  Although plasmonic nanotweezers can achieve manipulation on a scale smaller
than the diffraction limit, direct trapping of sub-10~nm bioparticles in an
aqueous environment without modifications remains challenging. Here, we
demonstrate enzyme delivery-trapping and dynamic manipulation at the
single-entity level by employing photothermal-assisted trapping via
metamaterial optical tweezers at low trapping laser intensities. By analyzing
the probability density function, we are able to distinguish dielectric
particles from biomolecules. For enzyme-related data, the presence of two peaks
in violin plots indicates conformational changes or interactions with the
environment. We also observe that increasing the laser intensity increases the
local temperature, resulting in enzyme aggregation. This study provides an
alternative approach for identifying single enzymes and dielectric particles by
combining plasmonic fields and photothermal heat, while paving the way for
label-free characterization of biomolecules at the single-particle level.
