Cylindrical sensor geometry for absorbance-based fiber-optic ammonia sensors

Area of Science:

• Analytical Chemistry
• Chemical Sensors
• Optical Sensing

Background:

• Traditional ammonia sensors often face limitations in response time and sensitivity.
• Chromophoric indicator dyes offer potential for ammonia detection but require optimized optical geometries.
• Existing sensor designs may suffer from long diffusion paths or susceptibility to stray light.

Purpose of the Study:

• To introduce and evaluate a novel cylindrical geometry for fiber-optic ammonia sensors.
• To investigate the impact of this geometry on sensor performance metrics such as response time, sensitivity, and limit of detection.
• To demonstrate the utility of chromophoric indicator dyes in the proposed sensor design.

Main Methods:

• A cylindrical sensor design was developed, trapping indicator dye solution within a gas-permeable tube.
• Fiber-optic probes were employed for light delivery and collection through the indicator solution.
• Sensors utilizing Bromothymol Blue were tested under varying operational modes.
• Analytical performance was assessed by measuring ammonia levels and response characteristics.

Main Results:

• The cylindrical geometry allows for long optical path lengths, suitable for chromophoric dyes.
• Diffusion path independence from optical path length led to rapid response times.
• Sensors achieved steady-state responses within 13-16 minutes for 200 nM ammonia.
• Limits of detection ranged from 150 to 20 nM, indicating high sensitivity.
• Negligible stray radiation was observed, validating the optical path length estimation.

Conclusions:

• The proposed cylindrical fiber-optic sensor geometry significantly enhances ammonia detection capabilities.
• This design overcomes limitations of conventional geometries, offering a promising platform for sensitive and rapid ammonia sensing.
• The sensor demonstrates excellent analytical performance, particularly when using a single discrete aliquot of indicator solution.