Establish the properties of drug delivery complexes with certainty and detail
Have complete confidence that you know and understand the properties of the particle systems being used in complex drug products. TRPS is the only method that provides an adequate framework of certainty, resolution and accuracy for the measurement of the key particle parameters for nanomedicine. These include the real size distribution, particle concentration, particle charge and charge distribution. Traditionally the nanomedicine field has relied on DLS measurement, sometimes backed up by TEM. DLS is now an inappropriate and obsolete technology for complex nanomedicine products. TRPS on the other hand offers users the certainty they need, and sufficient detail to be able to measure and analyse subtle changes in the particle complexes and their effects on performance.
Measure true number-based size distribution
TRPS measures and automatically calibrates the real size and size distribution of nanoparticles, with the size being the actual size of the particle not the hydrodynamic diameter, which varies with electrolyte concentration. TRPS adds an additional layer of certainty by providing the concentration of particles in each size band. A 2-D histogram of concentration vs size is the correct way to describe nanomedicine particles. A vague wavy line on a log scale is not. Particle number and size are both required to design and predict the particle interactions and drug loading and dosage. Nanomedicine therapy utilises particles to carry the drugs to their location. Therefore the practitioner needs to be able to account for all the particles and the drugs carried, which requires particle number and size to be known at different stages of the process and particularly at the point of delivery. Particle number and the real size distribution are essential components of physico-chemical equivalence. Particle number and size are also required when assessing particle aggregation because the number of particles will reduce and the size of each aggregate will correspondingly increase. Size and particle number really matter in your nanomedicine work so measure them properly with TRPS.
Present credible data, respected by the FDA
While there are various regulations around the use of nanomaterials, regulators are primarily concerned with certainty and predictability of the complex drug products that they need to assess and manage. Due to the ineffectiveness of traditional nanoparticle measurement technologies, DLS in particular, current nanomedicine regulation is mainly based on highly prescriptive production methods and documentation. The theory behind this is presumably that if the same procedures are followed then the end product should be the same. Apart from the theory itself being dubious, it is a very cumbersome and expensive way to manage the projected uptake of nanomedicines in clinical use. The industry is well behind in the use of best practice measurement systems. Adopting modern methods such as TRPS would result in increased confidence in the products, reduced development costs and reduced time to market. Physico-chemical equivalence and biological effect are the two primary considerations. Is the product what it’s meant to be? Does it have the effect it’s meant to have? Certain, accurate and detailed particle measurement can resolve these issues. At present that is only achievable with TRPS.
Count individual particles reliably
Concentration, the number of particles/ml, is fundamentally important in nanomedicine and the validation of complex drug products. Accurate concentration measurements are crucial in understanding dosage, drug loading and in-vivo particle interactions. Particle concentration is also necessary to properly understand such things as aggregation, the bio-interactions of nanoparticles, the effects of filtering on a sample, freeze-thaw changes etc. In a heterogeneous mixture, the full range of particles may not be measured. It is therefore necessary to specify the size range to which the measured concentration applies. That also applies to average particle size actually. TRPS is the only technology that measures the concentration of particles in fluids in a specified particle size range. The data should really be displayed on a concentration vs size plot, which is the default setting in TRPS systems.
TRPS displays the concentration data on a linear scale. Other technologies, such as NTA, only offer log scale display and log scale accuracy, which is insufficient for biomedical use. During the various production and usage stages, by using concentration and known volumes, a proper account of particle number can be maintained, which is an important aid in product development. Again, log scale accuracy is insufficient for that purpose.
Measure the zeta-potential of each particle
In nanomedicine a major requirement is the accurate determination of key physicochemical particle properties such as number, size and surface charge, because these properties influence the outcome of nano-bio interactions. It has been shown that the in vivo fate of a nanoparticle relies on its surface charge. The unique capability of TRPS to simultaneously measure particle size and zeta potential (as a measure of surface charge) reproducibly on a particle-by-particle basis with high accuracy represents a very effective approach for investigating and understanding nano-bio interactions. The single-particle nature of TRPS charge measurement enables the discrimination of subpopulations within a sample and the accurate determination of the zeta potential distribution of complex samples. Figure 1 shows an example of TRPS measurements of mixed PC and PG phospholipid liposomes. The data shows that the different lipids form different particles, which can only be proven through single particle charge measurement.
Study particle interaction dynamically
TRPS can use accurate size, number and single particle charge measurement to monitor and analyse biochemical reactions involving nanoparticles. The binding of charged ligands onto the surface of a particle will typically alter its net charge. Such reactions occur in a time dependent manner according to the affinity constant of the binding reaction and the concentration of the ligand. TRPS can provide users the opportunity to perform in real-time, particle ligand or particle-particle interactions. As charged ligands accumulate on the surface of particles, the net charge (zeta potential) of the particles will change in a time dependent manner, which can be measured and analysed.
Experimentally, such interactions can be demonstrated using biotinylated-single stranded DNA reacting with particles that have streptavidin molecules on the surface. As the highly charged DNA molecules accumulate on the particles, the net negative charge increases. The figure (left) demonstrates such a reaction occurring in real time in the fluid cell of the qNano. The fluid cell contains streptavidin coated particles. After 30 seconds the recording is paused, biotinylated DNA (1pmol in this case) is added to the fluid cell and recording recommenced. The DNA binding to the particles causes a rapid increase in particle velocity through the pore because the particles are increasing in negative charge and electrophoretic mobility (upper graph red trace, showing the reduction in duration, which is the inverse of the velocity). A control trace showing particles without DNA demonstrate a constant mean FWHM (blue trace). As DNA accumulates on the surface of the particles, the frequency of translocation events also increases because of the increased electrophoretic mobility (red trace lower graph).
Such experimentation is applicable where any binding reaction involves differentially charged components, for example ligands such as DNA or RNA based aptamers reacting with vesicles with a particular surface marker or similarly using antibodies combined with a charged reporter molecule.
- Larger or more? Nanoparticle characterisation methods for recognition of dimers
- A comparative study of submicron particle sizing platforms: Accuracy, precision and resolution analysis of polydisperse particle size distributions
- Pitfalls and Novel Applications of Particle Sizing by Dynamic Light Scattering
- Characterization of a Nanoparticulate Drug Delivery System Using Scanning Ion Occlusion Sensing
- Multimodal Dispersion of Nanoparticles: A Comprehensive Evaluation of Size Distribution with 9 Size Measurement Methods