Selective uptake and modulation of nanometal surface energy transfer from quantum dot to Au nanoparticle across lipid bilayer of liposomes

Abstract

Understanding the initial adsorption and subsequent translocation of nanoparticles (NPs) across the phospholipid bilayer of liposome find importance in drug delivery and in vivo bio-imaging applications. Herein, we have investigated the time-dependent selective uptake of 2.0 ± 0.3 nm-sized CdTe quantum dots (QDs) into small unilamellar vesicles (SUV) of dipalmitoylphoshatidylcholine (DPPC) in its gel phase and subsequent alteration of nanometal surface energy transfer (NSET) in the presence of 18.0 ± 0.2 nm-sized citrate-capped gold NPs (Au NPs). The interactions between CdTe QD and Au NP across the lipid bilayer of DPPC liposome has been explored by monitoring the NSET process using fluorescence spectroscopy. The time-dependent selective partitioning of QDs into the liposomal phase has been demonstrated using confocal laser scanning microscopy (CLSM) and atomic force microscopy (AFM). It has been observed that instant mixing of QDs and Au NPs with liposomes does not alter the extent of NSET between QD-Au NP pair relative to that in the absence of liposome. However, equilibrating the binary mixture of liposome and QDs for 24 h at room temperature leads to the formation of liposome encapsulated QD (LipQD) which does not take part in NSET with aqueous phase Au NPs. In contrast, equilibrating the ternary mixture of QDs, liposomes, and Au NPs for 24 h results in the formation of Au NP adsorbed QD-encapsulated liposomes (AuLipQD) which exhibit moderate amount of NSET from encapsulated QDs to the adsorbed Au NPs at the surface of liposomes. It has been observed that the efficiency of NSET decreases from 62% in bulk aqueous medium to 24% in AuLipQD complex. Our present findings may be useful to understand the fundamental interaction of other metal and semiconductor NPs with liposomes and cell membrane for various drug-delivery and bio-imaging applications.