Waveguide surface plasmon resonance biosensor for the aqueous environment

We report the fabrication and performance of gold coated waveguide surface plasmon resonance biosensors. Biotin-avidin binding reactions at the sensor surface were observed. The output power of the sensor showed a decrease of 32% on binding a dual layer of biotin-avidin

Study of luminol electrochemiluminescence with a planar optical waveguide for peroxide sensor application

The work presented in this paper is aiming at the development of a highly sensitive, specific, cheap and widely applicable new sensor based on the combination of optical and electrochemical techniques. In addition to the analytically valuable information of light intensity generated, the light transient resulting from a double potential step experiment contains kinetic information for both the electrochemical step as well as for the successive diffusion and chemical steps in the reaction layer. The comparison of transients due to short range waveguide-evanescent field coupling as shown in Fig. 2 and those obtained by measuring light over the full depth of the diffusion layer in Fig. 3 can be used to obtain such information

Second harmonic generation response by gold nanoparticles at the polarized water/2-octanone interface: from dispersed to aggregated particles

Gold nanoparticles with a diameter of approximately 20 nm have been observed at the polarized water/2-octanone interface by the nonlinear optical technique of second harmonic generation. Electric field induced adsorption of the gold particles at this liquid/liquid interface is clearly observed and confirms that these are negatively charged. The process is quasi-reversible at high potential sweep rates, but aggregation at the interface is observed at slower sweep rates through the loss of the nonlinear optical signal. The time evolution of the second harmonic signal is also reported during potential step experiments. After a rapid increase due to adsorption, a continuous decrease in the nonlinear optical signal intensity is observed due to aggregation of the particles into large islands at the interface. Diffusion of these large islands at the interface was observed for a longer timescale through large signal fluctuations

Vascular Remodeling in Health and Disease

The term vascular remodeling is commonly used to define the structural changes in blood vessel geometry that occur in response to long-term physiologic alterations in blood flow or in response to vessel wall injury brought about by trauma or underlying cardiovascular diseases.1, 2, 3, 4 The process of remodeling, which begins as an adaptive response to long-term hemodynamic alterations such as elevated shear stress or increased intravascular pressure, may eventually become maladaptive, leading to impaired vascular function. The vascular endothelium, owing to its location lining the lumen of blood vessels, plays a pivotal role in regulation of all aspects of vascular function and homeostasis.5 Thus, not surprisingly, endothelial dysfunction has been recognized as the harbinger of all major cardiovascular diseases such as hypertension, atherosclerosis, and diabetes.6, 7, 8 The endothelium elaborates a variety of substances that influence vascular tone and protect the vessel wall against inflammatory cell adhesion, thrombus formation, and vascular cell proliferation.8, 9, 10 Among the primary biologic mediators emanating from the endothelium is nitric oxide (NO) and the arachidonic acid metabolite prostacyclin [prostaglandin I2 (PGI2)], which exert powerful vasodilatory, antiadhesive, and antiproliferative effects in the vessel wall

Plasmon interactions between gold nanoparticles in aqueous solution with controlled spatial separation

The effects of interparticle distance on the UV-visible absorption spectrum of gold nanocrystals aggregates in aqueous solution have been investigated. The aggregates were produced by ion-templated chelation of ω- mercaptocarboxylic acid ligands covalently attached to the nanoparticles surface. Variation of the ligand chain length provides control over the interparticle separation in the aggregates. The UV-visible spectra consist typically of a single particle band and a secondary band at higher wavelengths associated with the formation of aggregates in solution. The position of the latter depends on interparticle separation up to distances of ∼8 nm, in accordance with existing models. Potential applications therefore include distance sensitive labels or proximity probes. Conversely, variation of the ligand length allows the preparation of nanostuctured materials with tuned optical properties. © the Owner Societies 2006

Optoelectrochemical sensor for lead based on electrochemically-assisted solvent extraction

A thin film containing the complexing agent 2-(5-bromo-2-pyridylazo)-5-(diethylamino)phenol (BrPADAP) deposited on the surface of an indium tin oxide (ITO) electrode has been used as a colorimetric sensor for lead. The sensor is based on a new electrochemically assisted solvent extraction method. When a cathodic potential was applied to the thin-film sensing layer, lead ions were extracted from the aqueous solution into the film resulting in an increase of absorbance at 550 nm. The magnitude of the absorbance change was linearly dependent on the concentration of lead in the range 0–5 ppm with an estimated limit of detection for a simple spectrophotometric method better than 250 ppb. The sensor was reset for a fresh measurement by applying an anodic potential. The prospects for using this electroassisted extraction method in conjunction with the optical waveguide evanescent field detection as a new integrated sensor for trace analysis are discussed. A sensitivity better than 10 ppb is predicted for this configuration

Electrochemically controlled optical waveguide sensors

Optical techniques are at the forefront of modern analytical methods due to their inherent high specificity. From the point of view of sensor technology, the transfer of chemical information into a measurable signal is of utmost importance. In this respect, planar optical waveguides show great promise for realising novel chemical and biological sensors which use evanescent fields to probe specifically sensitised films on the waveguide surface. Such sensors may detect changes in the refractive index of films using, for example, surface plasmon resonance (SPR) [1], light emission from the binding of proteins labelled with fluorophores [2], or the change in absorption spectrum of a film caused by a chemical reaction [3]. The use of photolithography in integrated optics technology allows mass production of complex multisensors on small and robust substrates. Electrochemical methods allow electrical resetting of reactions, or improved sensitivity through phase-sensitive detection

Detection of glucose via electrochemiluminescence in a thin-layer cell with a planar optical waveguide

Light generated by luminol electrochemiluminescence is coupled into a simple planar optical waveguide and is collected with a photomultiplier tube and a photon counter unit. The waveguide is mounted to a thin-layer cell which is connected to a flow injection analysis system. The waveguide is coated with indium tin oxide and modified with covalently attached glucose oxidase. The range of detection for glucose is 0-10 mM (correlation coefficient r = 0.9974), with a detection limit of 0.3 mM