The monitoring of pH and free chlorine concentration in drinking water is important for water safety and public health. However, existing laboratory-based analytical methods are laborious, inefficient, and costly. This thesis focuses on the development of an easy-to-use, sensitive, and low-cost drinking water quality monitoring system for pH and free chlorine. An inkjet printing technology with a two-step thermolysis process in air is developed to deposit palladium/palladium oxide (Pd/PdO) films as potentiometric pH sensing electrodes. The redox reaction between PdO and hydronium ions generates the sensor output voltage. A large PdO percentage in the film provides a high sensitivity of ~60 mV/pH. A defect-free Pd/PdO film with small roughness contributes to a fast response and a high stability. When the Pd ink is thermalized in low vacuum, the deposited Pd/PdO film shows a bilayer structure. The residual oxygen in the low vacuum environment assists the decomposition of organic ligands for Pd to form a thin and continuous layer beneath submicron Pd aggregates. The oxidized bilayer film behaves as a temperature sensor with a sensitivity of 0.19% resistance change per °C, which can be used to compensate the sensed pH signals. Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is drawn by hand to form a free chlorine sensor. Free chlorine oxidises PEDOT:PSS, whose resistivity increment indicates the free chlorine concentration in the range of 0.5-500 ppm. Also, we simplified an amperometric free chlorine sensor based on amine-modified pencil leads. The simplified sensor is calibration-free, potentiostat-free, and easy-to-use. The pH, temperature, and free chlorine sensors are fabricated on a common substrate and connected to a field-programmable gate array board for data processing and display. The sensing system is user-friendly, cheap, and can accurately monitor real water samples. / Thesis / Doctor of Philosophy (PhD) / Sensitive, easy-to-use, and low-cost pH and free chlorine monitoring systems are important for drinking water safety and public health. In this thesis, we develop an inkjet printing technology to deposit palladium/palladium oxide films for potentiometric pH sensors and resistive temperature sensors. The different electrical and electrochemical properties of the palladium/palladium oxide films are realized by creating different film morphologies using different ink thermolysis atmospheres. The developed pH and temperature sensors are highly sensitive, fast in response, and stable. For free chlorine sensors, a hand drawing process is used to deposit poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate), which is an indicator for the free chlorine concentration over a wide range. We also developed a calibration-free free chlorine sensors based on modified pencil leads. Such a free chlorine sensor is integrated with the pH and temperature sensors, and an electronic readout system for accurate on-site drinking water quality monitoring at low cost is demonstrated.

The monitoring of pharmaceuticals, heavy metal, pH and free chlorine concentration in drinking water is important for public health and the environment. However, conventional laboratory-based analytical methods are labor-intensive, expensive, and time consuming. This thesis focuses on developing an integrated, highly sensitive, easy-to-use, and low-cost pharmaceuticals, heavy metal, pH and free chlorine sensing system for drinking water quality monitoring. A low-temperature, solution-processed modification of multi-walled carbon nanotubes (MWCNT) with β-cyclodextrin (βCD) on glassy carbon electrode is developed for detecting low levels of acetaminophen. The adsorption properties of βCD are combined with the high surface area of carbon nanotubes towards enhanced electrochemical sensing of acetaminophen with a limit of detection of 11 nM and linear range from 0.05-300 μM. Also, a systematic investigation is carried out using four types of modified MWCNT-βCD. A novel, one-step approach called Steglich esterification modified MWCNT-βCD results in large effective surface area, and fast electron transfer towards sensitive detection of acetaminophen and 17β-estradiol (E2, primary female sex hormone) in the range of 0.005–20 and 0.01–15 μM, with low detection limits of 3.3 and 2.5 nM, respectively. The similar MWCNT-βCD modified electrodes can also detect heavy metal ion (lead, Pb2+) with a limit of detection of <10 ppb. Low frequency noise behavior of these sensors are studied. A spin-coated Pd/PdO based pH sensor, and amine-modified carbon electrode-based free chlorine sensor are fabricated on a common substrate together with the pharmaceuticals and heavy metal sensors. A Wheatstone-bridge temperature sensor is fabricated based on silicon and PEDOT:PSS on another substrate. All the sensors are connected to an Arduino microcontroller based data acquisition system with a smartphone application interface. The integrated sensing system is easy-to-use, low-cost, and can provide accurate monitoring data with real drinking water samples. / Dissertation / Doctor of Philosophy (PhD) / Low-cost, easy-to-use, and sensitive monitoring system for pharmaceuticals, heavy metal, pH and free chlorine in drinking water is crucial for public health safety. In this thesis, we develop solution-based synthesis of multi-walled carbon nanotubes modified by β-cyclodextrin for electrochemical sensing of pharmaceuticals and heavy metal. The modification approaches are compared and characterized to analyze their electrochemical behavior and sensing performances. The developed sensors are highly sensitive toward the detection of acetaminophen (a widely used pain-killer) and estrogen hormone in drinking water. We also develop a modified spin-coating technique to deposit palladium/palladium oxide films for potentiometric pH sensor, a calibration-free free chlorine sensor based on modified carbon electrode, and a resistive temperature sensor. The developed pH, free chlorine and temperature sensors are highly sensitive, and stable with fast response time. All the sensors are integrated and interfaced with a custom-made and smartphone-controlled electronic readout system for accurate and on-site drinking water quality monitoring at low cost.