Biodegradable ion-selective nanosensors with p-diethylaminophenol functionalized rhodamine as chromoionophore for metal ions measurements

A new rhodamine derivative functionalized with a p-diethylaminophenol moiety together with two interacting pH-sensitive sites (PHX2) has been utilized as an electrically charged chromoionophore in ion-selective nano-optodes for the first time. The PHX2-based ion-selective nanosensors were prepared by a simple precipitation method with biodegradable polycaprolactone (PCL) and tributyl O-acetylcitrate (ATBC) as the polymer matrix. The obtained nanoparticles exhibited a hydrodynamic diameter of about 180 nm with water in oil conformation. The PHX2-based biodegradable nano-optodes can respond to pH from 5 to 12 in the presence of cation exchanger. Such nano-optodes were further applied to prepare fluorescent cation selective nano-optodes with incorporated ionophores based on ion-exchange sensing mechanism. For model ions Na⁺ and K⁺, the prepared nanosensors showed decreased absorbance intensity in the presence of the increasing ion concentrations. The cytotoxicity of Na⁺- and K⁺-selective nanosensors at the highest concentration for 24 h displayed above 85 % cell viability, indicating low toxicity and high biocompatibility. Chemically induced intracellular sodium concentration change in HepG2 cells was also successfully monitored in real time. The results proved that the new fluorescent chromoionophore was fully functional in ionophore-based biodegradable nano-optodes. Such biodegradable nanosensors appear to be promising in biomedical monitoring and disease therapy.