All of the reagents used in the experiment were freshly prepared, and the experimental procedures were carried out at room temperature under a dark condition. A stimulation buffer consisting of 1 × HBSS, 5 mM HEPES, 0.5 mM IBMX, and 0.1% BSA (pH 7.4) was freshly prepared. cAMP (10 nM) and PDE4B (0.5 µM, 5 µM, and 10 µM) were prepared using the stimulation buffer, and Eu-cAMP tracer (1/150 dilution) and ULight-anti-cAMP (1/300 dilution) were prepared using the cAMP detection buffer. Roliparm (10 µM) and roflumilast (10 µM) were prepared using DMSO. Commercial inks were completely removed, washed with deionized water and 100% ethanol, and then completely air-dried in a hot air oven. Finally, printing solutions were refilled into the respective cartridges.