A review of recent advances in the use of complex metal nanostructures for biomedical applications from diagnosis to treatment

Complex metal nanostructures represent an exceptional category of materials characterized by distinct morphologies and physicochemical properties. Nanostructures with shape anisotropies, such as nanorods, nanostars, nanocages, and nanoprisms, are particularly appealing due to their tunable surface plasmon resonances, controllable surface chemistries, and effective targeting capabilities. These complex nanostructures can absorb light in the near-infrared, enabling noteworthy applications in nanomedicine, molecular imaging, and biology. The engineering of targeting abilities through surface modifications involving ligands, antibodies, peptides, and other agents potentiates their effects. Recent years have witnessed the development of innovative structures with diverse compositions, expanding their applications in biomedicine. These applications encompass targeted imaging, surface-enhanced Raman spectroscopy, near-infrared II imaging, catalytic therapy, photothermal therapy, and cancer treatment. This review seeks to provide the nanomedicine community with a thorough and informative overview of the evolving landscape of complex metal nanoparticle research, with a specific emphasis on their roles in imaging, cancer therapy, infectious diseases, and biofilm treatment. This article is categorized under: Diagnostic Tools > In Vivo Nanodiagnostics and Imaging Therapeutic Approaches and Drug Discovery > Nanomedicine for Infectious Disease Diagnostic Tools > Diagnostic Nanodevices.

Mucoadhesive Mesoporous Silica Particles as Versatile Carriers for Doxorubicin Delivery in Cancer Therapy

Due to their structural, morphological, and behavioral characteristics (e.g., large volume and adjustable pore size, wide functionalization possibilities, excellent biocompatibility, stability, and controlled biodegradation, the ability to protect cargoes against premature release and unwanted degradation), mesoporous silica particles (MSPs) are emerging as a promising diagnostic and delivery platform with a key role in the development of next-generation theranostics, nanovaccines, and formulations. In this study, MSPs with customized characteristics in-lab prepared were fully characterized and used as carriers for doxorubicin (DOX). The drug loading capacity and the release profile were evaluated in media with different pH values, mimicking the body conditions. The release data were fitted to Higuchi, Korsmeyer-Peppas, and Peppas-Sahlin kinetic models to evaluate the release constant and the mechanism. The in vitro behavior of functionalized silica particles showed an enhanced cytotoxicity on human breast cancer (MCF-7) cells. Bio- and mucoadhesion on different substrates (synthetic cellulose membrane and porcine tissue mucosa)) and antimicrobial activity were successfully assessed, proving the ability of the OH- or the organically modified MSPs to act as antimicrobial and mucoadhesive platforms for drug delivery systems with synergistic effects.

Fast Microwave-Assisted Synthesis, Calcination and Functionalization of a Silica Mesoporous Nanomaterial: UVM-7

We report here, for the first time, the use of a solid state microwave source for the synthesis, calcination and functionalization of a UVM-7 based hybrid mesoporous silica material. The synthesis of the UVM-7 material is obtained in 2 min at low power (50 W) by the combination of a microwave irradiation and the atrane route. Moreover, it has been successfully calcined and functionalized in just 13 and 4 min respectively with microwave assisted procedures. A total synthesis comprising each individually optimized step, can be executed in only 4 h including work-up, by contrast to a typical synthesis that comprises several days. Savings higher than one order or magnitude are obtained in time and energy. Our example is a proof of concept of the potential use of solid state microwave generators for the ultrafast on-command preparation of hybrid nanomaterials due to their accurate control and accelerating properties.

Finite Element Models of Gold Nanoparticles and Their Suspensions for Photothermal Effect Calculation

(1) Background: The ability of metal nanoparticles to carry other molecules and their electromagnetic interactions can be used for localized drug release or to heat malignant tissue, as in the case of photothermal treatments. Plasmonics can be used to calculate their absorption and electric field enhancement, which can be further used to predict the outcome of photothermal experiments. In this study, we model the nanoparticle geometry in a Finite Element Model calculus environment to calculate the effects that occur as a response to placing it in an optical, electromagnetic field, and also a model of the experimental procedure to measure the temperature rise while irradiating a suspension of nanoparticles. (2) Methods: Finite Element Method numerical models using the COMSOL interface for geometry and mesh generation and iterative solving discretized Maxwell's equations; (3) Results: Absorption and scattering cross-section spectrums were obtained for NanoRods and NanoStars, also varying their geometry as a parameter, along with electric field enhancement in their surroundings; temperature curves were calculated and measured as an outcome of the irradiation of different concentration suspensions; (4) Conclusions: The results obtained are comparable with the bibliography and experimental measurements.

A Multilayered Mesoporous Gold Nanoarchitecture for Ultraeffective Near-Infrared Light-Controlled Chemo/Photothermal Therapy for Cancer Guided by SERS Imaging

Surface-enhanced Raman scattering (SERS) imaging has emerged as a promising tool for guided cancer diagnosis and synergistic therapies, such as combined chemotherapy and photothermal therapy (chemo-PTT). Yet, existing therapeutic agents often suffer from low SERS sensitivity, insufficient photothermal conversion, or/and limited drug loading capacity. Herein, a multifunctional theragnostic nanoplatform consisting of mesoporous silica-coated gold nanostar with a cyclic Arg-Gly-Asp (RGD)-coated gold nanocluster shell (named RGD-pAS@AuNC) is reported that exhibits multiple "hot spots" for pronouncedly enhanced SERS signals and improved near-infrared (NIR)-induced photothermal conversion efficiency (85.5%), with a large capacity for high doxorubicin (DOX) loading efficiency (34.1%, named RGD/DOX-pAS@AuNC) and effective NIR-triggered DOX release. This nanoplatform shows excellent performance in xenograft tumor model of HeLa cell targeting, negligible cytotoxicity, and good stability both in vitro and in vivo. By SERS imaging, the optimal temporal distribution of injected RGD/DOX-pAS@AuNCs at the tumor site is identified for NIR-triggered local chemo-PTT toward the tumor, achieving ultraeffective therapy in tumor cells and tumor-bearing mouse model with 5 min of NIR irradiation (0.5 W cm^-2 ). This work offers a promising approach to employing SERS imaging for effective noninvasive tumor treatment by on-site triggered chemo-PTT.

Multifunctional plasmonic-magnetic nanoparticles for bioimaging and hyperthermia

Multicompartment nanoparticles have raised great interest for different biomedical applications, thanks to the combined properties of different materials within a single entity. These hybrid systems have opened new avenues toward diagnosis and combination therapies, thus becoming preferred theranostic agents. When hybrid nanoparticles comprise magnetic and plasmonic components, both magnetic and optical properties can be achieved, which are potentially useful for multimodal bioimaging, hyperthermal therapies and magnetically driven selective delivery. Nanostructures comprising iron oxide and gold are usually selected for biomedical applications, as they display size-dependent properties, biocompatibility, and unique physical and chemical characteristics that can be tuned through highly precise synthetic protocols. We provide herein an overview of the most recent synthetic protocols to prepare magnetic-plasmonic nanostructures made of iron oxide and gold, to then highlight the progress made on multifunctional magnetic-plasmonic bioimaging and heating-based therapies. We discuss the advantages and limitations of the various systems in these directions.

Growing Gold Nanostars on SiO2 Nanoparticles: Easily Accessible, NIR Active Core–Shell Nanostructures from PVP/DMF Reduction

A new synthesis strategy towards gold-coated silica nanoparticles is presented. The method provides an efficient, reliable and facile-coating process of well-defined star-shaped shell structures, characterized by UV-Vis, TEM, PXRD, DLS and zeta-potential measurements. A marked red shift of the Au-based plasmonic band to the region of the first biological window is observed offering great potential for future research of biological applications.

Near-Infrared Light-Responsive SERS Tags Enable Positioning and Monitoring of the Drug Release of Photothermal Nanomedicines In Vivo

Understanding the in vivo behavior of photothermal nanomedicines (PTNMs) is important for drug development and evaluation. However, it is still very challenging. Herein, two key parameters, i.e., the depth of PTNMs under biological tissue and the drug release ratio of PTNMs in vivo, can be revealed by a near-infrared (NIR) light-responsive surface-enhanced Raman scattering (SERS) strategy. The fabricated PTNMs were composed of waxberry-like gold nanoparticles, model drug curcumin, and an elaborately selected NIR light-responsive Raman reporter (3,3'-diethylthiatricarbocyanine iodide, DTTC). The response mechanism of DTTC to NIR light was investigated as photodegradation. NIR light irradiation heated the gold nanoparticles, triggered the release of a model drug, and simultaneously decreased the SERS intensity of the PTNMs. In vitro experiment results revealed that the SERS intensity decrease could well reflect the depth of PTNMs with a correlation coefficient of more than 0.99. On this basis, after in situ SERS detection, the depth of PTNMs in a tumor could be revealed with satisfactory accuracy. Moreover, the decrease in the SERS intensity of PTNMs showed a highly similar trend to the increase in the drug release, suggesting that it could be used for real-time monitoring of drug release of PTNMs. This study not only opens a new avenue for the release study of many inactive fluorescent and Raman drugs of PTNMs but also provides an effective way for reporting the depth, which greatly promotes the application of PTNMs in vivo.

Brachytherapy Approach Using 177Lu Conjugated Gold Nanostars and Evaluation of Biodistribution, Tumor Retention, Dosimetry and Therapeutic Efficacy in Head and Neck Tumor Model

Brachytherapy can provide sufficient doses to head and neck squamous cell carcinoma (HNSCC) with minimal damage to nearby normal tissues. In this study, the β^--emitter ¹⁷⁷Lu was conjugated to DTPA-polyethylene glycol (PEG) decorated gold nanostars (¹⁷⁷Lu-DTPA-pAuNS) used in surface-enhanced Raman scattering and photothermal therapy (PTT). The accumulation and therapeutic efficacy of ¹⁷⁷Lu-DTPA-pAuNS were compared with those of ¹⁷⁷Lu-DTPA on an orthotopic HNSCC tumor model. The SPECT/CT imaging and biodistribution studies showed that ¹⁷⁷Lu-DTPA-pAuNS can be accumulated in the tumor up to 15 days, but ¹⁷⁷Lu-DTPA could not be detected at 24 h after injection. The tumor viability and growth were suppressed by injected ¹⁷⁷Lu-DTPA-pAuNS but not nonconjugated ¹⁷⁷Lu-DTPA, as evaluated by bioluminescent imaging. The radiation-absorbed dose of the normal organ was the highest in the liver (0.33 mSv/MBq) estimated in a 73 kg adult, but that of tumorsphere (0.5 g) was 3.55 mGy/MBq, while intravenous injection of ¹⁷⁷Lu-DTPA-pAuNS resulted in 1.97 mSv/MBq and 0.13 mGy/MBq for liver and tumorsphere, respectively. We also observed further enhancement of tumor-suppressive effects by a combination of ¹⁷⁷Lu-DTPA-pAuNS and PTT compared to ¹⁷⁷Lu-DTPA-pAuNS alone. In conclusion, ¹⁷⁷Lu-DTPA-pAuNS may be considered as a potential radiopharmaceutical agent for HNSCC brachytherapy.

Overview of polyethylene glycol-based materials with a special focus on core-shell particles for drug delivery application

Polyethylene glycols (PEG) are water-soluble nonionic polymeric molecules. PEG and PEG-based materials are used for various important applications such as solvents, adhesives, adsorbents, drug delivery agents, tissue engineering scaffolds, etc. The coating of nanoparticles with PEG forms core-shell nanoparticles. The PEG-based core-shell nanoparticles are synthesized for the development of high-quality drug delivery systems. In the present review, we first explained the basics and various applications of PEGs and PEG-based composites materials and then concentrated on the PEG-based core-shell nanoparticles for biomedical applications specifically their use in drug delivery.

Optimization of the GSH-Mediated Formation of Mesoporous Silica-Coated Gold Nanoclusters for NIR Light-Triggered Photothermal Applications

Cancer light-triggered hyperthermia mediated by nanomaterials aims to eliminate cancer cells by inducing localized temperature increases to values superior to 42 °C, upon irradiation with a laser. Among the different nanomaterials with photothermal capacity, the gold-based nanoparticles have been widely studied due to their structural plasticity and advantageous physicochemical properties. Herein, a novel and straightforward methodology was developed to produce gold nanoclusters coated with mesoporous silica (AuMSS), using glutathione (GSH) to mediate the formation of the gold clusters. The obtained results revealed that GSH is capable of triggering and control the aggregation of gold nanospheres, which enhanced the absorption of radiation in the NIR region of the spectra. Moreover, the produced AuMSS nanoclusters mediated a maximum temperature increase of 20 °C and were able to encapsulate a drug model (acridine orange). In addition, these AuMSS nanoclusters were also biocompatible with both healthy (fibroblasts) and carcinogenic (cervical cancer) cells, at a maximum tested concentration of 200 μg/mL. Nevertheless, the AuMSS nanoclusters’ NIR light-triggered heat generation successfully reduced the viability of cervical cancer cells by about 80%. This confirms the potential of the AuMSS nanoclusters to be applied in cancer therapy, namely as theragnostic agents.

Novel multi-stimuli responsive functionalized PEG-based co-delivery nanovehicles toward sustainable treatments of multidrug resistant tumor

The efficacy of ongoing anticancer treatment is often compromised by some barriers, such as low drug content, nonspecific release of drug delivery system, and multidrug resistance (MDR) effect of tumors. Herein, in the research a novel functionalized PEG-based polymer cystine-(polyethylene glycol)2-b-(poly(2-methacryloyloxyethyl ferrocenecarboxylate)2) (Cys-(PEG45)2-b-(PMAOEFC)2) with multi-stimuli sensitive mechanism was constructed, in which doxorubicin (DOX) was chemical bonded through Schiff base structure to provide acid labile DOX prodrug (DOX)2-Cys-(PEG45)2-b-(PMAOEFC)2. Afterwards, paclitaxel (PTX) and its diselenide bond linked PTX dimer were encapsulated into the prodrug through physical loading, to achieve pH and triple redox responsive (DOX)2-Cys-(PEG45)2-b-(PMAOEFC)2@PTX and (DOX)2-Cys-(PEG45)2-b-(PMAOEFC)2@PTX dimer with ultrahigh drugs content. The obtained nanovehicles could self-assemble into globular micelles with good stability based on fluorescence spectra and TEM observation. Moreover, there was a remarkable "reassembly-disassembly" behavior caused by phase transition of micelles under the mimic cancerous physiological environment. DOX and PTX could be on-demand released in acid and redox stress mode, respectively. Meanwhile, in vivo anticancer studies revealed the significant tumor inhibition of nanoformulas. This work offered facile strategies to fabricate drug nanaovehicles with tunable drug content and types, it has a profound significance in overcoming MDR effect, which provided more options for sustainable cancer treatment according to the desired drug dosage and the stage of tumor growth.

Visible-to-NIR-Light Activated Release: From Small Molecules to Nanomaterials

Photoactivatable (alternatively, photoremovable, photoreleasable, or photocleavable) protecting groups (PPGs), also known as caged or photocaged compounds, are used to enable non-invasive spatiotemporal photochemical control over the release of species of interest. Recent years have seen the development of PPGs activatable by biologically and chemically benign visible and near-infrared (NIR) light. These long-wavelength-absorbing moieties expand the applicability of this powerful method and its accessibility to non-specialist users. This review comprehensively covers organic and transition metal-containing photoactivatable compounds (complexes) that absorb in the visible- and NIR-range to release various leaving groups and gasotransmitters (carbon monoxide, nitric oxide, and hydrogen sulfide). The text also covers visible- and NIR-light-induced photosensitized release using molecular sensitizers, quantum dots, and upconversion and second-harmonic nanoparticles, as well as release via photodynamic (photooxygenation by singlet oxygen) and photothermal effects. Release from photoactivatable polymers, micelles, vesicles, and photoswitches, along with the related emerging field of photopharmacology, is discussed at the end of the review.

Activation Strategies in Image-Guided Nanotherapeutic Delivery

Therapeutic nanomaterials serve as an important platform for drug delivery under image guidance. Despite significant growth and broad applications, their design specifics remain a subject of continued interest primarily due to multifunctional factors involved, ranging from nanomaterial properties, imaging modalities, and therapeutic agents to activation strategies. This review article summarizes key findings on their design characteristics with a particular interest in strategies developed for therapeutic activation (release). First, their activation can be controlled using either an endogenous factor including low pH and glutathione or an external stimulation by light, ultrasound, or electromagnetic field. The former is passively controlled from a spatiotemporal aspect compared to the latter, which is otherwise actively controlled through drug linker photolysis, nanomaterial disassembly, or gate opening. Second, light stimulation serves a most notable strategy due to its essential role in controlled drug release, photothermal activation (hyperthermia), and photodynamic production of reactive oxygen species (ROS). Third, some of those activation strategies that rely on ultrasound, photothermal, photoacoustic, magnetic field, or X-ray radiation are dually functional due to their role in imaging modalities. In summary, this review article presents recent advances and new insights that pertain to nanotherapeutic delivery systems. It also addresses their technical limitations associated with tissue penetration (light), spatial resolution (ultrasound, hyperthermia), and occurrence of cellular resistance (ROS).

Aptamer-Functionalized Gold Nanostars for on-Demand Delivery of Anticancer Therapeutics

Gold nanostars (AuNS) are promising carriers for targeted delivery of therapeutic oligonucleotides, but their potential in fabricating an on-demand drug release system in a facile and robust way remains to be explored. In this paper, we used a model aptamer (HApt), acting not only as a target ligand but also as a natural thermal-responsive material, to decorate AuNS. The prepared gold nanoconstruct, HApt@AuNS, displayed stoichiometric loading capacity of the anthracycline drug doxorubicin (Dox). The on-demand drug release was realized by illuminating nanoconstructs with near-infrared (NIR) light. Furthermore, a higher degree of Dox release from the nanoconstructs was achieved in an acidic environment, compared to neutral conditions. The in vitro experiments showed that Dox-intercalation did not affect the cell uptake efficiency of HApt@AuNS, which could enter cells through clathrin-mediated endocytosis and microtubule-dependent active transport to lysosomes. Dox-loaded HApt@AuNS exhibited intracellular on-demand drug release and enhanced toxicity against cancer cells by NIR-irradiation.

Lab and Pilot-Scale Synthesis of MxOm@SiC Core-Shell Nanoparticles

The addition of light ceramic particles to bulk technological materials as reinforcement to improve their mechanical properties has attracted increasing interest in the last years. The metal matrix composites obtained using nanoparticles have been reported to exhibit an improvement of their properties due to the decrease in the size of the ceramic additives to the nanoscale. Additionally, important effects such as the dispersion of the nanoparticles, wettability, and low reactivity can be controlled by the modification of the nanoparticles' surface. In this work, we present the preparation of core-shell M_xO_m@SiC nanoparticles with different shell compositions. The accurate and reproducible preparation is developed both at the lab and pilot scale. The synthesis of these core-shell nanoparticles and their scale-up production are fundamental steps for their industrial use as additives in metal matrix composites and alloys. Powder X-ray diffraction and energy dispersive X-ray (EDX) coupled with scanning transmission electron microscopy (STEM) are used to corroborate the formation of the core-shell systems, whereas line scan-EDX analysis allows measuring the average shell thickness.