Rapid Colorimetric pH-Responsive Gold Nanocomposite Hydrogels for Sensing Applications

Area of Science:

• Nanomaterials Science
• Materials Chemistry
• Sensor Technology

Background:

• Surface functionalization of metallic nanoparticles (NPs) enables the creation of stimuli-responsive sensors.
• Gold nanoparticles (GNPs) functionalized with 3-mercaptopropionic acid (MPA) are pH-sensitive due to MPA's carboxyl group ionization.

Purpose of the Study:

• To synthesize and characterize MPA-functionalized GNPs (GNPs-MPA).
• To incorporate GNPs-MPA into hydrogel materials using the breathing-in/breathing-out (BI-BO) method.
• To evaluate the pH-responsive optical and colorimetric properties of the resulting nanocomposites.

Main Methods:

• Synthesis of GNPs-MPA and their doping into hydrogels via the BI-BO method.
• UV-Vis spectroscopy to analyze surface plasmon resonance (SPR) and full width at half maximum (FWHM) for pH sensing.
• Transmission and scanning electron microscopy (TEM/SEM) to observe nanoparticle behavior with pH changes.

Main Results:

• GNPs-MPA solutions and hydrogels exhibited pH sensitivity in the 3-5 range, changing color from red to indigo as pH decreased.
• The doped hydrogels showed higher FWHM sensitivity (55 nm) compared to solutions (20 nm).
• Nanoparticle dispersion and aggregation were synchronized with pH variations, confirmed by microscopy.

Conclusions:

• The developed GNPs-MPA hydrogels are effective colorimetric pH sensors with instantaneous response times.
• The BI-BO method successfully incorporated GNPs into hydrogels, demonstrating unique pH-dependent optical properties.
• This work presents a novel approach for creating advanced nanocomposite materials for practical sensor applications.