Optical trapping of microalgae at 735–1064 nm: Photodamage assessment

Optical trapping and binding of particles in an optofluidic stable Fabry–Pérot resonator with single-sided injection

“…This is predictable as this behavior is related to the natural diffusion process of the particles. For the trapped pattern, the 1D array of the separated 1 30 almost instantaneous diffused after switching the laser off, as shown in Movie 1 of the ESI; so it can be claimed to be in order of fractions of a second. One can conclude that diffusion time of the particles was roughly proportional to their size, as predicted by the Stokes-Einstein relation, when the 35 trapped particle density was low.…”

“…Note the fundamental resonance peaks, there are other side peaks corresponds to other modes supported by these types of resonators. 31 The system is observed by a stereo microscope and the results are recorded by a C-MountCMOS camera attached to 30 the microscope.…”

“…Now concerning the second phenomenon of particles' 25 clustering or accumulation, it happens thanks to the optical binding for larger beads and even with the 1 m µ diameter beads at high concentrations, where the existence of the particles disturbs the field trapping configuration significantly. Such arrangement is not necessarily initiated by optical traps dictated by externally 30 imposed field gradient. The mere presence of the objects in the area illuminated by the optical field exhibits its own field tapestry and even any new particle added in its vicinity, leads to a new spatial distribution.…”

“…[1][2][3][4] To overcome the bulky, free space universaloptical tweezers, 25 the use of optical integrated structures and optical resonators is being extensively investigatedto achieve on-chip, low power and compact size optical traps; which led to the development of different configurations to achieve localization control and/or simple manipulation. To name some of these on-chip optical 30 trapping modules: evanescent fields from waveguides and Whispering Gallery Mode resonators,in the form of ring resonators, 5 disks, 6 or spheres 7 are used to propel particles along the light propagating path.Multimode-interference (MMI) structures 8 and photonic crystals 9 are used to trap particles at 35 specific locations. Among all these techniques, none has the full three-dimensional (3D) handling capabilities provided by the conventional optical tweezers.So-far, the best miniaturized configuration regarding simplicity, and low optical power in tradeoffs with trapping and manipulationperformance is probably 40 the counter-propagating dual-beam trap thatis formed by two single-mode optical fibers.…”

“…28 Further on-chip implementation inside a resonant cavity provides in situ capabilities spectroscopy analysis. Of course one needs to pay special 30 attention to the viability of the biological sample exposed to light, which can be preserved at low optical powers, especially when choosing suitable working wavelengths in the near region; for example Escherichia coli bacterial cells show minimum damage at wavelengths 970 nm and 830 nm, 35 microalgal cells are preserved when exposed in the 886 range. 30 The study of biological particles is not considered for the moment in this paper, whose focus is intended to provide a better understanding of the optical trapping and optical binding mechanisms of micro-particles inside an optofluidic resonant 40 cavity.…”