Surface enhancement effects in the sensing of anions at redox-active molecular films are investigated in detail and rationalised based on a consideration of the dielectric binding microenvironment.

Methods that enable the sensitive and label-free detection of protein biomarkers are well-positioned to make potentially significant contributions to diagnostics and derived personalized healthcare. In support of this goal, a myriad of (electrochemical) methodologies have been developed; recently, electrochemical capacitance spectroscopy emerged as an impedance-derived approach which, in employing surface-confined redox-transducers, circumvents problems associated with the use of solution-phase redox-probes. Herein, we expand this scope by utilizing phytic acid-doped polyaniline as a novel redox-charging polymer support enabling the reagentless assaying of C-reactive protein in serum with good sensitivity. The construction of the sensory interface via electropolymerization allows facile tuning of the surface coverage and redox (capacitive) properties of the polymers, which, in turn, modulate both assay selectivity, fouling, and sensitivity. Significantly, this methodology is readily extendable to a wide range of electrode materials and analytes.

The development of real-life applicable ion sensors, in particular those capable of repeat use and long-term monitoring, remains a formidable challenge. Herein, we demonstrate, in a proof-of-concept, the real-time voltammetric sensing of anions under continuous flow in a 3D-printed microfluidic system. Electro-active anion receptive halogen bonding (XB) and hydrogen bonding (HB) ferrocene-isophthalamide-(iodo)triazole films were employed as exemplary sensory interfaces. Upon exposure to anions, the cathodic perturbations of the ferrocene redox-transducer are monitored by repeat square-wave voltammetry (SWV) cycling and peak fitting of the voltammograms by a custom-written MATLAB script. This enables the facile and automated data processing of thousands of SW scans and is associated with an over one order-of-magnitude improvement in limits of detection. In addition, this improved analysis enables tuning of the measurement parameters such that high temporal resolution can be achieved. More generally, this new flow methodology is extendable to a variety of other analytes, including cations, and presents an important step towards translation of voltammetric ion sensors from laboratory to real-world applications.

After binding to its cell surface receptor angiotensin converting enzyme 2 (ACE2), severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) enters the host cell through directly fusing with plasma membrane (cell surface pathway) or undergoing endocytosis traveling to lysosome/late endosome for membrane fusion (endocytic pathway). However, the endocytic entry regulation by host cell remains elusive. Recent studies show ACE2 possesses a type I PDZ binding motif (PBM) through which it could interact with a PDZ domain-containing protein such as sorting nexin 27 (SNX27). In this study, we determined the ACE2-PBM/SNX27-PDZ complex structure, and, through a series of functional analyses, we found SNX27 plays an important role in regulating the homeostasis of ACE2 receptor. More importantly, we demonstrated SNX27, together with retromer complex (the core component of the endosomal protein sorting machinery), prevents ACE2/virus complex from entering lysosome/late endosome, resulting in decreased viral entry in cells where the endocytic pathway dominates. The ACE2/virus retrieval mediated by SNX27–retromer could be considered as a countermeasure against invasion of ACE2 receptor-using SARS coronaviruses.

No abstract