Electrostatically Directed Visual Fluorescence Response of DNA-Functionalized Monolithic Hydrogels for Highly Sensitive Hg²⁺ Detection

Abstract

Hydrogels are crosslinked hydrophilic polymer networks with low optical background and high loading capacity for immobilization of biomolecules. Importantly, the property of hydrogel can be precisely controlled by changing the monomer composition. This feature, however, has not been investigated in the rational design of hydrogel-based optical sensors. We herein explore electrostatic interactions between an immobilized mercury binding DNA, a DNA staining dye (SYBR Green I), and the hydrogel backbone. A thymine-rich DNA was covalently functionalized within monolithic hydrogels containing a positive, neutral, or negative backbone. These hydrogels can be used as sensors for mercury detection since the DNA can selectively bind Hg 2+ between thymine bases inducing a hairpin structure. SYBR Green I can This document is the Accepted Manuscript version of a Published Work that appeared in final form in Applied Materials and Interfaces, copyright © American Chemical Society after peer review and technical editing by publisher. To access the final edited and published work see http://dx.doi.org/10.1021/am101068c2 then bind to the hairpin to emit green fluorescence. For the neutral or negatively charged gels, addition of the dye in the absence of Hg 2+ resulted in intense yellow background fluorescence, which was attributed to SYBR Green I binding to the unfolded DNA. We found that by introducing 20% positively charged allylamine monomer, the background fluorescence was significantly reduced. This was attributed to the repulsion between positively charged SYBR Green I by the gel matrix as well as the strong binding between the DNA and the gel backbone. The signal-to-background ratio and detection limit was respectively improved by six and nine-fold using the cationic gel instead of neutral polyacrylamide gel.This study helps understand the electrostatic interaction within hydrogels, showing that hydrogels can not only serve as a high capacity matrix for sensor immobilization, but can also actively influence the interaction between involved molecules.

Aptamer-Functionalized Hydrogel Microparticles for Fast Visual Detection of Mercury(II) and Adenosine

“…11,12 Hydrogels are particularly attractive for making optical sensors. [13][14][15][16][17][18][19] Biomolecular immobilization occurs not only on gel surface but also throughout the whole gel matrix, allowing for high loading capacity. Due to its porous nature, all the immobilized probes are accessible to generate a strong signal.…”

Metal‐Induced Specific and Nonspecific Oligonucleotide Folding Studied by FRET and Related Biophysical and Bioanalytical Implications

“…For example, DNA binding dyes such as SYBR Green I (SG) have also been used to design Hg II sensors. [28,30,44,45] Hg II induced DNA hairpin formation, upon which SG can bind to increase its fluorescence ( Figure 7A). Fluorescence spectra of the sensor in the absence and presence of Hg II are shown in Figure 7B and the increase of the fluorescence intensity can be observed.…”

Oligonucleotide-functionalized hydrogels as stimuli responsive materials and biosensors

“…Based on the Hg 2+ sensing hydrogel described above, we prepared also cationic gels containing allylamine and anionic gels containing 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS, see Figure 8A for structure). 99 Interestingly, the AMPS gel showed a similar yellow-to-green fluorescence change upon Hg 2+ addition, but the cationic gel showed significantly reduced background fluorescence in the absence of Hg 2+ ( Figure 8B). SG can bind to ds-DNA through strong intercalation and minor groove binding but to ss-DNA through weak electrostatic interactions.…”