Abstract: Described herein are methods for improved partitioning between high and low affinity nucleic acid ligands identified through the SELEX method, termed Flow Cell SELEX. The Flow Cell SELEX method achieves partitioning between high and low affinity nucleic acid ligands using surface plasmon resonance technology. The method of the present invention presents a new and powerful approach to select nucleic acid ligands by providing a partitioning method which 1) enables a significant increase in the efficiency of partitioning from traditional partitioning methods used in SELEX, 2) allows for real time monitoring of the partitioning of the high affinity ligands from the low affinity ligands 3) allows for the ability to select for a nucleic acid ligand having specific kinetic properties, 4) does not rely on radiolabeling or other means of tagging for detection, and 5) allows for use of smaller amounts of target than in traditional methods of SELEX.