Au Grid Research Articles

A Sandwich Enzyme Electrode Giving Electrochemical Scavenging of Interferents

A ‘sandwich’ bielectrode system is described for a glucose oxidase amperometric electrode, which uses an outer scavenger electrode to remove ascorbic acid interference from the measurement of enzyme generated hydrogen peroxide. An Au grid electrode is proposed as the scavenger, which can be coated with Teflon (AF 1600), to provide a substrate diffusion limiting barrier and thus extend the linear range of the electrode. A small sample: enzyme ratio is investigated, whereby the glucose from the sample is depleted during the measurement, such that a ‘total’ glucose measurement can be obtained by integration of the current signal. The integrity of the measurements are compared in the presence and absence of ascorbic acid and it is shown that the scavenger electrode is able to remove about 80% of the ascorbate from reaching the inner Pt working electrode. This preliminary system model is briefly tested with samples of lemon juice and the ascorbate interference removal demonstrated.

Polyaniline-based membranes for gas electrodes

Nafion®—PANI and free-standing PANI membranes have been prepared according to literature methods and characterized by cyclic voltammetry and ac impedance. They have then been used for assessing the feasibility of electrochemical reactions at the PANI/gas interface. To this aim the membranes, one face of which bore a vacuum deposited Au grid, were interposed between a gas and an aqueous acid solution. Oxidation of SO 2 and N 2H 4 and reduction of NO 2 and O 2 in the gas phase have been studied.

A scanning photoelectron microscope (SPEM) at the NSLS

We are in the process of developing and commissioning a scanning photoelectron microscopy (SPEM) at the X1A beamline of the National Synchrotron Light Source (NSLS). It is desigend to make use of the Soft X-ray Undulator (SXU) at the NSLS. This high brightness source illuminates a Fresnel zone plate, which forms a focused probe, ⩽0.2 µm in size, on the specimen surface. A grating monochromator selects the photon energy in the 400-800 eV range with an energy resolution of better than 1 eV. The expected flux in the focus is in the 5 × 107-109 photons/s range. A single pass Cylindrical Mirror Analyzer (CMA) is used to record photoemission spectra, or to form an image within a fixed electron energy bandwidth as the specimen is mechanically scanned.As a first test, a 1000 mesh Au grid was successfully imaged with a resolution of about 1 µm and the CMA tuned to the Au 4f photoelectron peak. Once it is commissioned, a program is planned which will utilize the microscope to study beam sensitive systems, such as thin oxide/sub-oxide films of alumina and silica, and ultimately various adsorbates on these films.

Scanning photoelectron microscope with a zone plate generated microprobe

We describe instrumentation of a scanning photoelectron microscope (SPEM), which we are presently developing and commissioning at the X1A beamline of the National Synchrotron Light Source (NSLS). This instrument is designed to use the soft-X-ray undulator (SXU) at the NSLS as a high-brightness source to illuminate a Fresnel zone plate, thus forming a finely focused probe, ≤ 0.2 μm in size, upon the specimen surface. A grating monochromator selects the photon energy in the 400–800 eV range with an energy resolution better than 1 eV. The expected flux in the focus is in the range 5 × 10 7–10 9 photons s −1. A single pass cylindrical mirror analyzer (CMA) is used to record photoemission spectra, or to form an image within a fixed electron energy bandwidth as the specimen is mechanically scanned. As a first test, a 1000-mesh Au grid was successfully imaged with Au 4f primary photoelectrons, achieving a resolution of about 1 μm.

Immunogold labelling of neutral endopeptidase 24.11 (enkephalinase), on human neutrophils and neutrophil cytoplasts

We have documented the presence of neutral endopeptidase 24.11 (NEP), on the surface of human neutrophils (PMN) and PMN cytoplasts. Cytoplasts are whole cell preparations which contain cytomatrix, but lack internal membranes and organelles ,such as nuclei and lysosomal granules. These structures have been extracted mechanically, leaving the plasma membrane “outside-out” topology intact. Cytoplasts are very useful in correlative studies of cell surface structure and function. Biochemically, the membrane component of cytoplasts is predominantly plasma membrane; structurally, chemical activity may be localized to domains of the intact cell surface. NEP is a membrane-bound metalloendopeptidase present in human PMN' s. We have marked NEP on the plasma membranes of PMNs and PMN cytoplasts via pre-embedding iramunocytochemistry. We used scanning electron microscopy (SEM) with backscattered electron imaging (BEI) to visualize Au labelled anti-NEP on the surface of a large number of cells. Transmission electron microscopy (TEM) was used to confirm the presence of the enzyme on PMN's and PMN cytoplasts.Suspensions of PMN or PMN cytoplasts (2 x 106 cells/ml) were fixed for 8 min at room temp. in 0.25% glutaraldehyde in phosphate buffered saline (PBS) pH 7.2 rinsed in PBS, treated with 0.1% glycine in PBS for 10 rain and then incubated for 15 min in 5% normal goat serum (NGS) in 0.1% bovine serum albumin dissolved in PBS (BSA/PBS). Following this step, cells were incubated for 20 min in anti- NEP antibody, rinsed in BSA/PBS, incubated in goat anti-rabbit IgG coupled to 15nm colloidal Au particles (GARG15) for 1 h and again rinsed in PBS. Postfixation for 30 min in 2.5% glutaraldehyde and PBS rinsing followed. For SEM a drop of cell suspension was put on a polylysine- treated Formvar-carbon-coated Au grid and cells were allowed to settle and attach for 30 min. The grid was rinsed in water, dehydrated and critical point dried. Cells were coated with carbon before viewing by SEM. For TEM, following immunolabelling, cells were post-fixed in OsO4, rinsed, dehydrated and embedded in Epon for sectioning.