Abstract:
A bioelectronic device comprising a current carrying conductor and an electromagnet enabling frequency modulated biomolecular interaction control via the application of varying magnetic fields to magnetically labelled biomolecules. The device further comprises a magnetoresistive sensor located in proximity to the said conductor and carrying on its surface probe molecules. The device enables reducing assay times by using said magnetic field generating current carrying conductor in combination with an external oscillating magnetic field generator (electromagnet).

Description:
INTRODUCTION  
       [0001]     The invention relates to detection of biomolecules.  
         [0002]     It is known to provide a magnetic field sensor to detect magnetically labelled biomolecules. However, present biosensor and biochip devices (based on different types of sensor) utilise either: conventional (slow, diffusion-controlled) liquid phase molecular recognition reaction conditions (such as nucleic acid hybridisation conditions in DNA microarrays), which are fixed for any one detection experiment; or they employ electric fields to enhance the rates of biomolecular immobilisation or hybridisation processes by charge effects, primarily to reduce assay times. These techniques offer little control over the molecular recognition (sensing) conditions, other than changing the pH, salt or chemical composition of the sample medium (usually an aqueous phase buffering medium) by fluid flow. This is also a relatively slow process. Ferreira H A et al., “Biodetection using magnetically labelled biomolecules and arrays of spin valve sensors” Journal of Applied Physics, American Institute of Physics. New York, US, vol. 93, no. 10, 15 May 2003 (2003-05-15), pages 7281-7286, ISSN: 0021-8979 discloses a bioelectronic device comprising a current carrying conductor located adjacent, a magnetoresistive sensor having immobilized on its surface probe molecules adapted to capture magnetically labelled biomolecules. The present invention differs from the previous disclosure in that it provides an electromagnet adapted to apply an external varying magnetic field for moving the magnetically labelled target biomolecules over the sensor zone.  
         [0003]     Li Guanxiong et al., “Detection of single micron-sized magnetic bead and magnetic nanoparticles using spin valve sensors for biological applications” Journal of Applied Physics, American Institute of Physics. New York, US, vol. 93, no. 10, 15 May 2003 (2003-05-15) pages 7557-7559, ISSN:0021-8979, Baselt D R et al., “A biosensor based on magnetoresistance technology” Biosensors &amp; Bioelectronics, Elsevier Science Publishers, Barking, GB, vol. 13, no. 7-8, 3 June 1998 (1998-06-03), pages 731-739, ISSN: 0956-5663 and Edelstein R L et al., “The Barc Biosensor Applied to the Detection of Biological Warfare Agents” Biosensors &amp; Bioelectronics, Elsevier Science Publishers, Barking, GB, vol. 14, No. 10/11, January 2000 (2000-01), pages 805-813, ISSN: 0956-5663 describe bioelectronic systems comprising an electromagnet used to operate the magnetoresistive sensor. In the present invention the electromagnet is adapted to apply an external varying magnetic field in order to move target biomolecules enabling a considerable reduction of the assay time.  
         [0004]     Wirix-Speetjens R et al., “On-chip magnetic particle transport by alternating magnetic field gradients” IEEE Transactions on Magnetics IEEE USA, vol. 40, no. 4, July 2004 (2004-07), pages 1944-1946, ISSN: 0018-9464 discloses the possibility of attracting magnetic particles by two DC current carrying conductors having saw-tooth shape and moving said particles along said conductors by alternating the current between said conductors (page 1944). The present invention provides a reduction on the assay time by moving the biomolecules along the sensor zone due to the additional provision of an electromagnet.  
         [0005]     The invention is therefore directed towards providing an improved bio-electronic device for detection of biomolecules.  
       STATEMENTS OF INVENTION  
       [0006]     According to the invention, there is provided a bioelectronic device comprising a current carrying conductor and an electromagnet enabling frequency modulated biomolecular interaction control via the application of varying magnetic fields to magnetically labelled biomolecules.  
         [0007]     In one embodiment, further comprising a biomolecular sensor located in proximity to the conductor.  
         [0008]     In another embodiment, the device is integrated in a chip.  
         [0009]     In a further embodiment, the conductor is in a pattern having one or more lines in close proximity and the sensor is located between the lines.  
         [0010]     In one embodiment, the sensor is a magnetoresistive sensor.  
         [0011]     In another embodiment, the sensor and the conductor together form a micro-electromagnetic unit arrayed onto the chip.  
         [0012]     In a further embodiment, there is a plurality of said units on the chip, and they are electronically addressable.  
         [0013]     In one embodiment, the chip surface is functionalised with a probe.  
         [0014]     In another embodiment, the probe is patterned.  
         [0015]     In a further embodiment, the micro-electromagnetic unit generates electromagnetic fields in two phases, a first DC phase to attract biomolecules, and a second phase with an alternating magnetic field and frequency modulation.  
         [0016]     In one embodiment, the alternating magnetic field is in the plane of the chip and orthogonal to the direction of the proximal conductor.  
         [0017]     In another embodiment, the DC and AC phases are applied simultaneously.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0018]     The invention will be more clearly understood from the following description of some embodiments thereof, given by way of example only with reference to the accompanying drawings in which:  
         [0019]      FIG. 1  is a representation of a current conductor of a bioelectronic device of the invention;  
         [0020]      FIG. 2  is a representation of an alternative conductor, incorporating a spin valve sensor;  
         [0021]      FIG. 3  is a representation of interlinking of sensing units;  
         [0022]      FIGS. 4 and 5  are diagrams showing operation of the device;  
         [0023]      FIG. 6  is a diagram illustrating the device in use in perspective;  
         [0024]      FIG. 7  includes cross-sectional and plan views of a device with relative size of a biomolecule illustrated;  
         [0025]      FIG. 8  is a series of diagrams showing operation of the device in more detail;  
         [0026]      FIG. 9  includes diagrams showing energy plots across the device;  
         [0027]      FIGS. 10 and 11  are diagrams of alternative devices of the invention; and  
         [0028]      FIGS. 12 and 13  are images showing a device active surface at different stages of use. 
     
    
       [0029]     The invention provides a bio-electronic device of multiple microfabricated electronic units on a single chip. The device is used to controllably place, detect and manipulate biomolecules labelled with micrometer or nanometer sized magnetic beads or particles. Application domains include DNA chips, protein chips, biosensors, diagnostics and biomolecular interaction studies.  
         [0030]     Magnetic fields either generated on-chip using current carrying structures or applied to the chip using an electromagnet effect the rapid focusing, manipulation and detection of magnetically labelled biomolecules and allow the study of a wide range of conditions on biomolecular interaction events including recognition events (e.g. DNA hybridisation) and biomolecular release (e.g. DNA dehybridisation).  
         [0031]     The device comprises on-chip micro-fabricated current carrying metallic lines to facilitate the precisely controlled movement of magnetically labelled biomolecules at on-chip biosensor sites and the investigation of frequency modulated biomolecular interaction. A probe biomolecule (or species) is immobilised over a designated area of the chip within a defined current line structure fabricated with or without associated on-chip sensors (preferably magnetoresistive, magnetic-field, electric field or optical sensors) and magnetically labelled target biomolecules are introduced to the fluid on the chip (preferably using controlled fluid flow via microfluidic channels). The magnetically labelled target biomolecules (or species) are rapidly focussed at a specifically designed micron-sized electromagnetic unit consisting of the current carrying line and a sensor or array of sensors fabricated within the line, using a current passed through the line structure.  
         [0032]     Referring to  FIG. 1 a  “U-shaped” current line fabricated on-chip and passivated with silicon dioxide is shown. The dimensions of the line are represented by “t” (thickness), “w” (width), “l” (length), and “s” (space between the arms of the line). A function generator is used to apply an alternating magnetic field in the vicinity of the current line to enable the controlled movement of the magnetically labelled target species back and forth across the probe covered (sensor) area. Frequency modulation is then used to facilitate the manipulation of the interaction of the probe and target species. The magnetically labelled target biomolecules or species are repeatedly passed across the probe biomolecules or species within the unit at a speed dictated by the chosen frequency. The micro-electromagnetic unit can be used to control the contact time between the sensor bound biomolecule or species and the magnetically labelled biomolecule or species and to investigate the effect of different frequencies on the interaction of the two species e.g. biomolecular recognition events (such as nucleic acid hybridisation or protein-protein interaction) or biomolecular release mechanisms (such as the nucleic acid dehybridisation or the unbinding of proteins with particular affinity such as antibody-antigen). Biochip or biomolecular toolboxes based on the fabrication of numerous microfabricated electromagnetic units per chip potentially enable improved hybridisation efficiencies, diagnostic dehybridisation data, and highly specific discrimination between very similar target biomolecules such as single base mutations in nucleic acid sequences (single nucleotide polymorphisms SNPs), which are extremely important in the diagnosis of genetic diseases.  
         [0033]     The device comprises on-chip microfabricated current (AC or DC) carrying metallic lines (e.g. composed of aluminium, copper or gold) with or without a magnetic component (e.g. nickel-iron cladding layer) and with variable design (geometry and geometrical dimensions), which facilitate, through the passage of current, the creation of current density gradients and consequently on-chip local magnetic fields of varying strength. The narrower parts of the fabricated lines, which produce a higher magnetic field are used to attract magnetic microspheres or nanoparticles (carriers, functionalised with biomolecules), to a particular region of the chip and also allow the precise manipulation of the movement of the magnetic labels in the immediate vicinity. A simple example of such a line design is shown in  FIG. 1 .  
         [0034]     The device may also include a sensor or sensor array (magnetoresistive, magnetic or non-magnetic) integrated within the current carrying line design (in the area in which the magnetic labels are focussed and manipulated). An example shown in  FIG. 2  features a U-shaped magnetoresistive spin valve sensor fabricated within the U-shaped current line. The sensor or sensors could be linear, rectangular, square, U-shaped, meander or spiral in shape and may be a spin-valve, planar Hall sensor, magnetic tunnel junction, other magnetic field sensor or non-magnetic (e.g. optical) sensor in the case where the magnetic labels have an additional label enabling detection (e.g. fluorescence). The combination of the current carrying line and the sensor/s constitutes a “micro-electromagnetic unit”, which can be operated as a single unit, paired ( FIG. 3 ) or arrayed on the chip (see “prototype”). These units can be electronically addressed either individually or as pairs or groups simultaneously or sequentially. More specifically,  FIG. 3  shows an example of how sensing units (current line and sensor/s) can be linked together using common current and sensor lines, facilitating a larger number of sensing units per chip. The current line is narrower at the U-shaped feature in order to increase the current density in that area of the line and hence increase the magnetic field produced in that area.  
         [0035]     A “probe” biomolecule or species of interest (biological, clinical, diagnostic or academic) to the user, which may be naturally occurring, biologically or chemically synthesized, chosen for the detection of the binding of a secondary, complementary target biomolecule is immobilised across the surface of the chip, spotted, arrayed or otherwise patterned preferably across the area of the sensor or sensing unit to achieve a single or multi-probe chip ( FIG. 4 ). The immobilised biomolecule may be nucleic acid (DNA, RNA), a protein (antibody, receptor), a peptide, a synthetic molecule (synthon), a cell or a micro-organism.  FIG. 4  shows a cross-sectional scheme through the chip showing the preferred placement of probe biomolecules across the chip surface in the sensor or sensor-free zone between the two arms of the U-shaped current line.  
         [0036]     A magnetic label (or carrier) is functionalised with a “target” biomolecule or species and introduced (using a pipette, a syringe or controlled microfluidics) into the fluid (usually a biological buffering medium) on the chip after positioning of the probe biomolecule/s or species ( FIG. 5 ).  
         [0037]      FIG. 5  shows a cross sectional scheme through the chip showing the attraction of magnetically labelled target biomolecules to the two arms of the U-shaped current line and the subsequent controlled movement of the magnetically labelled target biomolecules back and forth across the sensor zone between the two arms of the current line. The former is effected using a DC current through the U-shaped line and the latter via the application of an AC field using an electromagnet positioned above the chip. The magnetic label can vary in size (most probably from a few nanometers to a few micrometers in diameter), chemical and magnetic composition (polymer, co-polymer matrix or encapsulated iron-oxide or transition metal ion containing) and magnetic content (5-100%). The magnetically labelled target species may be a biomolecule (a synthon, nucleic acid or protein) or (in principle) it may be a cell or microorganism.  
         [0038]     An electromagnet, either external to the chip/chip carrier and positioned in such a way as to apply and regulate a magnetic field in the appropriate plane and direction on-chip (e.g. horseshoe magnet or coil), or an on-chip fabricated micro-electromagnet for the same use.  
         [0000]     Device Operation  
         [0039]     The functioning of a single micro-electromagnetic unit is represented schematically in  FIGS. 5 and 6 . One method of using the device is as follows:  
         [0040]     The chip surface is pre-functionalised with a particular probe or number of probe species, preferably patterned in the designated area or areas associated with the on-chip current line feature/s (e.g. within the arms of a U-shaped current line). The magnetically labelled target species or heterogeneous mixture (soup) of magnetically labelled target species is then introduced into the fluid (water or buffer) over the chip (FIGS.  5 / 6 ). A current is then passed through the current line structure ( FIG. 7 ) attracting and focussing the magnetically labelled target species at a particular region of the current line structure (e.g. both sides or arms of the U-shaped current line). When sufficient numbers of magnetically labelled targets have accumulated (usually on a timescale of seconds), an alternating magnetic field is then applied across the current line structure (e.g. across the U-shaped current line) in the plane of the chip and at a right angle to the length of U-shaped current line (see central arrow in  FIG. 6 ).  
         [0041]     In more detail,  FIG. 6  is a schematic representation of a single functional unit of the invention showing the four basic features: (1) A “U-shaped” current line; (2) A sensor or sensor-free area between the arms of the U-shaped current line (depicted here with a U-shaped spin valve sensor as in  FIG. 2 ); (3) Probe biomolecules immobilised over the sensor or sensor-free area and (4) Magnetically labelled target biomolecules introduced into the fluid on the chip. The U-shaped current line is used to create an attractive magnetic force (F 1 ) using a DC current, focussing the magnetically labelled target biomolecules at each arm of the current line. An alternating magnetic field is then applied across the line structure to create a force (F 2 ), which controllably moves the magnetically labelled target biomolecules back and forth from one arm of the U-shaped current line to the other across the probe biomolecule area.  FIG. 7  shows a cross sectional (top) and top view (below) schematics of U-shaped current line structure showing the dimensions used to calculate the magnetic force or energy produced by the line on the magnetic label at a given current (I) and at a given distance from the current line. The current creates a horizontal (y-axis) magnetic field {right arrow over (H)} y =H y {right arrow over (e)} y  and a vertical magnetic field {right arrow over (H)} z =H z {right arrow over (e)} z  at a height  
         a   =     h   +   t   +     ⅆ     2   ⁢                   ,       
 
 t is the thickness of the passivating layer on the chip and h is the thickness of the current line and d is the diameter of the magnetic label. 
 
         [0042]     Referring to  FIG. 8 , this shows a cross sectional schematic to show: (a) How magnetically labelled target species are attracted to the arms of the U-shaped current line by a magnetic force F 1 ; (b) The alternating force F 2  that moves the magnetic labels back and forth across the probe functionalised area (within the U-shaped current line) as a result of the applied alternating magnetic field (magnetic label velocity being frequency dependent) and; (c) The way in which this process saturates the probe species area with magnetically labelled target species.  FIG. 9  shows a cross sectional schematic through (top) and across (below) a U-shaped current line showing the direction of a current (I) through the line and an applied alternating magnetic field (H), producing a fluctuating magnetic energy profile (see chart, au=arbitrary units) effecting the movement of the magnetic labels from one arm of the U-shaped line to the other.  
         [0043]     The alternating field causes the magnetically labelled targets to move back and forth from one side of the U-shaped structure to the other at a frequency dependent velocity ( FIG. 8 ). During this period of operation the frequency may be varied as required effecting changes in the movement and behaviour of the magnetic labels, local temperature changes and potentially, chemical or conformational changes in the probe or target species. A profile showing the changes in magnetic energy which occur during the application of the alternating field is shown in  FIG. 9 .  
         [0000]     Alternative Methods of Use Include:  
         [0044]     Firstly, the DC current through the current line structure and the AC magnetic field may be applied simultaneously from the beginning of the experiment. Secondly, the nature of the current passed through the line may also be AC used in combination with a DC applied field (with or without an AC component). Thirdly, the current passed through the current line may have an AC and DC component in combination with an applied field having both AC and DC components. The applied field may also be in a vertical direction to the line as opposed to horizontal for other line geometries.  
         [0000]     This Technique Enables the Experimentalist to:  
         [0000]    
       
         
           
              (i) Focus and hence concentrate target species at sensor or sensor-free sites on-chip, enabling the use of low target concentrations.  
              (ii) To control the contact time (via magnetic label velocity) between probe and target species in order to optimise the binding of probe and target  
              (iii) To effect local temperature changes  
              (iv) To effect frequency dependent probe and target binding studies  
              (v) To effect frequency dependent probe and target release studies 
 
 Structural Parameters 
 
           
         
       
     
         [0050]     The current carrying metallic lines used to attract and manipulate the magnetically labelled biomolecules may be simple or complex in design. They may be single narrow lines, U-shaped, V-shaped (tapered), meander, spiral or circular (loop) used in combination with vertical or horizontal applied magnetic fields. The dimensions are on the micrometer scale, but could be as large as millimetre or as small as nanometer (which in principle could be used to attract and manipulate single nanometer-sized magnetic labels). As an example, the U-shaped current carrying metallic structures ( FIG. 1 ) could be fabricated with dimensions of length (l) from 10 μm to 1 mm, width (w) 2-20 μm, space between the arms of the U-shape (s) 2-20 μm and thickness (t) 100-500 nm. However, functional structures with dimensions outside of these values are feasible.  
         [0051]     The nature of the sensor (optional), probe species, target species and electromagnet may vary. The magnetic labels used may also vary in content, but would almost certainly be of nanometer to low micrometer in diameter.  
         [0000]     Operational Parameters  
         [0052]     The current passed through the metallic structures (U-shaped or otherwise) has certain constraints. The minimum current must generate a magnetic field (in a certain region of the line e.g. the U-shape) of sufficient magnitude to attract and move magnetic labels of a particular mass, diameter and magnetic composition. The maximum current must not generate sufficient heat to damage the structure (or generate electromigration) and/or the probe and target biological species (denaturation or cell damage). For U-shaped structures with specific dimensions defined under “structural parameters” above, the current passed may be &gt;10 and &lt;200 mA. The alternating magnetic field applied to the structure via an on-chip or external electromagnet can also vary. The range of the alternating field that can be used depends on the device used to create the field (horseshoe magnet, coil or on-chip structure) and the current passed through the device. It is known that an increase in the field increases the force acting on the magnetic labels, but as yet the constraints on the magnitude of the field that can be used are unknown (i.e. the field used must be &gt;0 Oe).  
         [0053]     The range of the frequency applied to the magnetic labels in the desired region of the chip (preferably a sensor region) can be divided into two regimes: At a particular range (dependent on several features of the invention, including the current line structure and the magnetic labels used) the applied frequency effects the velocity with which the magnetic labels are moved back and forth across the desired region. For the current line structure featured in  FIG. 1 , a frequency range of 0.1-20 Hz moves 250 nm sized magnetic labels (Nanomag-D, Micromod, Germany) back and forth from one arm of the U-shaped line to the other at velocities which can easily be distinguished by eye via a microscope positioned above the chip. At frequencies above this range (for the stated current line structure) the magnetic labels no longer appear to move, but may vibrate. Thus once positioned in the desired region the interaction of a magnetically labelled target species with a probe species (preferably sensor-bound) can be studied at a much wider range of frequency (0.1 Hz to GHz range). This frequency range can be used to perform biological interaction studies. The application of AC magnetic fields may also be used to effect on-chip local temperature changes (increase) by power absorption from the magnetic label.  
         [0054]     The micro-electromagnetic units described can be fabricated as single units or arrays on-chip to facilitate multi-probe or multi-analyte detection devices or biomolecular toolboxes for the study of biomolecular recognition. The first aspect of prototype design is the layout of the chip. The chip dimensions (usually mm scale) are defined and the available chip surface is used as efficiently as possible in such a way as to maximize the active sensing area within each sensing unit, to incorporate appropriate reference sensors and yet avoid electrical, magnetic or thermal cross-talk between sensors or on-chip current line structures. A differential sensor set-up uses a reference sensor in a Wheatstone bridge architecture to enable thermal and electrical drift compensation between a biologically active sensor and an biologically inactive sensor. The design of a first prototype based on the combination of U-shaped current line structures with spin-valves sensors is shown in  FIGS. 10 and 11 .  FIG. 10  shows a single micro-electromagnetic unit (a) of the device featuring a U-shaped current line structure (shaded) combined with a U-shaped magnetoresistive spin-valve sensor (black). These units can be fabricated and electronically addressed as individual units or connected to further units as shown in (b) two micro-electromagnetic units connected by common current and sensor lines. Note how the current line structure is tapered in width toward the U-structure in order to increase current density in the U-shaped parts of the line.  FIG. 11  shows (a) an array of micro-electromagnetic units defined in the centre of a chip in four rows of six units, each comprised of one U-shaped current line and U-shaped spin valve sensor. (b) An 8×8 mm chip showing the contact pads (□) and lines connecting current lines for the 4×6 array of micro-electromagnetic units. The connection lines are designed to allow units to be electronically addressed either individually, as pairs or as an array.  
         [0055]     This chip was fabricated with twenty four U-shaped current line structures each having a U-shaped spin valve sensor fabricated within the arms of the U-shaped current line. A single micro-electromagnetic unit and a pair of such units fabricated with common connecting lines are shown in  FIG. 10 . An array of twenty four (four rows of six units) and the full chip layout (including contact pads) is shown in  FIG. 11 . The chips were fabricated on 3″ silicon wafers using microelectronic processing techniques under cleanroom conditions. The structures are defined using laser lithography and sensor materials were deposited by sputtering. The integrity of the on-chip structures was then assessed via microscopic inspection and electrical resistance measurements. A protective (passivation) layer was deposited over the chip structures to prevent corrosion of the chip surface by fluids applied during the chemical and biological reactions. This material (substrate) should also provide ease of surface functionality for the immobilisation of biomolecules or cells and ideally show low non-specific adherence of magnetic labels, polymers, proteins, nucleic acids and cells. Sputtered silicon dioxide or silicon nitride are suitable. Only the electrical contacts at the outer edges of the chip remain free of the passivation material. The wafer is then diced into individual chips (in this instance 8×8 mm in dimension) and each chip is mounted in a chip carrier for easy connection to hardware. The contacts are wire bonded to the contact pads (shown as squares around the edge of the chip layout in  FIG. 11   b ), which are then protected by a silicon gel or microfluidic channels are used to control fluid flow across the chip.  
       EXAMPLES  
       [0056]     A sensor-free chip was fabricated with U-shaped current lines to demonstrate the “proof of principle” of the device using DNA-DNA hybridisation (i.e. the binding of a DNA probe with a complementary magnetically labelled DNA target) as a model for the use of the invention to (i) perform a rapid DNA hybridisation experiment and (ii) effect a frequency manipulated biomolecular recognition process.  
         [0000]     Chip and Probe Preparation  
         [0057]     The on-chip U-shaped current line structures were fabricated with dimensions ( FIG. 1 ) 100 μm long, 10 μm wide and 3000 Å thick with a space between the arms of the U-shaped line of 10 μm and passivated (covered) with a layer of silicon dioxide of 2000 Å. Probe DNA molecules (50mer oligonucleotides corresponding to a specific sequence in the cystic fibrosis transmembrane regulator (CFTR) gene, where the most common cystic fibrosis mutation delF508 occurs) were immobilised across the full chip surface. The chip was placed within the electronic set-up (associated hardware) equilibrated in a hybridisation buffer (50 mM histidine buffer) and positioned beneath the zoom lens of a microscope (Leica DMLM) fitted with a camera (JVC) in order to record images of the movement and binding (hybridisation) of the magnetic labels on the chip surface.  
         [0000]     Target Preparation  
         [0058]     Double stranded target DNA (consisting of a 96 bp sequence having a region of DNA complementary to the probe DNA sequence) was 3′-end biotinylated (Pierce kit) and incubated for 2 hours with 250 nm Nanomag-D magnetic labels (Micromod) functionalised with streptavidin. This solution was then centrifuged in a benchtop centrifuge in order to spin down (pellet) the magnetic labels, which were then resuspended and washed in phosphate buffer, 100 mM, pH7.2. This provided magnetic nanoparticles functionalised with probe-complementary target DNA. This preparation was boiled at 95° C. for 5 mins and immersed in ice prior to the experiment to produce single stranded magnetically labelled target DNA.  
         [0000]     Experimental Conditions  
         [0059]     A current of 40 mA (DC) was passed through the U-shaped current line structure and the magnetically labelled target DNA was added to the chip (to give a biological target concentration of approx. 100 μM (picomolar). The magnetic labels were observed to move toward the U-shaped current line and accumulate on the top of the line. After 2 mins an alternating external magnetic field of +/−18.4 Oe rms was applied across the U-shaped line (at a right angle to the length of the arms of the U-shaped line in the plane of the chip). Simultaneously a pulse generator was used to apply a particular frequency to the chip. After 5 mins the process was stopped, the chip surface washed with buffer (100 mM phosphate buffer containing 150 mM sodium chloride, pH 7.2) and an image of the chip surface in the region of the U-shaped line was recorded. The chip surface was then re-equilibated in hybridiation buffer (50 mM histidine) and the same process was then repeated for a period of 20 mins and a further image of the chip surface was recorded. In one experiment, a frequency of 0.2 Hz was used during the process and in a second identical experiment a frequency of 10 Hz was applied.  
         [0000]     Results  
         [0060]     The respective images of the chip surface at times 0, after 5 mins and after a further 20 mins are shown in FIGS.  12 / 13  respectively, illustrating: (i) Rapid hybridisation (5-25 mins) of probe and magnetically labelled target DNA; (ii) Increased hybridisation of the magnetically labelled target DNA with surface immobilised probe DNA in the area in between the arms of the U-shaped line as compared with the chip surface outside of the U-shaped line region and; (iii) A potential frequency effect on the degree of the hybridisation between the magnetically labelled target and the surface-bound probe.  
         [0061]     In more detail,  FIG. 12  shows images of an on-chip U-shaped current line structure at different stages during a magnetic field assisted DNA hybridisation experiment. A cystic fibrosis (CF) oligonucleotide probe (50mer) was immobilised across the whole chip surface and 250 nm magnetic particles (Nanomag-D, Micromod, Germany) functionalised with the complementary target DNA sequence were introduced. A direct current of 40 mA was passed through the line to attract the magnetic particles to the line and an alternating magnetic field of +/−18.4 Oe rms and an applied frequency of 0.2 Hz. Hybridisation of the DNA was assessed by visualisation of the particles on and in between the line structure at time (a) 0 mins, and after washing at time (b) 5 mins and (c) 20 mins operation of the device.  FIG. 13  shows images of an on-chip U-shaped current line structure at different stages during a magnetic field assisted DNA hybridisation experiment. A cystic fibrosis (CF) oligonucleotide probe (50mer) was immobilised across the whole chip surface and 250 nm magnetic particles (Nanomag-D, Micromod, Germany) functionalised with the complementary target DNA sequence were introduced. A direct current of 40 mA was passed through the line to attract the magnetic particles to the line and an alternating magnetic field of +/−18.4 Oe rms and an applied frequency of 10 Hz. Hybridisation of the DNA was assessed by visualisation of the particles on and in between the line structure at time (a) 0 mins, and after washing at time (b) 5 mins and (c) 20 mins operation of the device.  
         [0062]     It will be appreciated that the invention offers both reduced assay times and the ability of the user to vary the biomolecular recognition conditions rapidly during the detection (sensing) process. The ability to change the way in which the molecular recognition process occurs in-situ, allows the user the potential to optimise the molecular interaction process and the detection process and to study the recognition process in an entirely new way. The invention allows the alteration of temperature and the determination of local temperatures on-chip, the control of contact time between sensor-bound probe biomolecules and (magnetic-field) controlled magnetically labelled target biomolecules and most significantly the ability to study biomolecular recognition processes at different applied frequencies. This offers the development of devices that can be used to perform unique frequency controlled on-chip biomolecular interaction experiments.  
         [0063]     The invention would be attractive to licensees as it offers a biomolecular toolbox for the study of specific biological recognition processes and a detection system with the potential to discern small structural differences in heterogeneous biomolecular target compositions. This could be applied to drug screening, cell screening, antibody-antigen engineering or single base nucleic acid base mismatch mutation detection in the diagnosis of genetic diseases.  
         [0064]     The invention is not limited to the embodiments described but may be varied in construction and detail.