A Metal Ion-Responsive Spiropyran-Based Fluorescent Color-Changing Hydrogel

Area of Science:

• Materials Science
• Nanotechnology
• Chemical Sensing

Background:

• Hydrophilic spiropyran in hydrogels has low fluorescence quantum efficiency, limiting applications.
• Metal plasmon resonance can enhance fluorescence, but integration challenges exist.

Purpose of the Study:

• To develop a spiropyran-based fluorescent hydrogel sensor with enhanced fluorescence intensity.
• To improve the practical application of spiropyran in hydrogel matrices for sensing.

Main Methods:

• Copolymerization of N,N'-bis(acryloyl)cystamine-modified Au nanoparticles (Au NPs), spiropyran, and N-isopropylacrylamide.
• Engineering an inverted pyramid-structured surface for anti-reflection and plasmonic enhancement.
• Molecular modification for improved Au NP dispersion and prevention of fluorescence quenching.

Main Results:

• Achieved a 10.2-fold increase in hydrogel fluorescence intensity.
• Demonstrated dual colorimetric and fluorescent responsiveness to heavy metal ions.
• Sensing of Zn²⁺ with a limit of detection as low as 0.803 μM.
• Hydrogel showed over 10 cycles of photo-isomerization and ion responsiveness.

Conclusions:

• The hybrid hydrogel system effectively integrates metal plasmon resonance for enhanced fluorescence.
• The engineered surface microstructure and plasmonic effects boost sensor performance.
• The developed sensor offers a promising platform for sensitive and reusable heavy metal ion detection.