Embodiments of the invention provide non-natural bifunctional nucleotides having both nuclease resistance and nucleic acid synthesis blocking properties and methods of sequencing nucleic acids that employ non-natural bifunctional nucleic acids. Additional embodiments provide non-natural oligonucleotides and methods for sequencing nucleic acids using the non-natural oligonucleotides. Methods according to embodiments of the invention employ electronic detection and fluorescent detection of nucleic acid sequencing reactions.