Top-Down Nanofabrication and Characterization of 20 nm Silicon Nanowires for Biosensing Applications

A top-down nanofabrication approach is used to develop silicon nanowires from silicon-on-insulator (SOI) wafers and involves direct-write electron beam lithography (EBL), inductively coupled plasma-reactive ion etching (ICP-RIE) and a size reduction process. To achieve nanometer scale size, the crucial factors contributing to the EBL and size reduction processes are highlighted. The resulting silicon nanowires, which are 20 nm in width and 30 nm in height (with a triangular shape) and have a straight structure over the length of 400 μm, are fabricated precisely at the designed location on the device. The device is applied in biomolecule detection based on the changes in drain current (I_ds), electrical resistance and conductance of the silicon nanowires upon hybridization to complementary target deoxyribonucleic acid (DNA). In this context, the scaled-down device exhibited superior performances in terms of good specificity and high sensitivity, with a limit of detection (LOD) of 10 fM, enables for efficient label-free, direct and higher-accuracy DNA molecules detection. Thus, this silicon nanowire can be used as an improved transducer and serves as novel biosensor for future biomedical diagnostic applications.     

Determination of adenosine 3',5'-cyclic monophosphate levels in tissues of the free living nematode, Panagrellus redivivus.

1. Tissue levels of adenosine 3', 5'-cyclic monophosphate (c-AMP) were determined by a protein binding assay in mixed populations of the free living nematode Panagrellus redivivus. 2. The values were 2.6 pmoles/mg dry weight (range 1.3-3.4 pmoles). 3. The identity of the c-AMP assayed was confirmed by both anion exchange and TLC as well as enzymatic degradation.     

Self-aggregation, a new property of cardiac fatty acid-binding protein. Predictable influence on energy production in the heart

The binding isotherm of 2-(10-carboxydecyl)-2-hexyl-4,4-dimethyl-3-oxyloxazolidine to the 12,000 molecular weight cytoplasmic fatty acid-binding protein purified from pig's heart and as analyzed by electron spin resonance is shown to be sigmoidal and dependent on protein concentration. Its maximum binding capacity, Vmax, is 9.81 microM X g-1 when the protein concentration is 1.98 g . liter-1 and 14.33 microM . g-1 when the concentration is 0.198 g . liter-1. The molar ellipticity, theta, measured by circular dichroism at 225 nm in the protein range of 0.2-3 g . liter-1 is also shown to depend on concentration, with two maxima at 1.7 and 1.2 g . liter-1. The rotational correlation time, tau eff, of a spin-labeled N-(2,2,5,5-tetramethyl-3-carbonyl-pyrroline-1-oxyl)imidazole specifically bound to tyrosine residues of the protein surface, as analyzed by electron spin resonance, is decreasing as a function of protein concentration. To account for these three concentration-dependent variations, we suggest that the protein self-aggregates since these variations will not be found if the protein is monomeric. A very significant influence of this aggregation property of the protein on the activity of fatty acid-dependent membrane-bound enzymes is predicted by a model analysis and, thus, should be considered as a new parameter in the control of energy production in the heart.     

Determination of guanosine 3',5'-cyclic-monophosphate in tissues of the free living nematode, Panagrellus redivivus.

1. Tissue levels of guanosine 3',5'-cyclic monophosphate (c-GMP) were determined by radioimmunoassay in mixed-age populations of the free living nematode Panagrellus redivivus. 2. Cyclic-GMP was identified by chromatography (ion exchange and thin-layer) and by enzymatic degradation.     

Electrochemical-based biosensors for detection of Mycobacterium tuberculosis and tuberculosis biomarkers

Abstract

Early detection of tuberculosis (TB) reduces the interval between infection and the beginning of treatment. However, commercially available tests cannot discriminate between BCG-vaccinated healthy persons and patients. Also, they are not suitable to be used for immunocompromised persons. In recent years, biosensors have attracted great attention due to their simple utility, accessibility, and real-time outputs. These sensors are increasingly being considered as pioneering tools for point-of-care diagnostics in communities with a high burden of TB and limited accessibility to reference laboratories. Among other types of biosensors, the electrochemical sensors have the advantages of low-cost operation, fast processing, simultaneous multi-analyte analyzing, operating with turbid samples, comparable sensitivity and readily available miniaturization. Electrochemical biosensors are sub-divided into several categories including: amperometric, impedimetric, potentiometric, and conductometric biosensors. The biorecognition element in electrochemical biosensors is usually based on antibodies (immunosensors), DNAs or PNAs (genosensors), and aptamers (aptasensors). In either case, whether an interaction of the antigen–antibody/aptamer or the hybridization of probe with target mycobacterial DNA is detected, a change in the electrical current occurs that is recorded and displayed as a plot. Therefore, impedimetric-based methods evaluate resistance to electron transfer toward an electrode by a Nyquist plot and amperometric/voltammetric-based methods weigh the electrical current by means of cyclic voltammetry, square wave voltammetry, and differential pulse voltammetry. Electrochemical biosensors provide a promising scope for the new era of diagnostics. As a consequence, they can improve detection of Mycobacterium tuberculosis traces even in attomolar scales.     

Palaeoenvironment shifts during last ~ 500 years and eutrophic evolution of the Wular Lake,Kashmir Valley,India

Limnology - Multi-proxy analysis of lake sediments provides high-resolution and reliable palaeoclimate records. The present study aims to investigate the palaeoenvironmental changes and eutrophic...