Electrochemical detection of protein post-translational modifications: Phosphorylation and nitration of amyloid-beta (1–16)

Polymerase incorporation of 4-nitrophenyl modified 2'-deoxyuridine-5'-triphosphates into double-stranded DNA for direct electrochemical detection

Three novel 2'-deoxyuridine-5'-triphosphates modified with 4-nitrophenyl groups via various linkers (dUTP-N1, dUTP-N2, and dUTP-N3) were tested as bearers of reducible electroactive labels as well as substrates suitable for enzymes used in polymerase chain reaction (PCR) and recombinase polymerase amplification (RPA) with a potential application to direct electrochemical detection of double-stranded deoxyribonucleic acid (dsDNA). In cyclic and square wave voltammograms on carbon screen printed electrodes, the labeled dUTP have demonstrated distinct reduction peaks at potentials of -0.7 V to -0.9 V (phosphate buffer, pH 7.4). The reduction peak currents of dUTP-N derivatives were found to increase with their molar concentrations. The dUTP-N3 with a double bond in the linker had the lowest reduction potential (about 100 mV less negative) among the derivatives studied. Further, dUTP-N nucleotides were tested as substrates in PCR and RPA to incorporate the electroactive labels into 90, 210, or 206 base pair long dsDNA amplicons. However, only a dUTP-N1 derivative with a shorter linker without the double bond demonstrated satisfactory compatibility with both PCR and RPA, though with a low reaction output of modified dsDNA amplicons (at 100% substitution of dTTP). The dsDNA amplicons produced by PCR with 85% substitution of dTTP by the dUTP-N1 in the reaction mixture were successfully detected by square wave voltammetry at micromolar concentrations at high square wave frequency.

Electrochemical Analysis in Studying β-Amyloid Aggregation

β-amyloid (Aβ) is comprised of a group of peptides formed as a result of cleavage of the amyloid precursor protein by secretases. Aβ aggregation is considered as a central event in pathogenesis of Alzheimer's disease, the most common human neurodegenerative disorder. Molecular mechanisms of Aβ aggregation have intensively being investigated using synthetic Aβ peptides by methods based on monitoring of aggregates, including determination of their size and structure. In this review, an orthogonal approach to the study of Aβ aggregation is considered, which relies on electrochemical registration of the loss of peptide monomers. Electrochemical analysis of Aβ (by voltammetry and amperometric flow injection analysis) is based on registration of the oxidation signal of electroactive amino acid residues of the peptide on an electrode surface. The Aβ oxidation signal disappears, when the peptide is included in the aggregate. The advantages and disadvantages of electrochemical analysis for the study of spontaneous and metal-induced aggregation of Aβ, comparative analysis of various peptide isoforms, and study of the process of complexation of metal ions with the metal-binding domain of Aβ are discussed. It is concluded that the combined use of the electrochemical method and the methods based on detection of Aβ aggregates makes it possible to obtain more complete information about the mechanisms of peptide aggregation.

Electrochemical Amino Acid Sensing: A Review on Challenges and Achievements

The rapid growth of research in electrochemistry in the last decade has resulted in a significant advancement in exploiting electrochemical strategies for assessing biological substances. Among these, amino acids are of utmost interest due to their key role in human health. Indeed, an unbalanced amino acid level is the origin of several metabolic and genetic diseases, which has led to a great need for effective and reliable evaluation methods. This review is an effort to summarize and present both challenges and achievements in electrochemical amino acid sensing from the last decade (from 2010 onwards) to show where limitations and advantages stem from. In this review, we place special emphasis on five well-known electroactive amino acids, namely cysteine, tyrosine, tryptophan, methionine and histidine. The recent research and achievements in this area and significant performance metrics of the proposed electrochemical sensors, including the limit of detection, sensitivity, stability, linear dynamic range(s) and applicability in real sample analysis, are summarized and presented in separate sections. More than 400 recent scientific studies were included in this review to portray a rich set of ideas and exemplify the capabilities of the electrochemical strategies to detect these essential biomolecules at trace and even ultra-trace levels. Finally, we discuss, in the last section, the remaining issues and the opportunities to push the boundaries of our knowledge in amino acid electrochemistry even further.

Electrochemical detection of different p53 conformations by using nanostructured surfaces

Protein electrochemistry represents a powerful technique for investigating the function and structure of proteins. Currently available biochemical assays provide limited information related to the conformational state of proteins and high costs. This work provides novel insights into the electrochemical investigation of the metalloprotein p53 and its redox products using label-free direct electrochemistry and label-based antibody-specific approaches. First, the redox activities of different p53 redox products were qualitatively investigated on carbon-based electrodes. Then, focusing on the open p53 isoform (denatured p53), a quantitative analysis was performed, comparing the performances of different bulk and nanostructured materials (carbon and platinum). Overall, four different p53 products could be successfully discriminated, from wild type to denatured. Label-free analysis suggested a single electron exchange with electron transfer rate constants on the order of 1 s-1. Label-based analysis showed decreasing affinity of pAb240 towards denatured, oxidized and nitrated p53. Furthermore, platinum nanostructured electrodes showed the highest enhancement of the limit of detection in the quantitative analysis (100 ng/ml). Overall, the obtained results represent a first step towards the implementation of highly requested complex integrated devices for clinical practices, with the aim to go beyond simple protein quantification.