Cheng, Ying, Yang, Reugen Mah Han, Alejandro, Fernando Maya, Li, Feng, Balavandy, Sepideh Keshan, Wang, Liang, Breadmore, Michael, Doyle, Richard, Naidu, Ravi. Elsevier; 2021. Current applications of colourimetric microfluidic devices (smart phone based) for soil nutrient determination.