Single particle measurement for accurate particle size and size distribution analysis of sample populations.
Particle sizing
- Absolute size
- Size distribution
- Multiple populations
- Aggregation analysis
- Population resolution
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Background
Izon's SIOS technology platform offers a new and convenient solution for evaluation of particle size and size distribution of nano-sized particle samples in a fluid. The single particle detection methodology of SIOS ensures an accurate size distribution output without the averaging effects inherent in other size analysis technologies.
A discrete blockade event signal is recorded by the system each time a particle traverses the nanopore. These individually discriminated measurements are built up into a total population view of the sample. The magnitude of a measured blockade signal is a key indicator of the volume (or equivalent diameter) of the particle that has passed through the pore. This information allows
- evaluation of absolute particle size
- particle size distribution and volume fraction analysis
- resolution of distinct particle populations within a single sample
- gating of selected particle populations within a sample based on size
Particles of different sizes produce distinctly different blockade magnitude signals. The blockade magnitude response provides a direct correlation to the size of each particle.
Absolute size analysis
The relationship between measured blockade event magnitude (nA) and particle volume allows the evaluation of the absolute size of particles in a sample.
The example on the left demonstrates measurement of a polystyrene nanoparticle sample with three distinct size populations. The histogram shows the magnitude of blockade events measured from this sample. Three distinct populations are visible with the larger blockade magnitude values corresponding to larger particles. The peak of each population corresponds to the mean volume (and hence equivalent diameter) of the nanoparticles. The SEM image confirms the presence of three populations at 220nm, 400nm and 780nm diameter. Analysis of the peak magnitude value as a function of particle volume (figure insert) shows a close linear relationship between particle volume and blockade magnitude response across the wide range of particle sizes present in this sample.
Histogram of blockade event magnitude values recorded from a polystyrene particle sample demonstrates a trimodal response, indicative of three particle populations distinguished by size. Insert: the blockade magnitude scales linearly in response to increased particle volume across the full range of particle sizes present in the sample.
SEM image of polystyrene particle sample confirms the presence of three populations at around 220nm, 400nm and 780nm in diameter.
Size distribution and volume fraction analysis
The relationship between measured blockade magnitude and particle volume allows the evaluation of the distribution of particle size within a sample. A key application is the analysis of volume fraction of aggregates within a sample.
In the example on the left the clear single particle response peak is used as a reference to evaluate the volume fraction of aggregation present in the sample. In this case 16.4% of the sample produced a magnitude response at least equivalent to a particle with twice the volume of the single particles in the sample. 8.3% of the sample response was from particles with at least 3 times the volume of the single particles.
Equivalent volume analysis of the blockade magnitude response is used to evaluate aggregation levels in a polystyrene particle sample treated with avidin to cause binding.
Gating and tunability
Izon's dynamically adjustable nanopores provide a unique tunability to the SIOS measurement system. A sensitive mechanical actuator provides the capability to control the passage of particles through the nanopore sensing zone, allowing selective gating of particles within a sample based on their size.
The system can be tuned to allow particles with a wide variety of sizes to flow through the nanopore under the same conditions, providing the ability to accurately analyse highly poly-disperse samples.
The sensitivity of the system is demonstrated in the figure on the left. As the applied stretch on the nanopore (x value) is reduced from 46.6mm to 44.7mm the particles (polystyrene) are selectively gated from passing through based on their size until at low applied stretch values only the smallest particles are allowed to translocate. The measurement at the largest applied stretch value (46.6mm) displays a wide range of blockade event magnitudes reflecting the full range of particles sizes in the sample.
The dynamic control of particles in the SIOS system is achieved through the unique tunable nature of Izon's dynamically adjustable nanopores. This allows selective gating of particles in a sample based on size as demonstrated in this figure