Colony lift immunoassay utilizing antibody-coupled liposomes encapsulating HRP

The liposome immunoblotting assay was applied to colony lift immunoassay for detection of colonies expressing target protein (scFv) with higher signal intensity. Only edges of blotted samples on the membrane were developed by a direct blotting method, because cells adsorbed on the surface of the membrane plugged openings of pores and physically prevented interaction between the antigen and immunoliposomes. By an indirect blotting method, uniform signals with higher density were successfully observed from blotted membranes by use of immunoliposomes. Immunoliposome of large unilamellar vesicles (immuno-LUVs) showed the highest S/N ratio among three kinds of liposomes. In the colony lift imunoassay utilizing immuno-LUVs, the signal density was three times higher, compared with the conventional assay, while their background levels were almost same. Consequently, a higher S/N ratio could be attained for detection of colonies secreting active scFv. Thus, this method is useful to screen colonies expressing target protein with higher sensitivity.