Average particle size as determined by TEM analysis and zeta potential of the PS nanoparticles in water (pH = 6.8) and Tyrode's-HEPES buffer (pH = 7.3).

Nanoparticle	Average particle size + SD (nm)	Zeta potential ± SD (mV)
		Water	Tyrode's-HEPES buffer
PS-25	25.2 ± 4.9	−42.5 ± 2.0	−39.4 ± 1.9
PS-50	50.4 ± 4.9	−50.8 ± 1.6	−35.8 ± 1.6
PS-119	119.2 ± 8.5	−35.9 ± 0.7	−31.7 ± 1.3
PS-151	150.6 ± 9.7	−46.1 ± 1.1	−25.2 ± 1.8
PS-201	200.7 ± 10.7	−56.3 ± 1.2	−33.7 ± 1.4