Resources Selection Guide: Streptavidin Biosensor for Biotin Tag Capture A quick reference to match each probe to analyte size, sample type, and assay needs Biotin-streptavidin capture is one of the strongest non-covalent interactions available for BLI, but a single streptavidin (SA) chemistry doesn’t serve every assay well. Analyte size, sample complexity, and whether you need to reuse the surface across multiple ligands all require different biosensor properties. Gator® Bio offers five streptavidin biosensor options: three single-use probes (SA, SA XT, SMAP) and two reusable kits (Flex SA, Regen SA). Surface properties and optical performance of each probe are tailored for different assay needs. Running more than one probe type during method development can unlock improved performance for your specific assay. Access the full details and recommendations by downloading the Selection Guide PDF: Download Selection Guide Choosing by analyte size Analyte size is one of the first filters to apply. The figure and table below maps common analyte sizes and types to the probes worth evaluating first. Figure 1. Recommended analyte molecular weight ranges for different streptavidin biosensor probes offered by Gator Bio. Analyte TypeRecommended Probes to EvaluateSmall molecules ≥ 150 DaSMAPOligomers/peptides ≥ 1.5 kDaSMAP, SA XT, Regen SAProteins/antibodies, 15 – 150 kDaSA, SA XT, Flex SA, Regen SALNPs, VLPs, large complexes ≤ 2 MDaSA XT Table 1: Recommended streptavidin probe options to evaluate for common analyte types and size ranges. SMAP is the only probe built specifically for small molecules. SA XT is the one chemistry that spans the highest range, from 1.5 kDa oligomers up to 2 MDa complexes like LNPs and VLPs. For standard 15–150 kDa protein and antibody work, SA, SA XT, Flex SA, and Regen SA all apply. Which of the four you pick from there comes down to reuse needs and sample complexity, covered below. Probe details SA ProbesSA captures biotinylated proteins across the standard 15 – 150 kDa range and is built for crude samples, including serum and lysates. It delivers the best precision of CV ≤ 6 % within-tray for most sample types, with reproducible kinetics. SA XT ProbesSA XT pairs its streptavidin surface with a design that reduces mass transport effects from very large analytes, giving it a recommended molecular weight range of up to 2 MDa. Built on Gator’s XT Optics technology, this probe adds up to 3x signal-to-noise over SA probes allowing it to confidently resolve kinetics of analytes down to 1.5 kDa. SMAP ProbesSmall Molecule Analysis Probes (SMAP) combine a high-density streptavidin surface with XT Optics to extend detection down to small molecular weight analytes, and are well suited to small molecule and peptide kinetics. Flex SA ProbesFlex SA is a reusable kit that strips and reactivates the streptavidin layer between experiments, giving you a clean surface for each assay. It’s built for repeated experiments with crude samples or moderate-throughput biotinylated protein screening in the 15–150 kDa range, and regenerates 10+ times. Regen SA (RSA) ProbesRegen SA (RSA) uses an engineered streptavidin surface that regenerates with a standard protocol with the kit’s proprietary regeneration solution. Built on XT Optics, it is ideal for high-throughput screening of both low molecular weight analytes and larger proteins, regenerating up to 10 times. Because the engineered surface binds biotin less tightly than native streptavidin, Regen SA isn’t recommended for kinetic interactions with KD below 100 pM. Long biotin linkers improve capture performance; AviTags are not recommended for this probe. For more details and recommendations, download the full guide: Download Selection Guide FAQs What’s the difference between SA, SA XT, and SMAP streptavidin biosensors? All three are single-use probes. SA covers the standard 15–150 kDa protein and antibody range. SA XT extends that range from 1.5 kDa up to 2000 kDa, adding VLPs, LNPs, and nanodiscs. SMAP is built specifically for small molecules and peptides starting at 150 Da. Which streptavidin biosensor should I use for small molecules or peptides? SMAP is built for small molecular weight analytes and peptide kinetics. SA XT and Regen SA also cover oligomers and peptides down to 1.5 kDa. Which biosensor should I use for LNPs, VLPs, or other large complexes? SA XT is the recommended probe for large complexes up to 2 MDa, including LNPs, VLPs, and nanodiscs. What’s the difference between Flex SA and Regen SA? Both are reusable kits that regenerate. Flex SA strips and reactivates the streptavidin layer itself between runs and is built for crude samples or moderate-throughput screening in the 15–150 kDa range. Regen SA uses an engineered streptavidin surface that regenerates without removing the layer and offers up to 3x higher signal with XT Optics, though it isn’t recommended for kinetic interactions with KD below 100 pM. Can streptavidin biosensors be reused? Flex SA and Regen SA are both designed for repeated reuse, regenerating 10 or more times. SA, SA XT, and SMAP are single-use probes, though analyte-only removal is possible under sample-dependent conditions, leaving the ligand on the probe for reuse. Are AviTag-labeled proteins compatible with all streptavidin biosensors? AviTag is compatible with SA, SA XT, SMAP, and Flex SA. It is not recommended for Regen SA, as longer linkers provide better capture performance on the engineered streptavidin. Due to the compact nature of AviTags, some samples may experience steric hindrance of the biotin tag to the streptavidin capture surface resulting in some dissociation. If this occurs, using long linkers (eg. PEG4 or LC/LC-LC) can also improve capture on SA, SA XT, SMAP and Flex SA probes. What biotinylation linker works best for Regen SA probes? Long linkers such as LC-LC-Biotin, PEG4-Biotin, or biotin-dT are recommended for Regen SA for best capture performance. Get in touch Still not sure which probe fits your application? Get in touch with us at [email protected]. Shop now Find the right biosensors for your research. Explore the Gator Bio catalog and shop biosensors for your biolayer interferometry assays. Browse complete biosensor catalog