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Liposome is one of popular materials in biotechnology due to the special characteristics: hydrophilic inner space inside liposome and hydrophobic space between liposome bilayers. In this study, liposome was used for two applications: liposome immunoassay and active cell targeting. For both applications, the surface of liposome was biofunctionalized with antibody or recombinant human epidermal growth factor (EGF). Liposome was prepared based on DPPC, DCP, and cholesterol by film rehydration method. Liposome immunoassay (LIA) is based on enzyme immunoassay (EIA) but the detection sensitivity could be significantly enhanced by biofunctionalized immunoliposomes encapsulating horse radish peroxidase (HRP). Therefore, enzyme encapsulated liposomes are very useful to detect a small amount of analyte with enhanced signal. As a model antibody, anti-rabbit IgG antibody was immobilized on the liposome surface by iminothiolane reaction. Unbound anti-rabbit IgG antibody was removed by gel permeation chromatography. 4-chloro-naphtol was used as a HRP substrate. This substrate can be penetrated into liposome inner space and be accumulated inside of liposome after nzyme reaction. This causes denser signal than conventional EIA (6 times higher signal density at 1 μg/mL rabbit IgG concentration and 16 times higher LOD). By decreasing the spot volume, signal density from LIA did not changed. This shows that LIA can be applied to small amount
analyte detection in a small volume. Another application of liposome in this study was a carrier for active cell targeting. Liposome was biofunctionalized with EGF by BAM (biological anchor for cell membrane) molecule. BAM is consisted of oleyl group conjugated to NHS (N-hydroxysuccinimide) and PEG2000 (polyethylene glycol). EGF was reacted with NHS moiety on BAM and unreacted EGF was removed by gel permeation chromatography. Then EGF-BAM complex was incubated with liposome particle; this complex could be effectively inserted to the bilayers of a liposomal vesicle through lipophilc interaction. By this post-insertion method, EGF is only immobilized on the outside of liposome particle. Uptake of BAM inserted liposome to macrophage cell (RAW 264.7) was investigated by confocal microsopy. Compared with unmodified liposome, BAM inserted liposome has 2 times lower uptaken level; this is resulted from PEG moiety of BAM. Also, EGF-BAM inserted liposome was incubated with breast cancer cell line (MCF-7 and MDA-MB-231 cell). EGF-BAM inserted liposome has specificity only to EGF receptor overexpressed cell (MDA-MB-231 cell). In addition, biofunctionalized liposome encapsulating an anti-cancer drug (doxorubicin) selectively killed only MDA-MB-231 cell.