Essays/linkedin/24-05-17 label free

🧪 Label-free optical methods are great tools to characterize samples with little overhead, but their lack of specificity may require some further thinking for broader adoption.

Fluorescence labelling became a default approach for many biological assays. From an ELISA test, to flow-cytometry or PCR. The core advantage of labeling is its specificity, and particular spectral fingerprinting which allows to separate it from background signals.

But at small scales and in relevant environments labeling adds extra dimensions of complexity.

While microscopy pushed for the absolute limits of single fluorescent-molecule detection, quantitative measurements need to be done extremely carefully.

Relying on fluorescence labelling to measure whether a lipid nanoparticle (LNP) was loaded with RNA or not opens many questions. For example, labeling efficiency across a membrane, specificity, and stability. Which leads to the need to perform orthogonal measurements (with and without labeling) to increase the reliability on the observations.

This is the gap that label-free methods can target. Relatively well-behaved samples where one expects specific sub-populations. For example: loaded and empty LNP's, broken particles, etc.

And in this context, single-particle measurements will be fundamental to explore biases in sample preparation, storage conditions, and quality control. What if small particles are always loaded and bigger particles are always empty?

The same concerns are present across platforms, not just LNP's. AAVs, liposomes and, in a near future, exosomes, all struggle with the same questions.

Besides DLS, what other label-free methods do you routinely use?

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