One-step homogeneous immunoassay for small analytes

Timo Pulli (Corresponding Author), Matti Höyhtyä, Hans Söderlund, Kristiina Takkinen

Research output: Contribution to journalArticleScientificpeer-review

65 Citations (Scopus)


We have developed a one-step, homogeneous noncompetitive immunoassay for small analytes using recombinant antibodies and morphine as the model analyte. A highly specific antibody against the immune complex (IC) formed between an anti-morphine antibody and morphine was selected from a naïve scFv phage display library. The in vitro phage library selection procedure avoids the difficulties associated with the production of anti-IC antibodies by animal immunization. The anti-morphine and the anti-IC antibodies were labeled with a pair of fluorescence resonance energy transfer (FRET) fluorophores. In the FRET assay the labeled antibodies were incubated with saliva samples spiked with morphine, codeine, or heroin. Within 2 min, 5 ng/mL morphine, which is clearly under the recommended cutoff level, was detected without cross-reactivity to codeine or heroin. This assay principle is also widely applicable to other small analytes.
Original languageEnglish
Pages (from-to)2637 - 2642
Number of pages6
JournalAnalytical Chemistry
Issue number8
Publication statusPublished - 2005
MoE publication typeA1 Journal article-refereed


  • immunoassay
  • antibodies
  • detection
  • drug detection
  • drug abuse

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