Benchmarks and the signal from the double mutant was< 1%(see Supplementary Figure S2). Comparing these observations to those reported on microarrays by Goff and colleagues (10) suggests that microtiter plate assays are better able to discriminate miRNAs differing by only 1 or 2 bases. We also found that the use of dextran sulfate as a volume excluder in the miRNA hybridization buffer at a concentration of 2%–3% increased the output signal, presumably by favoring the hybridization of sample to target probe.

The optimal mass of dendrimer/well was determined to be 60 ng/well. HRP-labeled dendrimers (30 HRPs/dendrimer) gave a signal over noise ratio (S/N) about 5-fold greater than biotinylated dendrimers (960 biotins/dendrimer) chased with SA-HRP. This could be explained by the inability of the larger (four-layer) biotinylated dendrimer to bind as many targets as the smaller (two-layer) HRP-labeled dendrimer, due to steric hindrance. Alternatively, having the HRP directly attached to minimize extra steps may also be advantageous. The output signal achieved with the different dendrimer conjugates is summarized in Supplementary Table S2. The smallest discernible analytical signal was determined according to the International Union of Pure and Applied Chemistry’s (IUPAC’s) definition (14). For the control oligonucleotides (Supplementary Figure S3) under the more stringent conditions, it was found to be 0.048 absorbance units, which