posted on 2016-02-22, 06:37authored bySari Pihlasalo, Antti Kulmala, Anita Rozwandowicz-Jansen, Pekka Hänninen, Harri Härmä
A sensitive and rapid assay for the quantification of
proteins,
based on sample protein adsorption to Eu3+-chelate-labeled
nanoparticles, was developed. The lanthanide ion of the surface-conjugated
Eu3+ chelate is dissociated at a low pH, decreasing the
luminescence signal. The increased concentration of the sample protein
prevents dissociation of the chelate, leading to a high luminescence
signal due to the nanoparticle-bound protein. The assay sensitivity
for the quantification of proteins was 130 pg for bovine serum albumin
(BSA), which is an improvement of nearly 100-fold from the most sensitive
commercial methods. The average coefficient of variation for the assay
of BSA was 8%. The protein-to-protein variability was sufficiently
low; the signal values varied within a 28% coefficient of variation
for nine different proteins. The developed method is relatively insensitive
to the presence of contaminants, such as nonionic detergents commonly
found in biological samples. The existing methods tested for the total
protein quantification failed to measure protein concentration in
the presence of bacterial cell lysate. The developed method quantified
protein also in samples containing insoluble cell components reducing
the need for additional centrifugal assay steps and making the concept
highly attractive for routine laboratory work.