Functionalization of Inorganic Nanoparticles for Bioimaging Applications

Abstract

Modern biomedical imaging technologies have led to significant advances in diagnosis and therapy. Because most disease processes occur at the molecular and cellular levels, researchers continue to face challenges in viewing and understanding these processes precisely and in real time. The ideal imaging resolution would be in nanometers, because most biological processes take place on this length scale. Therefore, the functionalization of nanoparticles (NPs) and their use in therapeutic and diagnostic applications are of great interest. Molecular and cellular imaging agents made from inorganic NPs have been developed to probe such biological events noninvasively. The conjugation of tiny NPs with specific biomolecules allows researchers to target the desired location, reduce overall toxicity, and boost the efficiency of the imaging probes. In this Account, we review recent research on the functionalization of NPs for bioimaging applications. Several types of NPs have been employed for bioimaging applications, including metal (Au, Ag), metal oxide (Fe(3)O(4)), and semiconductor nanocrystals (e.g. quantum dots (QDs) and magnetic quantum dots (MQDs)). The preparation of NPs for bioimaging applications can include a variety of steps: synthesis, coating, surface functionalization, and bioconjugation. The most common strategies of engineering NP surfaces involve physical adsorption or chemisorption of the desired ligands onto the surface. Chemisorption or covalent linkages are preferred, and the coated NPs should possess high colloidal stability, biocompatibility, water solubility, and functional groups for further bioconjugation. Many of the functionalization techniques that have been reported in the literature suffer from limitations such as complex synthesis steps, poor biocompatibility, low stability, and hydrophobic products. Coating strategies based on chemisorption and ligand exchange often provide a better way to tailor the surface properties of NPs. After conjugation with the appropriate targeting ligands, antibodies, or proteins, the NPs may exhibit highly selective binding, making them useful for fluorescence imaging, magnetic resonance imaging (MRI), positron emission tomography (PET) imaging, and multimodal imaging.

Evaluation of cytotoxicity, biophysics and biomechanics of cells treated with functionalized hybrid nanomaterials

“…Their carbonaceous nature, resonance Raman scattering, photoluminescence, strong near-infrared optical absorption, notable photothermal therapy properties, close structural resemblance with biomolecules and the possibility of tethering various functional groups on the surface of CNTs promote their application for multimodal therapy, as carrier for therapeutics, in diagnosis, for prosthesis delivery, and as a matrix for fabricating tissue regeneration scaffolds [2 -7]. Metal nanoparticles (NPs) or quantum dot-conjugated CNTs have been used as labelling, imaging and tracking agents [2,8,9]. Folic acid and nucleic acid aptamers are examples of targeting moieties studied for cancer therapy that can bind specifically to target cells [10,11].…”

Gold nanoclusters as novel optical probes for in vitro and in vivo fluorescence imaging

“…Conjugation of imaging agents with biomolecules such as antibodies, enzymes, DNA, or oligosaccharides is a prerequisite to their use as biological probes for specific fluorescence imaging (Erathodiyil and Ying 2011), because it enables researchers to target desired locations within cells, tissues, and organs, reduce overall toxicity, and boost the efficiency of the imaging probes Retnakumari et al 2010). This research has as yet seen rather slow progress for AuNCs.…”

Functionalized nanomaterials: their use as contrast agents in bioimaging: mono- and multimodal approaches

“…Therefore, the coating strategies based on chemisorption and ligand exchange often provide a better way to finely tune the surface properties of NPs. After conjugation with the appropriate targeting ligands, antibodies, or proteins, fluorescent NPs also exhibit highly selective binding, making them useful for targeting and imaging (Table 4 ) [465].…”

“…Functionalization can also help in addressing NP toxicity aspects [12,354,358,465,468,493,494] . Indeed, properly protected NPs, conjugated or coated with biocompatible materials, can be used for the fabrication of various functional systems with multimodality as well as targeting properties, reduced toxicity, and proper removal from the body.…”