Label-Free Identification of Carbonaceous Particles Using Nonlinear Optical Microscopy

Area of Science:

• Biomedical Optics
• Nanotoxicology
• Materials Science

Background:

• Ambient carbonaceous particles (CPs), including carbon black (CB), black carbon (BC), and brown carbon (BrC), pose increasing health risks.
• Understanding the composition and source of CPs is crucial for assessing their toxicity.
• Accurate identification and quantification of CPs within biological samples are essential for toxicological research.

Purpose of the Study:

• To develop a novel nonlinear optical imaging approach for identifying CPs in biologically relevant environments.
• To establish a label-free method for detecting carbonaceous nanoparticles (NPs) compatible with biomedical imaging.
• To investigate the potential of nonlinear optical properties for differentiating CPs in complex biological matrices.

Main Methods:

• Development of a nonlinear optical imaging technique utilizing femtosecond pulsed laser excitation at 1300 nm.
• Characterization of the unique visible light fingerprint of carbon black (CB) and brown carbon (BrC) nanoparticles (NPs).
• Application of time-domain fluorescence lifetime imaging (FLIM) to analyze spectral emission features of CPs.
• Testing the method with CPs embedded in agarose gel and within *in vitro* mammalian cells.

Main Results:

• Demonstrated a unique visible light fingerprint for CB and BrC NPs under specific laser excitation.
• Successfully identified CPs in agarose gel and *in vitro* mammalian cells using the developed nonlinear optical approach.
• FLIM analysis provided supporting spectral evidence for CP identification.
• The nonlinear optical method is label-free and complementary to conventional fluorescent staining techniques.

Conclusions:

• A novel nonlinear optical imaging method enables label-free identification of carbonaceous particles (CB, BrC) in biological contexts.
• The technique offers a valuable tool for nanotoxicology and understanding the health impacts of ambient particulate matter.
• This approach provides complementary information to traditional biological staining, enhancing contextualization in biomedical research.