Determination of the Wall Thickness of Block Copolymer Vesicles by Fluorescence Lifetime Imaging Microscopy

Abstract

This study reports on the characterization of reporter dye‐loaded block copolymer vesicles (polymersomes) of PS115‐b‐PAA15 (polystyrene‐block‐poly(acrylic acid)) and PEG114‐b‐PLA167 (poly(ethylene glycol)‐block‐poly(lactic acid)) and their drying behavior by fluorescence lifetime imaging microscopy (FLIM). The characteristic changes of the fluorescence decay components of the dye calcein incorporated in the three different local nanoenvironments, namely, the solvated dye, dye associated with the vesicle wall, and dried agglomerated dye, are observed by FLIM during the drying of vesicles. The amplitude ratio R1/2 of the components attributed to the solvated dye in the vesicle interior with a lifetime τ1 ≈ 3.9 ns to the one attributed to calcein associated with the wall with a lifetime τ2 ≈ 1.5 ns is found to decrease exponentially with drying time. The time constants, which are found to depend linearly on the radius of the vesicle, yield by extrapolation to zero vesicle diameter an estimate of the polymersome wall thickness. For PS115‐b‐PAA15 and PEG114‐b‐PLA167 vesicle wall thicknesses r0 of 16 ± 5 nm and 28 ± 4 nm, respectively, are observed, which are in favorable agreement with transmission electron and atomic force microscopy data.

Probing of local polarity in poly(methyl methacrylate) with the charge transfer transition in Nile red

“…Prominent examples are the properties of substrate-supported ultrathin polymer films, in which the values of the glass transition temperature ( T g ) and segmental mobilities were found to be altered. Likewise, this holds for transport properties, including polymer nanocapsule membrane permeability [1], enzyme-triggered bacterial sensors [2–5] and intelligent self-controlled drug delivery systems [4,6–10], as well as dynamics of polymers at interfaces [11].…”

“…To be able to understand local properties of polymers, in particular in nanoenvironments of polymeric vesicles (polymersomes), comprising a hydrophilic corona and a hydrophobic wall [1,12], or in substrate-supported ultrathin films [13], the analysis of the photophysical properties of tracer dye molecules was found to be beneficial. In time-resolved fluorescence measurements and dye diffusion studies, the nanoenvironments in polymersomes could be assigned [1,12], solute transport be characterized [1] and segment mobilities inferred [13], respectively. For other purposes the oxazine tracer dye Nile red (NR, Fig.…”

Giant Biodegradable Poly(ethylene glycol)‐block‐Poly(ε‐caprolactone) Polymersomes by Electroformation

“…We have shown previously that the fluorescence lifetime τ of reporter dyes affords a handle to analyze the local environment of dyes in nanoassemblies of polymers, at interfaces and func tional films. [39][40][41] The characteristic fluorescence lifetimes of dyes can be analyzed by recording decay curves after a short excitation pulse or, e.g., by timecorrelated singlephoton counting (TCSPC). The exponential decay curves depend strongly on the local properties, such as hydrogen bonding, but also rigidity, dielectric constant or viscosity, near the dye molecules.…”

“…In general, fitting of the decay data with a series of exponential terms yields the characteristic life times and contributions (weights) of those to the decay. [39][40][41] First, the exponential decay of calcein in water (concentration 10 × 10 −6 m) was investigated by using a liquid cell and setting the confocal focus into the bulk solution. The result shows a mono exponential decay with a lifetime τ 1 of 3.9 ns, which is in agreement with the literature.…”

Recent advances in hybrid measurement methods based on atomic force microscopy and surface sensitive measurement techniques

“…143,144 Although FLIM is typically featured in biological studies, it also nds application in polymer science and surface analysis. 109,145 A combination of FLIM with AFM potentially yields information of biological processes occurring inside cells, which would not be possible without FLIM.…”