Use of octadecyl silica as an alternative non-conventional solid phase in immunoradiometric assays

The use of chemically modified silica (octadecyl silica or Si-C18), a liquid chromatography stationary reverse phase, is proposed as an alternative solid phase for immunoradiometric assays (IRMAs). Si-C18 and polyvinylchloride solid phases were compared in their efficiency to detect a murine plasma protein (sex-limited protein or Slp) in a two site-two antibody IRMA. Si-C18 is at least as sensitive as PVC since Slp could be detected in plasmas diluted 1 128 000 and 1 64 000 respectively. The fact that 1 mg of Si-C18 can adsorb 5-14 times more protein than a PVC well is in agreement with the larger relative surface of Si-C18 beads (approximately 50 cm²/mg), compared with the PVC (approximately 1 cm²/well). These results strongly suggest that the Si-C18 matrix, saturated with specific antibodies, could be an exceptional probe to rescue and detect antigenic moieties diluted in large volumes of complex biological fluids.