pH value determination for selenium nanoparticle-conjugated recombinant nucleoprotein. Photographs of centrifuge, resuspending (a) the test strip naked results (b), auxiliary judgment result (c), morphology of Se-NP (d), Se-NP-nucleoprotein (e), size analysis (f) and combined effect (g) are shown. C: Control line; G: Test line for IgG detection; M: Test line for IgM detection; PDI: Polymer dispersity index; Se-NP: Selenium nanoparticle.