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1.
Langmuir ; 35(17): 5821-5829, 2019 Apr 30.
Artigo em Inglês | MEDLINE | ID: mdl-30955327

RESUMO

The electroadsorption of proteins at aqueous-organic interfaces offers the possibility to examine protein structural rearrangements upon interaction with lipophilic phases, without modifying the bulk protein or relying on a solid support. The aqueous-organic interface has already provided a simple means of electrochemical protein detection, often involving adsorption and ion complexation; however, little is yet known about the protein structure at these electrified interfaces. This work focuses on the interaction between proteins and an electrified aqueous-organic interface via controlled protein electroadsorption. Four proteins known to be electroactive at such interfaces were studied: lysozyme, myoglobin, cytochrome c, and hemoglobin. Following controlled protein electroadsorption onto the interface, ex situ structural characterization of the proteins by FTIR spectroscopy was undertaken, focusing on secondary structural traits within the amide I band. The structural variations observed included unfolding to form aggregated antiparallel ß-sheets, where the rearrangement was specifically dependent on the interaction with the organic phase. This was supported by MALDI ToF MS measurements, which showed the formation of protein-anion complexes for three of these proteins, and molecular dynamic simulations, which modeled the structure of lysozyme at an aqueous-organic interface. On the basis of these findings, the modulation of protein secondary structure by interfacial electrochemistry opens up unique prospects to selectively modify proteins.

2.
Analyst ; 142(17): 3194-3202, 2017 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-28758647

RESUMO

Fucoidans are sulfated polysaccharides mostly derived from algae and used in a number of applications (e.g. nutrition, cosmetics, pharmaceuticals and biomaterials). In this study, the electrochemical behaviour of fucoidans extracted from two algal species (Undaria pinnatifida and Fucus vesiculosus) was assessed using voltammetry at an array of micro-interfaces formed between two immiscible electrolyte solutions (µITIES) in which the organic electrolyte phase was gelled. Cyclic voltammetry revealed an adsorption process when scanning to negative potentials, followed by a desorption peak at ca. -0.50 V on the reverse scan, indicating the electroactivity of both fucoidans. U. pinnatifida fucoidan showed a more intense voltammetric signal compared to F. vesiculosus fucoidan. In addition, use of tridodecylmethylammonium (TDMA+) or tetradodecylammonium (TDDA+) as the organic phase electrolyte cation provided improved detection of both fucoidans relative to the use of bis(triphenylphosphoranylidene)ammonium (BTPPA+) cation. Application of adsorptive stripping voltammetry provided a linear response of current with fucoidan concentration in the range 2-20 µg mL-1 for U. pinnatifida fucoidan (with TDMA+) and 10-100 µg mL-1 for F. vesiculosus fucoidan (with TDDA+). The combination of TDMA+ in the organic phase and adsorptive pre-concentration for 180 s afforded a detection limit of 1.8 µg mL-1 fucoidan (U. pinnatifida) in aqueous phase of 10 mM NaOH and 2.3 µg mL-1 in synthetic urine (pH adjusted). These investigations demonstrate the electroactivity of fucoidans at the µITIES array and provide scope for their detection at low µg mL-1 concentrations using this approach.

3.
Anal Chem ; 88(5): 2596-604, 2016 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-26853853

RESUMO

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.

4.
Anal Chim Acta ; 893: 34-40, 2015 Sep 17.
Artigo em Inglês | MEDLINE | ID: mdl-26398420

RESUMO

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.


Assuntos
Técnicas Eletroquímicas , Ensaios Enzimáticos/métodos , Géis/química , Muramidase/análise , Solventes/química , Adsorção , Animais , Galinhas , Eletrodos , Oxirredução , Água/química
5.
Chem Commun (Camb) ; 50(80): 11829-32, 2014 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-25156670

RESUMO

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.


Assuntos
Géis/química , Muramidase/química , Adsorção , Animais , Galinhas , Desenho de Equipamento , Estrutura Terciária de Proteína , Espectrometria de Massas por Ionização por Electrospray/instrumentação , Eletricidade Estática , Água/química
6.
Analyst ; 138(20): 6192-6, 2013 Oct 21.
Artigo em Inglês | MEDLINE | ID: mdl-23971076

RESUMO

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.


Assuntos
Insulina/análise , Microextração em Fase Líquida/métodos , Soroalbumina Bovina/análise , Animais , Bovinos
7.
Anal Bioanal Chem ; 405(11): 3801-6, 2013 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-23239183

RESUMO

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

Assuntos
Técnicas Eletroquímicas/métodos , Eletrólitos/química , Hemoglobinas/análise , Adsorção , Animais , Bovinos , Limite de Detecção
8.
Chem Asian J ; 7(11): 2559-61, 2012 Nov.
Artigo em Inglês | MEDLINE | ID: mdl-22829567

RESUMO

Between the phases: 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.


Assuntos
Líquidos Iônicos/química , Muramidase/química , Água/química , Adsorção , Técnicas Eletroquímicas , Muramidase/metabolismo , Temperatura
9.
Anal Chem ; 84(5): 2505-11, 2012 Mar 06.
Artigo em Inglês | MEDLINE | ID: mdl-22243435

RESUMO

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.


Assuntos
Técnicas Eletroquímicas , Muramidase/química , Adsorção , Animais , Galinhas , Eletrólitos/química , Miniaturização , Muramidase/metabolismo , Soluções/química , Fatores de Tempo
10.
IEEE Trans Biomed Eng ; 58(9): 2521-7, 2011 Sep.
Artigo em Inglês | MEDLINE | ID: mdl-21642037

RESUMO

A characterization of gastrointestinal fluids has been performed by means of an electrochemical sensor that has potential for clinical in vivo and in vitro monitoring applications. The sensor comprised a three-electrode cell with a counter, reference, and four working electrodes, Au, Pt, Ir, and Rh. Cyclic voltammetry was used to obtain chemical information from faecal water (in vitro) and gut model (in vivo) fluids. Stable voltammetric responses were obtained for both fluids at these noble metal working electrodes. The responses differed in shape that demonstrated the discrimination capability and the potential for practical use as a tool for gastrointestinal fluid investigation. The analysis of the stability profiles in faecal water over a 14-h duration has indicated a possible adsorption mechanism with the formation of a biolayer on the sensor surface. The stability in gut model fluids over a 42-h duration has demonstrated a more stable profile, but the mechanisms involved are more complicated to determine.


Assuntos
Técnicas Eletroquímicas/instrumentação , Fezes/química , Conteúdo Gastrointestinal/química , Biotecnologia , Técnicas Eletroquímicas/métodos , Eletrodos , Desenho de Equipamento , Humanos , Metais Pesados/química , Modelos Biológicos , Água/química
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