Fluorescence-based free chlorine sensor for water quality monitoring

Overview

This solution offers a fluorescence-based sensing approach for detecting free chlorine in water. Free chlorine is widely used as a disinfectant in drinking water, industrial process water, and recreational water systems, and accurate monitoring is essential for safety and regulatory compliance. The technology exploits the fluorescence quenching effect that free chlorine has on certain fluorescent chemicals and materials. When these materials are exposed to free chlorine, their fluorescence intensity decreases in a measurable way, enabling quantitative detection. Detection limits as low as 0.5 micromolar have been reported in published studies using similar chemistries.

The research team has prior experience developing comparable fluorescence-based sensors for ammonia and pH measurement in water, providing a strong foundation for extending the approach to free chlorine detection.

Technical specifications

Core sensing principle:

• Fluorescent chemicals and materials such as Green fluorescent protein, bovine serum albumin stabilized gold nanoclusters, and fluorescent carbon dot-rhodamine B composites emit fluorescence between 400 and 600 nm when excited at wavelengths between 320 and 420 nm
• Free chlorine quenches this fluorescence through a combination of chemical bond interactions and energy transfer mechanisms
• The degree of quenching correlates with free chlorine concentration, enabling quantitative measurement

Proposed sensor architecture:

• Optical components including a light-emitting diode (LED) light source, filters, and a photodetector
• A chemical sensor layer that reacts with free chlorine, immobilized using silica sol-gel encapsulation, a widely used method for immobilizing industrially relevant enzymes and chemicals
• A microcontroller-based printed circuit board (PCB) that modulates the LED signal and processes the fluorescence response collected by the detector

Key features:

• Builds on validated lab-based instrument demonstrations reported in multiple publications
• Silica sol-gel encapsulation enables stable immobilization of the sensing chemistry
• Compact, microcontroller-based design supports potential field deployment

Technology readiness level

The underlying fluorescence quenching chemistry has been demonstrated in published research using lab-based instruments, with reported detection limits as low as 0.5 micromolar. The research team has prior experience developing similar fluorescence-based sensors for ammonia and pH in water. The next phase of development focuses on building a complete sensor device, with the chemical sensor development expected to require the majority of the effort. Silica sol-gel encapsulation, a well-established immobilization technique, will be used to stabilize the sensing chemistry. The technology is currently at an early-to-mid stage of development, transitioning from validated laboratory chemistry toward an integrated, deployable sensor platform.