Unmodified Nanoparticles Research Articles

Recent Advances of Modified TiO2 Nanostructure as Heterogeneous Catalyst in Organic Transformations

This review highlights the different strategies of modified TiO2 nanostructure as heterogeneous catalyst in organic transformations. The modification in TiO2 nanostructure have been achieved by doping with metal and non-metal, composing with other material such as metals, metal oxides, nonoxides, semiconductor and nanostructure carbon materials. The influence of modification in TiO2 nanostructure on catalytic properties in organic synthesis also discussed. Different modifications of TiO2 extend the catalyst selectivity and reusability over unmodified TiO2 nanoparticles. Recent investigations have shown that modified TiO2 nanostructures utilised as active catalysts or catalyst support in organic transformations including C-C, C-N, C-S, C-O bond formation reactions, multicomponent reactions (MCR), oxidation- reductions.

Surface Modification of TiO₂-Al₂O₃ Nanoparticles for the Enhancement of the Rheological Properties of Base Lubricating Oil

Lubricating oils are used in moving parts to minimize friction. The use of Nanofluids can enhance the properties of lubricants. The aim of this work is an enhancement of the rheology properties of base oil. The surface modification was conducted for inorganic nanoparticles (NPs) TiO₂-Al₂O₃ with oleic acid (OA) in this research. The OA renders the TiO₂-Al₂O₃ surface hydro-phobic. The OA-treated NPs show very stable dispersion in lubricating oil even after more than one month, compared with the unmodified NPs. The surface modification of NPs was characterized by Fourier transform infrared spectroscopy (FTIR). In this research, treated TiO2-Al₂O₃ are added to raw Iraqi lubricating oil 40 stock as a hybrid Nanofluid to study the rheology properties such as kinematic viscosity, viscosity index, and the stability of nano-fluid. Four different concentrations were prepared with a range of 0.2% to 1% by weight. Pour points and flashpoint was also identified. The TiO₂-Al₂O₃ nano lubricant shows a significant improvement in the viscosity index by 5.3–9.1 %, while the flashpoint increased by 5.8 – 14.36 % comparing with base oil.

Effect of the Modified and Unmodified ZnO Nanoparticle on the different Properties of Silicon Elastomer

The aim of the present study is to establish the synthesis of the antibacterial prosthetic liner with artificial limb mediated ZnO nanoparticle and the evaluation of their different properties and antibacterial activity. So thatwe used both modified and unmodified ZnO nanoparticle prepared silicone rubber nanocomposite using in the production of prosthetic liner that being antibacterial and prevent may occur.With the addition of 1,2,3,4,and 5 pphr (part per hundred rubber) of modified and unmodified ZnO nanoparticle it was noted that as, the concentration of both type ZnO nanoparticle compression, hardness, modulus, elongation, tear resistance, tensile strength, and specify gravity decrease. Composite contain modified ZnO nanoparticle still has higher mechanical properties than that contain unmodified nanoparticle the work suggested to use little amount of nanoparticle to get better mechanical and antibacterial properties because the propagation of nanoparticle near the surface of the nanocomposite prepared.

Improving the stability of nanofluids via surface-modified titanium dioxide nanoparticles for wettability alteration of oil-wet carbonate reservoirs

The main challenge of the application of nanofluids for enhanced oil recovery (EOR) in oil-wet carbonate reservoirs is maintaining their stability under high-temperature and high-salinity which is normally seen in reservoir conditions. In this work, surface-modified TiO2 nanoparticles were synthesized by N-(2-Aminoethyl)−3-Aminopropyltrimethoxysilane (AEAPTMS) as a coupling agent for surface modification of nanoparticles. Zeta potential and dynamic light scattering analyses were used to evaluate the stability of the prepared nanofluids. Results indicated that nanofluids had high stability in 90 °C and 20 wt% salinity. The influence of nanofluids on wettability alteration of carbonate rocks was studied by measuring the contact angle value. Untreated rock samples were strongly oil-wet, with water advancing and receding contact angles of 165.1° and 166.2°, respectively. After treatment with 3wt% concentration of surface-modified TiO2 nanoparticles, the rock plate wettability changed to a water-wet state, with water advancing and receding contact angles of 37.6° and 48.2°, respectively. Suggested surface-modified TiO2 nanoparticles were more effective in wettability alteration of the rock surfaces compared to the un-modified TiO2 nanoparticles. Furthermore, higher concentration of nanoparticles, higher the ability of the nanoparticles on changing the rock wettability.

Stability and thermal conductivity of TiO2/water nanofluids: A comparison of the effects of surfactants and surface modification

In this study, Surface modification technique is applied to prepare γ-glycidoxypropyltrimethoxysilane (GPTMS) modified TiO2/water nanofluids. Three surfactants and unmodified nanoparticles are added into de-ionized water to prepare surfactant added nanofluids. The characteristics of modified nanoparticles are firstly investigated. The results show that the grafting efficiency of GPTMS increases with reacting temperature and reactant mass ratio of GPTMS to nanoparticles. The stability and thermal conductivity of prepared nanofluids are investigated. The results show that the nanofluids prepared by adding Sodium dodecyl sulfate (SDS) and unmodified nanoparticles have moderate stability. The nanofluids prepared by GPTMS modified nanoparticles show excellent stability, which can be stable for 49 days and have the largest zeta potential. For all prepared nanofluids, thermal conductivity increases with temperature and nanoparticle concentration. The addition of SDS has limited contributions in thermal conductivity of nanofluids, while GPTMS modified nanofluids have higher thermal conductivity and long term thermal conductivity consistency.

Surface Modification of Nanoparticles Enhances Drug Delivery to the Brain and Improves Survival in a Glioblastoma Multiforme Murine Model.

Glioblastoma multiforme (GBM) is the most malignant type of brain tumor and has an extremely poor prognosis. Current treatment protocols lack favorable outcomes, and alternative treatments with superior efficacy are needed. In this study, we demonstrate that loading paclitaxel (PTX) in a polymeric, nanoparticulate delivery system is capable of improving its brain accumulation and therapeutic activity. We independently incorporated two different positively charged surface modifiers, poly(amidoamine) (PAMAM) and poly(ethylenimine) (PEI), onto poly(lactic-co-glycolic acid) (PLGA)-polyethylene glycol (PEG), PLGA-PEG, nanoparticles (NPs) using a modified nanoprecipitation technique that assures the formation of nanosized particles while exposing the positively charged polymer on the surface. The prepared NPs underwent comprehensive analyses of their size, charge, in vitro permeability against a BBB cell line, and in vivo biodistribution. Our results demonstrated the successful fabrication of positively charged NPs using PAMAM or PEI. Importantly, significant improvement in brain accumulation (in vivo) was associated with NPs containing PAMAM compared to unmodified NPs or NPs containing PEI. Finally, the efficacy of PAMAM-modified NPs loaded with PTX was evaluated with orthotopic human GBM xenografts in a mouse model, and the data demonstrated improved survival and equivalent safety compared to soluble PTX. Our data substantiate the importance of surface chemistry on the magnitude of NP accumulation in the brain and pave the way for further in vivo evaluation of chemotherapeutic drugs against GBM that have previously been overlooked because of their limited ability to cross the BBB.

One Pot Silica Nanoparticle Modification and Doxorubicin Encapsulation as pH-Responsive Nanocarriers, Applying PEG/Lysine Aqueous Two Phase System

Providing an efficient system for drug delivery and chemotherapy has always been an important issue. Here, we have presented an aqueous two-phase system (ATPS) based on polyethylene glycol and lysine, which can partition doxorubicin (DOX) as an anticancer drug successfully. Addition of SiO2 nanoparticles to ATPS increased the partitioning of doxorubicin (DOX) as an anticancer drug from 47.92 in the absence of nanoparticles to 92.33 due to interactions between drug and nanoparticles. This novel biocompatible ATPS simultaneously modified the surface of SiO2 nanoparticles and loaded doxorubicin (DOX) on the modified SiO2 using hydrogen bonding interactions in one pot. Modification of the surface of SiO2 provides an opportunity for achieving a stimulus-sensitive drug delivery system. The formation of nanoformulation and its characteristics were investigated using microscopy, spectroscopy, and thermal analysis. Drug release study demonstrated that DOX is loaded on nanoformulations efficiently with an encapsulation efficiency of 63.84% and shows lower release in physiological environment compared to the unmodified nanoparticles. While in acidic conditions of pH 5.5, a significant increase was observed in the release profile. MTT assay on MCF-7 cancer cells confirmed that the nanoformulations were non-toxic and DOX-loaded nanocarrier showed anticancer behavior. These results indicate that the prepared nanoformulations are promising nanocarriers for controlled drug release purposes.

Biosynthesized unmodified silver nanoparticles: A colorimetric optical sensor for detection of Hg2+ ions in aqueous solution

Under the catalysis of microwave radiation, silver nanoparticles (AgNPs) were synthesized in situ by reducing silver ions (AgNO3) using the phenolic hydroxyl groups of the tyrosine domain in silk sericin. The dispersion synthesized nano-biocomposite was characterized using different analytical instruments. The surface Plasmon resonance (SPR) absorption band observed at 412 nm in UV–visible (UV–vis) spectra confirm the generation of AgNPs. The FCC crystal structure and generation of Ag0 atoms were revealed by powder X-ray diffraction analysis and X-ray photoelectron spectroscopy respectively. Transmission electron microscopy (TEM) was used to investigate the distribution, shape evolution, size of AgNPs, and the finding revealed a spherical morphology with an average size of 8.4 nm. The sericin synthesized AgNPs were used to detect mercury ions (Hg2+) in an aqueous solution selectively and sensitively, and the interaction response was monitored using UV–vis spectroscopy. As Hg2+ was added to AgNPs, the overall absorbance dropped significantly, and the color changed from yellow to colorless. With the best linearity fit (R2 = 0.995) in the concentration range of 10–100 ppb, the maximum of detection (LOD) was about 15 ppb. Bio-based AgNPs can prove to be an excellent material for optical sensors.

Assessment of characteristics and weather stability of acrylic coating containing surface modified zirconia nanoparticles

In this work, the acrylic resin coatings contained ZrO2 nanoparticles modified with (3-glycidyloxypropyl)triethoxysilane (GPTES) were prepared by stirring with vibrating ultra-sonication method. Some characteristics of the modified ZrO2 nanoparticles were measured by Infrared Spectroscopy (IR), X-ray Diffraction Analysis (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), Thermal Gravimetric Analysis (TGA), and Dynamic Light Scattering (DLS) techniques and compared to those of the unmodified ZrO2 nanoparticles. The effect of ZrO2 nanoparticles modified with various GPTES content on abrasion resistance, morphology, thermal and weather stability of acrylic resin coating was investigated. The obtained results showed using 3 wt% of GPTES, the GPTES was grafted on surface of the ZrO2 nanoparticles with the grafted amount of 0.068 mmol/g. The abrasion resistance and weather durability of acrylic resin coating were enhanced significantly in the presence of modified ZrO2 nanoparticles. The acrylic resin coatings filled by ZrO2 nanoparticles modified with GPTES are promising for the applications in daily life and in civil engineering construction.

Enhanced morphology and hydrophilicity of PVDF flat membrane with modified CaCO3@SMA additive via thermally induced phase separation method

Modified CaCO3@SMA nanoparticles obtained by coordination reaction between poly(styrene-co-maleic anhydride) (SMA) and calcium carbonate (CaCO3) nanoparticles were adopted as additive to prepare polyvinylidene fluoride (PVDF) flat membrane via thermally induced phase separation (TIPS) method with dioctyl phthalate (DOP) and dibutyl phthalate (DBP) as mixed diluent. The CaCO3 nanoparticles modified by SMA effectively reduced the adverse agglomeration of nanoparticles and made the additive disperse evenly in PVDF matrix. The presence of modified CaCO3@SMA changed the membrane morphology from dispersed spherulites with large pores to fuzzy dendrite structures with uniform pore sizes. The membrane pore sizes, pore size distribution and tensile strength were significantly improved compared to both virgin membranes and those containing unmodified CaCO3 nanoparticles. After the CaCO3 was pickled, the porosity and the connectivity between membrane pores were greatly enhanced, resulting in a significant increase in pure water flux. At the same time, the amphiphilic SMA fixed in and on the membrane surface improved the hydrophilic and anti-fouling properties demonstrated in a three-cycle test. The present study provided a potential TIPS method for the fabrication of PVDF membrane combined with a simple strategy of modified inorganic particle additive.

Biofilm Responsive Zwitterionic Antimicrobial Nanoparticles to Treat Cutaneous Infection.

To avert the poor bioavailability of antibiotics during S. aureus biofilm infections, a series of zwitterionic nanoparticles containing nucleic acid nanostructures were fabricated for the delivery of vancomycin. The nanoparticles were prepared with three main lipids: (i) neutral (soy phosphatidylcholine; P), (ii) positively charged ionizable (1,2-dioleyloxy-3-dimethylaminopropane; D), and (iii) anionic (1,2-dipalmitoyl-sn-glycero-3-phospho((ethyl-1′,2′,3′-triazole) triethylene glycolmannose; M) or (cholesteryl hemisuccinate; C) lipids. The ratio of the anionic lipid was tuned between 0 and 10 mol %, and its impact on surface charge, size, stability, toxicity, and biofilm sensitivity was evaluated. Under biofilm mimicking conditions, the enzyme degradability (via dynamic light scattering (DLS)), antitoxin (via DLS and spectrophotometry), and antibiotic release profile was assessed. Additionally, biofilm penetration, prevention (in vitro), and eradication (ex vivo) of the vancomycin loaded formulation was investigated. Compared with the unmodified nanoparticles which exhibited the smallest size (188 nm), all three surface modified formulations showed significantly larger sizes (i.e., 222–277 nm). Under simulations of biofilm pH conditions, the mannose modified nanoparticle (PDM 90/5/5) displayed ideal charge reversal from a neutral (+1.69 ± 1.83 mV) to a cationic surface potential (+17.18 ± 2.16 mV) to improve bacteria binding and biofilm penetration. In the presence of relevant bacterial enzymes, the carrier rapidly released the DNA nanoparticles to function as an antitoxin against α-hemolysin. Controlled release of vancomycin prevented biofilm attachment and significantly reduced early stage biofilm formations within 24 h. Enhanced biocompatibility and significant ex vivo potency of the PDM 90/5/5 formulation was also observed. Taken together, these results emphasize the benefit of these nanocarriers as potential therapies against biofilm infections and fills the gap for multifunctional nanocarriers that prevent biofilm infections.

Accumulation and Effect of Silver Nanoparticles Functionalized with Spirulina platensis on Rats.

The effect of unmodified and functionalized Spirulina platensis biomass silver nanoparticles on rats during prolonged oral administration was assessed. Silver nanoparticles were characterized by using transmission electron microscopy, while their uptake by the biomass was confirmed using scanning electron microscopy and energy dispersive analysis. The content of silver in the different organs of rats after a period of administration (28 days) or after an additional clearance period (28 days) was ascertained by using neutron activation analysis. In animals administrated with the unmodified nanoparticles, the highest content of silver was determined in the brain and kidneys, while in animals administrated with AgNP-Spirulina, silver was mainly accumulated in the brain and testicles. After the clearance period, silver was excreted rapidly from the spleen and kidneys; however, the excretion from the brain was very low, regardless of the type of nanoparticles. Hematological and biochemical tests were performed in order to reveal the effect of nanoparticles on rats. The difference in the content of eosinophils in the experimental and control groups was statistically significant. The hematological indices of the rats did not change significantly under the action of the silver nanoparticles except for the content of reticulocytes and eosinophils, which increased significantly. Changes in the biochemical parameters did not exceed the limits of normal values. Silver nanoparticles with the sizes of 8–20 nm can penetrate the blood–brain barrier, and their persistence after a period of clearance indicated the irreversibility of this process.

Advantages of polydopamine coating in the design of ZIF-8-filled thin-film nanocomposite (TFN) membranes for desalination

In this study, zeolitic imidazolate framework-8 (ZIF-8) nanoparticles coated with polydopamine (PDA) were synthesized and used to prepare thin film nanocomposite (TFN) membranes for desalination. Structures, properties, and desalination performances of the membranes were systematically compared with those of membranes containing unmodified ZIF-8 nanoparticles or not containing ZIF-8, revealing the significance of the PDA coating on the overall performance of the TFN membranes. The PDA coating provided ZIF-8 nanoparticles with dispersibility in water and resistance to hydrochloric acid as a by-product of interfacial polymerization, which allowed them to be uniformly dispersed in the selective layer without agglomeration and deterioration of the crystalline structure. These are very important for the improvement of the permeability and stability of TFN membranes while maintaining the selectivity. In addition, the PDA coating inhibited the direct contact of ZIF-8 with an organic foulant, which dramatically enhanced the fouling resistance of the membranes.

Surface modified nanoparticles: a green catalyst for the reduction of ketones

In the present study, a creative and eco-friendly synthetic method was demonstrated for the reduction of ketones using surface modified metal oxide nanoparticles (MO NPs). Nickel oxide, iron oxide and copper oxide nanoparticles were biosynthesized from the aqueous immature fruit extract of Cocos nucifera and the nanoparticle’s surface was modified using glycerol to improve the catalytic efficiency. Surface modification of the nanoparticles enhanced the catalytic activity of nanoparticles as compared to the unmodified metal oxide nanoparticles (MO NPs) for the reduction of ketones. Among the MO NPs used as catalysts for the reduction of acetophenone derivatives, glycerol modified iron oxide nanoparticles showed greater results with 74%–91% of yield due to its uniform morphology. The catalyst retained its stability even after seven repeated cycles of reaction.

Ultrasound-Assisted Microencapsulation of Soybean Oil and Vitamin D Using Bare Glycogen Nanoparticles.

Ultrasonically synthesized core-shell microcapsules can be made of synthetic polymers or natural biopolymers, such as proteins and polysaccharides, and have found applications in food, drug delivery and cosmetics. This study reports on the ultrasonic synthesis of microcapsules using unmodified (natural) and biodegradable glycogen nanoparticles derived from various sources, such as rabbit and bovine liver, oyster and sweet corn, for the encapsulation of soybean oil and vitamin D. Depending on their source, glycogen nanoparticles exhibited differences in size and ‘bound’ proteins. We optimized various synthetic parameters, such as ultrasonic power, time and concentration of glycogens and the oil phase to obtain stable core-shell microcapsules. Particularly, under ultrasound-induced emulsification conditions (sonication time 45 s and sonication power 160 W), native glycogens formed microcapsules with diameter between 0.3 μm and 8 μm. It was found that the size of glycogen as well as the protein component play an important role in stabilizing the Pickering emulsion and the microcapsules shell. This study highlights that native glycogen nanoparticles without any further tedious chemical modification steps can be successfully used for the encapsulation of nutrients.

Smart Modification on Magnetic Nanoparticles Dramatically Enhances Their Therapeutic Properties.

Simple SummaryIn this work, a smart gemcitabine delivery system based on magnetic nanoparticles (MNP) is proposed. Gemcitabine (GEM) is a chemotherapeutic agent usually employed as monotherapy for the treatment of pancreatic cancer. Unfortunately, this drug presents short half-life and high toxicity in non-tumoral tissues. Thus, new efficient drug delivery systems are needed. In this regard, we modified MNP to attach this drug via disulfide bonds (MNP-GEM) to promote the selective release of GEM in pancreatic cancer cells, and the great potential of our proposed nanocarrier for biomedical applications is broadly assessed. Remarkably, this modification has proved to prevent the unspecific binding of proteins, reduced the cytotoxic effect of the drug in non-cancerous cells, improved the internalization in pancreatic cancer cells, and its activity was synergistically enhanced in combination with magnetic hyperthermia.Magnetic nanoparticles (MNP) are employed as nanocarriers and in magnetic hyperthermia (MH) for the treatment of cancers. Herein, a smart drug delivery system composed of MNP functionalized with the cytotoxic drug gemcitabine (MNP-GEM) has been thoroughly evaluated. The linker employed is based on a disulfide bond and allows the controlled release of GEM under a highly reducing environment, which is frequently present in the cytoplasm of tumor cells. The stability, MH, and the interaction with plasma proteins of the nanoparticles are evaluated, highlighting their great potential for biological applications. Their cytotoxicity is assessed in three pancreatic cancer cell lines with different sensitivity to GEM, including the generation of reactive oxygen species (ROS), the effects on the cell cycle, and the mechanisms of cell death involved. Remarkably, the proposed nanocarrier is better internalized than unmodified nanoparticles, and it is particularly effective in PANC-1 cells, resistant to GEM, but not in non-tumoral keratinocytes. Additionally, its combination with MH produces a synergistic cytotoxic effect in all cancer cell lines tested. In conclusion, MNP-GEM presents a promising potential for treating pancreatic cancer, due to multiple parameters, such as reduced binding to plasma proteins, increased internalization, and synergistic activity when combined with MH.

Synthesis of Polyaniline Coated Magnesium and Cobalt Oxide Nanoparticles through Eco-Friendly Approach and Their Application as Antifungal Agents.

Plant-mediated synthesis of nanoparticles exhibits great potential to minimize the generation of chemical waste through the utilization of non-toxic precursors. In this research work, we report the synthesis of magnesium oxide (MgO) and cobalt oxide (Co3O4) nanoparticles through a green approach using Manilkara zapota leaves extract, their surface modification by polyaniline (PANI), and antifungal properties against Aspergillus niger. Textural and structural characterization of modified and unmodified metal oxide nanoparticles were evaluated using FT-IR, SEM, and XRD. The optimal conditions for inhibition of Aspergillus niger were achieved by varying nanoparticles’ concentration and time exposure. Results demonstrate that PANI/MgO nanoparticles were superior in function relative to PANI/Co3O4 nanoparticles to control the growth rate of Aspergillus niger at optimal conditions (time exposure of 72 h and nanoparticles concentration of 24 mM). A percentage decrease of 73.2% and 65.1% in fungal growth was observed using PANI/MgO and PANI/Co3O4 nanoparticles, respectively, which was higher than the unmodified metal oxide nanoparticles (67.5% and 63.2%).

Tailoring Reaction Pathways by Tuning the Surface Composition of AuPt Nanocatalysts for Enhanced Formic Acid Oxidation

Pt-based nanocatalysts are universally applied in direct formic acid fuel cells. For Pt-based nanocatalysts, formic acid oxidation involves two pathways: dehydrogenation and dehydration. Dehydration, due to the production of CO, can poison the surface of the catalyst and thus reduce the catalytic efficiency. The tuning of the composition of Pt-based nanocrystals can effectively improve selectivity for dehydrogenation, especially for AuPt nanocrystals. However, it is still a challenge to tune the composition of AuPt nanocrystals in a nanometer size. Herein, we put forward a remarkably effortless technique for tailoring reaction pathways of formic acid oxidation by tuning the surface composition of AuPt nanocatalysts. Compared with the unmodified AuPt nanoparticles and commercial Pt/C nanocatalysts, the modified AuPt nanoparticles exhibit significantly enhanced catalytic properties. It shows a mass activity of 1.94 mA mgPt–1 at 0.61 V versus the reversible hydrogen electrode, 19.4 times and 7.5 times higher than that of Pt/C nanocatalysts (0.1 mA mgPt–1) and Pt-rich Au@Pt nanoparticles (0.26 mA mgPt–1), respectively. Meanwhile, it also exhibits that the specific activity of modified AuPt nanoparticles is 7.89 mA cm–2 at 0.61 V, 46.4 times and 7.2 times higher than that of the Pt/C reference (0.17 mA cm–2) and Pt-rich Au@Pt nanoparticles (1.09 mA cm–2), respectively.

Green Synthesized Unmodified Silver Nanoparticles as Reproducible Dual Sensor for Mercuric Ions and Catalyst to Abate Environmental Pollutants

Green Synthesized Unmodified Silver Nanoparticles as Reproducible Dual Sensor for Mercuric Ions and Catalyst to Abate Environmental Pollutants

Assessment of Some Characteristics and Properties of Zirconium Dioxide Nanoparticles Modified with 3-(Trimethoxysilyl) Propyl Methacrylate Silane Coupling Agent

This study presents the results of surface modification of zirconium dioxide (ZrO2) nanoparticles by 3-(trimethoxysilyl) propyl methacrylate silane coupling agent by assessing some characteristics and properties of modified ZrO2 nanoparticles by infrared spectroscopy, thermogravimetric analysis, size distribution, zeta potential, and field emission scanning electron microscopy methods. The modified and unmodified ZrO2 nanoparticles have been used as nanoadditives for organic coatings based on acrylic emulsion resin. The abrasion resistance of acrylic coating was evaluated according to ASTM E968-15. The obtained results show that ZrO2 nanoparticles were functionalized successfully with 3-(trimethoxysilyl) propyl methacrylate silane. The modified ZrO2 nanoparticles exhibit a positive effectiveness in the enhancement of the abrasion resistance of acrylic resin coating compared to unmodified ZrO2 nanoparticles.