Colorimetric Visualization Using Polymeric Core–Shell Nanoparticles: Enhanced Sensitivity for Formaldehyde Gas Sensors

• Main Authors: Jae Jung Park, Yongsoo Kim, Chanmin Lee, Jun-Won Kook, Donghyun Kim, Jung-Hyun Kim, Ki-Seob Hwang, Jun-Young Lee
• Format: Article
• Language: English
• Published: MDPI AG 2020-04-01
• Series: Polymers
• Subjects: core–shell nanoparticle; colorimetric sensor; formaldehyde; polyethyleneimine; pH indicator
• Online Access: https://www.mdpi.com/2073-4360/12/5/998

Although equipment-based gas sensor systems (e.g., high-performance liquid chromatography) have been widely applied for formaldehyde gas detection, pre-treatment and expensive instrumentation are required. To overcome these disadvantages, we developed a colorimetric sensor based on polymer-based core–shell nanoparticles (PCSNPs), which are inexpensive, stable, and exhibit enhanced selectivity. Spherical and uniform poly(styrene-co-maleic anhydride) (PSMA)/polyethyleneimine (PEI) core–shell nanoparticles were prepared and then impregnated with Methyl Red (MR), Bromocresol Purple (BCP), or 4-nitrophenol (4-NP) to construct colorimetric sensors for formaldehyde gas. The intrinsic properties of these dyes were maintained when introduced into the PCSNPs. In the presence of formaldehyde, the MR, BCP, and 4-NP colorimetric sensors changed to yellow, red, and gray, respectively. The colorimetric response was maximized at a PEI/PSMA ratio of four, likely owing to the high content of amine groups. Effective formaldehyde gas detection was achieved at a relative humidity of 30% using the MR colorimetric sensor, which exhibited a large color change (92%) in 1 min. Advantageously, this stable sensor allowed sensitive and rapid naked-eye detection of low formaldehyde concentrations (0.5 ppm). Hence, this approach is promising for real-time formaldehyde gas visualization and can also be adapted to other colorimetric gas sensor systems to improve sensitivity and simplicity.