The one advantage of using DNS assay to detect maltose production is the formation of a soluble and colored product compound.
The reaction that occurs between maltose and DNS in the assay is a redox reaction (reduction and oxidation) such that maltose gets oxidized and becomes Maltonic Acid while the DNS gets reduced into reduced DNS. The intensity of orange/brown /red color of reduced DNS is proportionately related to the amount of Maltose in the solution.