly improves the sensitivity of the plasmonic biosensor compared to bioplasmonic paper fabricated using immersion approach. Furthermore, plasmonic calligraphy also serves as a simple and efficient means to isolate multiple test domains on a single test strip, which facilitates multiplexed biodetection and multi-marker biochips. Plasmonic calligraphy, which can be potentially automated by implementing with a robotic arm, serves as an alternate path forward to overcome the limitations of conventional ink-jet printing.
Project description:Graphene Quantum dots (GQDs) are used as a surface-enhanced Raman substrate for detecting target molecules with large specific surface areas and more accessible edges to enhance the signal of target molecules. The electrochemical process is used to synthesize GQDs in the solution-based process from which the SERS signals were obtained from GQDs Raman spectra. In this work, GQDs were grown via the electrochemical process with citric acid and potassium chloride (KCl) electrolyte solution to obtain GQDs in a colloidal solution-based format. Then, GQDs were characterized by transmission electron microscope (TEM), Fourier-transform infrared spectroscopy (FTIR), and Raman spectroscopy, respectively. From the results, SERS signals had observed via GQDs spectra through the Raman spectra at D (1326 cm<sup>-1</sup>) and G (1584 cm<sup>-1</sup>), in which D intensity is defined as the presence of defects on GQDs and G is the sp<sup>2</sup> orbital of carbon signal. The increasing concentration of KCl in the electrolyte solution for 0.15M to 0.60M demonstrated the increment of Raman intensity at the D peak of GQDs up to 100 over the D peak of graphite. This result reveals the potential feasibility of GQDs as SERS applications compared to graphite signals.
Project description:Graphene, which has a linear electronic band structure, is widely considered as a semimetal. In the present study, we combine graphene with conventional metallic surface-enhanced Raman scattering (SERS) substrates to achieve higher sensitivity of SERS detection. We synthesize high-quality, single-layer graphene sheets by chemical vapor deposition (CVD) and transfer them from copper foils to gold nanostructures, i.e., nanoparticle or nanohole arrays. SERS measurements are carried out on methylene blue (MB) molecules. The combined graphene nanostructure substrates show about threefold or ninefold enhancement in the Raman signal of MB, compared with the bare nanohole or nanoparticle substrates, respectively. The difference in the enhancement factors is explained by the different morphologies of graphene on the two substrates with the aid of numerical simulations. Our study indicates that applying graphene to SERS substrates can be an effective way to improve the sensitivity of conventional metallic SERS substrates.
Project description:Surface enhanced Raman spectroscopy (SERS) is an attractive analytical technique, which enables single-molecule sensitive detection and provides its special chemical fingerprints. During the past decades, researchers have made great efforts towards an ideal SERS substrate, mainly including pioneering works on the preparation of uniform metal nanostructure arrays by various nanoassembly and nanotailoring methods, which give better uniformity and reproducibility. Recently, nanoparticles coated with an inert shell were used to make the enhanced Raman signals cleaner. By depositing SERS-active metal nanoislands on an atomically flat graphene layer, here we designed a new kind of SERS substrate referred to as a graphene-mediated SERS (G-SERS) substrate. In the graphene/metal combined structure, the electromagnetic "hot" spots (which is the origin of a huge SERS enhancement) created by the gapped metal nanoislands through the localized surface plasmon resonance effect are supposed to pass through the monolayer graphene, resulting in an atomically flat hot surface for Raman enhancement. Signals from a G-SERS substrate were also demonstrated to have interesting advantages over normal SERS, in terms of cleaner vibrational information free from various metal-molecule interactions and being more stable against photo-induced damage, but with a comparable enhancement factor. Furthermore, we demonstrate the use of a freestanding, transparent and flexible "G-SERS tape" (consisting of a polymer-layer-supported monolayer graphene with sandwiched metal nanoislands) to enable direct, real time and reliable detection of trace amounts of analytes in various systems, which imparts high efficiency and universality of analyses with G-SERS substrates.
Project description:This study examines the improvements in surface-enhanced Raman scattering (SERS) performance achieved when silver nanodendritic structures are coated with various graphene-based materials, namely graphene oxide (GO), reduced graphene oxide (rGO), and graphene nanoplatelets (GNPs). The tests are performed on our unique SERS-active substrates, prepared on the surface of planar microelectrode chips using an electric field-guided Ag nanoparticle assembly process. The graphene-based materials are introduced into the substrate by means of an in-house spray-coating technique. The SERS enhancement effect of each coating is examined as a function of spray nozzle passes (N) and optimal values are identified for each coating type. The enhancements found for GO, rGO, and GNP (6?9 graphene layers thick) coatings are 2.3 (N = 25), 2.5 (N = 5), and 1.6 (N = 1), respectively. Additionally, in comparison with their uncoated counterparts, substrates coated with rGO (N = 5) are shown to enhance the intensity of the methamphetamine (5 ppb) spectrum in artificial saliva by approximately 3-fold. Overall, it can be concluded that the introduction of GO or rGO to the SERS substrate using spray-coating, a simple and also scalable method, can produce substantial SERS performance enhancement.
Project description:Surface-enhanced Raman scattering (SERS) has been extensively investigated as an effective approach for trace species detection. Silver nanostructures are high-sensitivity SERS substrates in common use, but their poor chemical stability impedes practical applications. Herein, a stable and sensitive SERS substrate based on the hybrid structures of graphene/silver film/laser-textured Si (G/Ag/LTSi) was developed, and a simple, rapid, and low-cost fabrication approach was explored. Abundant nanoparticles were directly created and deposited on the Si surface via laser ablation. These aggregated nanoparticles functioned as hotspots after a 30 nm Ag film coating. A monolayer graphene was transferred to the Ag film surface to prevent the Ag from oxidation. The SERS behavior was investigated by detecting R6G and 4-MBT molecules. The experimental results indicate that the maximum enhancement factor achieved by the G/Ag/LTSi substrate is over 10⁷ and less than 23% SERS signals lost when the substrate was exposed to ambient conditions for 50 days. The covering graphene layer played crucial roles in both the Raman signals enhancement and the Ag nanostructure protection. The stable and sensitive SERS performance of G/Ag/LTSi substrate evince that the present strategy is a useful and convenient route to fabricate large-area graphene-silver plasmonic hybrids for SERS applications.