A BIOSENSOR WITH INTEGRATED ANTENNA AND MEASUREMENT METHOD FOR BIOSENSING APPLICATIONS

Abstract

The present invention relates to a biosensor (1) which enables the concentration of a desired molecule inside a liquid in the medium, and essentially comprises at least one metallic plate (2) which functions as a ground plate, and which is preferably manufactured from aluminum, at least one dielectric substrate (3) which is located on top of the metallic plate (2), at least one split-ring resonator (4) which is realized on top of the dielectric substrate (3), and which is coated with a dielectric layer, at least two symmetrical antennas (5) which are realized on the same plane with the split-ring resonator (4) on the substrate (3), at least two ports (6) where a network analyzer is connected with the antennas (5) via SMA (SubMiniature Version A) connectors.

Claims

1. A biosensor, which enables measuring the concentration of a desired molecule inside a liquid medium, comprising: at least one metallic plate which functions as a ground plate, and which is preferably manufactured from aluminum; at least one dielectric substrate which is located on top of the metallic plate; and at least one split-ring resonator which is realized on top of the dielectric substrate, and characterized by at least two symmetrical antennas which are realized on the same plane with the electrically passive split-ring resonator on top of the dielectric substrate and which are exciting the electrically passive split-ring resonator by emitting electromagnetic waves, the metallic plate which enables the electromagnetic waves emitted from the antennas to be transmitted to the electrically passive split-ring resonator by reflecting the said electromagnetic waves, and at least two ports where a network analyzer is connected to the antennas.

2. The biosensor according to claim 1, characterized by two symmetrical monopole patch antennas.

3. The biosensor according to claim 1, characterized by a SMA connector which enables the connection with the antennas.

4. The biosensor according to claim 1, characterized by metallic structures which are formed in order to be excited with a magnetic field perpendicular to its own plane at a resonant frequency blown as magnetic resonance (f.sub.m) and behaves as a LC resonator, and the geometry of which is a result of lithography and wearing with oxygen plasma.

5. The biosensor according to claim 1, characterized by split-ring resonator which is coated with a dielectric layer that is a parylene (P) layer.

6. The biosensor according to claim 1, characterized by substrate which is manufactured from FR4 material.

7. The biosensor according to claim 1, characterized by substrate which is manufactured from alumina material.

8. The biosensor according to claim 1, characterized by substrate which is manufactured from mica material.

9. A method which enables determining the concentration of a desired molecule inside a liquid in the medium by using a biosensor, wherein the biosensor, which enables measuring the concentration of a desired molecule inside a liquid medium, comprises: at least one metallic plate which functions as a ground plate, and which is preferably manufactured from aluminum; at least one dielectric substrate which is located on top of the at-least one metallic plate; and at least one split-ring resonator which is realized on top of the dielectric substrate, and characterized by at least two symmetrical antennas which are realized on the same plane with the electrically passive split-ring resonator on top of the dielectric substrate and which are exciting the electrically passive split-ring resonator by emitting electromagnetic waves, the metallic plate which enables the electromagnetic waves emitted from the antennas to be transmitted to the electrically passive split-ring resonator by reflecting the said electromagnetic waves, at least two ports where a network analyzer is connected to the antennas, wherein the method is characterized by the steps of incubating probe molecules in a certain concentration (for example FGF-2) on the surface of split-ring resonator coated with a dielectric layer, placing a droplet in a certain volume on a certain location on the split-ring resonator at room temperature, and waiting for a determined time in order to coat the area subjected to incubation with the probe molecules (for example FGF-2) uniformly, applying an electric signal on two symmetrical antennas which are coplanar with the split-ring resonator, converting the said electric signal to electromagnetic wave by the antennas and exciting the split-ring resonator, measuring the transmission and reflection characteristics of split-ring resonator with a vector network analyzer, drying the surface, placing a droplet comprising a second molecule (for example heparin (H)) in a certain volume and concentration, applying an electric signal on two symmetrical antennas which are coplanar with the split-ring resonator, converting the said electric signal to electromagnetic wave by the antennas and exciting the split-ring resonator, measuring the transmission and reflection characteristics of split-ring resonator again with a vector network analyzer, comparing the transmission and reflection characteristics of split-ring resonator which are measured to reference measurements, and thus determining the concentration of the second molecule added to the medium.

10. The method according to claim 9, characterized by reference measurements, which are obtained by a) incubating probe molecules in a certain concentration (for example FGF-2) on the surface of split-ring resonator coated with a dielectric layer, b) placing a droplet in a certain volume on a certain location on the split-ring resonator at room temperature, and waiting for a determined time in order to coat the area subjected to incubation with the said probe molecules (for example FGF-2) uniformly, c) drying the surface, placing a droplet comprising a second molecule (for example heparin (H)) in a certain volume with a certain concentration, applying an electric signal on two symmetrical antennas which are coplanar with the split-ring resonator, d) converting the said electric signal to an electromagnetic wave by the antennas and exciting the split-ring resonator, e) measuring the transmission and reflection characteristics of split-ring resonator again with a vector network analyzer and recording the data.

11. The biosensor according to claim 2, characterized by a SMA connector which enables the connection with the antennas.

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Description

BRIEF DESCRIPTION OF DRAWINGS

[0025] A biosensor developed to fulfill the objectives of the present invention is illustrated in the accompanying figures, in which:

[0026] FIG. 1 is the perspective view of the inventive biosensor.

[0027] FIG. 2a is the schematic view showing the locations of deionized water droplets in volume of 16 μL on the metallic plate in one embodiment of the invention.

[0028] FIG. 2b is the measured reflection (s11) characteristic.

[0029] FIG. 2c is the measured transmission (s21) characteristic.

[0030] FIG. 3a is the experiment schematic showing the functionalization of biosensors with biomolecules.

[0031] FIG. 3b is the reflection (s11) characteristic measured during experiments.

[0032] FIG. 3c is the transmission (s21) characteristic measured during experiments.

[0033] FIG. 4 is a curve showing the observed linear decrease in resonant frequency relative to heparin molecular concentration increase.

[0034] The components shown in the figures are each given reference numbers as follows:

[0035] 1. Biosensor

[0036] 2. Metallic plate

[0037] 3. Substrate

[0038] 4. Split-ring resonator

[0039] 5. Antenna

[0040] 6. Port

[0041] F. FGF-2

[0042] U. Heparin

[0043] L. Water droplet

[0044] P. Parylene

[0045] K1. Location—1

[0046] K2. Location—2

[0047] K3. Location—3

[0048] K4. Location—4

[0049] N. Nominal

[0050] s11. Reflection

[0051] s21. Transmission

[0052] DETAILED DESCRIPTION OF INVENTION

[0053] A biosensor (1), which enables the concentration of a desired molecule inside a liquid in the medium, essentially comprises [0054] at least one metallic plate (2) which functions as a ground plate, and which is preferably manufactured from aluminum, [0055] at least one dielectric substrate (3) which is located on top of the metallic plate (2), [0056] at least one split-ring resonator (4) which is realized on the dielectric substrate (3), and which is coated with a dielectric layer, [0057] at least two symmetrical antennas (5) which are realized on the same plane with the split-ring resonator (4) on top of the substrate (3), [0058] at least two ports (6) where a network analyzer is connected to the antennas (5) via SMA (SubMiniature Version A) connectors.

[0059] The three-dimensional schematic of the inventive biosensor (1) is shown in FIG. 1. The inventive biosensor (1) is comprised of a split-ring resonator (4) formed of split metallic ring realized on top of a dielectric substrate (3) and two symmetrical monopole antennas (5). The connection with the antennas (5) is achieved through ports (6) via the SMA (SubMiniature Version A) connectors. The dielectric substrate (3) is on a metallic plate (2) functioning as a ground plate and preferably manufactured from aluminum.

[0060] In a preferred embodiment of the invention, biosensor (1) is realized on a FR4 substrate (3) which is commonly used for printed circuit boards. In another embodiment of the invention, the substrate (3) of the biosensor (1) can also be manufactured on dielectric ceramics such as alumina, and mica. The fabrication of the biosensor (1) is realized with standard printed circuit board methods. After the definition of metallic structures on the FR4 substrate (3), there is a thin Parylene (P) material deposition process. Parylene (P) is a biocompatible material used for anchoring the biomolecules on the biosensor. The deposition process is performed at room temperature using chemical vapor deposition, and its geometric definition is performed using lithography and oxygen plasma etching. The resulting metallic structure behaves as a kind of LC resonator, and it can be excited with a magnetic field perpendicular to its own plane in a frequency known as magnetic resonance (f.sub.m). Such excitation induces a current circulating around the ring. In accordance with the equivalent modelling with the lumped elements, the resonant frequency is given by the following equation:

[00001]$\begin{array}{cc}{f}_m=\frac{1}{2.Math.\pi .Math.\sqrt{C_{\mathrm{eff}}.Math.L_{\mathrm{eff}}}},C_{\mathrm{eff}}=C_g+C_s& \left(\mathrm{Equation}.Math..Math.1\right)\end{array}$

C.sub.eff in this equation gives the efficient capacitance, and L.sub.eff gives efficient inductance; and these parameters are determined by the geometric design. Efficient capacitance is determined by two capacitance values which are parallel to each other. The first one of these is gap capacitance modeled with C.sub.g, its value is given by the following equation:

[00002]$\begin{array}{cc}{C}_g={\mathrm{.Math.}}_{\mathrm{eff}}.Math.\frac{h.Math..Math.\omega }{g}+{\mathrm{.Math.}}_{\mathrm{eff}}\left(h+g+w\right)& \left(\mathrm{Equation}.Math..Math.2\right)\end{array}$

h, w and g in this equation is the thickness and width of the metallic structure, and the slit gap. Capacitance (C.sub.s) is associated with the surface charges changes with r which is the radius of the ring, and its value is given by the following equation:

[00003]$\begin{array}{cc}{C}_s=2.Math.{\mathrm{.Math.}}_{\mathrm{eff}}.Math.\frac{\left(h+\omega \right)}{\pi }.Math..Math.\ln .Math..Math.\left(\frac{4.Math.r}{g}\right)& \left(\mathrm{Equation}.Math..Math.3\right)\end{array}$

As it can be seen from equation 2 and equation 3, effective permittivity (ε.sub.eff) of the media surrounding the split-ring resonator (4) is present as a multiplier in the surface and gap capacitances. In summary, a change in effective permittivity can shift the resonant frequency.

[0061] In order to measure the electromagnetic characteristics of the structure, a pair of identical monopole antennas (5) is realized in the sample plane with the split-ring resonator (4) symmetrically. The electromagnetic wave emitted from the antennas (5) is reflected from the aluminum plate (2) used as a ground plane and transmitted to the split-ring resonator (4). The emitted wave interacts with the split-ring resonator (4), and significantly increases the transmission (s21) in the vicinity of f.sub.m frequency which the resonant frequency of magnetic resonance. The said transmission (s21) characteristic was examined according to relative permittivity change, and the sensor applications were considered.

[0062] A prototype was manufactured in order to be used in biosensing applications. The details of the application are as follows:

[0063] The scattering circuit parameters of the biosensor (1) were measured by means of a vector network analyzer. In this process, both reflection (s11) and transmission (s21) parameters were characterized by using SMA connectors shown in FIG. 1. Reflection (s11) and transmission (s21) measurements were repeated by placing deionized water droplets (L) to different points of split-ring resonator (4) coated with a thin layer of Parylene (P). The volume of each water droplets (L) was measured as 16 μL with 2% precision. The location of the points on the split-ring resonator (4) at which the droplets are placed is shown in FIG. 2a. Deionized water droplets (L) increase the gap capacitance or surface capacitance according to their location on the split-ring resonator (4).

[0064] The reflection (s11) and the transmission (s21) characteristics of this experience are given in FIG. 2b. The characteristic measured when there is no droplet (L) on the biosensor (1) and called as nominal (N) created a resonant frequency with a value of 2.12 GHz. The measured reflection (s11) is high until the resonant frequency due to ground plate, and the reflection decreases sharply at the resonant frequency. The transmission (s21) is low outside of the resonant frequency where it peaks.

[0065] The resonant frequency of the metallic ring decreases due to relative permittivity increases created by the deionized water droplets (L). As a control experiment, deionized water droplets (L) were dried and measurement was repeated; and it was experimentally seen that the resonant frequency returned to the nominal value (N).

[0066] When Location —1 (K1) and. Location —2 (K2) given in FIG. 2a are loaded with deionized water, because they are on the same symmetry axis, the biosensor (1) shows minimal shift in resonant frequency (1%). Since the Location —1 (K1) is present on the split ring resonator (4) gap, deionized water dropped on this point both changes the gap and surface capacitance. The dominant capacitance of the split-ring resonator (4) mentioned here is the capacitance originated from the surface loads. Larger shifts in the resonance frequency occur when the deionized water droplets (L) are placed in Location —3 (K3) and Location —4 (K) points. The change in relative frequency in this case corresponds to 14.5%. Since the biosensor (1) is reciprocal, the same results were obtained when the ports (6) of the network analyzers are interchanged. Furthermore, we should state that the electromagnetic wave emitted from the antennas (5) is not planar and the location of the antennas affects the resonant characteristic.

[0067] Biomolecular measurements were performed in order to demonstrate the use of split-ring resonator (4) based biosensor (1) as biosensor experimentally. In these measurements, the interaction between the FGF-2 (fibroblast growth factor 2, F) and heparin (H) was monitored. Specifically, prepared Murine recombinant FGF-2 (F) and low molecular weight heparin (H) molecules (Enoxaparin, Sanofi, Paris, France) were used in the experiments. FG-2 (F) is known as a molecule playing an important role in biological processes such as embryogenesis, angiogenesis and wound healing. Heparin (H) binds the FGF-2 (F) molecules through a specific domain with high affinity.

[0068] The experiments started with measuring reflection (s11) and transmission (s21) spectra. The surface of the biosensor (1) coated with parylene (P) was incubated with FGF-2 (F) molecules in a certain concentration (for example 140 μg/ml). A droplet in volume of 10-μL was placed on Location —4 (K4) at room temperature, and left there for 30 minutes. Therefore, the area subjected to incubation was uniformly coated with FGF-2 (F). In the next step, the surface was dried and heparin (H) droplet in a certain volume and concentration (in volume of 20 μL, and in concentration of 10 μg/ml) was placed. The schematic of the experiment is shown in FIG. 3a. Then, the surface was dried again and this time a drop of heparin (H) molecule in volume of 20 μL and in concentration of 20 μg/ml was placed. This experimental cycle continued increasing, the heparin (H) concentration. In each step, reflection (s11) and transmission (s21) spectra were measured. The recorded spectra are given in FIG. 3b and FIG. 3c. As final step, a control experiment was performed by using deionized water with a volume of 20 μL.

[0069] Incubation with the FGF-2 molecules in a volume of 10 μL changes the elective permittivity of the biosensor (1). The change corresponding to this situation is a 3.5% decrease in resonant frequency. Adding heparin (H) molecules caused a further decrease in resonant frequency since the increase in permittivity due to the heparin (H) molecules binding the FGF-2 molecules. Resonant frequency change measured upon adding heparin molecules in concentration of 10 μg/ml was as 10%. The decrease in resonant frequency is proportional with the increase in the molecular concentration of heparin (H). A control experiment with deionized water brought the resonant frequency to the value incubated with the FGF-2 molecules. From these results, it is evident that the effect of molecular interaction on biosensor (1) response was measured.

[0070] The change in resonant frequency relative to molecular concentration is given in FIG. 4. According to this graph, there is a linear dependency within measurement limits, and the sensitivity was measured as 3.7 kHz/(ng/ml). It is possible to measure interaction between molecules with sub ng/ml levels with a frequency resolution of 1 kHz at the measurement frequency band.

[0071] Using the inventive biosensor (1), in a method enabling them measurement of the transmission (s21) and reflection (s11) characteristics of split-ring resonator (4), and in order to determine the concentration of a desired molecule in a liquid in the medium the following steps are performed: first probe molecules (for example FGF-2) in a certain concentration are incubated on the surface of split-ring resonator (4) coated with a dielectric layer. In order to coat the split-ring resonator (4) area subjected to incubation with the said probe molecules (for example FGF-2) uniformly, a droplet in a certain volume is placed on a certain location on the split-ring resonator (4) at room temperature, and left for a predetermined period of time. Second, the surface of the split-ring resonator (4) is dried, and a droplet comprising a second molecule is placed (for example heparin (H)) in a certain volume and concentration. In order to measure the concentration of molecule in the said droplet, first an electric signal is applied on two symmetrical antennas (5) which are coplanar with the split-ring resonator (4). The said electric signal is converted into electromagnetic wave by the antennas (5) and transmitted to the split-ring resonator (4), and the split-ring resonator (4) is excited via the said electromagnetic waves. Then, the transmission (s21) and reflection (s11) characteristics of split-ring resonator (4) are measured using a vector network analyzer connected to the antennas (5) through ports (6) of the biosensor (1).

[0072] In order to determine the concentration of a desired molecule in a liquid in the medium, transmission (s21) and reflection (s11) characteristics of split-ring resonator before the second molecule (for example heparin (H)) is added to the medium are measured, and the obtained characteristics are compared. For this, first the abovementioned first step is performed. In first step, probe molecules in a certain concentration (for example FGF-2) are incubated on the surface of split-ring resonator (4) coated with a dielectric layer. In order to coat the split-ring resonator (4) is subjected to incubation with the said probe molecules (for example FGF-2) uniformly, a droplet in a certain volume is placed on a certain location on the split-ring resonator (4) at room temperature, and left for a predetermined period of time. An electric signal is applied on two symmetrical antennas (5) which are coplanar with the split-ring resonator (4). The said electric signal is converted into electromagnetic wave by the antennas (5) and transmitted to the split-ring resonator (4), and the split-ring resonator (4) is excited via the said electromagnetic waves. Then, the transmission (s21) and reflection (s11) characteristics of split-ring resonator (4) are measured with a vector network analyzer. The measured characteristic is considered as a reference.

[0073] These reference characteristic values which are obtained are compared with the transmission (s21) and reflection (s11) characteristics of the split-ring resonator (4) after the second molecule is added to the medium. By referencing the shift in resonant frequency due to the second molecule added to the medium (which are towards lower frequencies), the concentration of the second molecule in the medium (for example heparin (H)) is determined easily. This process is determined considering the characteristic values, which are recorded before in one embodiment of the invention. In another embodiment of the invention the concentration value of the second molecule in the medium is determined by calculating the shift in resonant frequency with respect to a control unit and comparing with pre-recorded data.