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

Abstract

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.

Morphological Analysis of PSMA/PEI Core–Shell Nanoparticles Synthesized by Soap-Free Emulsion Polymerization

“…In addition, a decrease was observed in the CO stretching band at 1265 cm −1 , which confirmed that a reaction occurred between the carboxyl groups of the open ring of MA and PEI, implying the successful binding of PEI to PSMA. These results are in agreement with the published reports [ 36 ].…”

“…PEI was added to PSMA according to the molar ratios listed in Table 2 . Changes in the PSMA/PEI core–shell particle size owing to the differences in the amount of PEI added were reported in a previous study [ 36 ]; however, the morphological changes induced by varying the feed ratios of PEI and particle dispersion were not mentioned. Thus, in this study, the changes in the particle size and distribution were analyzed based on PEI addition and interpreted as shown in Figure 4 a–f.…”

“…The synthesis technique of a previous study [ 36 ] was used for fabricating the core-PSMA and PSMA/PEI core–shell structures ( Scheme 1 ). A double-jacket reactor of 250 mL was equipped with a cooling condenser.…”

“…The polymerization of styrene (St) occurs within hollow PAM particles, while AM continues to polymerize in the outer part of the PAM shell. The emulsions produced formed films, which were of good transparency in the absence of surfactant [ 35 , 36 ].…”

3D Printing Filaments Facilitate the Development of Evanescent Wave Plastic Optical Fiber (POF) Chemosensors

“…A raw analysis of the LoDs is, however, difficult to perform, since the various optical sensors use different sampling times, are non-regenerable dosimeters, belong to the laboratoryassays category (and not deployable sensors), or have calculated their LoD using a different method to ours. For instance, Suzuki et al and Guo et al describe disposable colorimetric dosimeters showing lower detection limits of 50 and 10 ppbv for sampling times of 15 and 20 min, respectively [30,31], whereas Park et al have reported colorimetric nanoparticles displaying a LoD of 500 ppbv for 1 min sampling time [32].…”