Ligand‐Binding Mediated Gradual Ionic Transport in Nanopores

Abstract

Selective binding of metal ions to their receptors at the cell membranes is essential for immune reactions, signaling, and opening/closing of the ion channels. Such ligand‐binding‐based pore activities inspire scientists to build metal‐ion‐responsive mesoporous films that can interact with metal ions to tune the ionic nanopore transport. However, to apply these mesoporous films in novel sensing and separation applications, their ligand‐binding‐triggered ionic pore transport needs to be understood fundamentally toward programming the transport of both anions and cations simultaneously and gradually. Herein, it is shown how Ca2+ ion concentration and attachment to the different chemistry silica nanopores tunes finely the nanopore transport of both anions and cations, especially for phosphate‐containing polyelectrolyte (PMEP) functionalized mesopores. This biased ligand binding can gradually regulate the transport of anions and cations, whereas pores without polymers can gradually regulate only the anionic transport. Last, pore polymer functionality related to Ca2+ ion binding also diverts the pores’ adsorption/desorption (reversibility) response. Almost fully reversible Ca2+ binding is observed in non‐functional pores and non‐reversible Ca2+ binding at the PMEP‐modified pores. It is also demonstrated that non/functional pores, even at sub‐µm concentrations, bind only divalent Ca2+ ions, but they are not selective to trivalent Al3+ ions.

Electropolymerization of Polydopamine at Electrode-Supported Insulating Mesoporous Films

“…Measurements of one series were repeated, until a constant current density in relation to the electrolyte exposure time was reached. Anodic peak current densities ( i p,a ) were quantified from the peaks in the oxidation part after defining a proper baseline correction as explained in the literature. , A previous study by Alberti et al showed that similar mesoporous films might get damaged after a critical time and continuous electrochemical investigations, which could influence the collected data . To avoid such risks in our measurement, while studying the nanopore transport of a film, we changed the measurement position (where the film was in contact with the electrolyte at the 0.21 cm 2 opening) every time the electrolyte was changed (having a different pH and/or ionic probe).…”

“…After forming or attaching various stimuli-responsive polymer units in their nanopores in a controlled amount, at a defined location, and with tailored stimuli-responsive units, these hybrid mesoporous films could be suitable for applications such as sensing or separation . Recent examples showed that compared to pristine silica nanopores, similar pores with stimuli-responsive polymer units show significant improvements in various material properties such as sensing the nanomolar concentration of ions with memory effect, ion concentration regulation such as electrokinetic ion transport, or gradual control of ionic pore accessibility. , However, many of these polymer functionalization strategies of nanopores remain challenging to implement (e.g., multistep synthesis protocols) and provide limited functionality to the nanopores, e.g., by only charging positively or negatively under changing pH conditions or requiring additional pore functionalities to regulate other ion transport tasks. Therefore, research on the functionalization of nanopores with polymers continues to seek new, straightforward methods to fabricate nanopore films with zwitterionic polymer functionalities and smart-gating.…”