Systems for differentiating the lengths of nucleic acids of interest in a sample are provided. The system includes a microfluidic device, a detector, and a software system. The microfluidic device includes an amplification microchannel or microchamber containing a reaction mixture under conditions that provide one or more amplicons of the nucleic acid of interest. The detector is integral with or proximal to the microfluidic device and is configured to detect the amplicons as one or more signals from a homogenous mixture. The software system interprets one or more coincidentally detected signals to indicate lengths of one or more individual nucleic acid molecules of interest, thereby differentiating the lengths of the nucleic acids of interest.