Optical assembling dynamics of individual polymer nanospheres investigated by single-particle fluorescence detection

Abstract

When a laser beam is focused into colloidal nanoparticle suspensions, a number of nanoparticles can be confined in the focal spot due to an optical gradient force. To reveal the assembling dynamics of polymer nanoparticles, the assembling process was investigated by analyzing the time evolution of the fluorescence intensity of the nanoparticles. In a dilute suspension of 100-nm-sized particles, a stepwise increase of the fluorescence intensity corresponding to a trapped single nanoparticle was observed. Statistical analysis revealed that the initial assembling rate of nanoparticles was proportional to the laser power and concentration of particle suspensions as expected from the diffusion equation. In 40-nm-sized particle suspensions, blinking profiles of fluorescence intensity were obtained, in which 2-3 particles were simultaneously trapped and then escaped from the focal point. It is considered from statistical analyses and two-dimensional Monte Carlo simulations that this assembling phenomenon is attributable to cluster formation assisted by optical trapping.

Light at work: The use of optical forces for particle manipulation, sorting, and analysis

“…Masuhara's group performed many pioneering experiments on optical trapping of nanoparticles. They studied optically induced assembly of several kinds of polymers [377][378][379] and nanoparticles [380][381][382][383] in the trap, pushing the size of the trapped nanoparticles down to 10-20 nm.Stable optical trapping of gold nanoparticles of sizes ranging from 18 to 254 nm using single-beam OT has been demonstrated by Hansen et al [384]. Forty nanometer diameter gold nanoparticles trapped and manipulated with OT also served as probes in the scanning near-field optical microscopy [385].…”

Optical trapping through the localized surface-plasmon resonance of engineered gold nanoblock pairs

“…On such process, the increase and decrease of the light scattered from particles are done in one step. On the other hand, the scattered light must gradually increase and decrease for optical trapping of multiple particles, as proved in the previous study [24,25]. In addition, as aforementioned, the average number of nanoparticles in the observation volume is estimated to be 1.6 x 10 −3 particles.…”

Laser trapping dynamics of 200 nm-polystyrene particles at a solution surface

“…1 Ever since this innovative work was reported by Ashkin, the technique has been widely employed as optical tweezers to trap and manipulate micrometer-sized objects without mechanical contact in many fields of physics, optics, and biology. 2,3 For nanometer-sized objects, this technique has been applied to J-aggregates 4 , polymers 5,6 , liquid-like clusters of amino acids 7 , quantum dots 8-10 as well as various nanoparticles [11][12][13] . In dilute solution, a single nanometer-sized object is trapped at the focal spot and the trapped object can be analyzed individually and manipulated arbitrarily.…”

“…Such laser trapping induced-assembly formation was demonstrated with long-chain polymers, liquidlike clusters of amino acids, quantum dots, and polystyrene nanoparticles. [5][6][7][8]12,13 The formation dynamics was investigated by analyzing time evolution of emission or backscattered light intensity under their laser trapping. 5,7,8,13 The intensity was increased with their trapping in the focal volume and finally saturated when the focal volume was fully occupied by the objects trapped.…”