Coumarin–Calix[4]arene Conjugate-Anchored SiO(2) Nanoparticles as an Ultrasensor Material for Fe(3+) to Work in Water, in Serum, and in Biological Cells

[Image: see text] A coumarin-appended calixarene derivative (CouC4A) and a hybrid material generated by covalently linking this onto a silica surface (CouC4A@SiO(2)) were synthesized and were characterized by various analytical, spectroscopy, and microscopy methods. Both these materials are capable of sensing Fe(3+) with greater sensitivity and selectivity. The sensitivity is enhanced by 30,000 fold on going from a simple solution phase to the silica surface with the limit of Fe(3+) detection being 1.75 ± 0.4 pM when CouC4A@SiO(2) is used, and the sensing is partially reversible with phosphates, while it is completely reversible with adenosine 5′-triphosphate (ATP). While the calix precursor, CouC4A, has a limitation to work in water, anchoring this onto SiO(2) endowed it with the benefit of its use in water as well as in buffer and thereby extends its application toward Fe(3+) sensing even in the biorelevant medium such as fetal bovine serum and human serum. The hybrid material is biocompatible and shows ∼90% cell viability in the case of MDA-MB231 and 3T3 cell lines. CouC4A@SiO(2) functions as a reversible sensor for Fe(3+) with the use of ATP in vitro as well as in biological cells. Thus, the inorganic–organic hybrid material, such as, CouC4A@SiO(2), is an indispensable material for sensitive and selective detection of Fe(3+) in a picomolar range in solution and in nanomolar to micromolar range in biorelevant fluids and biological cells, respectively.