Smart polymer-based calcium-ion self-regulated nanochannels by mimicking the biological Ca2+-induced Ca2+ release process

In nature, ion channels play key roles in controlling ion transport between cells and their surroundings. Calcium ion (Ca2+)-induced Ca2+ release (CICR), a critical control mechanism for Ca2+ channels, occurs due to a Ca2+ concentration gradient working in synergy with ryanodine receptors, which are famously known as calcium sparks. Inspired by this self-regulated biological process, a smart Ca2+ concentration-modulated nanochannel system was developed by integrating a poly{N-isopropylacrylamide-co-acrylamide-[4-(trifluoromethyl) phenyl]-2-thiourea(0.2)-co-acrylamideDDDEEKC(0.2)} (denoted as PNI-co-CF3-PT0.2-co-DDDEEKC0.2) three-component copolymer onto the nanochannels of a porous anodic alumina (PAA) membrane. In this smart polymer design, the DDDEEKC hepta-peptide unit has an extraordinary binding affinity with Ca2+ through coordination bonds, while CF3-PT functions as a hydrogen bond mediation unit, facilitating the remarkable conformational transition of the PNI main chain in response to Ca2+-specific adsorption. Due to these futures, the dynamic gating behaviors of the modified nanochannels could be precisely manipulated by the Ca(2+)concentration. In addition, the sensitive Ca2+ response, as low as 10 pM with a high specificity toward Ca2+ capable of discriminating Ca2+ from other potential interference metal ions (e.g., K+, Cu2+, Mg2+, Zn2+, Fe3+, and Al3+), remarkable morphological change in the nanochannel and satisfactory reversibility indicate the great potential of Ca2+-responsive polymers for the fabrication of biodevices and artificial nanochannels.