Label-free as-grown double wall carbon nanotubes bundles for Salmonella typhimurium immunoassay

Background: A label-free immunosensor from as-grown double wall carbon nanotubes (DW) bundles was developed for detecting Salmonella typhimurium. The immunosensor was fabricated by using the as-grown DW bundles as an electrode material with an anti-Salmonella impregnated on the surface. The immunosensor was electrochemically characterized by cyclic voltammetry. The working potential (100, 200, 300 and 400 mV vs. Ag/AgCl) and the anti-Salmonella concentration (10, 25, 50, 75, and 100 μg/mL) at the electrode were subsequently optimized. Then, chronoamperometry was used with the optimum potential of 100 mV vs. Ag/AgCl) and the optimum impregnated anti-Salmonella of 10 μg/mL to detect S. typhimurium cells (0-109 CFU/mL). Results: The DW immunosensor exhibited a detection range of 102 to 107 CFU/mL for the bacteria with a limit of detection of 8.9 CFU/mL according to the IUPAC recommendation. The electrode also showed specificity to S. typhimurium but no current response to Escherichia coli. Conclusions: These findings suggest that the use of a label-free DW immunosensor is promising for detecting S. typhimurium

Micro-cylinder biosensors for phenol and catechol based on layer-by-layer immobilization of tyrosinase on latex particles: Theory and experiment

Abstract Microelectrode sensors for phenol and catechol are described, based on the sequential immobilization of polystyrene sulphonate, polyallylamine, tyrosinase and polyallylamine again, onto micrometer scale latex spheres, followed by the adsorption of the spheres onto electrochemically pretreated carbon fibres. The steady state responses of the fibres are analyzed in terms of a cylindrical diffusionkinetic model. It is deduced that the adsorbed latex particles provide a relatively open film structure, resulting in a diffusion coefficient only one order of magnitude lower than the solution value, and that at minimum 2-3% of the immobilized enzyme is catalytically active. The optimised sensors exhibit linear ranges to phenol and catechol of 7-56.5 lM and 2-19.7 lM respectively, with sensitivities of 0.15 A M À1 cm À2 and 1.72 A M À1 cm À2 respectively. The limiting factor to sensor stability is desorption of latex from the fibres

Lateral flow assay modified with time-delay wax barriers as a sensitivity and signal enhancement strategy

Altres ajuts: this work is also funded by the CERCA Program/Generalitat de CatalunyaThe ease of use, low cost and quick operation of lateral flow assays (LFA) have made them some of the most common point of care biosensors in a variety of fields. However, their generally low sensitivity has limited their use for more challenging applications, where the detection of low analytic concentrations is required. Here we propose the use of soluble wax barriers to selectively and temporarily accumulate the target and label nanoparticles on top of the test line (TL). This extended internal incubation step promotes the formation of the immune-complex, generating a 51.7-fold sensitivity enhancement, considering the limit of quantification, and up to 96% signal enhancement compared to the conventional LFA for Human IgG (H-IgG) detection

Nanochannels for diagnostic of thrombin-related diseases in human blood

Selected Papers from the World Congress on Biosensors.A high sensitive voltammetric method for rapid determination of thrombin spiked in whole blood by taking advantage of both aptamer-based recognition and the use of a nanoporous membrane has been developed. The nanoporous membrane not only acts as platform for the thrombin recognition but also as filter of the micrometric components such as white and red blood cells, consequently minimizing matrix effects. The protocol involves a sandwich format in the inner walls (200nm diameter) of an anodized alumina oxide filter membrane (AAO). The analytical signal, by DPV oxidation of [Fe(CN) 6] 4-, is based on the blockage in the pores which affects the diffusion of [Fe(CN) 6] 4- to the screen-printed carbon electrotransducer (SPCEs) modified with the membrane. By labeling the anti-thrombin IgG with AuNPs followed by silver enhancement a greater passive signal enhancement in comparison to the membrane blockage has been observed. The contribution of both electrostatic/steric effects in this blockage due to the subsequent formation of the aptamer-thrombin complex and the final sandwich assay is investigated. The efficiency of the system is also monitored by microscopic techniques. The resulted biosensing system allows detecting thrombin spiked in whole blood at very low levels (LOD 1.8ngmL -1) which are within the range of clinical interest for the diagnostic of coagulation abnormalities as well as pulmonary metastasis. © 2012 Elsevier B.V.We acknowledge MICINN (Madrid) for the projects PIB2010JP-00278 and IT2009-0092, the E.U.'s support under FP7 contract number 246513“NADINE” and the NATO Science for Peace and Security Programme's support under the project SfP 983807. W.C. acknowledges a Ph.D. scholarship from the Royal Golden Jubilee Project of the Thailand Research Fund.Peer Reviewe