Pei Zou

Label-free and ultrasensitive colorimetric detection of DNA based on target-triggered quadratic amplification strategy.

Highly sensitive detection of DNA plays a crucial role in biomedical research and clinical diagnosis. Herein, we developed a simple, label-free, isothermal, and ultrasensitive colorimetric method for amplified detection of DNA on the basis of a new quadratic amplification strategy. With the presence of three ingeniously designed hairpin structures and Exonuclease III (Exo III), the target DNA can trigger two independent cycles of reactions: hairpin assembly reaction and Exo III cleavage reaction, which are designed to initiate target DNA recycling amplification and reporter DNA amplification, respectively. Therefore, the proposed method exhibits a high sensitivity toward target DNA with a detection limit of as low as 81 fM, and it can discriminate mismatched DNA from completely matched target DNA. Furthermore, this method could be used as a universal tool for the detection of various DNA sequences and might be further extended for the detection of aptamer-binding molecules.

G-quadruplex DNAzyme-based chemiluminescence biosensing platform based on dual signal amplification for label-free and sensitive detection of protein

Detection of ultralow concentration of specific protein plays a key role in biotechnological applications and medical diagnostics. In this study, we demonstrate an amplified chemiluminescence biosensing platform for sensitive detection of protein. The biosensing platform ingeniously combines target-catalyzed hairpin assembly and Exo III-assisted signal amplification. A catalytic G-quadruplex-hemin DNAzyme is further employed to stimulate the generation of chemiluminescence in the presence of luminol and H2O2. These designs together allow a high sensitivity for the biotarget, human α-thrombin, resulting in a detection limit of 0.92 pM, and it is much lower than previous reported studies. In addition, the proposed biosensing platform is versatile. By conjugating with various recognition units, it could be employed to sensitive detect various DNA-binding proteins and might find wide applications in biomedical fields.

HIGHLY EFFICIENT AND VERSATILE ACETYLATION OF ALCOHOLS, PHENOLS AND AMINES CATALYZED BY METHYLENEDIPHOSPHONIC ACID (MDP) UNDER SOLVENT-FREE CONDITIONS

Methylenediphosphonic Acid (MDP) was found to be a simple, cheap and reusable heterogeneous catalyst for the acetylation of structurally diverse alcohols, phenols and amines with acetic anhydride under solvent-free conditions at room temperature. This method showed preferential selectivity for the acetylation of the amino group in the presence of hydroxyl group. The method is very mild and the yields were in excellent.

Methyl 4-nitro­benzoate

In the molecule of the title compound, C8H7NO4, the nitro group is approximately coplanar with the benzene ring [dihedral angle = 0.6 (1)°], while the dihedral angle between the methoxycarbonyl group and the benzene ring is 8.8 (1)°. In the crystal structure, weak intermolecular aromatic C—H⋯Ocarboxyl and C—H⋯Onitro hydrogen-bonding interactions are present.

Strategy for the detection of mercury ions by using exonuclease III-aided target recycling

Herein, a simple, highly sensitive and selective exonuclease III (Exo III)-based sensor was developed for mercury ions Hg2+ detection without the need of complicated, high-cost and time-consuming labeling. In this strategy, two oligonucleotides were employed for the experiment design. DNA1 was prepared with one DNA strand which was designed as a quadruplex-forming oligomer, and which was constructed as 3′-protruding to ensure the probe cannot be digested by Exo III. When the target Hg2+ is introduced into the sensing system, it associates with DNA1 and DNA2 to form double strand DNAs (DNA1/DNA2 duplexes) which have a blunt 3′-terminus. Exo III then can degrade part of DNA1, releasing the DNA1 and Hg2+, and ultimately liberating the G-rich oligomer. This released G-rich oligomer folds into a G-quadruplex structure and thus allows the formation of DNAzyme in the presence of hemin. The formed DNAzyme can effectively catalyze the H2O2-mediated oxidation of ABTS, giving rise to a change in solution color. The released DNA1 and Hg2+ are free to bind to another 3′-protruding terminus of DNA1 to trigger a new digestion reaction, leading to significant amplification of the signal. The present new strategy shows a limit of detection as low as 66 pM and excellent selectivity toward Hg2+ over a wide range of metal ions.

Dimethyl 5-amino-2,4,6-triiodo­isophthalate

The title compound, C(10)H(8)I(3)NO(4), crystallizes with two mol-ecules in the asymmetric unit. The I atoms and the benzene ring plane in the two mol-ecules are approximately coplanar, the I atoms deviating by -0.1631 (1), 0.0704 (1) and -0.0507 (1) Å from the mean plane of the benzene ring in one mol-ecule and by 0.1500 (1), -0.0034 (1) and -0.1213 (1) Å in the other. The planes of the ester groups are almost orthogonal to those of the benzene rings in both mol-ecules, forming dihedral angles of 83.5 (3), 76.4 (3), 97.3 (1) and 75.7 (1)°. The mean planes of the benzene rings in two mol-ecules are inclined at 69.8 (3)° with respect to each other. In the crystal, inter-molecular I⋯O inter-actions link the mol-ecules into infinite chains. In addition, N-H⋯O and non-classical C-H⋯O hydrogen bonds are observed.

Ethyl 2-(2-methyl-4-nitro-1H-imidazol-1-yl)acetate.

In the title compound, C8H11N3O4, the dihedral angle between the imidazole ring and the ethyl acetate plane is 103.1 (8)°. The crystal packing is stabilized by weak intermolecular C—H⋯O and C—H⋯N hydrogen bonds.

Methyl 4-chloro-3,5-dinitro­benzoate

In the molecule of the title compound, C8H5ClN2O6, the two nitro groups and the ester group make dihedral angles of 29.6 (1)°, 82.3 (1)° and 13.7 (1)°, respectively, with the benzene ring. In the crystal structure weak C—H⋯O interactions are present.

Ethyl 3-carb-oxy-5-nitro-benzoate.

In the title compound, C10H9NO6, the carboxy, ethoxycarbonyl and nitro groups form dihedral angles of 3.8 (1), 4.5 (1) and 164.8 (1)°, respectively, with the mean plane of the benzene ring. In the crystal structure, molecules lying about inversion centers are linked through O—H⋯O hydrogen bonds. C—H⋯O interactions are also present.

Crystal structure of N-(2-hy-droxy-eth-yl)-5-nitro-isophthalamic acid monohydrate.

In the title compound, C10H10N2O6·H2O, the carboxylic acid group and the nitro group are essentially coplanar with the benzene ring [maximum deviation = 0.0264 (9) Å], while the amide group is oriented at a dihedral angle of 9.22 (5)° with respect to the benzene ring. In the crystal, classical O—H⋯O and N—H⋯O hydrogen bonds and weak C—H⋯O interactions link the organic molecules and water molecules of crystallization into a three-dimensional supramolecular architecture.