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Nanoparticles

Nanoparticles are ultrafine units used in many different fields, from the biomedical sector and pharmaceutics to energy storage technologies. Due to their size, they are difficult to track and measure, but it’s essential to know their properties so they can be designed to fulfill their purpose.

Different measurement technologies can be used to produce and characterize nanoparticles, such as microwave synthesis, atomic force microscopy, dynamic light scattering, SAXS, x-ray diffraction, laser diffraction, and many more.

On this page, you will find specific research topics, for example, the generation of hexagonal flower-like wurtzite-type zinc oxide structures for energy storage purposes with microwave synthesis, and the drug delivery capability of nanoparticle systems and RNA nanoparticles for gene silencing, analyzed and investigated with dynamic light scattering (DLS) and electrophoretic light scattering (ELS).

You will also find a study of the investigation of synthesis parameters on the growth of semiconducting nanoparticles with X-ray diffraction aluminum particles for nanolithography conducted with an AFM, and the results of an investigation on ferric nanoparticle complexes for intravenous application via SAXS, DLS, and ELS. Anton Paar’s highly precise instruments for your research on nanoparticles have been used for decades at top universities and research facilities worldwide. 

Synthesis of nanomaterials with biological activities

Introduction

Gold nanoparticles are of considerable interest due to their widespread potential for biomedical applications, especially cancer treatment. On the one hand, functionalization of the nanoparticle surface allows for tuning pharmacological properties of the resulting nanomaterials. On the other hand, the naturally occurring sulfated polysaccharide fucoidan also reveals antitumoral and other biological properties. Microwave heating provides an ultrafast 2-step method to combine both components to generate a potentially highly effective compound for cancer therapy.

Experimental

In a 30 mL vial, a certain amount of macroalgae Fucus vesiculosus was suspended in water (1:25 w/v) and extracted under microwave heating at 170 °C for 1 min.  After cooling, the mixture was centrifuged and the aqueous phase was mixed with CaCl2 and left overnight. The solid was filtered off and the filtrate was diluted with EtOH and kept in a refrigerator for 8 h. The precipitate formed was centrifuged and dried.

In a G10 vial, the freshly prepared fucoidan extract was dissolved in water. Gold (III) chloride trihydrate was added and the vial was subjected to microwave irradiation.

After cooling, the precipitate formed was centrifuged, repeatedly washed with water and sonicated. The colloidal nanoparticles were stored at 4 °C until further use.

Results and discussion

Different concentrations of the extract were used to evaluate the colloidal stability of the resulting nanoparticles. The fucoidan acts as both reducing and capping agent in the formation of the gold nanoparticles. The fucoidan yield of the microwave extraction is in accordance with literature data, but was achieved in a much shorter time than with conventional systems. Also, the subsequent generation of functionalized nanoparticles was much quicker under microwave irradiation compared to conventional heating. Scanning transmission electron microscopy revealed an average particle size of 10 nm, which is an ideal size for biomedical evaluations. These particles were thus evaluated for antitumoral activity in cancer therapy.

Fig 1. Schematic pathway of synthesis and application of fucoidan-functionalized gold nanoparticles

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Source:

R. J. B. Pinto et al., Materials 2020, 13, 1076

Application Database Entry:

Synthesis of fluorine containing polyionic nanoparticles for battery research

Introduction

There has been a lot of research in recent years with fluorine containing polyanionic compounds as potential electrode material in rechargeable batteries. By varying the constituting compounds, the electrochemical properties of the material can be tuned.  Microwave heating should facilitate the rather tricky reaction conditions, and at some point, this involves critical-to-handle hydrofluoric acid or fluoride-generating compounds, and typically requires extremely high temperatures far beyond 300 °C. Slight adaptations of the common procedure lead to an efficient method to generate various polyanionic systems.

Experimental

Iron nitrate nonahydrate was dehydrated for 2 h under vacuum and then dissolved in a glove box in 30 mL benzyl alcohol overnight. Lithium methoxide and crystalline phosphoric acid were dissolved in the mixture, then 0.9 mL of a 20 M solution of HF in MeOH were carefully added. After stirring for 1 h an aliquot (max. 6 mL) was filled in a 10 mL silicon carbide vessel. The vessel was sealed and subjected to microwave irradiation. The target temperature was achieved within a 4 min ramp.

After cooling, the precipitate was centrifuged and redispersed in ethanol and water several times. Finally, the powder obtained was dried at 65 °C overnight.

Results and discussion

Cobalt chloride or vanadium chloride can be used as metal precursors as well, under otherwise identical sol-gel conditions, to generate corresponding tavorite-type lithium-cobalt and lithium-vanadium phosphate fluorides. Using the unique silicon carbide (SiC) vessel for the Monowave reactors was essential, as standard glass vials could be attacked and damaged by the hydrofluoric acid under these elevated temperature conditions. The nanoparticles were structurally characterized by X-ray diffraction, transmission electron microscopy and FTIR spectroscopy. The microwave-generated crystals showed much better uniformity than conventionally prepared species. The resulting nanomaterials were used to generate battery electrodes with carbon black and were tested for their electrochemical activity.

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Source:

N. Goubard-Bretesché et al., Chem. Eur. J. 2019, 25, 6189–6195

N. Goubard-Bretesché et al., Mater. Chem. Front. 2019, 3, 2164–2174

Application Database Entry:

Particle characterization of drug delivery nanoparticle systems: Liposomes and micelles

Introduction

Small unilamellar liposomes/vesicles (SUVs) are spherical structures <100 nm bound by a single lipid bilayer, which are used as carriers for targeted drug delivery, and also constitute new frontiers in vaccine formulation. SUV preparation by detergent-removal method consists in generating a mixture of amphiphilic lipids and a detergent, then removing the latter by dialysis. By monitoring both the size and the zeta potential of particles using a Litesizer 500, we determined the optimal ratio between phospholipids and either taurocholic acid (TA) or sodium cholate (SC) detergents for SUV generation. Furthermore, the dynamics of SUV formation during the detergent-removal process could be investigated by performing measurements before and after different dialysis steps.

Experimental

Sample preparation: The SUVs were prepared using phosphatidylcholine and two different anionic detergents: sodium cholate hydrate (SC) and taurocholic acid sodium salt (TA). A lipid concentration of 10 mg/ml was used, and different lipid/detergent molar ratios were tested: 1:0.5; 1:1; 1:2. The dialysis was carried out by means of a cellulose membrane tubing system with a 14 kDa molecular weight cut-off. A Tris buffer with a concentration of 50 mM and a pH of 7.25 was used to perform the dialysis. Buffer changes were performed every 2 h for 2 cycles, then every 10 h for a further 2 cycles (total dialysis duration: 24 h).

Characterization technique: The particle size analysis and zeta potential analysis was conducted on a Litesizer 500.

Results and discussion

The 1:2 ratio returned the smallest SUV size for both detergents, with mean values of 47 nm (for TA) and 56 nm (for SC). For the 1:2 lipid/sodium cholate mixture, mixed micelles were detected before dialysis as a small peak at about 6 nm (Figure 1, a). After dialysis, the monodisperse distribution showed a single peak around 60 nm, confirming the formation of SUVs (Figure 1, b).

The change in particle size and zeta potential during the dialysis process for the mixture lipid/sodium cholate at molar ratio 1:2 were analyzed after 4 h and 24 h of dialysis. The particle size showed a significant decrease already after the second buffer change and no remarkable difference was noted after 24 h of dialysis. On the contrary, the zeta potential increased continuously after dialysis.

Figure 1: Particle size distribution by intensity before dialysis (a) and after dialysis for molar ratio 1:2 between lipid/sodium cholate

Figure 2: Particle size and zeta potential before dialysis, after 4h and 24h of dialysis

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Characterization of ferric nanoparticle complexes for intravenous application

Introduction

Ferric nanoparticles, stabilized in iron-oligosaccharide complexes, are commonly used for intravenous iron therapy. The application of such complexes ensures a controlled release of iron in the bloodstream. Infusions comprising iron complexes with high-molecular-weight ligands have often been associated with complications, which can be overcome by using low-molecular-weight preparations such as iron sucrose. Pharmaceutical products strictly require a full and thorough characterization of the formulation: for nanostructured materials, dedicated analytical methods such as small-angle X-ray scattering (SAXS) combined with dynamic and electrophoretic light (DLS, ELS) provide comprehensive structural information on the nanoscale.

Experimental

Two different iron preparations, ferric carboxymaltose and iron sucrose, were investigated. Both the particle size and zeta potential were measured with a Litesizer 500 instrument. DLS provided the particle size in terms of the hydrodynamic radius, whereas the zeta potential – calculated by using the Hueckel approximation – characterized the stability of the colloidal dispersions. SAXS measurements were performed on the SAXSpoint instrument equipped with a Primux 100 micro X-ray source. To obtain the particle shape as well as information on the internal structure, the measured scattering data were processed with the Indirect Fourier Transformation (IFT) approach.

Results and discussion

DLS results prove that both iron preparations exhibited a narrow size distribution with an average hydrodynamic particle diameter of around 12 nm (Fe sucrose) and 24 nm (Fe carboxymaltose), respectively. SAXS revealed that the Fe sucrose particles had a close-to-spherical shape. In contrast, the Fe carboxymaltose particles had a cylindrical, rod-like shape. Zeta potential results indicate a different stability of the preparations: Fe sucrose had a high absolute value of 29.5 mV, suggesting an excellent colloidal stability. In contrast, the low value for Fe carboxymaltose (6.8 mV) suggests that the preparation could aggregate and sediment, which would shorten shelf life. The present work shows that by applying the three complementary techniques, SAXS, DLS and ELS, a comprehensive structural characterization of the iron-carbohydrate preparations can be achieved.

Figure 1. DLS results. Particle size distribution of Fe carboxymaltose (left) and Fe sucrose (right).

Figure 2. SAXS results: p(r) functions (i.e. pair-distance distribution functions) of Fe carboxymaltose (left, spherical shape) and Fe sucrose (right, cylindrical shape)

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Determination of particle size and zeta potential of RNA nanoparticles for gene silencing

Introduction

Single-stranded micro-RNAs (miRNA) are short RNA sequences able to promote gene silencing by inhibiting the translation of the target gene’s messenger RNA. This is why they are currently used in vaccine formulation. However, in this example we focused on the micro-RNA miR-27a and its capacity to suppress the expression of the adipogenic marker PPARg (Peroxisome proliferator- activated receptor gamma), thereby blocking adipocyte differentiation. For this reason, miR-27a-protamine nanoparticles may represent a new therapeutic approach to prevent metabolic complications associated with diabetes and obesity. Since nanoparticle properties such as size and zeta potential may influence particle uptake by target cells and/or tissues in vivo, light scattering technologies represent an important tool to investigate the physicochemical properties of miRNA-delivery systems.

Experimental

Sample preparation: Salmon protamine (grade IV) and the miRNA mimic mmu-miR-27a-3p (sequence
5'-UUCACAGUGGCUAAGUUCCGC-3') were used for the nanoparticle preparation at room temperature. Nanoparticles formed spontaneously due to electrostatic interactions after thorough mixing of miRNA and protamine. To investigate the influence of varying proportions of miRNA relative to protamine on the particles’ physicochemical properties, nanoparticles with a miRNA:protamine mass ratio ranging from 2:1 down to 1:7 were prepared. A final miRNA concentration of 50 µg/ml was always used for nanoparticle formation.

Characterization technique: The final miRNA protamine nanoparticles were characterized via particle size and zeta potential with the Litesizer 500.

Results and discussion

The change of miRNA:protamine mass ratio had an impact on the particle size and zeta potential (Figure 1). The nanoparticles ranged in size from 100 nm to almost 200 nm, with the largest particles generated by a 1:1 ratio of miRNA to protamine. Zeta potential showed a shift from negative to positive values according to the amount of positively charged protamine or negatively charged nucleic acid. From a miRNA:protamine mass ratio of 1:3 or lower, both particle size and zeta potential seemed to plateau, suggesting that protamine might be present in excess and not integrated in the particles anymore when exceeding 3 times the amount of miRNA.

Figure 1: miRNA-protamine-nanoparticles with 50 µg/ml miRNA concentration characterized by particle size (n=6, bars) as peak intensity or hydrodynamic diameter and by zeta potential (n=3, squares)

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Determination of the particle size of TiO₂ pigment

Introduction

In the cosmetics industry, nano- and microparticles are used to enhance product performance and meet the high expectations of consumers. Particle size affects different properties such as skin feel, texture, color and UV absorbance. Moreover, the European Commission has issued a regulation to guarantee the safety of cosmetic products, making it necessary to characterize raw materials for the cosmetic industry, and final products. Here we demonstrate that PSA is a well-suited tool for characterizing titanium-dioxide pigment in terms of particle size distribution.

Experimental

TiO2 pigment was measured both in the liquid and dry dispersion mode using a PSA 1190 LD. For each sample, a repetition series of three consecutive measurements was performed. The Mie approximation was applied for the calculation by using the value of 2.56 and 0.1 as refractive index and absorption index, respectively. For the liquid measurement, the sample was pre-dispersed in 1 g/L sodium hexametaphospate and the external sonicator was applied for 2 min at 80 % power; the measurement was performed using a fast stirrer (350 rpm) and medium pump (120 rpm) setting. Dry measurements were conducted with 50 % vibrator duty cycle, 50 Hz vibratory frequency and pressure of 250 mBar for 10 sec.

Results and discussion

The primary particles of TiO2 powder were measured using the liquid dispersion; the agglomerate size was determined using the dry dispersion unit. Figure 1 displays the particle size distribution and volume-weighted D-values obtained for both dispersions. The primary particles in the liquid dispersion (Figure 1, red curve) show a narrow and monomodal particle size distribution. The sample measured in dry mode is polydisperse with agglomerates >10 µm (Figure 1, black curve). For both dispersions, the relative standard deviation (RSD %) measured over 3 repetitions was <5 %.

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Nanoparticle concentration determination in solution

Introduction

Different concentrations of nanoparticles are used in several applications, e.g. colloid solutions or pharmaceuticals. The main functions in this field are drug delivery and controlled release systems. Nanoparticles can influence these processes and support a quick release of medicine, but can also lead to harmful consequences if the concentration is too high. The refractive index correlates with the concentration of particles in a solution, and a measurement provides within seconds a reliable result for nanoparticle concentration and can already be used for solution volumes of 10µL.

Experimental

For an established method, e.g. “Human Serum/Plasma Total Solids” or customer function, it is just necessary to apply a drop of 10 µL or more to the measurement surface of the Abbemat refractometer. The chosen method will automatically show the concentration of the substance.

For newly developed products, a serial dilution is used to determine the concentration-to-refractive-index ratio. The correlation function is used afterwards in the customer method and provides fast results for unknown particle concentration.

Results and discussion

The refractive index for concentration measurement of nano-particles is already used in a wide range of applications and can be easily adapted to new formulations. The accuracy is 0.05 g/100 g or 0.00002 nD.

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Application report & research source:

  • Refractometer_Overview_Application_Methods_20-05
  • Refractive Index Measurement of Pharmaceutical Solids: A Review of Measurement Methods and Pharmaceutical Applications DOI: 10.1016/j.xphs.2019.06.029

Investigation of synthesis parameters on growth of semiconducting nanoparticles

Introduction

Zinc sulfide (ZnS) and zinc oxide (ZnO) belong to the group of II-IV semiconductors and have potential applications in fields such as solar cells, infrared windows, lasers, displays and sensors. Various synthesis methods for both materials have been developed, but faster and cheaper procedures are still the subject of ongoing investigations.

Here we use an established synthesis procedure using zinc acetate (Zn(OAc)2) and thioacetamide as precursors for ZnS nanoparticles. These particles can be easily oxidized to ZnO nanoparticles by heating up to 600 °C in air. The formation of ZnS is investigated by in-situ XRD which gives additional information about the influence of temperature, heating rate, and waiting time on the size of the resulting nanoparticles and also on the time needed for complete oxidation to ZnO.

Experimental

XRD investigations were carried out on a laboratory powder X-ray diffractometer equipped with an XRK 900 Rector Chamber from Anton Paar. The diffractograms were recorded using CuKɑ radiation at constant temperature in the range from 25 to 600 °C. The measurement time for each diffractogram was 10 minutes. 

Zn(OAc)2 (purity: 99.99 %) and thioacetamide (purity: 99.0 %) were ground separately for 10 minutes. Afterwards an equimolar mixture was prepared and homogenized by further grinding for 10 minutes. The obtained reaction mixture was filled in a Macor sample holder of XRK 900. The synthesis of the ZnS nanoparticles was performed under a nitrogen atmosphere (1 bar pressure) and the following oxidation to ZnO nanoparticles was performed in air.

Results and discussion

With the XRK 900 Reactor Chamber it is possible to monitor the growth of ZnS nanoparticles in-situ. Precise temperature measurement and control allow the synthesis parameters to be varied, which gives valuable information about the growth process and the resulting size of the nanoparticles. The possibility to work in air with XRK 900 also allows the in-situ investigation of the oxidation of ZnS to ZnO nanoparticles. The reaction time can be optimized, helping to lower the cost of an up-scaled process. 

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