Flexible Surface-enhanced Raman Scattering Substrate Research Articles

Transparent and Flexible Surface-Enhanced Raman Scattering (SERS) Sensors Based on Gold Nanostar Arrays Embedded in Silicon Rubber Film.

Integration of surface-enhanced Raman scattering (SERS) sensors onto transparent and flexible substrates enables lightweight and deformable SERS sensors which can be wrapped or swabbed on various nonplanar surfaces for the efficient collection and detection of analytes on various surfaces. However, the development of transparent and flexible SERS substrates with high sensitivity is still challenging. Here, we demonstrate a transparent and flexible SERS substrate with high sensitivity based on a polydimethylsiloxane (PDMS) film embedded with gold nanostar (GNS) assemblies. The flexible SERS substrates enable conformal coverage on arbitrary surfaces, and the optical transparency allows light interaction with the underlying contact surface, thereby providing highly sensitive detection of analytes adsorbed on arbitrary metallic and dielectric surfaces which otherwise do not provide any noticeable Raman signals of analytes. In particular, when the flexible SERS substrates are covered onto metallic surfaces, the SERS enhancement is greatly improved because of the additional plasmon couplings between GNS and metal film. We achieve the detection capability of a trace amount of benzenethiol (10-8 M) and enormous SERS enhancement factor (∼1.9 × 108) for flexible SERS substrates on Ag film. In addition, because of the embedded structure of GNS monolayers within the PDMS film, SERS sensors maintain the high sensitivity even after mechanical deformations of stretching, bending, and torsion for 100 cycles. The transparent and flexible SERS substrates introduced in this study are applicable to various SERS sensing applications on nonplanar surfaces, which are not achievable for hard SERS substrates.

Self-assembly of Ag nanoparticles on the woven cotton fabrics as mechanical flexible substrates for surface enhanced Raman scattering

Flexible surface-enhanced Raman scattering (SERS) substrates were fabricated based on the natural woven cotton fabrics by a simple self-assembly method in which silver nanoparticles (Ag NPs) were deposited on the fabric. The SERS signal can be controlled by changing the assemble cycle times, leading to different decorated Ag amount on the surface of woven cotton fabrics. SERS woven cotton fabrics displayed excellent reproducibility and SERS sensitivity with a detection limit of p-Aminothiophenol (PATP) at 10−7 M. Moreover, the SERS woven cotton fabrics exhibited remarkable flexibility and practicality, allowing for a close contact the samples surface by swabbing. The approach could be readily extended to other fabrics, such as wool fabrics and other natural fiber fabrics, paving on a new way for the low-cost, portable and flexible SERS substrates.

Ag2O@Ag core-shell structure on PMMA as low-cost and ultra-sensitive flexible surface-enhanced Raman scattering substrate

We report a simple method to fabricate Ag2O@Ag core-shell nanostructure employed as SERS (surface enhanced Raman scattering) active substrate. The Ag2O shell was fabricated via the oxidation of AgNPs with the assist of laser irradiation in atmosphere. In this way, the prepared Ag2O@Ag hybrid system possesses ultrasensitivity, homogeneity, reproducibility and chemical stability by virtue of ultra-thin inner shell. The minimum detectable concentration of R6G was presented as low as 10−11 M. The enhancement factor of Ag2O@Ag core-shell nanostructure using R6G as probe molecules was found to be as high as 6 × 107. Furthermore, the flexible Ag2O@Ag/PMMA SERS substrate were first presented and the SERRS (surface enhanced resonance Raman scattering) spectra of the R6G on this substrate were investigated. The characteristic peaks of R6G with concentration from 10−5–10−11 M can be also easily observed by detecting from both sides of the flexible substrate. A good linear response between SERRS intensity and R6G concentration from 10−5 to 10−11 M was obtained. For practical application, the Ag2O@Ag/PMMA hybrids flexible SERS substrate was used for real-time and in-situ detection of chlorpyrifos with 10−7 M on cucumber and apple peels. These results are exactly consistent with the DFT simulation on chlorpyrifos pesticide and confirm that the Ag2O@Ag/PMMA hybrids flexible SERS substrate is highly promising for food safety field in the future.

Flexible and robust SERS active substrates for conformal rapid detection of pesticide residues from fruits

Flexible surface enhanced Raman scattering (SERS) substrates have advantage over the conventional rigid substrates as they can conform to the underlying object for the efficient extraction of target molecules from complex surfaces. Here, we demonstrate a simple and facile method for fabricating large area SERS-active, flexible and robust substrate for conformal and rapid extraction and detection of trace molecules. The novel SERS substrate was fabricated by embedding Ag nanorods into the polydimethylsiloxane (PDMS) polymer. The AgNRs embedded SERS substrates exhibited a high sensitivity and excellent reproducibility for analytes employed, demonstrating a direct application in trace detection for on-field applications. The in situ SERS measurements on these flexible substrates under mechanical tensile strain conditions were performed. Our results show that flexible SERS substrates can withstand a tensile strain (ε) value as high as 30% without losing SERS performance. The functionality of AgNRs embedded PDMS SERS substrate was demonstrated by directly extracting trace amount (∼10−9g/cm2) of thiram pesticide directly from fruit peels via simple “paste and peel off” method.

Silver nanotriangles-loaded filter paper for ultrasensitive SERS detection application benefited by interspacing of sharp edges

The strongly enhanced electromagnetic “hotspots” from the edges and tips of nanoplates are highly preferred to significantly promote the surface enhanced Raman scattering (SERS) activity. Here, Ag nanotriangles with a sharp edge of 20nm were prepared by the reduction of AgNO3 using N,N-Dimethylformamide (DMF) with the assistance of Polyvinyl pyrrolidone (PVP). By loading of Ag nanotriangles onto the filter paper, a flexible SERS substrate with good activity and reproducibility was obtained and the ultratrace detection of p-aminothiophenol (pATP) with a concentration as low as 10−8M was achieved. The sharp edges and tips boosted SERS activity was proved by the finite element method modeling of the plasmonic properties of Ag nanotriangles with different edge thicknesses (10 − 80nm), Ag nanosheets with different tip acutances (squares and hexagons) together with Ag nanorods, nanocubes and nanospheres. The experimental and theoretical results confirmed that the interspacing created by filter paper plays an important role in enhancing the overall SERS activity. Furthermore, it is shown that the present silver nanotriangles-loaded filter paper SERS substrate can be employed to sensitive and selective detecting ultratrace military explosives picric acid (PA) of 10−6M.

Flexible and mechanical strain resistant large area SERS active substrates

We report a cost effective and facile way to synthesize flexible, uniform, and large area surface enhanced Raman scattering (SERS) substrates using an oblique angle deposition (OAD) technique. The flexible SERS substrates consist of 1 μm long, tilted silver nanocolumnar films deposited on flexible polydimethylsiloxane (PDMS) and polyethylene terephthalate (PET) sheets using OAD. The SERS enhancement activity of these flexible substrates was determined using 10(-5) M trans-1,2-bis(4-pyridyl) ethylene (BPE) Raman probe molecules. The in situ SERS measurements on these flexible substrates under mechanical (tensile/bending) strain conditions were performed. Our results show that flexible SERS substrates can withstand a tensile strain (ε) value as high as 30% without losing SERS performance, whereas the similar bending strain decreases the SERS performance by about 13%. A cyclic tensile loading test on flexible PDMS SERS substrates at a pre-specified tensile strain (ε) value of 10% shows that the SERS intensity remains almost constant for more than 100 cycles. These disposable and flexible SERS substrates can be integrated with biological substances and offer a novel and practical method to facilitate biosensing applications.

Large area flexible SERS active substrates using engineered nanostructures

Surface enhanced Raman scattering (SERS) is an analytical sensing method that provides label-free detection, molecularly specific information, and extremely high sensitivity. The Raman enhancement that makes this method attractive is mainly attributed to the local amplification of the incident electromagnetic field that occurs when a surface plasmon mode is excited at a metallic nanostructure. Here, we present a simple, cost effective method for creating flexible, large area SERS-active substrates using a new technique we call shadow mask assisted evaporation (SMAE). The advantage of large, flexible SERS substrates such as these is they have more area for multiplexing and can be incorporated into irregular surfaces such as clothing. We demonstrate the formation of four different types of nanostructure arrays (pillar, nib, ellipsoidal cylinder, and triangular tip) by controlling the evaporation angle, substrate rotation, and deposition rate of metals onto anodized alumina nanoporous membranes as large as 27 mm. In addition, we present experimental results showing how a hybrid structure comprising of gold nanospheres embedded in a silver nano-pillar structure can be used to obtain a 50× SERS enhancement over the raw nanoparticles themselves.