Optical trapping and manipulation
Can a living cell act as a lens that beats the diffraction limit?
Open access · cc by · source: Europe PMC
A spherical cell half-submerged in water and held above a mirror focuses light into a spot small enough to image 100 nm features and trap single nanoparticles.
Study at a glance
- Design
- Other — Lab optics experiments using fibre-trapped spherical cells as lenses to image nanostructured test samples and trap nanoparticles, compared with COMSOL simulations
- N
- No single N; many test samples (nanosphere arrays, DVD/Blu-ray gratings, nanopatterned letters, gold dimer) and cell types; reproducibility tested with repeated imaging by one trapped cell
- Population
- Living yeast, bacterial, red blood and stem cells used as microlenses over engineered nanostructures
- Outcome
- Focal spot size, imaging resolution and magnification, trapping stiffness and potential depth
Structured fields used in claim comparison tables when every cited study has a complete layer.
Key findings
Half-immersed cells focused light to spots with waist radii of 270 to 370 nm depending on wavelength, and over a mirror the simulated spot shrank to 200 nm, below half a wavelength. Cells about 4 μm across magnified features about four times, resolving 100 nm lines that a normal microscope could not. Trapped nanoparticles gave a stiffness of 0.41 pN/nm/W, close to the simulated 0.46, and their fluorescence was about 70 times brighter than before trapping.
Methodology
The researchers trapped single spherical cells such as yeast and red blood cells on a tapered optical fibre and positioned them over test samples. They measured how tightly the cells focused light at different immersion depths and wavelengths, used them to image nanosphere arrays, disc gratings, nano-written letters and human epithelial cells, and used the focused near-infrared spot to trap fluorescent 50 nm polystyrene particles. Simulations of the light field and optical forces were compared with the experiments.
Limitations
The work is a demonstration on a small number of engineered test samples rather than a systematic benchmark across many cells, so variability between cells is not well quantified. The field of view is only as large as the cell, so wide-field images require scanning and reconstruction, which is proposed but not shown. Cells have uneven internal refractive index and can change shape or move organelles, which the authors acknowledge can distort images. Simulations assumed a perfectly symmetric, uniform cell, which is why predicted resolution differs from the measured value.
How this study connects
Role on claims
Each row is a claim on a concept or method page where this paper supports, challenges, or qualifies the statement. Roles are hand-checked — not a model guess.
Trapped biological objects can act as microlenses.
Traps are used to position natural or cellular lenses: trapped lipid droplets boosted fluorescence roughly sixfold and raised filament contrast from 14.8% to 62.5%, and a trapped cell over a mirror resolved 100 nm lines and gave a nanoparticle trap stiffness of 0.41 pN/nm/W.
Evidence for the claim as stated.
Size dependence of trap stiffness runs opposite in different mechanisms: opto-thermoelectric traps held smaller particles more stiffly, whereas conventional gradient-force tweezers generally trap larger particles more strongly.
Evidence for the claim as stated.
Open questions
Tensions this paper is part of
From concept pages' “where studies disagree.” Disagreement means the same question; scope means different assays, populations, or outcomes.
Size dependence of trap stiffness runs opposite in different mechanisms: opto-thermoelectric traps held smaller particles more stiffly, whereas conventional gradient-force tweezers generally trap larger particles more strongly.
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