3D Photothermal Manipulation of Droplet for Biological Applications

3D light manipulation of water droplets at low temperatures via a local photothermal effect presents a fundamental challenge. Herein, we propose a novel light strategy for 3D manipulation of a water droplet in an immiscible oil phase using a 532 nm laser beam in which the photothermal conversion materials of carbon powders are dispersed in the oil for absorbing the 532 nm laser energy. The local photothermal effect creates temperature gradients at the oil-air and water-oil interfaces, leading to the thermocapillary flow. By controlling the laser beam position, moving speed, and irradiation mode, a water droplet can stably suspend in the oil and freely move with a complex path, presenting flexible and precise 3D manipulation of low-temperature droplets. Remarkably, the adaptability of this strategy to biological applications is demonstrated by the manipulation of diverse biodroplets while preserving their functionality. Moreover, the droplet temperature and internal flow can be well controlled, behaving like a "micro-shaker" for enhancing cell cultivation. This work represents an innovative strategy for 3D light manipulation of water droplets, which holds promise in various applications.