Recent advances in green carbon dots (2015–2022): synthesis, metal ion sensing, and biological applications

• Aisha Kanwal,
• Naheed Bibi,
• Sajjad Hyder,
• Arif Muhammad,
• Hao Ren,
• Jiangtao Liu and
• Zhongli Lei

Beilstein J. Nanotechnol. 2022, 13, 1068–1107, doi:10.3762/bjnano.13.93

Biomimetic chitosan with biocomposite nanomaterials for bone tissue repair and regeneration

• Se-Kwon Kim,
• Sesha Subramanian Murugan,
• Pandurang Appana Dalavi,
• Sebanti Gupta,
• Sukumaran Anil,
• Gi Hun Seong and
• Jayachandran Venkatesan

Beilstein J. Nanotechnol. 2022, 13, 1051–1067, doi:10.3762/bjnano.13.92

• graphene oxide/hydroxyapatite/chitosan composites was verified by an MTT assay using A549 cells. The results revealed that the cell viability of A549 cells exceeded 23%, showing that the composites slowed osteosarcoma progression [71]. Graphene oxide-modified chitosan/polyvinylpyrrolidone developed

• nanofibrous structures imitating the native extracellular matrix. The potential use of this membrane for tissue engineering applications was demonstrated by using rat bone marrow mesenchymal stem cells. The cell viability of the chitosan scaffolds with 0, 0.5, 1, 1.5, and 2% of graphene oxide content was

• evaluated by an MTT assay. The results show that chitosan with 2% of graphene oxide has the highest cell viability. The acridine orange–propidium iodide staining was carried out after 24 h of incubation with developed nanofibers: live cells were stained in green and dead cells were stained in red, which

Gelatin nanoparticles with tunable mechanical properties: effect of crosslinking time and loading

• Agnes-Valencia Weiss,
• Daniel Schorr,
• Julia K. Metz,
• Metin Yildirim,
• Saeed Ahmad Khan and
• Marc Schneider

Beilstein J. Nanotechnol. 2022, 13, 778–787, doi:10.3762/bjnano.13.68

• matrix. Thus, the flexibility of the matrix is not influenced as the added macromolecule is also straightforwardly incorporated and co-crosslinked. Cell viability To address potential cell viability-reducing effects of the particle formulations, these were tested on the epithelial adenocarcinoma cell

• line A549 and the human primary cell-derived cell line hAELVi. The cell viability was measured after incubation of blank and FITC-loaded particle formulations in concentrations ranging from 0.001 to 1 mg/mL for 4 h or 24 h with a MTT assay. No time or concentration-dependent reduction of the A549 or

• hAELVi cell viability below 80% relative to the controls could be detected, in neither case of exposure to blank particles or FITC-dextran-loaded particles (Figure 4). Conclusion By inactivation of the crosslinking reagent, it was possible to stop the crosslinking reaction precisely. In this way, the

Detection and imaging of Hg(II) in vivo using glutathione-functionalized gold nanoparticles

• Gufeng Li,
• Shaoqing Li,
• Rui Wang,
• Min Yang,
• Lizhu Zhang,
• Yanli Zhang,
• Wenrong Yang and
• Hongbin Wang

Beilstein J. Nanotechnol. 2022, 13, 549–559, doi:10.3762/bjnano.13.46

• . synthesized a novel probe using gold nanoparticles modified by rhodamine B isothiocyanate and poly(ethylene glycol) (RBITC-PEG-GNPs) [21]. A cytotoxicity assay showed that a cell viability of 95–100% was maintained during the incubation with RBITC-PEG-GNPs with different concentrations from 0 to 80 nM. Thus

• , GNPs-GSH-Rh6G2 demonstrates that gold nanoparticles can improve cell viability, indicating good biocompatibility [61]. To evaluate the release behavior of GNPs-GSH-Rh6G2, the triggered release of RGCOOH started when 30 μL Hg2+ was added to the solution. Figure 7 shows that the molecule was released

• acquired using an OLYMPUS CKX41 inverted fluorescence microscope (Olympus, Japan)/Leica SP5 laser scanning confocal microscope (Leica, Germany). Cell viability was measured by a PectraMax190 microplate reader (Molecular, USA). HPLC-MS was performed on an Agilent-ABQSTAR Pulsar (Agilent, Germany) with a

Ethosomal (−)-epigallocatechin-3-gallate as a novel approach to enhance antioxidant, anti-collagenase and anti-elastase effects

• Çiğdem Yücel,
• Gökçe Şeker Karatoprak,
• Sena Yalçıntaş and
• Tuğba Eren Böncü

Beilstein J. Nanotechnol. 2022, 13, 491–502, doi:10.3762/bjnano.13.41

• ], which are used for transdermal penetration studies and to determine cytotoxic concentrations of many samples. According to 3-(4,5-dimethyldiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) tests, the cell viability was found to be 64.4% or higher for the hydroethanolic solution (30% v/v), ETH

• dose determined based on cell viability results of 50% or more is appropriate [22][28]. In previous studies, the cytotoxic effect of EGCG, whose antioxidant effect has been proven many times, has been investigated, especially on cancer cell lines. Although there is no cytotoxicity study on the L929

• , version two, was used. Percentage of cell viability of L929 cells incubated with samples for 24 h. (Values are expressed as mean ± standard deviation, n = 6). Scanning electron microscopy image of ETHs. The changes in the PS, ZP, and PDI of the: (A, B and C) suspended ETHs at 4 and 25 °C. (Values are

Micro- and nanotechnology in biomedical engineering for cartilage tissue regeneration in osteoarthritis

• Zahra Nabizadeh,
• Mahmoud Nasrollahzadeh,
• Hamed Daemi,
• Mohamadreza Baghaban Eslaminejad,
• Ali Akbar Shabani,
• Mehdi Dadashpour,
• Majid Mirmohammadkhani and
• Davood Nasrabadi

Beilstein J. Nanotechnol. 2022, 13, 363–389, doi:10.3762/bjnano.13.31

Coordination-assembled myricetin nanoarchitectonics for sustainably scavenging free radicals

• Xiaoyan Ma,
• Haoning Gong,
• Kenji Ogino,
• Xuehai Yan and
• Ruirui Xing

Beilstein J. Nanotechnol. 2022, 13, 284–291, doi:10.3762/bjnano.13.23

• serum (FBS) and 1% (v/v) penicillin/streptomycin. 3T3 cells at a density of 1 × 105 cells per well were incubated with different concentrations of MZG (equivalent concentration of Myr: 0, 10, 20, 40, 80, and 100 µM) for 24 h. The cell viability was tested with the methyl thiazolyl tetrazolium (MTT

• was evaluated. After the treatment of 3T3 cells with different concentrations of MZG for 24 h, 100 µM of H2O2 was used to treat the 3T3 cells. The capability of protecting cells from damage was accessed by the cell viability assay. After that, 2′7′-dichlorodihydrofluorescein diacetate (DCFH-DA) dye

• experiments The cytotoxicity of antioxidants is of importance for biomedical applications. Therefore, the cytotoxicity of MZG nanoparticles was assessed by incubating 3T3 cells and determining the cell viability via MTT assay [40]. 3T3 cells were treated with different concentrations of MZG nanoparticles

Photothermal ablation of murine melanomas by Fe₃O₄ nanoparticle clusters

• Xue Wang,
• Lili Xuan and
• Ying Pan

Beilstein J. Nanotechnol. 2022, 13, 255–264, doi:10.3762/bjnano.13.20

• diameter of 329.2 nm. They are highly absorptive at the near-infrared wavelength of 808 nm and efficient at locally converting light into heat. In vitro experiments using light-field microscopy and cell viability assay showed that Fe3O4 NPCs, in conjunction with near-infrared irradiation, effectively

• during NIR irradiation NPCs caused overt apoptosis and necrosis in a dosage-dependent manner (Figure 3a). The strongest effect was observed for the sample with 0.25 mg/mL NPCs. NPCs alone, on the contrary, did not affect cell viability at low concentrations and only caused signs of mild cellular toxicity

• -based nanoparticles, this method has long been regarded as the gold standard for cell viability and proliferation studies, and thus been applied extensively in studies of metal-containing nanoparticles [18][19][20]. In accordance with our flow cytometry findings, the MTT viability assay showed that in

Effects of drug concentration and PLGA addition on the properties of electrospun ampicillin trihydrate-loaded PLA nanofibers

• Tuğba Eren Böncü and
• Nurten Ozdemir

Beilstein J. Nanotechnol. 2022, 13, 245–254, doi:10.3762/bjnano.13.19

• mechanical properties of nanofibers. Enhanced mechanical properties are known to improve cell viability and differentiation [34]. The mechanical properties of all PLA nanofibers (PLA, PLA/PCL, and PLA/PLGA) are suitable. However, the production of PLA/PLGA nanofibers provides an advantage as it leads to

• improved mechanical properties compared to those of PLA nanofibers and PLA/PCL nanofibers, improving cell viability and differentiation. Conclusion Nanofibers can be effectively used in tissue engineering and controlled drug delivery due to their structural properties, which are morphologically similar to

• thus a decrease in the mechanical properties of the PLA nanofibers. PLA/PLGA nanofibers may be advantageous for improving cell viability and differentiation thanks to its advanced mechanical properties compared to those of PLA nanofibers. Nevertheless, the mechanical properties of all nanofibers

Engineered titania nanomaterials in advanced clinical applications

• Padmavati Sahare,
• Paulina Govea Alvarez,
• Juan Manual Sanchez Yanez,
• Gabriel Luna-Bárcenas,
• Samik Chakraborty,
• Sujay Paul and
• Miriam Estevez

Beilstein J. Nanotechnol. 2022, 13, 201–218, doi:10.3762/bjnano.13.15

• adhesion and proliferation of hFOB. Their results also showed a noticeable reduction in cell viability with a higher percent of TiO2 (7 wt %). An antibacterial study of these fabricated structures implied that a minimum of 5 wt % concentration of TiO2 is sufficient for achieving the desired antibacterial

• can support and initiate cancer growth, the cytotoxicity of W. somnifera-synthesized TiO2 nps was tested against the human hepatic cancer cell line HepG2 and a concentration-dependent decrease in cell viability of HepG2 cells was discovered [93]. Thabet et al. also showed the antifungal efficiency of

• (Figure 5) by inducing apoptosis in a caspase-dependent manner. Cytotoxicity tests of TiO2 nps showed 95% cell viability, ensuring its broad application in biomedicine for cancer therapeutics. Moreover, TiO2 nps increases the DOX accumulation in tumor cells while limiting the harmful side effects caused

Theranostic potential of self-luminescent branched polyethyleneimine-coated superparamagnetic iron oxide nanoparticles

• Rouhollah Khodadust,
• Ozlem Unal and
• Havva Yagci Acar

Beilstein J. Nanotechnol. 2022, 13, 82–95, doi:10.3762/bjnano.13.6

• factor receptor (EGFR). Pro-apoptotic polyinosinic–polycytidylic acid sodium (PIC) was delivered to HeLa cells with SPION@bPEI and caused a dramatic reduction in the cell viability at otherwise non-toxic nanoparticle concentrations, proving that bPEI coating is still an effective component for the

• mean. The statistical analysis was conducted using ANOVA and two-sample unequal variances were used to calculate the p-values between groups. All cell viability percentages were presented as percentages of the control viability. Fluorescence imaging To investigate the in vitro optical imaging potential

• delivery of PIC into the cells at an N/P ratio of 30. The cell viability decreased by 20–40–70% with 0.9, 1.8 and 2.7 µg of PIC, respectively, delivered to the cells with an increasing dose of the SPION@bPEI/PIC. Especially at 10 and 20 µg of nanoparticles/mL dose, all the toxicity is originated from the

Biocompatibility and cytotoxicity in vitro of surface-functionalized drug-loaded spinel ferrite nanoparticles

• Sadaf Mushtaq,
• Khuram Shahzad,
• Tariq Saeed,
• Anwar Ul-Hamid,
• Bilal Haider Abbasi,
• Nafees Ahmad,
• Waqas Khalid,
• Muhammad Atif,
• Zulqurnain Ali and
• Rashda Abbasi

Beilstein J. Nanotechnol. 2021, 12, 1339–1364, doi:10.3762/bjnano.12.99

• screening results for HepG2 and HT144 (Figure 4a) cells showed a strong cytotoxic effect (% viability < 50%) upon treatment with drug-loaded NPs compared to nontreated cells (NTC). This cytotoxic effect was prominent when compared to free drug controls, where cell viability was up to 70–80%, indicating

• of cell viability were plotted for all doses (Figure 4b) and IC50 values were determined (Table 8). In both cell lines, drug-functionalized NPs caused almost 45–50% reduction in cellular viability at a concentration of 1 µg/mL, and the cellular viability decreased even further at higher doses. In

Self-assembly of amino acids toward functional biomaterials

• Huan Ren,
• Lifang Wu,
• Lina Tan,
• Yanni Bao,
• Yuchen Ma,
• Yong Jin and
• Qianli Zou

Beilstein J. Nanotechnol. 2021, 12, 1140–1150, doi:10.3762/bjnano.12.85

• storage modulus (G') value of about 2000 Pa, and can be used for imaging three-dimensional cytoskeletal materials. After human mesenchymal stem cells (hMSCs) were cultured for 72 h in the 3D fiber hydrogel, the cell viability in the 3D gel was subsequently verified. Only a few dead cells were observed

Use of nanosystems to improve the anticancer effects of curcumin

• Andrea M. Araya-Sibaja,
• Norma J. Salazar-López,
• Krissia Wilhelm Romero,
• José R. Vega-Baudrit,
• J. Abraham Domínguez-Avila,
• Carlos A. Velázquez Contreras,
• Ramón E. Robles-Zepeda,
• Mirtha Navarro-Hoyos and
• Gustavo A. González-Aguilar

Beilstein J. Nanotechnol. 2021, 12, 1047–1062, doi:10.3762/bjnano.12.78

• anticancer photodynamic therapy [140][141], in which this combined approach induces mitochondria-dependent apoptosis (70% of cell viability inhibition) in a human head and neck cancer cell line (AMC-HN3), as compared to individually using F-CUR (10% inhibition) or phototherapy (50% inhibition). The apoptosis

• greater potential to produce ROS [143]. A similar behavior was observed in cervical carcinoma cell lines treated with nanoemulsion-photostimulated CUR, where cell viability was reduced to <5% and an increase in caspase-3 and caspase-7 activity was apparent [144]. Inostroza et al. [112] reported the

The role of deep eutectic solvents and carrageenan in synthesizing biocompatible anisotropic metal nanoparticles

• Nabojit Das,
• Akash Kumar and
• Raja Gopal Rayavarapu

Beilstein J. Nanotechnol. 2021, 12, 924–938, doi:10.3762/bjnano.12.69

• -directing surfactant [60]. They carried out an in vitro cytotoxicity study exposing Hep-G2 and A549 cells to CTAB- and C12EDMAB-capped gold nanorods. The researchers observed a considerable difference in cell viability at the same concentration levels. Much earlier, a chemical method introduced by Chenxu Yu

Comprehensive review on ultrasound-responsive theranostic nanomaterials: mechanisms, structures and medical applications

• Sepand Tehrani Fateh,
• Lida Moradi,
• Elmira Kohan,
• Michael R. Hamblin and
• Amin Shiralizadeh Dezfuli

Beilstein J. Nanotechnol. 2021, 12, 808–862, doi:10.3762/bjnano.12.64

• inertial cavitation, occurring near or within the droplet, cause the dispersed medium to vaporize [135][136]. It has been shown that ADV can decrease cell viability through the disruption of cell membranes [114]. Some researchers have suggested that ADV can cause cell death while increasing the penetration

Silver nanoparticles induce the cardiomyogenic differentiation of bone marrow derived mesenchymal stem cells via telomere length extension

• Khosro Adibkia,
• Ali Ehsani,
• Asma Jodaei,
• Ezzatollah Fathi,
• Raheleh Farahzadi and
• Mohammad Barzegar-Jalali

Beilstein J. Nanotechnol. 2021, 12, 786–797, doi:10.3762/bjnano.12.62

• that Ag-NPs induced mESCs cell cycle arrest at the G1 and S phases through inhibition of the hyperphosphorylation of Retinoblastoma protein [12]. Kalishwaralal et al. reported that Ag-NPs could inhibit cell proliferation, cell viability, and cell migration through activating caspase-3 and suppressing

• ) formation as cardiac and liver markers [31]. In the present study, the in vitro effect of Ag-NPs was investigated on cardiac differentiation potency as well as TL of MSCs. The suitable concentration of Ag-NPs which prolong the cell viability of MSCs was determined by MTT assay as previously examined by

A review on nanostructured silver as a basic ingredient in medicine: physicochemical parameters and characterization

• Gabriel M. Misirli,
• Kishore Sridharan and
• Shirley M. P. Abrantes

Beilstein J. Nanotechnol. 2021, 12, 440–461, doi:10.3762/bjnano.12.36

• concentrations of Ag+ for 24 h indicate that a concentration of 2.5 ppm decreased cell viability by 60% whereas 5.0 ppm decreased cell viability by 100% in comparison to the control case. On the other hand, 30 ppm of AgNPs prepared immediately before the biological tests, in a system without oxygen and with a

• carrier gas to expel all dissolved oxygen (to prevent oxidation and release of silver ions) reported no reduction in cell viability compared to control [127]. Treatment of burns in rats with AgNPs were carried out both in vitro and in vivo. No significant differences in the levels of urea, creatinine, and

Doxorubicin-loaded gold nanorods: a multifunctional chemo-photothermal nanoplatform for cancer management

• Uzma Azeem Awan,
• Abida Raza,
• Shaukat Ali,
• Rida Fatima Saeed and
• Nosheen Akhtar

Beilstein J. Nanotechnol. 2021, 12, 295–303, doi:10.3762/bjnano.12.24

• cytotoxicity against HepG2 (carcinogenic) and 3T3 (non-carcinogenic) cells was evaluated. Cells were treated for 12 h with PSS-GNRs and analyzed using the MTT assay. As shown in Figure 4, cells treated with PSS-GNRs had no significant reduction in cell viability compared to control cells. The viability

• conjugated one. The cytotoxic efficiency of the DOX-loaded PAA-PEG-GNRs was found to be similar to free DOX and improved with an increase in their concentrations [36]. In a previous study, cell viability was significantly decreased down to 57% using GNR-DOX-cRGD, whereas free DOX demonstrated the highest

Characterization, bio-uptake and toxicity of polymer-coated silver nanoparticles and their interaction with human peripheral blood mononuclear cells

• Sahar Pourhoseini,
• Reilly T. Enos,
• Angela E. Murphy,
• Bo Cai and
• Jamie R. Lead

Beilstein J. Nanotechnol. 2021, 12, 282–294, doi:10.3762/bjnano.12.23

• well characterized, including their transformations during exposure. Additionally, we have assessed bio-uptake quantification, using mass spectrometry, and toxicity/cell viability after exposing human PBMCs to AgNPs at clinically relevant concentrations. We also compared the toxicity of AgNPs with

• . However, for the AgNO3 treatment, this ratio increased in a dose-dependent manner (Table 2). Impact of PVP-AgNPs and Ag ions on viability and metabolic activity of PBMCs Cell membrane integrity as a marker for cell viability was measured by LDH release; a greater LDH release is an indication of more

• control group. Results for cell viability and metabolic activity of PBMCs for each person are presented in Supporting Information File 1, Figure S4 and Figure S5, respectively. The Pearson correlation coefficient was calculated to assess the relationship between uptake and cytotoxicity (LDH assay) of PVP

Differences in surface chemistry of iron oxide nanoparticles result in different routes of internalization

• Barbora Svitkova,
• Vlasta Zavisova,
• Veronika Nemethova,
• Martina Koneracka,
• Miroslava Kretova,
• Filip Razga,
• Monika Ursinyova and
• Alena Gabelova

Beilstein J. Nanotechnol. 2021, 12, 270–281, doi:10.3762/bjnano.12.22

• experiments with the positive controls confirmed the ability of endocytic inhibitors to block the specific route of endocytosis. None of the endocytic inhibitors affected cell viability and proliferation activity with the exception of nocodazole (Noc) (Supporting Information File 1, Figure S2). Short-term

• based on the cell viability determined by MTT assay (Supporting Information File 1, Figure S5 and Figure S6). All inhibitors were purchased from Sigma-Aldrich (Slovakia). The cells exposed to culture medium were used as negative control and cells exposed only to MNPs for 1 h were considered as a

The nanomorphology of cell surfaces of adhered osteoblasts

• Christian Voelkner,
• Mirco Wendt,
• Regina Lange,
• Max Ulbrich,
• Martina Gruening,
• Susanne Staehlke,
• Barbara Nebe,
• Ingo Barke and
• Sylvia Speller

Beilstein J. Nanotechnol. 2021, 12, 242–256, doi:10.3762/bjnano.12.20

• coatings of positively charged plasma-polymerized allylamine (PPAAm) or negatively charged Au were used, see below. Viability tests (MTS) were performed on glass, sputter-deposited Au, polydimethylsiloxane (PDMS), and PPAAm coating with native titanium and cell culture plastic as reference. Cell viability

Effect of different silica coatings on the toxicity of upconversion nanoparticles on RAW 264.7 macrophage cells

• Cynthia Kembuan,
• Helena Oliveira and
• Christina Graf

Beilstein J. Nanotechnol. 2021, 12, 35–48, doi:10.3762/bjnano.12.3

• concentration (c = 200 µg/mL), the cell viability after exposure to UC@thin_NH2 was approx. 51 ± 5%, whereas in the UC@thick_NH2 sample, the cell viability was 75 ± 6%. At the lowest concentration (c = 12.5 µg/mL) the cell viability was 110 ± 12% for UC@thin_NH2 and 95 ± 14% for UC@thick_NH2. UC@thin_RBITC_NH2

• highest concentration values (c = 150 and 200 µg/mL) of UC@thick_NH2, no significant difference in the cell viability was observed between the two values. The cytotoxicity of pure silica without a UCNP core (sample SiO2@RBITC_NH2) was also measured. The cell viability at the lowest concentration was 83

• present study. The sample UC@thin_NH2 has a larger hydrodynamic diameter than the sample UC@thick_NH2 in DMEM and the situation is reversed for sample UC@thin_RBITC_NH2 and sample UC@thick_RBITC_NH2. However, in both cases the cell viability increases with shell thickness. Since the light scattering is

PEG/PEI-functionalized single-walled carbon nanotubes as delivery carriers for doxorubicin: synthesis, characterization, and in vitro evaluation

• Shuoye Yang,
• Zhenwei Wang,
• Yahong Ping,
• Yuying Miao,
• Yongmei Xiao,
• Lingbo Qu,
• Lu Zhang,
• Yuansen Hu and
• Jinshui Wang

Beilstein J. Nanotechnol. 2020, 11, 1728–1741, doi:10.3762/bjnano.11.155

• , the same volume of fresh PBS was supplied in the release medium. The concentration of released DOX in all samples was determined by measuring the UV absorbance. The cumulative release rate of DOX was calculated and the measurements were repeated for three times, averaging the results. Cell viability

• dissolve the formazan crystals. The absorbance of the final solution was measured at a wavelength of 570 nm using a microplate spectrophotometer (SpectraMax iD5) to calculate the cell viability. Groups without treatment were used as control. Cellular uptake of DOX-loaded nanocarriers The drug delivery in

• tissues. The DOX molecules are retained in the carriers and subsequently rapidly released from nanotubes at the targeted tumor sites with a slightly acidic environment [42]. Cell viability Cytotoxicity assessment results of different blank carriers and DOX-loaded nanocarrier formulations are shown in

Cardiomyocyte uptake mechanism of a hydroxyapatite nanoparticle mediated gene delivery system

• Hiroaki Komuro,
• Masahiro Yamazoe,
• Kosuke Nozaki,
• Akiko Nagai and
• Tetsuo Sasano

Beilstein J. Nanotechnol. 2020, 11, 1685–1692, doi:10.3762/bjnano.11.150

• (PBS) to remove detached dead cells and the formazan crystals were solubilized in DMSO. The absorbance was measured using a microplate reader at 570 nm. The relative cell viability (%) compared to non-treated cells was calculated by [abs] sample/[abs] control × 100. Transfection efficiency assay HL-1

• approximately 1.3 wt % [24]. Cytotoxicity assay Dose-dependent cytotoxicity of HAp/pDNA complexes on HL-1 cells was investigated in the concentration range of 0.1–10 µg/mL. The 3-(4,5-dimethylhiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay was used to assess cytotoxicity. No differences in cell

• viability were observed among the three concentrations of HAp/pDNA complexes used at 24 and 72 h (Figure 2). The results suggested that HAp exhibits little cytotoxicity within the concentration range used in this study. Transfection efficiency To test the gene transfection potential of the HAp nanoparticle