Liquid metal nanoparticles (LM NPs) have attracted significant attention owing to their unique properties and wide range of potential applications from electronics to biomedicine. In this study, we investigate the surface chemistry of eutectic gallium indium (EGaIn) NPs using different phosphonic acid derivatives in aqueous media. Our findings show that EGaIn NPs exhibit significant surface chemical composition changes when exposed to these ligands in solution during the ultrasonication-assisted synthesis in water, displaying optimal long-term colloidal stability in alkaline media. Interestingly, it is demonstrated for the first time that the use of sulfur-containing phosphonic acids, particularly phosphorothioates, leads to improved colloidal suspension stability and higher control over the NP size distribution. In addition, using a phosphorothioate derivative with a terminal N-hydroxysuccinimide group, a novel synthetic conjugation strategy to incorporate redox-active molecules, in particular ferrocene, onto the NP surface has been developed, permitting broadening of their potential applications in (electro)catalysis and sensing.