Development of label-free detection systems targeting food-borne pathogens

Food-borne pathogens and food safety-related outbreaks have come to the forefront over recent years. Estimates on the annual cost of sicknesses, hospitalizations, and deaths run into the billions of dollars. There is a large body of research on the subject of detection of food-borne pathogens, however, the widely accepted current systems are limited by high reagent costs, lengthy time to completion, and expensive equipment. This work has been developed with the goal of focusing on minimizing the time and reagent cost of two of the most common types of rapid, food-borne pathogen detection systems, i.e. immunoassays and real-time polymerase chain reaction assays. The first aim was to develop the proof-of-concept methodology for a label-free immunoassay technique utilizing photonic crystal biosensors targeting bacteria, specifically E. coli O157:H7. In this project, it is shown that detergent-lysing of the cells and extraction of their membrane antigens allows for the detection of down to 1E7 CFU/mL. Optimization of the blocking scheme takes the assay one step further and allows for specific detection of E. coli O157:H7 over E. coli K12. The second aim was to develop a label-free method for determining changes in DNA concentration as it relates to food-borne pathogen-targeted polymerase chain reaction assays. For this goal, impedance spectroscopy studies were carried out to characterize the system???s capability in determining changes in concentration of purified DNA in DI water. To adequately measure the change in DNA concentration in a PCR solution, it was necessary to go through a purification and precipitation step to minimize the effects of primers, PCR reagents, and especially excess salts. It was shown that the purification and precipitation of the fully amplified PCR reaction showed a similar trend to the pure DNA in DI water characterization tests. In developing the two versions of label-free detection systems, this work has brought cheaper, faster, smaller biosensors one step closer to reality

Substitution effects on the temperature vs. magnetic-field phase diagrams of the quasi-1D effective Ising spin-1/2 chain system BaCo2_2V2_2O8_8

BaCo$_2$V$_2$O$_8$ is a one-dimensional antiferromagnetic spin-1/2 chain system with pronounced Ising anisotropy of the magnetic exchange. Due to finite interchain interactions long-range antiferromagnetic order develops below $T_{\rm N} \simeq 5.5$ K, which is accompanied by a structural distortion in order to lift magnetic frustration effects. The corresponding temperature $vs.$ magnetic-field phase diagram is highly anisotropic with respect to the magnetic-field direction and various details are still under vivid discussion. Here, we report the influence of several substitutions on the magnetic properties and the phase diagrams of BaCo$_2$V$_2$O$_8$. We investigate the substitution series Ba$_{\text{1-x}}$Sr$_{\text{x}}$Co$_{\text{2}}$V$_{\text{2}}$O$_{\text{8}}$ over the full range $0\le x \le 1$ as well as the influence of a partial substitution of the magnetic Co$^{2+}$ by small amounts of other magnetic transition metals or by non-magnetic magnesium. In all cases, the phase diagrams were obtained on single crystals from magnetization data and/or high-resolution studies of the thermal expansion and magnetostriction.Comment: 10 pages, 10 figure

Considerations on using SU-8 as a construction material for high aspect ratio structures

This paper discusses two material aspects of SU-8 that have up till now been insufficiently documented. We present initial results on the outgassing behavior and a study on the dielectric properties of SU-8 at high bias voltage. The dielectric strength is determined to be at least 2 MV/cm. These elements are investigated in the light of plans to manufacture an SU-8 based Micro-Channel Plate (MCP). Although the outgassing properties and dielectric strength are favorable the patterning capabilities are expected to limit the use of such an MCP