We report a series of 2'-deoxyribonucleoside triphosphates bearing dicarba-nido-undecaborate ([C2B9H11](1-)), [3,3'-iron-bis(1,2-dicarbollide)](-) (FESAN, [Fe(C2B9H11)(2)](2-)) or [3,3'-cobalt-bis(1,2-dicarbollide)](-) (COSAN, [Co(C2B9H11)(2)](2)(-)) groups prepared either through the Sonogashira cross-coupling or the CuAAC click reaction. The modified dN(X)TPs were substrates for KOD XL DNA polymerase in enzymatic synthesis of modified DNA through primer extension (PEX). The nido-carborane- and FESAN-modified nucleotides gave analytically useful oxidation signals in square-wave voltammetry and were used for redox labeling of DNA. The redox-modified DNA probes were prepared by PEX using tailed primers and were hybridized to electrode (gold or glassy carbon) containing capture oligonucleotides. The combination of nido-carborane- and FESAN-linked nucleotides with 7-ferrocenylethynyl-7-deaza-dATP and 7-deaza-dGTP allowed polymerase synthesis of DNA fully modified at all four nucleobases, and each of the redox labels gave four differentiable and ratiometric signals in voltammetry. Thus, the combination of these four redox labels constitutes the first fully orthogonal redox coding of all four canonical nucleobases, which can be used for determination of nucleobase composition of short DNA stretches in one simple PEX experiment with electrochemical readout.