Stable in Biocompatible Buffers Silver Nanoisland Films for SERS

Abstract

We investigated the stability of silver nanoisland films, which were formed on glass surface by the method of out-diffusion, in biocompatible buffers and the applicability of the films in surface enhanced Raman scattering (SERS). We have shown that silver nanoisland films are stable in one of the most widespread in biological studies buffer—phosphate buffer saline (PBS), and in 1:100 water-diluted PBS, in the PBS-based buffer, in which NaCl is replaced by the same amount of NaClO4, and in acidic phosphate buffer. At the same time, the replacement of NaCl in PBS by N(CH3)4Cl leads to the degradation of the nanoislands. It was shown that after exposure to PBS the nanoisland films provided a good SERS signal from a monolayer of 1,2-di(4-pyridyl)ethylene (BPE), which makes silver nanoisland films promising for biosensor applications. Additionally, in our experiments, we registered for the first time that silver nanoparticles formed in the bulk of the samples dissolved after exposing to PBS, while nanoislands on the glass surface stayed unchanged. We associate this phenomenon with the interaction of ions contained in PBS solution with silver, which results in the shift of corresponding chemical equilibrium.

Raman Scattering Study of Amino Acids Adsorbed on a Silver Nanoisland Film

“…Thus, when glass with SNF is immersed in PBS solutions, the contribution to Raman scattering from the molecules that “interact” with SPR of nanoislands (bound molecules) is dominant. This is because the “interaction” results in a several-orders-of-magnitude enhancement of Raman scattering (up to ~10 4 [ 20 ]).…”

“…SNFs, which are ensembles of silver nanoparticles randomly distributed over a glass surface, were prepared by doping a soda-lime glass slide (Agar Scientific Ltd., Essex, UK) with silver ions via silver-to-sodium ion-exchange and annealing the silver-containing glass in a hydrogen atmosphere, as described elsewhere [ 16 , 20 ]. For ion-exchange, we immersed the slide for 20 min in AgNO 3 -NaNO 3 melt containing 5 wt.% of AgNO 3 (LenReactiv, St. Petersburg, Russia) heated to 325 °C.…”

“…It has been previously shown that SNF could enhance the Raman spectra of various molecules [ 16 , 17 , 18 , 19 ]. We have recently shown that SNFs formed by out-diffusion are not inherently stable in phosphate buffer saline solution (PBS), which is widely used in biochemical and cell studies, and other buffer systems [ 20 ]. The film gradually reacts with the medium and releases silver ions into the solution, but its ability to enhance Raman scattering is retained.…”

Raman Scattering Study of Amino Acids Adsorbed on A Silver Nanoisland Film

“…SNF which are ensembles of silver nanoparticles randomly distributed over glass surface were prepared by doping a soda-lime glass slide (Agar Scientific Ltd., Essex, UK) with silver ions via silver-to-sodium ion-exchange and annealing the silver-containing glass in a hydrogen atmosphere [10]. For the ion-exchange we immersed the slide for 20 min in AgNO 3 -NaNO 3 melt containing 5 wt.% of AgNO 3 (LenReactiv, St. Petersburg, Russia) heated to 325 °C.…”

“…It was shown previously that SNF can enhance the Raman spectra of various molecules [8,9]. We have recently shown that SNFs formed by out-diffusion are not inherently stable in phosphate buffer saline solution (PBS), which is widely used in biochemical and cell studies, and other buffer systems [10]. The film gradually reacts with the medium releasing silver ions into the solution, but its ability to enhance Raman scattering is retained.…”