High sensitivity sensor for tagged magnetic bead bioassays

Abstract

The preferred embodiments of the present invention use MRAM technology to detect a shift in the magnetic switching field of a sensor. The shift in the magnetic switching field is caused by the presence of magnetic tagged beads. By measuring the magnitude of the shift in the magnetic field and correlating the magnitude of the shift to the presence of the target molecules, accurate measurements regarding the presence of the target molecules can be made.

1 .- 13 . (canceled)  
     
     
         14 . An apparatus comprising: 
 a magnetoresistive sensor, said magnetoresistive sensor comprising at least one magnetoresistive random access memory (MRAM) element, wherein the MRAM element may be in a first state or a second state;    a surface, said surface comprising at least one activated area adapted to receive a plurality of magnetic beads, which when attached to said at least one activated area of said magnetoresistive sensor, alter at least one switching point in time from the first state to the second state, in response to an application of a switching current signal to the MRAM element.    
     
     
         15 . The apparatus of  claim 14  further comprising a housing containing said magnetoresistive sensor, said housing comprising a magnetic shield.  
     
     
         16 . The apparatus of  claim 14  wherein said plurality of magnetic beads comprises a plurality of magnetite Fe 2 0 3  beads.  
     
     
         17 . The apparatus of  claim 14  further comprising a modulated AC current applied to said at least one MRAM element.  
     
     
         18 . The apparatus of  claim 14  further comprising a plurality of target molecules, at least one of said plurality of target molecules being attached to at least one of said plurality of magnetic beads.  
     
     
         19 . The apparatus of  claim 14  wherein said at least one MRAM element comprises a multilayer magnetic element, said multi-layer magnetic element comprising: 
 a substrate; a first electrode multilayer stack; a spacer layer; and    a second multilayer stack.    
     
     
         20 . The apparatus of  claim 19  wherein said first electrode multilayer stack comprises: 
 a base metal layer, said base metal layer being formed on said substrate;    a seed layer, said seed layer being formed on said base metal layer;    a template layer, said template layer being formed on said seed layer;    an antiferromagnetic pinning layer, said antiferromagnetic pinning layer being formed on said template layer; and    a fixed ferromagnetic layer, said ferromagnetic layer being formed on and exchange coupled with said antiferromagnetic pinning layer.    
     
     
         21 . The apparatus of  claim 19  wherein said second electrode multilayer stack comprises: 
 a free ferromagnetic layer; and    a protective contact layer.    
     
     
         22 . The apparatus of  claim 14  wherein said at least one activated area comprises an asymmetrical monolayer positioned at one end of said at least one MRAM element.  
     
     
         23 . A method of detecting at least one target molecule using a magnetoresistive random access memory (MRAM) element, wherein the MRAM element may be in a first state or a second state, comprising the steps of: 
 monitoring at least one switching point in time from the first state to the second state, in response to the application of a switching current signal to the MRAM element;    detecting a shift in the at least one switching point in time from the first state to the second state, in response to at least one magnetic bead attaching to a magnetoresistive sensor incorporating said MRAM element; and    using said shift to identify the presence of at least one target molecule, said target molecule being attached to said at least one magnetic bead.    
     
     
         24 . The method of  claim 23 , wherein the switching current signal is pulsed at a predetermined frequency.  
     
     
         25 . The method of  claim 23 , wherein the switching current signal is provided to a plurality of programming conductors associated with the MRAM element.  
     
     
         26 . The method of  claim 25 , wherein the plurality of programming conductors are current lines that produce a magnetic switching field for switching the MRAM element from the first state to the second state.  
     
     
         27 . The method of  claim 23 , wherein said step of detecting the at least one target module further comprises the steps of: 
 calculating a first differential between the at least one switching point in time and a second switching point in time; and    calculating a second differential between a third switching point in time and a fourth switching point in time.    
     
     
         28 . The method of  claim 23  further comprising modulating said switching current signal using amplitude modulation.  
     
     
         29 . The method of  claim 23  further comprising the step of shielding said MRAM element from at least one external magnetic field.  
     
     
         30 . An apparatus for detecting at least one target molecule using a magnetoresistive random access memory (MRAM) element, wherein the MRAM element may be in a first state or a second state, comprising: 
 means for monitoring at least one switching point in time from the first state to the second state, in response to the application of a switching current signal to the MRAM element;    means for detecting a shift in the at least one switching point in time from the first state to the second state, in response to at least one magnetic bead attaching to a magnetoresistive sensor incorporating said MRAM element; and    means for using said shift to identify the presence of at least one target molecule, said target molecule being attached to said at least one magnetic bead.    
     
     
         31 . The apparatus of  claim 30 , wherein the switching current signal is pulsed at a predetermined frequency.  
     
     
         32 . The apparatus of  claim 30 , wherein the switching current signal is provided to a plurality of programming conductors associated with the MRAM element.  
     
     
         33 . The apparatus of  claim 32 , wherein the plurality of programming conductors are current lines that produce a magnetic switching field for switching the MRAM element from the first state to the second state.  
     
     
         34 . The apparatus of claim  39 , wherein said means for detecting the at least one target module further comprises: 
 means for calculating a first differential between the at least one switching point in time and a second switching point in time; and    means for calculating a second differential between a third switching point in time and a fourth switching point in time.    
     
     
         35 . The apparatus of  claim 30  further comprising means for modulating said switching current signal using amplitude modulation.  
     
     
         36 . The apparatus of  claim 23  further comprising means for shielding said MRAM element from at least one external magnetic field.