Affinity Directed Surface Functionalization of Two Different Metal Nanoparticles by a Natural Ionophore: Probing and Removal of Hg and Al Ions from Aqueous Solutions.

In this work, we report affinity controlled surface modifications of two different metal nanoparticles (MNPs) using a hydrophilic natural ionophore (microbial chelator) aeruginic acid (abbreviated as HL) that possesses two different types of binding pockets viz. O/O from carboxylic acid group and N/O from a phenol-thiazole moiety. Preferred binding of the former donor set (i.e., O/O) on to the surface of silver nanoparticles (AgNPs) has resulted in a colorimetric nanomaterial HL@AgNPs, which showed naked eye observable easy detection of Hg in aqueous HEPES buffer at pH 7.4, even in the presence of other metal ions. On the other hand, excellent affinity of the phenol-thiazole moiety (i.e., N/O) for iron nanosurfaces (FeNPs) develops a fluorogenic nanomaterial HL@FeNPs. Brilliant emission behavior of this nanomaterial enabled it to be useful for highly selective recognition of Al under identical experimental conditions. Remarkable fluorescence enhancement (122-folds) of HL@FeNPs upon addition of Al remain unchanged even in the presence of other competing metal ions. The nanomaterials HL@AgNPs and HL@FeNPs could even detect the target analytes instantly offering lower detection limits of 2 and 80 nM, respectively. Presence of toxic metal ions as environmental pollutant demands for dual-functional materials capable of performing the task of probing cum removal. Surface functionalizations of the nanomaterials of silver and iron with HL have also resulted two removal agents that can efficiently and easily extract Hg and Al ions from contaminated water, respectively. We are not aware of any work that highlights the manifold utilization of a microbial chelator (i.e., natural ionophore) in the facile construction of different metal nanoparticles for environmental applications such as detection cum removal of toxic metal ions from aqueous solutions.