SERS substrate

The first SERS experiments were performed with electrochemically roughened electrodes and metal colloids, and many other types of suitable SERS substrates are known - e.g. metal island films, metal films over nanoparticles (see Fig. 4.58, below) or rough substrates, gratings, and sputter-deposited metal particles. 

SERS substrates with bare metal surfaces irreversibly adsorb thioorganics (Eig. 4.59) and other compounds and can thus serve for the detection and identification of very low gas or solution concentrations of these substances [4.303]. SERS is especially well suited for the analysis of traces of gases, because it combines measurement of surface concentration with extremely high sensitivity. A monolayer in a typical focus of a laser with a diameter of 10 pm has a mass in the range of 10 femtograms even smaller amounts of substance are easily detectable, because 1% of a monolayer in a region 1-pm in diameter results in SERS of sufficient intensity. 

Fang C, Agarwal A, Devi Buddharaju K et al (2008) DNA detection using nanostructured SERS substrates with Rhodamine B as Raman label. Biosens Bioelectron 24 216-221... 

Occasionally, arrangements with a fibre as sensing element (Figure 7-c) are used, in particular for SERS measurements (the fibre is then coated with the SERS substrate). When using such a layout, it must be taken into account that also the Raman scattering caused by the waveguide material is recorded and must be filtered out. The same applies to arrangements where a window or any other optical element illuminated by the excitation radiation is in the field of view of the collection optics. 

For trace analysis in fluids, some Raman sensors (try to) make use of the SERS effect to increase their sensitivity. While the basic sensor layout for SERS sensors is similar to non-enhanced Raman sensors, somehow the metal particles have to be added. Other than in the laboratory, where the necessary metal particles can be added as colloidal solution to the sample, for sensor applications the particles must be suitably immobilised. In most cases, this is achieved by depositing the metal particles onto the surfaces of the excitation waveguide or the interface window and covering them with a suitable protection layer. The additional layer is required as otherwise washout effects or chemical reactions between e.g. sulphur-compounds and the particles reduce the enhancement effect. Alternatively, it is also possible to disperse the metal particles in the layer material before coating and apply them in one step with the coating. Suitable protection or matrix materials for SERS substrates could be e.g. sol-gel layers or polymer coatings. In either... 

Murphy T., Schmidt H., Kronfeldt H., Use of sol-gel techniques in the development of surface-enhanced Raman scattering (SERS) substrates suitable for in situ detection of chemicals in sea-water, Appl. Phys. B, 1999 69(2) 147-150. 

A host of biological compounds (e.g., proteins, amino acids, lipids, fats, fatty acids, DNA, RNA, antibodies, enzymes) have been studied via SERS. The extensive progress in the development of dependable SERS substrates over the past few decades has promoted the application of SERS in the rapidly expanding field of biotechnology, as is demonstrated in several... 

Solid SERS Substrates Based on Metallic Nanostructures... 

SERS Substrates Based on Metal-Coated Quartz Posts... 

Silver nanoparticles embedded in various solid porous media (Figure 3d) have recently been investigated as stable SERS substrates with the potential for selective detection. The in situ production of these nanoparticles in solid... 

Chen, Y.-C., et al., Silver-decorated carbon nanotube networks as SERS substrates. Journal of Raman Spectroscopy, 2011. 42(6) p. 1255-1262. 

SERS substrates for use in biosamples have to meet a number of requirements They have to be close to the molecules to be probed, hence mobile... 

Freeman RG, Grabar KC, Allison KJ, Bright RM, Davis JA, Guthrie AP, Hommer MB, Jackson MA, Smith PC, Walter DG, Natan MJ. Self-assembled metal colloid monolayers an approach to SERS substrates. Science 1995, 267, 1629-1632. 

Carron KT, Kennedy BJ. Molecular-specific chromatographic detector using modified SERS substrates. Analytical Chemistry 1995, 67, 3353-3356. 

Chemically deposited films on frosted glass slides provide a more facile and reproducible approach to SERS substrates. One such approach [31], which has proven to be very successful, involves the initial preparation of Tollen s reagent. The reagent is prepared by adding about 10 drops of fresh 5% sodium hydroxide solution to 10 mL of 2 to 3% silver nitrate solution, whereupon a dark-brown AgOH precipitate is formed. This step is followed by the dropwise addition of concentrated NH4OH, at which point the... 

The adsorbates were applied through incubation of the cleaned SERS substrates in a 10 nM solution of Rhodamine 6G in water. SERS intensities... 

Conventional SERS substrates typically have disordered nanoscale features, such as that found in electrochemically roughened Au or Ag surfaces.170 SERS substrates can also be rationally designed by lithography, by self-assembly, or a combination of the two. Both supramolecular and nanoscale self-assembly methods can be used to fabricate two-dimensional Au nanoparticle arrays with tunable optical properties.33 171172 For example, macrocyclic surfactants based on resorcinarenes (a subclass... 

The use of surface-enhanced Raman spectroscopy (SERS) for trace explosive detection was first investigated during the late 1990s [48], Thereafter [49], SERS detection of 2,4-DNT vapor to 1 ppb was demonstrated. Within a year [50], a field-portable unit had demonstrated a limit of detection (LOD) of 5 ppb vapor DNT and the ability to locate buried land mines. More recently [51], nano-engineered SERS substrates have been employed, and ppb sensitivity for some nerve agent and explosive simulants has been demonstrated. Baker et al. [52] have published a review of the literature in 2005, focusing on SERS techniques and substrate development, for explosives detection. 

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