With many desirable properties such as ease of synthesis, small size, lack of immunogenicity, and versatile chemistry, aptamers represent a class of targeting ligands that possess tremendous potential in molecular imaging applications. Non-invasive imaging of various disease markers with aptamer-based probes has many potential clinical applications such as lesion detection, patient stratification, treatment monitoring, etc. In this review, we will summarize the current status of molecular imaging with aptamer-based probes. First, fluorescence imaging will be described which include both direct targeting and activatable probes. Next, we discuss molecular magnetic resonance imaging and targeted ultrasound investigations using aptamer-based agents. Radionuclide-based imaging techniques (singlephoton emission computed tomography and positron emission tomography) will be summarized as well. In addition, aptamers have also been labeled with various tags for computed tomography, surface plasmon resonance, dark-field light scattering microscopy, transmission electron microscopy, and surface-enhanced Raman spectroscopy imaging. Among all molecular imaging modalities, no single modality is perfect and sufficient to obtain all the necessary information for a particular question. Thus, a multimodality probe has also been constructed for concurrent fluorescence, gamma camera, and magnetic resonance imaging in vivo. Although the future of aptamer-based molecular imaging is becoming increasingly bright and many proof-of-principle studies have already been reported, much future effort needs to be directed towards the development of clinically translatable aptamer-based imaging agents which will eventually benefit patients.
Keywords: Aptamers, molecular imaging, cancer, positron emission tomography, DNA/RNA, fluorescence, personalized medicine