FRET Imaging Approaches for in Vitro and in Vivo Characterization of Synthetic Lipid Nanoparticles

Abstract

DiI and DiD, two fluorophores able to interact by FRET (Förster resonance energy transfer), were coencapsulated in the core of lipid nanocapsules (LNCs) and nanoemulsions (LNEs), lipophilic reservoirs for the delivery of drugs. The ability of FRET imaging to provide information on the kinetics of dissociation of the nanoparticles in the presence of bovine serum albumin (BSA) or whole serum, or after incubation with cancer cells, and after systemic administration in tumor-bearing mice, was studied. Both microscopic and macroscopic imaging was performed to determine the behavior of the nanostructures in a biological environment. When 2 mg/mL FRET LNEs or LNCs were dispersed in buffer, in the presence of unloaded nanoparticles, BSA, or in whole serum, the presence of serum was the most active in destroying the particles. This occurred immediately with a diminution of 20% of FRET, then slowly, ending up with still 30% intact nanoparticles at 24 h. LNCs were internalized rapidly in cultured cells with the FRET signal decreasing within the first minutes of incubation, and then a plateau was reached and LNCs remained intact during 3 h. In contrast, LNEs were poorly internalized and were rapidly dissociated after internalization. Following their iv injection, LNCs appeared very stable in subcutaneous tumors implanted in mice. Intact particles were found using microscopic FRET determination on tumor sections 24 h after injection, that correlated well with the 8% calculated noninvasively on live animals. FRET investigations showed the potential to determine valid and reliable information about in vitro and in vivo behavior of nanoparticles.

Time‐Controllable Lipophilic‐Drug Release System Designed by Loading Lipid Nanoparticles into Polysaccharide Hydrogels

“…The DLS data suggested partial destabilization of LNPs when released from the gels with possible formation of micelles and aggregates. We previously determined that such lipid nanoparticles were stable in solutions for concentrations above 2–5 mg mL −1 of lipids but destabilized in the long term (24 h and more) in more diluted conditions …”

Quantum dot/methylene blue FRET mediated NIR fluorescent nanomicelles with large Stokes shift for bioimaging

“…FRET pair 35 encapsulated nanomicelles, as a promising fluorescent contrast nanoprobe, are expected to overcome those above pivotal drawbacks, making them higher qualified contrast agents for bioimaging. 18 22 In our previous work, RuBpy and methylene blue FRET pair encapsulated fluorescent silica nanoparticles was developed as large Stokes shifting nanoprobe for in vivo NIR 45 small animal imaging. 16 It is well known that semiconductor quantum dots (QDs) have unique photophysical properties of continuous absorption spectra, narrow and tunable emission, and high photostability, and have attracted widespread attentions in the fields of bioimaging, and especially, QDs can afford as an 50 efficient donor in the developing of FRET nanoprobes.…”

Visualization photofragmentation‐induced rhodamine B release from gold nanorod delivery system by combination two‐photon luminescence imaging with correlation spectroscopy

“…Fluorescence correlation spectroscopy (FCS), an ultrasensitive and noninvasive single‐molecule detection technique, is widely applied in biological and biophysical research, particularly in cell membrane and inside the cells . Compared with the previous methods for quantifying drug release, FCS is more suitable for quantified study the non‐invasive drug release in situ or in highly hydrophobic drugs that are poorly soluble in water . Based on the fluorescence fluctuation of the nanodelivery system generated by diffusion and chemical reaction in the laser focus volume, FCS can easily disclose the brightness, concentration and diffusion behavior of nanodelivery system during the laser irradiation .…”