In the area of optical micro-manipulations Bessel beams are well known for their unique properties such as
non-diffracting propagation over a large area or their ability to reconstruct themselves after passing a disturbing
obstacle. In this paper we demonstrate how the spatial spectrum phase modulation of such Bessel beam can
be used for its precise three-dimensional position control or even splitting it in several parallel Bessel beams.
Applying these features to a simple computer-driven interactive setup enabled us to guide selected particles
between remote planes demonstrating the possibility of active sorting of micro-objects. In the case of two axially
shifted co-axial Bessel beams a system of counter-propagating Bessel beams can be obtained using a mirror. The
interference of such counter-propagating beams provide a standing-wave axial modulation of the field intensity.
The position of this standing wave peaks can be controlled altering phase of one of the beams leading to the
concept of an 'Optical conveyor belt' for transport of micro-objects. However, using a time-sharing between the
two beams causes that the interference is suppressed, but their correct axial overlap assures a stable position for
object confinement. This geometry can be used then for real-time interactive three-dimensional position control
of several objects. Such light fields have broader applications, for example in two-photon processes in biophysics
such as photoporation of living cells providing transport of modified DNA from surrounding medium inside the
cell volume and consequent synthesis of fluorescent protein.
Efficient DNA delivery into single living cells would be a very powerful capability for cell biologists for elucidating basic cellular functions but also in other fields such as applied drug discovery and gene therapy. The ability to gently permeate the cell membrane and introduce foreign DNA with the assistance of lasers is a powerful methodology but requires exact focusing due to the required two-photon power density. Here, we demonstrate a laser-mediated delivery method of the red fluorescent protein DS-RED into Chinese hamster Ovary (CHO) cells. We used an elongated beam of light created by a Bessel beam (BB) which obviates the need to locate precisely the cell membrane, permitting two-photon excitation along a line leading to cell transfection. Assuming a threshold for transfection of 20%, the BB gives us transfection over twenty times the axial distance compared to the Gaussian beam of equivalent core diameter. In addition, by exploiting the BB property of reconstruction, we demonstrate successful transfection of CHO cells which involves the BB passing through an obstructive layer and re forming itself prior to reaching the cell membrane. In the light of this exciting result, one can envisage the possibility of achieving transfection through multiple cell monolayer planes and tissues using this novel light field, eliminating this way the stringent requirements for tight focusing.