High density, covalent attachment of DNA to silicon wafers for analysis by MALDI-TOF mass spectrometry

A method is described for the covalent attachment of DNA to a solid surface at high density for hybridization detection by mass spectrometry. A silicon wafer is functionalized to place an amino group on the surface; a heterobifunctional cross-linking agent is then reacted with the primary amine to incorporate an iodoacetamido group. An oligodeoxynucleotide containing a 3'- or a 5'-disulfide is treated with a reducing agent, resulting in a terminal free thiol, which is then coupled to the iodoacetamido surface, Analysis of the surface reveals that the amount of covalently bound oligodeoxynucleotide is 250 fmol of DNA/mm(2) with similar to 40% of the immobilized oligodeoxynucleotides available for hybridization, Matrix-assisted laser desorption/ionization time-of-flight mass spectrometric (MALDI-TOF MS) analysis reveals that the covalent linkage to the support remains intact, only the annealed strand is desorbed by the laser, and the amount of DNA hybridized to the array is sufficient for detection.