In situ formation of silver nanostructures produced via laser irradiation within sol–gel derived films and their interaction with a fluorescence tagged protein

Abstract

The presence of a conducting metal surface is known to affect the emission of a fluorophore in its proximity. This can lead to an enhancement in its fluorescence intensity along with a decrease in the fluorescence lifetime. This phenomenon, sometimes known as metal enhanced fluorescence, has implications in the area of sensing and "lab on a chip" applications. Here controlled, localised use of metallic structures can be advantageous in enhancing the detection of a fluorescent signal. The sol-gel technique has been demonstrated as a useful method by which to produce a biocompatible material. The versatility of the reaction allows for the inclusion of metal ions, which can form metallic nanostructures permitting the potential enhancement of fluorescence to be exhibited. In this work we incorporate silver nitrate within silica sol-gel derived films produced using a simple procedure at relative low temperatures (close to ambient). A compact time-resolved fluorescence microscope equipped with a semiconductor laser was used to photoactivate the silver ions to form localised metallic structures within the films. Patterning was achieved by computer control of the microscope stage and using the laser in CW mode. The films were characterised using AFM and UV-vis spectroscopy to ascertain the presence of the photoactivated silver nanostructures. The effect of the presence of these structures was elucidated by studying the time-resolved fluorescence of FITC labelled bovine serum albumin adsorbed to the films, where a decrease in the lifetime of the FITC label was observed in the location of the nanostructures.

The Influence of Silver Nanostructures Formed in situ in Silica Sol–Gel Derived Films on the Rate of Förster Resonance Energy Transfer

“…Also AFM imaging of the surface of the film before and after exposure to light indicated the appearance of surface features similar to those previously reported by us [23] and others [32,33] and attributed to the formation of silver nanostructures. Figure 1 shows the fluorescence emission spectra of R6G in water and sol-gel films.…”

“…[23] The solgel films presented here are good model systems for future biological sensor applications and we have demonstrated that molecular recognition systems and lab-on-a-chip devices can be developed using this methodology.…”

“…Silica sol-gel films were prepared following the method outlined in our previous paper. [23] Rhodamine 6G (R6G) (200 mL, 0.01 m) along with AgNO 3 (100 mL, 4 m) were added to the sol prior to dip coating slides. Films were then kept in the dark until used.…”

“…[27][28][29] We have recently demonstrated that silver ions can be incorporated into sol-gel films and reduced using light to form silver nanoparticles at targeted areas on the film. [23] In that work, metal-enhanced fluorescence for a fluorescent labelled protein was demonstrated. An advantage of using sol-gel films for biosensor applications is that the surface can be easily modified to covalently…”

“…[20] Thermal treatments to incorporate silver into silica glass have also been reported, [21,22] as well as the reduction of silver salt by light in the presence of water. [23,24] Sol-gel-manufactured thin films have wide application in sensing technologies, in particular for biosensing applications because of their high porosity and large internal surface areas. [25] This allows for the incorporation of biomolecules and the achievement of molecular recognition.…”