Functionalization of micro- and nano-apertures with chromate-selective solvent polymeric membrane

A new miniaturization approach to create micro- and nanoscale ion selective electrodes (ISEs) was demonstrated and the concept tested with an environmentally relevant chromate-selective membrane consisting of 7.7:62.2:31.1 wt % Aliquat336:2-NPOE:PVC. Apertures of 100 nM and 30 μM dimensions were made using MEMS fabrication techniques and functionalized through a macroscale application of solvent polymeric membrane. Performance studies for the microscale ISE showed a response slope of −58.6 ± 5.6 mV decade−1 and limit of detection (LOD) of 2.1 × 10−5 ± 1.1 × 10−5 M, versus −65.2 ± 4.2 mV decade−1 and 1.8 × 10−5 ± 6 × 10−6 M for the nanoscale ISE. This was consistent with control studies with carefully conditioned coated wire electrodes, which demonstrated a response slope of −61.7 ± 2.4 mV decade−1 and a LOD of 3.0 × 10−6 ± 1 × 10−6 M. Response times for the best micro- and nanoscale ISEs were in the 10-20 s timeframe. Electrical resistance measurements were in the GΩ range for the microscale ISEs and nanoscale ISEs. Appropriate ISE geometry was confirmed through AFM measurements and calculations based on electrical properties for micro- and nanoscale apertures. These micro- and nanoscale ISEs are expected to have significant impact in the field of microscale analytical processes.