Portable Multispectral Imaging System for Sodium Nitrite Detection via Griess Reaction on Cellulose Fiber Sample Pads

Area of Science:

• Analytical Chemistry
• Spectroscopy
• Chemical Sensing

Background:

• The Griess reaction is a common method for detecting nitrite ions.
• Paper-based substrates offer a low-cost platform for chemical sensing.
• Existing methods for nitrite detection may lack portability or accuracy.

Purpose of the Study:

• To develop and validate a portable multispectral imaging (MSI) system for sensitive sodium nitrite detection.
• To investigate the spectral characteristics of nitrite-induced azo dyes on paper substrates.
• To enhance detection accuracy using a normalized difference index (NDI) approach.

Main Methods:

• A custom-built portable MSI system (360-940 nm) was integrated with computer vision.
• Sodium nitrite detection was performed using the Griess reaction on para-aminobenzoic acid (PABA) and sulfanilamide (SA) substrates.
• Spectral absorption was analyzed, and a normalized difference index (NDI) was calculated using optimal spectral bands.
• Performance was evaluated against varying illumination and compared with smartphone RGB imaging.

Main Results:

• MSI images showed increased absorption (darker regions) with higher sodium nitrite concentrations.
• The NDI, calculated from MSI data, demonstrated a stronger correlation with nitrite concentration than single spectral bands.
• NDI improved the coefficient of determination (R² ) by ~19-20% for both PABA-NED and SA-NED substrates.
• The MSI-based NDI significantly outperformed conventional smartphone RGB imaging.

Conclusions:

• The portable MSI system offers a robust, rapid, and non-destructive method for on-site chemical analysis.
• The NDI framework enhances image interpretability and enables effective data analysis for chemical detection.
• This approach provides a practical guideline for developing advanced, portable chemical sensing systems.