Josephson radiation threshold detector.

A Josephson radiation threshold detector (JRTD) that is based on the threshold behaviour of a current bias Josephson junction (CBJJ) is designed and fabricated for infrared radiation (IR@1550nm) detection at low temperatures. To achieve the optimal performance, we develop a binary hypothesis detection method to calibrate Josephson threshold behaviours (i.e. the switching current distributions of the CBJJ with the Al/AlOx/Al junction) in the absence and presence of radiation. In the absence of IR radiation, the junction transitioned with a measurable voltage drop across the junction, and this signal was treated as the events of hypothesis H0. The events of junction transition observed in the presence of the IR radiation served as hypothesis H1. Considering the usual Gaussian noise and based on statistical decision theory, the accumulated data of the measured switching current distributions are processed, and the threshold sensitivity of the demonstrated JRTD device is estimated. The minimum detectable IR radiation power of the proposed detector is approximately 0.74 pW, which corresponds to the photon rate of 5.692 × 106 photons/second. Further optimisation of JRTDs to implement the desired binary detection of a single photon is still a subject of argument, at least theoretically.

A novel aptasensor for thrombin detection based on alkaline phosphatase decorated ZnO/Pt nanoflowers as signal amplifiers.

To remedy the problems caused by the introduction of an additional electron mediator and realize signal amplification, a new strategy has been presented to construct an electrochemical aptasensor for thrombin detection based on the cascade electrocatalysis of alkaline phosphatase (ALP) and Pt nanoparticle (PtNP)-functionalized ZnO nanoflowers.

Novel potentiometric immunosensor for hepatitis B surface antigen using a gold nanoparticle-based biomolecular immobilization method.

A novel potentiometric immunosensor for the detection of hepatitis B surface antigen has been developed by means of self-assembly to immobilize hepatitis B surface antibody on a platinum disk electrode based on gold nanoparticles, Nafion, and gelatin as matrices in this study. The modification procedure of the immunosensor was further characterized by using cyclic voltammetry and the enzyme-linked immunosorbent assay (ELISA) method. The detection is based on the change in the electric potential before and after the antigen-antibody reaction. In contrast to the commonly applied methods (e.g., the glutaraldehyde crosslinking procedure), this strategy could allow for antibodies immobilized with a higher loading amount and better retained immunoactivity, as demonstrated by the potentiometric measurements. A dynamic concentration range of 4-800 ng ml(-1) and a detection limit of 1.3 ng ml(-1) were observed. Analytical results of several human serum samples obtained using the developing technique are in satisfactory agreement with those given by ELISA. In addition, the technique presents some distinct advantages over the traditional sandwich format in that the analyzing performances are direct, rapid, and simple without multiple separation and labeling steps.

A highly sensitive PVC membrane iodide electrode based on complexes of mercury(II) as neutral carrier.

A novel solvent polymeric membrane electrode based on bis(1,3,4-thiadiazole) complexes of Hg(II) is described which has excellent selectivity and sensitivity toward iodide ion. The electrode, containing 1,4-bis(5-methyl-1,3,4-thiadiazole-2-yl-thio)butanemercury(II) [Hg(II)BMTB(NO3)4], has a Nernstian potentiometric response from 2.0 x 10(-8) to 2.0 x 10(-2) mol L(-1) with a detection limit of 8.0 x 10(-9) mol L(-1) and a slope of -59.0+/-0.5 mV/decade in 0.01 mol L(-1) phosphate buffer solution (pH 3.0, 20 degrees C). The selectivity sequence observed is iodide>bromide>thiocyanate>nitrite>nitrate>chloride>perchlorate>acetate>sulfate. The selectivity behavior is discussed in terms of the UV-Vis spectrum, and the process of transfer of iodide across the membrane interface is investigated by use of the AC impedance technique. The electrode was successfully applied to the determination of iodide in Jialing River and Spring in Jinyun Mountains, with satisfactory results.

Study of a bis-furaldehyde Schiff base copper(II) complex as carrier for preparation of highly selective thiocyanate electrodes.

A new highly selective thiocyanate electrode based on N,N'-bis-(furaldehyde)-1,2-phenylenediamine-dipicolyl copper(II) complex [Cu(II)-BFPD] as neutral carrier is described. The electrode has an anti-Hofmeister selectivity sequence: SCN->I->Sal->ClO4->Br->NO2->Cl->NO3->SO4(2-)>SO3(2-)>H2PO4- and a near-Nernstian potential linear range for thiocyanate from 1.0x10(-1) to 5.0x10(-6) mol L(-1) with a detection limit 2.0x10(-6) mol L(-1) and a slope of 57.5 mV decade(-1) in pH 5.0 of phosphate buffer solution at 20 degrees C. The response mechanism is discussed on the basis of results from A.C. impedance measurement and UV spectroscopy. The anti-Hofmeister behavior of the electrode results from a direct interaction between the central metal and the analyte ion and a steric effect associated with the structure of the carrier. The electrode has the advantages of simplicity, fast response, fair stability and reproducibility, and low detection limit. The selectivity of electrodes based on [Cu(II)-BFPD] exceeds that of classical anion-sensitive membrane electrodes based on ion exchangers such as lipophilic quaternary ammonium or phosphonium salts. Application of the electrode for determination of thiocyanate in waste water samples from a laboratory and a gas factory, and in human urine samples, is reported. The results obtained were fair agreement with the results obtained by HPLC.

Design of Schiff base complexes of Co(II) for the preparation of iodide-selective polymeric membrane electrodes.

The response characteristics of some iodide-selective solvent polymeric membrane electrodes based on with N,N'-bis(salicylaldehyde-n-octyl) diimine cobalt(II) (Co(II)SAODI) which is a more lipophilic substitute for a previously reported iodide-carrier are described. The electrode doped with Co(II)SAODI into a plasticized poly(vinyl chloride) membrane exhibits an anti-Hofmeister selectivity pattern with high selectivity toward iodide, long lifetime and small interference from H(+). Quartz crystal microgravimetric measurements and ac impedance experiments show that the excellent selectivity for iodide is related to the unique interaction between the carriers and iodide and steric effect associated with the structure of the Schiff base ligands.

DNA optical sensor: a rapid method for the detection of DNA hybridization.

A DNA optical sensor system is proposed based on the combination of sandwich solution hybridization, magnetic bead capture, flow injection and chemiluminescence for rapid detection of DNA hybridization. Bacterial alkaline phosphatase (phoA) gene and Hepatitis B virus (HBV) DNA were used as target DNA. A biotinylated DNA probe was used to capture the target gene onto the streptavidin-coated magnetic beads and a calf intestine alkaline phosphatase (CAP)-labelled DNA probe was used for subsequent enzymatic chemiluminescence detection. The detection cycle was less than 30 min, excluding the DNA hybridization time, which was about 100 min. Both the phoA gene and HBV DNA could be detected at picogramme or femtomole level. No response signal was obtained when target DNA did not exist in the sample. Successive sample detection could be made by removing the magnetic field and a washing step.

Chemically modified electrode based on poly[tetra(4-aminophenyl)porphyrin] as a pH sensor.

A chemically modified platinum electrode with coated poly[tetra(4-aminophenyl)porphyrin] has been used as a potentiometric pH sensor. It gives a linear response over the pH range 1.5-13.7 with a slope of 55 mV/pH (at 20 degrees ). The sensor has fair resistance to erosion of hydrofluoric acid and to interference of a coexisting redox couple. The sensor can be used for pH determination and end-point indication for potentiometric titration of hydrofluoric acid with sodium hydroxide. The a.c. impedance of the polymer membrane has also been studied.