Ultrasensitive voltammetric detection of underivatized oligonucleotides and DNA

Electrochemical detection of nucleotides, ssDNA, and dsDNA was accomplished by using sinusoidal voltammetric detection at copper microelectrodes. Generally, detection of these molecules utilizes the electroactive nature of adenine and guanine residues at most electrode surfaces. The detection approach used in this study is based on the electrocatalytic oxidation of sugars and amines at copper surfaces. All nucleotides and DNA molecules comprise a ribose sugar backbone and primary amines present on the different nucleobases. Consequently, the detection approach is universal to all types of nucleotides. As the number of sugar moieties increases with the length of an oligonucleotide, the detection sensitivity is enhanced for bigger oligonucleotides. Irreversible adsorption of these oligonucleotides and other biomacromolecules like dsDNA on the electrode surface was avoided with sinusoidal voltammetry since it is a scanning electrochemical technique. The sensitivity of the detection strategy is, however, still preserved due to the effective decoupling of the faradaic signal from the capacitive background currents in the frequency domain. The ssDNA and dsDNA were detected in the picomolar concentration range. The electrochemical signal due to dsDNA is actually higher than that due to ssDNA due to the larger number of easily accessible sugars on the outer perimeter of a dsDNA double helix compared to those on a ssDNA of the same size. This is in contrast to the existing electrochemical detections techniques based on the electroactivity of the nucleobase.