**2. Materials and Methods**

#### *2.1. Sample Preparation*

Tissue samples were dissected on ice, weighted and placed in three volumes of 140 mM NaCl containing 10 mM Hepes-NaOH pH 7.4, 1 mM EDTA and 1 mM dithiothreitol. The tissues were homogenized using a Teflon pestle tissue grinder (5 passes) and centrifuged at 3000× *g* for 20 min. The supernatant was collected, filtered on the 0.45 μm pore membrane and stored at −85 ◦C until analysis. A fractionation procedure was also studied based on salting-out methodology. The homogenate sample (300 μL) was mixed with 400 μL of saturated NaCl (5 M) and 300 μL of 100% acetonitrile (ACN) for 10 min and centrifuged at 3000× *g* for 5 min. Polystyrene NPs readily partitions in the upper ACN layer and was collected for chromatographic analysis.
