Liquid Cladding Mediated Optical Fiber Sensors for Copper Ion Detection.

Area of Science:

• Photonics and Sensing Technologies
• Environmental Monitoring
• Analytical Chemistry

Background:

• Accurate detection of heavy metal ions like copper (Cu²⁺) is crucial for environmental and public health.
• Existing methods for Cu²⁺ detection can be complex, costly, or lack sensitivity for trace amounts.
• Label-free optical sensing offers a promising alternative for real-time, sensitive analyte detection.

Purpose of the Study:

• To develop and demonstrate a label-free optical fiber sensor for the sensitive detection of copper ions (Cu²⁺) in aqueous solutions.
• To investigate the sensing mechanism based on liquid cladding and numerical aperture modulation.
• To functionalize the sensor for enhanced Cu²⁺ capture and achieve a low limit of detection.

Main Methods:

• Utilizing a multimode optical fiber with a removed polymer cladding section to act as the sensing head.
• Employing the principle of liquid cladding, where Cu²⁺ solutions modulate the fiber's numerical aperture (NA).
• Functionalizing the fiber core with chitosan-conjugated ethylenediaminetetraacetic acid (EDTA) for selective Cu²⁺ chelation.

Main Results:

• The optical fiber sensor demonstrated a minimum resolvable refractive index change of 2.48 × 10^-6.
• Achieved a highly sensitive limit of detection for Cu²⁺ at 1.62 nM (104 ppt), well below drinking water standards.
• Exhibited a broad dynamic detection range of 1 mM, suitable for various water quality assessments.

Conclusions:

• The developed label-free optical fiber sensor provides a highly sensitive and effective method for detecting copper ions in water.
• The sensor's simple design and functionalization offer potential for miniaturization and in-situ monitoring of heavy metals.
• This technology holds promise for developing compact, cost-effective, and highly sensitive heavy metal sensors for environmental applications.