Stepwise Ligand-induced Self-assembly for Facile Fabrication of Nanodiamond-Gold Nanoparticle Dimers via Noncovalent Biotin-Streptavidin Interactions

Versatile nanodiamond-based tools for therapeutics and bioimaging

Nanodiamonds (NDs) are a remarkable class of carbon-based nanoparticles in nanomedicine which have recently become a hot topic of research due to their unique features including functionalization versatility, tunable opto-magnetic properties, chemical stability, minimal cytotoxicity, high affinity to biomolecules and biocompatibility. These attractive features make NDs versatile tools for a wide range of biologically relevant applications. In this feature article, we discuss the opto-magnetic properties of negatively charged nitrogen vacancy (NV^-) centres in NDs as fluorescence probes. We further discuss the frequently used chemical methods for surface chemistry modification of NDs which are relevant for biomedical applications. The in vitro and in vivo biocompatibility of modified NDs is also highlighted. Subsequently, we give an overview of recent state-of-the-art biomedical applications of NDs as versatile tools for bioimaging and detection, and as targeting nanocarriers for chemotherapy, photodynamic therapy, gene therapy, antimicrobial and antiviral therapy, and bone tissue engineering. Finally, we pinpoint the main challenges for NDs in biomedical applications which lie ahead and discuss perspectives on future directions in advancing the field for practical applications and clinical translations.

Gold Nanoparticles Are an Immobilization Platform for Active and Stable Acetylcholinesterase: Demonstration of a General Surface Protein Functionalization Strategy

Immobilizing enzymes onto abiological surfaces is a key step for developing protein-based technologies that can be useful for applications such as biosensors and biofuel cells. A central impediment for the advancement of this effort is a lack of generalizable strategies for functionalizing surfaces with proteins in ways that prevent unfolding, aggregation, and uncontrolled binding, requiring surface chemistries to be developed for each surface-enzyme pair of interest. In this work, we demonstrate a significant advancement toward addressing this problem using a gold nanoparticle (AuNP) as an initial scaffold for the chemical bonding of the enzyme acetylcholinesterase (AChE), forming the conjugate AuNP-AChE. This can then be placed onto chemically and structurally distinct surfaces (e.g., metals, semiconductors, plastics, etc.), thereby bypassing the need to develop surface functionalization strategies for every substrate or condition of interest. Carbodiimide crosslinker chemistry was used to bind surface lysine residues in AChE to AuNPs functionalized with ligands containing carboxylic acid tails. Using amino acid analysis, we found that on average, 3.3 ± 0.1 AChE proteins were bound per 5.22 ± 1.25 nm AuNP. We used circular dichroism spectroscopy to measure the structure of the bound protein and determined that it remained essentially unchanged after binding. Finally, we performed Michaelis-Menten kinetics to determine that the enzyme retained 18.2 ± 2.0% of its activity and maintained that activity over a period of at least three weeks after conjugation to AuNPs. We hypothesize that structural changes to the peripheral active site of AChE are responsible for the differences in activity of bound AChE and unbound AChE. This work is a proof-of-concept demonstration of a generalizable method for placing proteins onto chemically and structurally diverse substrates and materials without the need for surface functionalization strategies.

Dynamic nanoassembly-based drug delivery systems on the horizon

Self-assembly in nature creates matter with complex structures and unpredictable designs; disordered building blocks spontaneously organize into ordered structures to achieve specific functions. Self-assembly begins to play an important role in the design of advanced drug delivery as well. Though, the behavior of 'dynamic nanoassembly-based drug delivery systems' (DNDDS) in biological media and cells remains poorly understood, while this is highly critical for controlling spatiotemporal drug release from DNDDS in vivo. To deepen the understanding of tailor-made DNDDS, this contribution in the Oration - New Horizons section of the Journal of controlled Release aims to highlight nature-inspired designs, construction principles, and controllable functionalities of DNDDS and how they are triggered by endogenous and exogenous stimuli. Furthermore, biomedical applications of tailor-made DNDDS for accurate diagnosis and precise treatment of diseases, including tumors, neurological diseases, injuries and infections are discussed. Finally, current challenges and future perspectives of DNDDS are briefly outlined.

De Novo Design of Functional Coassembling Organic-Inorganic Hydrogels for Hierarchical Mineralization and Neovascularization

Synthetic nanostructured materials incorporating both organic and inorganic components offer a unique, powerful, and versatile class of materials for widespread applications due to the distinct, yet complementary, nature of the intrinsic properties of the different constituents. We report a supramolecular system based on synthetic nanoclay (Laponite, Lap) and peptide amphiphiles (PAs, PAH3) rationally designed to coassemble into nanostructured hydrogels with high structural integrity and a spectrum of bioactivities. Spectroscopic and scattering techniques and molecular dynamic simulation approaches were harnessed to confirm that PAH3 nanofibers electrostatically adsorbed and conformed to the surface of Lap nanodisks. Electron and atomic force microscopies also confirmed an increase in diameter and surface area of PAH3 nanofibers after coassembly with Lap. Dynamic oscillatory rheology revealed that the coassembled PAH3-Lap hydrogels displayed high stiffness and robust self-healing behavior while gas adsorption analysis confirmed a hierarchical and heterogeneous porosity. Furthermore, this distinctive structure within the three-dimensional (3D) matrix provided spatial confinement for the nucleation and hierarchical organization of high-aspect ratio hydroxyapatite nanorods into well-defined spherical clusters within the 3D matrix. Applicability of the organic-inorganic PAH3-Lap hydrogels was assessed in vitro using human bone marrow-derived stromal cells (hBMSCs) and ex vivo using a chick chorioallantoic membrane (CAM) assay. The results demonstrated that the organic-inorganic PAH3-Lap hydrogels promote human skeletal cell proliferation and, upon mineralization, integrate with the CAM, are infiltrated by blood vessels, stimulate extracellular matrix production, and facilitate extensive mineral deposition relative to the controls.

Large and Externally Positioned Ligand-Coated Nanopatches Facilitate the Adhesion-Dependent Regenerative Polarization of Host Macrophages

Macrophages can associate with extracellular matrix (ECM) demonstrating nanosequenced cell-adhesive RGD ligand. In this study, we devised barcoded materials composed of RGD-coated gold and RGD-absent iron nanopatches to show various frequencies and position of RGD-coated nanopatches with similar areas of iron and RGD-gold nanopatches that maintain macroscale and nanoscale RGD density invariant. Iron patches were used for substrate coupling. Both large (low frequency) and externally positioned RGD-coated nanopatches stimulated robust attachment in macrophages, compared with small (high frequency) and internally positioned RGD-coated nanopatches, respectively, which mediate their regenerative/anti-inflammatory M2 polarization. The nanobarcodes exhibited stability in vivo. We shed light into designing ligand-engineered nanostructures in an external position to facilitate host cell attachment, thereby eliciting regenerative host responses.

Advances and challenges for fluorescence nanothermometry

Fluorescent nanothermometers can probe changes in local temperature in living cells and in vivo and reveal fundamental insights into biological properties. This field has attracted global efforts in developing both temperature-responsive materials and detection procedures to achieve sub-degree temperature resolution in biosystems. Recent generations of nanothermometers show superior performance to earlier ones and also offer multifunctionality, enabling state-of-the-art functional imaging with improved spatial, temporal and temperature resolutions for monitoring the metabolism of intracellular organelles and internal organs. Although progress in this field has been rapid, it has not been without controversy, as recent studies have shown possible biased sensing during fluorescence-based detection. Here, we introduce the design principles and advances in fluorescence nanothermometry, highlight application achievements, discuss scenarios that may lead to biased sensing, analyze the challenges ahead in terms of both fundamental issues and practical implementations, and point to new directions for improving this interdisciplinary field.

Probing and manipulating embryogenesis via nanoscale thermometry and temperature control

Understanding the coordination of cell-division timing is one of the outstanding questions in the field of developmental biology. One active control parameter of the cell-cycle duration is temperature, as it can accelerate or decelerate the rate of biochemical reactions. However, controlled experiments at the cellular scale are challenging, due to the limited availability of biocompatible temperature sensors, as well as the lack of practical methods to systematically control local temperatures and cellular dynamics. Here, we demonstrate a method to probe and control the cell-division timing in Caenorhabditis elegans embryos using a combination of local laser heating and nanoscale thermometry. Local infrared laser illumination produces a temperature gradient across the embryo, which is precisely measured by in vivo nanoscale thermometry using quantum defects in nanodiamonds. These techniques enable selective, controlled acceleration of the cell divisions, even enabling an inversion of division order at the two-cell stage. Our data suggest that the cell-cycle timing asynchrony of the early embryonic development in C. elegans is determined independently by individual cells rather than via cell-to-cell communication. Our method can be used to control the development of multicellular organisms and to provide insights into the regulation of cell-division timings as a consequence of local perturbations.

Surface-Engineered Gold Nanoclusters with Biological Assembly-Amplified Emission for Multimode Imaging

Here, we develop bifunctional ligand-engineered gold nanoclusters (AuNCs) as signal amplifying reporters for multimode imaging. Modified streptavidin (SA) and biotin alkyl acid-based ligands were applied to AuNCs to form AuNC-SA and AuNC-biotin. The zwitterionic ligands promoted bioassembly and avoided nonspecific adsorption. The AuNCs resisted aggregation-induced quenching and showed strong emission benefited from biological self-assembly. The engineered AuNCs featured stable emission, a large two-photon absorption cross section, long fluorescence lifetime, and good biocompatibility. Thus, cell-expressed antigen-induced protein-binding events were effectively converted into signals from the biological assemble of AuNCs. We performed a comprehensive assay of specific antigens and the cell structure, through one-photon imaging, two-photon imaging, and fluorescence lifetime imaging of AuNCs in a simple, sensitive, and reliable way.