Detection of haemoglobin using an adsorption approach at a liquid – liquid microinterface array

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 <pI) in the aqueous phase, it undergoes a potential-dependent adsorption and complexation, at the interface, with the anions of the organic phase electrolyte. When utilised as a simple and fast preconcentration step, consisting of adsorbing the protein at the interface, in conjunction with voltammetric desorption. This opens up the ITIES to the adsorptive stripping voltammetry (AdSV) approach. Utilising a 60 s adsorption step and linear sweep voltammetry, a linear response to Hb concentration in aqueous solution over the range 0.01 – 0.5 µM was achieved. The equation of the best-fit straight-line was Ip = 7.46 C - 0.109, R = 0.996, where Ip is the peak current (nA) and C is haemoglobin concentration (µM). The calculated detection limit (3s) was 48 nM for a 60 s preconcentration period, while the relative standard deviation was 13.3 % for 6 successive measurements at 0.1 µM Hb. These results illustrate the prospects for simple, portable and rapid label-free detection of biomacromolecules offered by electrochemistry at arrays of liquid-liquid microinterfaces

Electrochemical studies toward proteomic analysis

This thesis provides the basis for a label-free bioanalytical platform using electrochemical analysis at liquid –liquid interfaces. The possibility to detect biomolecules such as proteins in a label-free manner via adsorption and ion-transfer was achieved. Several pre-treatment steps used in proteome analysis, such as protein pre-concentration and digestion, were studied. The results demonstrate the promise of this strategy for the detection and identification of proteins

An Electrochemical Sensing Platform Based on Liquid-Liquid Microinterface Arrays Formed in Laser-Ablated Glass Membranes

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. © 2016 American Chemical Society

Fingerprinting the tertiary structure of electroadsorbed lysozyme at soft interfaces by electrostatic spray ionization mass spectrometry

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

Stripping voltammetric detection of insulin at liquid–liquid microinterfaces in the presence of bovine albumin

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

Void-Assisted Ion-Paired Proton Transfer at Water-Ionic Liquid Interfaces.

At the water-trihexyl(tetradecyl)phosphonium tris(pentafluoroethyl)trifluorophosphate ([P14,6,6,6 ][FAP]) ionic liquid interface, the unusual electrochemical transfer behavior of protons (H(+) ) and deuterium ions (D(+) ) was identified. Alkali metal cations (such as Li(+) , Na(+) , K(+) ) did not undergo this transfer. H(+) /D(+) transfers were assisted by the hydrophobic counter anion of the ionic liquid, [FAP](-) , resulting in the formation of a mixed capacitive layer from the filling of the latent voids within the anisotropic ionic liquid structure. This phenomenon could impact areas such as proton-coupled electron transfers, fuel cells, and hydrogen storage where ionic liquids are used as aprotic solvents

Behavior of Lysozyme at the Electrified Water/Room Temperature Ionic Liquid Interface

The globular protein lysozyme was adsorbed and desorbed under electrochemical conditions at the water/room temperature ionic liquid microinterface array; the electrochemical desorption process provides a basis for protein detection at these interfaces

Investigation of a solvent-cast organogel to form a liquid-gel microinterface array for electrochemical detection of lysozyme

Ion transfer at aqueous-organogel interfaces enables the non-redox detection of ions and ionisable species by voltammetry. In this study, a non-thermal method for preparation of an organogel was employed and used for the detection of hen-egg-white-lysozyme (HEWL) via adsorptive stripping voltammetry at an array of aqueous-organogel microinterfaces. Tetrahydrofuran solvent casting was employed to prepare the organogel mixture, hence removing the need for heating of the solution to be gelled, as used in previous studies. Cyclic voltammetry of HEWL at the microinterface array revealed a broad adsorption process on the forward scan, at positive applied potentials, followed by a desorption peak at ca. 0.68 V, indicating the detection of HEWL in this region. Application of an adsorption step, where a constant optimized potential of 0.95 V was applied, followed by voltammetric detection provided for a linear response range of 0.02-0.84 μM and a detection limit of 0.030 μM for 300 s adsorption. The detection limit was further improved by utilizing differential pulse stripping voltammetry, resulting in detection limits of 0.017 μM, 0.014 μM, and 0.010 μM for adsorptive pre-concentration times of 60, 120 and 300 s, respectively, in unstirred solutions. These results are an improvement over other methods for the detection of HEWL at aqueous-organic interfaces and offers a basis for the label-free detection of protein

Fabrication and characterization of a miniaturized planar voltammetric sensor array for use in an electronic tongue

A planar voltammetric sensor array for use in an electronic tongue was fabricated using a combinationof microfabrication techniques. The techniques of e-beam evaporation and pulsed laser deposition wereapplied to prepare a device that contained all of the electrodes integrated on a silicon die (6mm×6 mm).The working electrodes were metals gold, platinum, iridium and rhodium. They were characterized bySEM and EDX, and by electrochemical investigation of the packaged dies with cyclic voltammetry insolutions of sulfuric acid and of ferrocene carboxylic acid in aqueous buffer solution. The robustness andreproducibility of the devices were assessed by potential cycling in acid solution

Electrochemical stability of PEDOT for wearable on-skin application

Conducting polymers are promising candidates for wearable devices due to mechanical flexibility combined with electroactivity. While electrochemical measurements have been adopted as a central transduction method in many on-skin sensors, less studied is the stability of the active materials (in particular poly3,4-ethylenedioxythiophene, PEDOT) in such systems, particularly for “on-skin” applications. In this study, several different variants of doped PEDOT are fabricated and characterized in terms of their (electrical, physical, and chemical) stability in biological fluid. PEDOT doped with tosylate (TOS) or polystyrenesulfonate (PSS) are selected as prototypical forms of conducting polymers. These are compared with a new variant of PEDOT co-doped with both TOS and PSS. Artificial interstitial fluid (aISF) loaded with 1% wt/vol bovine serum albumin is adopted as the testing medium to demonstrate the stability in dermal applications (i.e., conducting polymer microneedles or coatings on microneedles). A range of techniques such as cyclic voltammetry and electrochemical impedance spectroscopy are used to qualify and quantify the stability of the doped conducting polymers. Furthermore, this study is extended by using human skin lysate in the aISF to demonstrate proof-of-concept for stable use of PEDOT in wearable “on-skin” electronics.</p