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Biomimetic supercontainers for size-selective electrochemical sensing of molecular ions

View Article: PubMed Central - PubMed

ABSTRACT

New ionophores are essential for advancing the art of selective ion sensing. Metal-organic supercontainers (MOSCs), a new family of biomimetic coordination capsules designed using sulfonylcalix[4]arenes as container precursors, are known for their tunable molecular recognition capabilities towards an array of guests. Herein, we demonstrate the use of MOSCs as a new class of size-selective ionophores dedicated to electrochemical sensing of molecular ions. Specifically, a MOSC molecule with its cavities matching the size of methylene blue (MB+), a versatile organic molecule used for bio-recognition, was incorporated into a polymeric mixed-matrix membrane and used as an ion-selective electrode. This MOSC-incorporated electrode showed a near-Nernstian potentiometric response to MB+ in the nano- to micro-molar range. The exceptional size-selectivity was also evident through contrast studies. To demonstrate the practical utility of our approach, a simulated wastewater experiment was conducted using water from the Fyris River (Sweden). It not only showed a near-Nernstian response to MB+ but also revealed a possible method for potentiometric titration of the redox indicator. Our study thus represents a new paradigm for the rational design of ionophores that can rapidly and precisely monitor molecular ions relevant to environmental, biomedical, and other related areas.

No MeSH data available.


Near-Nerstian response of a simulated wastewater sample (collected from the Fyrisån in Uppsala, Sweden) to MB.
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f3: Near-Nerstian response of a simulated wastewater sample (collected from the Fyrisån in Uppsala, Sweden) to MB.

Mentions: To illustrate that the above proof-of-concept protocols can be applied in a more practical setting that involves a more complex analyte, we conducted a simulated wastewater experiment with water collected from the Fyris River (Fyrisån) in the city of Uppsala. By adding controlled amounts of the “pollutant” MB+, the response curve for the simulated wastewater remained near-Nernstian, although an apparent shift of the detection limit was observed (Fig. 3). We attribute this shift to a decrease in the oxygen content of Fyrisån’s water caused by microorganisms found in the river water42. The loss of oxygen due to microorganisms after collection of the water sample produces a reducing environment, which can in turn decrease the actual MB+ ion concentration by a certain amount and cause a small shift in the response curve. This speculation was confirmed by a control experiment, in which an equal amount of MB+ was dissolved in DI water and the water from Fyrisån. The UV-vis absorption showed a lower concentration of MB+ in the river water (Fig. 3), indicating that MB+ was indeed being partially reduced. It should also be noted that, despite the reduction of MB+, the inclusion of wastewater to the system is not expected to change the detection limit of the ISE since the ISE responds to the MB+ only in the cationic form. Thus, the detection of MB+ by MOSC based ISEs provides a possible method for potentiometric titration of the redox indicator, an exciting aspect we are pursuing in future studies.


Biomimetic supercontainers for size-selective electrochemical sensing of molecular ions
Near-Nerstian response of a simulated wastewater sample (collected from the Fyrisån in Uppsala, Sweden) to MB.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5385547&req=5

f3: Near-Nerstian response of a simulated wastewater sample (collected from the Fyrisån in Uppsala, Sweden) to MB.
Mentions: To illustrate that the above proof-of-concept protocols can be applied in a more practical setting that involves a more complex analyte, we conducted a simulated wastewater experiment with water collected from the Fyris River (Fyrisån) in the city of Uppsala. By adding controlled amounts of the “pollutant” MB+, the response curve for the simulated wastewater remained near-Nernstian, although an apparent shift of the detection limit was observed (Fig. 3). We attribute this shift to a decrease in the oxygen content of Fyrisån’s water caused by microorganisms found in the river water42. The loss of oxygen due to microorganisms after collection of the water sample produces a reducing environment, which can in turn decrease the actual MB+ ion concentration by a certain amount and cause a small shift in the response curve. This speculation was confirmed by a control experiment, in which an equal amount of MB+ was dissolved in DI water and the water from Fyrisån. The UV-vis absorption showed a lower concentration of MB+ in the river water (Fig. 3), indicating that MB+ was indeed being partially reduced. It should also be noted that, despite the reduction of MB+, the inclusion of wastewater to the system is not expected to change the detection limit of the ISE since the ISE responds to the MB+ only in the cationic form. Thus, the detection of MB+ by MOSC based ISEs provides a possible method for potentiometric titration of the redox indicator, an exciting aspect we are pursuing in future studies.

View Article: PubMed Central - PubMed

ABSTRACT

New ionophores are essential for advancing the art of selective ion sensing. Metal-organic supercontainers (MOSCs), a new family of biomimetic coordination capsules designed using sulfonylcalix[4]arenes as container precursors, are known for their tunable molecular recognition capabilities towards an array of guests. Herein, we demonstrate the use of MOSCs as a new class of size-selective ionophores dedicated to electrochemical sensing of molecular ions. Specifically, a MOSC molecule with its cavities matching the size of methylene blue (MB+), a versatile organic molecule used for bio-recognition, was incorporated into a polymeric mixed-matrix membrane and used as an ion-selective electrode. This MOSC-incorporated electrode showed a near-Nernstian potentiometric response to MB+ in the nano- to micro-molar range. The exceptional size-selectivity was also evident through contrast studies. To demonstrate the practical utility of our approach, a simulated wastewater experiment was conducted using water from the Fyris River (Sweden). It not only showed a near-Nernstian response to MB+ but also revealed a possible method for potentiometric titration of the redox indicator. Our study thus represents a new paradigm for the rational design of ionophores that can rapidly and precisely monitor molecular ions relevant to environmental, biomedical, and other related areas.

No MeSH data available.