A homogeneous immunoassay technology based on liposomes and the complement system enables one-step, no-wash, rapid diagnostics directly in serum

Liposomes are a well-established carrier and controlled release system in medicine and bioanalysis. Their biomimetic capabilities are harnessed for the development of a reliable homogeneous assay platform technology that lends itself to high-throughput screening and point-of-care applications since no wash or separation steps are needed. It was developed for fluorescent, chemiluminescent, and electrochemical detection strategies and applied to antibodies directed against small or polymeric molecules and peptides as model analytes. The simplicity of the approach is achieved as mere binding of analytes or analyte-associated entities to the liposome surface leads to the activation of the complement system, which in turn lyses the liposomes. Released encapsulated marker molecules are quantified and directly correlated to the analytes. Control over the liposome chemistry, including cholesterol content, surface chemistry, and encapsulants, was identified to be key to ensure their general serum and storage stability (more than 40 months at 4 °C and up to 4 weeks at 37 °C) and their efficient and specific response to complement activity. Additional assay conditions of relevance included the concentration of liposomes and their ratio to serum proteins, the amount of complement trigger per liposome, and the activity of complement proteins. Understanding and being able to control the liposomes enable various analysis strategies including the quantification of analytes, determination of complement activity, and evaluation of the therapeutic application potential of antibodies. A time-resolved version of the assay even allows the study of the complex actions of the complement system.