Dimension 3100

The images of coated and uncoated fiber surfaces were obtained by a SEM (JSM-6700F, JEOL) and an AFM (Dimension 3100, Digital Instruments). The cross-sections were prepared by a FIB following a standard preparation method³⁸ (details in Supplementary Method B), before characterization by a TEM (JEM-100CXII, JEOL). The cross-sections were also characterized and confirmed by a 3D surface optical profilometer (Wyko NT 3300, Veeco). The TiO₂ layer masses (m_TiO2) on the optical fibers were measured gravimetrically by the weight of the optical fibers before and after the dip-coating/drying cycles. The porosity of the TiO₂ coating layers, which is defined as the fraction of the total pore volume over the volume of the TiO₂ layer, was calculated using Eq. (9). $\mathrm{Porosity}=1-\frac{m_{\mathrm{TiO}2}}{{\rho }_{\mathrm{TiO}2}\mathrm{\cdot }L\mathrm{\cdot }\pi d\mathrm{\cdot }D}$ where ρ_TiO2 is the true density of the TiO₂ particles (4.26 g/mL at 25 °C obtained from Sigma-Aldrich), L is the TiO₂ coating length, d is the diameter of optical fibers, and D is the thickness of the TiO₂ coating layers, which was determined by the cross-sectional profiles of TiO₂-QOFs from SEM images. The TiO₂ patchiness was calculated by dividing the optical fiber surface in direct contact with TiO₂ nanoparticles by the total surface of the optical fiber determining from TEM cross-section images.

A dispersion of NP (10 µL) was drop cast on freshly cleaned mica substrates and air-dried. To image the blank and loaded NPs obtained from EDE, Cyrene or PEG 400 method, a Dimension 3100 (Digital Instruments, Veeco, Santa Barbara, CA) equipped with a Nanoscope IV controller as well as a JPK-Nanowizard (JPK BioAFM, Bruker Nano, Berlin, Germany) was used. Standard tapping mode silicon cantilevers from Bruker (model RTESPA 300, Bruker, Santa Barbara, CA) with a resonance frequency around 300 kHz in air, a spring constant in the range of 20 to 80 N/m, and a tip radius of less than 10 nm (typically 7 nm) were used for height imaging.