Proof-of-concept study of a CD-type microfluidic titration system with an ISFET sensor for microlitre-scale analysis

Conventional titration methods rely on bulky equipment, large sample volumes, and manual reagent handling, limiting their integration into portable and microlitre-scale analytical platforms. This constraint persists despite the growing demand for compact chemical quantification tools in decentralized diagnostics and environmental monitoring. A key challenge remains the lack of precise, automated titration systems that can operate without external pumps, fragile electrodes, or complex tubing. To address this gap, we present a CD-type centrifugal microfluidic device integrated with an ion-sensitive field-effect transistor (ISFET) sensor for automated acid-base titration in microlitre-scale samples. Rotation-driven fluid control is employed in the lab-on-a-disc system, enabling sequential acid addition without external pumps or valves. The 3D-printed microfluidic chip incorporates ten reagent reservoirs connected to an outer reaction chamber, allowing precise titrant delivery through controlled rotational speeds. The ISFET sensor, featuring a Ta₂O₅ sensing membrane and a carbon-based reference electrode, exhibited high sensitivity (51.3 mV/pH) and notable linearity (R² = 0.9929) across a broad pH range. Titration experiments using 300 μL of a sodium carbonate solution and 0.1 mol/L hydrochloric acid successfully revealed equivalence points associated with carbonate neutralization, closely matching the results obtained with a commercial pH meter. These findings validate the measurement reliability and reproducibility of the device and demonstrate its potential as a portable and low-cost titration platform. The proposed approach advances the miniaturization and automation of titration methods, offering promising applications in field-deployable chemical analysis, marine biogeochemistry, and point-of-care diagnostics.