Atmospheric Pressure Plasma Induced Ionization Fluorescence Spectroscopy for Label-Free Optical Characterization of Organic and Inorganic Particulate Materials

Atmospheric-pressure plasma optical emission spectroscopy (OES) is a promising technique for rapid, and label-free characterization of particulate materials because of its ability to generate material-dependent optical emission signatures under ambient conditions. In this work, an enhanced plasma-induced ionization fluorescence spectroscopy (PIFS) platform based on an open atmospheric-pressure discharge configuration is presented for the characterization of representative organic and inorganic particulate materials. The PIFS system uses two porous nickel electrodes separated by a dielectric (glass) spacer to generate a stable DC plasma discharge while simultaneously providing a large effective discharge nanotextured surface for plasma-particle interactions. Unlike our previously reported PIFS platforms, the porous-electrode architecture enhances plasma stability and promotes localized electrostatic particle accumulation, thereby improving plasma-particle interactions and measurement reproducibility. Optical emission generated during particle excitation was collected using a fiber-optic probe coupled to an Ocean Insight QE Pro spectrometer with approximately 1 nm spectral resolution. Representative organic materials, consisting of bee pollen, cellulose, and lactate, together with inorganic materials such as rust particles (iron oxide), sodium chloride, and blowing dust, were investigated at particle loadings of 1, 3, and 6 mg. The measured spectra revealed distinct emission fingerprints over the visible and near-infrared spectral regions. Bee pollen and iron oxide showed the largest spectral modifications, whereas cellulose, sodium chloride, and blowing dust produced comparatively smaller perturbations of the plasma emission profile. Quantitative comparison of characteristic emission wavelengths at 590, 660, 775, and 950 nm further indicated that each material possesses a unique normalized intensity distribution suitable for spectral discrimination. Analysis of the influence of particle loading showed increasing emission intensity for bee pollen, relatively stable responses for cellulose, lactate, and sodium chloride, and a decreasing response for blowing dust, due to particle deposition, optical attenuation and insulation of electrode surfaces. The proposed experimental platform provides a simple, reproducible, and cost-effective approach for plasma-based particulate characterization and demonstrates considerable potential for environmental monitoring, aerosol identification, and industrial process diagnostics.