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To be or not be a … Sensor

The ability to detect metal ions in chemical and biomedical systems is of paramount importance. Accordingly, the development of sensors and imaging agents able to detect metal ions with high sensitivity and selectivity is an ongoing challenge. For example, Pd(II) is known to have deleterious effects on cellular processes as well as causing possible sensitizing of the skin. As such, governments issue guidance on the safe levels of palladium exposure in food, cosmetics, medicines, and workplace exposure. Adherence to such guidance requires reliable and accurate sensing technologies which have well-characterized and understood sensing mechanisms.

In a recent study by Nika Žurga and colleagues in the deMello group has uncovered critical issues and anomalies with a recently reported Pd(II) sensor based on a small molecule coumarin (C460). Whilst this previous study claimed that C460 is a robust and sensitive Pd(II) sensor, Žurga demonstrated that C460 is in fact a very poor Pd(II) sensor, and should not be used under any circumstances. Specifically, the team show that the effect previously reported as Pd(II) sensing is really a result of the molecule’s ability to act as a pH sensor over an extremely narrow pH range. The source study used PdCl2 as the Pd(II) source without realizing that PdCl2 is actually insoluble in water! Investigations concluded that HCl was used a solubilizing agent. Such an approach protonates the amine group on C460, which in turn inhibits intramolecular charge transfer and reduces fluorescence. To prove this variation a result of pH variations and not Pd(II), the authors titrated both C460 with PdCl2 as well as a control C460 solution across a range of pH values.

This work furthers research on the topic of Pd(II) sensing by reframing a previous study and highlights the need to provide an accurate and complete description of experimental methods used to generate data in scientific publications.

Written by Nathan Khosla

Read the published article here.

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