Photogravitactic Microswimmers

TY - JOUR

T1 - Photogravitactic Microswimmers

AU - Singh, Dhruv

AU - Uspal, William

AU - Popescu, Mihail

AU - Wilson, Laurence George

AU - Fischer, Peer

PY - 2018/6/19

Y1 - 2018/6/19

N2 - Phototactic microorganisms are commonly observed to respond to natural sunlight by swimming upward against gravity. This study demonstrates that synthetic photochemically active microswimmers can also swim against gravity. The particles initially sediment and, when illuminated at low light intensities exhibit wall-bound states of motion near the bottom surface. Upon increasing the intensity of light, the artificial swimmers lift off from the wall and swim against gravity and away from the light source. This motion in the bulk has been further confirmed using holographic microscopy. A theoretical model is presented within the framework of self-diffusiophoresis, which allows to unequivocally identify the photochemical activity and the phototactic response as key mechanisms in the observed phenomenology. Since the lift-off threshold intensity depends on the particle size, it can be exploited to selectively address particles with the same density from a polydisperse mixture of active particles and move them in or out of the boundary region. This study provides a simple design strategy to fabricate artificial microswimmers whose two- or three-dimensional swimming behavior can be controlled with light.

AB - Phototactic microorganisms are commonly observed to respond to natural sunlight by swimming upward against gravity. This study demonstrates that synthetic photochemically active microswimmers can also swim against gravity. The particles initially sediment and, when illuminated at low light intensities exhibit wall-bound states of motion near the bottom surface. Upon increasing the intensity of light, the artificial swimmers lift off from the wall and swim against gravity and away from the light source. This motion in the bulk has been further confirmed using holographic microscopy. A theoretical model is presented within the framework of self-diffusiophoresis, which allows to unequivocally identify the photochemical activity and the phototactic response as key mechanisms in the observed phenomenology. Since the lift-off threshold intensity depends on the particle size, it can be exploited to selectively address particles with the same density from a polydisperse mixture of active particles and move them in or out of the boundary region. This study provides a simple design strategy to fabricate artificial microswimmers whose two- or three-dimensional swimming behavior can be controlled with light.

KW - Janus particles

KW - artificial microswimmers

KW - light-driven micromotors

KW - phototaxis

KW - self-propulsion

UR - http://www.scopus.com/inward/record.url?scp=85042541652&partnerID=8YFLogxK

U2 - 10.1002/adfm.201706660

DO - 10.1002/adfm.201706660

M3 - Article

SN - 1616-301X

VL - 28

JO - ADVANCED FUNCTIONAL MATERIALS

JF - ADVANCED FUNCTIONAL MATERIALS

IS - 25

M1 - 1706660

ER -