Ion-sensitive field-effect transistors (ISFETs), although they have attracted considerable attention as effective immunosensors, have still not been adopted for practical applications owing to several problems: (1) the poor sensitivity caused by the short Debye screening length in media with high ion concentration, (2) time-consuming preconditioning processes for achieving the highly-diluted media, and (3) the low durability caused by undesirable ions such as sodium chloride in the media. Here, we propose a highly sensitive immunosensor based on a self-amplified transistor under dual gate operation (immuno-DG ISFET) for the detection of hepatitis B surface antigen. To address the challenges in current ISFET-based immunosensors, we have enhanced the sensitivity of an immunosensor by precisely tailoring the nanostructure of the transistor. In the pH sensing test, the immuno-DG ISFET showed superior sensitivity (2085.53 mV per pH) to both standard ISFET under single gate operation (58.88 mV per pH) and DG ISFET with a non-tailored transistor (381.14 mV per pH). Moreover, concerning the detection of hepatitis B surface antigens (HBsAg) using the immuno-DG ISFET, we have successfully detected trace amounts of HBsAg (22.5 fg mL(-1)) in a non-diluted 1× PBS medium with a high sensitivity of 690 mV. Our results demonstrate that the proposed immuno-DG ISFET can be a biosensor platform for practical use in the diagnosis of various diseases.
Seamless tubing of C-250 maraging steel manufactured by the flow forming technique was joined by the electron beam welding process. Various post-welding heat treatments were conducted to improve the overall mechanical properties of the welded tubing. For the 480uC/6 h/air cooling post-weld aging treated maraging steel, a significant increment of 11% reversion austenite was present in the weld metal. Only the tensile strength of this aging treated metal met the required specification while its percentage elongation reached only 50% of the specification, attaining only 35% of the strength of the parent metal. For the post-welded solutionzaging treated maraging steel, only the yield strength met the specification. Moreover, a significant amount of reversion austenite pools was also present at the grain boundaries of the material located at the weld metal. Although the homogenisation treatment could improve the hardness of the weld metal, it failed to have the tensile strength of the steel met the specification.
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