Synthesis and modeling of calix[4]pyrrole wrapped Au nanoprobe for specific detection of Pb(II): Antioxidant and radical scavenging efficiencies

Abstract Newly synthesized Au nanoparticles (AuNPs) capped by calix[4]pyrrole tetrahydrazide (CPTH) has been explored for the colorimetric and fluorimetric detection of Pb(II) ions. The molecular modeling studies reveal the surface mediated properties of CPTH around AuNPs. It is observed that reduction of Au(III) to Au(0) occurs due to the presence of hydrazide groups of CPTH and charge transfer preferably through N atoms and carbonyl group. These interactions further govern the stability of the CPTH-AuNPs. The optical sensing of Pb(II) was carried out in water and the linear range of detection falls between 10 nM and 1 μM concentration range. Moreover, a concomitant pink-to-violet color change is observed providing a useful optical method of detecting Pb(II) in water. The mechanistic insights for the sensing of Pb(II) is based on the overarching hypothesis that Pb(II)ions disturbs the non-covalent interactions of the capping CPTH ligand around the Au° particles causing aggregation of CPTH-AuNPs. The aggregation of CPTH-AuNPs has been elucidated by TEM and DLS experiments. Also, the plausible binding behavior of CPTH-AuNPs with Pb(II) due to hydrogen bonding interactions through –NH groups is discussed. CPTH-AuNPs have also shown their utility for analysis of Pb(II) in industrial waste water and human serum samples. The ability of CPTH-AuNPs for its in vitro anti-oxidant activity and radical scavenging efficiencies has been studied. Thus, the present study suggests notable potential of supramolecular functionalized nanoparticles as a promising chemosensor for toxic ions and a beneficial tool for biomedical applications.