MP-SPR Navi TM 220A Naali SPR was used to measure the effect of tether length on NAv/BPT interaction. SPR sensors with gold surface are cleaned in the same way as explained for AuNPs/APT experiment and then mounted in the SPR. The sensor is then equilibrated in water and a solution of BPT (1mM in milli-Q water) is flowed to reach the desired tether surface coverage which is achieved by manually interrupting the solution flowing above the sensor.