Multiscale Live Imaging Using Förster Resonance Energy Transfer (FRET) for Evaluating the Biological Behavior of Nanoparticles as Drug Carriers

Development of a Compensated Förster Resonance Energy Transfer Imaging for Improved Assessment of the Intrapulmonary Distribution of Polymeric Nanoparticles

Inhalation-based drug delivery systems have gained attention as potential therapeutic options for various respiratory diseases. Among these systems, nanoparticles are being explored as drug carriers because of their ability to deliver therapeutic agents directly to the lungs. It is essential to accurately evaluate the intrapulmonary behavior of nanoparticles to optimize drug delivery and achieve selective targeting of lung lesions. Prior research used the Förster resonance energy transfer (FRET) phenomenon to study the in vivo behavior of nanoparticles as drug carriers. In this study, image reconstruction involving bleed-through compensation was used to quantitatively assess the behavior of FRET nanoparticles in the lungs. When the nanoparticles for FRET fluorescence imaging, which employed 1,1'-dioctadecyl-3,3,3',3'-tetramethylindodicarbocyanine, 4-chlorobenzenesulfonate salt (DiD) as the donor and as 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine iodide (DiR) the acceptor, were administered to mouse lungs, whole-body in vivo imaging could not compensate for the influence of respiration and heartbeat. However, ex vivo imaging of excised lungs enabled the quantitative evaluation of the time-concentration profiles and distribution of nanoparticles within the lungs. This imaging technique is particularly useful for the development of inhalable nanoparticles that specifically target the lesions and exhibit controlled-release capabilities within the lungs.

FRET as the tool for in vivo nanomedicine tracking

Advanced drug delivery system utilizing a nanocarrier is the major application of nanotechnology on pharmacotherapeutics. However, despite the promising benefits and a leading trend in pharmaceutical research, nanomedicine development suffers from a poor clinical translation problem as only a handful of nanomedicine products reach the market yearly. The conventional pharmacokinetic study generally focuses only on monitoring the level of a free drug but ignores the nanocarrier's role in pharmacokinetics. One hurdle is that it is difficult to directly track intact nanocarriers in vivo to explore their pharmacokinetics. Although several imaging techniques such as radiolabeling, nuclear imaging, fluorescence imaging, etc., have been developed over the past few years, currently, one method that can successfully track the intact nanocarriers in vivo directly is by Förster resonance energy transfer (FRET). This review summarizes the application of FRET as the in vivo nanoparticle tracker for studying the in vivo pharmacokinetics of the organic nanocarriers and gives elaborative details on the techniques utilized.

Understanding Förster Resonance Energy Transfer in the Sheet Regime with DNA Brick-Based Dye Networks

Controlling excitonic energy transfer at the molecular level is a key requirement for transitioning nanophotonics research to viable devices with the main inspiration coming from biological light-harvesting antennas that collect and direct light energy with near-unity efficiency using Förster resonance energy transfer (FRET). Among putative FRET processes, point-to-plane FRET between donors and acceptors arrayed in two-dimensional sheets is predicted to be particularly efficient with a theoretical 1/r⁴ energy transfer distance (r) dependency versus the 1/r⁶ dependency seen for a single donor-acceptor interaction. However, quantitative validation has been confounded by a lack of robust experimental approaches that can rigidly place dyes in the required nanoscale arrangements. To create such assemblies, we utilize a DNA brick scaffold, referred to as a DNA block, which incorporates up to five two-dimensional planes with each displaying from 1 to 12 copies of five different donor, acceptor, or intermediary relay dyes. Nanostructure characterization along with steady-state and time-resolved spectroscopic data were combined with molecular dynamics modeling and detailed numerical simulations to compare the energy transfer efficiencies observed in the experimental DNA block assemblies to theoretical expectations. Overall, we demonstrate clear signatures of sheet regime FRET, and from this we provide a better understanding of what is needed to realize the benefits of such energy transfer in artificial dye networks along with FRET-based sensing and imaging.

Measuring calibration factors by imaging a dish of cells expressing different tandem constructs plasmids

Three-cube Förster resonance energy transfer (FRET) method is the most extensively applied approach for live-cell FRET quantification. Reliable measurements of calibration factors are crucial for quantitative FRET measurement. We here proposed a modified TA-G method (termed as mTA-G) to simultaneously obtain the FRET-sensitized quenching transition factor (G) and extinction coefficients ratio (γ) between donor and acceptor. mTA-G method includes four steps: (1) predetermining the ratio ranges of the sensitized emission of acceptor (F_C ) to the donor excitation and donor channel image (I_DD [(DA])) for all FRET plasmids; (2) culturing the cells which express every FRET plasmid in one dish respectively; (3) distinguishing and marking the cells expressing different FRET plasmids by detecting their F_C /I_DD (DA) values; (4) linearly fitting F_C /I_AA (DA) (acceptor excitation and acceptor channel image) to I_DD (DA)/I_AA (DA) for different kinds of cells. We implemented mTA-G method by imaging tandem constructs cells with different FRET efficiency cultured in one dish on different days, and obtained consistent G and γ values. mTA-G method not only circumvents switchover of different culture dishes but also keep the constant imaging conditions, exhibiting excellent robustness, and thus will expands the biological applications of quantitative FRET analysis in living cells.