SPINTRONIC MAGNETIC NANOPARTICLE SENSORS WITH AN ACTIVE AREA LOCATED ON A MAGNETIC DOMAIN WALL

• US 20110037463A1
• Filed: 04/22/2009
• Published: 02/17/2011
• Est. Priority Date: 04/23/2008
• Status: Active Grant

• Current Assignee: Politecnico di Milano
• Original Assignee: Politecnico di Milano
• Inventors: Vavassori, Paolo, Bertacco, Riccardo
• Granted Patent: US 8,779,763 B2
• Time in Patent Office: Days
• US Class Current: 324/244
• CPC Class Codes: G01N 33/54346 Nanoparticles
• CPC Class Codes: G01R 33/1284 Spin resolved measurements; Influencing spins during measurements, e.g. in spintronics devices G01R33/093 takes precedence; semiconductor devices using spin polarized carriers H01L29/66984

Abstract

A sensor is described for detecting the presence of a magnetic nanoparticle (N). The sensor is arranged on a support (1), on which a plurality of non-magnetic contacts (Iin, GND, V1, V2) electrically conductively connected to the sensor is disposed. The contacts are adapted to be connected to means for measuring magnetoresistance. The sensor includes a planar ferromagnetic nanostructure (3), comprising a detection area (31) shaped as a strip bent to form a corner. The detection area is adapted to selectively assume, as a response to an applied magnetic field, a first spin configuration comprising a transverse “head-to-head” domain wall (TW), and a second spin configuration, wherein such domain wall (TW) is absent. The transition from the first configuration to the second configuration is affected by the proximity of a magnetic nanoparticle (N) to the detection area.

Claims

1. A sensor for detecting the presence of a magnetic nanoparticle (N), said sensor being arranged on a support (1), on which also a plurality of non-magnetic contacts (Iin, GND, V1, V2) is arranged, electrically conductively connected to the sensor, said contacts being adapted to be connected to means for measuring magnetoresistance on the sensor,

characterized in that it includes a planar ferromagnetic structure (3), comprising a detection area (31), shaped as a strip bent to form a corner, said detection area being adapted to selectively assume, as a response to an applied magnetic field, a first spin configuration comprising a transverse “

head-to-head”

domain wall (TW), and a second spin configuration, wherein such a domain wall (TW) is absent, wherein said transition from the first configuration to the second configuration is provided for an applied magnetic field, having a component which is parallel to one of the angled sides of the detection area with an intensity higher than a transition threshold (H_1x);

said transition threshold, magneto-resistively detectable, being affected by the proximity of a magnetic nanoparticle (N) to the detection area

2. The sensor according to claim 1, wherein the nanostructure (3) consists of the detection area (31), on which opposite ends, relative terminal discs (32) are placed.

3. The sensor according to claim 2, wherein said contacts comprise a pair of injection contacts (Iin, GND) arranged from opposite ends of the detection area (31), which are adapted to enable the injection of an electric current through the detection area (31), and a pair of reading contacts (V1, V2) arranged from opposite ends of the detection area (31), which are adapted to enable a measurement of the potential difference (V_A, V_B) between the ends of the detection area (31).

4. The sensor according to at least one of the preceding claims, wherein in said first spin configuration the “

head-to-head”

domain wall (TW) is so as to trap and trail towards the detection area (31) a magnetic nanoparticle.

5. The sensor according to at least one of the preceding claims, wherein the sensor is arranged so as to perform single molecule detection and/or to be employed in systems for synthesis at a single molecule level and/or analysis at a single molecule level.

6. A sensor array for detecting target molecules, to which magnetic nanoparticles (N) are bound as markers, said sensor array comprising a support (1) provided with:

a plurality of detection sites (DS), to which respective binding molecules are associated, adapted to selectively bind with said target molecules, and respective sensors, each being adapted to detect the presence of a magnetic nanoparticle (N) in the respective detection site (DS),

characterized in that each sensor is realized in accordance with at least one of the preceding claims.

7. The array according to claim 6, wherein said sensors are arranged to form a plurality of side by side sensor chains (300), wherein each sensor chain is made by a plurality of one-piece nanostructures (3), each one-piece nanostructure being made by the detection area (31) shaped as a strip bent to form a corner, at the ends of which respective terminal discs (32) are placed, said one-piece nanostructures being connected, so that each one-piece nanostructure shares a terminal disc (32) with the following one.

8. The array according to claim 7, wherein said contacts comprise a plurality of injection contacts (Iin, GND;

Ii_in, GND), adapted to enable the injection of an electric current through the detection area (31) of each one-piece nanostructure, and a plurality of reading contacts (310, 320;

410, 420), adapted to enable a measurement of the potential difference between the ends of the detection area (31) of each unit nanostructure.

9. The array according to claim 8, wherein said reading contacts (310, 320) are arranged such that the detection areas (31) of the one-piece nanostructures corresponding, in position on the different sensor chains (300), are connected in parallel, said sensor chains being connected in parallel to a pair of said injection contacts (Iin, GND) to allow the simultaneous injection of respective electric currents through the sensor chains (300).

10. The array according to claim 8, wherein said reading contacts (410, 420) are two and are simultaneously connected to the different sensor chains (300), and are arranged so that the detection areas (31) of each sensor chain are connected in series, each sensor chain being connected to a respective contact (Ii_in) of said injection contacts to allow the independent injection of a respective electric current through each sensor chain.

11. A method for detecting target molecules, to which magnetic nanoparticles (N) as markers are linked, the method comprising the following steps:

providing a sensor array according to one of claims from 6 to 10,

applying a first magnetic field, in order to obtain said first spin configuration in each nanostructure (3), and subsequently removing said first magnetic field;

delivering a biological sample containing said target molecules above the detection sites (DS);

applying a second magnetic field in order to switch said first spin configuration to said second spin configuration in each nanostructure (3), and subsequently removing said second magnetic field;

removing the target molecules, not chemically linked to the binding molecules, from the detection sites (DS);

applying a third magnetic field in order to obtain, again, said first spin configuration in each nanostructure (3), and subsequently removing said third magnetic field; and

carrying out measurements of the critical transition field from said first spin configuration into said second spin configuration through magnetoresistance measurements on the sensors, through said plurality of contacts.