Dual Mode Rapid Plasmonic Detections of Chemical Disinfectants (CMIT/MIT) Using Target-Mediated Selective Aggregation of Gold Nanoparticles

Chemical disinfectants such as 5-chloro-2-methylisothiazol-3(2H)-one/2-methyl-4-isothiazolin-3-one (CMIT/MIT) have been widely used in commercial products and humidifiers to prevent the growth of microorganisms. However, as continuous inhalation of CMIT/MIT is a fatal health risk, the concentration of its commercially available form is strictly regulated. Nonetheless, there are limited reports on effective methods for the quick and easy detection of CMIT/MIT. In this study, we have demonstrated rapid and convenient plasmonic methods for the dual-mode detection of CMIT/MIT using gold nanoplasmonic particles (GNPs) and understood the underlying molecular mechanism via additional analyses with microscopic and spectroscopic tools. In the presence of CMIT/MIT, the GNPs can rapidly aggregate due to molecular specific interactions with their capping agents and resultant reaction products. This target-mediated aggregation of the GNPs is represented by a visible color change of the solution from red to purple within just 3 min. By adjusting the reaction ratio between the CMIT/MIT and the GNPs, we could observe a marked color change at the regulation level (15 ppm) with naked eyes without any instruments. In addition, the concentration-dependent Raman spectral change in the reaction solution allows us to crosscheck the observed colorimetric responses both quantitatively and qualitatively based on molecular fingerprint spectra. Therefore, our detection protocol provides a powerful way to develop a high-throughput screening method to ensure that the level of the CMIT/MIT ingredients remains within the regulatory concentration.