Electrochemical adsorption and voltammetry of hen-egg-white-lysozyme (HEWL) was studied at an array of microinterfaces between two immiscible electrolyte solutions (μITIES). Adsorption of the protein was achieved at an optimal applied potential of 0.95 V, after which it was desorbed by a voltammetric scan to lower potentials. The voltammetric peak recorded during the desorption scan was dependent on the adsorption time and on the aqueous phase concentration of HEWL. The slow approach to saturation or equilibrium indicated that protein reorganization at the interface was the rate-determining step and not diffusion to the interface. For higher concentrations and longer adsorption times, a HEWL multilayer surface coverage of 550 pmol cm(-2) was formed, on the basis of the assumption that a single monolayer corresponded to a surface coverage of 13 pmol cm(-2). Implementation of adsorption followed by voltammetric detection as an adsorptive stripping voltammetric approach to HEWL detection demonstrated a linear dynamic range of 0.05-1 μM and a limit of detection of 0.03 μM, for 5 min preconcentration in unstirred solution; this is a more than 10-fold improvement over previous HEWL detection methods at the ITIES. These results provide the basis for a new analytical approach for label-free protein detection based on adsorptive stripping voltammetry.

Lysozyme can be electrochemically detected after adsorption at an electrified gel-water interface. Ex situ characterization by electrostatic spray ionization mass spectrometry provides insights into the interfacial detection mechanism by allowing changes to the tertiary structure of electroadsorbed lysozyme to be fingerprinted for the first time.

Electrochemistry at the interface between two immiscible electrolyte solutions (ITIES) provides a platform for label-free detection of biomolecules. In this study, adsorptive stripping voltammetry (AdSV) was implemented at an array of microscale ITIES for the detection of the antidiabetic hormone insulin. By exploiting the potential-controlled adsorption of insulin at the ITIES, insulin was detected at 10 nM via subsequent voltammetric desorption. This is the lowest detected concentration reported to-date for a protein by electrochemistry at the ITIES. Surface coverage calculations indicate that between 0.1 and 1 monolayer of insulin forms at the interface over the 10-1000 nM concentration range of the hormone. In a step toward assessment of selectivity, the optimum adsorption potentials for insulin and albumin were determined to be 0.900 V and 0.975 V, respectively. When present in an aqueous mixture with albumin, insulin was detected by tuning the adsorption potential to 0.9 V, albeit with reduced sensitivity. This provides the first example of selective detection of one protein in the presence of another by exploiting optimal adsorption potentials. The results presented here provide a route to the improvement of detection limits and achievement of selectivity for protein detection by electrochemistry at the ITIES.

The behaviour of haemoglobin (Hb) at the interface between two immiscible electrolyte solutions (ITIES) has been examined for analytical purposes. When Hb is fully protonated under acidic conditions (pH

Arrays of microscale interfaces between two immiscible electrolyte solutions (μITIES) were formed using glass membranes perforated with microscale pores by laser ablation. Square arrays of 100 micropores in 130 μm thick borosilicate glass coverslips were functionalized with trichloro(1H,1H,2H,2H-perfluorooctyl)silane on one side, to render the surface hydrophobic and support the formation of aqueous-organic liquid-liquid microinterfaces. The pores show a conical shape, with larger radii at the laser entry side (26.5 μm) than at the laser exit side (11.5 μm). The modified surfaces were characterized by contact angle measurements and X-ray photoelectron spectroscopy. The organic phase was placed on the hydrophobic side of the membrane, enabling the array of μITIES to be located at either the wider or narrower pore mouth. The electrochemical behavior of the μITIES arrays were investigated by tetrapropylammonium ion transfer across water-1,6-dichlorohexane interfaces together with finite element computational simulations. The data suggest that the smallest microinterfaces (formed on the laser exit side) were located at the mouth of the pore in hemispherical geometry, while the larger microinterfaces (formed on the laser entry side) were flatter in shape but exhibited more instability due to the significant roughness of the glass around the pore mouths. The glass membrane-supported μITIES arrays presented here provide a new platform for chemical and biochemical sensing systems.

The increase interests in wearable device market are triggered by healthcare monitoring. Common examples are pulse, heart rate and temperature monitors. Wearable technology has opened up new path for non-invasive diagnostic and therapeutic technologies via sensing of biomarker/drug from the liquid extracted on skin including sweat (Bandodkar & Wang, 2014; Liu et al., 2017). The increasing demand of integrating electronic technology in wearable devices is driven by needs for individual monitoring remotely at home, often called as ubiquitous health care (Choudhuri et al., 2019). In addition, wearable devices allow continuous, long time monitoring at any place, anytime (Bohr et al., 2019). Mechanical and electrical responsive conducting polymers (CPs), plus high flexibility and stretch-ability contribute to recent accelerate growth of publications involving conducting polymer in wearable and skin-attachable device. Metals and silica (semiconductors) are inorganic materials that are generally regarded as highly conductive but are rigid and inflexible. The concept of organic conductors/semiconductors has arisen since the discovery of highly conducting polyacetylene by Hideki Shirakawa, working along with Alan MacDiarmid and physicist Alan Heeger in 1977 (Shirakawa et al., 1977). The most apparent advantage of organic electronics as compared to inorganic is that they are highly flexibility and they are lightweight. These properties are ideal for wearable sensors. Conducting polymers with long-term electrical and chemical stability such as polypyrrole (PPy), poly(3,4-ethylenedioxy-thiophene) (PEDOT) and polyaniline (PANi) (Figure 1) have gained popularity in this field (Puiggali-Jou et al., 2019; Talikowska et al., 2019). Doping counterions in close proximity to the extended pi-bond significantly improve CP conductivity. These doped CPs have electrical conductivities ranging from >1 S/cm to >1000 S/cm aligning CPs with the inorganic semiconductors, for example silicon

The formation of cytochrome c oligomers was induced at liquid−gel and liquid−liquid interfaces via electroadsorption. At an optimum interfacial potential (Eads=0.975 V), the protein was accumulated at these soft interfaces. It was found that as the concentration of adsorbed protein increased, a single voltammetric peak evolved into double and triple peaks (tads=300 s). Analysis of the protein that accumulated at the interfaces by polyacrylamide gel electrophoresis indicated the presence of oligomeric species, corresponding to dimers (ca. 27 kD), trimers (ca. 35 kD), and even larger species (>250 kD) after prolonged electroadsorption (tads=2 h) at macro‐scale soft interfaces. Accordingly, it was possible to electrochemically induce oligomerisation at these soft interfaces, which can be tuned through experimental factors such as interfacial potential difference, electroadsorption time, and bulk solution concentration. These results suggest the use of electrochemistry at soft interfaces as a strategy for the investigation of protein oligomerisation and its inhibition.

Electrochemical immunosensors are an emerging technology for the fast, sensitive, and reliable diagnosis of diseases from bodily fluids. These sensors work by detecting a change in current upon analyte binding to an immuno‐functionalized electrode. Current methods of electrode functionalization are lengthy processes involving self‐assembled monolayer formation and wet chemistry biofunctionalization. Herein, thin films deposited from the plasma phase of oxazoline precursors are investigated and optimized as an alternative approach for electrode functionalization. The plasma‐enabled method has the advantage of being substrate independent and allows the spontaneous binding of biomolecules in physiological buffer. Surface sensitive analysis techniques are employed to characterize the thickness, reactivity, and stability of the thin films before investigating their electrochemical properties on indium tin oxide and gold electrodes including the feasibility to reduce charge transfer resistance with gold nanoparticles. Last, these films are employed to develop an immunosensor for the detection of free epithelial cell adhesion molecule with a limit of detection of 8.7 ng mL−1.