Sensitive detection of a serum biomarker based on peptide nucleic acid-coupled dual cycling reactions

Serum level of disease markers may provide important guidance for diagnosis and prognosis. In this work, a sensitive and specific method suitable for direct serum detection of biomarkers is developed based on peptide nucleic acid (PNA)-coupled DNA cycling reactions with dual amplification. In this method, PNA released from a target-triggered homogeneous DNA cycling is employed to initiate an interface DNA cycling, and both of the cycling reactions are based on polymerase-assisted strand displacement reaction. Consequently, two PNA-coupled DNA cycling steps can take place simultaneously in one-pot, leading to greatly enhanced limit of detection and simplified operation. This method has also been successfully applied for evaluating serum insulin in pregnant women as an indicator of gestational diabetes mellitus. So the application of this method in real bio-samples may allow it to hold considerable potential in clinical practice. In addition, since there is no requirement for specific sequence of aptamer, the strategy proposed can be extended for the detection of many other protein markers and peptide-hormones in the future.     

A novel electrochemical method to detect cell surface carbohydrates and target cells

Glycosylation of cell surfaces is a critical factor in many biological processes; however, the lack of effective analytical tools for the detection of cell surface carbohydrates has been the bottleneck for probing into the processes. In this paper, a novel electrochemical method is presented for the analysis of cell surface carbohydrates, which can be also used to detect the target cells. Firstly, 5-hydroxy-3-hexanedithiol-1,4-naphthoquinone (JUG_thio), the electrochemical reporter, and anti-selectin aptamer are successively modified onto the surface of a gold electrode. Different concentrations of intestinal human colon adenocarcinoma (LS180) cells are employed as the target cells for this study. Consequently, the specific carbohydrates on the surfaces of LS180 cells and anti-selectin aptamers will compete for combination with selectin in the system. As a result, the oxidation signal of JUG_thio is changed and the detection of the cell surface carbohydrates can be achieved easily and sensitively. Furthermore, the proposed method can be used to specifically detect LS180 cells in a wide concentration range, from 10³ to 10⁷ cells/mL, with a good linear relationship and low detection limit, which might be promising for the diagnosis of cancer and some other diseases in the future.     

Electrochemical study of photovoltaic effect of nano titanium dioxide on hemoglobin

Nano titanium dioxide (TiO2) and hemoglobin (Hb) were co-modified on pyrolytic graphite (PG) electrode to study the photovoltaic effect of TiO2 nanoparticles (NPs) on the electron transfer reactivity and catalytic activity of the protein. By means of cyclic voltammetry (CV) and FTIR measurements, the study was characterized in both aerobic and anaerobic environments. Experimental results revealed that the factors which mainly interacted with Hb were electron/hole pairs and reactive oxygen species (ROS) generated by the photovoltaic effect when TiO2 NPs were irradiated under ultraviolet (UV) light. The electron/hole pairs generated on the surface of TiO2 would influence the structure of Hb gently, so the electron transfer reactivity and catalytic ability of the protein slightly changed. In contrast, ROS interacted with Hb intensively, which brought in much conformational change to Hb and its active centers, and even cause some damage. Consequently, the electron transfer reactivity and catalytic activity of Hb changed with a process of increasing initially and decreasing afterwards.     

A new strategy for a DNA assay based on a target-triggered isothermal exponential degradation reaction

An ultra-sensitive, fast, simple and easily operated method for sequence-specific detection of polynucleotides is proposed herein, which is based on a novel target-triggered isothermal exponential degradation reaction (TT-isoTexpDR) and the color change of probe-functionalized gold nanoparticles.     

Sensing phenothiazine drugs at a gold electrode co-modified with DNA and gold nanoparticles.

DNA and gold nanoparticles are co-immobilized at a gold electrode through elaborate self-assembly processes. This configuration has proven to be useful as a sensor for phenothiazine drugs, taking advantage of the well-known, relatively large surface area of gold nanoparticles and the strong intercalation between dsDNA and phenothiazine drugs. This modified electrode has demonstrated good sensitivity and stability towards the oxidation of two model phenothiazine drugs: promethazine and chlorpromazine. A linear dependence between the concentration of phenothiazine drugs and the peak current is observed, with a concentration range of 2.0 x 10(-5)-1.6 x 10(-4) M and 1.0 x 10(-5)-1.2 x 10(-4) M, and a detection limit of 1.0 x 10(-5) M and 7.0 x 10(-6) M, for promethazine and chlorpromazine, respectively.     

Direct application of gold nanoparticles to one-pot electrochemical biosensors

Gold nanoparticles (AuNPs) have been widely employed for the fabrication of electrochemical biosensors. In most cases, AuNPs are immobilized on the surface of an electrode, so they are difficult to be regenerated, making the use of the biosensor unfriendly. In this work, by adopting AuNPs directly as the electrolytes, we have developed a novel AuNPs-based electrochemical detection system. In brief, AuNPs-catalyzed oxidation of glucose is combined with a HRP-catalyzed reaction as well as an electrocatalytic reaction to compose cascade reactions in the electrolyte. Thus, the intensity of the electrocatalytic signals has quantitative relation with the concentration of glucose, and favors the sensitive detection of glucose. Furthermore, because the catalysis of AuNPs may be blocked under the interaction with single-stranded DNA and unblocked in the presence of a complementary sequence, detection of DNA and even single-nucleotide polymorphism can thereby been achieved. This one-pot detection system can be operated and regenerated very easily, since all the components are integrated in the electrolytes of AuNPs, and the unmodified electrode can be reused after being rinsed. This concept by integrating the advantages of sensitive electrochemical detection with the easy-to-operate nanocolloidal system may also promote the development of other kinds of electrochemical biosensors.     

Electrochemistry of xanthine oxidase and its interaction with nitric oxide.

With the help of nanocrystalline TiO2, the direct electrochemistry of xanthine oxidase (XOD) was achieved and two pairs of redox waves were observed. The interaction between XOD and nitric oxide (NO) was also investigated. The experimental results reveal that NO can be reduced at a XOD-nano TiO2 film modified electrode. When the NO concentration was low, the reduced product, HNO, would inactivate the protein. However, when the NO concentration was high, HNO would continue to react with NO to form N2O2- and N3O3-, which would not inhibit XOD, and thus the amount of active protein did not decrease any further.     

An electrochemical biosensor for nitric oxide based on silver nanoparticles and hemoglobin.

A nitric oxide (NO) biosensor based on silver nanoparticles was fabricated with high sensitivity and selectivity as well as stability. Silver nanoparticles could preserve the microstructures of hemoglobin, but the electrochemical reactivity of the protein and its detection sensitivity toward NO could be greatly enhanced. Accordingly, a NO biosensor was developed. The linear concentration range was from 1.0 x 10(-6) to 5.0 x 10(-5) M. Its detection limit was 3.0 x 10(-7) M with a sensitivity of 0.0424 microA microM(-1) NO. The possible co-existing compounds would not interfere with the detection.     

Electrochemistry of sinapine and its detection in medicinal plants

Sinapine (O-sinapoyl choline) is a crucial component, with much medicinal value, of many dietary and medicinal plants. It has been found that sinapine gives an electrochemical response at a pyrolytic graphite electrode. The electrochemical properties of sinapine have been investigated. The peak current in the cyclic voltammogram is linear in the concentration range 1.9×10^–6–2.5×10^–4 mol L^–1 and the limit of detection is 9.9×10^–7 mol L^–1. These properties can be applied to the determination of sinapine in extracts from three kinds of medicinal plant. The electrochemical method reported here is highly selective, sensitive, and stable.