Abstract
Optical tweezers have great potential in microbiology for holding and manipulating single cells under a microscope. However, the methodology to use optical tweezers for live cell studies is still at its infancy. In this work, we determined suitable parameters for stable trapping of single Escherichia coli bacteria, and identified the upper limits of IR-exposure that can be applied without affecting viability. We found that the maximum tolerable IR-exposure is 2.5-fold higher when employing oscillating instead of stationary optical trapping (20 J and 8 J, respectively). We found that good stability of cells in an oscillating trap is achieved when the effective trap length is 20% larger than the cell length, the oscillation frequency higher than 100 Hz and the trap oriented perpendicular to the medium flow direction. Further, we show, using an IR power just sufficient for stable holding, that bacteria remain viable during at least 30 min of holding in an oscillating trap. In this work, we established a method for long-term stable handling of single E. coli cells using optical tweezers. This work will pave the way for future use of optical tweezers in microbiology.
Highlights
Optical tweezers have great potential in microbiology for holding and manipulating single cells under a microscope
To facilitate optical trapping and long-term observation of E. coli, a microfluidic setup was used in combination with an air-pressurized system to control the flow of medium
We identified operational procedures that allow handling and imaging of single E. coli cells with optical tweezers, while minimizing negative effects on cell growth and protein synthesis
Summary
Optical tweezers have great potential in microbiology for holding and manipulating single cells under a microscope. To allow for the visualization of the long axis of the cell, apart from applying techniques like dual-beam or holographic trapping to the setup[11,13,17], a single optical beam can be moved with high frequency along a distance comparable to the cell length, which will create an effective linear trap with a length twice the oscillation amplitude, forcing the cell to align along the focal plane[18,19,20,21] Such oscillating trapping of rod-shaped bacteria can be achieved by a range of settings (for instance, for the scanning frequency and trap length), and eventual effects of these settings on stability of holding and viability of trapped bacteria are yet to be investigated. It is unclear what the optimal way of trapping is for rod-shaped bacteria, and what the limits are for the use of OT in microbiological research
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