Sunscreen nanoparticles

One of the most frequent questions we get at SOLVE is if we can characterize and quantitate nanoparticles in food and cosmetic products. ”Of course we can” said our scientists, ”let’s show them!”

Many consumer products contain nanoparticles – diameter 1-100 nanometers (one nanometer is 0.000001 millimeter). The most known product is probably sunsceen, where nanoparticles (typically titanium dioxide, TiO2, or zinc oxide, ZnO) are added to reflect UV radiation but without giving the ghostly look.

Several manufacturers argue that the added nanoparticles clump together in the sunscreen formula (forming aggregates) resulting in that no or few individual nanoparticles are present in the products.

sunscreen

Let's perform a study using the AF4 technique

We analyzed an ordinary kid’s sunscreen spray from a local pharmacy (with ”Titanium Dioxide (nano)” in the ingredients list) in order to show that we easily can detect and characterize potential nanoparticles using AF4.

Our scientists extracted the TiO2 particles in order not to influence or modify them and then injected them into the AF4 instrument. With AF4 connected online to detectors (such as MALS, dRI) it is possible to quantify and determine particle size (and size distribution) without the use of calibration standards.

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The analyzed sunscreen contains nanoparticles, with diameters ranging from approx. 30 to 250 nm.

Verify that it really is TiO2

We collected fractions from the peak in AF4 (left figure, 2.5-7.5 min and 7.5-12-5 min) and determined the content of Ti by ICP-MS. We could verify that the particles are titanium dioxide and that the concentration was higher in the second part of the peak.

Helping nano-entities discover their nano-identity

Having a polydisperse nanomaterial? Nanoparticles are often characterized by techniques such as dynamic light scattering (DLS) and/or imaging methods such as transmission electron microscopy (TEM) and scanning electron microscope (SEM).

The suitability of these methods to measure polydisperse samples is sometimes questioned because they have considerable draw backs such as extreme bias towards small numbers of larger particles (DLS) or deriving measurements from a small number of particles (TEM). However, asymmetric flow field flow fractionation (AF4) is a suitable technique to measure complex sample (samples containing one or more type of analyte), and being a separation technique it gives the opportunity to collect different sub-fractions from the sample for further analysis. AF4 is quickly being recognized as the technique of choice for detailed particle analysis among those working in the nano area.

At SOLVE we have many years of experience characterizing nanoparticles such as gold and silver nanoparticles, silica and amorphous silica, core-shell nanoparticles, coated nanoparticles, iron oxide nanoparticles, non-spherical nanoparticles and environmental colloids. Here is an example of a multicore magnetic nanoparticle with a relatively broad size distribution characterized with DLS and AF4.

The size distribution by intensity obtained from DLS (Fig. 1) overestimated the size distribution towards larger sizes when compared to measurements done in AF4 (Fig. 3). When using AF4, three populations were visible in the elution profile (Fig 2), suggesting a core particles without coating (I) coated nanoparticles (II) and particle aggregates (III), while DLS showed only one population. Additionally, the conformation parameter (rrms/rh) was determined from AF4 to be about 0.75, suggesting spherical dense particles.

Figure 1. DLS: Hydrodynamic diameter of multicore magnetic nanoparticle by intensity.

Figure 1. DLS: Hydrodynamic diameter of multicore magnetic nanoparticle by intensity.

Figure 2. AF4: Elution profile of multicore magnetic nanoparticle showing differential refractive index signal (blue), light scattering signal (red), and hydrodynamic diameter (green).

Figure 2. AF4: Elution profile of multicore magnetic nanoparticle showing differential refractive index signal (blue), light scattering signal (red), and hydrodynamic diameter (green).

Figure 3. AF4: Hydrodynamic diameter of multicore magnetic nanoparticle obtained from elution time

Figure 3. AF4: Hydrodynamic diameter of multicore magnetic nanoparticle obtained from elution time

A spoon full of levan…

At SOLVE we have developed a robust, reliable, fast and green method (no harmful chemicals or by products are generated) to accurately characterize levan with respect to molar mass and size distributions using asymmetric flow field-flow fraction coupled with online multiangle light scattering and differential refractive index (AF4-MALS/dRI) detection.

Successful characterization of raw levans with molar masses up to 1010 g/mol and radii up to 400 nm has been achieved. The AF4-MALS/dRI method allows detailed assessment of the raw levan and monitoring of production scale processing to yield a final levan polysaccharide with the desired molar mass and size range. Furthermore, the AF4-MALS/dRI method has been central in laboratory research aimed at identifying optimum processing conditions, assessing long term solution and dry storage stability, and monitoring low levels of macromolecular contaminates in the levan.

Levan is non-toxic, odorless, and tasteless polysaccharide with potential uses in pharmaceutical, medical, cosmetic, food, and textile applications. Fructose is the repeating base unit from which levan is made, and levan can be sourced from either bacteria production or isolated from plants.

The use/performance of levan in specific applications is dependent, in part, on it physicochemical properties such as molar mass, size and branching density. These properties must fall within predetermined tolerances to yield material with similar batch-to-batch performance characteristics. It is critical to be able to fully characterize levan as a raw material and then track changes in physicochemical properties during levan processing to ensure batch-to-batch reproducibility. However, levan is a polydisperse material with respect to molar mass (104–1010 g/mol), size (~20 nm to several hundred nm) and branching (2 – 12 %). Additionally, batch-to-batch and supplier-to-supplier variations of physicochemical properties are observed in raw levans and may be independent of the conditions used to produce the polysaccharide (i.e., type of bacteria and any post collection processing). This places an incredibly high demand on the analytical methods used to characterize the physicochemical properties of levan.

At SOLVE we are experts in the characterization of levan and other polysaccharides. Contact us with any questions you have and we can help you solve them.