Electroinjection of colloid particles and biopolymers into single unilamellar liposomes and cells for bioanalytical applications

A combined electroporation and pressure-driven microinjection method for ef ficient loading of biopolymers and colloidal particles into single-cell-siz ed unilamellar liposomes was developed. Single liposomes were positioned be tween a similar to2-mum tip diameter solute-filled glass micropipet, equipp ed with a Pt electrode, and a 5-mum-diameter carbon fiber electrode. A tran sient, 1-10 ms, rectangular waveform de voltage pulse (10-40 V/cm) was appl ied between the electrodes, thus focusing the electric field over the lipos ome. Dielectric membrane breakdown induced by the applied voltage pulse cau sed the micropipet tip to enter the liposome and a small volume (typically 50-500 x 10(-15) L) of fluorescein, YOYO-intercalated T7-phage DNA, 100-nm- diameter unilamellar liposomes, or fluorescent latex spheres could be injec ted into the intraliposomal compartment. We also demonstrate initiation of a chemical intercalation reaction between T2-phage DNA and YOYO-1 by dual i njection into a single giant unilamellar liposome. The method was also succ essfully applied for loading of single cultured cells.