Analysis of nucleotides and oligonucleotides immobilized as self-assembled monolayers by static secondary ion mass spectrometry.
Nucleic acid constituents can be bound to a metal surface in the form of self-assembled monolayers. Binding is achieved either through ionic interactions with a self-assembled 2-aminoethanethiol monolayer or by direct covalent binding of a dithiophosphate oligonucleotide to a metal surface through a sulfur-metal bond. Nucleotides, polynucleotides (both normal and a dithiophosphate analog) and double-stranded DNA have all been bound to surfaces. When the surfaces are interrogated using static secondary ion mass spectrometry (SIMS), the surface-bound nucleic acid constituents are observed in the form of the characteristic protonated nucleic acid base ions (BH2+). While a silver foil substrate was found to provide the highest absolute signal, vapor-deposited gold yields the best signal-to-noise ratio for ionically bound deoxyguanosine monophosphate. Under comparable conditions, a Cs+ projectile produces a 10-fold increase in the secondary ion signal relative to a Ga+ projectile. The experiment has been extended to a triple-quadrupole instrument where tandem mass spectrometric experiments on ionically immobilized dGMP showed the characteristic loss of ammonia from the released BH2+ ion. When a 'biomimetic' surface formed by ionically immobilizing double-stranded DNA is exposed to a solution containing ethidium bromide, ions corresponding to the non-covalent adduct are readily detectable using SIMS. This adduct and the nucleic acid constituents can be monitored at levels below 10 fmol.
Patrick
J S
JS
Purdue University, Department of Chemistry, West Lafayette, IN 47907-1393.
Cooks
R G
RG
Pachuta
S J
SJ
D004247:DNA / Q000032:analysis; D006147:Guanine / Q000032:analysis; D009711:Nucleotides / Q000032:analysis* / Q000737:chemistry; D009841:Oligonucleotides / Q000032:analysis* / Q000737:chemistry; D018629:Spectrometry, Mass, Secondary Ion; D013438:Sulfhydryl Compounds
D009711:Nucleotides; D009841:Oligonucleotides; D013438:Sulfhydryl Compounds; D006147:Guanine; D004247:DNA