This study examines the relationship between polymer surface conformation and colloid stability using single-stranded DNA as a model polymer and a biochemical technique called hydroxyl radical footprinting (HRF). The DNA polymer (dT40B) has a diblock copolymer architecture with an uncharged and relatively hydrophobic block and an equally long negatively charged block. In a previous report, we showed that HRF could be used to probe the surface conformation of dT40B when the molecule is adsorbed to charge-modified latex particles at moderate salt concentrations (0.05 M NaCl). Here, we present additional HRF results for this model polymer and examine the relationship between the polymer’s surface conformation and its effect on latex particle coagulation rates. When the bare latex particles are positively charged, the DNA adsorbs in a flat conformation and particle stability depends on polymer surface coverage. In this case, the DNA influences particle stability by altering the net surface charge of the latex particles. When the bare particles are negatively charged and the salt concentration is high (1 M NaCl), the DNA diblock copolymer forms a polymer brush layer on the latex surface at high polymer surface density. The brush layer stabilizes the particles, presumably through steric interactions that develop on close particle-particle approach.