Synthesis and characterization of biocompatible nanodiamond-silk hybrid material

Silk Fibroin Coated Magnesium Oxide Nanospheres: A Biocompatible and Biodegradable Tool for Noninvasive Bioimaging Applications

Fluorescent nanoparticles (NPs) have been increasingly studied as contrast agents for better understanding of biological processes at the cellular and molecular level. However, their use as bioimaging tools is strongly dependent on their optical emission as well as their biocompatibility. This work reports the fabrication and characterization of silk fibroin (SF) coated magnesium oxide (MgO) nanospheres, containing oxygen, Cr³⁺ and V²⁺ related optical defects, as a nontoxic and biodegradable hybrid platform for bioimaging applications. The MgO-SF spheres demonstrated enhanced emission efficiency compared to noncoated MgO NPs. Furthermore, SF sphere coating was found to overcome agglomeration limitations of the MgO NPs. The hybrid nanospheres were investigated as an in vitro bioimaging tool by recording their cellular uptake, trajectories, and mobility in human skin keratinocytes cells (HaCaT), human glioma cells (U87MG) and breast cancer cells (MCF7). Enhanced cellular uptake and improved intracellular mobilities of MgO-SF spheres compared to MgO NPs was demonstrated in three different cell lines. Validated infrared and bright emission of MgO-SF NP indicate their prospects for in vivo imaging. The results identify the potential of the hybrid MgO-SF nanospheres for bioimaging. This study may also open new avenues to optimize drug delivery through biodegradable silk and provide noninvasive functional imaging feedback on the therapeutic processes through fluorescent MgO.

Protein detection enabled using functionalised silk-binding peptides on a silk-coated optical fibre

We report a new approach to functionalise optical fibres to enable protein sensing, which controls the sensor molecule location either within the fibre tip coating or isolated to its exterior. This control dictates suitability for protein sensing.

Electrospun Nanodiamond-Silk Fibroin Membranes: A Multifunctional Platform for Biosensing and Wound-Healing Applications

Next generation wound care technology capable of diagnosing wound parameters, promoting healthy cell growth, and reducing pathogenic infections noninvasively would provide patients with an improved standard of care and accelerated wound repair. Temperature is one of the indicating biomarkers specific to chronic wounds. This work reports a hybrid, multifunctional optical material platform-nanodiamond (ND)-silk membranes as biopolymer dressings capable of temperature sensing and promoting wound healing. The hybrid structure was fabricated through electrospinning, and 3D submicron fibrous membranes with high porosity were formed. Silk fibers are capable of compensating for the lack of an extracellular matrix at the wound site, supporting the wound-healing process. Negatively charged nitrogen vacancy (NV^-) color centers in NDs exhibit optically detected magnetic resonance (ODMR) and act as nanoscale thermometers. This can be exploited to sense temperature variations associated with the presence of infection or inflammation in a wound, without physically removing the dressing. Our results show that the presence of NDs in the hybrid ND-silk membranes improves the thermal stability of silk fibers. NV^- color centers in NDs embedded in silk fibers exhibit well-retained fluorescence and ODMR. Using the NV^- centers as fluorescent nanoscale thermometers, we achieved temperature sensing in 25-50 °C, including the biologically relevant temperature window, for cell-grown ND-silk membranes. An enhancement (∼1.5× on average) in the temperature sensitivity of the NV^- centers was observed for the hybrid materials. The hybrid membranes were further tested in vivo in a murine wound-healing model and demonstrated biocompatibility and equivalent wound closure rates as the control wounds. Additionally, the hybrid ND-silk membranes exhibited selective antifouling and biocidal propensity toward Gram-negative Pseudomonas aeruginosa and Escherichia coli, while no effect was observed on Gram-positive Staphylococcus aureus.

Properties of Engineered and Fabricated Silks

Silk is a protein-based material which is predominantly produced by insects and spiders. Hundreds of millions of years of evolution have enabled these animals to utilize different, highly adapted silk types in a broad variety of applications. Silk occurs in several morphologies, such as sticky glue or in the shape of fibers and can, depending on the application by the respective animal, dissipate a high mechanical energy, resist heat and radiation, maintain functionality when submerged in water and withstand microbial settling. Hence, it's unsurprising that silk piqued human interest a long time ago, which catalyzed the domestication of silkworms for the production of silk to be used in textiles. Recently, scientific progress has enabled the development of analytic tools to gain profound insights into the characteristics of silk proteins. Based on these investigations, the biotechnological production of artificial and engineered silk has been accomplished, which allows the production of a sufficient amount of silk materials for several industrial applications. This chapter provides a review on the biotechnological production of various silk proteins from different species, as well as on the processing techniques to fabricate application-oriented material morphologies.

Intrinsic fluorescence of selenium nanoparticles for cellular imaging applications

Nanoparticles hold great potential in contributing to high-resolution bioimaging as well as for biomedical applications. Although, selenium (Se) nanoparticles (NPs) have been investigated owing to their potential roles in therapeutics, the imaging capability of these NPs has never been explored. This manuscript identifies the intrinsic fluorescence of Se NPs, which is highly beneficial for nanoscale imaging of biological structures. The emission of individual NPs and its evolution with time is explored. The photoluminescence spectra has revealed visible to near infrared emission for Se NPs. The work finally reflects on the role of this intrinsic fluorescence for in vitro imaging and tracking in fibroblast cells, without the need of any additional tags. This technique would overcome the limitations of the conventionally used methods of imaging with tagged fluorescent proteins and dyes, preventing possible adverse cellular effects or phototoxicity caused by the added fluorescent moieties.

A Novel High Mechanical Property PLGA Composite Matrix Loaded with Nanodiamond-Phospholipid Compound for Bone Tissue Engineering

A potential bone tissue engineering material was produced from a biodegradable polymer, poly(lactic-co-glycolic acid) (PLGA), loaded with nanodiamond phospholipid compound (NDPC) via physical mixing. On the basis of hydrophobic effects and physical absorption, we modified the original hydrophilic surface of the nanodiamond (NDs) with phospholipids to be amphipathic, forming a typical core-shell structure. The ND-phospholipid weight ratio was optimized to generate sample NDPC50 (i.e., ND-phospholipid weight ratio of 100:50), and NDPC50 was able to be dispersed in a PLGA matrix at up to 20 wt %. Compared to a pure PLGA matrix, the introduction of 10 wt % of NDPC (i.e., sample NDPC50-PF10) resulted in a significant improvement in the material's mechanical and surface properties, including a decrease in the water contact angle from 80 to 55°, an approximately 100% increase in the Young's modulus, and an approximate 550% increase in hardness, thus closely resembling that of human cortical bone. As a novel matrix supporting human osteoblast (hFOB1.19) growth, NDPC50-PFs with different amounts of NDPC50 demonstrated no negative effects on cell proliferation and osteogenic differentiation. Furthermore, we focused on the behaviors of NDPC-PFs implanted into mice for 8 weeks and found that NDPC-PFs induced acceptable immune response and can reduce the rapid biodegradation of PLGA matrix. Our results represent the first in vivo research on ND (or NDPC) as nanofillers in a polymer matrix for bone tissue engineering. The high mechanical properties, good in vitro and in vivo biocompatibility, and increased mineralization capability suggest that biodegradable PLGA composite matrices loaded with NDPC may potentially be useful for a variety of biomedical applications, especially bone tissue engineering.

Doxorubicin loaded nanodiamond-silk spheres for fluorescence tracking and controlled drug release

Nanoparticle (NP) based technologies have proved to be considerably beneficial for advances in biomedicine especially in the areas of disease detection, drug delivery and bioimaging. Over the last few decades, NPs have garnered interest for their exemplary impacts on the detection, treatment, and prevention of cancer. The full potential of these technologies are yet to be employed for clinical use. The ongoing research and development in this field demands single multifunctional composite materials that can be employed simultaneously for drug delivery and biomedical imaging. In this manuscript, a unique combination of silk fibroin (SF) and nanodiamonds (NDs) in the form of nanospheres are fabricated and investigated. The spheres were loaded with the anthracyline Doxorubicin (DoX) and the drug release kinetics for these ND-SF-DoX (NDSX) spheres were studied. NDs provided the fluorescence modality for imaging while the degradable SF spheres stabilized and released the drug in a controlled manner. The emission and structural properties of the spheres were characterized during drug release. The degradability of SF and the subsequent release of DoX from the spheres were monitored through fluorescence of NDs inside the spheres. This research demonstrates the enormous potential of the ND-SF nanocomposite platforms for diagnostic and therapeutic purposes, which are both important for pharmaceutical research and clinical settings.

Fluorescent Nanodiamond Silk Fibroin Spheres: Advanced Nanoscale Bioimaging Tool

High resolution bioimaging is not only critical to the study of cellular structures and processes but it also has important applications in drug delivery and therapeutics. Fluorescent nanodiamonds (NDs) are excellent candidates for long-term bioimaging and tracking of biological structures at the nanoscale. Encapsulating NDs in natural biopolymers like silk fibroin (SF) widens their biomedical applications. Here we report the synthesis, structural and optical characterization of ND incorporated SF nanospheres. The photoluminescence from optical defects within the NDs is found to increase when encapsulated in the SF spheres. The encapsulated NDs are applied in vitro to investigate the intracellular mobility compared to bare NDs. The diffusion rate of encapsulated NDs is shown to improve due to SF coating. These ND-SF spheres are envisioned as highly suitable candidates for bioinjectable imaging and drug release carriers for targeted drug delivery applications.

Micro-concave waveguide antenna for high photon extraction from nitrogen vacancy centers in nanodiamond

The negatively charged nitrogen-vacancy colour center (NV⁻ center) in nanodiamond is an excellent single photon source due to its stable photon generation in ambient conditions, optically addressable nuclear spin state, high quantum yield and its availability in nanometer sized crystals. In order to make practical devices using nanodiamond, highly efficient and directional emission of single photons in well-defined modes, either collimated into free space or waveguides are essential. This is a Herculean task as the photoluminescence of the NV centers is associated with two orthogonal dipoles arranged in a plane perpendicular to the NV defect symmetry axis. Here, we report on a micro-concave waveguide antenna design, which can effectively direct single photons from any emitter into either free space or into waveguides in a narrow cone angle with more than 80% collection efficiency irrespective of the dipole orientation. The device also enhances the spontaneous emission rate which further increases the number of photons available for collection. The waveguide antenna has potential applications in quantum cryptography, quantum computation, spectroscopy and metrology.

Lifetime Reduction and Enhanced Emission of Single Photon Color Centers in Nanodiamond via Surrounding Refractive Index Modification

The negatively-charged nitrogen vacancy (NV(-)) center in diamond is of great interest for quantum information processing and quantum key distribution applications due to its highly desirable long coherence times at room temperature. One of the challenges for their use in these applications involves the requirement to further optimize the lifetime and emission properties of the centers. Our results demonstrate the reduction of the lifetime of NV(-) centers, and hence an increase in the emission rate, achieved by modifying the refractive index of the environment surrounding the nanodiamond (ND). By coating the NDs in a polymer film, experimental results and numerical calculations show an average of 63% reduction in the lifetime and an average enhancement in the emission rate by a factor of 1.6. This strategy is also applicable for emitters other than diamond color centers where the particle refractive index is greater than the refractive index of the surrounding media.

Emission Properties of Fluorescent Nanoparticles Determined by Their Optical Environment

The emission rate of a radiating dipole within a nanoparticle is crucially dependent on its surrounding refractive index environment. In this manuscript, we present numerical results on how the emission rates are affected for nanoparticles in a homogenous and substrate environment. These results are general, applicable to any refractive index distribution and emitter.