The effect of probe density and target concentration on single molecule detection on microarrays. Top panel illustrates the effect of hybridization of different target concentrations to a miroarray spot, containing probe molecules at normal spotting density (diagonal stripes). Single molecules can only be resolved when the labeled target molecule is below a threshold concentration (solid red circles); above the threshold, the density of signals is too high to detect single molecules. Bottom panel illustrates the effect of hybridization of different target concentrations to a single molecule microarray, containing probe molecules at a density low enough for single molecules to be resolved. Single molecules are resolved irrespective of the concentration of the labeled target; extension of the dynamic range is illustrated.
