Tunable Resistive Pulse Sensing (TRPS) vs Nanoparticle Tracking Analysis (NTA)
Tunable Resistive Pulse Sensing (TRPS) and Nanoparticle Tracking Analysis (NTA) are two techniques based on very different principles. Both are used to measure the physical characteristics of particles, as is required by many growing fields across biotherapeutics, nanomedicine, virology, and extracellular vesicles. While all of these disciplines call for the analysis of samples containing heterogenous particles, the techniques available for nanoparticle measurement vary greatly in their precision, accuracy and resolution capabilities.
Differences in Resolution Capabilities
The extent to which a technique can be used to identify difference between sample characteristics is limited in part by its resolution capabilities. Although both Tunable Resistive Pulse Sensing (TRPS) and Nanoparticle Tracking Analysis (NTA) measurements are based on the analysis of individual particles, major differences in their resolution capabilities have been revealed in systematic comparative studies (Vogel et al. 2021, Caputo et al. 2021)
TRPS analysis of a quadrimodal sample, for example, reveals four clearly distinguishable peaks, representing the four subpopulations known to be present.
When using NTA to analyse quadrimodal samples of polystyrene particles, however, the peaks showing particle size distribution are wide and overlapping. The lower resolution makes it difficult to identify all subpopulations – and subsequently, obtain precise information about particle size distribution in the sample.
Enquire about TRPSHow Does TRPS Measure Nanoparticles?
Tunable Resistive Pulse Sensing (TRPS) is a true single-particle technique which uses changes in electrical current to evaluate individual particles suspended in an electrolyte solution as they move between electrodes through a tunable nanopore. Current flow is monitored, and each particle is detected as it passes through the nanopore, due to the transient change in current that is subsequently created.
Physical characteristics of particles in the sample are obtained via the analysis of resulting blockades, which represent individual particles. Specifically, particle volume is directly proportional to blockade magnitude, and particle concentration is precisely calculated from the particle flow rate measured at several different applied pressures. Zeta potential is derived via measurements of electrophoretic mobility, which is calculated from the velocity with which the particle traverses the nanopore.
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How Does NTA Measure Nanoparticles?
In contrast with the true single-particle nature of Tunable Resistive Pulse Sensing (TRPS), Nanoparticle Tracking Analysis (NTA) uses the tracking of particle motion via light scattering to assess the mean squared displacement of particles moving under Brownian motion, in a sample chamber illuminated by a laser beam. The tracking of particles enables a diffusion constant to be calculated, which is used in the Stokes-Einstein equation to calculate hydrodynamic diameters. The Stokes-Einstein equation also takes into account the temperature and viscosity of the suspension. Particle concentration calculations are based on the number of particles tracked in an estimated illumination volume.
Why Choose TRPS Over NTA?
Tunable Resistive Pulse Sensing (TRPS) is a single-particle measurement technique that generates high-resolution data on the physical characteristics of nanoparticles. Given the direct relationships that exist between blockade characteristics and physical properties of nanoparticles, TRPS enables true particle-by-particle analysis. The resulting high-resolution measurements enable you to gain deep insights on particle characteristics. Different sized nanopores are available to facilitate a range of particle sizes, from 40 nm to 11 µm in diameter, and only 35 μL of sample is needed for a TRPS measurement. With TRPS, the use of standardised calibration particles and ability to monitor the signal-to-noise ratio in real time ensures that conditions are optimised and maintained throughout the calibration and measurement process.
In contrast, the resolution capabilities of Nanoparticle Tracking Analysis (NTA) are relatively lower; NTA struggles to properly resolve subpopulations of multimodal samples and has been shown to overestimate particle concentration, making it more difficult to compare samples with confidence.
NTA measurements have also been shown to be very sensitive to and dependent on instrument settings, such as camera sensitivity, and also require knowledge of the optical properties of the particles being analysed. At the lower limit of particle detection, the refractive indices of the solvent and particles play a role in determining the detectable size limit. At times, these parameters must be estimated, which creates potential sources of error
Comparing TRPS to NTA
Tunable Resistive Pulse Sensing (TRPS)
Nanoparticle Tracking Analysis (NTA)
Particle size is directly proportional to blockade magnitude; each particle is measured individually.
Wide size range; particles from 40 nm - 11 µm can be measured using appropriately sized nanopores.
Different sized nanopores are needed to cover the entire size range.
Can resolve subpopulations in multimodal samples.
Calculated directly from blockade frequency, using standardised calibration particles of known size and concentration.
Automated data processing with user-friendly data visualisation interface.
Parameters are actively monitored to ensure they are optimised for the measurement of calibration and sample particles.
