Bridging from Metallic Nanoclusters to Biomedical in Understanding Physicochemical Interactions at the Nano–Bio Interface

Abstract

many important applications. When the metal NPs size (usually 10-100 nm) is further reduced to the size comparably to the Fermi wavelength of the electron, exhibit the electronic and optical properties which can distinguish them from NPs. [1][2][3] Small NCs have no plasmonic properties (not characteristic SPR absorption peak) and due to their small size exhibit quantum confinement effects (discrete electronic energy levels, not the energy bands found in nanoparticles) and are not conductors any more. Therefore, when the NCs interact with light, they possess some electronic properties through HOMO-LUMO (highest occupied and lowest unoccupied molecular orbital) electronic transitions. [4][5][6] In this review, the properties on the basis of photoexcitation energy are divided into two categories: when the photoexcitation energy is equal to or more than the bandgap (photon energy ≥ bandgap energy) and when the photoexcitation energy is far above the ionization energies of atoms such as X-and γ-rays (photon energy ≥ bandgap energy). About the first category, it was found that the relaxation from the excited state proceeds mainly from a nonradiative (via electron injection and energy transfer) [4] or radiative (luminescence) energy transfer. [7] And the relaxation in the second category is based on secondary products generation (Figure 1).For clarity and illustrating simplicity, the biomedical applications discussed in this review are categorized based on their physicochemical properties and all of them are schematically summarized (as shown in Figure 1). For example, when discussing the enzymatic activity of NCs, it is suggested that based on this feature, these types of nanostructures are used in biomedical applications such as photodynamic therapy, infection therapy, biosensing, etc. Photon Energy ≥ Bandgap Energy Radiative DecayLuminescence: The luminescence of NCs is caused by intraband and interband electronic transitions of metal core or due to the ligand-to-metal charge transfer (LMCT) and ligand-to-metalmetal charge transfer (LMMCT) (Figure 1 1)). It is not yet well defined whether this luminescence is fluorescence (i.e., from The current review is a guideline for a physicist/chemist/biologist/physician in the introduction of metallic nanocluster (NC) applications and selection of a suitable one from a medical perspective. Metallic nanoclusters have gained attention during recent years owing to their advantages of superior optical characteristics, long lifetime, and biocompatibility for nanomedicine applications, including biolabeling, biosensing, catalysis, bioimaging, drug/ gene delivery, and therapeutic agent in comparison to the semiconductor quantum dot analogs. Here their basic physicochemical properties are being introduced, and they are linked to biomedical opportunities. Introducing the needed concepts of noble metal-based nanomaterials is being tried here, along with giving a correct comprehension of the reason for its use in a particular part of biomedical over the last 20 years. Moreover, in each ...

Recent Progress on Ligand-Protected Metal Nanoclusters in Photocatalysis

“…Monolayer-protected clusters are less aggressive and relatively more stable than gas-phase clusters containing unsatisfied valence electrons in their free state. Currently, further studies on these factors and their impacts on optical properties have set forth new developments in catalysis, biosensing, bioimaging, gene therapy, and drug delivery [ 13 , 23 , 24 , 25 , 26 ]. Tailoring a cluster’s distinctive optical and electronic properties by enhancing parameters such as its formal charges, geometry, metal composition, and ligand plays a pivotal role in photocatalysis [ 27 ].…”

Cell Membrane‐Coated AuNPs as a New Biomimetic Platform for ROS Scavenger Provides Cytoprotection from Apoptosis Induced by Oxidative Stress

“…[7] Depending on the type of nanomaterials, they can show their antioxidant activity through catalase-or glutathione peroxidaseor superoxide dismutase-like activity. [3,[8][9] For example graphene oxide supported selenium nanocomposite [10] and vanadia nanowires [11] were reported with excellent glutathione peroxidase-like activity for cytoprotection, or cerium oxide NPs, [12,13] Co 3 O 4 NPs, [14] Au nanorods, core-shell Au@Pt nanorods, core-shell Au@Pd nanorods [3] exhibit antioxidant properties-dependent catalase mimetic activity. A number of nanoparticles like carbon nanoclusters [15] and melanin NPs [16] have also been proposed with superoxide dismutase-like activity.…”