Micropatterned microwave resonator with microcavity arrays for ultrasensitive, label-free quantification of aquatic microplastics

Abstract

The pervasive presence of microplastics (MPs) in the environment poses significant challenges due to their recalcitrant nature and wide distribution. Conventional detection methodologies remain constrained by insufficient sensitivity and intricate operational requirements. Herein, we present a micro-spiral structured microwave sensing platform manufactured using integrated passive device (IPD) technology for label-free MP quantification in both deionized (DI) water and tap water. Both interdigital capacitor (IDC) and IPD resonators, optimized for optimum performance by software simulation, rely on the dielectric perturbation effect for detection. Specifically, variations in MP concentrations and size within the sensitive area modify the local dielectric properties, leading to capacitance changes and resonance frequency shifts. Systematic experiments demonstrate that increasing MP concentrations elevate local dielectric permittivity, thereby proportionally reducing IDC capacitance. For tap water analysis, the IDC demonstrates detection limits of 23.75 particles· μL⁻¹ (≤5 μm MPs) and 18.70 particles·μL⁻¹ (≥16 μm MPs). In contrast, the IPD-based sensing platform achieves markedly enhanced performance, with detection limits reduced to 0.52 particle·μL⁻¹ (≤5 μm) and 2.58 particles·μL⁻¹ (≥16 μm), accompanied by sensitivities of 2.88 MHz·particle·μL⁻¹ and 0.89 MHz·particle·μL⁻¹, respectively. Furthermore, resonance amplitude depth analysis enables differentiation between aqueous environments, expanding application versatility. The platform's miniaturized architecture (<1 mm×1 mm) with rapid response positions it as a viable solution for field-deployable MPs monitoring systems, thereby advancing environmental toxicology assessments and pollution mitigation strategies.