Xiuping He

In this paper, horseradish peroxidase-mimicking DNAzyme (HRP-DNAzyme) and Prussian blue (PB)-gold (Au) nanocomposites were designed as versatile electrochemical sensing platforms for the amplified detection of DNA, Hg(2+) and adenosine triphosphate (ATP). By the conjugation of the target probe with the capture probe, a conformational change resulted in the formation of HRP-DNAzyme on the PB-Au modified electrode. The redox of HRP-DNAzyme (red) was efficiently carried out in the presence of H2O2, in which PB acted as a mediator stimulating the biocatalytic functions of HRP-DNAzyme and actuated a catalytic cycle bringing an amplified signal. Specific recognition of the target DNA, Hg(2+) and ATP allowed selective amperometric detection of the target molecule. The detection limits of DNA, Hg(2+) and ATP were 50 nM, 30 pM and 3 nM, respectively. The highlight of this work is that the catalytic cycle between PB-Au nanocomposites and HRP-DNAzyme was adequately utilized in the amplificatio...

Ag(+) is known to bind very strongly with cytosine-cytosine (C-C) mismatches in DNA duplexes to form C-Ag(+)-C base pairs. Exonuclease III (Exo III) can catalyze the stepwise removal of mononucleotides of duplex DNA. In this work, we study Exo III activity on DNA hybrids containing C-Ag(+)-C base pairs. Our experiments show that Ag(+) ions could intentionally trigger the activity of Exo III towards a designed cytosine-rich DNA oligonucleotide (C-rich probe) by the conformational change of the probe. Our sensing strategy uses this conformation-dependent activity of Exo III, which is controlled through the cyclical shuffling of Ag(+) ions between the solid DNA hybrid and the solution phase. This interesting conversion has led to the development of an ultrasensitive detection platform for Ag(+) ions with a detection limit of 0.03 nM and a total assay time possible within minutes. This simple detection strategy could also be used for the detection of other metal ions which exhibit specific interactions with natural or synthetic bases.

In the present study, ultrasensitive detection of Ag(+) is demonstrated by a biocatalytic signal amplification system which is realized by only one DNA sequence based electrical contacted enzyme structure and the Au nanoparticles/Carbon nanodots (AuNPs/C-dots) composite immobilization platform. In the presence of Ag(+), with the interaction of cytosine-Ag(+)-cytosine (C-Ag(+)-C), cytosine-rich DNA sequence labeled with methylene blue (MB) molecules near 5' end and Glucose Oxidase (GOx) at 3' end, has a self-hybridization and then forms a duplex-like structure which makes MB and GOx approach the AuNPs/C-dots modified electrode. MB units can then act as a relay that electrically contacts GOx with the AuNPs/C-dots modified electrode and activate the bioelectrocatalyzed oxidation of glucose to glucose acid. In consequence, based on the bioelectrocatalyzed signal amplification on the AuNPs/C-dots platform, Ag(+) could be quantitatively detected in the range of 10(-11)-10(-5) M with a low detection limit of 3 pM. Also, there is an excellent selectivity against other interferential metal ions. The detection of Ag(+) ions was realized by Ag(+) self-induced conformational change of DNA scaffold which involved only one oligonucleotide showing its convenience and availability.

Determination of nucleotide kinase activity is valuable due to its importance in regulating nucleic acid metabolism. Herein, we describe a strategy for simply and accurately determining nucleotide kinase activity by TiO2 nanotubes mediated signal transition and Au nanoparticles amplification. In this method, DNA containing 5'-hydroxyl group is self-assembled onto a gold electrode and used as a substrate for T4 polynucleotide kinase (PNK). By the specific immobilization affinity of TiO2 nanotubes with the phosphorylated DNA, TiO2 nanotubes were linked with phosphorylated substrate DNA on the electrode. And then Au nanoparticles modified 5'-phosphate DNA was conjugated with the TiO2 nanotubes and hybridized with methylene blue labeled signal DNA. Because gold nanoparticles have high loading of signal indicator methylene blue, the electrochemical signal is generated and amplified. It presents an excellent performance with wide linear range and low detection limit. Additionally, inhibition effects of some salts have also been investigated. The developed method is a potentially useful tool in researching the interactions between proteins and nucleic acids and provides a diversified platform for a kinase activity assay.

Cisplatin is a representative of cytotoxic and antineoplastic metallodrugs used for the treatment of various malignancies. In this paper, an enzyme-free amplification platform involving an autonomous target triggered process that yields the formation of the hemin/G-quadruplex DNAzyme wires was designed for the detection of cisplatin. Given the virtue of hemin/G-quadruplex DNAzyme wires (supersandwich DNAzyme structure) containing many units of hemin/G-quadruplex DNAzyme, an amplified electrochemical signal was achieved. Based on the combination of cisplatin with the guanine of the designed hemin/G-quadruplex DNAzyme supersandwich DNA structure, changing this structure and decreasing its catalytic effect on H2O2, it was used for the study on the analysis of cisplatin. With the concentration of the cisplatin increasing, the conformational change of the supersandwich DNA structure changed gradually. Then a relationship between the concentration of the cisplatin and the obtained electrochemical signal can be established. The detection concentration range of cisplatin was from 0.05 to 5 μM with a low detection limit of 20 nM using a signal three-fold the background noise and the correlation coefficient is 0.9993. The proposed approach is able to provide unique opportunities as simplicity in design and easy operations. Therefore, the proposed sensor presents remarkably high sensitivity and selectivity.

Based on the protecting effect of folate receptor (FR) toward folic acid (FA) modified DNA and the signal amplification of supersandwich DNA structure, we designed an interesting electrochemical biosensor for FR. In the present system, with the increase of FR, protecting more FA bound DNA from hydrolysis by exonuclease I (Exo I), FA bound DNA will hybridize to form more supersandwich DNA structure resulting in an increased electrochemical signal. A relationship between the concentration of the target protein, FR, and the obtained electrochemical signal can be established. The signal was obtained by the catalysis on H₂O₂ in the system containing Fc and hemin/DNAzyme. The detection concentration range of FR was from 1.0 to 20.0 ng/mL with an achieved detection limit of 0.3 ng/mL which approached clinically relevant concentrations of FR.