Optical Extraction of Single Microplastics Followed by Online Molecular and Elemental Characterization

Area of Science:

• Environmental Science
• Analytical Chemistry
• Materials Science

Background:

• Accurate microplastic (MP) characterization in complex matrices is challenging.
• Single particle inductively coupled plasma-mass spectrometry (SP ICP-MS) detects MPs by carbon mass and size but struggles with small particles and distinguishing polymers.
• Existing methods lack the ability to identify polymer types and reduce background noise in complex samples.

Purpose of the Study:

• To develop and demonstrate a novel trimodal analytical platform for online, single-particle microplastic characterization.
• To integrate optofluidic force induction (OF2i), single particle Raman spectroscopy (SP Raman), and SP ICP-MS.
• To improve the detection and calibration capabilities for microplastics in complex matrices.

Main Methods:

• Developed an optical extraction mechanism using a laser vortex beam to immobilize microplastics.
• Integrated OF2i with SP Raman for polymer identification and SP ICP-MS for elemental analysis and size determination.
• Demonstrated matrix exchange via optical trapping to reduce background signals for SP ICP-MS.

Main Results:

• Achieved improved mass and size detection limits for microplastics (1.0 μm and 0.6 pg C/particle for 5 μm polystyrene).
• Successfully identified polymer types (e.g., polyamide-6) and quantified carbon mass in complex matrices like soil.
• Demonstrated a 28-fold improvement in mass detection limit and a 3.1-fold improvement in size detection limit.

Conclusions:

• The novel trimodal platform enables online, multimodal characterization of microplastics at single-particle resolution.
• Optical extraction significantly enhances microplastic detection and polymer identification capabilities, overcoming limitations of traditional SP ICP-MS.
• The developed method offers a powerful tool for analyzing microplastics in complex environmental samples and can be extended to other nano- and microstructures.