A paper-based colorimetric assay system for sensitive cysteine detection using a fluorescent probe.

Area of Science:

• Analytical Chemistry
• Biochemistry
• Chemical Sensing

Background:

• Cysteine (Cys) is a crucial amino acid involved in various biological processes.
• Sensitive and selective detection methods for Cys are essential for diagnostics and research.
• Existing methods may be costly, complex, or lack portability.

Purpose of the Study:

• To develop a novel fluorescent probe for the colorimetric detection of cysteine.
• To create a simple, sensitive, and cost-effective method for Cys quantification.
• To validate the probe's performance in real biological samples.

Main Methods:

• Synthesis of a fluorescent probe by combining resorufin and 7-nitrobenzofurazan.
• Characterization of the probe using FT-IR, fluorescence, mass spectrometry, and NMR.
• Colorimetric detection on paper-based devices with smartphone-based readout and image analysis.
• Validation of linearity, limit of detection, selectivity, and application in human plasma.

Main Results:

• The probe exhibited a color change from light yellow to red upon reaction with Cys.
• Linear response observed for Cys concentrations from 0.04 to 70.04 μM (R = 0.9965).
• Achieved a low limit of detection of 16 nM with minimal interference from other substances.
• Successfully quantified Cys in human plasma with high recovery rates (99.7%–100.4%).

Conclusions:

• The developed fluorescent probe offers a sensitive and selective method for Cys detection.
• Smartphone-based colorimetric analysis provides a low-cost and portable detection platform.
• The method demonstrates significant potential for Cys determination in real-world biological samples.