Low-cost PCB-integrated polymer waveguide sensor for gas detection

An optical waveguide sensor formed directly on low-cost PCB substrates is presented for the first time. The device integrates polymer waveguides functionalized with chemical dyes, photonic and electronic components and allows multiple-gas detection. © 2011 OSA.

Interfacial immobilization of monoclonal antibody and detection of human prostate-specific antigen.

Antibody orientation and its antigen binding efficiency at interface are of particular interest in many immunoassays and biosensor applications. In this paper, spectroscopic ellipsometry (SE), neutron reflection (NR), and dual polarization interferometry (DPI) have been used to investigate interfacial assembly of the antibody [mouse monoclonal anti-human prostate-specific antigen (anti-hPSA)] at the silicon oxide/water interface and subsequent antigen binding. It was found that the mass density of antibody adsorbed at the interface increased with solution concentration and adsorption time while the antigen binding efficiency showed a steady decline with increasing antibody amount at the interface over the concentration range studied. The amount of antigen bound to the interfacial immobilized antibody reached a maximum when the surface-adsorbed amount of antibody was around 1.5 mg/m(2). This phenomenon is well interpreted by the interfacial structural packing or crowding. NR revealed that the Y-shaped antibody laid flat on the interface at low surface mass density with a thickness around 40 Å, equivalent to the short axial length of the antibody molecule. The loose packing of the antibody within this range resulted in better antigen binding efficiency, while the subsequent increase of surface-adsorbed amount led to the crowding or overlapping of antibody fragments, hence reducing the antigen binding due to the steric hindrance. In situ studies of antigen binding by both NR and DPI demonstrated that the antigen inserted into the antibody layer rather than forming an additional layer on the top. Stability assaying revealed that the antibody immobilized at the silica surface remained stable and active over the monitoring period of 4 months. These results are useful in forming a general understanding of antibody interfacial behavior and particularly relevant to the control of their activity and stability in biosensor development.

Dynamic modulation of detection window in conducting polymer based biosensors.

Here we demonstrate a novel application that employs the ion exchange properties of conducting polymers (CP) to modulate the detection window of a CP based biosensor under electrical stimuli. The detection window can be modulated by electrochemically controlling the degree of swelling of the CP associated with ion transport in and out of the polymer. We show that the modulation in the detection window of a caffeine imprinted polypyrrole biosensor, and by extension other CP based biosensors, can be achieved with this mechanism. Such dynamic modulation in the detection window has great potential for the development of smart biosensors, where the sensitivity of the sensor can be dynamically optimized for a specific test solution.

Detection of molecular interactions with modified ferrocene self-assembled monolayers.

Ferrocene-terminated self-assembled monolayers (Fc-SAMs) are one of the most studied molecular aggregates on metal electrodes. They are easy to fabricate and provide a stable and reproducible system to investigate the effect of the microenvironment on the electron transfer parameters. We propose a novel application for Fc-SAMs, the detection of molecular interactions, based on the modification of the SAM with target-specific receptors. Mixed SAMs were fabricated by coimmobilization on Au electrodes of thiolated alkane chains with three different head groups: hydroxy terminating head group, ferrocene head group, and a functional head group such as biotin. Upon binding, the intrinsic electric charge of the target (e.g., streptavidin) modifies the electrostatic potential at the plane of electron transfer, causing a shift in the formal potential E degrees '. The SAMs were characterized by AC voltammetry. The detection mechanism is confirmed by measurements of formal potential as a function of electrolyte pH.

Porphyrin detection in denatured cnidarian tissue extracts

Porphyrin metabolic disruption from exposure to xenobiotic contaminants such as heavy metals, dioxins, and aromatic hydrocarbons can elicit overproduction of porphyrins. Measurement of porphyrin levels, when used in conjunction with other diagnostic assays, can help elucidate an organism’s physiological condition and provide evidence for exposure to certain toxicants. A sensitive microplate fluorometric assay has been optimized for detecting total porphyrin levels in detergent solubilized protein extracts from symbiotic, dinoflagellate containing cnidarian tissues. The denaturing buffer used in this modified assay contains a number of potentially interfering components (e.g., sodium dodecyl sulfate (SDS), dithiothreitol (DTT), protease inhibitors, and chlorophyll from the symbiotic zooxanthellae), which required examination and validation. Examination of buffer components were validated for use in this porphyrin assay; while the use of a specific spectrofluorometric filter (excitation 400 ± 15 nm; emission 600 ± 20 nm) minimized chlorophyll interference. The detection limit for this assay is 10 fmol of total porphyrin per μg of total soluble protein and linearity is maintained up to 5000 fmol. The ability to measure total porphyrins in a SDS protein extract now allows a single extract to be used in multiple assays. This is an advantage over classical methods, particularly when tissue samples are limiting, as is often the case with coral due to availability and collection permit restrictions.