Water contamination is a main inducement of human diseases. It is an important step to monitor the water quality in the water distribution system. Due to the features of large size, high cost, and complicated structure of traditional water determination sensors and devices, it is difficult to realize real-time water monitoring on a large scale. In this paper, we present a multi-parameter sensor chip, which is miniature, low-cost, and robust, to detect the pH, conductivity, and temperature of water simultaneously. The sensor chip was fabricated using micro-electro-mechanical system (MEMS) techniques. Iridium oxide film was electrodeposited as the pH-sensing material. The atomic ratio of Ir(III) to Ir(IV) is about 1.38 according to the X-ray photoelectron spectroscopy (XPS) analysis. The pH sensing electrode showed super-Nernstian response (−67.60 mV/pH) and good linearity (R² = 0.9997), in the range of pH 2.22 to pH 11.81. KCl-agar and epoxy were used as the electrolyte layer and liquid junction for the solid-state reference electrode, respectively, and its potential stability in deionized water was 56 h. The conductivity cell exhibited a linear determination range from 21.43 $\mathsf{\mu }\mathrm{S}/\mathrm{cm}$ to 1.99 $\mathrm{mS}/\mathrm{cm}$ , and the electrode constant was 1.566 cm⁻¹. Sensitivity of the temperature sensor was 5.46 $\mathsf{\Omega }/°\mathrm{C}$ . The results indicate that the developed sensor chip has potential application in water quality measurements.

Heavy metal ion pollution problems have had a terrible influence on human health and the environment. Therefore, the monitoring of heavy metal ions is of great practical significance. In this paper, an electrochemical three-electrode system was fabricated and integrated on nitrocellulose membrane (NC) by the use of magnetron sputtering technology, which exhibited a uniform arrangement of porous structure without further film modification. This paper-based sensor chip was used for Cu²⁺ detection by square-wave stripping voltammetry (SWSV). Within the ranges of 5~200 μg·L⁻¹ and 200~1000 μg·L⁻¹, it showed good linearity of 99.58% and 98.87%, respectively. The limit of detection was 2 μg·L⁻¹. On the basis of satisfying the detection requirements (10 μg·L⁻¹), the integrated sensor was small in size and inexpensive in cost. Zn²⁺, Cd²⁺, Pb²⁺ and Bi³⁺ were also detected by this paper-based sensor chip with good linearity.

As an important means to protect water resources, water quality detection is of great social and economic significance. Water quality detection sensors processed by micro-electro-mechanical system (MEMS) technology have the advantages of low-cost, small size, and high sensitivity. In this paper, a multi-parameter water quality detection integrated sensor chip is further studied, and a portable detection system using this chip is developed. Temperature, pH, oxidation-reduction potential (ORP), conductivity and concentration of copper ions (Cu²⁺) are selected as typical water quality parameters. Experiments of sensor calibrations using this portable detection system were performed in standard solutions. The sensor has a sensitivity of −57.34 mV/pH in pH detection and 5.95 Ω/°C in temperature response. ORP is directly detected by Pt microelectrode on the chip and the relative error is less than 3%. The electrode constant of the sensor is 1.416 cm⁻¹ and the linearity is 0.9995 in conductivity detection. With the gold nanoparticles deposited on the electrode, the detection peak of Cu²⁺ appears at 280 mV and the sensor shows good linearity to the concentration of Cu²⁺ in the range of 0–0.6 mg/L. The detection limit of Cu²⁺ concentration is 2.33 μg/L. Through measurement and calculation, the accuracy of the portable system is within 4%. This portable multi-parameter water quality detection system with the MEMS-based integrated chip shows great potential in the field and fast detection.

Poly(3,4-ethylenedioxythiophene) (PEDOT) films were prepared by electro-oxidation on Au microelectrodes in an aqueous solution. Electrolyte solutions and polymerization parameters were optimized prior to overoxidation. The effect of overoxidation time has been optimized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS), which results in the film overoxidized for 45 s at 1.35 V presenting a strong adsorption. The other one-step overoxidation film prepared by direct CV ranging from −0.6 V to 1.35 V was polymerized for comparison. Scanning electron microscope (SEM) analysis and Fourier transform infrared (FTIR) spectroscopy were used for monitoring morphological changes and the evolution of functional groups. Both of them indicate increased abundant oxygen functional groups and roughness, yet the products exhibit dendritic morphology and piles of spherical protrusions, respectively. Moreover, double-step overoxidized film showed better electrochemical performance toward lead ion sensing. These characterizations highlight some novel properties that may be beneficial for specific sensing applications.

An ultramicro interdigital array electrode modified by palladium-gold was developed for nitrate detection in neutral water. The ultramicro interdigital array electrode was fabricated based on silicon substrate by Micro Electro-Mechanical System (MEMS) technique. The nanostructured palladium-gold (Pd-AuNPs) composite sensing film was electrodeposited on the surface of a working electrode by electrochemical method. The synergistic effect of Pd-AuNPs composite was investigated and its enhancement of the catalytic activity and stability was revealed. The Pd-AuNPs modified electrode showed good linearity (R² = 0.99) from 1 mg/L to 15 mg/L (as N) for nitrate determination in a neutral water environment (pH = 7.2), with a sensitivity of 4.7 μA·mg⁻¹·L. The results showed that the developed Pd-AuNPs-modified ultramicro interdigital array electrode chip can achieve sensitive and environmentally-friendly detection for nitrate in neutral water.

A microband electrode array modified with palladium-tin bimetallic composite has been developed for nitrate determination. The microband electrode array was fabricated by Micro Electro-Mechanical System (MEMS) technique. Palladium and tin were electrodeposited successively on the electrode, forming a double-layer structure. The effect of the Pd-Sn composite was investigated and its enhancement of catalytic activity and lifetime was revealed. The Pd-Sn modified electrode showed good linearity (R² = 0.998) from 1 mg/L to 20 mg/L for nitrate determination with a sensitivity of 398 μA/(mg∙L⁻¹∙cm²). The electrode exhibited a satisfying analytical performance after 60 days of storage, indicating a long lifetime. Good repeatability was also displayed by the Pd-Sn modified electrodes. The results provided an option for nitrate determination in water.