Electrochemical Sensing of Curcumin: A Review.

Curcumin is a natural polyphenol derived from turmeric () root that has been used for centuries as a spice, coloring agent, and medicine. Curcumin presents anti-inflammatory, antioxidant, anticarcinogenic, antimicrobial, antiviral, antimalarial, hepatoprotective, thrombosuppressive, cardiovascular, hypoglycemic, antiarthritic, and anti-neurodegenerative properties. It scavenges different forms of free radicals and acts on transcription factors, growth factors and their receptors, cytokines, enzymes, and genes, regulating cell proliferation and apoptosis.

Electrochemistry of Flavonoids: A Comprehensive Review.

Flavonoids represent a large group of aromatic amino acids that are extensively disseminated in plants. More than six thousand different flavonoids have been isolated and identified. They are important components of the human diet, presenting a broad spectrum of health benefits, including antibacterial, antiviral, antimicrobial, antineoplastic, anti-mutagenic, anti-inflammatory, anti-allergic, immunomodulatory, vasodilatory and cardioprotective properties.

Advances in Electrochemical Biosensor Technologies for the Detection of Nucleic Acid Breast Cancer Biomarkers.

Breast cancer is the second leading cause of cancer deaths in women worldwide; therefore, there is an increased need for the discovery, development, optimization, and quantification of diagnostic biomarkers that can improve the disease diagnosis, prognosis, and therapeutic outcome. Circulating cell-free nucleic acids biomarkers such as microRNAs (miRNAs) and breast cancer susceptibility gene 1 (BRCA1) allow the characterization of the genetic features and screening breast cancer patients. Electrochemical biosensors offer excellent platforms for the detection of breast cancer biomarkers due to their high sensitivity and selectivity, low cost, use of small analyte volumes, and easy miniaturization.

Electrochemistry of chemotherapeutic alkylating agents and their interaction with DNA.

Alkylating agents were among the first anticancer drugs to be discovered and continue to be the most commonly used in chemotherapy. They are electrophiles that react with the ring nitrogen and extracyclic oxygen atoms of DNA bases, forming covalent adducts that further lead to cross-linking of DNA strands, abnormal base pairing or DNA strand breaks. The investigation and quantitative analysis of alkylating agents in biological samples are essential for monitoring the therapy progression and efficiency, understanding their pharmacokinetics and develop new more effective and specific chemotherapeutical drugs.

8-oxoguanine and 8-oxodeoxyguanosine Biomarkers of Oxidative DNA Damage: A Review on HPLC-ECD Determination.

Reactive oxygen species (ROS) are continuously produced in living cells due to metabolic and biochemical reactions and due to exposure to physical, chemical and biological agents. Excessive ROS cause oxidative stress and lead to oxidative DNA damage. Within ROS-mediated DNA lesions, 8-oxoguanine (8-oxoG) and its nucleotide 8-oxo-2'-deoxyguanosine (8-oxodG)-the guanine and deoxyguanosine oxidation products, respectively, are regarded as the most significant biomarkers for oxidative DNA damage.

DNA Electrochemical Biosensors for In Situ Probing of Pharmaceutical Drug Oxidative DNA Damage.

Deoxyribonucleic acid (DNA) electrochemical biosensors are devices that incorporate immobilized DNA as a molecular recognition element on the electrode surface, and enable probing in situ the oxidative DNA damage. A wide range of DNA electrochemical biosensor analytical and biotechnological applications in pharmacology are foreseen, due to their ability to determine in situ and in real-time the DNA interaction mechanisms with pharmaceutical drugs, as well as with their degradation products, redox reaction products, and metabolites, and due to their capacity to achieve quantitative electroanalytical evaluation of the drugs, with high sensitivity, short time of analysis, and low cost. This review presents the design and applications of label-free DNA electrochemical biosensors that use DNA direct electrochemical oxidation to detect oxidative DNA damage.

Nanostructured material-based electrochemical sensing of oxidative DNA damage biomarkers 8-oxoguanine and 8-oxodeoxyguanosine: a comprehensive review.

Oxidative DNA damage plays an important role in the pathogenesis of various diseases. Among oxidative DNA lesions, 8-oxoguanine (8-oxoG) and its corresponding nucleotide 8-oxo-2'-deoxyguanosine (8-oxodG), the guanine and deoxyguanosine oxidation products, have gained much attention, being considered biomarkers for oxidative DNA damage. Both 8-oxoG and 8-oxodG are used to predict overall body oxidative stress levels, to estimate the risk, to detect, and to make prognosis related to treatment of cancer, degenerative, and other age-related diseases.

Natural phenolic antioxidants electrochemistry: Towards a new food science methodology.

Natural phenolic compounds are abundant in the vegetable kingdom, occurring mainly as secondary metabolites in a wide variety of chemical structures. Around 10,000 different plant phenolic derivatives have been isolated and identified. This review provides an exhaustive overview concerning the electron transfer reactions in natural polyphenols, from the point of view of their in vitro antioxidant and/or pro-oxidant mode of action, as well as their identification in highly complex matrixes, for example, fruits, vegetables, wine, food supplements, relevant for food quality control, nutrition, and health research.

Calcium channel blocker lercanidipine electrochemistry using a carbon black-modified glassy carbon electrode.

Lercanidipine, a third-generation dihydropyridine calcium L-type channel blocker, redox behavior at different carbon electrode materials, in a wide pH range, using cyclic, square-wave, and differential pulse voltammetry, was studied. A comparison was made between unmodified glassy carbon electrode (GCE) and boron-doped diamond electrode (BDDE), and GCE and BDDE modified with a carbon black (CB) nanoparticle embedded within a dihexadecylphosphate (DHP) nanostructured film (CB-DHP/GCE and CB-DHP/BDDE). Lercanidipine oxidation, for 3.

Electrochemical assay for 20S proteasome activity and inhibition with anti-cancer drugs.

The majority of eukaryotic regulated protein turnover is performed by the proteasome, a multi-catalytic enzyme. Due to the fact that proteasome enzyme abnormal functioning was observed in different malignant cells, the proteasome is becoming a target for medical treatment. In order to evaluate the mechanisms of action of pharmaceutical compounds on proteasome enzyme inhibition, detecting and characterizing its activity is essential.

Electrochemical and AFM Characterization of G-Quadruplex Electrochemical Biosensors and Applications.

Guanine-rich DNA sequences are able to form G-quadruplexes, being involved in important biological processes and representing smart self-assembling nanomaterials that are increasingly used in DNA nanotechnology and biosensor technology. G-quadruplex electrochemical biosensors have received particular attention, since the electrochemical response is particularly sensitive to the DNA structural changes from single-stranded, double-stranded, or hairpin into a G-quadruplex configuration. Furthermore, the development of an increased number of G-quadruplex aptamers that combine the G-quadruplex stiffness and self-assembling versatility with the aptamer high specificity of binding to a variety of molecular targets allowed the construction of biosensors with increased selectivity and sensitivity.

Electrochemistry of Alzheimer Disease Amyloid Beta Peptides.

Alzheimer's disease (AD) is a widespread form of dementia that is estimated to affect 44.4 million people worldwide. AD pathology is closely related to the accumulation of amyloid beta (Aβ) peptides in fibrils and plagues, the small oligomeric intermediate species formed during the Aβ peptides aggregation presenting the highest neurotoxicity.

Amyloid Beta Peptide VHHQ, KLVFF, and IIGLMVGGVV Domains Involved in Fibrilization: AFM and Electrochemical Characterization.

The time-dependent structural modifications and oxidation behavior of specifically chosen five short amyloid beta (Aβ) peptides, Aβ, Aβ, Aβ, Aβ, and Aβ, fragments of the complete human Aβ peptide, were investigated by atomic force microscopy (AFM) and voltammetry. The objective was to determine the influence of different Aβ domains (VHHQ that contains electroactive histidine H residues, KLVFF that is the peptide hydrophobic aggregation core, and IIGLMVGGVV that is the C-terminus hydrophobic region), and of Aβ peptide hydrophobicity, in the fibrilization mechanism. The short Aβ peptides absence of aggregation or the time-dependent aggregation mechanisms, at room temperature, in free chloride media, within the time window from 0 to 48 h, were established by AFM via changes in their adsorption morphology, and by differential pulse voltammetry, via modifications of the amino acid residues oxidation peak currents.

Amyloid-β peptides time-dependent structural modifications: AFM and voltammetric characterization.

The human amyloid beta (Aβ) peptides, Aβ1-40 and Aβ1-42, structural modifications, from soluble monomers to fully formed fibrils through intermediate structures, were investigated, and the results were compared with those obtained for the inverse Aβ40-1 and Aβ42-1, mutant Aβ1-40Phe(10) and Aβ1-40Nle(35), and rat Aβ1-40Rat peptide sequences. The aggregation was followed at a slow rate, in chloride free media and room temperature, and revealed to be a sequence-structure process, dependent on the physicochemical properties of each Aβ peptide isoforms, and occurring at different rates and by different pathways. The fibrilization process was investigated by atomic force microscopy (AFM), via changes in the adsorption morphology from: (i) initially random coiled structures of ∼0.

Atomic Force Microscopy and Voltammetric Investigation of Quadruplex Formation between a Triazole-Acridine Conjugate and Guanine-Containing Repeat DNA Sequences.

The interactions of the Tetrahymena telomeric repeat sequence d(TG4T) and the polyguanylic acid (poly(G)) sequence with the quadruplex-targeting triazole-linked acridine ligand GL15 were investigated using atomic force microscopy (AFM) at a highly oriented pyrolytic graphite and voltammetry at a glassy carbon electrode. GL15 interacted with both sequences, in a time dependent manner, and G-quadruplex formation was detected. AFM showed the adsorption of quadruplexes as small d(TG4T) and poly(G) spherical aggregates and large quadruplex-based poly(G) assemblies, and voltammetry showed the decrease and disappearance of GL15 and guanine oxidation peak currents and appearance of the G-quadruplex oxidation peak.

Quadruplex nanostructures of d(TGGGGT): influence of sodium and potassium ions.

The Tetrahymena telomeric repeat sequence d(TG4T) contains only guanine (G) and thymine (T) bases and has medical and nanotechnological applications because of its ability to self-assemble into stiff tetra-molecular parallel-stranded G-quadruplexes. The hexadeoxynucleotide d(TG4T) was studied using atomic force microscopy (AFM) on the highly oriented pyrolytic graphite surface and differential pulse (DP) voltammetry at a glassy carbon electrode. The d(TG4T) single-strands self-assembled into G-quadruplex structures, very fast in K(+) ions solution and slowly in Na(+) ions containing solution.

Self-assembled G-quadruplex nanostructures: AFM and voltammetric characterization.

G-rich oligodeoxynucleotides (ODNs) have great medical and nanotechnological potential, because they can self-assemble into G-quadruplexes and higher-order nanostructures. The folding properties of d(G)10, d(TG9) and d(TG8T) ODNs were studied using atomic force microscopy (AFM) and voltammetry at carbon electrodes. Single-stranded ODNs, in Na(+) containing solutions and for short incubation times, were detected using AFM as network films and polymeric structures and using voltammetry by the occurrence of only the guanine oxidation peak.

Thrombin-Binding Aptamer Quadruplex Formation: AFM and Voltammetric Characterization.

The adsorption and the redox behaviour of thrombin-binding aptamer (TBA) and extended TBA (eTBA) were studied using atomic force microscopy and voltammetry at highly oriented pyrolytic graphite and glassy carbon. The different adsorption patterns and degree of surface coverage were correlated with the sequence base composition, presence/absence of K(+), and voltammetric behaviour of TBA and eTBA. In the presence of K(+), only a few single-stranded sequences present adsorption, while the majority of the molecules forms stable and rigid quadruplexes with no adsorption.

Lipoic acid-palladium complex interaction with DNA, voltammetric and AFM characterization.

The mechanism of interaction of lipoic acid-palladium complex (LAPd) with double-stranded DNA (dsDNA), as well as the adsorption process and the redox behaviour of LAPd, of its ligand lipoic acid (LA), and of the LAPd-containing dietary supplement, Poly-MVA, were studied using atomic force microscopy (AFM) and voltammetry at highly oriented pyrolytic graphite (HOPG) and glassy carbon electrodes. In the presence of small concentrations of LAPd molecules, the dsDNA molecules appeared less knotted and bended, and more extended on the HOPG surface, when compared with the dsDNA molecules adsorbed from the same dsDNA solution concentration. The voltammetric results demonstrated the interaction of both LAPd and Poly-MVA with dsDNA, but no oxidative damage caused to dsDNA was detected.

Interaction of imatinib with liposomes: voltammetric and AFM characterization.

The interaction of imatinib with 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC) and 2-oleoyl-1-stearoyl-sn-glycero-3-phosphocholine (OSPC) liposomes and the adsorption of DPPC and OSPC were studied using atomic force microscopy (AFM) at highly oriented pyrolytic graphite (HOPG) and differential pulse voltammetry at glassy carbon electrode (GCE). The HOPG induces the rupture of the liposomes and allows the lipids to adsorb along one of the three axes of symmetry of the HOPG basal planes, forming well-ordered lamellar structures. After interaction, both DPPC monolayers and DPPC-imatinib complexes are adsorbed onto HOPG.

AFM nanometer surface morphological study of in situ electropolymerized neutral red redox mediator oxysilane sol-gel encapsulated glucose oxidase electrochemical biosensors.

Four different silica sol-gel films: methyltrimethoxysilane (MTMOS), tetraethoxysilane (TEOS), 3-aminopropyltriethoxysilane (APTOS) and 3-glycidoxypropyl-trimethoxysilane (GOPMOS) assembled onto highly oriented pyrolytic graphite (HOPG) were characterized using atomic force microscopy (AFM), due to their use in the development of glucose biosensors. The chemical structure of the oxysilane precursor and the composition of the sol-gel mixture both influenced the roughness, the size and the distribution of pores in the sol-gel films, which is relevant for enzyme encapsulation. The GOPMOS sol-gel film fulfils all the morphological characteristics required for good encapsulation of the enzyme, due to a smooth topography with very dense and uniform distribution of only small, 50 nm diameter, pores at the surface.

Adsorption of synthetic homo- and hetero-oligodeoxynucleotides onto highly oriented pyrolytic graphite: atomic force microscopy characterization.

DNA adsorption on electrode surfaces is of fundamental interest for the development of DNA-based biosensors. The free adsorption of 10-mer synthetic oligodeoxynucleotides (ODNs) onto highly oriented pyrolytic graphite (HOPG) surfaces was studied using Magnetic AC mode atomic force microscopy (MAC Mode AFM). The mechanism of interaction of nucleic acids with carbon electrode surfaces was elucidated, using 10-mer synthetic homo- and hetero-ODNs sequences of known base sequences, because they allow clear interpretation of the experimental data.

DNA imaged on a HOPG electrode surface by AFM with controlled potential.

Single-molecule AFM imaging of single-stranded and double-stranded DNA molecules self-assembled from solution onto a HOPG electrode surface is reported. The interaction of DNA with the hydrophobic surface induced DNA aggregation, overlapping, intra- and intermolecular interactions. Controlling the electrode potential and using the phase images as a control method, to confirm the correct topographical characterization, offers the possibility to enlarge the capability of AFM imaging of DNA immobilized onto conducting substrates, such as HOPG.