Microscale solute flow probed with rotating microbead trapped in optical vortex

The dynamics of solute flow in the microscopic chamber can be studied with optical tweezers. A method based on metallic microbeads trapped focused vortex beam is proposed. This annular a twisted wavefront exerts torque reflective object placed inside dark core vortex. induced rotational movement bead sensitive to local viscosity changes surrounding medium, for example during ongoing dissolution process. Two experimental configurations are described, both relying tracing angular velocity time. In one-bead configuration concentration studied. two-bead case direction and speed probed spatial resolution single micrometers. We approach elementary problem sucrose diffusion water. surprising impression reverse was observed. Further investigation led discovery that this phenomenon originates from stream-like mid-depth measurement chamber. rotating microbead applies various solid liquid substances may become useful technique microfluidics research.