Cu²⁺-Directed Liposome Membrane Fusion, Positive-Stain Electron Microscopy, and Oxidation

Abstract

Natural lipid headgroups contain a few types of metal ligands, such as phosphate, amine, and serine, which interact with metal ions differently. Herein, we studied the binding between Cu and liposomes with four types of headgroups: phosphocholine (PC), phosphoglycerol (PG), phosphoserine (PS), and cholinephosphate (CP). Using fluorescently headgroup-labeled liposomes, Cu strongly quenched the CP and PS liposomes, whereas quenching of PC and PG was weaker. Dynamic light scattering indicated that all of the four liposomes aggregated at high Cu concentrations, and ethylenediaminetetraacetic acid (EDTA) only restored the original size of the PC liposome, implying fusion of the other three types of liposomes. The leakage tests revealed that the integrity of PC liposomes was not affected by Cu, but the other three liposomes leaked. Under TEM, all of the liposomes show a positive-stain feature in the presence of Cu and Cu-stained individual liposomes with a short incubation time (<1 min). The oxidative catalytic property of Cu was also tested, and a tight binding by the PS liposome inhibited the activity of Cu. Finally, a model of interaction for each liposome was proposed, and each one has a different metal-binding and interaction mechanism.

Charge and Coordination Directed Liposome Fusion onto SiO2 and TiO2 Nanoparticles

“…DOCP flips the headgroup to expose the phosphate, leading to a net negative charge. , To remove this charge, DOCPe was also studied, in which the phosphate is capped by an ethyl group. DOPS is also negatively charged, but it has more versatile chemistry for metal coordination. ,, These lipids are in the fluid phase at room temperature, and each can form single-component liposomes. For each liposome, we are interested in knowing whether they are adsorbed by SiO 2 and TiO 2 NPs and if they further form SLBs (Figure E).…”

“…In addition, the p K a values of their surface hydroxyl groups (e.g., electrostatic interactions) have been focused on as the main difference between SiO 2 and TiO 2 , while their chemical interaction with lipids has not been carefully considered . Recently, studies on the binding of metal ions and metal oxides to lipids have attracted increasing attention. − In this context, we want to re-examine these two surfaces with a few more lipids. Our goal is to understand the inorganic surfaces and lipids at the same time by varying the headgroup chemistry and pH.…”

Promoting DNA Adsorption by Acids and Polyvalent Cations: Beyond Charge Screening

“…The measurement of DNA adsorption with metal ions needs to be carefully performed with control groups. For example, samples should be centrifuged and the supernatant needs to be added with a metal chelator such as EDTA to determine if the decreased fluorescence intensity is due to adsorption or quenching . Using UV–vis absorbance at 260 nm to quantity DNA can also be used when the initial DNA concentration is high (>1 μM) and nanoparticle interferences are removed .…”

Liposome‐Boosted Peroxidase‐Mimicking Nanozymes Breaking the pH Limit

“…The calcein fluorescence was excited at 485 nm and monitored at 515 nm for 500 s, and 2 μL Fe 3 O 4 nanoparticles (50 μg mL −1 ) were added at the time of 100 s. Then, 5 μL of 10 % Triton X‐100 was added to fully rupture the liposomes. Each group was measured at least 3 times [52, 53] …”