Preparation of AgBr quantum dots via electroporation of vesicles

Electric field-induced transient pore formation (reversible electroporation) in the bilayer membrane of synthetic large unilamellar vesicles (LUV) is used as a novel method for the preparation of angstrom size quantum dots of the indirect band gap semiconductor AgBr. With Ag+ ions encapsulated in 178 nm diameter LUVs of dioleoylphosphatidylcholine (DOPC) and Br- ions placed in the bulk medium, the reaction Ag+ + Br- --> AgBr and subsequent clustering of the product are initiated by the application of a 500 mu s long high-voltage (E = 6 kV/cm) electric square pulse to the vesicular suspension. The slow growth of clusters (taking several hours) on the exterior surface of the vesicles is monitored through the blue-shift followed by a redshift of their UV absorption band. At the turn-around point (269 nm) of the spectral band-shift, the size of the AgBr clusters is estimated to be similar to 5 Angstrom, the smallest achieved by colloid chemical methods.