Liquid biopsy has become an essential tool for cancer diagnostics and cfDNA (cell-free DNA), including ctDNA (circulating tumor DNA) is an essential biomarker for cancer characterization, such as measurement of cfDNA concentration, mutation, and methylation analysis of ctDNA. Since ctDNA is only a small proportion of cfDNA, direct ctDNA concentration measurement is not easy unless the mutation nature of ctDNA is known. Since the cfDNA is proportional to the ctDNA level, measuring ctDNA can be done by directly measuring the cfDNA. cfDNA quantification has been approved as a biomarker or potential biomarker in many research papers.

However, there is no standard method for quantification of cfDNA. Although qPCR and fluorescent dye-binding methods are often used, most of the studies using these methods need to extract DNA for cfDNA concentration measurement.