Colorimetric Affordable Test Strips (CATS)


A rapidly growing global population, economic development, and changing consumption patterns have added an immense burden on scarce potable water resources. Additionally, the accumulation of emerging pollutants (EPs) such as pharmaceuticals, solvent, cosmetics etc. are warranting attention due to their widespread occurrence, toxicity and difficulties in removal by conventional treatment. The presence of EPs in wastewater discharge from domestic, industrial and agriculture sources has been confirmed. Notably, India’s contribution to EPs in aquatic environment comprises of 57% pesticides, 17% pharmaceuticals, 15% surfactants, 7% personal care products and 5% phthalates. To counter economic and environmental loss due to the presence of EPs in our waterways, recognition of tools for water quality monitoring is highly desirable. An efficient water monitoring tools provide a ways to detect pollution before it happens. Thus aiming for ” Prevention is better than cure” strategy. Nonetheless, analysis of EPs is a real analytical challenge as it require sophisticated instruments, skilled user and high inbuilt cost and time . So, there was the challenge/ questions in front of us. Will be never be able to include EPs as water quality parameters? Are there any means by which reliable detection of EPs at affordable cost can be carried out?

Action plan

Bottlenecks in water monitoring

  • Currently no method to analyze micropollutants onsite.
  • No portable naked-eye detection tools
  • Limited knowledge on digitalized detection

Detection of emerging contaminants

  • More than 3400 emerging pollutant in environment
  •  India’s contribution to emerging pollutant in aquatic environment is second highest followed by Brazil and South Africa

Target pollutant: Triethylamine

  • Triethylamine appears as a clear colorless liquid
  • Used extensively in pesticide and textile industry
  • Permissible limit 0.1 mM, by OSHA
  • Causes ‘blue haze’ and corneal edema

Digitalization of developed sensors

  • Enable storage of data and option of online monitoring
  • Combined with existing water missions
  • Warning system to prevent contamination

Our Solution

Sensor technologies were found to be an effective alternative to traditional monitoring methods in real samples in terms of fast response, high selectivity and sensitivity, minor pretreatment procedure, lower detection limit, and wide calibration window. However, two major challenge still remains are the portability and user friendliness of the sensor. Accordingly, we propose the detection of EPs like Triethylamine (TEA) by using colorimetric affordable test strip (CATS). With CATS one can identify TEA visibly by simple spot on, dip-check method. Briefly, the fabricated strips enable the detection by simply dipping the probe (CATS) in test solution/water/ wastewater and observing naked eye color change. Further the change in can be scanned with developed the software application and the data can be stored on server. The software application is easy to use and can be used any electronic device (mobile phones). Also, the system is capable of generating alert when the concentration of pollutants is above permissible limit.

Fabrication of CATS and Validation in lab

The fabrication of CATS was carried out by dip coating method, whereby the probe was dispersed in water and later on coated on the solid substrate (strip)

The fabricated strip was initially tested for stability, effect of temperature and then detection of TEA was validated. The dip and check method was used, whereby a small section of strip was dipped in TEA solution the changes were noted in terms of UV absorbance , visual and microscopic image. To check the effectiveness of detection in the at various concentrations, grey scale intensity before and after were measured. The selectivity of the sensor was validated with the presence of various other pollutants, where no color change was noticed.

Development of mobile app

The mobile app is designed to work in a few simple steps. It is self-instructive as it informs user the next steps . Typical workflow involves the following steps: click on app icon, connect with the device , enable calibration, select SMS options for data sharing, scan the image using phone camera, and finally, the recorded data. When the concentration is above the permissible limit a warning message is displayed to alert the user.

How feasible is our solution?

Often the colorimetric sensor technology are overlooked due to its limited assessment of the products in terms of sustainability, cost, effectiveness in detection of pollutants and so on. Considering these factor we have carried out the comparison of our product with traditional method available. Not only this using quantitative structure relationship activity (QSAR) and USEtox we have identified the risk associated with product (below 0.1 meaning no risk) and how the use of CATS can residue the health risk ( reduction in adult (16-21 year) health risk due to ingestion of contaminated water by 0.8) if enabled in current water monitoring systems.

QSAR modeling approach
Exposure pathway for pollutants

Potential consumers and partners

With the advantage of portability, high sensitivity, naked eye detection and cost- effectiveness, the CATS can be easily used in various industries, wastewater treatment plants, locals and government agencies. We have estimated the percent probability of the potential consumers via production- consumption approach. For instance, textile, pharmaceutical, and pesticides industries are major consumer of TEA, hence the probability of them using CATS is high. Simultaneously, as TEA is know to produce acute toxicity in farmers (during cultivation of wheat, the herbicide used contain TEA), seasonal monitoring using CATS can be carried out either by locals of via consumer social responsibility projects


CATS is low cost and easy to deployable method of water quality monitoring. Also, it concerns an important environment pollutant of water. Hence, its contribution to sustainability is in all three dimensions. The development of multiple probe like CATS for detection of other EPs brings can further accelerate the potential of the innovation and lead to the long term sustainability of the project. Accordingly in the future we aim develop a toolkit that can detect multiple EPs ( like caffeine, antibiotics etc.) and conventional pollutants. Furthermore we would like to extend work to Microcontroller Unit (MCU) interfaced monitoring and using IoT based application to monitor the quality of the water continuously in field.

Connect with us

Vaishali Choudhary

Kowsalya Vellingiri

Prof Ligy Philip

Department of Civil Engineering , Indian Institute of Technology Madras, India- 600036