MAGNETIC-PERMEABILITY MEASUREMENTS IN BIOANALYSIS AND BIOSENSORS

A new transducer concept in bioanalysis and biosensors, utilizing meas urements of magnetic permeability, is reported. A model system based o n dextran ferrofluid, concanavalin A immobilized to a carrier (Sepharo se), and glucose was used To demonstrate the feasibility of this appro ach, Direct ferromagnetic detection of the dextran ferrofluid was achi eved by using a measuring coil (transducer) in a Maxwell bridge, A sen sitivity of 21 mu V/(mu g Fe/mL) and a rsd value of 3.8% were obtained (n = 5), It was also demonstrated that a small, non-ferromagnetic met abolite (glucose) could be detected using a competitive approach. With an increasing concentration of glucose (20-40 mM), we observed a decr ease in the response (0.59-0.11 mV), Reference measurements performed on Sepharose without the biorecognition element, concanavalin A, show- ed no significant response (0.01 mV), Some potential advantages and dr awbacks of this novel type of magnetic transducer are discussed, The a dvantages include very low interference from the sample matrix as the transducer is only sensitive to ferromagnetic substances, which rarefy are present in samples, In addition, it is suggested that these trans ducers should be free from fouling, The new transducers are proposed t o provide the basis for a new group of affinity biosensors suitable fo r in vivo and in vitro use.