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A portable immunosensor coupled to laser-induced fluorescence (LIF) detection system has been successfully developed. It was applied to the quantitative determination of specific IgG antibodies against H. pylori present in human serum samples. This system is a relevant alternative tool for the diagnostic of peptic ulcer and gastritis diseases produced by H. pylori, which are recognized risk factors for the development of gastric mucosa associated lymphoid tissue lymphoma and gastric adenocarcinoma. More than 50% of the population has been affected by H. pylori, one of the most widespread infections around the world. Our proposed system combines the LIF detection, which offers great sensibility with the specificity of the immunological reactions and the microfluidic technology. The device has a central channel (CC) with packed H. pylori antigen immobilized on 3aminopropyl-modified controlled pore glass (AP-CPG). Antibodies in serum samples reacted immunologically with the immobilized antigen and then, they were determined using alkaline phosphatase (AP) enzyme-labeled second antibodies specific to human IgG. The 4-methylumbelliferyl phosphate (4-MUP), employed as enzymatic substrate, was converted to soluble fluorescent methylumbelliferone by AP, and this fluorescent product was finally quantified by LIF detection system. The calculated detection limits for LIF detection and the ELISA procedure were 0.17 and 2.1 UmL −1 , respectively, and the within-and between-assay coefficients of variation were below 5.1%.

A chemically modified carbon paste electrode was developed for the determination of silver by incorporating the ion-exchanger Dowex 50 W Â 12 into a conventional graphite-Nujol oil paste. Silver(I) was accumulated at the electrode surface from solutions of the sample under open circuit conditions, then reduced at constant potential in a separate 0.1 M HNO 3 solution and finally determined by square wave (Osteryoung) anodic stripping voltammetry. The influence of paste composition, acummulation/reduction time, possible interferences and other experimental variables on the height and shape of the anodic peak was examined in detail. For 5 min of accumulation, the linear range was from 1.62 mg L À1 to 0.8 mg L À1 with a detection limit of 0.27 mg L À1 . The dynamic range could be extended up to 2.5 mg L À1 (from 0.92 mg L À1 to 2.5 mg L À1 ) with 20 min of preconcentration. The method showed good tolerance for Cu 2þ , Fe 3þ , Cd 2þ , Zn 2þ , Pb 2þ , and Au 3þ . Interference from Hg 2þ up to 5 mg L À1 was avoided by masking with EDTA in the preconcentration step.

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