Development of a strategy for the optical detection of anions in water by using surface-modified gold nanoparticles

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A strategy will be developed in this research project for the optical detection of inorganic anions in water relying on the immobilization of known anion receptors on the surfaces of water-soluble gold nanoparticles. In the absence of their respective analytes, these nanoparticles will reside in solution in non-aggregated form and their size will give rise to a plasmon resonance causing the solution to exhibit a characteristic color. This color will change in the presence of suitable inorganic anions because of nanoparticle aggregation. Aggregation will be caused by specific interactions between the receptors bound to the surface of the nanoparticles and their anionic substrates. Advantages of such systems are the detection sensitivity, which is an effect of the multivalent interactions underlying nanoparticle aggregation and the detection selectivity, which can be controlled by the type of surface-bound receptor. Anion receptors that will be used will either be based on the anion-binding cyclopeptides developed in the own group or on other described types of receptors. The work will mainly aim at the detection of anionic water constituents typically present in drinking or ground water such as sulfate, phosphate, and chloride anions. In addition, toxic arsenate anions will also be considered as analytes. Systematic investigations involving the variation of surface composition of the nanoparticles and the type of bound receptor will show whether the concept underlying this project will allow the detection of anions in their relevant concentrations in water with sufficient selectivity even in the presence of potentially competing analytes. Thus, it should be possible to estimate at the end of the project whether practical applications exist for such detection systems, for example for the facile qualitative detection of arsenate in drinking water.