Conjugation polymer nanobelts: a novel fluorescent sensing platform for nucleic acid detection

Abstract

In this article, we report on the facile and rapid synthesis of conjugation polymer poly(p-phenylenediamine) nanobelts (PNs) via room temperature chemical oxidation polymerization of p-phenylenediamine monomers by ammonium persulfate in aqueous medium. We further demonstrate the proof-of-concept that PNs can be used as an effective fluorescent sensing platform for nucleic acid detection for the first time. The general concept used in this approach lies in the facts that the adsorption of the fluorescently labeled single-stranded DNA probe by PN leads to substantial fluorescence quenching, followed by specific hybridization with the complementary region of the target DNA sequence. This results in desorption of the hybridized complex from PN surface and subsequent recovery of fluorescence. We also show that the sensing platform described herein can be used for multiplexing detection of nucleic acid sequences.

Scheme 1.

A schematic diagram (not to scale) to illustrate the fluorescence-enhanced nucleic acid detection using PPPD nanobelt as a sensing platform.

Figure 1.

Low magnification SEM (a) and TEM (c) images of the products thus formed. (b and d) Indicates the corresponding high magnification images.

Figure 2.

Fluorescence emission spectra of P_HIV (50 nM) at different conditions: (a) P_HIV; (b) P_HIV + 300 nM T₁; (c) P_HIV + PN; (d) P_HIV + PN + 300 nM T₁. Curve e is the emission spectra of PN. Inset: linear relationship between F/F₀−1 (where F₀ and F are the fluorescence intensity without and with the presence of T₁, respectively) and T₁ concentration ranging from 30 to 300 nm. Excitation was at 480 nm, and the emission was monitored at 522 nm. All measurements were done in Tris–HCl buffer in the presence of 5 mM Mg²⁺ (pH: 7.4).

Figure 3.

(a) Fluorescence quenching of P_HIV (50 nM) by PN and (b) fluorescence recovery of P_HIV–PN by T₁ (300 nM) as a function of incubation time. Excitation was at 480 nm, and the emission was monitored at 522 nm. All measurements were done in Tris–HCl buffer in the presence of 5 mM Mg²⁺ (pH: 7.4).

Figure 4.

(a) Fluorescence emission spectra of P_HIV (50 nM) at different conditions: (a) P_HIV–PN complex; (b) P_HIV–PN complex + 300 nM T₁; (c) P_HIV–PN complex + 300 nM T₂; (d) P_HIV–PN complex + 300 nM T₃. Inset: fluorescence intensity histograms with error bar. (b) Fluorescence signal enhancement of P_HIV–PN complex upon incubation with T₁ and T₂ at 25 and 50°C, respectively. Excitation was at 480 nm, and the emission was monitored at 522 nm. All measurements were done in Tris–HCl buffer in the presence of 5 mM Mg²⁺ (pH: 7.4).

Figure 5.

(a) Fluorescence emission spectra of P_s (50 nM) at different conditions: (a) P_s–PN complex; (b) P_s–PN complex + 300 nM T_s1; (c) P_s–PN complex + 300 nM T_s2; (d) P_s–PN complex + 300 nM T_s3. Inset: fluorescence intensity histograms with error bar.

Figure 6.

Fluorescence intensity histograms of the probe mixture toward different target combinations in the presence of PN under excitation/emission wavelengths of 480/522, 587/606 and 643/665 nm/nm. All measurements were done in Tris–HCl buffer in the presence of 5 mM Mg²⁺ (pH: 7.4).