  Forces on a nanoparticle in an optical trap are analysed. Brownian motion is
found to be one of the major challenges to trap a nanoparticle. Accordingly,
suitable spatial electric field distribution of laser beam is suggested to
enhance the trapping force on a nanoparticle. Theoretical analysis is carried
out to obtain conditions for stable optical trap by incorporating the
temperature variation at large laser intensities. Numerical analysis is made
for single quantum dot of CdS in buffer solution irradiated by an Nd:YAG laser.
