Figure 1:

Examples of μPADs for inorganic species. (A) Three-dimensional hybrid colorimetric/electrochemical μPAD for simulataneously determining Fe, Ni, Cu, Cr, Cd, and Pb. Reproduced with permission from Ref. 73. Copyright 2014 American Chemical Society. (B) Multilayer device for quantifying ammonia using pH indicators. Adapted with permission from Ref. 93. Copyright 2015 American Chemical Society. (C) μPAD for measuring reactive phosphate; a removable sheet was placed between paper layers to improve shelf life. Adapted from Ref. 82 with permission from Elsevier. (D) μPAD for measuring nitrate and nitrite. Adapted with permission from Ref. 89. Copyright 2014 American Chemical Society.