Nucleic acid-functionalized polyacrylamide chains that are cooperatively cross-linked by i-motif and nucleic acid duplex units yield, at pH 5.0, DNA hydrogels exhibiting shape-memory properties. Separation of the i-motif units at pH 8.0 dissolves the hydrogel into a quasi-liquid phase. The residual duplex units provide, however, a memory code in the quasi-liquid allowing the regeneration of the hydrogel shape at pH 5.0.
Hydrogels are of great interest as a class of materials for tissue engineering, axonal regeneration, and controlled drug delivery, as they offer 3D interwoven scaffolds to support the growth of cells. Herein, we extend the family of the aromatic Fmoc-dipeptides with a library of new Fmoc-peptides, which include natural and synthetic amino acids with an aromatic nature. We describe the self-assembly of these Fmoc-peptides into various structures and characterize their distinctive molecular and physical properties. Moreover, we describe the fabrication of the bioactive RGD sequence into a hydrogel. This unique material offers new opportunities for developing cell-adhesive biomedical hydrogel scaffolds, as well as for establishing strategies to modify surfaces with bioactive materials.
A systematic study of the amplified optical detection of DNA by Mg(2+)-dependent DNAzyme subunits is described. The use of two DNAzyme subunits and the respective fluorophore/quencher-modified substrate allows the detection of the target DNA with a sensitivity corresponding to 1 × 10(-9) M. The use of two functional hairpin structures that include the DNAzyme subunits in a caged, inactive configuration leads, in the presence of the target DNA, to the opening of one of the hairpins and to the activation of an autonomous cross-opening process of the two hairpins, which affords polymer DNA wires consisting of the Mg(2+)-dependent DNAzyme subunits. This amplification paradigm leads to the analysis of the target DNA with a sensitivity corresponding to 1 × 10(-14) M. The amplification mixture composed of the two hairpins can be implemented as a versatile sensing platform for analyzing any gene in the presence of the appropriate hairpin probe. This is exemplified with the detection of the BRCA1 oncogene.
An enzyme-free amplified detection platform is described using the horseradish peroxidase (HRP)-mimicking DNAzyme as an amplifying label. Two hairpin structures that include three-fourths and one-fourth of the HRP-mimicking DNAzyme in caged, inactive configurations are used as functional elements for the amplified detection of the target DNA. In the presence of the analyte DNA, one of the hairpins is opened, and this triggers the autonomous cross-opening of the two hairpins using the strand displacement principle. This leads to the formation of nanowires consisting of the HRP-mimicking DNAzyme. The resulting DNA nanowires act as catalytic labels for the colorimetric or chemiluminescent readout of the sensing processes (the term "enzyme-free" refers to a protein-free catalyst). The analytical platform allows the sensing of the analyte DNA with a detection limit corresponding to 1 × 10(-13) M. The optimized system acts as a versatile sensing platform, and by coaddition of a "helper" hairpin structure any DNA sequence may be analyzed by the system. This is exemplified with the detection of the BRCA1 oncogene with a detection limit of 1 × 10(-13) M.
Copolymer chains consisting of acrylamide units and guanine (G)-containing oligonucleotide-tethered acrylamide units undergo, in the presence of K(+) ions, cross-linking by G-quadruplexes to yield a hydrogel. The hydrogel is dissociated upon addition of 18-crown-6 ether that traps the K(+) ions. Reversible formation and dissociation of the hydrogel is demonstrated by the cyclic addition of K(+) ions and 18-crown-6 ether, respectively. Formation of the hydrogel in the presence of hemin results in a hemin/G-quadruplex-cross-linked catalytic hydrogel mimicking the function of horseradish peroxidase, reflected by the catalyzed oxidation of 2,2'-azinobis-(3-ethylbenzthiazoline-6-sulfonic acid), ABTS(2-), by H2O2 to ABTS(·-) and by the catalyzed generation of chemiluminescence in the presence of luminol/H2O2. Cyclic "ON" and "OFF" activation of the catalytic functions of the hydrogel are demonstrated upon the formation of the hydrogel in the presence of K(+) ions and its dissociation by 18-crown-6 ether, respectively. The hydrogel is characterized by rheology measurements, circular dichroism, and probing its chemical and photophysical properties.
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