Adaptation of a surface plasmon resonance biosensor with miorofluidics foruse with small sample volumes and long contact times

The efficient delivery of sample to surface-immobilized sites is a key elem ent in biosensing, For a surface plasmon resonance (SPR) biosensor, this ha s been addressed by constant now through a microfluidic system with a sampl e injection loop (Sjloander, S,; Urbaniczky, C. Anal. Chem. 1991, 63, 2338- 2345), The present study describes an alternative mode of sample delivery w ithout constant unidirectional flow. It was implemented on a commercial Bia core X SPR biosensor equipped with a microfluidic cartridge, but with the f luidic handling performed by an externally computer-controlled syringe pump . We demonstrate that sample volumes as low as 2 muL can be reproducibly po sitioned to cover the sensor surfaces, manipulated in a serial fashion, eff iciently mixed by applying an oscillatory now pattern, and fully recovered. Compared to the traditional continuous unidirectional now configuration, w e found very similar kinetic responses at high analyte concentrations and s lightly slower responses at low concentrations, most likely due to depletio n of analyte from the small sample volumes due to surface binding. With the antibody-antigen systems tested, binding parameters were obtained that are generally within 10% of those from conventional experiments. In the new co nfiguration, biosensor experiments can be conducted without the usual const raints in the surface contact time that are correlated with sample volume a nd mass transport rate. This can translate to improved detection limits for slow reactions and can facilitate kinetic and thermodynamic binding studie s.