Triplex DNA formation-mediated strand displacement reaction for highly sensitive fluorescent detection of melamine

Mercury mediated DNA-Au/Ag nanocluster ensembles to generate a gray code encoder for biocomputing

Boolean operations utilizing DNA as a platform for biocomputing have become a promising tool for next-generation bio-molecular computers. In the whole process of any binary data transmission, bit errors are unavoidable and commonly occur. Cascades of exclusive-OR (XOR) operations show the great potential to evaluate these errors by introducing a parity generator (pG) and a parity checker (pC). Herein, we constructed a DNA hybrid architecture platform employing a chemosensing ensemble of mercury-mediated DNA-Au/Ag nanoclusters (M-Au/Ag NCs) to operate unconventional pG/pC for "error detection". Taking advantage of pG/pC, the transmitted and received data is converted to secure information using a binary to gray code encoder. To the best of our knowledge, this is the first molecular gray code encoder for biocomputing, which discovers an exciting avenue to protect information security through sophisticated logic circuits.

Rational design of an allosteric G-quadruplex aptamer probe for ultra-sensitive detection of melamine in milk

Efficient and accurate detection of melamine in dairy products remains a crucial yet challenging task. Herein, an allosterically modulated G-quadruplex-integrated aptamer is rationally designed with thymine-rich recognition termini for melamine binding. The detection process is facile by simply introducing the analyte into the mixture consisting of G-quadruplex aptamer probes, exonuclease III, and thioflavin T (ThT). The detection feasibility is confirmed by the polyacrylamide gel electrophoresis and fluorescence measurement results. This exonuclease III-assisted signal amplifiable approach works well in a linear range from 0.1 nM to 0.1 μM. Moreover, a detection limit as low as 83 pM is easily achieved, which is almost five orders of magnitude smaller than the maximum allowable melamine levels (about 8 μM) defined by many countries all over the world. The whole assay time for each test is no longer than 1 h. Additionally, the scheme is highly specific and satisfactory recovery rates (from 91% to 104%) are readily obtained when challenged with melamine-spiked milk samples. Therefore, the label-free, turn-on, low-cost, and time-efficient method can be used for reliable detection of melamine in an easily manipulated and ultra-sensitive manner, which may find its utilization in the field of food safety, biomedical engineering, and clinical diagnosis.

A Universal Paper-Based Electrochemical Sensor for Zero-Background Assay of Diverse Biomarkers

This paper describes a universal paper-based electrochemical sensing platform that uses a paper modified with signal molecule-labeled DNA and a screen-printed electrode along with target recognition solutions to achieve the detection of multiple types of biomarkers. These assays rely on the target-induced synthesis of Mg²⁺-dependent DNAzyme for catalyzing the cleavage of substrate DNA from paper, which have been demonstrated by using microRNA recognition probe for miR-21, a phosphorylated hairpin probe for alkaline phosphatase, and a DNA aptamer for carcinoembryonic antigen assays, respectively. Taking advantages of the high specific target-triggered polymerization/nicking and DNAzyme-catalyzed signal amplification, the present assays enable highly sensitive and selective detection of these targets with zero-background. These assays can also be applied to detect target in spiked serum samples, demonstrating the potential for point-of-care detection of clinical samples.

Bimetallic cerium/copper organic framework-derived cerium and copper oxides embedded by mesoporous carbon: Label-free aptasensor for ultrasensitive tobramycin detection

We reported a novel bimetallic cerium/copper-based metal organic framework (Ce/Cu-MOF) and its derivatives pyrolyzed at different temperatures, followed by exploiting them as the scaffold of electrochemical aptamer sensors for extremely sensitive detection of trace tobramycin (TOB) in human serum and milk. After the calcination at high temperature, the meal coordination centers (Ce and Cu) were transferred to metal oxides containing various chemical valences, such as Ce(III), Ce(IV), Cu(II) and Cu(0), which were embedded within the mesoporous carbon network originated from the organic ligands (represented by CeO₂/CuO_x@mC). Owning to the strong synergistic effect among the metal oxides, mesoporous carbon, and small cavities and open channels of MOF, the as-prepared CeO₂/CuO_x@mC nanocomposites not only possess good electrochemical activity but also exhibit strong bioaffinity toward the aptamer strands. By comparing the electrochemical biosensing peroformances using on the Ce/Cu-MOF- and the series of CeO₂/CuO_x@mC-based aptasensors, the constructed CeO₂/CuO_x@mC₉₀₀-based (calcinated at 900 °C) aptasensor exhibits an extremely low detection limit of 2.0 fg mL^-1 within a broad linear TOB concentration range from 0.01 pg mL^-1 to 10 ng mg L^-1. It demonstrates that the proposed aptasensor is substantially superior to those previously reported in the literature, along with high selectivity, good stability and reproducibility, and acceptable applicability in human serum and milk. Thereby, the newly fabricated aptasensing approach based on bimetallic CeO₂/CuO_x@mC has a considerable potential for the quantitative detection of antibiotics in the food safety and biomedical field.

DNA-fueled target recycling-induced two-leg DNA walker for amplified electrochemical detection of nucleic acid

Taking advantage of the homogeneous and heterogeneous electrochemical biosensors, a simple, sensitive, and selective electrochemical biosensor is constructed by combining entropy-driven amplification (EDA) with DNA walker. This electrochemical biosensor realizes the biorecognition and EDA operation in homogeneous solution, which is beneficial to improve the recognition and amplification efficiency. A two-leg DNA walker generated by EDA can walk on the surface of gold electrode for cleaving the immobilized substrate DNA and releasing the electroactive labels, giving rise to a significant decrease of the electrochemical signal. The immobilization of the electroactive labels ensures the reproducibility and reliability of the biosensor. The present cascade amplification assay can be applied to detect target DNA with a detection limit of 0.29 fM, and base mutations can be easily distinguished. Moreover, the proposed electrochemical biosensor shows a satisfactory performance for the detection of target DNA in human serum. Thus, the novel electrochemical biosensor holds promising potential for a future application in disease diagnosis.

Convenient and sensitive colorimetric detection of melamine in dairy products based on Cu(ii)-H2O2-3,3′,5,5′-tetramethylbenzidine system

The illegal adulteration of melamine in dairy products for false protein content increase is a strong hazard to human health. Herein, a simple and sensitive colorimetric method was developed for the quantification of melamine in dairy products based on a Cu²⁺-hydrogen peroxide (H₂O₂)-3,3′,5,5′-tetramethylbenzidine (TMB) system. In this strategy, Cu²⁺ exhibits peroxidase-like activity and can catalyze the oxidation of TMB to oxidized TMB (oxTMB) in the presence of H₂O₂ with a blue colour change of the solution. However, the presence of melamine quickly interacts with H₂O₂ leading to the consumption of H₂O₂ and thus strongly hinders the oxidation of TMB. Under the optimal conditions, the absorbance change of oxTMB has a linear response to the concentration of melamine from 1 to 100 μM with a detection limit of 0.5 μM for melamine. The proposed method has many merits including more simplicity, good selectivity, and more cost-effectiveness without using any nanomaterials. The method was further successfully applied to detect melamine in dairy products including milk and infant formula powder.

Convenient and sensitive colorimetric detection of melamine in dairy products based on a Cu(ii)-H₂O₂-3,3′,5,5′-tetramethylbenzidine system was reported.