“…Strong chemical bonding of Trp to the surface is supported by the fact that it is not eliminated after numerous washings. Trp complexes can be formed with participation of carboxyl [28,33], amino group [34][35][36], and -electron system of indole [27,37,38]. Coordination of Trp through carboxyl group seems more possible in surface complexes, with protonated ␣-amino group oriented to the solution and thus stabilizing the nanoparticle.…”