Characterization of Phospholipid Bilayer Formation on a Thin Film of Porous SiO₂ by Reflective Interferometric Fourier Transform Spectroscopy (RIFTS)

Abstract

Classical methods for characterizing supported artificial phospholipid bilayers include imaging techniques such as atomic force microscopy and fluorescence microscopy. The use in the past decade of surface-sensitive methods such as surface plasmon resonance and ellipsometry, and acoustic sensors such as the quartz crystal microbalance, coupled to the imaging methods, have expanded our understanding of the formation mechanisms of phospholipid bilayers. In the present work, reflective interferometric Fourier transform spectrocopy (RIFTS) is employed to monitor the formation of a planar phospholipid bilayer on an oxidized mesoporous Si (pSiO(2)) thin film. The pSiO(2) substrates are prepared as thin films (3 μm thick) with pore dimensions of a few nanometers in diameter by the electrochemical etching of crystalline silicon, and they are passivated with a thin thermal oxide layer. A thin film of mica is used as a control. Interferometric optical measurements are used to quantify the behavior of the phospholipids at the internal (pores) and external surfaces of the substrates. The optical measurements indicate that vesicles initially adsorb to the pSiO(2) surface as a monolayer, followed by vesicle fusion and conversion to a surface-adsorbed lipid bilayer. The timescale of the process is consistent with prior measurements of vesicle fusion onto mica surfaces. Reflectance spectra calculated using a simple double-layer Fabry-Perot interference model verify the experimental results. The method provides a simple, real-time, nondestructive approach to characterizing the growth and evolution of lipid vesicle layers on the surface of an optical thin film.

Optical characterization of porous silicon monolayers decorated with hydrogel microspheres

“…Indeed, we observed a single peak in the FFT spectrum for our hybrid structure which corresponds to layer 2 (pSi film). This result is in accordance with studies on the deposition of lipid vesicles onto pSi layers monitored by RIFTS [24,25]. Presumably, the low refractive index of layer 1, composed of polyNIPAM spheres and surrounding solution, is responsible for the absence of the other two peaks in the FFT spectrum.…”

Real‐Time Optical Detection of Stabilized Artificial G‐Quadruplexes Under Confined Conditions

“…[17,18] Numerous optical (bio)sensors have been developed using reflective interferometric Fourier transform spectroscopy (RIFTS). [19][20][21][22] Rugate filters of pSi multilayers that feature a sinusoidal variation of the depth mesoporosity and a strong peak in their reflectivity spectrum reflect a single color without a Fourier transform operation. [22] We hypothesized that, under pSi confinement, the transformation between the G-ribbon and G-quadruplex phases of distinct molecular packing density would result in a change in the refractive index of the pSi structure (Figure 1 b), which can be detected as the corresponding shift of the effective optical-thickness value in its fast Fourier interference pattern (Figure 1 c).…”

Photonic porous silicon as a pH sensor

“…Here, three interfaces are present: air-pDEAEA, pDEAEA-pSi, and pSi-Si bulk. In the literature, the relationship between the thickness and the refractive index of the layers deposited at the surface of the pSi and the variation in amplitude in the reflectance spectra is well established [16,25]. Here, the transfer matrix method from the program SCOUT was used to calculate a layer thickness of pDEAEA on the top of the pSi film.…”