Abstract

The development of portable, easy-to-use, and reliable analytical tools is essential for environmental monitoring of contaminants, particularly in settings with limited access to laboratory infrastructure. In diagnostics area, recent advancements in tablet-based sensing technologies have shown the promise for enabling simple, rapid and user-friendly detection with minimal preparation. Motivated by the need to support and improve public health, this thesis is dedicated to the development of tablet-based sensors that enable rapid, user-friendly, and affordable detection of environmental contaminants. In this context, this research focuses on the development of innovative tablet-based sensors for on-site detection of (1) copper in water and (2) nitrite in soil, which provide precise reagent dosages, enhanced portability, and reliable performance in resources with limited facilities.
In the case of copper detection, the sensor utilizes an auto-mixing tablet that simplifies the process by incorporating all necessary reagents into a single solid form. This ensures precise dosing, offering a simple, quick, and user-friendly alternative in compare with traditional methods such as including inductively coupled plasma detector, atomic absorption spectroscopy, surface plasmon resonance detector and X-ray fluorescence spectrometry. Copper detection is vital as excessive copper levels in drinking water and natural water bodies can pose serious health risks, including gastrointestinal distress, liver or kidney damage, and neurodegenerative diseases, also contribute to environmental pollution. The tablet initiates a colourimetric reaction with 2,2’-biquinoline-4,4’-dicarboxylic acid (bicinchoninic acid) within two minutes, producing a measurable color change indicative of copper concentration. Unlike conventional tablets that require manual mixing, the effervescence and auto-mixing feature enhances reagent dissolution and improves usability. The sensor demonstrated working range of 0 to 2.5 ppm, with a detection limit of 0.3 ppm, which are adequate for monitoring copper contamination considering that The World Health Organization (WHO) has set the permissible limit for copper ions (Cu²⁺) in drinking water at 2.0 mg/L (2 ppm). However, Cu²⁺ concentrations in some local water sources exceed this threshold. Therefore, there is an urgent need to develop highly sensitive and selective methods for Cu²⁺ detection.

Interference tests confirmed the sensor’s selectivity for copper. The sensor’s selectivity complements its sensitivity, providing reliable detection of copper at low concentrations with minimal influence from other potential contaminants. While analyses of real water samples validated its accuracy and practical applicability. Stability assessments over three months of room temperature showed consistent performance, highlighting the sensor’s long-term usability. The tablet format provides a portable, pre-measured detection system that eliminates the need for laboratory preparation, making it an effective solution for real-time copper monitoring, particularly in regions with restricted access to analytical tools.
In the case of nitrite detection, this study presents two tablet-based sensors: (1) a Dual Reagent Tablet, which contains separate sulfanilamide (SUL) and N-(1-naphthyl)ethylenediamine (NED) reagents in two distinct tablets; and (2) an All-in-One Integrated Reagent Tablet, which combines all necessary reagents into a single tablet, simplifying the detection procedure. Nitrite contamination harms ecosystems by reducing oxygen levels, disrupting biodiversity, and producing toxic compounds such as nitrosamines, while posing human health risks such as methemoglobinemia, neurological disorders, and increased cancer risk. Therefore, effective soil monitoring is crucial for pollution control and sustainable agriculture. Both utilize a pullulan matrix to encapsulate reagents in solid form, enhancing stability and practicality. Each sensor enables rapid soil nitrite measurements within 2 minutes through a colourimetric reaction, producing a pink/purple azo dye as an indicator. Furthermore, unlike traditional methods requiring manual pH adjustment, these tablet sensors incorporate a buffering system to maintain optimal acidic conditions for the reaction, ensuring reliable performance across diverse sample environments without external acidification. The tablets also ensure consistent reagent dosages, removing the need for laboratory preparation and providing a portable, pre-measured platform for on-site nitrite detection in complex soil matrices. The Dual Reagent Tablet demonstrated a detection limit of 3 µM, while the All-in-One Tablet achieved a detection limit of 5 µM, both with a working range up to 400 µM. Interference experiments confirmed selectivity for nitrite, and analyses of real soil samples validated the method’s accuracy and applicability. Stability assessments over six weeks at room temperature showed consistent performance, demonstrating the long-term usability of these sensors.