Laser Controlled Manipulation of Microbubbles on a Surface with Silica‐Coated Gold Nanoparticle Array

• Published in: Small (Weinheim an der Bergstrasse, Germany) Germany), 2023-12, Vol.19 (49), p.e2302939-n/a
• Main Authors: Li, Xiaolai, Wang, Fulong, Xia, Chenliang, The, Hai Le, Bomer, Johan G., Wang, Yuliang
• Format: Article
• Language: English
• Subjects: Actuators; Arrays; bubble bouncing; Concentration gradient; detachment; Gold; gold nanoparticles; Irradiation; Lasers; Microfluidics; Microrobots; Nanoparticles; Nanotechnology; Particle image velocimetry; plasmonic bubbles; Robustness (mathematics); Silicon dioxide; Substrates; thermal Marangoni flow
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.202302939

Microbubble generation and manipulation play critical roles in diverse applications such as microfluidic mixing, pumping, and microrobot propulsion. However, existing methods are typically limited to lateral movements on customized substrates or rely on specific liquids with particular properties or designed concentration gradients, thereby hindering their practical applications. To address this challenge, this paper presents a method that enables robust vertical manipulation of microbubbles. By focusing a resonant laser on hydrophilic silica‐coated gold nanoparticle arrays immersed in water, plasmonic microbubbles are generated and detach from the substrates immediately upon cessation of laser irradiation. Using simple laser pulse control, it can achieve an adjustable size and frequency of bubble bouncing, which is governed by the movement of the three‐phase contact line during surface wetting. Furthermore, it demonstrates that rising bubbles can be pulled back by laser irradiation induced thermal Marangoni flow, which is verified by particle image velocimetry measurements and numerical simulations. This study provides novel insights into flexible bubble manipulation and integration in microfluidics, with significant implications for various applications including mixing, drug delivery, and the development of soft actuators. Plasmonic bubbles nucleated on a silica‐coated gold nanoparticle array detach instantly upon the cessation of laser irradiation. Subsequently, the interplay of buoyancy force and optothermally induced thermal Marangoni force enables manipulation of the detached microbubbles via straightforward on/off switching of laser pulses, enabling continuous bubble bouncing and bubble flow formation.