Off-diagonal Giant Magnetoimpedance Biosensor

In recent years,the application of magnetic biosensors in molecular detection is an active and emerging research topic.Magnetic biosensors use magnetic particles as markers of biomolecules,analyzing molecular concentrations by detecting magnetic particles.Common magnetic biosensors include Hall biosensors,Magnetoresistive biosensors,and Fluxgate biosensors.The magnetic biosensor has the advantages of high sensitivity,low cost and convenient operation,which makes up for the deficiencies of the existing detection methods and has broad application prospects.The Off-diagonal giant magnetoimpedance sensor is a highly sensitive magnetic sensor that can detect pT-level biological magnetic fields and has potential for the detection of magnetic particles.An ultrasensitive off-diagonal GMI biosensor system was produced in this paper.The system utilized a simple PDMS chip for magnetic bead?MB?-labeled immunoreactions and an off-diagonal GMI magnetic sensor as a magnetic signal acquisition device.The PDMS chip is separated from the magnetic sensor.An APTES self-assembled monomolecular?SAM?having a terminal group of amino groups was prepared on the glass substrate of the single-open chamber of PDMS chip for immobilization of the analyte,and then the analyte was labeled with MBs.The off-diagonal GMI magnetic sensor used a Co-rich glass-coated amorphous wire wound with a coil as a sensing element.The induced voltage was read from the coil end,and the second harmonic in the induced voltage was picked up by the LC circuit.After processed by the integrated circuit,the second harmonic was converted into a DC voltage signal that was linear with the external magnetic field(H_ext)in a range of±1.2Oe.The GMI biosensor with high sensitivity has been obtained and then applied to biological detection.The following work has been done:1.This biosensor system was applied to detect functionalized MBs.Due to the superparamagnetism of the MBs,a H_ext was required to magnetize MBs and cause the beads to produce a detectable dipole field.Simultaneously,it adjusted the sensitivity of the sensor?S₁?.In this paper,the sensitivity of the sensor for MBs detection?S₂?was investigated.The intensity of the dipole field from MBs was increased under a higher H_ext but the sensitivity of the sensor was decreased.There was a competitive relationship between the two,and the optimal H_ext was 1.1 Oe from experiment.In addition,the size of the open chamber in the PDMS chip affected the results of the MBs detection.A higher detection limit was achieved with a PDMS chip with an open chamber of 3 mm compared to a 2 mm chamber.2.The biosensor system was used to detect cancer biomarkers and bacteria.In the range of 100 fg/mL-1?g/mL,the biosensor can achieve linear detection of the liver cancer marker alpha-fetoprotein?AFP?with a detection limit as low as 100 fg/mL.The detection range of prostate specific antigen?PSA?was from 1 ng/mL to 10?g/mL with a detection limit of 1 ng/mL.In addition,the detection of Salmonella can be achieved in the range of 50 CFU/mL-5E5 CFU/mL through sandwich immunoassay.The detection time was about 4-5 hours,which is much lower than the traditional culture method.