Hello,
I am making lipid nanoparticles using the thin film hydration method. Formula is DODMA:DSPC:Cholesterol:DSG-PEG2000 at 60:20:17.5:2.5 %mM in 5mM total.
After hydration in sodium acetate pH4, sonication and extrusion, I dyalise the LNPs in PBS pH7.4. When I measure the size using DLS the results are great, but when measuring the z-potential, since DODMA is at its isoelectric point at pH7.4, it neutralizes and the charge is around -2mV but the conductivity is really high (20mS/cm) probably due to the PBS ionic strenght, and therefore the quality is not so good.
The thing is that when I remove the lipids from the malvern folded capillary cell, they become very purple. I have repeated the experiment and saw the same purple colour, also did it with just with PBS and no change in colour ofc.
Mainly out of curiosity, but does anyone know why this happens??
Are you trying to obtain a zeta potential distribution? PBS should not be used to measure zeta potential.
Yes, I realised that after. I am using low ionic buffers (25mM Sodium acetate) or deionized ultrapure water now. Thanks though!
DI water is useless to maintain nanoparticles in suspension and to measure zeta potential. If you are trying to generate a zeta potential distribution, the sample is being "burned".
Dear Omar Gonzalez-Ortega and Alan F Rawle
Thanks for your answers, if I may ask, since the z potential is so important, what do you recommend I resuspend the LNPs to be able to measure it? I will use the nanoparticles for in vitro lipofection and future in vivo work.
Papers that use ionizible lipids dialyse them against PBS or HEPES. Of course, that would give a neutral charge and negatively affect the stability of the LNPs right?
The usual background liquid is akin to millimolar (0.001M) sodium or potassium chloride. The vital pH control (zeta potential is meaningless without a quoted pH) can be effected by low molarity NaOH and HCl.
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