Biomedical imaging, utilizing Metal–organic frameworks (MOFs) and Covalent organic frameworks (COFs), offers noninvasive disease diagnosis and treatment assessment with diverse applications.
Developments in biomedical imaging enables the visualization, evaluation, and quantification of biological processes at the molecular and cellular levels in a noninvasive means.
It shows great potential in the earlier diagnosis of diseases, on-going assessment of treatments, and optimization of disease therapeutic protocols, greatly encouraging the diagnosis of diseases.
Imaging agents, such as fluorescent small molecules and imaging contrast agents are the core and foundation of biomedical imaging, which are employed to generate signals or enhance the signal contrast in targeted tissues.
In the past decade, Metal–organic frameworks (MOFs) and Covalent organic frameworks (COFs) have been shown great potential for used as imaging agents and have been extensively investigated in this field.
In the past several years, owing to the facile functionalization, diversiform structures and compositions, and large porosities of MOFs, MOF-incorporated imaging techniques are widely used in optical imaging, computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography (PET) imaging.
Optical Imaging:
Optical imaging is a minimally invasive technique whereby light illumination is used to visualize tissue. In general, luminescent MOF materials are being extensively researched at the moment in the context of several optical imaging applications.
CT Imaging:
CT imaging provides a direct 3D visualization of the internal structures of a scanned object based on X-ray attenuation. The high-Z number elements such as iodine, barium, and bismuth in MOFs can be chosen as CT contrast agents. For example, a gold-nanoparticle-incorporated MIL-88 MOF as a multifunctional diagnostic agent to give high-quality CT scans.
MRI:
The signals of MRI provide precise anatomical-structure maps and help to detect diseases and other anomalies. Gadolinium-based small molecules are the most commonly used contrast agents; thus, Gd-based MOFs arose as logical MRI contrast agent candidates. To avoid toxicity concerns with Gd, some researchers have switched their attention to other metal-based MOFs such as Fe-based MOFs and Mn-based MOFs.
COFs have good photostability owing to the long-range crystal domain and eclipsed π-π stacking structure. In addition to, the tunable structure and constituent make it has adjustable fluorescence, functionalized surface chemistry.
Therefore, COFs are used as potential agents for fluorescence imaging. Fluorescence imaging is a forceful technology for achieving accurate diagnosis and visualize therapeutic process.
Fluorescence imaging is also employed to investigate the functions of biological molecules in an inherent microenvironment on account of its high sensitivity, noninvasiveness, rapid response capability, and real-time performance analysis.
References:
Sayan B.; et al. Biomedical integration of metal-organic frameworks[J]. Trends in Chemistry, 2020, 2, 467-479.
Feng L.L.; et al. Recent advances in covalent organic framework-based nanosystems for bioimaging and therapeutic applications[J]. ACS Materials Letters, 2020, 2, 1074-1092.
