Optical tweezers induced photodamage in living cells quantified with digital holographic phase microscopy

Optical tweezers are a versatile technique to manipulate living biological specimen in a contact-less way. The interaction with living cells can be performed, for example, through direct manipulation of cell organelles or by movement of an internalized particle within the cytoplasm. However, the risk of damage that the trapping beam may induce in the biological sample due to the energy deposition has to be considered. This optically induced damage or photodamage depends mainly on the wavelength of the trapping beam, the exposure time and the biological specimen that is investigated. In this work, we explore a method to analyse the photo damage in living cells in a multimodal biophotonic workstation that is based on combining a holographic optical tweezers (HOT) microscope with a self-interference digital holographic microscopy (DHM) module. A time-dependent investigation shows that no observable changes in the cell morphology are induced at room conditions with the used laser power of the trapping beam during periods of time < 20 min of laser application. In addition, results from investigations of the photodamage increasing the working temperature to 37°C demonstrate that the optical tweezers beam can provoke severe but reversible morphology changes in the cell.