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Keywords:

  • Mesoporous materials;
  • Sensors, chemical;
  • Sensors, optical

Abstract

With recent advances in mesostructured materials and nanotechnologies, new methods are emerging to design optical sensors and biosensors, and to develop highly sensitive solid sensors. Here, highly sensitive, low cost, simple nanosensor designs for naked-eye detection of toxic metal ions are successfully developed by the immobilization of commercially available α,β,γ,δ-tetrakis(1-methylpyridinium-4-yl)porphine p-toluenesulfonate (TMPyP) and diphenylcarbazide (DPC), and chemically synthesized 4-n-dodecyl-6-(2-thiazolylazo) resorcinol (DTAR) and 4-n-dodecyl-6-(2-pyridylazo) phenol (DPAP) chromophore molecules into spherical nanosized cavities and surfaces. A rational strategy was crucial to develop optical nanosensors that can be used to control accurate recognition and signaling abilities of analyte species for ion-sensing purposes. This is the first reported evidence of the significant key factors of the development of receptors as ‘indicator dyes' and surface-confinement materials as ‘carriers' to broadening the applicability of optical chemical sensors for selective discrimination of trace levels of toxic analytes. In all the nanosensor design techniques presented here, a dense pattern of immobilized hydrophobic ‘neutral' and hydrophilic ‘charged' chromophores with intrinsic mobility, as a result of extremely robust constructed sequences on nanoscale structures, is a 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 cadmium ions to low levels of concentration in the range of 10–9 to 10–10M. Optimization of control sensing conditions is established to achieve enhanced signal response and color intensities. These chemical nanosensors are reversible and have the potential to serve effectively in on-site field analysis of environmental samples, which eliminates the necessity for instrument-dependent analysis. Moreover, these new classes of optical cage sensors exhibit long-term stability of signaling and recognition functionalities that in general provide extraordinary sensitivity, selectivity, reusability, and fast kinetic detection and quantification of various deleterious metal ions in our environment.