Size-dependent steady state saturation limit in biomolecular transport through nuclear membranes.

The nucleus preserves the genomic DNA of eukaryotic organisms and maintains the integrity of the cell by regulating the transport of molecules across the nuclear membrane. It is hitherto assumed that small molecules having a size below the passive permeability limit are allowed to diffuse freely to the nucleus while the transport of larger molecules is regulated via an active mechanism involving energy. Here we report on the kinetics of nuclear import and export of dextran molecules having a size below the passive permeability limit.

Confocal imaging of single BaTiO nanoparticles by two-photon photothermal microscopy.

We report on the development of a nonlinear optical microscopic technique based on two-photon absorption induced photothermal effect capable of detecting individual nonfluorescent nanoparticles with high sensitivity. The method which is inherently confocal makes use of near infrared excitation at high repetition rates and would be of interest in deep tissue imaging. We demonstrate the applicability of the technique by imaging single BaTiO nanoparticles, a potential biomolecular label having high photostability, in a scattering environment at fast time scales with a pixel dwell time of 80 μs.

Laser scanning photothermal microscopy: fast detection and imaging of gold nanoparticles.

We report on the design and construction of a laser scanning photothermal microscope and present images of gold nanoparticles of size as small as 5 nm. Laser scanning method allows fast image acquisition at 80 μs pixel dwell time so that a 500 × 500 pixel image is acquired in 20 s. Photothermal imaging at fast time scales can have potential applications in variety of fields including tracking of biomolecular transport processes.