What is sample stickiness - and why should it be measured?

What is sample stickiness?

When proteins are added to any assay apparatus, there is often an off-target interaction with the protein and the material of the apparatus. Stickiness is the attractive force or the charge between the surface of the assay apparatus and the protein. It is one of the most common interactions in biophysical assays that is both difficult to identify and resolve. This non-functional interaction causes issues in assay optimisation and disrupts data analysis and interpretation by interfering with the modality of the protein.

Isn’t stickiness just the same as viscosity?

Not at all. Viscosity is a property of a sample that describes its ability to move and flow, a measurement that is made independently of the material it may interact with. Viscosity is a vital, inherent biophysical characteristic of all materials.

Stickiness is the measurement of the attractive interaction between two different materials: in this case, when the assay apparatus and the sample come in contact with each other. This property can have undesired effects on the functionality of the protein and the readout from the assay.

Both are important when it comes to biophysical assays and sample quality control and should be measured and understood before proceeding with data analysis.

Then why is it important to know?

Knowing the stickiness of your sample gives you the chance to be fully aware about interactions between your protein and different materials that will lead to downstream errors and misinterpretations of your data. Without this knowledge, time is wasted on analysing unreliable assay outcomes. Identifying stickiness provides the opportunity to account for the problem as well as the ability to strategically resolve the issue using e.g.surface coating of apparatus materials.

Knowing the stickiness of your sample gives you the chance to be fully aware about interactions between your protein and different materials that will lead to downstream errors and misinterpretations of your data.

How can I measure stickiness, and what can I do about it?

Using FIDA technology brings this sample parameter easily into your quality control routine. How does it work? The radial diffusion of the sample during a FIDA measurement provides a distribution of the sample molecules, which is fitted with a Gaussian function during analysis. If the sample sticks to the walls of the FIDA capillary, a clearly visible tailing effect can be observed in the raw FIDA signal – no additional analysis required.

My sample is sticky - what should I do?

No matter the sample or the assay, there is a solution for identifying and solving stickiness with FIDA.

- Mild stickiness: Good news, in the Fidabio data analysis software, mild stickiness of the sample is tolerated without affecting the readout.

- Strong stickiness: Strong stickiness between the sample and the capillary can be resolved in two ways. The first method is to run the the sample on a hydrophilic, permanently coated capillary. The other way is to use a reversible surface coating. Both coated capillaries and surface coatings are available to all our users at shop.fidabio.com (user-access only). Alternatively, thanks to FIDA's high buffer tolerance, you can try to modify the buffer with e.g. salt or change its pH

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