An acid-base responsive AuI integrated contrast agent for Optical/CT double-modal imaging to detect pH change of...

The detection of pH change in the gastrointestinal tract (GIT) is invasive and the intestinal pH detection is even harder. Here, we develop an AuI integrated contrast agent (Au NCs@DA) for noninvasive GIT imaging to detect pH change. This agent is composed of gold nanoclusters (Au NCs) and diatrizoic acid (DA) and is extremely sensitive to the acid-base response. Au NCs@DA about 400 nm in size can be stable in acid solution and make the fluorescence intensity of Au NCs to drop significantly. After entering a neutral environment, Au NCs@DA can rapidly form sediment, and then its CT value and fluorescence increase. Alkaline pH can trigger the release of DA from Au NCs@DA to make its fluorescence intensity to recover. As entering GIT, Au NCs@DA can successively outline their anatomy for optical/CT double-modal imaging under gastrointestinal motility. The variations of the fluorescence and CT images triggered by different pH are also recorded to analyze the pH change of GIT. Furthermore, the clearance rate of stable Au NCs@DA in acid pH increases, which also can assist to evaluate pH value. Therefore, Au NCs@DA can definitely be an excellent candidate for the noninvasive detection of pH change in GIT through optical/CT double-modal imaging.