Analytical Sciences

Highly Sensitive and Rapid Assay of Substance P and Streptolysin O in Human Serum Using Immuno-liposomes and Gramicidin Channels

Misato SAKAMOTO,* Atsushi SHOJI,** and Masao SUGAWARA*

*Department of Chemistry, College of Humanities and Sciences, Nihon University, Sakurajyosui, Setagaya, Tokyo 156–8550, Japan
**School of Pharmacy, Tokyo University of Pharmacy and Life Science, 1432-1 Horinouchi, Hachioji, Tokyo 192–0392, Japan

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.

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