Chenchen Ge

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 Cu(2+) 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 Cu(2+) 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.

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.

An enzyme-free and label-free assay for copper(II) ion detection based on self-assembled DNA concatamers and Sybr Green I

An enzyme-free and label-free fluorescence turn on biosensor for amplified copper(II) ion (Cu(2+)) detection has been constructed based on self-assembled DNA concatamers and Sybr Green I. This assay is simple, inexpensive and sensitive, enabling quantitative detection of as low as 12.8 pM Cu(2+).

A lateral flow biosensor for rapid detection of DNA-binding protein c-jun.

A lateral flow biosensor based on an immuno-chromatographic assay has been developed for the detection of DNA-binding proteins. The biosensor is composed of four parts: a sample pad, a conjugate pad, a strip of nitrocellulose membrane and an absorbent pad. A DNA probe containing a specific protein binding consensus sequence is coated onto gold nanoparticles, while an antibody against the DNA-binding protein is immobilized onto a test zone of the nitrocellulose membrane. The target protein binds to the protein binding DNA sequence that is coated on the gold nanoparticles to form nanoparticle-DNA-protein complexes, and the complexes are then captured by the antibody immobilized on the test zone to form a red line for visual detection of the target protein. This biosensor was successfully applied to a DNA-binding protein, c-jun, and the developed biosensor allows for the rapid detection of down to 0.2 footprint unit of c-jun protein within 10 min. This biosensor was verified using HeLa cells and it visually detected c-jun activity in 100 μg of crude cell lysate protein. The antibody against c-jun used in the biosensor can distinguish c-jun from other nonspecific proteins, with high specificity.

An autonomous T-rich DNA machine based lateral flow biosensor for amplified visual detection of mercury ions

An autonomous thymine rich DNA machine as an amplification unit was developed for the sensitive detection of mercury ions with high specificity. Combined with a lateral flow biosensor, the amplified signal of Hg2+ can be read out by the naked eye with a detection limit of 5 nM.

A simple lateral flow biosensor for the rapid detection of copper(II) ions based on click chemistry

Copper(II) ions (Cu2+) at a high concentration are harmful to human health. Herein a simple and enzyme-free lateral flow biosensor for the rapid detection of Cu2+ based on copper(I) ion (Cu+)-catalyzed click chemistry has been constructed for the first time. In the presence of sodium ascorbate, Cu2+ was reduced to Cu+, which could catalyze the cycloaddition between azide-DNA and alkyne/biotin-DNA in aqueous solution. The ligated DNA product could then be immobilized onto the test zone of the lateral flow biosensor to form a red band which could be unambiguously read by the naked eye. Taking advantage of the optical properties of gold nanoparticles (AuNPs) and high efficiency and selectivity of Cu+-catalyzed click chemistry, this assay enabled the visual detection of Cu2+ as low as 100 nM with excellent specificity. In comparison with conventional methods, this biosensor is more simple to operate and more cost-effective to use, and therefore has great potential in point-of-care diagnosis and environmental monitoring.

A self-assembled deoxyribonucleic acid concatemer for sensitive detection of single nucleotide polymorphism.

Polymerase-free and label-free strategies for DNA detection have shown excellent sensitivity and specificity in various biological samples. Herein, we propose a method for single nucleotide polymorphism (SNP) detection by using self-assembled DNA concatemers. Capture probes, bound to magnetic beads, can joint mediator probes by T4 DNA ligase in the presence of target DNA that is complementary to the capture probe and mediator probe. The mediator probes trigger self-assembly of two auxiliary probes on magnetic beads to form DNA concatemers. Separated by a magnetic rack, the double-stranded concatemers on beads can recruit a great amount of SYBR Green I and eventually result in amplified fluorescent signals. In comparison with reported methods for SNP detection, the concatemer-based approach has significant advantages of low background, simplicity, and ultrasensitivity, making it as a convenient platform for clinical applications. As a proof of concept, BRAF(T1799A) oncogene mutation, a SNP involved in diverse human cancers, was used as a model target. The developed approach using a fluorescent intercalator can detect as low as 0.1 fM target BRAF(T1799A) DNA, which is better than those previously published methods for SNP detection. This method is robust and can be used directly to measure the BRAF(T1799A) DNA in complex human serum with excellent recovery (94-103%). It is expected that this assay principle can be directed toward other SNP genes by simply changing the mediator probe and auxiliary probes.