Ultrasound-accelerated immunoassay, as exemplified by enzyme immunoassay of choriogonadotropin

Abstract

The rate-limiting step in many solid-phase immunoassays is associated with the slow kinetics of binding of macro-molecular antigen with conjugate to the immobilized phase. We demonstrate that the use of ultrasonic energy to enhance mass transport across liquid/solid interfaces can dramatically accelerate antigen binding to immobilized antibodies. We use an ultrasound-accelerated procedure with an enzyme-channelling test strip containing glucose oxidase and specific antibody to the α-subunit of human choriogonadotropin (HCG) co-immobilized onto a cellulose support. A horseradish peroxidase conjugate of monospecific antibody to the β-subunit of HCG is used in the liquid phase to complete the immune 'sandwich.' Use of ultrasound to accelerate binding and of enzyme channelling to eliminate wash steps result in a simple two-incubation protocol by which 25 int. units of urinary HCG per liter can be detected visually in less than 20 min of assay time.