Nucleic Acid-Binding Dyes as Versatile Photocatalysts for Atom-Transfer Radical Polymerization

Abstract

Nucleic acid-binding dyes (NuABDs) are fluorogenic probes that light up after binding to nucleic acids. Taking advantage of their fluorogenicity, NuABDs have been widely utilized in the fields of nanotechnology and biotechnology for diagnostic and analytical applications. We demonstrate the potential of NuABDs together with an appropriate nucleic acid scaffold as an intriguing photocatalyst for precisely controlled atom-transfer radical polymerization (ATRP). Additionally, we systematically investigated the thermodynamic and electrochemical properties of the dyes, providing insights into the mechanism that drives the photopolymerization. The versatility of the NuABD-based platform was also demonstrated through successful polymerizations using several NuABDs in conjunction with diverse nucleic acid scaffolds, such as G-quadruplex DNA or DNA nanoflowers. This study not only extends the horizons of controlled photopolymerization but also broadens opportunities for nucleic acid-based materials and technologies, including nucleic acid-polymer biohybrids and stimuli-responsive ATRP platforms.

Scheme 1. PhotoATRP Mediated by NuABDs as the Photocatalyst in the Presence of Nucleic Acids

Figure 1

Representative ¹H NMR spectra for the determination of monomer conversion. (A) Conversion of OEOMA₅₀₀ was determined by comparing areas of the monomer peak (blue circle, ca. 4.38 ppm) and polymer (red circle, ca. 4.22 ppm). (B) The conversion of NIPAM was determined by using DMF as the internal standard and monitoring the decrease in the area corresponding to a proton in NIPAM (blue circle, ca. 5.8 ppm). (C) The conversion of HEMA was determined by using DMF as the internal standard and monitoring the decrease in the area corresponding to a proton in HEMA (blue circle, ca. 6.25 ppm).

Figure 2

Analysis of polymerization kinetics using salmon DNA (0.1 mg/mL) and GelGreen (10×). (A) First-order kinetic plot of ATRP of OEOMA₅₀₀. (B) Evolution of molecular weight (M_n,abs) and dispersity with monomer conversion. (C) GPC traces at each time point. Polymerization results and reaction conditions are presented in Table S4.

Scheme 2. (A,B) Reductive Quenching vs Oxidative Quenching Cycle for (A) GelGreen; and (B) GelRed; And (C) Proposed Mechanism of photoATRP Using NuABD as the Photocatalyst

Note that Cl–Cu^IIL, instead of Br–Cu^IIL, is the dominant Cu(II) complex due to the presence of excess chloride anions in PBS solution.

Figure 3

PhotoATRP using DNA-based nanostructures. (A) Light emission from ThT in the presence of the G-quadruplex. (B) Monomer conversion after photoATRP using ThT in the presence of different DNA scaffolds. Inset: GPC trace after photoATRP using 45AG and ThT under blue light (λ = 450 nm, 5.8 mW cm^–2) for 45 min in PBS. The polymerization results are summarized in Table S6. (C) SEM image of the DNFs. Inset: higher magnification (35,000×) image of a DNF. (D) Digital camera image of the DNF pellet before and after staining. (E) GPC traces after photoATRP using DNFs. The polymerization results are summarized in Table S7.