Controlling Bulk Optical Properties of Emissive Polymersomes through Intramembranous Polymer−Fluorophore Interactions

Abstract

Interdisciplinary investigation at the interface of chemistry, engineering, and medicine has enabled the development of self-assembled nanomaterials with novel biochemical and electro-optical properties. We have recently shown that emissive polymersomes, polymer vesicles incorporating porphyrin-based fluorophores, feature large integrated-emission oscillator strengths and narrow emission bands; these nanoscale assemblies can be further engineered to fluoresce at discrete wavelengths throughout the visible and near-infrared (NIR) spectral domains. As such, emissive polymersomes effectively define an organic-based family of soft-matter quantum-dot analogs that possess not only impressive optical properties, but also tunable physical and biomaterial characteristics relative to inorganic fluorescent nanoparticles.Here, we expand upon our initial studies on poly(ethyleneoxide)-block-poly(butadiene)-based vesicles to examine fluorophore membrane-loading in other polymersome systems. Through modulation of fluorophore ancilliary group substituents and choice of polymer chain chemistries, we are able to predictably control intramembranous polymer-fluorophore interactions; these phenomena, in turn, influence the nature of fluorophore solvation, local dielectric environment, and emission quantum yield within emissive polymersome assemblies. By utilizing different classes of vesiclegenerating diblock copolymers, including bioresorbable poly(ethyleneoxide)-block-poly(ε-caprolactone) (PEO-b-PCL) and poly(ethyleneoxide)-block-poly(γ-methyl-ε-caprolactone) (PEO-b-PMCL), we ascertain general principles important for engineering nanoscale optical vesicles. Further, this work heralds the first generation of fully-biodegradable fluorescent nanoparticles suitable for deep-tissue in vivo imaging.

Sensing membrane stress with near IR-emissive porphyrins

“…1C). These spectral red-shifts of PZn n fluorophores as a function of increasing polymersome membrane concentration have previously been shown to derive from increasingly narrower PZn-PZn torsional angle distributions centered about an increasingly diminished mean macrocycle-macrocycle torsional angle (13)(14)(15). Although membrane volumes remain constant, the available volume for fluorophore dispersion can change.…”

“…The structural and spectroscopic properties of a wide variety of PZn n -based emissive polymersomes have been reported (11)(12)(13)(14)(15). These studies, for example, correlated the observed emissive properties with PZn n concentration and structure, as a function of the nature of fluorophore spatial confinement within the polymer membrane (14).…”

“…It was shown that incorporating PZn n fluorophores into polymersomes at concentrations up to 10 mol % does not compromise the mechanical stability (critical aerial strain, polymer chain packing, and interfacial aqueous/membrane phenomena) of the vesicle assemblies (12). Because these studies characterize: (i) how PZn n structure and concentration impacts emission wavelength, emission intensity, and energy-transfer dynamics within membrane environments (14,15), (ii) how the nature of the membrane-forming polymer impacts PZn n emissive properties (13), (iii) how PZn n structural characteristics and concentration impact membrane mechanical stability (12), and (iv) how fluorophore structure dictates PZn n spatial distribution within a membrane (14), these emissive moieties define ideal probes of physical changes to membrane environments.…”

Polymersomes: A new multi-functional tool for cancer diagnosis and therapy

“…Because light scattering decreases with increasing wavelength, and hemoglobin and water absorption spectra have their nadir in the near infrared (NIR) spectral region, much work has been focused on developing NIR contrast agents for in vivo imaging studies [9]. To this end, Ghoroghchian et al have successfully loaded porphyrinbased near infrared fluorophores (NIRFs) into the hydrophobic bilayer membranes of PEO-b-PBD [9,10,53,54], PEO-b-PCL [54], PEO-b-PEE [54], and poly(ethylene oxide)-block-poly (methylcaprolactone) (PEO-bPmCL) [54] polymersomes.…”

One- and two-photon absorption of highly conjugated multiporphyrin systems in the two-photon Soret transition region

“…3 Of the many candidate materials for these applications, porphyrins are among the most highly polarizable organic molecules reported to date, and because of their enhanced nonlinear susceptibilities, 4-9 they are promising molecules for optical limiters, [10][11][12][13][14] for photodynamic therapy, 15 and as contrast agents for in vivo imaging and microscopy. [16][17][18][19] Highly conjugated multiporphyrin chromophores possess large third-order nonlinear susceptibilities, ͑3͒ . 6,20 The imaginary part of ͑3͒ is responsible for the process of twophoton absorption, and recent studies have reported enormous TPA cross sections ͑i.e., up to ϳ10 4 GM͒ in conjugated, meso-to-meso ethyne-and butadiyne-bridged ͑porphinato͒zinc͑II͒ ͑PZn͒ dimers and related structures that feature ethyne-arene-ethyne PZn-PZn linkages.…”