Microfluidic systems via optical sensor and ion-sensitive field-effect transistor for determination of cinnarizine, phosphate and ammonium

The integration of microfluidic systems with optical sensors and ion-sensitive field-effect transistors (ISFET) represents a significant advancement in analytical chemistry, enabling precise and selective determination of various analytes with high efficiency and sensitivity. This study focuses on design and invention of three microfluidic systems: 1) hexagonal microfluidics incorporating multi-reverse flow injection analysis (µMr-FIA) for multi-analysis of cinnarizine in vitro drug release; 2) a novel micro flow-through cell system (µF-LOCs) for phosphate determination in surface water samples; and 3) flow automatic system using ISFET for the real-time/online determination of ammonium in aquaculture water. Firstly, the multi-analysis system for in vitro drug release of cinnarizine was developed in a hexagonal shape. The microfluidics incorporating multi-reverse flow injection analysis (µMr–FIA) was applied for in-vitro dissolution of cinnarizine in tablet dosage form and the results were compared to those of UV–vis spectrophotometry. The reaction is based on the oxidation of cinnarizine by potassium permanganate in an acidic medium and the color change in the system was detected by six optical sensors (525nm). The result obtained higher speed of analysis and more convenient than UV method. Secondly, a novel micro flow-through cell lab-on-a-chip system (µF-LOCs) functioned as a mixing part and flow-through-cell was designed and fabricated on polymethyl methacrylate (PMMA) by laser etching and thermal bonding process for phosphate determination in surface water samples. The outside configuration of micro flow-through cell is the same size as a conventional spectrophotometric cuvette with a rectangular box (12 mm in width x 10 mm in length x 45 mm in height). This design effectively determined phosphate in surface water samples using reverse flow injection analysis (r-FIA) based on the reaction of phosphate and ammonium molybdate in an acidic condition at 880 nm of detection wavelength, achieving a limit of detection (LOD) of 6.0 µg P L-1, a linear range of 0.010–2.0 mg P L-1, and an R2 of 0.9985. This system demonstrated excellent performance characterized by wide linear ranges and low detection limits, rendering it suitable for phosphate determination in real samples.Finally, a novel real-time flow automatic system integrated with an NH4+-ISFET sensor was developed for determining ammonium in aquaculture samples. The ion-selective membrane (ISM) on a printed circuit board was prepared by drop casting a mixture of nonactin as an ammonium ionophore and poly(vinyl chloride-co-vinyl acetate-co-vinyl alcohol) (PVVV) and dioctyl sebacate (DOS) to create an NH4+-ISFET sensor. The limit of detection was found to be 0.060 mg L-1 with a linear range of 0.10 – 1000.0 mg L-1 and an R2 of 0.9986 at a sensitivity of 61.29 mV dec-1. The NH4+-ISFET sensor had a useful lifetime of more than 8 months. This proposed system has major advantages over contemporary methods, such as good performance, rapid response and long lifetime. Furthermore, the system facilitates instantaneous detection and real-time quantification of ammonium levels and allows monitoring of ammonium concentrations anywhere and anytime using internet-connected devices. It is useful to enhance water quality in aquaculture while mitigating the risks associated with fluctuating ammonium levels in aquatic environments.