Detection of C-Reactive Protein Using Histag-HRP Functionalized Nanoconjugate with Signal Amplified Immunoassay

Ultrasensitive detection of biomarkers is highly significant for disease prognosis and public health treatment. Despite wide acceptance in routine laboratory tests, the conventional enzyme-linked immunosorbent assay (ELISA) has been of limited use for early biomarker detection due to insufficient sensitivity and multiple long incubation time. Several nanoprobes have been introduced to circumvent the limitation, however, rapid, simple, and chemical-free nanoprobe synthesis and sensitive detection methods, particularly for ELISA, are still lacking. In this study, we have synthesized a gold nanoprobe, conjugated with multiple 6X-histidine (6X-his) peptide and nickel-horseradish peroxidase (Ni²⁺-HRP), for enhancing the colorimetric signal in ELISA. The developed nanoprobe has been tested for the detection of immunologically significant C-reactive protein (CRP) in ELISA format. The performance of designed probe is validated by testing standard and serum samples, and the detection limit of 32.0 pg/mL with R² = 0.98 is confirmed. Furthermore, a comparative analysis of the developed nanoprobe was performed with ELISA developed on conventional guidelines, the proposed immunoassay showed an increase of 12-fold sensitivity for detecting CRP due to the high loading of 6Xhis peptide and binding of multiple Ni²⁺-HRP on a gold nanoparticle. Additionally, the proposed assay provides a simple, fast, and cost-efficient (not requiring multiple antibodies) detection of CRP with easy nanoprobe synthesis. Moreover, the developed Histag-HRP functionalized nanoconjugate immunoassay is flexible and can be applied to other biomarkers efficiently by using disease specific antibody.