Reliable and simple methods are required for detection of low concentrations of cytokines and
some other proteins in complex biological fluids. This is especially important when monitoring
the immune responses under various physiological and pathophysiological conditions in vivo
or following production of these compounds in in vitro systems. Cytokines and other
immunologically active molecules are being predominantly detected by enzyme-linked
immunosorbent assays (ELISA) and newly also by immuno-polymerase chain reactions
(iPCR). New simplified variants of iPCR have recently been described where antibodies are
connected with multiple DNA templates through gold nanoparticles (Au-NPs) to form a new
class of detection reagents. In this study we compared functionalized Au-NP-based iPCR (NanoiPCR)
with standard ELISA and iPCR for the detection of interleukin (IL)-3 and stem cell factor
(SCF). The same immunoreagents (IL-3- and SCF-specific polyclonal antibodies and their
biotinylated forms) were used throughout the assays. The obtained data indicate that both
Nano-iPCR and iPCR are superior in sensitivity and detection range than ELISA. Furthermore,
Nano-iPCR is easier to perform than the other two methods. Nano-iPCR was used for
monitoring changes in concentration of free SCF during growth of mast cells in SCF-conditioned
media. The results show that growing cultures gradually reduce the amount of SCF in
supernatant to 25% after 5 days. The combined data indicate that Nano-iPCR assays may be
preferable for rapid detection of low concentrations of cytokines in complex biological fluids.