Design and modeling of a microfluidic platform for portable electrochemical analysis
Primary author: Daniel Molina
Faculty sponsor: Cornelius Ivory
Primary college/unit: Voiland College of Engineering and Architecture
A microfluidic platform for electrochemical analysis of flowing solutions was developed, consisting of an acrylic chip and three removable microelectrodes, each housed in a high-resistance plastic tube. The electrodes can be removed independently for cleaning, polishing or replacement. The sensing microelectrode is a 100-µm diameter platinum disk, located flush with the upper face of a 150 µm x 20 µm x 3 cm microchannel, smaller than previously reported for this type of electrodes, and with a total volume of 90 nanoliters, which minimizes the size of the samples required. The platform was evaluated by oxidizing a potassium ferrocyanide solution, a well-known electrochemical probe, at the sensing electrode. The electrical current signal increases with increasing applied potential until it reaches a limiting current. The value of this limiting current increases with the flow rate of the solution, so a better signal/noise ratio can be achieved at higher flow rates.
Numerical models can help us make predictions and serve as design aids without having to iterate physical prototypes. While microdisk channel electrodes have been simulated numerically before using a finite difference method in an ideal 3D geometry, here we predict the limiting current using finite elements in COMSOL Multiphysics®, which allowed us to easily explore variations in the microchannel geometry that have not previously been considered in the literature. Experimental and simulated currents showed the same trend but differed by 41% in simulations of the ideal geometry, which improved when channel and electrode imperfections were included.