Variable Sensing Ion Selectivity of the l‐Cysteine Capped ZnS:Mn Nanocrystals in Aqueous Solution

Abstract

Colloidal l‐cysteine (Cys)‐capped ZnS:Mn nanocrystals were synthesized and exposed to various pH conditions to modify their surface for further applications as photo‐chemical sensors. The observed zeta‐potential values indicated that the ZnS:Mn–Cys nanocrystals formed positive charged nanocrystal surface at pH 3 condition. Therefore, they were considered to be applied as an anion sensor. As a result, the fluorescence of the ZnS:Mn–Cys‐pH 3 nanocrystals was exclusively quenched by the addition of nitrite (NO2−) ions. In addition, the ZnS:Mn–Cys nanocrystals, which were exposed to pH 7 and pH 13, formed negatively charged surfaces, which were presumed to be applied as cation photosensors. Consequently, the fluorescence of the ZnS:Mn–Cys‐pH 7 nanocrystals were amplified by the addition of Zn2+ ions, whereas the most added metal ions caused quenching of the emission lights of the ZnS:Mn–Cys‐pH 7 nanocrystals. Moreover, the fluorescence of the ZnS:Mn–Cys‐pH 13 nanocrystals was quenched only when Cu2+ ions were added.