  Manipulation of micro and nanoscale particles suspended in a fluidic medium
is one among the defining goals of modern nanotechnology. Speckle tweezers (ST)
by incorporating randomly distributed light fields have been used to apply
detectable limits on the Brownian motion of micro-particles with refractive
indices higher than their medium. Indeed, compared to periodic potentials, ST
represents a wider possibility to be operated for such tasks. Here, we extend
the usefulness of ST into low index micro-particles. Repelling of such
particles by high intensity regions into lower intensity regions makes them to
be locally confined, and the confinement can be tuned by changing the average
grain intensity and size of the speckle patterns. Experiments on polystyrenes
and liposomes validate the procedure. Moreover, we show that ST can be used to
nano-particle (NP)-loaded liposomes. Interestingly, the different interactions
of NP-loaded and empty liposomes with ST enables collective manipulation of
their mixture using the same speckle pattern, which may be explained by
inclusion of the photophoretic forces on NPs in NP-loaded liposomes. Our
results on the different behavior between empty and non-empty vesicles may open
a new window on controlling collective transportation of drug micro-containers
along with its wide applications in soft matter.
