The high pH resistance and structural stability of HLNPs make them a good candidate for direct covalent surface modification in dispersion state. Here, we demonstrated amination of cured HL60NP by using the base-catalyzed oxirane ring-opening reaction (Figure ). In this reaction, glycidyltrimethylammonium chloride (GTMA) reacts with the aliphatic and phenolic hydroxyl groups present on the surfaces of cured HLNPs. The presence of amino groups alongside hydroxyl groups with different pKa renders the particles with pH-dependent colloidal dispersibility (Figure ). It is worth noting that the modified particles will precipitate upon pH neutralization that occurs during dialysis against deionized water, however upon decreasing or increasing pH they can be redispersed back to the colloidal state without any external modification such as sonication or manual shaking (Figure ). In contradiction to unmodified particles, the GTMA-modified particles show a positive zeta potential at pH 2 (+ 35 mV, Figure ) and do not coagulate at room temperature over an extended time duration (more than one month). It is also interesting to note that the quaternary ammonium groups rendered the particles with a narrower size distribution (Figure ). This approach can open a new window for targeting reactions at hydroxyl groups in the colloidal state instead of chemical modifications before the particle formation that could adversely affect the self-assembly and stability of the nanoparticles.