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Highly sensitive label-free techniques of DNA determination are particularly interesting in relation to the present development of the DNA sensors. We show that subnanomolar concentrations (related to monomer content) of unlabeled DNA can be determined using copper solid amalgam electrodes or hanging mercury drop electrodes in the presence of copper. DNA is first treated with acid (e.g., 0.5 M perchloric acid), and the acid-released purine bases are directly determined by the cathodic stripping voltammetry. Volumes of 5-3 microL of acid-treated DNA can easily be analyzed, thus making possible the determination of picogram and subpicogram amounts of DNA corresponding to attomole and subattomole quantities of 1000-base pair DNA. Application of this determination in DNA hybridization detection is demonstrated using surface H for the hybridization (superparamagnetic beads with covalently attached DNA probe) and the mercury electrodes only for the determination of DNA selectively captured at surface H.

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The sections in this article are Introduction History Nucleic Acid Samples Electrochemical Behavior of NA Components Adsorption/Desorption Behavior Mercury Electrodes Solid Electrodes Reduction and Oxidation Microanalysis of Nucleic Acid Components by Stripping Techniques Principles Reactions of Pyrimidine and Purine Bases with the Electrode Mercury Unusual Bases and Nucleosides Sparingly Soluble Compounds of Nucleic Acid Components with Copper Adsorption/Desorption Behavior of NAs Mercury Dropping Electrode Adsorption of Double‐stranded (Native) DNA Adsorption of Single‐stranded (Denatured) DNA Adsorption Kinetics at Mercury Dropping and Hanging Electrodes Electrochemical Impedance Spectroscopy ( EIS ) Other Techniques Adsorption of NAs on Other Electrodes DNA Adsorption to Charged Lipid Membranes Reduction and Oxidation of NAs on Different Electrodes Mercury Electrodes Reduction of Adenine and Cytosine Residues Anodic Signal of Guanine Residues Carbon Electrodes Other Solid Electrodes Analysis of NAs by Different Electrochemical Techniques Relations Between Structures and Electrochemical Responses of DNA DNA Structure on Electrode Surfaces Dependence of the ds DNA Signals at the HMDE on Potential Scanning Direction Opening of the DNA Double Helix Around −1.2  V (Region U ) Opening of ds DNA at Acid p Hs in a Wider Potential Range T Interactions of NAs with Small Molecules Reversible (Noncovalent) Interactions Inorganic Cations and Simple Metal Complexes Organic Metal Chelates Other Noncovalent DNA Binders Covalent Interactions Electroactive Markers of NAs Other Nucleic Acid Modifications DNA Conductivity Application of Electrodes in DNA Conductivity Studies Analytical Applications Sensors for DNA Hybridization Immobilization of DNA on the Electrode Detection of the Hybridization Event Redox Indicators Covalently Bound to DNA Indicator‐free Detection Systems. Intrinsic Electroactivity of DNA Changes in Interfacial Properties and DNA Conductivity Blocking and Interfacing the Transducer Electrocatalytic Reactions Detection of Point Mutations Sensors for DNA Damage Detection of DNA Strand Breaks Damage to DNA Bases Detection of Damaging Agents Specifically Interacting with DNA DNA Cleavage Controlled by Electrochemical Reactions Other Determinations Determination of ss DNA in an Excess of ds DNA Determination of RNA Traces in DNA Solutions Determination of Proteins Conclusion Addendum Acknowledgment

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The aggregation of a-synuclein, a 14 kDa protein, is involved in several human neurodegenerative disorders, including Parkinson×s disease. We studied native and in vitro aggregated a-synuclein by circular dichroism (CD), atomic force microscopy (AFM) and electrochemical methods. We used constant current chronopotentiometric stripping analysis (CPSA) to measure hydrogen evolution catalyzed by a-synuclein (peak H) at hanging mercury drop electrodes (HMDE) and square-wave stripping voltammetry (SWSV) to monitor tyrosine oxidation at carbon paste electrodes (CPE). To decrease the volume of the analyte, most of the electrochemical measurements were performed by adsorptive transfer (medium exchange) from 3 ± 6 mL drops of a-synuclein samples. With both CPE and HMDE we observed changes in electrochemical responses of a-synuclein corresponding to protein fibrillization detectable by CD, fluorescence and AFM. Aggregation-induced changes in peak H at HMDE were relatively large in strongly aggregated samples, suggesting that this electrochemical signal may find use in the analysis of early stages of asynuclein aggregation. This assumption was documented by marked changes in the peak H potential and height in samples withdrawn at the end of the lag and the beginning of the elongation phase. Native a-synuclein can be detected down to subnanomolar concentrations by CPSA.