Online Aerosol pH Detection Using 3D-Printed Microfluidic\nDevices with a Novel Magnetic SERS Sensor

Accurate\nmeasurement of aerosol pH is crucial for understanding\natmospheric processes and mitigating haze pollution. However, online\ndetection of aerosol pH is challenging due to the complex composition\nof single-particle matter and trace components. This study develops\na sensitive and selective sensor for the online detection of aerosol\npH using surface-enhanced Raman spectroscopy (SERS). A novel Fe<sub>3</sub>O<sub>4</sub>@SiO<sub>2</sub>@Au-<i>p</i>-aminothiophenol\n(FA-pATP) sensor was fabricated using a layer-by-layer self-assembly\nmethod, achieving enhanced uniformity and increased density of SERS-active\nhotspots. Magnetic aggregation was employed to further amplify the\nRaman signal. This sensor was integrated into a 3D-printed microfluidic\ndevice to facilitate online monitoring of aerosol pH. The FA-pATP\nsensor exhibited a significant increase in peak intensity ratio with\nrising pH, demonstrating high sensitivity and responsiveness due to\nstructural changes in the −NH<sub>2</sub> groups of pATP under\ndifferent pH conditions. The sensor demonstrated a linear pH response\nranging from 5 to 11. The 3D-printed microfluidic device, coupled\nwith the FA-pATP sensor, demonstrated notable performance in various\nenvironmental media, indicating strong anti-interference capabilities.\nThe proposed sensor shows great promise for real-time online monitoring\nof aerosol pH, with broad applications in environmental monitoring.