A novel fluorescence-based array biosensor: principle and application to DNA hybridization assays.

A novel fluorescence-based array biosensor targeted for field applications, such as environmental monitoring, has been developed, and successfully applied to DNA hybridization assays. The purpose was to meet the demand for automated, portable but easy-to-maintain systems allowing continuous flow monitoring of surface reactions. The biosensor presented here can be distinguished from the existing systems by the optical method used, which provides an enhanced simplicity and robustness, and enables a simple maintenance by potentially unskilled personnel. The system is based on a conventional microscope slide which acts both as transducer and biological array sensor. The excited fluorescence is guided by total internal reflection into the slide to the detector which is directly interfaced to the slide. Each region of the sensor array is successively optically interrogated, and the detection of the corresponding fluorescent emission synchronized. A real-time three-analyte analysis is thus feasible without any mechanical scanning movement or optical imaging systems as generally used in the existing instruments. The ability of the biosensor to operate in continuous flow for several tens of hours has been demonstrated. The biosensor has been assessed in terms of stability, and slide-to-slide reproducibility, which is found to be less than 3.7%, thus far below the standard biological reproducibility. DNA hybridization assays were performed to estimate a limit of detection, which was found to be 16 mol/microm(2), and to determine the reaction kinetics associated to the DNA model used. The developed biosensor is thus shown to be able to predict reaction kinetics, and to monitor in real time surface reactions between targets and probes.

Characterization and optimization of a real-time, parallel, label-free, polypyrrole-based DNA sensor by surface plasmon resonance imaging.

We describe in this paper a methodology to quantify multispot parallel DNA hybridizations and denaturations on gold surfaces by using, on one hand, a polypyrrole-based surface functionalization based on an electrospotting process and, on the other hand, surface plasmon resonance imaging allowing real-time measurements on several DNA spots at a time. Two characterization steps were performed in order to optimize the immobilization of oligonucleotide probes and, thus, to increase the signal-to-noise ratio of monitored hybridization signals: the first step consisted of characterizing the signal dependence upon the density of immobilized 15-mer probes, and, the second step, in analyzing the hybridization response versus spot thickness. We further demonstrated that a surface density of polypyrrole/DNA probes of approximately 130 fmol/ mm2 (590 pg/mm2) optimizes the hybridization signal that can be detected directly. Optimal thickness of the spot was found to be close to 11 nm. Specificity and regeneration steps on each spot have also been demonstrated successfully, showing this method to be very competitive and convenient in use.

[Gastroduodenal ulcers in young adults. An epidemiological study (author's transl)]. / Maladie ulcéreuse chez l'adulte jeune. Etude épidémiologique.

An epidemiological survey of gastroduodenal ulcers was carried ut in an homogenous population of 100000 young adults of National Service age, and the results were compared with those of a similar survey which had taken place 6 years previously. Between 1971 and 1977 the overall incidence of gastroduodenal ulcers had risen from 1,57 to 2.14 p. 1000, but there ws a sharper and more significant increase (from 0.14 to 0.41 p. 1000) in gastric ulcers during the same period. Some of the aetiological factors investigated, such as age of onset of the disease, closed or open community housing conditions, individual predisposition, family history of ulcers, family status and inaugural symptoms, had remained unchanged, but there appeared to be a growing tendency for the disease to strike predominantly students and executives. If this were confirmed, these two social categories would be those which bear the brunt of the increase in gastroduodenal ulcers observed during the last few years.

[Production of interferon and alpha 2-macroglobulin involvement in immune response during human viral hepatitis A (author's transl)]. / Production d'interféron et participation de l' alpha 2-macroglobuline à la réponse immunologique au cours de l'hepatite virale humaine de type A.

In viral hepatitis A, we could distinguish between monophasic and polyphasic forms. Monophasic and polyphasic hepatitis A induce the production of plasma interferon. Interferon level, elevated as early as the first days following the appearance of clinical signs, decreases and reaches a minimum value on the seventh day. A new rise of interferon is characterized by a maximum level on the twelfth day and a minimum level on the thirtieth. Beyond the first month we could still detect the presence of interferon. In the two forms of hepatitis, a complement system is activated both by classical and alternate pathways. IgM levels increase early, IgA levels remain unchanged. On the other hand, IgG levels, only slightly elevated in monophasic hepatitis A, are highly increased in polyphasic hepatitis A beyond the first month. Alpha 2-macroglobulin reaches levels above normal during convalescence in monophasic hepatitis A; on the contrary, in polyphasic hepatitis A, alpha 2-macroglobulin levles are above normal as early as the thirty first days of illness and remain above normal for several months. Elevated levels in alpha 2-macroglobulin may inhibit cellular immunity which is accountable for immunological injury of virus infected hepatocytes. We wonder whether this earlier increase in alpha 2-macroglobulin is responsible for the lasting character of viral infection observed in polyphasic hepatitis A.