Photoreactive and Electrochemical Properties of Vesicle Encapsulated Nanoparticles: Implications for Application in Retinal Stimulation

Electrical stimulation has previously been effective in neural cells activation within retinas affected by degenerative retinal disease. However current technology has at most allowed blind individuals to perceive light without significant resolution, as implants are limited by the spatial constraints of the eye. Photoreactive nanoparticles may provide a solution to this issue, as their small size would allow for the incorporation of higher numbers of stimulatory elements, thus increasing visual resolution. Semiconductive nanocrystal quantum dots (QDs) and gold nanoparticles (AuNPs) both exhibit photoreactive properties which may result in sufficient electrical stimulation to activate neural cells in the retina. This study investigated the electrochemistry and photoreactivity of QDs and AuNPs encapsulated within the hydrophobic region of small unilamellar lipid vesicles (SUVs) to evaluate their potential for application in retinal stimulation. Absorbance of the constructs was evaluated on the day of fabrication and 24 hours later to determine the ability of the particles to react to light while encapsulated, as well as to evaluate stability of the construct over time. Electrical impedance spectroscopy (EIS) was conducted at both time points to determine the electrochemical character of the bilayer and further evaluate construct stability. Although quantum dots may increase the stability of the bilayer over time and improve its capacitative properties, lipid encapsulation appears to obscure the photoreactive properties of the quantum dots. In the case of gold nanoparticles, the construct is initially stabilized but deteriorates more quickly than those SUVs containing quantum dots, as evidenced by an increase in substrate diffusion. Additionally, although these constructs are more photoreactive than those containing QDs, the increase in absorbance is observed primarily in a range below that of the visible spectrum, a feature which is of limited use for the proposed application. Further studies should investigate alternative methods of nanoparticle capping to improve stability and absorbance in this system.