Electrostatic-triggered exothermic antibody adsorption to the cellulose nanoparticles

Antibody-conjugated nanoparticles are used in a fields ranging from medicine to engineering. NanoAct® nanobeads are cellulose nanoparticles used in lateral flow assays that are highly water dispersible. In order to promote the adsorption of antibodies onto NanoAct® particles while maintaining their activity, we analyzed the adsorption onto NanoAct® particles thermodynamically and elucidated the adsorption mechanism. In an immunochromatographic assay, the amount of adsorbed antibody and the color intensity of the test line increased as the pH decreased. The zeta potential of the nanoparticles remained constant at around -30 mV over the pH range from 2 to 10. The model antibody had pI values between 6.2 and 6.8. Isothermal calorimetry analysis showed that adsorption of antibody to the NanoAct® particle is an endothermic reaction under low pH conditions, an exothermic reaction between pH 6 and pH 7, and a weakly exothermic reaction above pH 7. These data indicate that the changes in net charge of the antibody surface as a function of pH influence the pH dependence of antibody adsorption to the negatively charged NanoAct®. This suggests that increased positive charge on the antibody surface will result in a more sensitive NanoAct®-based immunoassay.