A simple naked eye detection of Pb<SUP>2+</SUP> on a gold nanocluster decorated disposable paper spot arrays

Abstract

Among all the heavy metal ions, Lead (Pb2+) has become a serious threat to human health and the environment. It is vital to develop an accurate system to monitor the Pb2+ level. Fluorescent and colorimetric sensors are one such system to detect Pb2+ with high accuracy. Herein, we used thiolated gold nanoclusters (GNC) decorated paper spot arrays for the detection of Pb2+ through a simple colorimetric method. The prepared GNC and the developed complex were well-studied using various characterizations. The addition of Pb2+ to GNC results in a slight shift in the absorption spectra from 485 nm to 534 nm. Further, GNC showed a broad emission peak centered around 650 nm, and the addition of Pb2+ resulted in an enhancement in the peak intensity, due to cation-induced-aggregation-induced emission enhancement (AIEE). The HR-TEM analysis confirms the spherical shape of the prepared GNCs with an average size of 2.60 nm. Whereas, the addition of Pb2+ onto GNC leads to the formation of an aggregated structure of size 6.17 nm due to the formation of a chelation complex. The GNC showed a particle size of 2 nm with a zeta potential of -16.45 mV, whereas the Pb2+@GNC complex exhibited an increment in an average size to 96 nm having a zeta potential of -19.67 mV, substantially demonstrating the capturing of Pb2+ by GNC. Overall, spectroscopic and surface morphology studies indicated aggregated induced emission (AIE) phenomena between GNC and Pb2+. The selective detection of Pb2+ by GNC was observed by the appearance of salmon pink to mauves colour and was captured using a smartphone. The developed paper spot array can detect up to 10 ppm of Pb2+. Further, the developed probe showed a distinguishable color change for Pb2+ along with other cations of interest such as Hg2+, Mg2+, K+, Mn2+, and Fe2+. Therefore, the present paper spot array could detect Pb2+ even in the presence of other metal ions due to its evident distinguishability. The fabricated GNC-embedded paper spot array obeys the new REASSURED criteria proposed by the World Health Organization (WHO) and could be used for on-spot detection of Pb2+.