Detection of gastric cancer in vivo using cy-apt 20. The feasibility of using aptamer cy-apt 20 for detecting gastric cancer in vivo was observed by IVIS Spectrum Imaging System (Caliper Life Sciences, Hopkinton, MA). AGS cells were subcutaneously injected into the left axillary regions of BALB/c nude mice and HepG2 and SW620 were transplanted as controls. 200 μl of physiological saline containing 1 nM of cy-apt 20 labeled with Cy5 was injected via tail vein when the tumor grown visible for the assessment. Equivalent Cy5-labled Lib ssDNA was also used as control. (A) The top row show visible tumor formation in the left axillae of the mice (circle notified). The mid-upper row show histopathological examination of the tumor formation. Tumor tissues were embedded in paraffin and stained with hematoxylin and eosin for the examination. The mid-lower row show there was no fluorescence signal detectable in all tumor sites using Cy5-labled Lib ssDNA. The bottom row show there were strong fluorescence signals in AGS tumor site using Cy5-labled cy-apt 20 imaged at 60 min after injection (arrow notified), whereas there was no fluorescence signal detectable in either tumor site of HepG2 or SW620. (B) quantification of the signal-to-background ratios of the tumor imaged using Cy5-labled cy-apt 20. The fluorescence signals of tumor relative to background were measured using Image J software and results were presented as fold changes vs. Background ± standard error.