A nitric oxide biosensor based on horseradish peroxidase/kieselguhr co-modified pyrolytic graphite electrode

A reagentless nitric oxide (NO) biosensor was prepared using a pyrolytic graphite (PG) electrode modified with a composite film containing horseradish peroxidase (HRP) and kieselguhr. Noticeably, the electron-transfer reactivity of HRP was significantly enhanced when incorporated in the inorganic kieselguhr material. Consequently, we observed the direct electrochemical response of HRP in this composite film, which would be otherwise electrochemically silent (in the absence of kieselguhr). Importantly, this modified electrode demonstrated nice catalytic activity, as well as high stability, towards the reduction of NO. The peak current related to NO was linearly proportional to its concentration from 2.0 x 10(-7) to 2.0 x 10(-5) mol/L, and the relative standard deviation was 4 % for five successive determinations at a NO concentration of 1.0 x 10(-5) mol/L. The critical level in concentration was estimated to be (4.0 +/- 0.3) x 10(-8) mol/L.     

Isolation and determination of p-hydroxybenzoylcholine in traditional Chinese medicine Semen sinapis Albae

A special component is isolated from Semen sinapis Albae (white mustard seed), a traditional Chinese medicine. According to the physical and chemical investigation and spectroscopic identification, this component can be known as p-hydroxybenzoylcholine bisulfate, a choline base. This component in the drug is also determined by RP-HPLC. A reversed-phase C₁₈ column is used to separate the p-hydroxybenzoylcholine with an eluent of methanol–0.05 mol/L monopotassium phosphate solution (30:70) (adjusted by phosphoric acid to pH 3.6) at the flow rate of 0.5 mL/min. Detection is carried out with a UV detector operated at 285 nm, and the column temperature is 25 °C. It reveals that there is 0.021% (w/w) of p-hydroxybenzoylcholine bisulfate in Semen sinapis Albae and 0.037% (w/w) in stir-baked Semen sinapis Albae.     

Electrochemical Determination of Cinnamtannin B1 with a Pyrolytic Graphite Electrode

Cinnamtannin B1 (trimeric proanthocyanidin), which is identified and isolated from the effective fraction of the root of Lindera aggregata (Sims) Kosterm, is one kind of condensed tannin used as an effective antipyrotic and antitumor agent. Its electrochemical response can be obtained at a pyrolytic graphite electrode. Consequently, an easily performed and sensitive method for the determination of cinnamtannin B1 is developed. The detection limit is estimated to be 1.0×10^–7M with the linear determination range of 2.0×10^–7M to 1.8×10^–6M. Five replicate analyses of 1.0×10^–6M cinnamtannin B1 yields an RSD value of 2.1%. Since the working electrode does not need to be modified with any other species, it is very stable, repeatable and easily treated, and this method therefore potentially useful in real sample analysis.     

Voltammetric Behavior of Strychnine, and its Determination in Strychno Nux-Vomica Seeds Extract

The voltammetric behavior of strychnine has been studied with a pyrolytic graphite (PG) electrode. The redox process taking place at the PG electrode is discussed. The cyclic voltammetric response has also been evaluated with respect to various experimental conditions, such as scan rate, pH of the supporting electrolyte, strychnine concentrations and accumulation time. A highly sensitive voltammetric method for the determination of strychnine is consequently developed. The linear calibration is in the range of 1×10⁻⁶ M – 1.1×10⁻⁴ M, with the limit of detection (LOD) being 1×10⁻⁸ M. The precision is excellent with a relative standard deviation (RSD) of 2.3%. The proposed cyclic voltammetric methodology has been applied to the determination of strychnine in the extract of Strychno nux-vomica seeds using the standard addition method. Consistent results have been obtained from both the electrochemical approach described here and the previously reported HPLC method.     

5,10,15-三(4-氨基)苯基-20-苯基卟啉的电聚合膜及其金属化膜的电分析化学研究

本文对新型结构的卟啉进行电化学聚合,制得聚卟啉修饰电极,并在此基础上直接进行金属化,得到金属化的Cu聚卟啉修饰电极。实验表明,聚卟啉修饰电极在pH1～6的范围,对pH的变化呈能斯特响应,斜率为59.8mV/pH;金属化Cu聚卟啉对pH也具有能斯特响应,范围为pH4～8,斜率为28.7mV/pH。可用于实际样品的测定。     

Electrochemical detection of DNA 3′-phosphatases based on surface-extended DNA nanotail strategy

Determination of DNA dephosphorylation is of great value due to its vital role in many cellular processes. Here we report a surface-extended DNA nanotail strategy for simple and ultrasensitive detection of DNA 3′-phosphatases by terminal deoxynucleotidyl transferase (TdT) mediated signal amplification. In this work, DNA probes labeled with thiols at their 5′ terminals and phosphoryls at 3′ terminals are immobilized on gold electrode and are used as substrates for DNA 3′-phosphatases, taking T4 polynucleotide kinase phosphatase (T4PNKP) as an example. T4PNKP can catalyze the dephosphorylation reaction of the substrate DNA, followed by the formation of a long DNA strand by TdT on its 3′ terminal hydroxyl, leading to an evident chronocoulometry signal enhancement. The proposal presents a considerable analytical performance with low detection limit and wide linear range, making it promise to be applied in the fields of DNA dephosphorylation related processes, drug discovery, and clinical diagnostics.     

Target induced dissociation (TID) strategy for the development of electrochemical aptamer-based biosensor

In this paper, we report a novel and more general signal-on strategy for the fabrication of electrochemical aptamer-based (E-AB) biosensor. The principle is that the interaction between the target and the aptamer strand may induce the formation and subsequent dissociation of target–aptamer complex from an electrode surface, and consequently, the remaining DNA strand on the electrode surface can hybridize again with a ssDNA containing an electrochemical probe. Differential pulse voltammetric studies have revealed that this target induced disassociation (TID) strategy is an effective signal-on method for the detection of ATP molecules with good selectivity. The TID strategy may also have several advantages, such as independence on the specific structure of either the aptamers or their complementary sequences and promotion of the generalization of E-AB sensors, the more convincible results due to the signal-on model, and the unnecessity to label the aptamers, which provides the optimized status for the reaction with the targets, etc.     

A set of logic gates fabricated with G-quadruplex assembled at an electrode surface

A G-quadruplex-hemin complex assembled at an electrode surface may exhibit "smart" behaviors under benign conditions, which can be further used in fabricating a set of logic gates. Desirably, these logic gates can be integrated into a logic network with the advantages of integrity, unification and reversibility.