11.2 Optical manipulation of cells and tissues

Optical manipulation techniques are revolutionizing biological research and medical treatments. From optical tweezers to laser microbeams, these tools allow scientists to trap, move, and analyze cells and molecules with incredible precision.

These techniques have wide-ranging applications, from sorting cells to controlling neural activity. By harnessing the power of light, researchers can now manipulate biological systems in ways that were once impossible, opening up new frontiers in medicine and biotechnology.

Optical Manipulation Techniques

Principles of Optical Trapping

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• Optical tweezers utilize focused laser beams to trap and manipulate microscopic particles
• Dielectric particles experience gradient force pulling them towards the laser focus
• Scattering force pushes particles along the beam propagation direction
• Balance between gradient and scattering forces enables stable trapping
• Trapping force depends on particle size, refractive index difference, and laser power
• Typical trapping forces range from piconewtons to nanonewtons

Advanced Optical Manipulation Methods

• Laser microbeam employs highly focused laser pulses to cut or ablate cellular structures
• Femtosecond lasers enable precise subcellular surgery with minimal collateral damage
• Optical stretcher uses two counter-propagating laser beams to deform cells
• Measures cellular mechanical properties (elasticity, viscosity)
• Optical force spectroscopy probes molecular interactions and mechanical properties
• Applies controlled forces to single molecules or cells using optical tweezers
• Force-extension curves reveal biomolecular behavior under tension

Applications in Biological Research

• Optical tweezers measure forces in molecular motors (kinesin, myosin)
• Investigate DNA mechanics and protein-DNA interactions
• Laser microbeam facilitates chromosome dissection and organelle ablation
• Optical stretcher analyzes mechanical properties of cancer cells vs. healthy cells
• Optical force spectroscopy studies protein folding and ligand-receptor binding kinetics

Cellular Applications

Cell Sorting and Manipulation

• Optical cell sorters use laser-induced forces to separate cells based on properties
• Refractive index differences enable label-free sorting of different cell types
• Combines microfluidics with optical forces for high-throughput sorting
• Optical tweezers position individual cells for precise microinjection or analysis
• Create organized cellular arrays for tissue engineering applications
• Manipulate cellular organelles without compromising cell membrane integrity

Membrane Permeabilization Techniques

• Photoporation uses focused laser pulses to create transient pores in cell membranes
• Enables introduction of exogenous molecules (DNA, proteins, drugs) into cells
• Femtosecond lasers achieve high efficiency and cell viability in photoporation
• Optoinjection combines optical tweezers with photoporation for targeted delivery
• Optical transfection introduces genetic material into cells using laser-induced pores
• Achieves higher specificity compared to chemical or electrical transfection methods

Light-Controlled Cellular Processes

• Optogenetics uses light-sensitive proteins to control cellular activities
• Channelrhodopsin-2 enables light-activated neuronal firing
• Halorhodopsin allows light-induced neuronal silencing
• Optogenetic tools control gene expression, protein localization, and enzyme activity
• Combines genetic engineering with optical manipulation for precise cellular control
• Applications include neuroscience research, cardiac pacing, and synthetic biology
• Optochemical genetics uses photocaged compounds for light-activated drug release
• Enables spatiotemporal control of cellular signaling pathways