Fabrication Of SERS-active Substrates Research Articles

3D structured laser engraves decorated with gold nanoparticle SERS chips for paraquat herbicide detection in environments

Fabrication of SERS-active substrates is a thrust area of research in the field of SERS. Here, we report the fabrication of a new SERS-active substrate composed of Au nanostructures grown on aluminum sheets marked with laser lines (L-Mark SERS chips). The SERS activity of these SERS chips exploited with environmentally important herbicide, paraquat, and dye molecule of methylene blue. Density functional theory (DFT) calculation was performed to theoretically study the molecular structure and Raman vibrational modes of the paraquat. A detailed discussion has been devoted to uniformity, reproducibility, and practical utility of the fabricated substrates. Especially, great amount of discussion has been given to paraquat detection in soil extracts. The results emanate the ultra-sensitive detection of paraquat, uniform enhanced signals over the substrates, and high reproducibility. The report successfully demonstrated the detection of paraquat in drinking water, tap water, agri-water, environmental water, and soil extracts. Liquid chromatography-mass spectrometry (LCMS) measurements were also performed to demonstrate the realiability of the SERS method. The L-Mark SERS chips based paraquat detection is simple, rapid, and sensitive. We propose that the present sensors hold the potential to be used in herbicide detection and monitoring in-the-field experiments.

One-step synthesis of highly-branched gold nanostructures and its application in fabrication of SERS-active substrates

In this paper, we reported a simple one-step synthesis of highly-branched gold nanostructures (HGNs) in high yields. The reduction of HAuCl4 was accomplished by dopamine hydrochloride in the reaction system. By varying the amount of dopamine hydrochloride, HAuCl4 and the reaction temperature, we managed to tune the size of the HGNs from 200 to 600 nm. Systematic analysis revealed that the optical properties and surface-enhanced Raman scattering (SERS) activities of the HGNs were highly dependent on their morphology and size. In terms of their SERS activities, it was found that the HGNs synthesized at 60 °C with 2.0 mL dopamine hydrochloride (53 mM), 0.4 mL HAuCl4 (50 mM) exhibited the largest SERS enhancement. When the HGNs were assembled onto the silicon wafers, outstanding SERS efficiency was obtained with a detection limit of 5×10-10 M of 4-mercaptobenzoic acid (4-MBA) and the analytical enhancement factor (AEF) was calculated to be 7×107. Besides, the 3-aminopropyltriethoxysilane (APTES)-functionalized substrates with the HGNs displayed remarkable signal reproducibility with relative standard deviation (RSD) of 3.57%. All these results demonstrated that the SERS-active substrates held great promise to be applied in trace-level molecule detection in the future.

Flexible surface-enhanced Raman scattering-active substrates based on nanofibrous membranes

Surface-enhanced Raman scattering (SERS) has emerged as an excellent analytical tool for the effective detection and fingerprint identification of various chemicals. Recently, significant progress has been made in the fabrication of SERS-active substrates using simple, inexpensive, and affordable methods. The full potential of universal SERS diagnostics will likely be realized with the development of approaches and devices capable of effectively detecting analytes on various surfaces as well as in multicomponent media. In addition, the combination of implantable or wearable SERS-active substrates and remote portable devices enables real-time diagnostics that ideally fit the concept of personalized medicine. In this paper, we summarize recent achievements in fabricating flexible SERS substrates made of cellulose paper, polymer membranes, and textile fibrous films. Emphasis is placed on the in-situ extraction and detection of various chemicals in real-world surfaces and complex media using flexible nanofibrous SERS platforms. The potential SERS applications and future perspectives in on-site diagnostics are also discussed.

Study of Signal-to-Background Ratio of Surface-Enhanced Raman Scattering: Dependences on Excitation Wavelength and Hot-Spot Gap

Signal-to-background ratio of surface-enhanced Raman scattering (SERS) plays an important role in the analytic applications of SERS. Its dependences on excitation wavelength and gap between metal particles were studied theoretically and experimentally. We show that this ratio is higher at smaller gaps for the same excitation wavelength and is higher for the wavelengths having higher values of the absolute values of the dielectric function of the metal. This study thus results in design guidelines in the fabrication of SERS-active substrates with high signal-to-background ratio.

Nanostructured plasmonic substrates for use as SERS sensors.

Plasmonic nanostructures strongly localize electric fields on their surfaces via the collective oscillations of conducting electrons under stimulation by incident light at a certain wavelength. Molecules adsorbed onto the surfaces of plasmonic structures experience a strongly enhanced electric field due to the localized surface plasmon resonance (LSPR), which amplifies the Raman scattering signal obtained from these adsorbed molecules. This phenomenon is referred to as surface-enhanced Raman scattering (SERS). Because Raman spectra serve as molecular fingerprints, SERS has been intensively studied for its ability to facilely detect molecules and provide a chemical analysis of a solution. Further enhancements in the Raman intensity and therefore higher sensitivity in SERS-based molecular analysis have been achieved by designing plasmonic nanostructures with a controlled size, shape, composition, and arrangement. This review paper focuses on the current state of the art in the fabrication of SERS-active substrates and their use as chemical and biosensors. Starting with a brief description of the basic principles underlying LSPR and SERS, we discuss three distinct nanofabrication methods, including the bottom-up assembly of nanoparticles, top-down nanolithography, and lithography-free random nanoarray formation. Finally, typical applications of SERS-based sensors are discussed, along with their perspectives and challenges.

Fabrication of SERS-Active Substrates by Electrochemical and Electroless Deposition of Metals in Macroporous Silicon

SERS-active substrates based on hybrid metallic nanovoids were formed by successive Ni electrodeposition and Ag electroless deposition in macroporous silicon. It was shown that the SERS signal intensity greatly depends on the morphology and elemental composition of hybrid melallization. Optimal regimes of metallization were found which provided fabrication of the most SERS-active substrates demonstrated 10-11 M detection limit for rhodamine R6G.

Fabrication of SERS-Active Substrates by Electrochemical and Electroless Deposition of Metals in Macroporous Silicon

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Fabrication of SERS Active Substrates by Nanoimprint Lithography

ABSTRACTA method for low-cost fabrication of SERS substrates in rapid and reproducible way based on nanoimprint lithography (NIL) method has been developed. The SERS enhancement for detection of Rhodamine 6G molecules is demonstrated on two model nanostructures comprising either Au nano-crescents or Ag nano-wells fabricated by this method. Numerical simulations based on discrete dipole approximation (DDA) method show that the observed enhancement of the SERS signal for the given geometries originates in hot-spots localized at the tips of the nanocrescent. For the nanowell, the hotspots are mainly localized inside the cavity, on the side of the nanodonut, or at the edge of the bottom nanodisc when it is excited by a laser at the wavelength of 785 nm.

Deposition Method for Preparing SERS-Active Gold Nanoparticle Substrates

Surface-enhanced Raman scattering or SERS, discovered some 20 years ago, has recently become a promising tool for routine biofluid assays in a clinical setting. Many attempts have been made to produce cheap and reproducible SERS-active substrates. In this study, we report on the fabrication of SERS-active substrates through the convective assembly of gold (Au) particles on electrostatically charged glass slides. We show that, by a proper control of the initial particle concentration in an evaporating Au suspension droplet, it is possible to obtain a closely packed colloidal film capable of generating SERS activity. Finally, AFM and SERS measurements of the resulting films reveal comparability in performance with previous silane-immobilized Au colloidal films. The minimum electromagnetic enhancement factor of our films is estimated to be about 2 x 10(4).