A portable amperometric ion sensor was fabricated by integrating silica isoporous membrane (SIM) and organogel composed of polyvinyl chloride and 1,2-dichloroethane (PVC-DCE) on a 3D-printed polymer chip. The detection of ionic species in aqueous samples could be accomplished by adding a microliter of sample droplet to the sensor and by identifying the ion-transfer potential and current magnitude at the water/organogel interface array templated by SIM. Thanks to the ultrasmall channel size (2-3 nm in diameter), high channel density (4 × 108 μm-2), and ultrathin thickness (80 nm) of SIM, the ensemble of nanoscopic water/organogel (nano-W/Gel) interface array behaved like a microinterface with two back-to-back hemispherical mass diffusion zones. So, the heterogeneous ion-transfer across the nano-W/Gel interface array generated a steady-state sigmoidal current wave. The detection of choline (Ch) and its derivatives, including acetylcholine (ACh), benzoylcholine (BCh), and atropine (AP), in aqueous samples was examined with this portable sensor. Using differential pulse stripping voltammetry (DPSV), the quantification of these analytes was achieved with a limit of detection (LOD) down to 1 μM. Moreover, the portable ion sensor was insensitive to various potential interferents that might coexist in vivo, owing to size-/charge-based selectivity and antifouling capacity of SIM. With this priority, the portable ion sensor was able to quantitatively determine Ch and its derivatives in diluted urine and blood samples. The LODs for Ch, ACh, AP, and BCh in urine were 1.12, 1.30, 1.08, and 0.99 μM, and those for blood samples were 3.61, 3.38, 2.32, and 1.81 μM, respectively.
Keywords: choline; ion sensor; liquid/organogel interface; portable; silica isoporous membrane.