Physicists’ fascination with the light-matter interaction shows
no sign of abating. Now, writing in Physical Review Letters,
Oliver Schmidt and colleagues at the Max Planck Institute for
the Science of Light in Erlangen, Germany, have demonstrated a
novel form of trapping micron-sized particles, a technique that
uses both light and thermal (optothermal) forces in tandem . The
branch of optical trapping started with the realization that
light can exert miniscule forces on mesoscopic objects via
radiation pressure (scattering) that guides or pushes
microparticles or cells. When combined with forces resulting
from the optical field gradient, this may result in single or
multiple traps. Besides the very evocative link to tractor beams
in science fiction, such trapping and guiding forces led to
profound advances: single-molecule biophysics, colloidal and
Brownian dynamics, and a deeper understanding of fundamental
light fields . In many of these applications, the trapped
microparticle is itself a carefully calibra