The interaction between different concentrations of tumor necrosis factor-α（TNF-α） and soluble tumors necrosis factor receptor-I（sTNFR-I） is studied by using an affinity biosensor-IAsys biosensor

and the data is analyzed by using the FASTfit program.sTNFR-I is immobilized on the cuvette surface with the density of（2.25 ng/mm

2

）

TNF-α then bound to immobilized sTNFR-I specifically in a dose-dependent manner.By FASTfit fitting

the responses fitted the biphasic association quite well

and the error is small and random.Kinetic constants for TNF-α binding to sTNFR-I are determined from the plots of k

on

versus the concentration of TNF-α:k

ass

=（4.21×10

4

L）·mol

-1

·s

-1

k

diss

=2.12×10

-2

s

-1

k

D

=5.05×10

-7

mol·L

-1

k

A

=1.99×10

6

L·mol

-1

.IAsys biosensor is able to monitor the binding and dissociating courses in real time with simple and quick operation

which provided an effective assay for kinetic analysis of TNF-α/sTNFR-I interaction.