Technical Tip: Preserving Biosensors for Long-Term Storage

Typically, biosensors are used immediately after immobilizing the protein of interest onto the biosensor surface. However, there may be times when you want to store prepared biosensors for more than 24 hours before use. Doing so can be particularly convenient if you are using the batch-immobilization technique to prepare large numbers of biosensors at one time.

This Technical Tip outlines a preservation and storage procedure that produces stable biosensors for most proteins. A biosensor storage stability validation protocol is also provided.

Biosensor Preservation

1. Prepare a preservation solution of 15% sucrose in PBS (w/v). A volume of 20 mL is sufficient to aliquot 200 µL per well for 96 wells. Pipette 200 µL of the solution into the appropriate wells of a 96 well plate.
2. After completing the batch immobilization protocol, remove the biosensors from the wash solution and incubate in the sucrose solution for 1–2 minutes.
3. Remove the biosensors from the sucrose and allow to dry. This can be done at room temperature for 5 minutes or in an incubator at 37°C for 1–2 minutes.
4. Store preserved biosensors in the original foil pouch with desiccant at room temperature.

Assaying Stability During Storage

Stability can be determined by testing preserved biosensors against a control sample at different storage times. Correctly stabilized biosensors will not show significant deterioration in binding over time.

Assay Setup

1. Use biosensors immediately after preservation to create a standard curve using the optimized assay protocol (this will be time point 0 days in the stability assay). Include additional replicates of a control sample at the mid-range of the assay.
2. At desired time points after preservation (for example 1 day, 2 days, 5 days, 14 days) use the same assay protocol to run replicate data at the mid-point control concentration.

Results and Data Analysis

(Note: the instructions below are for the Octet RED system. If using the Octet QK system, see Technical Note 9, Developing a Protein-Specific Quantitation Assay Using Streptavidin Biosensors for data analysis instructions.)

1. Load the files from the 0 day time point and analyze the standard curve from the experiment.
2. Use the standard curve generated on Day 0 to analyze subsequent days.
3. Compare performance over the time of storage. Correctly stabilized biosensors should show minimal loss in activity over the time they will be stored.

Time Point Tested Average Calculated mg/mL %CV(n=4) 0 Days 78.75 2% 1 day 77.32 4% 2 Days 80.55 2% 5 Days 77.87 2% 14 Days 77.88 2% Table 3: Example data showing the average calculated concentrations from a mid-point control sample. Data is shown for 5 time points ranging over 2 weeks. Replicates (n=4) were assayed at each time point. The data shows no detectable deterioration of performance and validates the stability of the preserved protein coated biosensors.

Table 3 shows the average calculated concentrations from a mid-point control sample. Data is shown for 5 time points ranging over 2 weeks. Replicates (n=4) were assayed at each time point. The data shows no detectable deterioration of performance and validates the stability of the preserved protein-coated biosensors.

Detailed information on assaying stability during storage, as well as several useful assay development procedures for Streptavidin Biosensors can be found in Technical Note 9: Developing a Protein-Specific Quantitation Assay Using Streptavidin Biosensors, available for download from www.fortebio.com.

For even more Biosensor selection information visit our biosensor types page.

Biosensor Quick Reference Guide

Fortebio offers the following biosensor surface chemistries for immobilization of proteins and subsequent analysis the Octet RED and Octet QK Systems.

Kinetics Assay Biosensor Selection Guide

Factor SBC (Kinetics Grade) SBC FA (Screening Grade) HBC (Kinetics Grade) HBC FA (Screening Grade) Super SA (Kinetics Grade) Amine Reactive APS Binding capacity S/N for small molecules (300-900 Daltons) on Octet RED S/N for peptides (500-2000 Daltons) on Octet RED S/N for small proteins (5-20kD) S/N for mid sized proteins (20-150kD) S/N for large proteins (>150kD) Short kinetics assays (off rate <15min Long kinetics assays (off rate >15min) Applications at high detergent concentrations (>1%) Immobilization of non-biotinylated proteins Custom quantitation Epitope mapping/binning Regeneration capable  = Not Advised      = Good      = Very Good      = Exellent

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