Plasticizer-free microspheres for ionophore-based sensing and extraction based on a methyl methacrylate-decyl methacrylate copolymer matrix

Plasticizer-free methyl methacrylate-decyl methacrylate (MMA-DMA) microspheres were prepared under mild, non-reactive conditions using a high-throughput particle generator. The particles were perfectly smooth and monodisperse, with a particle diameter of approximately 10.0 μm. In order to evaluate the suitability of the polymer as a matrix for bulk extraction processes, lipophilic sensing components were incorporated into the particles. Particles contained either a H⁺-selective chromoionophore (ETH 5294) only (type 1), or a K⁺-selective ionophore (BME-44), anionic sites (NaTFPB), and ETH 5294 (type 2). Type 1 particles responded according to an anion–proton coextraction mechanism and demonstrated Hofmeister selectivity by showing a preference for more lipophilic sample anions (ClO₄⁻>NO₃⁻>Cl⁻). Particles of type 2 functioned by way of an ion-exchange equilibrium and demonstrated a functional response for K⁺, with a dynamic range from 10⁻¹–10⁻⁴ M K⁺. These particles also exhibited selectivity comparable to that previously reported for analogous particles made from bis(2-ethylhexyl sebacate) (DOS)-plasticized poly(vinyl chloride) (PVC) and DMA-DOS. In addition, the behavior of both types1 and 2 particles was in agreement with analogous thin film optical sensors (optodes) prepared from MMA-DMA. With the advent of ionophore-based plasticizer-free microspheres a wide variety of ions may potentially be assessed using various popular bead-based sensing strategies, such as lab-on-a-chip technologies, bundled optical fiber arrays, and flow cytometry, without experiencing the deleterious effects resultant of plasticizer leaching.