Sensor for detecting trace IONS and method thereof

Abstract

A method for detecting multiple trace ions in a sample comprising: depositing the sample on a chromatographic plate comprising a porous substrate; a pre-concentration step comprising adding a plurality of ligands to the sample to form a mixture comprising ligands and its complexes 0 and then subjecting the mixture to a first ion concentration polarization (ICP) process according to the ions of interest to form a concentrated mixture of the ligands and its complexes; a separation step comprising subjecting the mixture to a second ion concentration polarization (ICP) process to induce the separation of the ligands and its complexes. The first ion polarization process enables increased interaction of the ions with the plurality of ligands to form a concentrated ligands 5 mixture and its ion complexes and the second polarization process separates the ligands from the ion complexes thereby enabling the detection of the targeted ions in the sample.

Description

SENSOR FOR DETECTING TRACE IONS AND METHOD THEREOFFIELD OF INVENTION

[0001] The present invention generally relates to sensing and detection of trace ions and more particularly to a sensor method of detecting trace ions in an aqueous sample.BACKGROUND

[0002] Detecting trace ions is of tremendous interest to investigate their properties and to determine if they pose a threat to the environment. Trace ion sensing typically requires a high- performance chromatography (HPLC) system equipped with a specialized separation column, coupled with a charge detector or a mass spectrometer. However, this would require sending of samples to laboratories.

[0003] There is a demand growing worldwide to develop efficient systems to detect trace ions especially heavy metal ions, however a great majority of the available techniques necessitate sophisticated equipment or well-controlled environment. These are normally laboratory-based techniques and are highly selective and sensitive but, require tedious sample preparation and preconcentration procedures, involve time-consuming and laborious procedures that can be carried out only by skilled professionals, as well as the use of expensive and complex instrumentation.

[0004] For instance, high performance liquid chromatography coupled with a mass spectrometer can separate and detect compounds with great precision, it is not suitable for circumstances where analysis and results have to be accessed rapidly, as laboratories with such equipment are not accessible and cost of analysis is deemed not cost effective or affordable by the person who needs it. Further, detection of low concentration of analytes on an HPLC system usually involves a larger volume of sample or a preconcentration step therefore requires laboratory equipment and / or apparatus.

[0005] Hence, there is a need for affordable and rapid method for the simultaneous detection of multiple ions that is less susceptible to interference from other ions.SUMMARY

[0006] In one aspect, the present invention provides a method for detecting multiple trace ions in a sample comprising: depositing the sample on a chromatographic plate comprising a porous substrate; a pre-concentration step comprising adding a plurality of ligands to the sample to form a mixture comprising ligands and its complexes and then subjecting the mixture to a first ion concentration polarization process according to the ions of interest to form a concentrated mixture of the ligands and its complexes; a separation step comprising subjecting the mixture to a second ion concentration polarization process to induce the separation of the ligands and its complexes; wherein the first ion polarization process enables increased interaction of the ions with the plurality of ligands to form a concentrated ligands mixture and its ion complexes and the second polarization process separates the ligands from the ion complexes thereby enabling the detection of the ions in the sample.

[0007] Advantageously, increasing interaction of the ions with the plurality of ligands improves uniformity and resolution of the chromatographic separation.

[0008] In an embodiment, the ICP process includes creating an electric field using a pair of electrodes.

[0009] In another embodiment, the first ICP process increases the interaction of the ions with the plurality of ligands by adjusting the polarity of the electric field in accordance with the ions of interest.

[0010] In a further embodiment, the second ICP process induces the separation of the ligands and its ion complexes by adjusting the polarity of the electrical field based on their interaction with the porous substrate and the electric field.

[0011] In yet a further embodiment, the electric field exerts attractive or repulsive forces on the ligands or its complexes based on their surface charge.

[0012] In an embodiment, the ligands include chromophores and / or fluorophores to bind with the ions of interest.

[0013] In an embodiment, the interaction duration of ions and the ligands during the preconcentration step is 60 seconds and below, and the separation step takes less than 3 minutes.

[0014] In an embodiment, one or more of the following ligands are selected to detect the indicated ions in the sample: i) Dithizone (Cd2+Mn3+, Fe, Co, Ni2+, Cu2+, and Zn2+) ii) 4'-Aminobenzo- 15 -crown 5 -Ether (Cd2+) iii) 4'-Aminobenzo-18-crown 6-Ether (K+) iv) Diamino-benzo-9-crown-3 (Be2+,) v) 4'-Aminobenzo-24-crown-8 (Cs+) vi) N,N'-Dibenzyl-4, 13 -diaza- 18-crown 6-Ether (Pb2+) vii) aza 15 -crown-5 (Pb2+) viii) 7, 16-Dibenzyl- 1 ,4, 10, 13 -tetraoxa-7, 16-diazacyclooctadecane (Pb2+) ix) Iron and 6-Thioguanine complex (As3+) x) Iron and 6-Amino-2 -mercaptobenzothiazole complex (As3+) xi) Iron and 4-Amino-6-hydroxy-2 -mercaptopyrimidine monohydrate complex (As3+) xii) 5 ,6-Benzo-4,7, 13 , 16,21 ,24-hexaoxa- 1 , 10-diazabicyclo [8.8.8]hexacos-5 -ene (Ra)

[0037] In another embodiment, the ligands are selected for detecting at least one of the following ions: Cd2+, K+, Be2+, Cs+, Pb2+, As3+, Ra, Mn, Fe, Co, Ni, Cu, and Zn.

[0038] Advantageously, multiple ligands are deposited on the porous substrate to detect multiple ions simultaneously.

[0039] In a further embodiment, the porous substrate includes silica gel and cellulose.

[0040] In an embodiment, the detection of ions includes analysing using a U V / VIS spectrometer with varying U V / VIS spectrums that correspond to the ligands or its complexes. Typically, analysing using a UV / VIS spectrometer with varying UV / VIS spectrums include the steps of calibrating the chromatographic plate with deionized water, and determining the location of ligands and its complexes.

[0041] In a further embodiment, the chromatographic plate includes a chemical resistant polyetheretherketone (PEEK) or polypropylene (PP) compound and an area coated with synthetic polymer compound for enhancing the concentration of ions. Typically, the synthetic polymer compound is sulfonated tetrafluoroethylene -based fluoropolymer-copolymer.

[0042] In a further aspect, the present invention provides a sensor for detecting multiple ions in a sample, the sensor comprising: a top portion comprising a pair of electrodes for creating an electrical field to initiate ion concentration polarization process (ICP); a bottom portion comprising a chromatographic strip having a pre-concentration section and a separation section; the concentration section comprises a sulfonated tetrafluoroethylene-based fluoropolymer- copolymer coating; wherein the electrodes are configured to switch on when the sample and a plurality of ligands are added to the pre-concentration section, to initiate a first ion concentration polarization process to increase interaction of ions in sample with the ligands to form a mixture of ligands and its complexes, and subsequently a second ion concentration polarization process to induce separation of the ligands and its complexes therefore enabling the targeted ions in the sample to be detected.

[0043] In an embodiment, the top portion further comprises a sample window and a detection window.

[0044] Advantageously, the top and bottom portions assembly allow simultaneous preconcentration and analysis to be carried out on a single chromatographic plate.

[0045] In a further embodiment, the pre-concentrating section comprises bends to allow better mixing of the sample with the ligands.

[0046] Advantageously, the separation section comprises a straight millifluidic channel which confines the flow within a channel and enhance the separation through capillary action.BRIEF DESCRIPTION OF DRAWINGS

[0047] The invention will be more understood by reference to the description below taken in conjunction with the accompanying drawings herein:

[0048] FIG. 1A shows the sensor device in accordance with a preferred embodiment of the present invention;

[0049] FIG. IB is a perspective view of the top portion of the sensor in accordance with an embodiment of the present invention;

[0050] FIG. 1C shows a top view of the bottom portion of the sensor in accordance with an embodiment of the present invention;

[0051] FIG. 2 provides examples of pre -concentration and separation process involving ICP and without ICP using the chromatographic plate of the present invention;

[0052] FIG. 3 provides examples of the steps for separating ligands and their complexes in accordance with the present invention; and

[0053] FIG. 4 shows a process of scanning the chromatographic plate with U V / VIS spectrometer.DETAILED DESCRIPTION

[0054] In line with the above summary, the following description of a number of specific and alternative embodiments is provided to understand the inventive features of the present invention. It shall be apparent to one skilled in the art, however that this invention may be practiced without such specific details. Some of the details may not be described at length so as not to obscure the invention. For ease of reference, common reference numerals will be used throughout the figures when referring to the same or similar features common to the figures.

[0055] Embodiments of the invention are described by way of illustration. As will be realized, the invention is capable of other and different embodiments and its several details are capable of modifications in various respects, all without departing from the scope of the present invention. Standard equipment or components may have not been illustrated since they are known in the art.

[0056] The present invention provides a method of detecting trace or small volume ions in a sample using a chromatography plate and applying ion concentration process (ICP) to the method to enhance the separation and detection of multiple ligands and its complexes formed when mixed with the ions in the sample, according to the strength of their interaction forces with the porous substrate of the chromatographic plate and the electric field between the electrodes. The methodfurther comprises qualitative and quantitative analysis of the chromatography plate using scanning spectrometer with an ultraviolet or visible light source (UV / Vis). The method of the present invention enables multiple ions to be detected simultaneously.

[0057] In a preferred embodiment, the method comprises depositing the sample on a chromatographic plate comprising a porous substrate; a concentration step comprising adding a plurality of ligands to the sample to form a mixture comprising ligands and its complexes; and a separation step comprising initiating an ion concentration polarization (ICP) process on the mixture to increase interaction of the ions in the samples with the ligands. The pre-concentration step enables interaction of the ions with the plurality of ligands to form a concentrated ligands mixture and its ion complexes; and then adjusting the ICP to induce separation of the ligands from the formed ion complexes based on their interaction with the porous substrate of the chromatographic plate; thereby enabling the detection of the targeted ions in the sample.

[0058] The porous substrate provides a surface that allows chromatographic separation of the ligands and their formed ion complexes. The substrate therefore provides a stationary phase platform for the chromatographic separation and may be formed from materials selected from a group comprising silica gel (SiCh) or cellulose.

[0059] In the preferred embodiment, the chromatographic plate is formed with silica gel or cellulose for thin layer chromatography in a flow channel cut out on a chemical resistant polyetheretherketone (PEEK) or polypropylene (PP) plate. The fabrication of the chromatographic plate comprises the following steps: forming PEEK or PP plates with a specific millifluidic flow channel manufactured by injection molding; depositing silica gel or cellulose slurry within the millifluidic flow channel; drying of the silica gel or cellulose slurry in a convection oven at 45 °C for 2 hours; applying Nafion coating near the concentrating region of the millifluidic channel deposit selected ligands with chromophores and / or fluorophores to bind with the ions of interest dissolved in a low boiling point solvent near the near the concentrating region of the millifluidic channel; drying the chromatographic bottom plate at 45 °C for 20 minutes.

[0060] The ligands selected include chromophores and / or fluorophores which results in varying UV / VIS spectral peak wavelengths and / or intensities between its pure and complexed form.Examples of ligands with UV chromophores and the respective ions of interest it is selective towards are shown in TABLE 1 below:

[0061] Adding the ligands to the sample increases the interaction of the ions with the ligands prior to separating the ligands from the ion complexes with reasonable resolution and therefore observed using a detector. The qualitative and quantitative analysis of the thin layer chromatography plates can be analyzed using scanning spectrometer with an ultraviolet or visible light source (UV / VIS).

[0062] The detection component includes using ligands with chromophores and / or fluorophores which exhibits differences in UV / VIS spectral peak wavelengths and / or intensities between its pure and complexed form. When these ligands and its complex are being separated using thechromatographic plate, which includes a millifluidic channel, they appear as spots with different UV / VIS spectral peak wavelengths and / or intensities (after the substrate is illuminated under UV and visible light) at different locations along the millifluidic channel relative to the strength of their interaction forces with the porous substrate. The spectral peak wavelengths and / or intensities will correspond to the concentration of the compound in the spot.

[0063] In use, the following sequence may be observed when testing a sample solution. First, an amount of the solution containing the ions is added to the sample window of the sensor. The sample then enters the concentrating region of the chromatographic channel. This channel comprises bends to allow for better mixing of the sample with the ligand(s) deposited in the ligand well. Upon addition of about 100 pL aqueous sample, the electrodes are. switched on to start the ion concentration polarization (ICP) process, and the polarity should be set according to the ions of interest. The first 0 to 60s is the concentration step, during which the ions are allowed to interact with the ligands and move towards the electrode with the opposite charge to itself. Following which, the polarity of the electrodes is switched or adjusted to induce separation of the ligands and its complexes based on their interaction forces with the stationary phase which is the porous substrate and the electric field. This step could take up to 3 minutes depending on the ligands used. The more polar groups on the ligand or its complex, the higher its interaction force with the substrate and the slower its flow along the chromatographic strip, while the electric field exerts attractive or repulsive forces on the ligands, or its complexes based on their surface charge. Further, the resolution of the chromatographic separation can be fine-tuned by changing the ICP electric field potential, waveform, and duration.

[0064] In another aspect, the present invention provides a sensor as shown in FIG. 1A. The sensor device assembled in accordance with a preferred embodiment of the present invention comprises a top portion (15) adapted to be assembled to a bottom portion (20). Now referring to FIG. IB, the top portion (15) comprises a pair of electrode wells (16) to support a pair of electrodes (16A) for creating an electrical field to initiate ion concentration polarization (ICP) process; a sample window (17) and a detection window (18). As shown in FIG. 1C, the bottom portion (20) comprises a chromatographic plate having a pre-concentration section (22), a separation section (23) and ligand well (24); wherein the concentration section (22) comprises a sulfonated tetrafluoroethylene -based fluoropolymer-copolymer (Nafion) coating (25) as the cation exchange material. The chromatography strip of the bottom portion (20) includes silica gel or cellulose deposited in a flow channel on a chemical resistant polyetheretherketone (PEEK) or polypropylene (PP) plate.

[0065] Accordingly, when the sample and a plurality of ligands are added to the pre-concentration section (22), the electrodes (16A) of the top portion (15) are configured to be switched on to initiate a first ion concentration polarization process to increase interaction of ions in sample with the ligands to form a mixture of ligands and its complexes, and subsequently initiating a second ion concentration polarization process to induce separation of the ligands and its complexes therefore enabling the targeted ions in sample to be detected.

[0066] The separation section (23) of the chromatographic plate comprises a straight millifluidic channel that confines the flow within the channel and enhance the separation through capillary action.

[0067] The sensor assembly can then be used to simultaneously concentrate and separate one or more ligands and their complexes with different ions at trace concentration with good resolution. The assembly may be placed on a specialized carriage with electrode connections which would connect to the electrode contact pads (30). The ion concentration polarisation (ICP) processes play a role in increasing the interaction of samples with ligands and then separating the ligands and its complexes as an additional driving force to the interaction forces with the millifluidic silica gel or cellulose channel of the chromatographic plate thereby improving uniformity and resolution.

[0068] Examples of concentration and separation steps involving ICP and without ICP using the chromatographic plate of the present invention are shown in FIG. 2, and examples of the step to separate the ligands and their complexes with the present invention are shown in FIG. 3. An example of a process of scanning the chromatographic plate with UV / VIS spectrometer is shown in FIG. 4

[0069] The method and sensor exploit the selectivity of different ligands to different ions and the varying interaction forces of the ligands with the substrate and the created surrounding electrical field to enable simple chromatographic separation of different ligands with different ions. Further, millifluidic chromatographic plate assembly allows for simultaneous preconcentration and analysis to be carried out. Separating the ligands and its complexes using electrical field is an additional driving force apart from the interaction forces with the millifluidic silica gel or cellulose channel thereby improving uniformity and resolution. The resolution of the chromatographic separation can be fine-tuned by changing the ICP electric field potential, waveform and duration.

[0070] While the invention has been described as required in terms in preferred embodiments and specific operating ranges and conditions, those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described.

Claims

CLAIMS1. A method for detecting multiple trace ions in a sample comprising: depositing the sample on a chromatographic plate comprising a porous substrate; a pre-concentration step comprising adding a plurality of ligands to the sample on the porous substrate to form a mixture comprising ligands and its complexes and then subjecting the mixture to a first ion concentration polarization (ICP) process according to the ions of interest to form a concentrated mixture of the ligands and its complexes; a separation step comprising subjecting the mixture to a second ion concentration polarization (ICP) process to induce the separation of the ligands and its complexes; wherein the first ion polarization process enables increased interaction of the ions with the plurality of ligands to form a concentrated ligands mixture and its ion complexes and the second polarization process separates the ligands from the ion complexes; thereby enabling the detection of the targeted ions in the sample.

2. The method according to Claim 1, wherein the first and second ICP processes includes creating an electric field using a pair of electrodes.

3. The method according to Claim 2, wherein the first ICP process increases the interaction of the ions with the plurality of ligands by adjusting the polarity of the electric field in accordance with the ions of interest.

4. The method according to any one of Claims 1-3, wherein the second ICP process induces the separation of the ligands and its ion complexes by adjusting the polarity of the electrical field based on their interaction with the porous substrate and the electric field.

5. The method according to any one of Claims 2-4, wherein the electric field exerts attractive or repulsive forces on the ligands or its complexes based on their surface charge.

6. The method according to Claim 1, wherein ligands include chromophores and / or fluorophores to bind with the ions of interest.

7. The method according to Claim 1, wherein the ions interact with the ligands during the concentration step for 60 seconds and below, and the separation step takes less than 3 minutes.

8. The method according to Claim 8, wherein the ligands are selected for detecting at least one of the following ions: Cd2+, K+, Be2+, Cs+, Pb2+, As3+, Ra, Mn, Fe, Co, Ni, Cu, and Zn.

9. The method according to -Claim 8, wherein one or more of the following ligands are selected to detect the indicated the ions in the sample: i) Dithizone (Cd2+Mn3+, Fe, Co, Ni2+, Cu2+, and Zn2+) ii) 4'-Aminobenzo- 15 -crown 5 -Ether (Cd2+) iii) 4'-Aminobenzo-18-crown 6-Ether (K+) iv) Diamino-benzo-9-crown-3 (Be2+,) v) 4'-Aminobenzo-24-crown-8 (Cs+) vi) N,N'-Dibenzyl-4, 13 -diaza- 18-crown 6-Ether (Pb2+) vii) aza 15 -crown-5 (Pb2+) viii) 7, 16-Dibenzyl- 1 ,4, 10, 13 -tetraoxa-7, 16-diazacyclooctadecane (Pb2+) ix) Iron and 6-Thioguanine complex (As3+) x) Iron and 6-Amino-2 -mercaptobenzothiazole complex (As3+) xi) Iron and 4-Amino-6-hydroxy-2 -mercaptopyrimidine monohydrate complex (As3+) xii) 5 ,6-Benzo-4,7, 13 , 16,21 ,24-hexaoxa- 1 , 10-diazabicyclo [8.8.8]hexacos-5 -ene (Ra)10. The method according to Claim 1, wherein multiple ligands are deposited on the porous substrate to detect multiple ions simultaneously.

11. The method according to Claim 1, wherein the porous substrate includes silica gel or cellulose.

12. The method according to Claim 1, wherein detection of ions includes analysing using a UV / VIS spectrometer with varying UV / VIS spectrums that correspond to the ligands or its complexes.

13. The method according to Claim 12, wherein analysing using a UV / VIS spectrometer with varying UV / VIS spectrums include the steps of calibrating the chromatographic plate with deionized water, and determining the location of ligands and its complexes.

14. The method according to Claim 1, wherein the chromatographic plate includes a chemical resistant polyetheretherketone (PEEK) or polypropylene (PP) and an area coated with synthetic polymer compound for enhancing the concentration of ions.

15. The method according to Claim 14, wherein the synthetic polymer compound is sulfonated tetrafluoroethylene-based fluoropolymer-copolymer.

16. A sensor for detecting multiple ions in a sample, the sensor comprising: a top portion comprising a pair of electrodes for creating an electrical field to initiate ion concentration polarization (ICP) process; a bottom portion comprising a chromatographic plate having a pre -concentration section and a separation section; the concentration section comprises a sulfonated tetrafluoroethylene-based fluoropolymer-copolymer coating; wherein when the sample and a plurality of ligands are added to the pre-concentration section of the bottom portion, the electrodes are configured to switch on when the sample and the plurality of ions are added to the pre -concentration section, to initiate a first ion concentration polarization process to increase interaction of ions in sample with ligands to form a mixture of ligands and its complexes, and subsequently initiating a second ion concentration polarization process to induce separation of the ligands and its complexes therefore enabling the targeted ions in sample to be detected.

17. The sensor according to Claim 16, wherein the top portion further comprises a sample window and a detection window.

18. The sensor according to Claim 16, wherein the pre-concentrating section comprises bends to allow better mixing of the sample with the ligands.

19. The sensor according to Claim 16, wherein the separation section comprises a straight millifluidic channel which confines the flow within a channel and enhance the separation through capillary action.

20. The sensor according to Claim 16, wherein the sensor further comprising electrode contact pads.

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