Cluster formation of nanoparticles in an optical trap studied by fluorescence correlation spectroscopy

Abstract

We report in situ observation of cluster growth of nanoparticles confined in an optical trapping potential by means of fluorescence correlation spectroscopy. When an optical trapping force caused by a highly focused laser beam acts on nanoparticle suspensions, the number of nanoparticles increases and an assembly can be formed at the focal spot. The decay times of fluorescence autocorrelation curves were investigated as a function of the irradiation time of the laser beam and the laser power. In the initial stage of the optical assembling, the decay time increases with the irradiation time of the laser beam. On the other hand, in the later stage, a decrease of the decay time was observed. This behavior is explained successfully by using two models of Brownian motion under weak and strong optical trapping. It was revealed that trapping and clustering of nanoparticles proceed simultaneously and clusters confined in the focal spot make larger aggregates spontaneously.

Millimeter-Scale Dense Liquid Droplet Formation and Crystallization in Glycine Solution Induced by Photon Pressure

“…[1][2][3] Over the past decades, the study on photon pressure in solution has progressed with the size reduction of target materials from microscale to nanoscale, [4][5][6] and actually, we have extended a series of experiments on the dynamics of photon pressure-induced association of nanoparticles, polymers, micelles, and J-aggregates in their solutions at room temperature. [7][8][9][10][11] As an example, polystyrene latex nanoparticles with 24 nm diameter were trapped and gathered by photon pressure, leading to their assemblies in a focal spot. 11 In single-molecule level, Osborne et al and Chirico et al separately reported that the diffusion of Rhodamine 6G molecules in the focal spot were suppressed under photon pressure, although no stable trapping was achieved.…”

“…[7][8][9][10][11] As an example, polystyrene latex nanoparticles with 24 nm diameter were trapped and gathered by photon pressure, leading to their assemblies in a focal spot. 11 In single-molecule level, Osborne et al and Chirico et al separately reported that the diffusion of Rhodamine 6G molecules in the focal spot were suppressed under photon pressure, although no stable trapping was achieved. 12,13 These results imply that photon pressure efficiently works even on small clusters or molecules, which have the sizes much smaller than the wavelength of the trapping laser.…”

Novel Nanobiosensing Using a Focused Laser Beam

“…This is called optical tweezers or optical trapping. Nanoparticles whose diameter is much less than the laser wavelength can be trapped as a group in the laser focus and their aggregates formed (Hosokawa et al 2005;Yoshikawa et al 2004;Tanaka et al 2009). We utilize the aggregation of Ag nanoparticles in an optical trap to analyze molecules adsorbed on the aggregates based on surface-enhanced Raman scattering (SERS) spectroscopy.…”

Optical trapping assembling of clusters and nanoparticles in solution by CW and femtosecond lasers

“…In the late 1980s, we demonstrated laser trapping of micrometer-sized particles in view of chemistry, developed various methodologies for their manipulation, ablation, and patterning in solution, and elucidated their dynamics [2]. Our trials were the first systematic study on spectroscopy and chemistry in small domains, and, in the middle of the 1990s, we started laser trapping studies on polymers, micelles, dendrimers, and nanoparticles of gold and polymers [3][4][5][6][7]. The 1064-nm laser irradiation gathers these nano-objects in solution and fills up just the focal volume, forming their assembly [8,9].…”