Preparation and characterization of antimony-doped SnO2 thin films on gold and silver substrates for electrochemical and surface plasmon resonance studies

A Sensitive and Stable Surface Plasmon Resonance Sensor Based on Monolayer Protected Silver Film

In this paper, we present a stable silver-based surface plasmon resonance (SPR) sensor using a self-assembled monolayer (SAM) as a protection layer and investigated its efficiency in water and 0.01 M phosphate buffered saline (PBS). By simulation, silver-based SPR sensor has a better performance in field enhancement and penetration depth than that of a gold-based SPR sensor, which are 5 and 1.4 times, respectively. To overcome the instability of the bare silver film and investigate the efficiency of the protected layer, the SAM of 11-mercapto-1-undecanol (MUD) was used as a protection layer. Stability experiment results show that the protected silver film exhibited excellent stability either in pure water or 0.01 M PBS buffer. The sensitivity of the silver-based SPR sensor was calculated to be 127.26 deg/RIU (refractive index unit), measured with different concentrations of NaCl solutions. Further, a very high refractive resolution for the silver-based SPR sensor was found to be 2.207 × 10⁻⁷ RIU, which reaches the theoretical limit in the wavelength of 632.8 nm for a SPR sensor reported in the literature. Using a mixed SAM of 16-mercaptohexadecanoic acid (MHDA) and a MUD layer with a ratio of 1:10, this immunosensor for the rabbit immunoglobulin G (IgG) molecule with a limit of detection as low as 22.516 ng/mL was achieved.

Development of a metal-chelated plasmonic interface for the linking of His-peptides with a droplet-based surface plasmon resonance read-off scheme

Monolayers of metal complexes were covalently attached to the surface of lamellar SPR interfaces (Ti/Ag/a-Si(0.63)C(0.37)) for binding histidine-tagged peptides with a controlled molecular orientation. The method is based on the activation of surface acid groups with N-hydroxysuccinimide (NHS), followed by an amidation reaction with (S)-N-(5-amino-1-carboxypentyl)iminodiacetic acid (NTA). FTIR and X-ray photoelectron spectroscopy (XPS) were used to characterize each surface modification step. The NTA modified SPR interface effectively chelated Cu(2+) ions. Once loaded with metal ions, the modified SPR interface was able to bind specifically to histidine-tagged peptides. The binding process was followed by surface plasmon resonance (SPR) in a droplet based configuration. The Cu(2+)-NTA modified interface showed protein loading comparable to commercially available NTA chips based on dextran chemistry and can thus be regarded as an interesting alternative. The sensor interface can be reused several times due to the easy regeneration step using ethylenediaminetetraacetic acid (EDTA) treatment.

Surface plasmon resonance on gold and silver films coated with thin layers of amorphous silicon-carbon alloys

The paper reports on a novel surface plasmon resonance (SPR) substrate architecture based on the coating of a gold (Au) or silver (Ag) substrate with 5 nm thin amorphous silicon-carbon alloy films. Ag/a-Si(1-x)C(x):H and Au/a-Si(1-x)C(x):H multilayers are found to provide a significant advantage in terms of sensitivity over both Ag and Au for SPR refractive index sensing. The possibility for the subsequent linking of stable organic monolayers through Si-C bonds is demonstrated. In a proof-of-principle experiment that this structure can be used for real-time biosensing experiments, amine terminated biotin was covalently linked to the acid-terminated SPR surface and the specific streptavidin-biotin interaction recorded.

Preparation and characterization of silver substrates coated with antimony-doped SnO2 thin films for surface plasmon resonance studies

This paper reports on the preparation of silver/antimony-doped tin oxide (Ag/SnO(2):Sb) hybrid interfaces using magnetron sputtering and their characterization. The influence of the Sn target composition (doping with 2 or 5% Sb) on the electrochemical and electrical characteristics of the hybrid interface was investigated using X-ray photoelectron spectroscopy (XPS), sheet resistance measurements, cyclic voltammetry, scanning tunneling microscopy (STM) and surface plasmon resonance (SPR). The best interface in terms of electrical conductivity and SPR signal is a hybrid interface with a 8.5 +/- 0.3 nm thick SnO(2):Sb layer obtained from a Sn target with 2% Sb deposited on 38 nm thick silver film. Different strategies to link functional groups onto the Ag/SnO(2):Sb interface are also presented.