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An experimental method is demonstrated to enhance the refractive index sensitivity (RIS) of gold (Au) ultrathin films used in a localized surface plasmon resonance (LSPR) sensor as an optical transducer using sequential temperature treatment in fabrication processes. The Au ultrathin films were fabricated by the vacuum thermal evaporation technique to deposit Au nanoparticles on a glass substrate, followed by annealing. The ultrathin layer of Au had a thickness of 1.13 nm. Furthermore, two different annealing times were employed in two different treatment processes with annealing temperature of 400 °C. The first treatment involved longer annealing times (8 h, 12 h, 24 h, and 36 h) and a normal cooling process (cooling rate: 0.02 °C/s); the second treatment involved shorter annealing times (1 min, 5 min, 10 min, and 30 min) and a quenching process (cooling rate: 25 °C/s). The Au ultrathin films were spectroscopically evaluated based on their morphology and optical properties in the transmissive mode integrated in a self-assembled optofluidic. The highest RIS of the Au ultrathin films was obtained at 240.45 nm/RIU for the short annealing time-quenching treatment and 90.85 nm/RIU for the long annealing time-normal cooling treatment. This method demonstrates the great potential toward fabrication of Au ultrathin films based LSPR for liquids sensing.

In this paper, we present a liquid-droplet-heating system using a surface acoustic wave (SAW) device. When liquid is placed on a Rayleigh-SAW-propagating surface, a longitudinal wave is radiated into the liquid. If the SAW amplitude increases, the liquid shows non-linear dynamics, such as vibrating, streaming, small droplet flying, and atomizing. This phenomenon is well known as SAW streaming. The liquid temperature is measured during the longitudinal wave radiation and found to increase. First, the mechanism of the liquid-heating effect is discussed on the basis of experimental results. The surface electrical condition is changed to investigate the effect of dielectric heating. The obtained results indicate that the radiated longitudinal wave causes liquid heating and the dielectric heating effect does not. Second, the fundamental properties of the liquid temperature are measured by varying the applied voltage, duty factor, and liquid viscosity. The liquid temperature is found to be proportional to the duty factor and the square of the applied voltage. Therefore, the liquid temperature can be controlled by these applied signals. Also, by using highly viscous solutions, the liquid temperature is increased to more than 100 °C. Moreover, for chemical applications, the possibility of periodic temperature control is tested by varying the duty factor. The obtained results strongly suggest that an efficient thermal cycler is realized. A novel application of the SAW device is proposed on the basis of SAW streaming.