A method for suppressing non-specific bindings between molecules, the method comprising: providing magnetic particles dispersed in a liquid, each of the magnetic particles having a magnetization; coating the magnetic particles with coating molecules; applying binding molecules mixed of first-type binding molecules and second-type binding molecules to the liquid, wherein the coating molecules are specifically binding with the first-type binding molecules and non-specifically binding with the second-type binding molecules; applying an alternating current (ac) magnetic field with a frequency level, wherein the frequency level causes suppression of the second-type binding molecules in binding with the coating molecules while the binding of the first-type binding molecules to the coating molecules remains, wherein the magnetic particles together with the first-type binding molecules or the second-type binding molecules as bound are rotated by the ac magnetic field to produce a centrifugal force to break binding of the second-type binding molecules to the coating molecules, wherein the frequency level of the ac magnetic field is determined by the steps of: measuring a first ac magnetoreduction signal for the specific binding of the first-type binding molecules under an ac magnetic field varying in a first ac frequency range; measuring a second ac magnetoreduction signal for the non-specific binding of the second-type binding molecules under an ac magnetic field varying a second ac frequency range; and determining the frequency level, according to quantities of the first ac magnetoreduction signal and the second ac magnetoreduction signal in varying with frequency, such that the non-specific binding of the second-type binding molecules is suppressed and the specific binding of the first-type binding molecules is retained. providing magnetic particles dispersed in a liquid, each of the magnetic particles having a magnetization; coating the magnetic particles with coating molecules; applying binding molecules mixed of first-type binding molecules and second-type binding molecules to the liquid, wherein the coating molecules are specifically binding with the first-type binding molecules and non-specifically binding with the second-type binding molecules; applying an alternating current (ac) magnetic field with a frequency level, wherein the frequency level causes suppression of the second-type binding molecules in binding with the coating molecules while the binding of the first-type binding molecules to the coating molecules remains, wherein the magnetic particles together with the first-type binding molecules or the second-type binding molecules as bound are rotated by the ac magnetic field to produce a centrifugal force to break binding of the second-type binding molecules to the coating molecules, wherein the frequency level of the ac magnetic field is determined by the steps of: measuring a first ac magnetoreduction signal for the specific binding of the first-type binding molecules under an ac magnetic field varying in a first ac frequency range; measuring a second ac magnetoreduction signal for the non-specific binding of the second-type binding molecules under an ac magnetic field varying a second ac frequency range; and determining the frequency level, according to quantities of the first ac magnetoreduction signal and the second ac magnetoreduction signal in varying with frequency, such that the non-specific binding of the second-type binding molecules is suppressed and the specific binding of the first-type binding molecules is retained. measuring a first ac magnetoreduction signal for the specific binding of the first-type binding molecules under an ac magnetic field varying in a first ac frequency range; measuring a second ac magnetoreduction signal for the non-specific binding of the second-type binding molecules under an ac magnetic field varying a second ac frequency range; and determining the frequency level, according to quantities of the first ac magnetoreduction signal and the second ac magnetoreduction signal in varying with frequency, such that the non-specific binding of the second-type binding molecules is suppressed and the specific binding of the first-type binding molecules is retained.