Probing the Growth Kinetics of Bioinspired Phenolic Nanocoating via Evanescent Wave Excited by Fiber-Optic Modal Interferometry

Bioinspired polydopamine (PDA) nanocoating poses one important measure to precisely customize functionalized surfaces, while its dynamic growth characteristics are still not fully understood. Herein, we develop a high-sensitivity and rapid-response fiber-optic modal interferometer (FMI) to <i>operando</i> probe the growth dynamics of PDA nanocoating at the solid-liquid interface. The proposed FMI was treated with HF corrosion to enhance the surface evanescent field, thereby improving the surface refractive index sensitivity. Thus, the FMI successfully monitored the adhesion behavior of the polydopamine coating on the surface of the optical fiber and the subsequent adsorption of biomolecules. Through further analysis of surface evanescent wave field, a model was established to correlate FMI's interference spectra with PDA nanocoating's thickness. The accuracy of these results was validated through multiple <i>ex situ</i> characterization and spectroscopic techniques. Finally, the fiber-optic modal interferometer successfully revealed growth kinetic characteristics of the PDA coating induced by CuSO₄/H₂O₂ under diverse operational conditions. This work may advance the evolution of surface-sensitive measurement technologies and surface phenolic chemistry.