Theoretical evaluation of a fiber-optic SPR biosensor based on a gold layer treated with thiol acid

In the present work, we have investigated the surface plasmons resonance (SPR) biosensor based on optical fiber applied for the detection of pathogenic bacteria (Escherichia coli), in order to overcome the stresses caused by the massive prism and to obtain a reliable and efficient miniature device. The modeling procedure is based on a matrix formalism developed for the optical studies of multilayer media. We have tested the response of the fiber optic biosensor based on a golden substrate functionalized with thiol acid. The results show that the SPR biosensor sensitivity is improved by treating the gold electrode with thiol. An improved SPR biosensor with a high resolution is obtained.

The Low Temperature Properties of Natural Rubber as Affected by Reaction with Thiol Acids

It has been demonstrated that the tendency of natural rubber to crystallize at low temperatures can be considerably reduced by the reaction of natural rubber with relatively small quantities of a thiol acid of the RCOSH type. Most thiol acids react already at room temperature with natural rubber. The reaction is very easy to carry out. A simple admixture with dry natural rubber, e.g., on a mixing mill or in an internal mixer, is sufficient. The reaction can also be carried out in solution or in latex. If amounts of thiol acids are used which do not exceed 1 mole %, pure gum vulcanizates can be obtained which show a strongly reduced tendency to crystallize and which nevertheless show a tensile strength of more than 150 kg/cm2. This may be explained by the fact that these rubbers still show appreciable crystallization upon stretching to elongation approaching the elongation at break, as indicated by the x-ray diffraction patterns of the stretched vulcanizates. If the thiol acid rubber vulcanizates are reinforced with carbon blacks, the tensile and tear strengths are much improved. Vulcanizates with very satisfactory room temperature properties are thus obtained, whilst the improved resistance to crystallization is retained, The abrasion resistance and the aging resistance are at least as good as those of comparable vulcanizates of unmodified natural rubber. If low temperature plasticizers are mixed into thiol acid rubbers, the glass point of the vulcanizates can be strongly reduced. TR 10 values as low as −80° C in pure gum vulcanizates and −69° C in carbon-loaded vulcanizates have been obtained. These rubbers, moreover, did not show any crystallization at low temperatures.

Crystallization in Natural Rubber. V. Chemically Modified Rubber

Small amounts of crosslinking have been shown to reduce the rate of crystallization of natural rubber by large factors. It has also been inferred from measurements on peroxide and sulfur vulcanizates of various kinds that sulfur combined in forms other than crosslinks may retard the crystallization process efficiently. A simple banned volume mechanism has been proposed to account for the influence of crosslinking and sidegroup combination on the rate and final extent of crystallization, and has been shown to predict the form of the observed dependences for crosslinked rubber, and approximately the relative magnitudes, but good quantitative agreement was not obtained. Measurements are described below of the rate and final extent of crystallization in natural rubber which has been modified by the chemical combination of sidegroups to the rubber molecule. It has not proved possible to account quantitatively for the observed rates of crystallization, but it is thought that a description of the extremely large effects found to accompany slight chemical modifications will be of general interest. The preparation of the modified rubbers is described elsewhere. The substances added were six thiol acids; namely, monochlorothiolacetic, trichlorothiolacetic, thiolbenzoic, 1-thiolnaphthoic, thiolsalicylic, and thiol-stearic acids. The reactions were carried out in the solid phase by addition of the thiol acid to purified rubber on an open mill, in solution by addition of the thiol acid to a solution of purified rubber in benzene, and in the latex phase.