Low-cost optical fiber sensor for continuous chloramine monitoring using molecularly imprinted polymer coatings

Overview

This solution is a compact, reagent-less optical fiber sensor designed for continuous monitoring of chloramine concentrations in water. Chloramines are widely used as disinfectants in municipal water systems, cooling towers, and industrial process water, where maintaining proper residual levels is critical for public health and regulatory compliance. Existing monitoring methods typically rely on wet-chemical assays that are intermittent, labor-intensive, and unsuitable for real-time process control. The proposed sensor addresses this gap by providing a probe-like device under 0.5 mm in diameter that delivers continuous, reagent-free measurement of chloramine species, including HOCl and NH2Cl.

Technical specifications

• Sensor architecture: A D-shaped optical fiber in which the exposed flat sidewall supports a lossy mode resonance coating that is highly sensitive to local refractive index changes.
• Recognition layer: Molecularly imprinted polymers (MIPs) engineered with specific binding affinity for chloramine-related species such as HOCl and NH2Cl. The MIPs bind or release target molecules as solution concentration changes, producing measurable shifts in refractive index.
• Readout: Refractive index changes are detected using commercially available optical instruments connected through standard fiber interfaces, eliminating the need for specialized readout hardware.
• Sensitivity benchmark: Prior work on the same sensing platform has demonstrated a detection limit of 0.5 ppb for perfluorinated compounds, suggesting strong sensitivity for chloramine targets as well.
• Form factor: Probe-like geometry under 0.5 mm in diameter, suitable for in-line deployment in water distribution and treatment systems.
• Reagent-free operation: No consumable chemicals are required for each measurement, reducing operating cost and maintenance.

Technology readiness level

The underlying D-shaped fiber sensing platform has been validated in a related application, moisture sensing in foods, where it achieved low detection limits for both food moisture content and relative humidity at room temperature, confirming the sensitivity of the platform. The proposed project extends this proven platform to chloramine detection through three stages over 12 months: synthesis of MIPs specific to HOCl and NH2Cl by MIP Diagnostics, Inc. in the UK; fiber sensor fabrication and MIP coating at Worcester Polytechnic Institute; and sensor characterization conducted jointly at WPI and the US Army Combat Capabilities Development Command Soldier Center. The technology is currently at an early-to-mid stage of development, with laboratory validation underway and field deployment expected to follow subsequent testing phases.