Fabrication Of SERS Substrates Research Articles

Fabrication of SERS substrates by laser restructuring of interconnected Au nanostructures for urea detection

We discuss a facile, fast, simple, and reproducible fabrication method to modulate the structural morphology of the SERS substrate to improve its performance. The interconnected Au network structure named as nanoporous Au (NP–Au) is prepared by the dealloying method and further exposed with varied laser power in order to check the effect of power variation on the morphology as well as on the SERS performance. The effectiveness of the substrate has been tested by detecting Rhodamine 6G as a probe molecule. The Raman results show a good linear relationship with the laser power increment up to 3.2 mW and after that, the signal becomes saturated for a further increment in the power. The substrate is able to enhance the signal up to 102-fold as well able to show all the characteristic peaks without any damage to the probe molecule. Morphological identification reveals that different sizes and shapes of the pores (open, diffused, and interlinked) are responsible for the SERS signal enhancement. Subsequently, the sensitivity of SERS substrate has been examined and the result suggested that the optimal concentration of Rhodamine is 10−9 M. Furthermore, the substrate possesses good uniformity by representing a relative standard deviation value of less than 15 %. The substrate potential for real-world application has been examined by identifying urea (pesticide) molecules. The prepared nanoporous substrate is able to show a well-intensified signal with ∼16-fold enhancement compared to planar Silicon substrate.

A self-cleaning SERS substrate based on flower-like Au@MoS2/Ag NPs with photocatalytic ability

Noble metals such as gold and silver play important role in the fabrication of SERS substrates, however, the high cost of noble metals has become an obstacle when SERS start to move out of the research laboratory and into practice. Recently, self-cleaning substrates have drawn more and more attention due to their recyclable ability and further reducing cost. In this work, a flower-like Au@MoS2/Ag NPs nanocomposite with core-shell structure was synthesized by hydrothermal method. The employment of MoS2 endows the substrate with a high adsorption capacity and photocatalytic ability. Finally, a highly sensitive, self-cleaning, and recyclable SERS substrate was constructed by combining the synergistic effect of noble metal nanoparticles (Au, Ag) and the photocatalytic ability of MoS2. Methylene blue (MB) was used to evaluate the SERS performances of the as-prepared substrate, and the results show that the as-prepared substrate has good signal uniformity with relative standard deviation (RSD) of 8.2 %, and good batch-to-batch stability with the RSDs of 4.9 %, 5.7 %, and 5.3 % at 1625 cm−1, 1401 cm−1, and 451 cm−1, respectively. In the range of 10−5–10−10 M, the concentration of the analyte showed a good linear relationship with the Raman peak intensity at 1625 cm−1, with the correlation coefficient R2 of 0.9821, and the detection limit was 8.9 × 10−11 M. In addition, the photocatalytic performance of the substrate was investigated, 97.1 % of the MB was degraded under the irradiation of the Xe lamp for 100 min, and the SERS signal remained at 62.8 % of the initial signal after 8 cycles. The flower-like Au@MoS2/Ag NPs self-cleaning SERS substrate developed in this work shows good renewable performance and is expected to be used as a new SERS substrate in food, medicine, environmental, and other analytical fields.

SERS determination and multivariate classification of antibiotics in chicken meat using gold nanoparticle-decorated electrospun PVA nanofibers.

The fabrication of SERS substrate by gold nanoparticle-decorated polyvinyl alcohol electrospun nanofibers which has been used to detect trace sensing of two widely used poultry antibiotics doxycycline hydrochloride and enrofloxacin is demonstrated. The performance of the backscattered Raman signals from the proposed SERS substrate has been initially evaluated with two standard Raman active compounds namely malachite green and rhodamine-6G. The limit of detection of the proposed substrate is estimated to be 7.32 nM. Following this, the usability of the proposed SERS substrate has been demonstrated through the detection of the aforementioned antibiotics in chicken meat samples. The presence of antibiotics in chicken meat sample has been validated with the standard analytical tool of liquid chromatography-mass spectrometry and the results were compared with the proposed sensing technique. Further, principal component analysis has been performed to classify the antibiotics that are present in the field-collected meat samples.

Fabrication of SERS substrates by femtosecond LIPAA for detection of contaminants in foods

Rapid and sensitive detection of contaminants in foods is crucial for minimizing potential health hazards to humans. In this work, we developed a SERS substrate fabricated by femtosecond laser induced plasma assisted ablation (fs LIPAA) for food contaminants detection. By tuning laser fluence, the distribution and size of silicon nanoparticles generated by fs LIPAA are studied. Hotspots with high uniformity can be created for SERS functionalization by decorating the substrate with a layer of silver film. It is found that the SERS performance is well optimized at a laser fluence of 5 J/cm2. The proposed Ag NPs/glass SERS substrate shows good uniformity with an enhancement factor of 2 × 105 via R6G Raman probe as compared to a traditional smooth Ag film. The detection limits of melamine in milk liquid and ciprofloxacin in water are both 1 ppm. The results demonstrate great potential to pave a new way to realize the use of SERS substrates in food safety.

Fabrication of SERS Substrates Using Au Nanoparticles Prepared by Laser Ablation in Distilled Water and Detection of Tetracycline at Low Concentrations

We studied to produce SERS substrates using gold (Au) nanoparticles (AuNPs) prepared by pulse laser ablation (PLA) in water. The colloidal Au NPs with average size of 23nm were deposited on a silicon wafer to form AuNPs/Si SERS substrate. Malachite green was chosen as a test analyte to examine the sensitivity of the SERS substrates. The SERS enhancement factor of the AuNPs/Si was found to be about 106. The high sensitivity of the AuNPs/Si substrates was confirmed by the SERS spectra of malachite green detected with high quality at concentrations of 0.1ppm. The SERS substrates can detect SERS spectra of tetracycline at low concentrations of around 1ppm.

Different number of silver nanoparticles layers for surface enhanced raman spectroscopy analysis

For application in practice, reducing the cost and simplifying the steps in fabrication of SERS substrates with excellent property are still the important factors. Here, a three-dimensional (3D) Ag nanoparticles (NPs) obtained by facile thermal evaporation is obtained for SERS. The Raman enhancement effect gradually become strong as the number of Ag NPs layers increase and attain the best until four layers Ag NPs deposited for the finite penetration depth of incident laser. The intensity of Raman signal collected from the four-layer Ag NPs substrate is around 11.3 times stronger than that from one-layer Ag NPs. Besides, the reproducibility of the SERS substrate was also significantly promoted as the layers of Ag NPs increases. The SERS substrate exhibits temporal stability and its enhancement factor attains 6.8×108. Furthermore, the SERS substrate can easily combine with some other blocks with superior SERS property and show better SERS ability. Additionally, the in-situ trace analyses in aquatic products were realized by flexible Ag NPs/PET substrate.

Fabrication of SERS substrates containing dense “hot spots” by assembling star-shaped nanoparticles on superhydrophobic surfaces

In this work, efficient SERS substrates containing dense hot spots were fabricated by assembling AuNS@Ag on SMCSL superhydrophobic platforms, based on an evaporation assembly technique.

A three-dimensional silver nanoparticles decorated plasmonic paper strip for SERS detection of low-abundance molecules

The fabrication of SERS substrates, which can offer the advantages of strong Raman signal enhancement with good reproducibility and low cost, is still a challenge for practical applications. In this work, a simple three-dimensional (3D) paper-based SERS substrate, which contains plasmonic silver-nanoparticles (AgNPs), has been developed by the silver mirror reaction. This paper strip was characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), etc. Pretreatment of the paper as well as the reaction time, temperature, and reagent concentrations for the silver mirror reaction were varied for further studies. With the optimized experimental parameters, the AgNPs synthesized and distributed in-situ on the paper strip could give more favorable SERS performance. The limit of detection (LOD) as low as 10−11M for Rhodamine 6G (R6G) and 10−9M for p-aminothiophenol (p-ATP) plus wide linear range for the log–log plot of Raman intensity versus analyte concentration were achieved. The detection of R6G in rain water was also carried out successfully. The merits of this protocol include low cost, easy operation, high sensitivity and acceptable stability, which make it ideal for the detection of environmental samples in trace amounts.

Fabrication of SERS substrate using nanoporous anodic alumina template decorated by silver nanoparticles

SERS substrate is fabricated using nanoporous anodic alumina membrane decorated by silver nanoparticles, which are self assembled on the surface as well as inside the pores to form a network structure of aligned cylindrical vertical wells creating artificial roughness on the surface of the membrane. When electromagnetic radiation falls on the rough surface, a strong electric field is created due to plasmon excitation on sharp edges of the network structure or at interparticle spacing known as ‘hot spots’. This enhanced electric field produces remarkable SERS effect from Raman active R6G molecules attached to silver nanoparticles when excited by a laser source.

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.