Paper microfluidic sensors towards on-site environmental analysis of soil nutrients

Al Hinai, Samira

Abstract

The increase in the world population leads to an increase in the need for production of crops. To optimise crop production fertilizer application needs to be managed by the farmer, consequently, regular information about the chemistry of the soil is required. There is a strong need for regular and in-field methods for the analysis of different essential nutrients in the soil which are in macro (e.g., nitrate) and micro (e.g., manganese) levels. Of the recently available lab techniques (e.g., IEC1, ICP-MS2) and commercial techniques3 (e.g., strips and palintest) some are not quantitative, some are expensive, some are time-consuming, and some combine all these disadvantages. Consequently, they are not practical, especially for low- and middle-income countries where agriculture is the main source of economy.
Here a simple (user-friendly) and low-cost workflow for routine monitoring of nitrate and manganese in soil samples, which is based on phone colourimetric paper-based sensor and cafetière extraction and meets on situ detection requirements, was developed.
Novel cafetière extraction was suggested for the first time for on-site extraction of soil nutrients. Cafetière consisted of plunger and meshes which provide the required mixing and filtration respectively. Initially nitrate determination workflow in soil was developed and tested with volunteers. The workflow requires 13 minutes total time for nitrate determination, 5 minutes extraction by cafetière (DIW solvent, 90% extraction efficiency) and 8 minutes detection by a phone-based colourimetric paper-based sensor. The PAD (paper-based analytical device) was able to detect as low as 27.10±2.64 mg kg-1 and 34.35±2.77 mg kg-1 of nitrate when a scanner and phone were used for the detection respectively. The developed PAD was small, portable, fast, easy to use, disposable, safe, low cost, robust (to interference and pH change), reliable and can be used in the field in a resource-limited setting. 97% of volunteers found the workflow easy and were able independently to perform the workflow for nitrate determination by following a simple instruction sheet.
Similarly, a workflow for manganese determination was developed in the lab to fit the field requirement. The workflow consists of two steps: 4 min cafetière extraction (NaCl solvent, 10% extraction efficiency) and 7 min detection (colourimetric paper-based sensor) with a total time of 11 minutes. The PAD was able to detect (LoD) 4.14±0.30 mg kg-1 and 5.12±1.88 mg kg-1 of manganese when a scanner and phone were used for the detection respectively. The developed PAD was inexpensive, easy to handle (based on dipping sample introduction) and with less toxic
The workflow showed promising results in detecting nutrients in the soil without the aid of an expert. This workflow will enable farmers in low-income countries to determine soil nutrient content using non-expensive, simple, and easily available methods and hence get enough information about the recommended fertilizer application. Consequently, this may improve the crop and hence the economy in these countries. In the future, the workflow needs to be supported with an app that enables the lay people to determine the result of the analysis by themselves and share it with researchers.

Citation

Al Hinai, S. (2023). Paper microfluidic sensors towards on-site environmental analysis of soil nutrients. (Thesis). University of Hull. https://hull-repository.worktribe.com/output/4617797

• Thesis Type: Thesis
• Deposit Date: Apr 2, 2024
• Publicly Available Date: Apr 12, 2024
• Keywords: Chemistry
• Public URL: https://hull-repository.worktribe.com/output/4617797
• Additional Information: Department of Chemistry; University of Hull
• Award Date: Mar 8, 2024