Tunable Resistive Pulse Sensing vs Dynamic Light Scattering
Tunable Resistive Pulse Sensing (TRPS) and Dynamic Light Scattering (DLS) are two particle measurement techniques based on very different principles. Both TRPS and DLS are used to varying degrees to assess the physical parameters and polydispersity of particle populations across many disciplines, including the nanomedicine/pharmaceutical industry (e.g. lipid nanoparticles and liposomes), virology, and the study of exosomes and other extracellular vesicles. Compared to TRPS, DLS is a relatively crude technique when it comes to resolving the size of heterogenous particles. This is problematic for the above applications, where such limitations prevent meaningful comparisons of different samples.
How Does TRPS Measure Nanoparticles?
Tunable Resistive Pulse Sensing (TRPS) monitors current flow through a tunable nanopore. Particles crossing the nanopore cause transient changes in the flow of an ionic current, which can be detected and analysed via the resulting blockades. Each particle size is determined for individual particles; blockade magnitude is proportional to particle size, and particle concentration is calculated from the particle flow rate measured at several different applied pressures. Zeta potential (a measure of the effective surface charge) is derived by measuring electrophoretic mobility, which is calculated based on the speed at which the particle traverses the nanopore.
Learn more about TRPSHow Does DLS Measure Nanoparticles?
Dynamic Light Scattering (DLS) involves applying a laser beam to the sample and monitoring fluctuations in the scattering intensity which results from the Brownian motion of the particles. The magnitude of the scattered intensity is a function of several parameters including particle size; therefore, by applying a scattering autocorrelation function and several assumptions, the average hydrodynamic diameter of particles in the sample can be calculated. Particle concentration cannot be measured using DLS.
Multi-Angle Dynamic Light Scattering (MADLS) is a variation of DLS which combines scattering information from multiple angles to deliver particle size distribution at a higher resolution than single-angle DLS. MADLS size measurements are obtained by analysing multiple scattering autocorrelation functions, usually recorded at three angles. The resulting intensity-weighted particle size distribution is then transformed into particle concentration distribution, using an equation which also takes into account other various factors including: the derived photon count rate from particle scattering, the derived photon count rate from a reference liquid, the instrument’s detection efficiency, and the optical properties of the particles and dispersant.
Why Choose TRPS over DLS?
For those looking to gain real insights into the size and concentration, or size and zeta potential, of particles in their sample, Tunable Resistive Pulse Sensing (TRPS) is a far superior technique. Unlike Dynamic Light Scattering (DLS), which is an ensemble technique that measures the average intensity of light scattered by particles in a solution, TRPS is a single-particle analytical method and uses more direct measurements of physical characteristics. This allows you to detect subtle differences between subpopulations of particles in your sample – differences which may be critical indicators of sample stability, aggregation, or differences in drug loading efficiency. With DLS, these subtle differences can easily be missed.
TRPS enables high-resolution particle measurement (40 nm to > 11 µm), allowing a wide range of particle types to be characterised. Unlike DLS, TRPS measurements are independent of the particle or dispersant’s optical properties, allowing you to confidently measure samples with heterogenous optical densities. With DLS, larger particles tend to be overestimated, distorting the particle distribution and obscuring smaller particles due to the sextic dependence of light-scattering intensity.
The ensemble approach of DLS limits subpopulation identification; a recent study showed Multi-Angle Dynamic Light Scattering (MADLS) failing to identify subpopulations within quadrimodal samples, whereas TRPS could identify all four subpopulations. Finally, whilst TRPS measures actual diameter, DLS can only measure hydrodynamic radius. Whilst this is not inherently inferior in many circumstances, the actual diameter may be favoured by some regulatory bodies in the nanomedicine space.
Enquire about TRPSContrasting TRPS and DLS Abilities in Different Applications
Given its ability to accurately and reproducibly resolve samples to a high level of resolution, Tunable Resistive Pulse Sensing (TRPS) lends itself to a wide range of applications across biological and pharmaceutical research and development. TRPS has filled the unmet need for precise characterisation for a range of particle types. In the context of measuring exosomes and other extracellular vesicles (EVs), TRPS is commonly used to identify differences in EV concentration under different physiological conditions, verify the presence of EVs via measurements of particle size distribution, and identify changes to zeta potential under different conditions (e.g. studies of EV storage conditions). In nanomedicine, TRPS has far-reaching applications, enabling stability and characterisation studies across the development of monoclonal antibodies, lipid nanoparticles, virus-like particle vaccines, and virus preparations. In summary, compared to DLS, TRPS can offer far deeper insights into the properties of your nanoparticles.
Light-scattering techniques like Dynamic Light Scattering (DLS) offer simple approaches to obtaining bulk estimates of the size and concentration of particles in solution. DLS and Multi-angle Dynamic Light Scattering (MADLS) are currently the most frequently used techniques for measuring particle size distribution in the submicron and nanometre range, respectively. However, the current frequency of use does not reflect the technique’s accuracy. Whilst DLS and MADLS are thought to be suitable for characterising particles from 1 nm to 3 µm in diameter in a monodisperse sample, the resolution of DLS is low for particles with diameters of <150 nm as the angular dependence of the light-scattering profile is low. For DLS, accurate knowledge of the optical properties of both particles and dispersant is required; therefore, unknown samples cannot be analysed in a sensible way. This is particularly important when it comes to applications such as extracellular vesicles which may vary in optical density, and in nanomedicine development where the optical density of a nanoparticle, or even a new formulation of the nanoparticle, might be unknown.
Comparing Tunable Resistive Pulse Sensing to Dynamic Light Scattering
Tunable Resistive Pulse Sensing (TRPS)
Dynamic Light Scattering (DLS)
Single-particle technique
Using appropriately sized nanopores, particles can be measured across a wide size range (40 nm–11 µm)
Automated data processing with user-friendly data visualisation interface.
Single-particle resolution
Number-weighted analysis
Diameter is directly proportional to blockade size
Can resolve populations in multimodal samples
Not dependent on optical properties of particles and dispersant
