Non-Conventional Fluorescence and Cytotoxicity of Two Aliphatic Hyperbranched Polymer Dots Having Poly(amic acid) Structures: Implications for Labeling Nanodrug Carriers

Abstract

In this study, we used one-pot A 2 + B 3 polymerizations to synthesize two aliphatic + alicyclic polymer dots (PDs) having non-conjugated hyperbranched structures, employing two types of dianhydrides as the A 2 components, possessing bridged bicyclic alkene (PD-BT) and non-alkene (PD-ET) units, and Jeffamine T403 polyetheramine (T403) as the B 3 components. We prepared PD-ET from commercially available ethylenediaminetetraacetic dianhydride (EDTAD, A 2 ) and T403 (B 3 ) and PD-BT from bicyclo[2.2.2]oct-7-ene-2,3,5,6-tetracarboxylic dianhydride (BCDA, A 2 ) and T403 (B 3 ). These two types of PDs possessed non-conjugated hyperbranched poly(amic acid) structures with terminal amino functional groups. PD-BT and PD-ET exhibited non-conventional fluorescence with emissions at 435 and 438 nm, respectively, and quantum yields of 12.8 and 14.0%, respectively. The fluorescence intensity of PD-ET was influenced by the pH, but PD-BT was less affected because of its rigid aliphatic bridged bicyclic structure. In aqueous solutions, the sizes of the PD-BT and PD-ET nanoparticles were 3−5 nm, and their net charges can be adjusted by varying the pH. These PDs were non-cytotoxic toward human MCF-7 breast cancer cells and human keratinocyte HaCaT cells at concentrations of 50 μg mL −1 for PD-BT and 500 μg mL −1 for PD-ET. Confocal microscopic bioimaging revealed that the PDs were located within the cells after treatment for 6 h. These PDs were easy to prepare, highly water-soluble, and possessed a large number of peripheral functional groups for further modification. Combined with their non-conventional fluorescence, they appear to have potential uses in bioimaging and as druglabeling carriers.

Nonconventional Fluorescent Hyperbranched Polymer Dots as Skin Nanocarriers Constructed from an Olefinic Aliphatic AB2-Type Monomer

“…Here, the excitation wavelength of the π-HBP solution was selected to provide a relatively high emission. The QY was calculated from the absorbance and integrated fluorescence spectra according to the equation for the relative fluorescence QY: 25,38…”

“…Our NCPDs displayed stable fluorescence and formed nanoscale particles in aqueous solutions. 25 In this present study, we constructed a π-AB 2 monomer featuring a π-bond and used it to synthesize a hyperbranched poly(amido acid) backbone (π-HBP), the surface of which presented a large number of carboxyl groups. Our π-HBP possessed tertiary amino groups that behaved as fluorescent centers and underwent CIE of the C�O groups within the dendritic structures.…”

“…Nonconventional photoluminescence (PL) processes with nonphotobleaching and nonphotoquenching can be powerful tools for in vitro and in vivo fluorescence observations. 19,20 We have previously built nonconventional HBPs with wholly aliphatic structures through AB 2 -type 31 and A 2 +B 3 -type 25 approaches, displaying blue light emissions at 395 and 438 nm; nevertheless, such blue PL has limited application for light penetration through animal tissue but could be enhanced deeply in the red region wavelength. 32−35 In this present study, to further shift the nonconventional PL toward the red end of the spectrum, we constructed π-HBP, an olefinic aliphatic π-AB 2 -type structure with internal alkene units to provide a relatively rigid molecular structure; it displayed red-shifting of its PL emission relative to that of the AB 2 -type HBP 31 without internal alkene units.…”

“…The nonconventional fluorescence observed with nonconjugated moieties can lead to strong fluorescence emissions with excellent photostability because of resistance to photobleaching and nonquenching effects. , Furthermore, nonconjugated HBP nanomaterials featuring multiple hydrogen-bonding interactions can have chemical structures similar to those of biopolymers, with excellent water solubility, chain flexibility, and structural tunability as well as the potential for facile one-pot preparation, environmental friendliness, and use in biological fluorescence imaging. − Nonconventional fluorescent polymers have been applied in various applications, including the detection of metal ions, bioimaging, and nanodrug formulation. − Yan et al synthesized a multicolor emissive hyperbranched polysiloxane (HBPSi) that they applied to detect metal ions and use as a nanocarrier; it exhibited multicolor fluorescence because of CIE and its cluster size . Interestingly, Yang et al used thiolactone chemistry to synthesize aliphatic polyamides (PAs) that could produce strong fluorescence as a result of polymerization-induced emissions (PIEs); these aliphatic PAs were applied to organelle-specific imaging.…”

“…In a previous study, we prepared two types of nonconventional fluorescent HBPs through an A 2 +B 3 strategy; we named them nonconjugated polymer dots (NCPDs), and they were a type of subluminophore-containing and cross-linked polymer. Our NCPDs displayed stable fluorescence and formed nanoscale particles in aqueous solutions . In this present study, we constructed a π-AB 2 monomer featuring a π-bond and used it to synthesize a hyperbranched poly­(amido acid) backbone (π-HBP), the surface of which presented a large number of carboxyl groups.…”