An integrated immunochromatographic device for C-reactive protein detection using hierarchical dendritic gold nanostructure films

Immunochromatographic test strips typically consist of sample pad, conjugate pad, nitrocellulose membrane, and absorbent pad. Even minute variations in the assembly of these components can lead to inconsistent sample-reagent interactions, thereby reducing reproducibility. In addition, the nitrocellulose membrane is susceptible to damage during assembly and handling. To address this issue, we propose to replace the sample pad, conjugate pad, and nitrocellulose membrane with hierarchical dendritic gold nanostructure (HD-nanoAu) films to develop a compact integrated immunochromatographic strip. The strip uses quantum dots as a background fluorescence signal and employs fluorescence quenching to detect C-reactive protein (CRP) in human serum. A 5.9 μm thick HD-nanoAu film was electrodeposited on an ITO conductive glass by the constant potential method. The wicking kinetics of the HD-nanoAu film was thoroughly investigated, and the results indicated that the film exhibited favorable wicking properties, with a wicking coefficient of 0.72 μm ms-0.5. The immunochromatographic device was fabricated by etching three interconnected rings on HD-nanoAu/ITO to designate sample/conjugate (S/C), test (T), and control (C) regions. The S/C region was immobilized with mouse anti-human CRP antibody (Ab1) labeled with gold nanoparticles (AuNPs), while the T region was preloaded with polystyrene microspheres decorated with CdSe@ZnS quantum dots (QDs) as background fluorescent material, followed by mouse anti-human CRP antibody (Ab2). The C region was immobilized with goat anti-mouse IgG antibody. After the samples were added to the S/C region, the excellent wicking properties of the HD-nanoAu film facilitated the lateral flow of the CRP-containing sample toward the T and C regions after binding to AuNPs labeled with CRP Ab1. In the T region, CRP-AuNPs-Ab1 formed sandwich immunocomplexes with Ab2, and the fluorescence of QDs was quenched by AuNPs. The ratio of fluorescence intensity in the T region to that in the C region was used to quantify CRP. The T/C fluorescence intensity ratio was negatively correlated with the CRP concentration in the range of 26.67-853.33 ng mL-1 (corresponding to 300-fold diluted human serum), with a correlation coefficient (R2) of 0.98. The limit of detection was 15.0 ng mL-1 (corresponding to 300-fold diluted human serum), and the range of relative standard deviation: 4.48-5.31%, with a recovery rate of 98.22-108.33%. Common interfering substances did not cause significant interference, and the range of relative standard deviation: 1.96-5.51%. This device integrates multiple components of conventional immunochromatographic strips onto a single HD-nanoAu film, resulting in a more compact structure that improves the reproducibility and robustness of detection, making it promising for point-of-care testing applications.