Grafting Commercial Surfactants (Brij, CiEj) and PEG to Electrodes via Aryldiazonium Salts

Formation of sparsely tethered bilayer lipid membrane on a biodegradable self-assembled monolayer of poly(lactic acid)

The utilization of biomimetic membranes supported by advanced self-assembled monolayers is gaining attraction as a promising sensing tool. Biomimetic membranes offer exceptional biocompatibility and adsorption capacity upon degradation, transcending their role as mere research instruments to open new avenues in biosensing. This study focused on anchoring a sparsely tethered bilayer lipid membrane onto a self-assembled monolayer composed of a biodegradable polymer, functionalized with poly(ethylene glycol)-cholesterol moieties, for lipid membrane integration. Real-time monitoring via quartz crystal microbalance, coupled with characterization using surface-enhanced infrared absorption spectroscopy and electrochemical impedance spectroscopy, provided comprehensive insights into each manufacturing phase. The resulting lipid layer, along with transmembrane pores formed by gramicidin A, exhibited robust stability. Electrochemical impedance spectroscopy analysis confirmed membrane integrity, successful pore formation, and consistent channel density. Notably, gramicidin A demonstrated sustained functionality as an ion channel upon reconstitution, with its functionality being effectively blocked and inhibited in the presence of calcium ions. These findings mark significant strides in developing intricate biodegradable nanomaterials with promising applications in biomedicine.

Highly Stretchable and Self-Adhesive Elastomers Based on Polymer Chain Rearrangement for High-Performance Strain Sensors

Polydimethylsiloxane (PDMS) has been widely used in many fields. However, the polymerization process of the siloxane chain is highly complex, and it is challenging to enhance the mechanical properties of PDMS elastomers significantly. We found that adding a small amount of polyoxyethylene lauryl ether (Brij-35) into siloxane polymers can result in B-PDMS elastomers with high tensile properties and strong adhesion. It is worth noting that this is the first study to improve the mechanical properties of PDMS using Brij-35. Here, we intensely studied a variety of process conditions that influence the cross-linking of PDMS, emphasizing the modification mechanism of the polymer chain. The hydroxyl groups in Brij-35 and the platinum catalyst in PDMS form a complex, which inhibits the cross-linking process of PDMS, not only forming a heterogeneous cross-linking network in the B-PDMS but also disentangling the strongly wound siloxane polymer chain, thereby rearranging the PDMS polymer chains. Furthermore, in order to prepare a strain sensor based on the B-PDMS elastomer under safe and convenient conditions, we prepared laser-scribed graphene powder (LSGP) by laser-scribing of graphene oxide (GO) films, and the LSGP and carbon nanotubes (CNTs) endowed the B-PDMS elastomers with excellent electrical properties. The sensor could firmly adhere to the skin and generate a high-quality response to a variety of human motions, and it could drive the robotic hand to grasp and lift objects accurately. The high-performance strain sensors based on B-PDMS have broad applications in medical sensing and biopotential measurement.

Electrochemically Deposited Molecular Thin Films on Transparent Conductive Oxide substrate: Combined DC and AC Approaches for Characterization

Transparent conductive oxides such as indium tin oxide (ITO) substrates are commonly employed as prime materials for optoelectronic applications. Enhancement in functions of such devices often compels stable and robust modification of the ITO substrate to improve its interfacial charge transfer characteristics. Thereby, in this work, naphthyl modifier multilayer films are fabricated on ITO substrate using conventional electrochemical reduction of 1-naphthyl diazonium salts (NAPH-D) via altering its concentration ranging from 2 mM to 12 mM with a step size of 2. Surface coverage was significantly tuned by varying NAPH-D concentration, keeping other parameters such as the number of scans and scan rate constant. For lower concentration (2 mM), the molecular thickness ~ 6 nm was obtained, whereas, with higher concentration (12 mM) produced around 15-18 nm thickness. Atomic force microscopy (AFM), cyclic voltammetry and electrochemical impedance spectroscopy (EIS) in the presence of a ferrocene redox probe also supports the formation of well packed molecular film grown on the ITO surface. Further, the wettability property of the grafted naphthyl film was investigated at different surface coverages and correlated with charge transfer resistance (Rct) obtained from EIS studies.

Building Tailored Interfaces through Covalent Coupling Reactions at Layers Grafted from Aryldiazonium Salts

Aryldiazonium ions are widely used reagents for surface modification. Attractive aspects of their use include wide substrate compatibility (ranging from plastics to carbons to metals and metal oxides), formation of stable covalent bonding to the substrate, simplicity of modification methods that are compatible with organic and aqueous solvents, and the commercial availability of many aniline precursors with a straightforward conversion to the active reagent. Importantly, the strong bonding of the modifying layer to the surface makes the method ideally suited to further on-surface (postfunctionalization) chemistry. After an initial grafting from a suitable aryldiazonium ion to give an anchor layer, a target species can be coupled to the layer, hugely expanding the range of species that can be immobilized. This strategy has been widely employed to prepare materials for numerous applications including chemical sensors, biosensors, catalysis, optoelectronics, composite materials, and energy conversion and storage. In this Review our goal is first to summarize how a target species with a particular functional group may be covalently coupled to an appropriate anchor layer. We then review applications of the resulting materials.

Electrodes for Membrane Surface Science. Bilayer Lipid Membranes Tethered by Commercial Surfactants on Electrochemical Sensors

Commercial surfactants, which are inexpensive and abundant, were covalently grafted to flat and transparent electrodes, and it appears to be a simple functionalization route to design biomembrane sensors at large-scale production. Sparsely tethered bilayer lipid membranes (stBLM) were stabilized using such molecular coatings composed of diluted anchor-harpoon surfactants that grab the membrane with an alkyl chain out of a PEGylated-hydrogel layer, which acts as a soft hydration cushion. The goal of avoiding the synthesis of complex organic molecules to scale up sensors was achieved here by grafting nonionic diblock oligomers (Brij58 = C _xH_{2 x+1}(OCH₂CH₂) _nOH with x = 16 and n = 23) and PEO short chains ((OCH₂CH₂) _nOH with n = 9 and n = 23) from their hydroxyl (-OH) end-moiety to a monolayer of -Ar-SO₂Cl groups, which are easy to form on electrodes (metals, semiconducting materials, ...) from aryl-diazonium salt reduction. A hybrid molecular coating on gold, with scarce Ar-SO₂-Brij58 and PEO oligomers, was used to monitor immobilization and fusion kinetics of DOPC small unilamellar vesicles (SUV) by both quartz crystal microbalance (QCM) and surface plasmon resonance (SPR) techniques. Using flat and transparent thin chromium film electrodes, we designed biosensors to couple surface sensitive techniques for membranes, including X-ray reflectivity (XRR), atomic force microscopy (AFM) with subnanometer resolution, and optical microscopy, such as fluorescence recovery after photobleaching measurements (FRAP), in addition to electrochemistry techniques (cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS)). The advantages of this biomembrane-sensing platform are discussed for research and applications.