The methods and apparatus disclosed herein concern nucleic acid sequencing by enhanced Raman spectroscopy. In certain embodiments of the invention, nucleotides are covalently attached to Raman labels before incorporation into a nucleic acid 13. Exonuclease 15 treatment of the labeled nucleic acid 13 results in the release of labeled nucleotides 16, 130, which are detected by Raman spectroscopy. In alternative embodiments of the invention, nucleotides 16, 130 released from a nucleic acid 13 by exonuclease 15 treatment are covalently cross-linked to silver or gold nanoparticles 140 and detected by surface enhanced Raman spectroscopy (SERS), surface enhanced resonance Raman spectroscopy (SERRS) and/or coherent anti-Stokes Raman spectroscopy (CARS). Other embodiments of the invention concern apparatus 10, 100, 210 for nucleic acid sequencing.