Hormone glucagon: electrooxidation and determination at carbon nanotubes

Abstract

The oxidation of glucagon, which is one of the key hormones in glucose homeostasis, was studied at electrodes modified with carbon nanotubes (CNT) that were dispersed in a polysaccharide adhesive chitosan (CHIT). Such electrodes displayed improved resistance to fouling, which allowed for the investigation of both the electrolysis/mass spectrometry and electroanalysis of glucagon. The off-line electrospray ionization and tandem mass spectrometric analyses showed that the -4 Da mass change to glucagon upon electrolysis at CNT was due to the electrooxidation of its tryptophan (W25) and dityrosine (Y10, Y13) residues. The methionine residue of glucagon did not contribute to its oxidation. The amperometric determination of glucagon yielded the limit of detection equal to ~20 nM (E = 0.800 V, pH 7.40, S/N = 3), sensitivity of 0.46 A M−1 cm−2, linear dynamic range up to 2.0 μM (R2 = 0.998), response time <5 s, and good signal stability. Free tryptophan and tyrosine yielded comparable analytical figures of merit. The direct amperometric determination of unlabeled glucagon at CHIT-CNT electrodes is the first example of a rapid alternative to the complex analytical assays of this peptide.

Direct and Continuous Monitoring of Multicomponent Antibiotic Gentamicin in Blood at Single-Molecule Resolution

“…To further evaluate whether low-molecular-weight biomolecules present in whole blood would affect the detection of gentamicin, we conducted tests on representative biomolecules, including glucose, lactate, dNTPs, positively charged amino acids, C-peptide, insulin, and glucagon. The individual detection experiments of representative biomolecules present in whole blood demonstrate that, within physiological concentration ranges, − these biomolecules do not significantly interfere with the detection of gentamicin, in which the result is consistent with the testing results of blank whole blood (Figures S14 and S15). The inherent anti-interference capability is crucial for point-of-care monitoring of gentamicin.…”

Editors’ Choice—Review—The Future of Carbon-Based Neurochemical Sensing: A Critical Perspective

“…Heterogeneity of carbon fiber's surface chemistry makes uniform modification tunability challenging as exposing specific plane interactions is impossible. In recent years we have witnessed the emergence of diamond [104][105][106][107][108][109][110] and CNT hybrid 24,27,[33][34][35]38,82,84,88,101 materials for improved electrochemical performance. These innovative materials have also found utility outside of the FSCV community, and researchers have fabricated hybrid electrode materials used to investigate neurochemicals with more traditional electrochemical detection techniques.…”

Review—Recent Advances in FSCV Detection of Neurochemicals via Waveform and Carbon Microelectrode Modification

“… 120 There are two different types of ENK that arise from proteolytic cleaving: methionine-enkephalin (M-ENK) and leucine-enkephalin (L-ENK). 121 , 122 The detection of ENKs, however, becomes difficult due to the presence of tyrosine which requires higher oxidation potentials and fouls the electrode surface. To overcome these challenges, the modified sawhorse waveform (MSW) was designed and used to detect M-ENK.…”