Oxidized carbon black nanoparticles as color label in a rapid vertical flow immunoassay for C-reactive protein...

The use of traditional colored labels does not fully address the challenges of low sensitivity in rapid tests and insufficient stability of the reagents employed and necessitates additional procedural steps or complex instrumentation to generate an analytical signal. Owing to their unique properties, carbon black nanoparticles (CBNPs) present a promising solution to these issues. However, the current scientific data regarding the reproducibility, scalability, and preservation of structural and functional stability of CBNP-based colored labels remains insufficient for their widespread adoption in routine laboratory practice. Therefore, we have developed and optimized a reproducible method for the functionalization of oxidized CBNP with recognition elements, aimed at producing highly efficient vertical flow immunoassays (VFIAs). Our results demonstrate that the resulting diagnostic reagents maintain their structural and functional properties for one year when stored at +4 °C or -20 °C. We have demonstrated for the first time the reproducibility of the method for producing diagnostic reagents based on oxidized CBNPs with monoclonal antibodies. The novel VFIA based on oxidized CBNPs for the determination of C-reactive protein demonstrates a limit of detection of 2.6 ng/mL compared to similar tests described in the literature. The developed assay allows for the determination of CRP with a visual detection limit of 4 ng/mL in the required concentration range with acceptable intra-assay/inter-day reproducibility and selectivity.