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Microfluidic devices have been demonstrated to be able to concentrate low-abundance analytes and to be integrated in point of care (POC) devices for the purpose of reducing equipment size and cost; however, the complications involved in the fabrication of microfluidic chips or microelectrodes can be challenging. Here, we present a simple and effective microfluidic device monolithically integrated with liquid metal-based microelectrodes for the transportation and concentration of molecules in dilute solutions. Numerical and experimental studies were combined to validate and optimize the performance of the presented co-designing microfluidic chip featured by a double T-shaped manifold microchannel, in which the electrokinetically induced pressure-driven flow and concentration process were fully characterized. The microfluidic chip was used in a fluorimetric assay based on fluorescence resonance energy transfer between the fluorophore labeled aptamer and molybdenum disulfide nanosheets for the detection of cortisol, a stress biomarker of humans. Both experimental and numerical results show that a concentration factor up to 83-fold can be achieved within 5 min. By avoiding cumbersome fabrication processes and mechanical equipment, the proposed co-designing concentrating strategy provides insights for the fabrication of compact microfluidic chips that facilitate the miniaturization of POC devices with enhanced detection limit and sensitivity. [ABSTRACT FROM AUTHOR]

Electrokinetics is a good fluid control tool in microfluidics and usually microelectrodes play important roles in such approach such as generating a desired electric field. Though the fabrication of two-dimensional (2D) microelectrodes has been relatively mature, they cannot generate uniform electric field in space. Three-dimensional (3D) microelectrodes developed more recently may solve the problem, however the fabrication process is usually complicated and requires micro-alignment platform. Non-toxic liquid metal is a good material for making electrodes that has been introduced into microfluidics. It can be injected directly into a microchannel to form an electrode, but its special physical properties make the injection process complex and difficult to control. In this study, we investigated an optimized manufacturing method of liquid metal microelectrode in a microchip by numerical analysis and experimental study. High quality microelectrodes on morphology and stability were successfully fabricated. A fluorescent enrichment experiment was performed using the developed microelectrode in a microfluidic chip. The result shows that the optimized fabrication method of microelectrode in this study provides a promising way for high quality and good performance liquid metal microelectrode formation, and paves the way for its versatile applications. [ABSTRACT FROM AUTHOR]