Investigating Ligand–Receptor Interactions at Bilayer Surface Using Electronic Absorption Spectroscopy and Fluorescence Resonance Energy Transfer

Abstract

We investigate interactions between receptors and ligands at bilayer surface of polydiacetylene (PDA) liposomal nanoparticles using changes in electronic absorption spectroscopy and fluorescence resonance energy transfer (FRET). We study the effect of mode of linkage (covalent versus noncovalent) between the receptor and liposome bilayer. We also examine the effect of size-dependent interactions between liposome and analyte through electronic absorption and FRET responses. Glucose (receptor) molecules were either covalently or noncovalently attached at the bilayer of nanoparticles, and they provided selectivity for molecular interactions between glucose and glycoprotein ligands of E. coli. These interactions induced stress on conjugated PDA chain which resulted in changes (blue to red) in the absorption spectrum of PDA. The changes in electronic absorbance also led to changes in FRET efficiency between conjugated PDA chains (acceptor) and fluorophores (Sulphorhodamine-101) (donor) attached to the bilayer surface. Interestingly, we did not find significant differences in UV−vis and FRET responses for covalently and noncovalently bound glucose to liposomes following their interactions with E. coli. We attributed these results to close proximity of glucose receptor molecules to the liposome bilayer surface such that induced stress were similar in both the cases. We also found that PDA emission from direct excitation mechanism was ∼2−10 times larger than that of the FRET-based response. These differences in emission signals were attributed to three major reasons: nonspecific interactions between E. coli and liposomes, size differences between analyte and liposomes, and a much higher PDA concentration with respect to sulforhodamine (SR-101). We have proposed a model to explain our experimental observations. Our fundamental studies reported here will help in enhancing our knowledge regarding interactions involved between soft particles at molecular levels.

Immunogenicity of antigen‐conjugated biodegradable polydiacetylene liposomes administered mucosally

“…With the preparation method described here, we synthesized highly reproducible LP-Ova (three batches). 26,27,37,38 Extensive dialysis of liposomes following conjugation reaction allowed for elimination of unconjugated Ova [ Fig. 2(A)] and for evaluation of immune responses to Ova-conjugated liposomes alone.…”

“…The liposomes used in this study were composed of three amphiphilic molecules: 10,12-pentacosadyinoic acid (PCDA), 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), and PCDA conjugated with N-hydroxysuccinimide (PCDA-NHS). 26,27 Incorporation of PCDA into lipid bilayers of liposomes provides physical and chemical stability and was shown to enhance the controlled released of encapsulated substances, 22,28 although the later property of PCDA liposomes was not exploited in this work. Due to the rigid structure formed by the ene-yne conjugation after polymerization of PCDA, the liposomes do not fuse with cell membranes and are able to maintain their structure in vivo (US Patent No.…”

Supramolecular core–glycoshell polythiophene nanodots for targeted imaging and photodynamic therapy

“…20 nm with respect to the P3HT dots alone, suggesting a change of the conjugated structure for the DCM upon binding to the polymer backbone. 30 The particle size of Gal-dot ( Fig. 2d) and Man-dot ( Fig.…”

Micro-motors: A motile bacteria based system for liposome cargo transport

“…Recently, synthetic small unilamellar vesicles (SUVs) were put to a great use for mimicking synaptic vesicles 5 . Furthermore, large and giant unilamellar vesicles (LUVs/GUVs) have been explored to mimic the cell membrane surface 20 21 22 . Combining liposome as a cargo system and natural machines as a carrier is an attractive option for building a better, biocompatible cargo system that could encapsulate drugs, genes or other desired molecules.…”

“…We intend to use a natural procedure that does not put extra strain on bacterial health and motility. Hence, we utilized the inherent property of bacteria by which it binds with gangliosides (glycolipids) 22 28 . Gangliosides naturally occur on the eukaryotic cells and have been strongly suggested to act as receptors for bacterial toxins (anchor for pathogen invasion) 28 .…”