Biomedical subjects

Sean J O'Shea

Publications and source records attributed to Sean J O'Shea.

4 recordsLinked to original sources

PubMed2006

Combinational application of surface plasmon resonance spectroscopy and quartz crystal microbalance for studying nuclear hormone receptor-response element interactions.

Conventional methodologies for studying protein-DNA complexes, such as electrophoretic mobility shift assays (EMSAs), lack the real-time sensitivity and precision to accurately characterize the complex dynamics of interactions between transcription factors and their binding sites. To better understand the interactions between estrogen receptor (ER) subtypes and the estrogen response elements (EREs), we employed surface plasmon resonance (SPR) spectroscopy and quartz crystal microbalance with dissipation measurement (QCM-D) and made the following observations: (1) base substitutions in ERE half-sites reduced binding affinity for both ERalpha and ERbeta, (2) ERalpha has a higher sequence specificity than ERbeta or there were more nonspecific interactions between ERbeta and control DNA, and (3) ERalpha bound ERE as dimers and ERbeta bound as tetramers. These findings highlight intrinsic differences in DNA-binding properties between receptor subtypes, which are not apparent based on the high degree of conservation (96% identity) in their DNA-binding domains and results from EMSA studies. With this study, we demonstrate the potential of utilizing SPR and QCM in combination for a comprehensive characterization of ER-DNA interactions, including sequence-dependent binding mechanisms and structural differences in ERalpha-DNA and ERbeta-DNA complexes.

DNA↗

PubMed2006

Direct adsorption and monolayer self-assembly of acetyl-protected dithiols.

The alpha,omega-dithiols, with sulfur-containing groups at both ends of the molecules, can be used to bridge a metallic gap. Functional self-assembled monolayers (SAMs) of these dithiols must "stand up" on the surface and expose one thiol group for further reaction. However, both parallel and upright surface orientations and multilayer formation can occur for alpha,omega-dithiols. We find SAMs deposited directly from acetyl protected dithiols (i.e., with no de-protection step) overcome these problems. We present a systematic study of adsorption kinetics from in situ surface plasmon resonance spectroscopy, X-ray photoelectron spectroscopy, and secondary ion mass spectroscopy of alkane- and oligo(phenylene ethylnylene)-based alpha,omega-dithioacetates on gold.

Journal Article↗

PubMed2003

Frequency interference between two mesa-shaped quartz crystal microbalances.

The multichannel quartz crystal microbalance (MQCM) is very attractive for biosensor applications. The principle of the MQCM design involves fabricating arrays of quartz microbalances on a single substrate, and it is important that the individual sensor performance is not influenced by the neighboring devices. Feasible ways to control the coupling of acoustical energy within a MQCM structure are to increase the difference in the resonance frequency between the electroded and unelectroded portions of the substrate; and a practical way to achieve this is to use mesa structures. In this paper, the frequency interference between two mesa-shaped quartz crystal microbalances is investigated using Mindlin's theory. The results show that even a very small mesa height (approximately 5% of the plate thickness) can greatly reduce the frequency interference and more effectively trap the acoustic energy. This allows for a broader design window and higher packing density for MQCM applications.

Biosensing Techniques↗

PubMed2002

Quartz tuning fork biosensor.

The use of quartz tuning forks for biosensor applications is investigated. The basis of the sensor is to coat the tuning fork surfaces with specific biomolecules and measure subsequent mass loading from the selective binding of complementary analytes. Two experimental set-ups are evaluated, direct mechanical excitation and self-excitation. Mechanical excitation is achieved by mounting the fork on a piezoelectric plate and it is found that the change in oscillation amplitude on adsorption can be monitored to give the change in mass. However, a major drawback is that the sensitivity is determined by the Q-factor, which varies significantly between different sensors and different experimental arrangements. In self-excitation mode, tuning fork motion is activated and detected by placing the fork within a tuned circuit. Using self-excitation mode, anti-human IgG modified tuning forks can sense the binding of human IgG in the range of 5-100 microg ml(-1). The significance of this study is that quartz tuning forks are routinely made using standard microfabrication process, thus suggesting the possibility of facile microfabrication of arrays of quartz sensors.

Audiometry↗