Towards applicable photoacoustic micro-fluidic pumps: Tunable excitation wavelength and improved stability by fabrication of Ag-Au alloying nanoparticles

Photoacoustic micro-fluidic pumps (PMPs) based on localized surface plasmon resonance (LSPR) of nanoparticles (NPs) can convert photo energy into kinetic energy of fluidic jetting therefore attracted considerable attentions in microfluidics and optofluidics. In this work, PMPs are fabricated using Ag-Au alloy NPs. Through solid-state-dewetting, alloy NPs are prepared of variable component ratios for tunable LSPR absorption between 440 and 530 nm. The relationship between NP morphology and optical properties are studied with the assistant of finite-difference time-domain (FDTD) simulation. Photoacoustic jets are observed through the excitation of both 450 and 532 nm lasers. Noticeably, with 450 nm laser, long lasting jets over 1 h are excited on Ag0.9Au0.1, which sharply contrast to the duration within 1 min on Ag0.2Au0.8 NPs with 532 nm laser, indicating the importance of material selection in performance improvement. Further investigation on jetting stability is performed according to the morphological evolution by laser striking, suggesting the enhanced stability can be related to the increased melting-point and thermal-stability of alloys. (C) 2021 Elsevier B.V. All rights reserved.