1. Introduction
Dynamic light scattering (DLS) is a widely utilized technique in many scientific and industrial sectors where the distribution of particle size and behavior of particles in solutions is crucial. With the recent appearance of well-known lipid nanoparticle (LNP)-based products, such as the SARS-CoV-2 vaccines from Pfizer, Inc.-BioNTech (BNT162b2), and Moderna, Inc. (mRNA-1273), its application to nanoparticles in medicine is becoming more and more significant
[1][2]. DLS is crucial for the characterization and quality assurance of vaccines and treatments based on nanoparticles. This text describes some fields where DLS has extensive applications. Having the capacity to measure particle size and distribution, besides measuring zeta potential and some other colloidal properties, such as molecular weight, makes DLS a practical device for various applications.
2. Pharmaceutical Industry and Human Health
In the pharmaceutical industry, DLS has applications for formulating the development of new medicaments, nanoparticle aggregation research, and protein characterization
[3][4][5]. For instance, DLS helps evaluate protein stability during the screening and characterization of drug candidates in the development of biopharmaceuticals
[6]. For evaluating blood stability
[7], zeta potential is a crucial metric in describing the electrostatic interaction between red blood cells in dispersed systems; therefore, it is critical to avoid hemagglutination, which is highly important in blood transfusion
[8] and blood storage
[9]. In some cases, there are applications in combination with other techniques, like the use of Raman spectroscopy with DLS in a single platform for the characterization of therapeutic proteins at high concentrations to monitor protein aggregation. Similar studies mention DLS using gold nanoparticles (Au NPs) for biomolecular detection, bioimaging, drug delivery, and photothermal therapy
[10]. For instance, zeta potential can be a practical guide when determining the equilibrium between the drug’s positive and negative charges to ensure adequate uptake and release phenomena
[8][11][12]. DLS is used to evaluate gold nanorods–protein interaction, and its characterization demonstrates that DLS is a valuable tool
[7][13].
Particle size (PS) and particle size distribution (PSD) have wide applications in various fields. Particle size is a crucial characteristic influencing cellular absorption, biodistribution, and drug release profile
[1]. For instance, controlling particle size in lipid nanoparticle (LNP)-based products used in the manufacturing of SARS-CoV-2 vaccines from Pfizer, Inc.-BioNTech (BNT162b2), and Moderna, Inc. (mRNA-1273) is a critical parameter
[1][14]. Hassett et al., in mice experimentation
[15], report that the hydrodynamic diameter of LNPs affects their biodistribution, stability, and circulation rate across the body and their cell absorption. LNPs act as delivery systems for mRNA vaccines, encapsulating and introducing the mRNA antigen into cells. Lipids, the building blocks of these LNPs, self-assemble into nanoscale particles to protect and insulate the delicate mRNA molecules. The consistency and stability of these lipid nanoparticles are crucial to the vaccinations’ effectiveness
[16][17]. Particle and protein aggregation is highly studied in the pharmaceutical sector, and DLS is a practical instrument that helps to control this property.
Another instance of using DLS in the pharmaceutical industry is in manufacturing magnetic nanoparticles, which have interesting medical applications for developing sensing and diagnostic systems. Lim et al. studied the size distribution and colloidal stability of magnetic nanoparticles (MNPs) using DLS
[18]. The authors mentioned that MNP with Fe
0 and Fe
3O
4 can be an effective nanoagent to remove pollutants from water.
3. Material Science
The application of DLS in the characterization of colloids, nanoparticles, and polymers in material science is extensive. Development and process control in the industries of paints, pigments, food and beverages, cosmetics, ceramics, and personal care products are some fields where DLS has some advantages over destructive tests, such as microscopic imaging, electrical sensing (Coulter) counters, hydrodynamic or field flow fractionation, disc centrifuge particle sizing, size exclusion chromatography, and scattering techniques, among others
[18][19]. Lim et al.
[18], using DLS, studied size distribution and colloidal stability of magnetic nanoparticles (MNPs). The authors contrasted DLS with transmission electron microscopy (TEM) and dark-field microscopy
[18], revealing both the advantages and disadvantages of DLS in measuring the size of MNPs. Specifically, zeta potential has applications in electrophoretic deposition (EPD) in the preparation of advanced materials
[20] and the separation of minerals using water, such as flotation, where the wetting of the mineral surface is affected by the oriented water layers on the solid surface, as well as the electric double layer (EDL) to control the flotation process with the point of zero charge (PZC) as a critical parameter
[8].
4. Environmental Protection, Remediation, and Toxicology
Some applications of DLS in measuring particle size are in environmental protection. Cai H. et al.
[21] applied ultrafiltration, DLS, pyrolysis, thermodesorption, and thermochemolysis coupled to chromatography/mass spectrometry (GC-MS) to separate, preconcentrate, quantify, and identify nanoplastics.
DLS helps characterize anthropogenic or natural organic materials, colloids, and particles on Earth’s surface, including air, water, or soil
[22], and its applications in nanoecotoxicology and environmental sciences. Tareq et al. mention interesting applications where DLS measurements detected nanomaterials’ presence in Tennessee’s river waters
[23]. Even though the particle’s properties, such as size, vary according to the analytical measurement method or equipment used
[24][25], combining and comparing results from other methods and determining the most reliable for your process is recommended.
Mylon et al.
[26] used the technique of DLS to measure the aggregation kinetics of a model virus, bacteriophage MS2, and identified the elements that make viruses unstable in aquatic environments. Mylon et al. describe the significance of biophysical interactions between viruses and their surfaces as a method to develop disinfection or viral eradication techniques. Among other exciting applications of DLS analysis is producing biofuel from algae to optimize the separation of algae mass from water; zeta potential plays an important role where charged algae cells are generated in contact with water
[8]. Our current development and technological progress generate excessive nanoparticle releases into the environment, demanding the close monitoring of air and water pollution. One option is using DLS to detect nanoplastics in various products for human consumption
[27].
Using DLS, Shahid et al. explained how to measure the hydrodynamic radius for extracting heavy metals from an aqueous solution. The authors extracted Co
+2 ions from water using poly (N-isopropylacrylamide-acrylamide-methacrylic acid) p(NAM) as an adsorbent
[28].
Overall, DLS can be utilized to monitor water and air quality by analyzing suspended particles and aggregates in water or air samples
[29]. Moreover, DLS can be employed to study suspended particles in soils or sediments
[30]. It contributes to understanding soil composition, structure, and possible environmental effects by determining particle sizes, their distribution, and their interactions.
5. Food Science
DLS has applications in characterizing food colloids, emulsions, and suspensions. Tosi et al.
[31] used DLS to quantify particle/molecular sizes, particle size distribution, and relaxations in complex fluids for food applications. They exposed the accuracy of this quantification, which is critical in evaluating the toxicity and exposure level of nanoparticles in foods. Evaluating quality, process control measures, and composition is beneficial in producing milk products and their stability. The casein’s particle size in milk affects its flavor. Large particle sizes tend to float up, causing phase separation (creaming). If the particle size is too small, it flocculates. The electrostatic charge that the particles carry is essential for the stability of the milk emulsion. Monitoring the particle size is crucial to ensure milk satisfies consumer demands, legal requirements, and shelf-life regulations
[32].
DLS is widely used for research in food science, and it plays an essential role in the characterization and evaluation of colloids, emulsions, and suspensions. Rao et al.
[33] described DLS as a faster and easier technique with lower limit detection to measure particle size than other techniques. One of the advantages of DLS is that sample preparation is minimal and noninvasive. Also, dynamic measurements in situ show immediate results. However, a disadvantage is that concentration is a limiting factor in this technique since the sample to be analyzed must be highly diluted to avoid multiple scattering.
Palm oil in water microemulsion is used as a delivery system for hydrophobic nutrients. In an accelerated stability study on palm oil in water microemulsion for 28 days, DLS was used to determine the stability of the microemulsion’s membrane. After 28 days, DLS showed a reduction in particle size, which explains that the membrane suffered breakage, creating smaller droplets; therefore, the stability decreased
[34].
DLS has been used in the characterization of nanoencapsulated food ingredients. In a study performed in encapsulated vitamins D3 and β-carotene in tripolyphosphate-chitosomes (TPP-Ch), at three different dilutions (100×, 500× and 1000×), DLS shows that, as dilution increases, aggregates decrease
[31]. Esposto et al.
[35] measured the encapsulation efficiency of α-carotene, β-carotene, and phenolic compounds in liposomes, chitosan (Ch), and TPP-Ch. DLS results showed that β-carotene had the highest encapsulation efficiency.
In summary, DLS is a useful analytical tool to characterize and evaluate food nanosystems. Also, it gives an insight into the product’s physical properties and behavior that ultimately will determine the food’s shelf life.
6. Toners, Inks, and Pigments
Another area where DLS plays an essential role due to controlled particle size and PSD is in the printing industry. Manufacturing toners and inks requires close particle size control to improve stability, printing quality, and shelf life. Inks and pigment dispersions tend to sediment, coalesce, and flocculate due to particle size changes, primarily due to particle agglomeration
[36].
DLS is a widely used technique for characterizing toner particles in the toner industry. A blend of polymer resin, colorants, and magnetic particles make up the small powder known as toner used in photocopiers and laser printers.
DLS can assess the toner particle size distribution and track aggregation and size changes over time. DLS measurements can help improve the formulation and manufacturing processes by giving information about the stability of toner suspensions. The zeta potential of toner particles, a measurement of the electrostatic repulsion between particles in a solution, can also be found via DLS. Their zeta potential can impact particle stability, aggregation, and adhesion.
However, at the same time, there is a need to develop more environmentally friendly pigments. Pandian et al. used DLS in their research to propose nanopigment colorants. These pigments derive from pulp and paper industrial waste black liquor due to their lignin content
[37].
This entry is adapted from the peer-reviewed paper 10.3390/mi15010024