Particle Charge Analysis Using Tunable Resistive Pulse Sensing (TRPS)

By AZoNano.com Staff Writers

Topics Covered

Introduction
Solution from Izon Science
Key Advantages of Izon’s TRPS technique
Applications in Nanomedicine
     Characterization of Liposome Modification by Size and Zeta-Potential
Conclusion
About Izon

Introduction

The characterization of nanoparticle systems involves the determination of size as well as the quantitative analysis of surface charge. The surface modification, stability, and behavior of particles can be monitored and predicted through the measurement of particle charge, or ζ-potential (zeta potential).

This analysis capability plays a key role in a variety of applications, such as the analysis of microvesicles and exosomes, the characterization of drug delivery systems, and use of biological coated particles as diagnostics.

Solution from Izon Science

The size and charge of nano and submicron particles can be simultaneously measured on a particle by particle basis using a TRPS system from Izon. With unique high resolution analysis capability, this innovative system serves as a sophisticated tool for researchers in nanotechnology and nanomedicine to gain new insights and advance a suite of fields ranging from drug delivery and nanomaterials to diagnostics.

Figure 1. Izon's TRPS System.

Izon’s TRPS technique allows for the simultaneous extraction of the size and ζ-potential of individual particles from the resistive pulse signal generated by them when they move across a dynamically adjustable nanopore, as shown in Figure 2.

As each pulse corresponds to a single particle, the information on hundreds to thousands of particles can be collected over a short analysis time, thus enabling a superior resolution and precise measurement of the overall sample distribution.

Figure 2. The ionic current between an upper and lower fluid cell filled with a solution of particles is monitored by a sensitive detector (2a). The characteristics of each pulse are directly dependent on the particle properties (2b). The forces acting on particles in the pore are: Fluid Velocity (momentum) (dark blue) - Directionally dependent and proportional to the applied pressure. Electrophoretic Mobility (green) - Proportional to particle charge (ζ-potential) and applied voltage. Electro-osmosis (red) - Proportional to the charge of the pore membrane and applied voltage (2c).

Key Advantages of Izon’s TRPS technique

The size, shape and velocity of the particle that pass through the nanopore decide magnitude, duration and shape of each pulse. Hence, the simulation of the fluidic (momentum) and electrophoretic forces which make the particles to move through the pore enable the extraction of the ζ-potential of particle from the generated pulse signal.

The measurement can be fine tuned by altering the applied pressure and voltage to the system. The ability to concurrently measure the size and ζ-potential of individual particles is a unique feature of this technique.

The size of the pore sensor can be dynamically tuned by stretching the elastic pore membrane. This allows for the analysis of a larger sample size range, improvement of measurement sensitivity, and fine tuning of the forces acting on the particles. This results in higher resolution measurements and provides a new method to investigate and understand the fundamental characteristic of nano-scale dispersions.

This new size and charge technique facilitates high resolution distribution measurements of polydisperse and complicated multimodal suspensions, as illustrated in Figure 3. This unique and in-depth readout of particle properties provides a new robust particle characterization technique.

Figure 3. Simultaneous size and charge measurement of a trimodal sample composed of three particle sets having different size/charge profiles, being 200, 240 and 350 nm and -35, -8 and -20 mV, respectively. The dotplot displays the properties for each particle measured and the histograms represent the cumulative property histograms.

Applications in Nanomedicine

Characterization of Liposome Modification by Size and Zeta-Potential

The ability to calculate the size and charge distribution is critical in a myriad of fields, especially in nanoparticle research and liposome-based drug delivery systems. This is due to the fact that the therapeutic delivery efficacy, effluent pathway, circulation time, localized accumulation, drug release profile, cellular uptake, and potential toxicity of drug delivery particles relies on their concentration, size and charge.

Moreover, it is possible to use the changes in particle size and charge for characterizing particle surface modifications, such as targeting molecule attachment or PEGylation, which is utilized to enhance their drug delivery properties, as depicted in Figure 4.

The TRPS technique has been utilized to determine the properties and corresponding modifications in liposomes obtained with and without the addition of a PEGgylated phospholipid. The size and ζ-potential of individual liposome (blue) and PEGylated liposome (red) particles are illustrated in the 2D dot plot. The associated size (top) and ζ-potential (left) concentration histograms demonstrate the distribution of these properties over the whole liposome suspension.

Figure 4. Particle-by-particle size and charge analysis of PEGylated and ‘normal’ Liposome Sample.

Besides the change in size, the high resolution of this approach also acquires data on the homogeneity of the PEGylation, which can be linked back to the width of the size and ζ-potential distributions. The new technique is offered with a hardware and software upgrade for existing users, or as a standard solution, which comes with Izon’s qNano particle analysis system.

Figure 5. Izon’s new Variable Pressure Module (VPM) and qNano System enables particle-by-particle assessment of size, charge and concentration.

Conclusion

Izon’s new analysis capability of concurrently determining both the size and charge of individual particles provides a new, higher resolution particle characterization technique against alternative averaging based techniques. With this system, researchers can gain insights and engineer their particulate systems to improve their ability to produce better, more effective, particulate materials.

About Izon

Izon Science has developed the world’s first nanopore based measurement system available for general use. Izon’s instruments are used for precise measurement and analysis of individual particles across a wide range of scientific fields including bionanotechnology, nanomedicine, vaccinology, microbiology, biomedical research, environmental science, and particle based nanoscience. Izon originated in New Zealand and now sells its products in 34 countries. It has its European headquarters in Oxford, UK and its US headquarters are in Cambridge, MA.

This information has been sourced, reviewed and adapted from materials provided by Izon.

For more information on this source, please visit Izon.

Date Added: Jul 19, 2013 | Updated: Jul 19, 2013
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