Biosensor for detecting a single magnetic label

Abstract

A biosensor may provide a magnetoresistive (MR) film comprising a nonmagnetic layer may be sandwiched between the two ferromagnetic layers. The MR film may be positioned on a substrate, where the edges of the MR film are in contact with leads. The leads may be in contact with pads. The sensors may provide quasi-digital readout that enable greatly enhanced sensitivity. In some embodiments, biosensors may be arranged as array of sensors. The array of sensors may be arranged as a symmetric or asymmetric N1×N2 array, where N1 and N2 are integers, N1 represents the number of sensors linked together in series, and N2 represents the number of sensor sets in parallel, where each sensor set may comprise one or more sensors. Further, the array of sensors may be coupled to a voltmeter, which may be a single voltmeter in that allows the sensors to all be probed simultaneously.

What is claimed is: 
     
         1 . A biosensor system comprising:
 a magnetoresistive (MR) sensor providing a quasi-digital response to a magnetic field sweep, the sensor comprising   a free layer that is ferromagnetic;   a pinned layer that is ferromagnetic; and   a nonmagnetic layer sandwiched between the free and the pinned layers, wherein when magnetization directions of the free and the pinned layers are parallel, the MR sensor is in a low-resistance state, and when the magnetization directions of the free and the pinned layers are perpendicular, the MR sensor is in a high-resistance state.   
     
     
         2 . The system of  claim 1 , wherein the pinned layer is a symmetric synthetic antiferromagnet or a ferromagnetic layer with its magnetization pinned by adjacent antiferromagnetic layer. 
     
     
         3 . The system of  claim 1 , wherein the free layer is an asymmetric synthetic antiferromagnet or a polycrystalline or amorphous ferromagnetic layer film. 
     
     
         4 . The system of  claim 1  further comprising a cap layer and a buffer/seed layer. 
     
     
         5 . The system of  claim 1 , wherein a design of the MR sensor aids switching as a single domain. 
     
     
         6 . The system of  claim 1 , wherein the MR sensor is part of an array of MR sensors. 
     
     
         7 . The system of  claim 6 , wherein the array of MR sensors are arranged in symmetric N×N array, where N sensor sets are interconnected in parallel with each of the sensor sets comprises N sensors interconnected in series. 
     
     
         8 . The system of  claim 6 , wherein the array of MR sensors are arranged in asymmetric N 1 ×N 2  array, where N 1  sensor sets are interconnected in parallel with each of the sensor sets comprises N 2  sensors interconnected in series. 
     
     
         9 . The system of  claim 6 , wherein a surface of the MR sensor is functionalized with a first analyte binding agent. 
     
     
         10 . A method for forming a biosensor comprising:
 depositing a magnetoresistive (MR) film on a substrate, wherein the MR film provides a quasi-digital response to a magnetic field sweep, and the MR film comprises a free layer that is magnetic,   a pinned layer that is magnetic, and   a nonmagnetic layer sandwiched between the free and the pinned layers, wherein when magnetization directions of the free and the pinned layers are parallel, the MR sensor is in a low-resistance state, and when the magnetization directions of the free and the pinned layers are perpendicular, the MR sensor is in a high-resistance state;   patterning the MR film into a desired pattern; and   depositing leads in contact with the MR film.   
     
     
         11 . The method of  claim 10 , wherein the patterning step for the MR film comprises the steps of depositing a first bilayer resist on the MR film and patterning the first bilayer resist into a first pattern that is a long line or a T-shaped structure, transferring the first pattern to the MR film, and removing the first bilayer resist, and the method further comprises the steps of:
 depositing a second bilayer resist on the MR film and the leads;   patterning the second bilayer resist into a second pattern that is a long line or a T-shaped structure orthogonal to the first pattern;   transferring the second pattern to the MR film and the leads;   removing the second bilayer resist; and   depositing pads on the leads.   
     
     
         12 . The method of  claim 10 , further comprising the step of using an anisotropic conducting film (ACF) to bond the biosensor onto a printed circuit board (PCB), wherein the ACF is a conductive paste sandwiched between two plastic liners. 
     
     
         13 . The method of  claim 10 , further comprising the steps of:
 applying an anisotropic conducting film (ACF) to contact pads on a printed circuit board (PCB);   aligning the biosensor to the PCB;   applying pressure to the ACF between the biosensor and the PCB; and   curing the ACF to permanently bond the biosensor to the PCB.   
     
     
         14 . The method of  claim 10 , wherein the free layer is an asymmetric synthetic antiferromagnet or a polycrystalline or amorphous ferromagnetic layer film, and the pinned layer is a symmetric synthetic antiferromagnet or a ferromagnetic layer with its magnetization pinned by adjacent antiferromagnetic layer. 
     
     
         15 . The method of  claim 10 , wherein the MR sensor is part of an array of MR sensors. 
     
     
         16 . The method of  claim 15 , wherein the array of MR sensors are arranged in symmetric N×N array or the array of MR sensors are arranged in asymmetric N 1 ×N 2  array, where N 1 ≠N 2 , N 1  represents a number of sensors in series, and N 2  represent a number of sensor sets in parallel.