Mesoporous Cage‐Like Silica Monoliths for Optical Sensing of Pollutant Ions

Abstract

Abstract An attractive means of improving pollution monitoring would be the use of simple, inexpensive, rapidly responsive and portable sensors. In this respect, selective optical sensing attracts much interest due to the use of ‘low‐tech’ spectroscopic instrumentation to detect relevant chemical species in biological and environmental processes. With recent advances in mesostructured materials and nanotechnologies, new methods are emerging to design optical sensors and biosensors and develop highly sensitive solid sensors. Recent developments have focused on tailoring specific sensors for the naked‐eye detection of highly toxic heavy metal ions such as lead, cadmium, antimony and mercury in aquatic samples. Sensitive, low‐cost, simple nanosensor designs have been successfully developed by the immobilization of hydrophobic and hydrophilic chromophore molecules into spherically nanosized cage cavities and surfaces. A rational strategy was crucial to the development of optical nanosensors that can be used to control the accurate recognition and signaling abilities of analyte species for ion‐sensing purposes. In this chapter, we report evidence of significant key factors in the development of receptors as ‘indicator dyes’ and surface‐confined materials as ‘carriers’ to broaden the applicability of optical chemical sensors for the selective discrimination of trace levels of toxic analytes. For the nanosensor design techniques described here, a dense pattern of immobilized hydrophobic ‘neutral’ and hydrophilic ‘charged’ chromophores with intrinsic mobility via extremely robust constructed sequences onto nanoscale structures was key to enhancing the sensing functionality of optical nanosensors. These nanosensor designs can be used as cage probe sinks with reliable control, for the first time, over the colorimetric recognition of highly toxic metal ions to low levels of ∼10 −9 M . Control sensing assays were established to achieve enhanced signal response and color intensities. Moreover, these new classes of optical cage sensor exhibited long‐term stability of signaling and recognition functionalities that provided extraordinary sensitivity, selectivity, reusability and rapid kinetic detection and quantification of deleterious metal ions in the environment. This chapter details recent developments in the efficient design of optical nanosensors that employ mesoporous materials as model carriers to control the accurate recognition and signaling abilities of analyte species for ion‐sensing purposes.