Analytische Chemie
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Integrating fluorescent probes with sensing matrices presents a major challenge because usually, when confined in a rather rigid matrix, fluorophores tend to behave completely different than for instance in the molecular state in solution. The lecture reviews the major strategies that have been devised recently to circumvent such issues with special focus on the works carried out in this field by BAM’s Chemical and Optical Sensing Division. Moreover, it will be shown that by using certain strategies not only can the response behavior be retained but synergistic effects can even endow the hybrid with a much better performance than the probe molecule alone.
Macrocycle-containing fluorescent probes continue to be one of the most popular classes of indicator molecules for the sensitive optical detection of ionic inorganic analytes, in particular metal ions, since the first integration of crown ether building blocks into chromophoric π systems more than 30 years ago. However, whereas a large multitude of such probes have been described for operation in organic or mixed aqueous environments, the step to realistic analytical media such as water samples, aqueous food extracts or body fluids is still scarce. On one hand, this is due to considerably low complex stability constants for instance for alkali and alkaline-earth metal ions. On the other hand, many classes of organic dyes that show favourable spectroscopic properties and ion-induced responses in organic solvents are not soluble in neat aqueous media and/or exhibit only significantly quenched fluorescence, even if transition metal ions are binding strongly to the receptor unit. A way to circumvent such problems in a rather simple manner is the steric incorporation of fluorescent probes into mesoporous silica nanomaterials. The local polarity in such pores, whether nascent or modified appropriately with functional silanes, resembles much more a quasi-organic environment while at the same time allowing for free diffusion of water and its cargo.
Two examples of powerful hybrid signalling systems will be presented, utilizing charge transfer-type indicator molecules that show inferior sensing properties in their molecular state. One example discusses mercury(II) determination over an extended concentration range and the other discusses silver(I) and mercury(II) discrimination simply on the basis of photophysical effects retained in the hybrid materials.