Light microscopy of PF4/heparin particles. Panels showing solutions containing mPF4 (200 μg/mL) alone (A) or mixed with UFH at 0.5 U/mL (B), 5 U/mL (C), or 50 U/mL (D) and subjected to light microscopy using highly collimated oblique illumination. Microscopic images were obtained using a 10 × magnification with an Olympus microscope (model no. BX41; Olympus America). Images were captured using a Microfibre Optronics camera (Goleta, CA) and analyzed with Picture frame Optronics software.