title: Biological microbeads for flow-cytometric immunoassays, enzyme titrations, and quantitative PCR.
abstract: BACKGROUND
  Introduction of microbeads into flow-cytometry has created a new scenario, making quantitative measurement of molecules dispersed in a homogeneous phase, with an extremely wide realm of already realized and potential applications possible. Development of this field has lead to specialized instrumentation and microbead arrays, dedicated to certain applications.
  
  
  METHODS
  Formaldehyde-fixed yeast and bacterial cells were conjugated with avidin and applied as microbeads, to establish a simple, convenient, flexible, and inexpensive flow-cytometric platform for various immunological and biochemical assays.
  
  
  RESULTS
  We have tested these "biological microbeads" for the simultaneous titration of human alpha-fetoprotein (AFP) and human Chorionic Gonadotropin (betahCG) hormone levels, for the titration of proteolytic and nucleolytic (restriction) enzymes, and for quantitative PCR, using biotinylated and fluorescent primers.
  
  
  CONCLUSIONS
  The use of biological microbeads for various immunological and biochemical assays has been demonstrated. The flow-cytometric methods proved to be at least as sensitive as the standard biochemical or immunological tests. For proteinase K activity measurements, a single enzyme molecule in the sample could be detected. The sensitivity, versatility, and low cost of the assays may advance flow-cytometry to become a central methodological platform in most laboratories. The biological microbeads offer virtually unlimited possibilities for fluorescent labeling (addressing), conjugation of ligand binding molecules, and they are easy to handle and perform well in a multiplex format.
authors.affiliation: Department of Biophysics and Cell Biology, Medical and Health Science Center, University of Debrecen, Debrecen, Hungary.
authors.forename: Judit
authors.initials: J
authors.lastname: Pataki
authors.forename: Miklós
authors.initials: M
authors.lastname: Szabó
authors.forename: Erika
authors.initials: E
authors.lastname: Lantos
authors.forename: Lóránt
authors.initials: L
authors.lastname: Székvölgyi
authors.forename: Mónika
authors.initials: M
authors.lastname: Molnár
authors.forename: Eva
authors.initials: E
authors.lastname: Hegedüs
authors.forename: Zsolt
authors.initials: Z
authors.lastname: Bacsó
authors.forename: János
authors.initials: J
authors.lastname: Kappelmayer
authors.forename: György
authors.initials: G
authors.lastname: Lustyik
authors.forename: Gábor
authors.initials: G
authors.lastname: Szabó
mesh_terms: D001360:Avidin / Q000737:chemistry; D019921:Biotinylation; D002364:Caseins / Q000737:chemistry; D018997:Chorionic Gonadotropin, beta Subunit, Human / Q000032:analysis; D004262:DNA Restriction Enzymes / Q000032:analysis; D019286:Endopeptidase K / Q000032:analysis; D004798:Enzymes / Q000032:analysis*; D005434:Flow Cytometry / Q000379:methods*; D005456:Fluorescent Dyes / Q000737:chemistry; D005557:Formaldehyde / Q000737:chemistry; D006801:Humans; D007118:Immunoassay / Q000379:methods; D008863:Microspheres; D016133:Polymerase Chain Reaction / Q000379:methods*; D012441:Saccharomyces cerevisiae / Q000737:chemistry; D013211:Staphylococcus aureus / Q000737:chemistry; D019809:Streptavidin / Q000737:chemistry; D017186:Titrimetry / Q000379:methods*; D000509:alpha-Fetoproteins / Q000032:analysis
chemical_list: D002364:Caseins; D018997:Chorionic Gonadotropin, beta Subunit, Human; D004798:Enzymes; D005456:Fluorescent Dyes; D000509:alpha-Fetoproteins; D001360:Avidin; D005557:Formaldehyde; D019809:Streptavidin; D004262:DNA Restriction Enzymes; D019286:Endopeptidase K