Nano-electrokinetic ion concentration in the ion enrichment zone.

To reveal the internal discipline and accurately identify the inflection point, the Poisson-Nernst-Planck equations combined with the Navier-Stokes equation are employed and a method based on the horizontal angle of the tangent line and the distance from a pointcut to the origin is presented. Utilizing a micromachining technique and a photopolymerization reaction, a polyacrylamide gel plug is integrated into a microchannel to form a micro-nanofluidic chip. With the chip, FITC concentration experiments are developed with the initial concentration of 10 nM. Experimental testing confirms the results and demonstrates that the concentration is increased at first and then decreased with the increasing of the electric potential. That variation trend should be attributed to a balance between the repulsive force and the electrophoresis effect. The research results also demonstrate that upon increasing the voltage, the horizontal angle first decreases and then increases corresponding with the reverse trend of the distance. For a given micro-nanochannel, the peak ion concentration can be obtained through decreasing the horizontal angle and increasing the distance. The results will help determine peak voltage. [ABSTRACT FROM AUTHOR]