Reversible Fluorescence Switching of Spiropyran-Conjugated Biodegradable Nanoparticles for Super-Resolution Fluorescence Imaging

Abstract

We report on the reversible fluorescence switching of biodegradable nanoparticles of spiropyranterminated poly(ε-caprolactone) (SP-PCL) for superresolution fluorescence imaging. SP-PCL was synthesized via ring-opening polymerization using hydroxyl-containing SP derivative as the initiator. SP-PCL solution in THF or dioxane exhibits fast photochromism from colorless to blue upon UV irradiation due to the transformation of SPs in SP-PCL into merocyanines (MCs). Although both SP-PCL solution and MC-PCL solution do not fluoresce, SP-PCL nanoparticle dispersion fabricated via nanoprecipitation in aqueous media, in which SP molecules were embedded into the hydrophobic PCL matrix, displays considerable green emission at 530 nm at an excitation wavelength of 420 nm. Upon <420 nm irradiation, the resulting MC-PCL nanoparticles show strong red emission at 650 nm when excited at 420 nm. SP-PCL nanoparticles display green−red dual-color intrinsic fluorescence switching upon alternated UV/vis illumination. Green emission from SP in SP-PCL nanoparticles is observed before UV irradiation while red emission from MCs in MC-PCL nanoparticles after UV irradiation. For both SP-PCL and MC-PCL nanoparticles, the critical excitation wavelength is determined at 420 nm, at which the photoinduced interconversion of MC-and SP-forms are found to be at equilibrium. Positive and inverse photoisomerizations monitored using time-dependent fluorescence spectra show that blue light excitation above 420 nm yields green emission of SPs in SP-PCL nanoparticles while light irradiation below 420 nm imparts photoisomerization (SP to MC) and thus red emission of MCs in MC-PCL nanoparticles. Green and red fluorescence can be optically switched and imaged under fluorescent microscopy. Biodegradable SP-PCL nanoparticles are demonstrated to be promising photoswitchable fluorophores for localization-based super-resolution microscopy, evidencing by resolving nanostructures with sub-50 nm resolution in poly(vinyl alcohol) (PVA) film and live cells.

Photo‐switchable spiropyran immobilized polystyrene beads using catechol chemistry

“…Prominent changes in fluorescence intensity were observed around 575–750 nm, indicating an increase in intensity following UV light irradiation and a decrease in intensity following visible light irradiation. Thus, the U V /Vis photoreversible characteristics of SP were also confirmed using fluorescence spectra …”

“…The photochromic material spiropyran possesses outstanding physical and chemical properties and therefore has been investigated for application in a wide range of fields, including chemical sensors, controlled release, data storage, photo‐controllable wettability, light switching applications, and mechanical sensors . Spiropyran can exist in two different forms, namely the ring‐closed colorless spiropyran (SP) and the ring‐open colored merocyanine (MC) form.…”

Ultraviolet–visible/fluorescence behaviors of a spiropyran/polydimethylsiloxane composite film under acid vapors

“…Herein, 425 nm was chosen as the excitation λ because the structural transformation of SP and MC was the least under this light . Under 425 nm light, the SP–PDMS composite film showed a moderate SP emission peak at 530 nm . As irradiated with 365 nm UV, the formed MC in the composite film gave a red emission peak at 640 nm.…”

FRET Phenomenon in Photoreversible Dual-Color Fluorescent Polymeric Nanoparticles Based on Azocarbazole/Spiropyran Derivatives

“…25,26,32 In recent years, materials with optically modulated properties, like fluorescence resonance energy transfer, have attracted much attention as a result of some advantages over conventional fluorescence dyes in broad range of scientific fields including biological diagnosis, cell labeling, imaging, and sensing tools. 23,33 Photoswitchable dual-color fluorescents are appropriate candidates especially due to their ability to distinguish fake signals made by adventitious fluorescent biomolecules from original ones. 34−36 Zhu and co-workers 37 integrated photoswitchable spyropiran and fluorescent perylene diimide dyes via covalently linkage into a polymeric nanoparticle to generate an optically addressable dual-color fluorescent system by means of emulsion polymerization.…”