The discovery of miRNAs as key regulators of the cellular machinery and their implication in diseases has blossomed research in miRNA detection. Conventional techniques such as quantitative reverse transcriptase polymerase chain reaction (qRT-PCR), northern blotting and microarray technologies have contributed significantly to the detection of miRNAs. But, areas of unmet need remained and emerging nanotechnology platforms have the potential to make the biosensing process simpler while maintaining good sensitivity and selectivity. To this effect, a gold nanoparticle (AuNP) scattering technique is presented, which shows the controlled formation of defined nanoassemblies through the hybridization of uniquely designed AuNP probes to its targeted miRNA. The defined assemblies exhibit a distinct size shift that can be detected through dynamic light scattering (DLS). Thus, instead of using DLS as a characterization tool as it is conventionally used for, herein, its potential use is demonstrated as a bioanalytical system. Using the let7 family miRNA, which associates with increasingly many medical conditions, as the model of study, we are able to achieve a limit of detection of 100 fmol and a selectivity discriminating close members of the let7 family. Potentially, detection can be done in 5 min, which also makes this a rapid detection system.