Highly sensitive and rapid assay of substance P and streptolysin O in human serum using immuno-liposomes and gramicidin channels.

A highly sensitive and rapid method for the determination of substance P (SP) and streptolysin O (SLO) in human serum is described. The assay is based on enriching the analyte by agglutination/precipitation of immuno-liposomes and enhancing the fluorescence intensity by gramicidin A channels. A mixture of the immuno-liposomes encapsulating a pH-sensitive fluorescence dye BCECF, gramicidin A and a given concentration of SP (or SLO) is preincubated in a solution and captured on anti-SP (or anti-SLO)-modified cover slips, followed by measuring fluorescence images after removing excess liposomes. The method allowed quantifying SP and SLO in the range from sub-pg mL(-1) to pg mL(-1), with detection limits of 0.32 pg mL(-1) and 8 fg mL(-1), respectively. The present method could determine SP and SLO in 50-125 times diluted human serum without any extraction steps. The assay can be completed within 60 min.