Solid-state optical sensing of ultra-trace Hg2+ ions using chromoionophoric probe anchored silica monolithic architectures

In this work, we manifest the fabrication of a simple, portable, and benign solid-state sensor for the quantification of toxic Hg2+ ions through ocular colorimetric sensing. The sensor fabrication is modulated through sol-gel process using two different block-polymer surfactants (PEO and F108) for the formation of mesoporous silica monolithic designs that are immobilized with tailor-made probe molecules. The crack-free porous silica monoliths are structurally engineered to form, (i) highly ordered honey-combed 3D cubic, and (ii) disoriented worm-like mesopore structures that facilitates homogeneous probe anchoring through constrained spatial orientations for the selective detection of ultra-trace Hg2+ ions. The monolithic sensor materials are characterized by FE-SEM, HR-TEM, p-XRD, SAED, EDAX, XPS, FT-IR, TGA, and N2 isotherm analysis. For ensuring unambiguous ion-sensing, analytical parameters such as solution pH, temperature, kinetics, probe concentration, sensor quantity, linear signal response, matrix tolerance, the limit of detection (LD), and quantification (LQ) are optimized. The LD and LQ values for probe anchored PEO-MSM based sensor are 0.61 & 2.05 ppb and for probe anchored F108-MSM based sensor are 0.22 & 0.72 ppb, respectively, in the corresponding linear response range of 0−100 ppb and 0−50 ppb of Hg2+, which has been validated by real-time analysis of natural water samples.