Ion‐Transfer Electrochemistry of Rat Amylin at the Water–Organogel Microinterface Array and Its Selective Detection in a Protein Mixture

Abstract

The behavior of proteins and polypeptides at electrified aqueous-organic interfaces is of benefit in label-free detection strategies. In this work, rat amylin (or islet amyloid polypeptide) was studied at the interface formed between aqueous liquid and gelled organic phases. Amylin is a polypeptide that is co-secreted with insulin from islet beta-cells and is implicated in fibril formation. In this study, rat amylin was used, which does not undergo aggregation. The polypeptide underwent an interfacial transfer process, from water to the gelled organic phase, under applied potential stimulation. Cyclic voltammetry revealed steady-state forward and peak-shaped reverse voltammograms, which were consistent with diffusion-controlled water-to-organic transfer and thin-film stripping or desorptive back-transfer. The diffusion-controlled forward current was greater when amylin was present in an acidic aqueous phase than when it was present in an aqueous phase at physiological pH; this reflects the greater charge on the polypeptide under acidic conditions. The amylin transfer current was concentration dependent over the range 2-10 μM, at both acidic and physiological pH. At physiological pH, amylin was selectively detected in the presence of a protein mixture, which illustrated the bioanalytical possibilities for this electrochemical behavior.

Electrochemistry of proteins at the interface between two immiscible electrolyte solutions

“…Another approach is to exploit the acid-base chemistry of proteins by adjusting the pH of an aqueous phase mixture so that only the target protein is cationic and detectable. This was demonstrated for the selective detection of amylin (rat) in mixture with a number of proteins, and made use of the fact that amylin's pI was higher than the proteins present so that it could be detected (noting that in this case, detection was based on an amylin ion transfer process, not complexation with organic phase anion) [31]. It is anticipated that sufficient selectivity for practical applications will not be achieved by these approaches, but ways to harness biomolecular recognition reagents at the ITIES will be developed, such as the attachment of aptamers at the ITIES [20].…”

Recent developments in electrochemistry at the interface between two immiscible electrolyte solutions for ion sensing

“…Different fabrication strategies to prepare these µITIES exist and have been reviewed elsewhere. 20,22 ITIES of microscopic dimensions are now routinely used under the form of a single µITIES [43][44][45][46][47][48]37,[49][50][51] ( Figure 1D) or of an array of µITIES [52][53][54][55][56][57][58][59][60][61][62][63][64][65][66][67][68][69][70] ( Figure 1E) allowing to reach limits of detection in the range of tens of nM with an analysis time of a couple of minutes. Diffusion of ionic species at µITIES has shown an asymmetric profile.…”

“…31,32,86 This experimental set-up could be used for the calibration-free determination of ion Target analytes. The sensing of molecules of biological interest (small organic molecules, 52,53,28,87 carbohydrates, 88,29 and proteins 26,[54][55][56]30,[57][58][59][60] ), synthetic organic molecules (drug molecules, 61,43,[62][63][64]81,89 pollutants 44,45,27,42 ) and inorganic species (both cations 36,46,31,32,47,48,33,37,38,49,65,34,39,40,51,50,66,41 and anions 67,35,68 ) has been extensively studied in the 2010-2015 period covered in thi...…”

Electroanalytical Opportunities Derived from Ion Transfer at Interfaces between Immiscible Electrolyte Solutions

“…Smaller polypeptides behave differently. For instance, the polypeptide rat amylin was detected via cyclic voltammetry under physiological conditions, [103] due to its high pI which can be advantageous if interferences can be discriminated by tuning the pH and it exhibited voltammograms consistent with its transfer across the ITIES.…”

“…This selection includes di-and tri-peptides, [32] melittin, [102] amylin, [103] protamine, [104] insulin, [105] myoglobin, [106] cytochrome c, [107] lysozyme, [21a, 108] hemoglobin [109] and albumin, [21d, 105c, 110] which are listed here in order of increasing molecular mass (<1 to ca. 66 kDa).…”