In Biacore systems, interactions occur in flow cells on a sensor surface. Interacting partners in solution are delivered to flow cells, formed when a microfluidic flow system is brought into contact with a sensor surface on which another interacting partner is immobilized. Several flow system designs have evolved;

In this configuration, sample is injected through flow cells, which can be opened and closed by a system of valves. Interactions may be analyzed in up to four flow cells, according to the system design. Selected flow cells may be used as on-line reference cells, allowing blank subtracted data to be presented directly on the screen during analysis.

Hydrodynamic addressing (HA) is a process by which multiple interactants may be immobilized on detection spots in a single flow cell, allowing simultaneous analysis of interactions. As there is no lag time between interactions, highly accurate reference subtraction allows the measurement of very rapid kinetics. Further, by immobilizing several interactants in one flow cell, comparative binding properties may be directly examined under optimal experimental conditions.

By adjusting the relative flow at the two inlets (one for the immobilized partner and the other for buffer), liquid can be directed to different addressable detection spots. The flow cell design allows rapid and efficient switching of flow between buffer and sample solutions and the transverse arrangement of the detection spots ensures that access of sample to all spots is simultaneous. Although the detection spots are addressed separately during immobilization, the injected sample flows over all spots simultaneously.

The design of this flow cell is a single broad channel through which sample is injected, interacting simultaneously with all spots on an array. After the sensor surface is spotted according to user specifications, a gasketed window with an inlet and an outlet valve is then positioned and hermetically sealed over the array to form the flow cell, which is then inserted into a Biacore Flexchip system. This system exploits a variant of SPR known as grating-coupled SPR (GC-SPR), in which incident light from above directly strikes the entire array, generating data from up to 400 interactions simultaneously.

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