Microfabricated, low-cost, high-sensitivity chlorine and pH sensor systems for water quality monitoring

Microfabricated, low-cost, high-sensitivity chlorine and pH sensor systems for water quality monitoringIntegrated Water Management

ABOUT THE PROJECT

This project will develop a low cost sensor that can easily determine the effect of chlorine as a disinfection strategy for highly contaminated water.

NOTABLE ACHIEVEMENTS (November 2016)

• Researchers have developed a palladium solution-based process as a pH sensor (reducing the overall cost of fabricated sensors)
• Researchers have printed functionalized single-walled carbon nanotubes, palladium, and silver using inkjet printers and have used them as pH sensors
• Researchers have created a highly-sensitive and selective, low-cost free chlorine sensor using novel surface functionalization material that will coat graphite
• The research has led to the filing of a US Provisional Patent (August 2015) by Si Pan, M. Jamal Deen, Raja Ghosh “Graphite based free-chlorine sensor”.

PROJECT UPDATE (April 2016)

Researchers developed a prototype pH sensing electrodes. The solution-processed Pd/PdO showed a repeatable pH sensitivity of ~65 mV/pH between pH=2 and 12, higher than most of electrochemical sensors. The response was fast (<20 s). The pH sensing electrodes were stable for over 60 days. The fabricated pH sensor can be integrated with other chemical and bio sensors for the determination of species that are pH dependent. The solution-based process reduces the cost of fabricated sensors (<$5).

Researchers have also developed a prototype of pH sensing electrodues using Inkjet-printed carbon nanotubes. Functionalized single-walled carbon nanotubes (SWCNT) were inkjet-printed as both pH sensing and electron conduction layers. The developed inkjet printing process can be applied to polymeric substrates such as liquid crystal polymer and polyethersulfone.

A highly sensitive and selective, low-cost free chlorine sensor has been developed.

A system for reading and displaying sensor signals was developed.  Key functions include data reading, analog-to-digital converting, data processing for calibration, voltage-to-pH conversion, and displaying. Real-time voltage reading and voltage-to-pH conversion and result display in simulated cases (use the output of a function generator as the output signal of a pH sensor).

Preliminary results on integrating low-cost tangential flow filtration module with the pH sensors. Found that the sensitivity decrease of the pH sensor was due to formation of biofilm and this can be ameliorated by integrating the sensor with a filtration module to prevent the formation of a biofilm on the sensor surface.

RESEARCH ABSTRACT

Low-cost, high-sensitivity, real-time and easy-to-use sensing systems are critically needed in developing nations in order for them to instantaneously acertain the quality of water available to their citizens.  At present, chlorine is the most widely used disinfection process and free chlorine considered as an indicator for the disinfection efficacy. Therefore, there is need for low-cost, easy-to-use, reliable and continuous monitoring systems of free chlorine.  The currently used methods such as iodometric titrations, colorimetric reactions, chromatography or chemiluminescence require addition of reagents, which make them complex. In addition, they require skilled technical knowledge to operate. Other methods, such as electrochemical detection, requires regular calibration.  This research proposes to use low-cost, microfabricated ion-sensitive field-effect transistor (ISFET)- type devices in conjunction with filtration / ion selective membranes for the sensing of free chlorine in water. An important characteristic of the sensor device is that it will use the same technology that has allowed for a dramatic lowering of the cost of electronics, computers and cell phones.

Sensors based on ISFET technology have not been previously used to detect free chlorine. Through the novel use of ISFET sensors and preprocessing microfluidic modules, we will eliminate the need to periodically calibrate these sensors and will be able to operate them in a reagent-free, easy-to-use, and automated manner. In addition, research will be conducted towards an anti-biofouling coating that will enable long-term reliable operation of the system. This innovation will allow for rapid and continous monitoring of water for free chlorine in an automated manner. Also, by using technologies compatible with the mainstream silicon semiconductor industry, the proposed sensors will be very low-cost and will be easily integrated with control and signal processing electronics to improve the sensors’ performance, as well as wireless transceivers for autonomous operation.