Enhanced sample preconcentration in microfluidic chip using graphene oxide–Nafion membrane

Abstract

An ion concentration polarization-based microfluidic sample preconcentration chip consisting of a polydimethylsiloxane microchannel and a graphene oxide (GO)–Nafion nanomembrane is fabricated using conventional MEMS techniques. The performance of the proposed device is evaluated using a fluorescein sample with an initial concentration of 10−5 M for membranes with three different GO–Nafion volume ratios (2:1, 3:1 and 4:1) and four different GO concentrations (0.3, 0.5, 1 and 2 wt%). It is shown that for a GO concentration of 0.3 wt%, a maximum preconcentration factor of approximately 50-fold is achieved using a GO–Nafion volume ratio of 3:1. Moreover, for the same volume ratio (3:1), a 60-fold enhancement of the sample concentration is obtained given a GO concentration of 0.5 wt%. Overall, the results show that compared to a pure Nafion membrane, the addition of GO yields an effective improvement in the sample preconcentration factor (i.e., 60-fold vs. 40-fold), but at the expense of a longer preconcentration time (30 min vs. 6 min 36 s). The superior concentration performance of the GO–Nafion membrane is attributed to the effects of dissociated carboxylate ions in attracting a greater number of cations into the membrane nanopores.