Optimization of PDE4B enzyme activity using the inkjet-printing method. (A) Fluorescence signal generated on parchment paper; (B) graph represents the average fluorescence intensity of the individual images (3A); (C) illustrates the intensity profile of the individual images (3A). Figure data A, B, and C were acquired as a function of dose and time point; and (D) the X-axis represents the number of mole of PDE4B printed per spot, the primary Y-axis represents the FRET signals produced in the presence of cAMP and PDE4B, and the secondary Y-axis represents the ejection volume of PDE4B.