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.

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