Herein, we developed an enzyme-free dual signal amplification magnetic relaxation switching biosensor to detect the high hazard chloramphenicol based on the significant advantages of the pipet platform (low cost and easy operation). The competitive immunoassay was carried out by coating the polydopamine-modified pipets with the antibody, causing a content change of trigger DNA-chloramphenicol-antigen conjugate (the first signal amplification) in the supernatant. This triggered the aggregation of magnetic nanoparticles with three-dimensional DNA network structures (the second signal amplification) for chloramphenicol quantitative analysis by changes in transverse relaxation time (T₂). The pipet platform can simplify the sample pretreatment process to eliminate the potential interference with magnetic probes. Its low-cost combined with the enzyme-free strategy greatly reduces the overall detection expenses. The antigen-driven dual signal amplification strategy not only has high sensitivity (1.37 pg/mL), but also provides an alternative path for the efficient combination of immunoassay and DNA signal amplification.