Abstract
Here we found that gold nanoparticles (AuNPs) enhance the optical force acting on vesicles prepared from phospholipids via hydrophobic and electrostatic interactions. A laser beam was introduced into a cuvette filled with a suspension of vesicles and it accelerated them in its propagation direction via a scattering force. The addition of the AuNPs exponentially increased the velocity of the vesicles as their concentration increased, but polystyrene particles had no significant impact on velocity in the presence of AuNPs. To elucidate the mechanism of the increased velocity, the surface charges in the vesicles and the AuNPs were controlled; the surface charges of the vesicles were varied via the use of anionic, cationic and neutral phospholipids, whereas AuNPs with positive and negative charges were synthesized by coating with citrate ion and 4-dimethylaminopyridine, respectively. All vesicles increased the velocity at different degrees depending on the surface charge. The vesicles were accelerated more efficiently when their charges were opposite those of the AuNPs. These results suggested that hydrophobic and electrostatic interactions between the vesicles and the AuNPs enhanced the optical force. By accounting for the binding constant between the vesicles and the AuNPs, we proposed a model for the relationship between the concentration of the AuNPs and the velocity of the vesicles. Consequently, the increased velocity of the vesicles was attributed to the light scattering that was enhanced when AuNPs were adsorbed onto the vesicles.
Highlights
In biological systems, vesicles play important roles that include the transportation of chemical substances into or out of cells, the storage of biosynthetic products and the digesting of nutrients [1,2,3]
We found that gold nanoparticles (AuNPs) enhance the optical force acting on vesicles prepared from phospholipids via hydrophobic and electrostatic interactions
The maximal numbers of adsorbed AuNPs were achieved when anionic vesicles were paired with cationic AuNPs, cationic vesicles were paired with anionic AuNPs and neutral vesicles were paired with anionic AuNPs
Summary
Vesicles play important roles that include the transportation of chemical substances into or out of cells, the storage of biosynthetic products and the digesting of nutrients [1,2,3]. Microfluidic devices have achieved high rates of recovery, but these require sophisticated fabrication techniques and complex pumping systems [20 –22] Compared with these separation methods, manipulation using optical force, which is generally employed in techniques such as laser trapping or the use of optical tweezers [23], is useful for the collection and manipulation of small droplets and vesicles [24 –27]. The enhanced collection speed was attributed to thermal convection and possible enhancement of light scattering, but the mechanism remained unclear with respect to the interaction between the vesicles and the AuNPs that may have influenced the light scattering, that is, the optical force acting on the vesicle. We elucidated the mechanism by which the interaction between the vesicles and the AuNPs enhances the acceleration of the vesicles by optical force. We revealed that acceleration is enhanced when AuNPs bind to vesicles via electrostatic and hydrophobic interactions
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