Chemical Deposition of Silver for the Fabrication of Surface Plasmon Microstructured Optical Fibre Sensors

Abstract

We compare the Tollens reaction, a simple chemical coating method, with the more commonly used RF sputtering technique for use in creating surfaces suitable for sensing applications based on surface plasmon resonance. Experiments show that by optimising the chemical process, these two approaches can produce surfaces that exhibit similar surface plasmon resonance (SPR) performance. Thus, the Tollens method is a viable one for coating the interior surfaces of a microstructured optical fibre. As a demonstration, this technique was applied to a microstructured optical fibre, and a 60-nm silver layer is produced along the entire length of a 1-m-long fibre. This is the first step towards the realisation of a SPR sensing device based on microstructured optical fibres.Keywords Surface plasmon resonance . Microstructure optical fibre Microstructured optical fibres (MOF) are an emerging platform for bio-sensing that can offer a large overlap between the guided light and the surrounding environment and that can work with tiny sample volumes (pL scale) [1]. Although to date, these fibres have primarily been used for fluorescence sensing applications [2, 3] which relies on the use of a sandwich assay as bio-sensing scheme, label-free alternatives based on surface plasmon resonance (SPR) have been proposed [4,5]. Such MOF-based SPR sensors have the potential to enable the excitation of multiple SPR resonances due to the curvature of the SPR surface (fibre core) while offering tuneability of the resonance wavelength from the visible to the near IR by modifying the fibre effective refractive index. It has been shown that the detection limit of such MOF SPR sensor should be close to 3×10 −5 RIU, comparable to the performance of the best existing fibres and waveguide-based sensors optimised for aqueous analytes [5].One reason this type of sensor has not been experimentally realised is due to the restricted geometry of MOFs, which in general mandates the use of coating techniques that are capable of coating the internal surfaces of micronscale holes within the fibre. This implies that conventional deposition techniques such as RF sputtering and thermal evaporation cannot be used. Chemical vapour deposition of silver has been proposed as one possible coating method that may work for these fibres [6]. However, this approach involves rather complex organometallic chemistry. A simpler and cheaper alternative is the Tollens reaction [7,8], which is a chemical technique that has been used successfully for the chemical deposition of silver nanoparticles for surface enhanced raman spectroscopy or more recently for the development of an electrochemical sensor inside a MOF [9]. So far, to the best of our knowledge, no systematic research has been conducted on the quality of the chemically deposited silver films that can be achieved with the Tollens reaction, and this is of particular importance for relating to SPR sensing. Within this paper, the influence of the different parameters involved in Tollens reaction are examined and the resultant...

Effect of surface roughness on metal enhanced fluorescence in planar substrates and optical fibers

“…Silver thin films of 50 nm thicknesses, previously determined to be optimal for SPs excitation [28], were deposited on standard microscope glass slides using two methods, electroless plating [28], and thermal evaporation [29]. Different deposition conditions, in particular deposition rates, were used for the thermal evaporation to vary the surface roughness of the deposited silver films [29].…”

“…Different deposition conditions, in particular deposition rates, were used for the thermal evaporation to vary the surface roughness of the deposited silver films [29]. Procedure reported by Boehm et al [28], was followed for fabrication of silver coatings using the electroless plating method. All substrates were thoroughly cleaned by sonication in acetone for 30 min, then rinsed with ethanol and deionized water prior silver thin film deposition.…”

Enzyme detection by surface plasmon resonance using specially engineered spacers and plasmonic labelling

“…Moreover it has been previously shown that the silver coating deposited using this chemical technique has the same optical properties as a silver film deposited by thermal evaporation [18] . The Tollens reaction (also known as the silver mirror reaction) consists of adding a solution of silver ammonium to a reducing agent, usually a sugar such as glucose, in order to produce silver nanoparticles that can subsequently be attached to a substrate [19] .…”

Optical fiber sensor based on surface plasmon resonance for rapid detection of avian influenza virus subtype H6: Initial studies

“…Optical-fiber-based SPR sensors have more advantages over conventional prism-based SPR sensors, particularly in terms of flexibility and cost . Currently, opticalfiber-based SPR sensors have been widely used in chemical sensors (Boehm et al, 2011) and gas sensors (Kim et al, 2005;Wang et al, 2013).…”