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The development of rapid and effective detection of pathogens is necessary to prevent bacterial infection. Herein, we constructed a novel polymerase chain reaction-dynamic light scattering (PCR-DLS) sensing assay for detecting Salmonella sensitively. First, the invA gene specific for Salmonella was designed with upstream and downstream primers containing oxyethylene glycol bridge blockers which could hybridize with DNA-functionalized gold nanoparticle probes (probes-AuNPs). And the probes were hybridized complementary to the trailing end of the primers, which resulted in the aggregation of AuNPs and the change of particle diameter that could be measured by DLS. The results show that the PCR-DLS assay could improve the detection sensitivity and the limit of detection (LOD) was as low as 4.0 CFU/mL in pure culture and 1.8 × 102 CFU/mL in the spiked skim milk samples, which the detection time was less than 2 h. In conclusion, this work provides a promising strategy for developing the DLS technique of detecting foodborne pathogens. [ABSTRACT FROM AUTHOR]

Sensitive, simple, and rapid pathogen separation and detection methods are essential for the early diagnosis and immediate medical treatment of bacterial infections. In this study, a novel strategy based on vancomycin (Van)-modified ovalbumin (OVA) mediated magnetic nanoprobes (MBs-OVA-Van) combined with multiplex polymerase chain reaction (mPCR) was developed for efficient isolation and detection of Staphylococcus aureus (S. aureus) and Bacillus cereus (B. cereus). Van conjugated to ovalbumin coated magnetic microcarrier via strong covalent interaction. In addition, Van binds through hydrogen bonds with d-alanyl-d-alanine moieties on the surface of gram-positive bacteria cell wall. Under optimum conditions, the MBs-OVA-Van showed that the capture efficiency (CE) for S. aureus and B. cereus in PBS and juice samples were around 91%, 92% and 89%, 85%, respectively. In addition, with a mixture containing both target bacteria in PBS and juice samples, the CE for S. aureus and B. cereus were recorded at about 90%, 91% and 80%, 84%, respectively. The MBs-OVA-Van plus mPCR method applied in PBS and juice samples for both bacteria showed limits of detection at 102 CFU mL-1 in a < 3 h total assay time. The results indicated that the method holds promise for isolation and enrichment of gram-positive bacteria with S. aureus and B. cereus as models. [ABSTRACT FROM AUTHOR]

A multiplex polymerase chain reaction (mPCR) with propidium monoazide (PMA) and internal amplification control (IAC) for the simultaneous detection of waterborne pathogens Salmonella spp., Pseudomonas aeruginosa, Bacillus cereus, and Escherichia coli O157:H7, was developed. This PMA-IAC-mPCR assay used four new specific primers based on the genes for invA, ecfX, cesB, and fliC, respectively. A 16S rRNA primer was chosen for IAC to eliminate false negative results. The photosensitive dye, propidium monoazide (PMA) was used to exclude signals from dead bacteria that could lead to false positive results. In pure culture, the limits of detection (LOD) were 101 CFU/ml for P. aeruginosa, 102 CFU/ml for both Salmonella spp. and E. coli O157:H7, and 103 CFU/ml for B. cereus, respectively. In addition, with a 6–8 h enrichment of all four bacteria that were combined in a mixture that was spiked in water sample matrix, the LOD was 3 CFU/ml for Salmonella spp., 7 CFU/ml for E. coli O157:H7, 10 CFU/ml for B. cereus and 2 CFU/ml for P. aeruginosa. This PMA-IAC-mPCR assay holds potential for application in the multiplex assay of waterborne pathogens. [ABSTRACT FROM AUTHOR]

We report in this article the microwave synthesis of relatively monodisperse, highly crystalline CdSe quantum dots (QDs) overcoated with Cd0.5Zn0.5S/ZnS multishells. The as-prepared QDs exhibited narrow photoluminescence bandwidth as the consequence of homogeneous size distribution and uniform crystallinity, which was confirmed by transmission electron microscopy. A high photoluminescence quantum yield up to 80% was measured for the core/multishell nanocrystals. Finally, the resulting CdSe/Cd0.5Zn0.5S/ZnS core/multishell QDs have been successfully applied to the labeling and imaging of breast cancer cells (SK-BR3). [ABSTRACT FROM AUTHOR]

Picogram levels of antibodies against the protective antigen (PA) of Bacillus anthracis were detected in an automated electrochemical sandwich-type enzyme-linked immunosorbant assay. The antibodies were captured and detected using an 8 × 3 array of 50-μm-diameter cavities. The reagent and sample volumes were as low as 200 nL in a less than 25-min assay from capture to signal generation. The electrochemical detection of the antibodies was demonstrated at 0.05–10 μg/mL containing only 10–5,000 pg antibodies. The limit of detection is 10 fg for a 200-nL sample. Detection of anti-PA immunoglobulin G performed in spiked normal human serum and fresh whole human blood did not show a significant difference from detection in a buffer. The initial automation of the assay involved the use of a digital syringe pump for the delivery of reagents to the capture surface. [ABSTRACT FROM AUTHOR]

The article outlines the benefits of miniaturized amperometric electrochemical systems and their applicability in DNA/RNA assays. Emphasizing recent applications for micro-organisms, the advantages offered by miniatured electrochemical methods over the spectroscopic analyses are discussed. Information on how the diminishing size of detecting electrode improves oligonucleotides detection and molecular recognition techniques is presented.

Detecting and enumerating fecal coliforms, especially Escherichia coli, as indicators of fecal contamination, are essential for the quality control of supplied and recreational waters. We have developed a sensitive, inexpensive, and small-volume amperometric detection method for E. coli β-galactosidase by bead-based immunoassay. The technique uses biotin-labeled capture antibodies (Ab) immobilized on paramagnetic microbeads that have been functionalized with streptavidin (bead–Ab). The bead–Ab conjugate captures E. coli from solution. The captured E. coli is incubated in Luria Bertani (LB) broth medium with the added inducer isopropyl β- D-thiogalactopyranoside (IPTG). The induced β-galactosidase converts p-aminophenyl β- D-galactopyranoside (PAPG) into p-aminophenol (PAP), which is measured by amperometry using a gold rotating disc electrode. A good linear correlation ( R2=0.989) was obtained between log cfu mL−1 E. coli and the time necessary to product a specific concentration of PAP. Amperometric detection enabled determination of 2×106 cfu mL−1 E. coli within a 30 min incubation period, and the total analysis time was less than 1 h. It was also possible to determine as few as 20 cfu mL−1 E. coli under optimized conditions within 6–7 h. This process may be easily adapted as an automated portable bioanalytical device for the rapid detection of live E. coli. [ABSTRACT FROM AUTHOR]