Janelle L. Coutts

A One-Step Homogeneous Immunoassay for Cancer Biomarker Detection Using Gold Nanoparticle Probes Coupled with Dynamic Light Scattering

A one-step homogeneous immunoassay for the detection of a prostate cancer biomarker, free-PSA (prostate specific antigen), was developed using gold nanoparticle probes coupled with dynamic light scattering (DLS) measurements. A spherical gold nanoparticle with a core diameter around 37 nm and a gold nanorod with a dimension of 40 by 10 nm were first conjugated with two different primary anti-PSA antibodies and then used as optical probes for the immunoassay. In the presence of antigen f-PSA in solution, the nanoparticles and nanorods aggregate together into pairs and oligomers through the formation of a sandwich type antibody-antigen-antibody linkage. The relative ratio of nanoparticle-nanorod pairs and oligomers versus individual nanoparticles was quantitatively monitored by DLS measurement. A correlation can be established between this relative ratio and the amount of antigen in solution. The light scattering intensity of nanoparticles and nanoparticle oligomers is several orders of magnitude higher than proteins and other typical molecules, making it possible to detect nanoparticle probes in the low picomolar concentration range. f-PSA in the concentration range from 0.1 to 10 ng/mL was detected by this one-step and washing-free homogeneous immunoassay.

A One-Step Highly Sensitive Method for DNA Detection Using Dynamic Light Scattering

A one-step homogeneous DNA detection method with high sensitivity was developed using gold nanoparticles (AuNPs) coupled with dynamic light scattering (DLS) measurement. Citrate-protected AuNPs with a diameter of 30 nm were first functionalized with two sets of single-stranded DNA probes and then used as optical probes for DNA detection. In the presence of target DNA, the hybridization between target DNA and the two nanoparticle probes caused the formation of nanoparticle dimers, trimers, and oligomers. As a result, the nanoparticle aggregation increased the average diameter of the whole nanoparticle population, which can be monitored simply by DLS measurement. A quantitative correlation can be established between the average diameter of the nanoparticles and the target DNA concentration. This DLS-based assay is extremely easy to conduct and requires no additional separation and amplification steps. The detection limit is around 1 pM, which is 4 orders of magnitude better than that of light-absorption-based methods. Single base pair mismatched DNAs can be readily discriminated from perfectly matched target DNAs using this assay.

The use of mechanical alloying for the preparation of palladized magnesium bimetallic particles for the remediation of PCBs

The kinetic rate of dechlorination of a polychlorinated biphenyl (PCB-151) by mechanically alloyed Mg/Pd was studied for optimization of the bimetallic system. Bimetal production was first carried out in a small-scale environment using a SPEX 8000M high-energy ball mill with 4-μm-magnesium and palladium impregnated on graphite, with optimized parameters including milling time and Pd-loading. A 5.57-g sample of bimetal containing 0.1257% Pd and ball milled for 3 min resulted in a degradation rate of 0.00176 min(-1)g(-1) catalyst as the most reactive bimetal. The process was then scaled-up, using a Red Devil 5400 Twin-Arm Paint Shaker, fitted with custom plates to hold milling canisters. Optimization parameters tested included milling time, number of ball bearings used, Pd-loading, and total bimetal mass milled. An 85-g sample of bimetal containing 0.1059% Pd and ball-milled for 23 min with 16 ball bearings yielded the most reactive bimetal with a degradation rate of 0.00122 min(-1)g(-1) catalyst. Further testing showed adsorption did not hinder extraction efficiency and that dechlorination products were only seen when using the bimetallic system, as opposed to any of its single components. The bimetallic system was also tested for its ability to degrade a second PCB congener, PCB-45, and a PCB mixture (Arochlor 1254); both contaminants were seen to degrade successfully.

Review on Transforming TiO 2 into a Visible-Light- Responsive Catalyst for Water and Air Purification

Photocatalytic oxidation (PCO) of organic contaminants is a promising air and water quality management technique which offers energy and cost savings compared to thermal catalytic oxidation (TCO). The most widely used photocatalyst, anatase TiO2, has a wide band gap (3.2 eV) requiring UV photons to activate it. Solar radiation consists of ~4-6% UV and 45% visible light at the Earth’s surface. Therefore, catalysts capable of utilizing these visible photons need to be developed to make PCO approaches more efficient, economical, and safe. Many approaches have been taken to make TiO2 visible-light-active (VLA) with varied degrees of success. Strategies attempted thus far fall into three categories based on their electrochemical mechanisms: 1) photosensitizing TiO2 with Dyes; 2) altering the band gap of TiO2; and 3) coupling TiO2 with a narrow band gap semiconductor. There are diverse technical approaches to implement each of these strategies. This paper presents a brief review of these approaches and their outcomes in terms of the photocatalytic activity and photonic efficiency of the resulting products under visible light. Although resulting visible-light-responsive (VLR) photocatalysts show promise, there is very few comparative studies on the performance of unmodified TiO2 under UV and the modified TiO2 under visible light. It was found that the UV-induced catalytic activity of unmodified TiO2 is much greater than the visible-light-induced catalytic activity of the VLR catalyst at the current state of technology. Furthermore, VLR-catalysts have much lower quantum efficiency than UV-catalysts. This stresses the need for continuing research in this area.