## 5 Noble Nanofluids
### Bimetallic Nanofluids
Additionally, the authors [PERSON] et al. [95] deposited gold and platinum bimetallic nanostructures on palladium nanocubes for oxidizing the glucose. The authors reported that in transient catalysis, the gold-palladium nanocubes showed a wide linear range between 0.25 mM and 14 mM and great sensitivity of around 13.6 \(\upmu\)A\(\cdot\)mM\({}^{-1}\cdot\)cm\({}^{-2}\) in determining the d-glucose in reference to the platinum-palladium nanocubes. The catalyst exhibited remarkable recoveries between 99.2% and 100.1% for sensing the d-glucose. Furthermore, the growth of platinum nanoparticles on gold nanoplates having enhanced photo response has also been published. Moreover, the researchers [PERSON] et al. [96] synthesized platinum with triangular gold nanopirisms and proposed them for hydrogen generation. Besides, the researchers [PERSON] and [PERSON] [97] developed a simultaneous reduction method to fabricate gold-platinum nanoparticles having stable and improved catalytic activity in the oxidation of glucose. Given that the gold-platinum nanoparticles exhibit a third order nonlinear phenomenon because of the intense optical Kerr effect, they can be great contenders to produce gyroscopic systems. The ultrasonic non-destructive testing evaluates the materials during the processing and after the fabrication. Controlling the characteristics of the materials by monitoring the structural inhomogeneity, phase transition, thermal conductivity, size, and dislocations that will forecast the potential uses of the materials can be accomplished through measuring the frequency dependent ultrasonic absorption. In the last years, many researchers have studied the ultrasonic behavior of aqueous solutions to better understand the underlying mechanisms to attain an improved control over the procedure. It has been confirmed that in fluidic suspensions, the dispersants tend to diminish the wave propagation caused by weak particle-liquid interactions, whilst the nanoparticles increase the wave propagation because of the enhnecd nanoparticle-fluid interactions. Figure 11 schematically represents a synthesis method for gold-platinum nanoparticles. The nanofluids can represent a case study for better understanding the governing mechanisms of the ultrasonic behavior in suspensions due to the great variety of possible manipulations that can be attained by the adjustment of their chemical composition and concentration. A reduced attenuating ability of the nanofluids might conduct to an improved performance in ultrasound imaging. The attenuation impacts also on the propagation of waves and signals in optical fibers, electrical circuits, and air, making such issue pivotal in the telecommunications field of actuation. Hence, there should be developed fluidic systems having increased wave propagation or mitigated attenuation for an improved  
Figure 11: Synthesis method for gold-platinum nanoparticles. Adapted from [97]. performance. The water-based metallic nanofluids are themselves a special alternative as they possess superior plasmonic characteristics [98] and ultrasound properties. Only a few research works were carried out on the ultrasonic features of the metallic nanofluids. In this sense, the authors [PERSON] et al. [99] verified a frequency dependent ultrasonic attenuation in the water-based gold and gold-platinum nanofluids. The gold and gold-platinum nanofluids were synthesized by the microwave-assisted citrate reduction. The nanofluids were characterized through X-ray diffraction, revealing a distinct two-phase bimetallic crystal structure with no alloy formation, The nanofluids were also characterized by UV-vis spectroscopy that showed two plasmonic bands in the bimetallic species having a aggregation tendency. The high-resolution microscopy analysis revealed spherical nanoparticles having sizes from 15 nm to 30 nm presenting marked lattice spacings of platinum and gold. The bimetallic nanofluids demonstrated a lower resistance to ultrasonic waves in respect to that of the gold nanofluids.