Development of a one-step immunochromatographic strip test using gold nanoparticles for the rapid detection of Salmonella typhi in human serum.

An immunochromatographic strip test using gold nanoparticles was developed for the rapid detection of Salmonella typhi (S. typhi) in human serum. The strip test based on the principle of sandwich immunoassay by the specific binding of antigens from S. typhi O901 and antibody of S. typhi O901 on a nitrocellulose membrane. Antibody-gold nanoparticle conjugate was used as the label and was coated onto a glass fiber membrane, which was used as a conjugate pad. To create a test and control zone, antibody of S. typhi O901 and an anti-IgG were dotted on the nitrocellulose membrane, respectively. Positive samples were displayed as red dots at the test and control zones of the nitrocellulose membrane, while negative samples resulted in a red dot only in the control zone. The limit of detection (LOD) was found to be 1.14×10(5) cfu mL(-1), which could be visually detected by the naked eye within 15 min. This strip test provided a lower detection limit and analysis time than a dot blot immunoassay (8.88×10(6) cfu mL(-1) for LOD and 110 min for reaction time). In addition, our immunochromatographic strip test was employed to detect S. typhi in human serum effectively, with high accuracy. This strip test offers great promise for a rapid, simple and low-cost analysis of S. typhi.

CdSe/ZnS quantum dots based electrochemical immunoassay for the detection of phosphorylated bovine serum albumin.

A CdSe/ZnS quantum dot (QD) based electrochemical immunoassay of phosphorylated bovine serum albumin (BSA-OP) as a protein biomarker is presented. The QDs were used as labels for amplifying electrochemical signals and were conjugated with a secondary anti-phosphoserine antibody in a heterogeneous sandwich immunoassay. In this assay, the model phosphorylated protein BSA-OP was added to the primary BSA antibody coated polystyrene microwells, and then the QD labeled anti-phosphoserine antibody was added for completing immunorecognition. Finally, the bound QD was dissolved in an acid-dissolution step and was detected by electrochemical stripping analysis. The measured current responses were proportional to the concentration of BSA-OP. Under optimal conditions, the voltammetric response was linear over the range of 0.5-500 ngmL(-1) of BSA-OP, with a detection limit of 0.5 ngmL(-1). It also shows good reproducibility with a relative standard deviation of 8.6%. This QD-based electrochemical immunoassay offers great promise for simple and cost-effective analysis of protein biomarkers.

Amperometric Determination of Sulfite by Gas Diffusion- Sequential Injection with Boron-Doped Diamond Electrode.

A gas diffusion sequential injection system with amperometric detection using aboron-doped diamond electrode was developed for the determination of sulfite. A gasdiffusion unit (GDU) was used to prevent interference from sample matrices for theelectrochemical measurement. The sample was mixed with an acid solution to generategaseous sulfur dioxide prior to its passage through the donor channel of the GDU. Thesulfur dioxide diffused through the PTFE hydrophobic membrane into a carrier solution of 0.1 M phosphate buffer (pH 8)/0.1% sodium dodecyl sulfate in the acceptor channel of theGDU and turned to sulfite. Then the sulfite was carried to the electrochemical flow cell anddetected directly by amperometry using the boron-doped diamond electrode at 0.95 V(versus Ag/AgCl). Sodium dodecyl sulfate was added to the carrier solution to preventelectrode fouling. This method was applicable in the concentration range of 0.2-20 mgSO32-/L and a detection limit (S/N = 3) of 0.05 mg SO3²-/L was achieved. This method wassuccessfully applied to the determination of sulfite in wines and the analytical resultsagreed well with those obtained by iodimetric titration. The relative standard deviations forthe analysis of sulfite in wines were in the range of 1.0-4.1 %. The sampling frequency was65 h-1.