I don't know what a DNSA assay is. But Sigma sells a kit.

Amylase enzymes are glycoside hydrolases, which cleave glucan linkages in polysaccharides such as starch or glycogen to release polysaccharide molecules. α-Amylase is found in animals, plants, and many fungi. In mammals, α-amylase is the predominant form of amylase and is one of the major enzymes of dietary digestion. Both the activity and the stability of α-amylase is dependent on calcium ions. In humans, α-amylase levels are highest in pancreatic and salivary secretions. Increased blood and urine levels of amylase occur due to pancreatic disorders and salivary trauma. Increased salivary amylase activity is also a marker for increased sympathetic nervous system activity.

The Amylase Activity Assay kit quantifies amylase activity in a variety of biological samples. The assay is quick, convenient, and sensitive. In this kit, amylase activity is determined using a coupled enzymatic assay, which results in a colorimetric (405 nm) product, proportional to the amount of substrate, ethylidene-pNP-G7, cleaved by the amylase. One unit is the amount of amylase that cleaves ethylidene-pNP-G7 to generate 1.0 μmole of p-nitrophenol per minute at 25 °C.

Yes. You can use iodine method instead

I mean starch-iodine method.