a b s t r a c t
A dual-analyte assay for the simultaneous determination of C-reactive protein (CRP) and D-dimer in human blood plasma based on a white light interference spectroscopy sensing platform is presented. Measurement is accomplished in real-time by scanning the sensing surface, on which distinct antibody
areas have been created, with a reflection probe used both for illumination of the surface and collection
of the reflected interference spectrum. The composition of the transducer, the sensing surface chemical
activation and biofunctionalization procedures were optimized with respect to signal magnitude and
repeatability. The assay format involved direct detection of CRP whereas for D-dimer a two-site immunoassay employing a biotinylated reporter antibody and reaction with streptavidin was selected. The assays were sensitive with detection limits of 25 ng/mL for both analytes, precise with intra- and interassay CV values ranging from 3.6% to 7.7%, and from 4.8% to 9.5%, respectively, for both assays, and
accurate with recovery values ranging from 88.5% to 108% for both analytes. Moreover, the values determined for the two analytes in 35 human plasma samples were in excellent agreement with those
received for the same samples by standard diagnostic laboratory instrumentation employing commercial
kits. The excellent agreement of the results supported the validity of the proposed system for clinical
application for the detection of multiple analytes since it was demonstrated that up to seven antibody
areas can be created on the sensing surface and successfully interrogated with the developed optical setup.