We investigated the electrochemical detection of aspartate transaminase (AST) and alanine transaminase (ALT) by using a multienzyme-modified electrode surface. Determination of the activities of transaminases in human serum is clinically significant because their concentrations and ratios indicate the presence of hepatic diseases or myocardial dysfunction. For electrochemical detection of AST and ALT, enzymes that participate in the reaction mechanism of AST and ALT, such as pyruvate oxidase (POX) and oxaloacetate decarboxylase, were immobilized on an electrode surface by using an amine-reactive self-assembled monolayer and a homobifunctional cross-linker. In the presence of suitable substrates such as L-aspartate (L-alanine) and α-ketoglutarate, AST and ALT generate pyruvate as an enzymatic end product. To determine the activities of AST and ALT, electroanalyses of pyruvate were conducted using a POX and ferrocenemethanol electron shuttle. Anodically generated oxidative currents from multienzyme-mediated reactions were correlated to AST and ALT levels in human plasma. On the basis of the electrochemical analysis, we obtained calibration results for AST and ALT concentrations from 7.5 to 720 units/L in human plasma-based samples, covering the required clinical detection range.

This paper presents the development of a reliable multi-liquid lab-on-a-chip (LOC), with a hand-operated mechanism, for the application in portable immunosensing systems. To control the transport of multiple liquids without any external equipment, we utilize capillary attraction force for filling and surface tension for stopping liquid flow. As a driving force, hydraulic pressure caused by the elastic deformation of a liquid reservoir transfers liquid stopped at passive valves. The proposed LOC successfully demonstrates a reliable sequential liquid transfer within the reaction channel. To highlight its feasibility as a portable diagnostic system, we performed the electrochemical immunoassay measuring antibody concentrations within the fabricated LOC. As a test biorecognition reaction, the anti-dinitrophenyl (DNP) antibody with an enzymatic catalysis was selected as the target analyte. The amplified signals obtained from this experiment indicated a high selectivity of the immunosensing LOC.

This paper presents the development of a hand-operated lab-on-a-chip (LOC) with latch mechanism for portable immunosensing applications. To control the transportation of multiple liquids without any external equipment, a capillary attraction force is used for filling liquid. Hydraulic pressure which is caused by the elastic deformation of the cover caps of the reservoir is used for exchanging liquids in the reaction channel. To prevent unwanted backward flow, the latches of the LOC, which consist of reversed mushroom-shaped elastic cover caps and rigid locking components, are used to retain the internal pressure in the reservoir. The electrochemical immunoassay measuring antibody concentrations are performed within the fabricated LOC to highlight its portability to be used as a diagnostic system. The immunosening mechanism applied to this LOC is the electrochemical signaling from the antigen-antibody interaction with the bioelectrocatalyzed enzymatic signal amplification. The proposed signaling strategy is based on the backfilling method, which does not require any complicated processes such as antibody labeling steps or any labeled secondary antibodies. As a modeling test of the immunoassay, the anti-dinitrophenyl (DNP) antibody with an enzymatic catalysis was selected as the target analyte.

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