Why you need to measure mRNA-LNP surface charge (and how to do it) 

Why you need to measure mRNA-LNP surface charge (and how to do it) 

In a previous blog we covered the importance of (and techniques for measuring) the size of lipid nanoparticles (LNPs). Here we turn our attention to surface charge, giving you expert insights into why and how best to measure it.  

Surface charge: a key measurement for LNPs

Interest in LNPs has exploded in recent years. And it’s easy to see why – these tiny vectors offer the potential to target some of the most challenging medical conditions and can be manufactured at scales often not possible with other drug delivery vectors.  

Developing and manufacturing LNP-based therapies and vaccines is still a big challenge. With LNPs being so complex, analytical characterization is exceptionally challenging — it can be hard to know which attributes to measure, and which analytical tools are going help answer your questions.  

A look beneath the surface of surface charge measurement  

So, what’s the deal with surface charge? Why should you measure it? And what can it tell you?   

Surface charge — otherwise known as zeta potential — is a crucial attribute to measure in LNP development. Not only does it offer insights into the in vivo fate and activity of your therapy (surface charge is perhaps the most important determinant of solubility and cell membrane interaction), but it can also give you information about the surface chemistry of your LNPs (and any modifications that may occur through development and manufacturing).  

ELS — the tool of choice for surface charge measurement  

Illustration of a capillary cuvette used in zeta potential measurements 
Figure1 Illustration of a capillary cuvette used in zeta potential measurements 

Electrophoretic light scattering (ELS) is the go-to technique for measuring the charge that your LNPs acquire in a particular medium.  

ELS is a straightforward technique that works on the principle of electrophoresis. The LNP solution is introduced into a cell containing two electrodes (see Figure 1), an electric field is applied across them, and the charged particles (in this case LNPs) migrate towards the oppositely charged electrode with a velocity related to their zeta potential. 

A laser is passed through the bottom of the cell, with the charged particles scattering the light. Since the scattered light is frequency shifted in proportion to the particles’ velocity, measuring the velocity this way enables analysts to calculate the zeta potential.   

Typically, ELS is used to explore LNP surface charge in phosphate-buffered saline (PBS) or a 10x diluted version of your sample, whereby analysts can validate the apparent surface charge of the LNP or evaluate different LNP formulations for stability and predicted uptake efficiency, respectively. (Of course, there are many more good reasons to apply ELS in characterizing LNPs, which you can discover in the eBook.) 

Getting the best surface charge measurements  

Importantly, several factors can impact the zeta potential of a particle, including:  

  • Changes in pH  
  • Ionic strength  
  • The concentration of other components in the solution  

To ensure reproducible zeta potential measurements, it’s crucial that you report the sample buffer you’ve used in your measurements, as well as the corresponding conductivity for the zeta potential value.  

Overcoming a key challenge  

Even if you take the above recommendations into account in your zeta potential measurements, you could still be impacted by perhaps the greatest challenge in zeta potential measurements: high-conductivity samples.  

LNP analysis eBook

Keen to know more about this challenge and how best to overcome it to ensure the most accurate surface charge measurements? Then check out our insight-packed eBook, “Overcoming challenges in LNP vector analysis: key tools, techniques, and considerations developed by our analytical experts.  

In it, we cover everything you need to know to more confidently characterize your LNPs, helping you

  • unlock deeper insights
  • minimize sample use
  • save time
  • and reduce costs.  

Discover more