RESUMEN
A multi-functional sensing system based on surface plasmon resonance (SPR) phenomenon using a square glass rod with two gold-deposited adjacent faces was developed in this work. This sensor system consists of a unpolarized light-emitting diode, a gold-deposited square glass rod, a polarizing beam splitter, and two photodiodes. The SPR responses of two adjacent faces are independently and simultaneously measured with a polarizing beam splitter and two PDs. The response property of the gold-deposited face was confirmed using methanol solutions of ethylene glycol. The response curve of the sensor of the 45 nm gold-deposited face was compared with the theoretical curve calculated using multi-layer Fresnel equations. It was confirmed that the experimental curve is similar to the theoretical one. An evaluation was carried out on the square glass rod, which has an unmodified face and Teflon AF2400 coated gold-deposited face as multi-functional sensor. It was confirmed that this sensor can simultaneously measure the ethanol concentration in the glucose mix solution and refractive index of the sample from the calibration curve. Since this sensor can measure multiple components simultaneously, expected applications to various fields include medical diagnosis, food analysis, and environmental monitoring.
RESUMEN
Gold oxides (0.1 - 2.0 nm thick) prepared from gold films by an oxygen-dc glow discharge using a gold discharge ring for 0.17 - 30 min at room temperature were characterized by X-ray photoelectron spectroscopy. The oxide thickness increased with increasing discharge time in contrast to the use of an aluminum ring, and thicker oxide films were obtained. The O 1s spectra show four components: I, II, III, and IV. Components I, II, and IV appear during the early formation periods (≤0.5 min). Components I and II are stable and assigned to hydroxyl groups on the surfaces. Component IV changes into component III (gold oxide) after longer discharge times (≥1 min). The gold oxides (2.0 nm thick) decompose after 15 d at room temperature and decompose immediately at temperatures exceeding 117°C. They also decompose under ultraviolet light irradiation (254, 302, and 365 nm) and decompose more rapidly in water vapor at the shorter wavelengths. The thicker nature of the gold oxides is advantageous for their preservation, and they were preserved in their oxidized state for 196 d in anhydrous dodecane in a dark atmosphere.
RESUMEN
The chemical properties of thin (â¼0.6 nm) gold oxide layers prepared by an oxygen-dc glow discharge from gold films at room temperature in various solvents and solutions were studied using a surface plasmon resonance (SPR)-based optical waveguide sensing system and X-ray photoelectron spectroscopy (XPS). New insights into the stability and reactivity of gold oxides under these conditions were obtained. The O 1s XPS spectra show three oxygen species, comprising components I, II, and III in the gold oxides, and components I and II are present in this order from the top surface of the oxide (component III). The gold oxide is stable in various solvents (water, methanol, ethanol, acetone, acetonitrile, diethyl ether, chloroform, hydrocarbons) for 10 - 30 min at room temperature. The gold oxide decomposes in aqueous 10-2 M solutions of acetaldehyde, hydrochloric acid, and sodium hydroxide during these periods. Gold oxide decomposition in these solutions was monitored by SPR and the decomposition rates were obtained. Decomposition of the gold oxides was confirmed and their surfaces were characterized after decomposition by XPS.
RESUMEN
A gold (Au)-deposited surface plasmon resonance (SPR)-based glass rod sensor that is coated with an α-mercaptoethyl-ω-methoxy polyoxyethylene (PEG thiol) layer (approximately 13 nm thick) and a Teflon AF2400 overlayer (12 µm thick) was used to detect the hydrocarbon and gasoline contents of automotive engine oil. Hydrocarbons and gasoline present in the engine oil penetrate through the porous Teflon layer and accumulate in the PEG thiol layer, and are then detected using the SPR sensor. The refractivities of the selective layers that contain a hydrocarbon on the Au-deposited glass rod sensor were estimated from the sensor responses when using light-emitting diodes (LEDs) with various operating wavelengths as light sources. Gasoline concentrations up to 10%, w/w in commercial engine oil can be measured directly using this sensor when it is coated with the selective layers. The responses of an SPR-based optical waveguide sensing system using Au films coated with identical selective layers were also measured. The results demonstrate the value of the Au-deposited SPR glass rod sensor coated with the selective layers for the detection of the gasoline content and fuel dilution of automotive engine oil.