Selective receptor-targeting peptide based agents have attracted considerable attention in molecular imaging of tumor cells that overexpress corresponding peptide receptors due to their unique properties such as rapid clearance from circulation as well as high affinities and specificities for their targets. The rapid growth of chemistry modification techniques has enabled the design and development of various peptide-based imaging agents with enhanced metabolic stability, favorable pharmacokinetics, improved binding affinity and selectivity, better imaging ability as well as biosafety. Among them, many radiolabeled peptides have already been translated into the clinic with impressive diagnostic accuracy and sensitivity. This review summarizes the current status in the development of peptide-based imaging agents with an emphasis on the consideration of probe design including the identification of suitable peptides, the chemical modification of probes and the criteria for clinical translation. Specific examples in clinical trials have been provided as well with respect to their diagnostic capability compared with other FDA approved imaging agents.

Traumatic brain injury (TBI) is one of the most dangerous acute diseases resulting in high morbidity and mortality. Current methods remain limited with respect to early diagnosis and real‐time feedback on the pathological process. Herein, a targeted activatable fluorescent nanoprobe (V&A@Ag2S) in the second near‐infrared window (NIR‐II) is presented for in vivo optical imaging of TBI. Initially, the fluorescence of V&A@Ag2S is turned off owing to energy transfer from Ag2S to the A1094 chromophore. Upon intravenous injection, V&A@Ag2S quickly accumulates in the inflamed vascular endothelium of TBI based on VCAM1‐mediated endocytosis, after which the nanoprobe achieves rapid recovery of the NIR‐II fluorescence of Ag2S quantum dots (QDs) owing to the bleaching of A1094 by the prodromal biomarker of TBI, peroxynitrite (ONOO−). The nanoprobe offers high specificity, rapid response, and high sensitivity toward ONOO−, providing a convenient approach for in vivo early real‐time assessment of TBI.

The delineation of brain gliomas margins still poses challenges to precise imaging and targeted therapy, mainly due to strong light attenuation of the skull and high background interference. With deep penetration and high sensitivity, photoacoustic (PA) imaging (PAI) in the second near‐infrared (NIR II) window holds great potential for brain gliomas imaging. Herein, mesoionic dye A1094 encapsulated in Arg‐Gly‐Asp‐modified hepatitis B virus core protein (RGD‐HBc) is designed and synthesized for effective NIR II PAI of brain gliomas. An aggregation‐induced absorption enhancement mechanism is discovered in vitro and in vivo. It is also demonstrated that A1094@RGD‐HBc, with an enhanced absorption in the NIR II window, displays ninefold PA signal amplification in vivo, allowing for precise PAI of the brain gliomas at a depth up to 5.9 mm. In addition, with the application of abovementioned agent, high‐resolution PAI and ultrasensitive single photon emission computed tomography images of brain gliomas are acquired with accurate co‐localization. Collectively, the results suggest great promise of A1094@RGD‐HBc for diagnostic imaging and precise delineation of brain gliomas in clinical applications.

Spectral domain optical coherence tomography is sensitive and specific in distinguishing PCV from nAMD. From these results, the presence of at least two out three signs (pigment epithelium detachment, double-layer sign, and thumb-like polyps) indicates a positive test and is therefore suggested to be the screening strategy for PCV.

An NIR ultrahigh absorbing croconium dye for amyloid (CDA) was designed and synthesized .