An Enhanced Strip Biosensor for Rapid and Sensitive Detection of Histone Methylation

Histone methylation is a crucial epigenetic modification of chromosomes. In this work, we describe an enhanced strip biosensor using oligonucleotide-functionalized gold nanoparticles as an enhancer probe (AuNP-DNA) for rapid and sensitive detection of histone methylation. In conventional strip biosensor, methylated histone is captured on the test zone through the formation of antibody/methylated histone/antibody-labeled AuNP sandwich structures. Whereas, in the enhanced strip biosensor, the AuNPs in the sandwich structures are dual labeled with an antibody and another oligonucleotide (c-DNA). The sequence of the c-DNA is complementary to the oligonucleotide on the enhancer probe. The enhancer probe, AuNP-DNA, hybridizes with the c-DNA on the dual labeled AuNPs, and the color intensity of the red band on the test zone is then enhanced dramatically. The enhanced strip biosensor has been used for the visual detection of trimethylated lysine 9 of histone H3 (H3K9me3) in 20 ng of histone extract from HeLa cells within 15 min. The detection limit is 10-fold and 15-fold lower than the conventional strip biosensor and Western blot, respectively

Colorimetric Detection of Copper(II) Ion Using Click Chemistry and Hemin/G-Quadruplex Horseradish Peroxidase-Mimicking DNAzyme

G-quadruplex-forming sequence can be formed through a copper­(I) ion (Cu⁺)-catalyzed click chemistry between azide- and alkyne-modified short G-rich sequences in aqueous solution, eliminating immobilization and washing steps of conventional assays. The source for Cu⁺ was generated from the reduction of Cu²⁺ with the reductant of sodium ascorbate. In the presence of hemin and K⁺, the self-assembly of hemin/G-quadruplex structure has the activity of horseradish peroxidase (HRP), which can catalyze its colorless substrate tetrazmethyl benzidine (TMB) into a colored product. Hence, the concentration of Cu²⁺ can be evaluated visually for qualitative analysis according to the color change of the solution, and the optical density (OD) value of the resulting solution at 450 nm was also recorded using a microplate reader for quantitative analysis