Serum (1:600 dilution) was spiked into synthetic urine (Surine™) to validate the protein harvesting ability of the Reactive Black 31 dye containing nanoparticles. The high abundance proteins remain in the supernatant, showing that they are not captured by the nanoparticles. A previously validated batch of nanoparticles was compared to a new batch and Surine™ (as a negative control). Lane 1: Benchmark unstained protein ladder, Lane 2: initial solution (1:600 serum), Lane 3: Surine™, Lane 4: supernatant of a previously validated RB31 NP batch, Lane 5: wash, Lane 6: elution, Lane 7: new batch of RB31 NP supernatant, Lane 8: new batch of RB31 NP wash, Lane 9: new batch of RB31 NP elution, Lane 10: supernatant negative control (Surine™), Lane 11: Surine™ wash, Lane 12: Surine™ elution.