Abstract: By coupling salmonella monoclonal antibody with carboxyl magnetic beads,immunomagnetic beads were produced,which were used as NMR molecular probes and biological sensors,pathogenic bacteria specially captured and detected in the samples so as to create a more rapid method to detect salmonella.Different sample solutions were put into the nuclear magnetic resonance apparatus to detect the spin relaxation time( T2) and examine the influence of different conditions to the value of T2. The experiment found that the sample value of T2 was influenced by the volume of immunomagnetic beads,the choice of buffer solution and the time of capturing.Through optimization experiment,curve variations T2 under different conditions were drawn with a result of ideal capturing conditions.Under the conditions that the capturing buffer solution was phosphate buffer solution( PBS)( 0.01 mol/L,p H7.4),the volume of immunomagnetic beads was 50 μg and the blending capturing time was 1.5 h,the curve of the sample value of T2 was perfect,detection linear range being 10~4¹0~7CFU / m L.A new method and approach was provided by this research,which was helpful to shorten the detection time and process and opened an immense space for the study of low field nuclear magnetic resonance.