Electrical bistability in self-assembled hybrid multilayers of phospholipid and nanoparticles

Photoluminescence modulation of silicon nanoparticles via highly ordered arrangement with phospholipid membranes

Highly ordered self-assembly of nanoparticles (NPs) in a large scale promises attractive potential in optical modulation of the NPs for illuminating, imaging and sensing applications. In this work, a type of multi-lamellar nanocomposite membranes composed of phospholipid multilayers and Si NPs sandwiched between each adjacent lipid layers was fabricated via a facile co-assembly method. X-ray reflectivity (XRR), grazing incident X-ray diffraction (GIXRD) and TEM measurements verified the highly ordered arrangement of NPs within the multilayers with a controlled in-plane inter-particle separation from ∼7 nm to ∼14 nm. Due to such an arrangement, the photoluminescence (PL) properties of the Si NPs were effectively modulated. Compared to the NPs in suspension or its pure film, the PL of the NPs in the membranes blue-shifted and remarkably narrowed, with the full-width-at-half-maximum (FWHM) value reduced from >110 nm of the pure Si NP film to below 43 nm. The radiative lifetime of the NPs was also significantly reduced from ∼16.7 ns to ∼3.3 ns depending on the inter-particle distance in the membrane. Meanwhile, the Si NPs within membranes maintained robust photostability under UV irradiation.

Stabilization of solid-supported phospholipid multilayer against water by gramicidin addition

It was demonstrated that hydrophobicity of solid supported planar dipalmitoyl phosphatidylcholine (DPPC) phospholipid multilayer can be greatly increased by incorporating a transmembrane protein, gramicidin, into the DPPC membrane. The contact angle of deionized water droplet on the gramicidin-modified DPPC membrane increased from 0° (complete wetting) without gramicidin to 55° after adding 15 mol % gramicidin. The increased hydrophobicity of the gramicidin-modified DPPC membrane allowed the membrane to remain stable at the air/water interface as well as underwater. The Au nanoparticles deposited on the gramicidin-modified DPPC membrane reproduced the characteristic surface plasmon resonance peak after being kept underwater or in phosphate-buffered saline solution for 5 days, attesting to the membrane stability in an aqueous environment. The enhanced underwater stability of the lipid multilayer substantially broadens the potential application of the lipid multilayer which includes biosensing, enzymatic fuel cell, surface enhanced Raman spectroscopy substrate.