Zinc oxide nanoparticles: a promising nanomaterial for biomedical applications

Subcellular targets of zinc oxide nanoparticles during the aging process: role of cross-talk between mitochondrial dysfunction and endoplasmic reticulum stress in the genotoxic response

Zinc oxide nanoparticles (ZnO NPs) are being produced abundantly and applied increasingly in various fields. The special physicochemical characteristics of ZnO NPs makes them incline to undergo physicochemical transformation over time (aging), which modify their bioavailability and toxicity. However, the subcellular targets and the underlying molecular mechanisms involved in the genotoxicity induced by ZnO NPs during aging process are still unknown. The present study found that the acute cytotoxic effects of fresh ZnO NPs was largely regulated by mitochondria-dependent apoptosis, which the level of cleaved Caspase-3 and mitochondria damage were significantly higher than that of 60 day-aged ZnO NPs. In contrast, aged ZnO NPs induced more reactive oxygen species (ROS) production and endoplasmic reticulum (ER) stress marker protein (BIP/GRP78) expression and their genotoxicity could be dramatically suppressed by either ROS scavengers (DMSO, CAT and NaN3) or ER stress inhibitor (4-PBA). Using mitochondrial-DNA deficient (ρ0) AL cells, we further found that ER stress induced by aged ZnO NPs was triggered by ROS generated from mitochondria, which eventually mediated the gentoxicity of aged NPs. Our data provided novel information on better understanding the contribution of subcellular targets to the genotoxic response of ZnO NPs during the aging process.

Bifunctional nano-Ag3PO4 with capabilities of enhancing ceftazidime for sterilization and removing residues

Since the efficacy of antibiotics towards bacteria is decreasing over time, the rising of antibiotic emission has become an increasingly grave issue. In this study, we proposed an integrated antibacterial nanotechnology without pollution residues, which synergistically enhances the antibacterial activity of ceftazidime by using the inorganic nano-Ag3PO4, and subsequently removes drug residues by photocatalysis. Ag3PO4 were synthesized using a simple ion-exchange method without any reducing agent or protectant. The combined antibacterial activity of Ag3PO4 and 22 kinds of antibiotics against Escherichia coli was first studied. The results showed that Ag3PO4 and ceftazidime exhibited the best synergistic effect. Next, the synergy mechanism was proposed, the non-chemical bond forces between Ag3PO4 and ceftazidime was determined by zeta potential analyzer, X-ray photoelectron spectroscopy (XPS) and infrared spectroscopy (IR). The interaction between antimicrobials and bacteria was further demonstrated by surface plasma resonance spectroscopy (SPR), scanning electron microscopy (SEM) and propidium iodide (PI) staining. In addition, the production of reactive oxygen species (ROS), the induction of oxidative stress and dissolution of silver ions in Ag3PO4 were studied and found out that only under light, could the ROS be generated. In conclusion, the synergistic effect of Ag3PO4 and ceftazidime is responsible for the joint destruction of cell wall.

Antibiotic potentiation and anti-cancer competence through bio-mediated ZnO nanoparticles

Zinc Oxide (ZnO) is currently used in nano-cosmeceuticals and nano-pharmaceuticals topically due to their multifunctional efficiency irrespective of the synthetic method. Bio-reducers are cosmopolitically famed to attain stable, reliable, and toxic free synthesis. Thus, the objective of the current study is to prepare ZnO NPs in a greener approach using Annona squamosa (AS) leaf extract and to evaluate their antibiotic potentiation capacity and anticancer activity. The novel synthetic process of ZnO NPs was performed without using any chemicals (reducing or stabilizing agents) or high temperature processing under continuous stirring and refluxion in the presence of oxygen environment. AS have renowned phytochemicals with medicinal properties. Therefore, the mounting of secondary metabolites onto ZnO NPs during synthesis as reducing, stabilizing, capping agents may impart additional biomedical efficacy. The ZnO NPs were prepared with the assessment of stabilization (characteristic peak at 375 nm) from absorbance spectra. Further, SEM, TEM, XRD, FTIR, and Raman analysis of AS-ZnO NPs were performed to elucidate the size, shape, nature, chemical structure and composition. The characterization techniques revealed particles of 20-50 nm size, hexagonal shaped crystalline structure with diverse phytochemicals and functional groups. In addition, AS-ZnO NPs were investigated for antibacterial activity along with antibiotic potentiating capability through combinational assay. Furthermore, the anticancer potential of AS-ZnO NPs was evaluated against HeLa cell line along with assessment of biocompatibility on HEK-293 cell line using MTT assay. Based on the findings, our study exploits green-synthesized ZnO NPs as an effective strategy for potentiation of antibiotic activity and anticancer activity in a biocompatible perspective.

Phytosynthesized metal oxide nanoparticles for pharmaceutical applications

Developments in nanotechnology field, specifically, metal oxide nanoparticles have attracted the attention of researchers due to their unique sensing, electronic, drug delivery, catalysis, optoelectronics, cosmetics, and space applications. Physicochemical methods are used to fabricate nanosized metal oxides; however, drawbacks such as high cost and toxic chemical involvement prevail. Recent researches focus on synthesizing metal oxide nanoparticles through green chemistry which helps in avoiding the involvement of toxic chemicals in the synthesis process. Bacteria, fungi, and plants are the biological sources that are utilized for the green nanoparticle synthesis. Due to drawbacks such as tedious maintenance and the time needed for the nanoparticle formation, plant extracts are widely used in nanoparticle production. In addition, plants are available all over the world and phytosynthesized nanoparticles show comparatively less toxicity towards mammalian cells. Secondary metabolites including flavonoids, terpenoids, and saponins are present in plant extracts, and these are highly responsible for nanoparticle formation and reduction of toxicity. Hence, this article gives an overview of recent developments in the phytosynthesis of metal oxide nanoparticles and their toxic analysis in various cells and animal models. Also, their possible mechanism in normal and cancer cells, pharmaceutical applications, and their efficiency in disease treatment are also discussed.

Antimicrobial surfaces with self-cleaning properties functionalized by photocatalytic ZnO electrosprayed coatings

Photoactive coatings of sol-gel ZnO suspensions were electrosprayed on glass substrates to produce self-cleaning antimicrobial functionalized surfaces. ZnO-functionalized materials exhibited a uniform external surface consisting of a pattern of microspheres with diameters in the 100-300 nm range. Electrospray allowed surface densities up to 0.30 mg cm^-2 that displayed considerable hydrophilicity. Water contact angle decreased with UV irradiation to values below 10°. Two different UV doses were tested by adjusting the irradiation time to simulate Summer-Spring and Winter-Fall conditions. The functionalized coatings showed excellent photocatalytic properties towards the photodegradation of Methylene blue. The electrosprayed surfaces also displayed antibacterial activity against Staphylococcus aureus, with >99.5% reduction in the number of culturable cells. The biocidal activity is attributed to the photogenerated reactive oxygen species on the surface of ZnO coatings and the bioavailable zinc ions produced from ZnO dissolution. The photoactive coatings kept surfaces free from bacterial colonization and biofilm formation.

Translating Nanomedicine to Comparative Oncology-the Case for Combining Zinc Oxide Nanomaterials with Nucleic Acid Therapeutic and Protein Delivery for Treating Metastatic Cancer

The unique anticancer, biochemical, and immunologic properties of nanomaterials are becoming a new tool in biomedical research. Their translation into the clinic promises a new wave of targeted therapies. One nanomaterial of particular interest are zinc oxide (ZnO) nanoparticles (NPs), which has distinct mechanisms of anticancer activity including unique surface, induction of reactive oxygen species, lipid oxidation, pH, and also ionic gradients within cancer cells and the tumor microenvironment. It is recognized that ZnO NPs can serve as a direct enzyme inhibitor. Significantly, ZnO NPs inhibit extracellular signal-regulated kinase (ERK) and protein kinase B (AKT) associated with melanoma progression, drug resistance, and metastasis. Indeed, direct intratumoral injection of ZnO NPs or a complex of ZnO with RNA significantly suppresses ERK and AKT phosphorylation. These data suggest ZnO NPs and their complexes or conjugates with nucleic acid therapeutic or anticancer protein may represent a potential new strategy for the treatment of metastatic melanoma, and potentially other cancers. This review focuses on the anticancer mechanisms of ZnO NPs and what is currently known about its biochemical effects on melanoma, biologic activity, and pharmacokinetics in rodents and its potential for translation into large animal, spontaneously developing models of melanoma and other cancers, which represent models of comparative oncology.

Macrocyclic Compounds for Drug and Gene Delivery in Immune-Modulating Therapy

For decades, macrocyclic compounds have been widely applied in various fields owing to essential physicochemical properties such as their rigid cyclic structures, geometric dimensions (diameter and height), hydrophobic cavity, and hydrophilic interface. This review is an attempt to summarize various research accomplishments involving macrocyclic compounds for drug and gene delivery in immune-modulating therapies: the structures and benefits of main host molecules, their mechanisms regulating the immune system from cell uptake to activation of dendritic cells and T helper lymphocytes, as well as their potential immunotherapy for different diseases. Macrocyclic compounds including cucurbiturils (CBs), calixarenes, pillararenes, cyclodextrins (CyDs), macrocyclic peptides and metallo-supramolecular compounds, have their own unique physicochemical properties and functional derivatizations that enable to improve the biocompatibility, responsiveness to stimuli, and effectiveness of immune-modulating therapy. Based on abundant clarifications of the biological immunity mechanisms, representative constructions of macrocyclic compounds for immune therapies have been conducted for the investigation of treatment of different diseases including cancer, atherosclerosis, Niemann-Pick type C1 disease (NPC1), diabetes, and inflammations. Although there are critical challenges that remain to be conquered, we believe the future of macrocyclic compounds in the immune-modulating therapy must be bright.

Zinc-Based Biomaterials for Regeneration and Therapy

Zinc has been described as the 'calcium of the twenty-first century'. Zinc-based degradable biomaterials have recently emerged thanks to their intrinsic physiological relevance, biocompatibility, biodegradability, and pro-regeneration properties. Zinc-based biomaterials mainly include: metallic zinc alloys, zinc ceramic nanomaterials, and zinc metal-organic frameworks (MOFs). Metallic zinc implants degrade at a desirable rate, matching the healing pace of local tissues, and stimulating remodeling and formation of new tissues. Zinc ceramic nanomaterials are also beneficial for tissue engineering and therapy thanks to their nanostructures and antibacterial properties. MOFs have large surface areas and are easily functionalized, making them ideal for drug delivery and cancer therapy. This review highlights recent developments in zinc-based biomaterials, discusses obstacles to overcome, and pinpoints directions for future research.

Zinc phosphate-based nanoparticles as a novel antibacterial agent: in vivo study on rats after dietary exposure

Background

Development of new nanomaterials that inhibit or kill bacteria is an important and timely research topic. For example, financial losses due to infectious diseases, such as diarrhea, are a major concern in livestock productions around the world. Antimicrobial nanoparticles (NPs) represent a promising alternative to antibiotics and may lower antibiotic use and consequently spread of antibiotic resistance traits among bacteria, including pathogens.

Results

Four formulations of zinc nanoparticles (ZnA, ZnB, ZnC, and ZnD) based on phosphates with spherical (ZnA, ZnB) or irregular (ZnC, ZnD) morphology were prepared. The highest in vitro inhibitory effect of our NPs was observed against Staphylococcus aureus (inhibitory concentration values, IC₅₀, ranged from 0.5 to 1.6 mmol/L), followed by Escherichia coli (IC₅₀ 0.8-1.5 mmol/L). In contrast, methicillin resistant S. aureus (IC₅₀ 1.2-4.7 mmol/L) was least affected and this was similar to inhibitory patterns of commercial ZnO-based NPs and ZnO. After the successful in vitro testing, the in vivo study with rats based on dietary supplementation with zinc NPs was conducted. Four groups of rats were treated by 2,000 mg Zn/kg diet of ZnA, ZnB, ZnC, and ZnD, for comparison two groups were supplemented by 2,000 mg Zn/kg diet of ZnO-N and ZnO, and one group (control) was fed only by basal diet. The significantly higher (P < 0.05) Zn level in liver and kidney of all treated groups was found, nevertheless Zn NPs did not greatly influence antioxidant status of rats. However, the total aerobic and coliform bacterial population in rat feces significantly decreased (P < 0.05) in all zinc groups after 30 d of the treatment. Furthermore, when compared to the ZnO group, ZnA and ZnC nanoparticles reduced coliforms significantly more (P < 0.05).

Conclusions

Our results demonstrate that phosphate-based zinc nanoparticles have the potential to act as antibiotic agents.

Decomposition of Bis(N-benzyl-salicydenaminato)zinc (II) Complex for the Synthesis of ZnO Nanoparticles to Fabricate ZnO-Chitosan Nanocomposite for the Removal of Iron (II) Ions from Wastewater

The whole world is faced with a huge challenge of the shortage of clean water due to industrialization and the intimidation of climate change. Poor water quality distresses many areas of human’s well-being. Although there are existing technologies for water treatments, many of these methods utilize toxic substances which create more problems into the environment. The preparation of bis(N-benzyl-salicydenaminato)zinc (II) complex and the synthesis of zinc oxide nanoparticles via the thermal decomposition of zinc complex together with the fabrication of ZnO-chitosan nanocomposites for the removal of iron (II) ions from wastewater is reported. The optical properties of the synthesized nanoparticles showed band edges that are red-shifted in wavelengths when the decomposition temperature was increased. The XRD patterns displayed the hexagonal ZnO phase for the synthesized nanoparticles. TEM images revealed spherical-shaped particles which became agglomerated when the temperature was increased. The parameters such as pH, contact time, and initial concentration were investigated during the water treatment. The pH = 6 was found to be optimum, and the highest percentage removal was recovered after three hours for both adsorbents.

A biomolecule-assisted one-pot synthesis of zinc oxide nanoparticles and its bioconjugate with curcumin for potential multifaceted therapeutic applications

Biodegradable ZnO nanoparticles with excellent biocompatibility prepared via a biogenic process have great potential as therapeutic agent-cum-drug carriers for cancer treatment.

Zinc overload mediated by zinc oxide nanoparticles as innovative anti-tumor agent

The predicted global cancer burden is expected to surpass 20 million new cancer cases by 2025. Despite recent advancement in tumor therapy, a successful cancer treatment remains challenging. The emerging field of nanotechnology offers great opportunities for diagnosis, imaging, as well as treatment of cancer. Zinc oxide nanoparticles (ZnO NP) were shown to exert selective cytotoxicity against tumor cells via a yet unknown mechanism, most likely involving the generation of reactive oxygen species (ROS). These nanoparticles are a promising therapeutic opportunity as zinc is a nontoxic trace element and its application in medically-related products is considered to be safe. We could show that ZnO NP can exert cytotoxic effects on several human tumor cell lines. There can be found ZnO NP concentrations which selectively damage tumor cells while human fibroblasts do not sustain lasting damage. Cytotoxicity is attributable to the release of zinc ions from the nanoparticles outside the cells as well as to a direct cell-nanoparticle interaction. This involves uptake of the particles into the tumor cells. With a silica shell the cytotoxicity can be delayed which can help in the future for a safe transport in the blood stream. Cellular damage finally cumulates in apoptotic cell death via zinc overload within 48 h after treatment with ZnO NP. A therapeutical perspective could be the targeted accumulation of ZnO NP at the tumor side to induce local zinc overload that substantially damages the tumor cells with no or low side effects. We suggest further studies to explore the potential of ZnO NP as an innovative anti-tumor agent.

A biocompatible high surface area ZnO-based molecularly imprinted polymer for the determination of meloxicam in water media and plasma

Ultrasound-assisted solid-phase microextraction (SPME) by a functionalized high surface area ZnO nanoparticle (NP)-based molecularly imprinted polymer (MIP) followed by UV-Vis spectrophotometry was described as a selective, economic and rapid technique which was established for the extraction and preconcentration of meloxicam (MEL) in water media and plasma.

Advanced chemical stability diagrams to predict the formation of complex zinc compounds in a chloride environment

A chemical stability map is advanced by incorporating ion complexation, solubility, and chemical trajectories to predict ZnO, Zn(OH)₂, ZnCO₃, ZnCl₂, Zn₅(CO₃)₂(OH)₆, and Zn₅(OH)₈Cl₂·H₂O precipitation as a function of the total Zn content and pH of an NaCl solution. These calculations demonstrate equilibrium stability of solid Zn products often not considered while tracking the consumed and produced aqueous Zn ion species concentrations through chemical trajectories. The effect of Cl-based ligand formation is incorporated into these stability predictions, enabling enhanced appreciation for the local corrosion conditions experienced at the Zn surface in chloride-containing environments. Additionally, the complexation of Cl⁻ with Zn²⁺ is demonstrated to compete with the formation of solid phases, making precipitation more difficult. The present work also extends the chemical stability diagram derivations by incorporating a Gibbs–Thompson curvature relation to predict the effect of nanoscale precipitate phase formation on species solubility. These thermodynamic predictions correlate well with experimental results for Zn corrosion in full and alternate NaCl immersion, and have far-reaching utility in a variety of fields requiring nanoscale, semiconductor, and/or structural materials.

Zinc corrosion product formation is thermodynamically predicted from the macro- to nanoscale through quantification of complexation, curvature, and chemical trajectory.

Effect of lithium and sodium ions on the size and morphology of ZnO nanoparticles synthesized by a glycerol–urea route

Addition of NaCl and LiCl salts to glycerol–urea synthesis leads to the formation of rods and small spheres of ZnO-NPs.

A novel pro-apoptotic role of zinc octacarboxyphthalocyanine in melanoma me45 cancer cell's photodynamic therapy (PDT)

Zn-based phthalocyanine acts as drug or photosensitizer in photodynamic therapy (PDT) for the treatment of cancer cells. The activated zinc octacarboxyphthalocyanine (ZnPcOC) reacts with oxygen, to generate reactive oxygen species for the damage of melanoma cancer cells, Me45. This in vitro study aimed at investigating the cytotoxic effects of different concentrations of ZnPcOC activated with a diode laser (λ = 685 nm) on Me45, and normal human fibroblast cells, NHDF. To perform this study 10⁴ cells/ml were seeded in 96-well plates and allowed to attach overnight, after which cells were treated with different concentrations of ZnPcOC (10, 20 and 30 μM). After 4 h, cells were irradiated with a constant light dose of 2.5; 4.5 and 7.5 J/cm². Post-irradiated cells were incubated for 24 h before cell viability was measured using the MTT viability assay. Data indicated that high concentrations of ZnPcOC (30 μM) in its inactive state are not cytotoxic to the melanoma cancer cells and normal fibroblasts. Moreover, the results showed that photoactivated ZnPcOC (30 μM) was able to reduce the cell viability of melanoma and fibroblast to about 50%, respectively. At this photosensitizing concentration the efficacy the treatment light dose of 2.5; 4.5 and 7.5 J/cm² was evaluated against Me45 cells. ZnPcOC at a concentration of 30 μM activated with a light dose of 2.5; 4.5 and 7.5 J/cm² was the most efficient for the killing of melanoma cancer cells. Melanoma cancer cells after PDT with a photosensitizing concentration of 30 μM ZnPcOC and a treatment light dose of 2.5; 4.5 and 7.5 J/cm² showed certain pro-apoptotic characteristics, such as direct inducer (early apoptosis) and long-term inducer, also (late apoptosis). This concludes that low concentrations of ZnPcOC, activated with the appropriate light dose, can be used to induce cell death in melanoma cells via ROS-induces apoptosis pathway, what was confirmed with cytometric ROS measurements. Our in vitro study showed that ZnPcOC mediated photodynamic therapy is an effective treatment option for melanoma Me45 cancer cells. 30 μM of ZnPcOC with the treatment light dose of 2.5 J/cm² from a LED diode laser source, with a wavelength of 685 nm, was adequate to destroy melanoma cancer cells via ROS-induced apoptosis pathway, with low killing effects on healthy NHDF normal fibroblasts.

Cytotoxicity and global transcriptional responses induced by zinc oxide nanoparticles NM 110 in PMA-differentiated THP-1 cells

Despite a wide production and use of zinc oxide nanoparticles (ZnONP), their toxicological study is only of limited number and their impact at a molecular level is seldom addressed. Thus, we have used, as a model, zinc oxide nanoparticle NM110 (ZnO110NP) exposure to PMA-differentiated THP-1 macrophages. The cell viability was studied at the cellular level using WST-1, LDH and Alamar Blue^® assays, as well as at the molecular level by transcriptomic analysis. Exposure of cells to ZnO110NP for 24 h decreased their viability in a dose-dependent manner with mean inhibitory concentrations (IC₅₀) of 8.1 μg/mL. Transcriptomic study of cells exposed to two concentrations of ZnO110NP: IC₅₀ and a quarter of it (IC₅₀/4) for 4 h showed that the expressions of genes involved in metal metabolism are perturbed. In addition, expression of genes acting in transcription regulation and DNA binding, as well as clusters of genes related to protein synthesis and structure were altered. It has to be noted that the expressions of metallothioneins genes (MT1, MT2) and genes of heat-shock proteins genes (HSP) were strongly upregulated for both conditions. These genes might be used as an early marker of exposure to ZnONP. On the contrary, at IC₅₀ exposure, modifications of gene expression involved in inflammation, apoptosis and mitochondrial suffering were noted indicating a less specific cellular response. Overall, this study brings a resource of transcriptional data for ZnONP toxicity for further mechanistic studies.

Crosstalk between Autophagy and Nanomaterials: Internalization, Activation, Termination

Nanomaterials (NMs) are comprehensively applied in biomedicine due to their unique physical and chemical properties. Autophagy, as an evolutionarily conserved cellular quality control process, is closely associated with the effect of NMs on cells. In this review, the recent advances in NM-induced/inhibited autophagy (NM-phagy) are summarized, with an aim to present a comprehensive description of the mechanisms of NM-phagy from the perspective of internalization, activation, and termination, thereby bridging autophagy and nanomaterials. Several possible mechanisms are extensively reviewed including the endocytosis pathway of NMs and the related cross components (clathrin and adaptor protein 2 (AP-2), adenosine diphosphate (ADP)-ribosylation factor 6 (Arf6), Rab, UV radiation resistance associated gene (UVRAG)), three main stress mechanisms (oxidative stress, damaged organelles stress, and toxicity stress), and several signal pathway-related molecules. The mechanistic insight is beneficial to understand the autophagic response to NMs or NMs' regulation of autophagy. The challenges currently encountered and research trend in the field of NM-phagy are also highlighted. It is hoped that the NM-phagy discussion in this review with the focus on the mechanistic aspects may serve as a guideline for future research in this field.

Comparative functional dynamics studies on the enzyme nano-bio interface

Introduction

Biomedical applications of nanoparticles (NPs) as enzyme inhibitors have recently come to light. Oxides of metals native to the physiological environment (eg, Fe, Zn, Mg, etc.) are of particular interest-especially the functional consequences of their enzyme interaction.

Materials and methods

Here, Fe₂O₃, zinc oxide (ZnO), magnesium oxide (MgO) and nickel oxide (NiO) NPs are compared to copper (Cu) and boron carbide (B₄C) NPs. The functional impact of NP interaction to the model enzyme luciferase is determined by 2-dimensional fluorescence difference spectroscopy (2-D FDS) and 2-dimensional photoluminescence difference spectroscopy (2-D PLDS). By 2-D FDS analysis, the change in maximal intensity and in 2-D FDS area under the curve (AUC) is in the order Cu~B₄C>ZnO>NiO>>Fe₂O₃>MgO. The induced changes in protein conformation are confirmed by tryptic digests and gel electrophoresis.

Results

Analysis of possible trypsin cleavage sites suggest that cleavage mostly occurs in the range of residues 112-155 and 372-439, giving a major 45 kDa band. By 2-D PLDS, it is found that B₄C NPs completely ablate bioluminescence, while Cu and Fe₂O₃ NPs yield a unique bimodal negative decay rate, -7.67×10³ and -3.50×10¹ relative light units respectively. Cu NPs, in particular, give a remarkable 271% change in enzyme activity. Molecular dynamics simulations in water predicted that the surfaces of metal oxide NPs become capped with metal hydroxide groups under physiological conditions, while the surface of B₄C becomes populated with boronic acid or borinic acid groups. These predictions are supported by the experimentally determined zeta potential. Thin layer chromatography patterns further support this conception of the NP surfaces, where stabilizing interactions were in the order ionic>polar>non-polar for the series tested.

Conclusion

Overall the results suggest that B₄C and Cu NP functional dynamics on enzyme biochemistry are unique and should be examined further for potential ramifications on other model, physiological or disease-relevant enzymes.

The Advancing of Zinc Oxide Nanoparticles for Biomedical Applications

Zinc oxide nanoparticles (ZnO NPs) are used in an increasing number of industrial products such as rubber, paint, coating, and cosmetics. In the past two decades, ZnO NPs have become one of the most popular metal oxide nanoparticles in biological applications due to their excellent biocompatibility, economic, and low toxicity. ZnO NPs have emerged a promising potential in biomedicine, especially in the fields of anticancer and antibacterial fields, which are involved with their potent ability to trigger excess reactive oxygen species (ROS) production, release zinc ions, and induce cell apoptosis. In addition, zinc is well known to keep the structural integrity of insulin. So, ZnO NPs also have been effectively developed for antidiabetic treatment. Moreover, ZnO NPs show excellent luminescent properties and have turned them into one of the main candidates for bioimaging. Here, we summarize the synthesis and recent advances of ZnO NPs in the biomedical fields, which will be helpful for facilitating their future research progress and focusing on biomedical fields.

Silver bullets: A new lustre on an old antimicrobial agent

Silver was widely used in medicine to treat bacterial infections in the 19th and early 20th century, up until the discovery and development of the first modern antibiotics in the 1940s, which were markedly more effective. Since then, every new antibiotic introduced to the clinic has led to an associated development of drug resistance. Today, the threat of extensive bacterial resistance to antibiotics has reignited interest in alternative strategies to treat infectious diseases, with silver regaining well-deserved renewed attention. Silver ions are highly disruptive to bacterial integrity and biochemical function, with comparatively minimal toxicity to mammalian cells. This review focuses on the antimicrobial properties of silver and their use in synergistic combination therapy with traditional antibiotic drugs.

Induction of necrotic cell death and activation of STING in the tumor microenvironment via cationic silica nanoparticles leading to enhanced antitumor immunity

Nanotechnology has demonstrated tremendous clinical utility, with potential applications in cancer immunotherapy. Although nanoparticles with intrinsic cytotoxicity are often considered unsuitable for clinical applications, such toxicity may be harnessed in the fight against cancer. Nanoparticle-associated toxicity can induce acute necrotic cell death, releasing tumor-associated antigens which may be captured by antigen-presenting cells to initiate or amplify tumor immunity. To test this hypothesis, cytotoxic cationic silica nanoparticles (CSiNPs) were directly administered into B16F10 melanoma implanted in C57BL/6 mice. CSiNPs caused plasma membrane rupture and oxidative stress of tumor cells, inducing local inflammation, tumor cell death and the release of tumor-associated antigens. The CSiNPs were further complexed with bis-(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP), a molecular adjuvant which activates the stimulator of interferon genes (STING) in antigen-presenting cells. Compared with unformulated c-di-GMP, the delivery of c-di-GMP with CSiNPs markedly prolonged its local retention within the tumor microenvironment and activated tumor-infiltrating antigen-presenting cells. The combination of CSiNPs and a STING agonist showed dramatically increased expansion of antigen-specific CD8+ T cells, and potent tumor growth inhibition in murine melanoma. These results demonstrate that cationic nanoparticles can be used as an effective in situ vaccine platform which simultaneously causes tumor destruction and immune activation.