FRET signals generated on parchment paper were analyzed using a fluorescent microscope (OLYMPUS, IX73), and the fluorescent images were captured using a charge-coupled device (CCD) as a function of wavelength. At 320/340 nm, the Eu-cAMP tracer was excited on parchment paper, which was mounted on the sample stage. The laser beam was purified by an interference filter, and it was reflected by a dichromatic mirror and focused on the paper with a 20 × objective lens. The fluorescence emission was transferred to Ulight-anti-cAMP at 665 nm, and was collected by the same microscope objective lens, which passed through a dichromatic mirror and was directed. A charge -coupled device (CCD) camera was used to detect the transmitted fluorescent beam. Light scattering was removed by a filter, which was placed in front of the CCD camera. The background (without sample) and fluorescent (with sample) images were captured. Image analysis was performed using commercially available software, MetaMorph, Version 7.1.3.0 (Molecular Devices). The average threshold values were acquired, and their percentage fluorescence intensity profiles were evaluated using the above-mentioned software.