Patent Application
20170082576
The present invention relates to low cost next generation robust bulk conducting and self standing polymer chip electrode for off-laboratory applications.
The current generation off-laboratory electrodes comprise mostly screen-printed and coated (PVD & CVD) electrodes. The major drawback of these electrodes is that the conducting components are not the integral part of the device, which get damaged/delaminated easily either by mechanical jerk, high deposition, high current or aging.
The electrodes made from conventional plasticizing polymers were called “Plastic Chip Electrode” (PCE) whereas it's another variant made with biodegradable plasticizing polymers were called “Biodegradable Plastic Chip electrode” (BPCE). Such electrodes were found comparable to the conventional noble metal and glassy carbon electrodes in various electrochemical applications like cyclic voltammetry of different redox couples, amperometric sensing of hydrogen peroxide, stripping voltammetry of heavy metals, electrodeposition of zinc and electropolymerization of aniline and 3,4-ethylenedioxythiophene in aqueous medium.
The most ancient mercury electrodes are not considered safe even for lab application due to its toxic and bio-accumulative nature. Carbon paste electrodes are fit for the lab-applications, albeit due to the morphological constrains and flabby nature, their practice in field-applications is not so convenient. Moreover they are not self-standing and the template supporting the carbon paste is an unwarranted species in the electrode. However the screen-printed electrodes due to its flat and sleek, self-standing, two dimensional geometry fits well for the field, on-site as well as more advanced applications like interdigitated array electrodes and lab-on-a-chip. Albeit the bottleneck with coated and screen printed electrodes is that the conducting layers are not the integral part of the composite and can easily get delaminated due to mechanical jerk or high current. Therefore, there was a need for an improved alternative of the surface coated electrodes having similar potentials but minimized shortcomings. Current invention addresses these problems. A flat, bulk-conducting and self-standing two dimensional electrode using graphite-polymer composite have been fabricated and used as electrode. Biodegradable polymer, poly (lactic acid) was also used in order to introduce environment-friendly and greener aspects in these electrodes. The kinetics of biodegradability of the BPCE was studied and compared with biodegradability of the pristine polymer used for its fabrication.
There are some related prior art which need to mention here to understand novelty of current invention. Although no similar product to subject electrodes is known
Reference may be made to the article by Jaroslav Heyrovsky, Philosophical Magazine 45 (1923) 303-315, where electrolysis of the alkali and alkaline earth metals over the dropping mercury electrode (DME) is reported. In DME a drop of mercury at the tip of capillary tube was used as electrode.
Reference may be made to the patent by B. A. Heller, RU55100, Jun. 30, 1939 and by Oscar Kanner; Edwin D. Coleman, U.S. Pat. No. 2,361,295, Oct. 24, 1944 where several modification in DME is reported for better applications of these electrodes.
Reference may be made to the article by J. Heyrovshy, The Analyst, 72 (1947) 229-234, where he explained the application of DME in polarography.
Reference may be made to the article by V. F. Gaylor, A. L. Conrad and J. H. Landerl, Anal. Chem. 29 (1957) 224 where wax-impregnated graphite electrode was reported.
Reference may be made to the article by R. N. Adams, Anal. Chem. 30 (1958) 1576 where carbon paste electrode through the dropping carbon electrode was reported.
Reference may be made to several patents where carbon paste electrodes were used in various applications; for example: in supercapacitor (JP 57046208B; 1 Jun. 1973), double layer capacitor (JP 59090919A; 25 May 1982), voltammetry (SU 1985-3981899; 21 Nov. 1985), electroanalysis (SU 1557510A1; 15 Apr. 1990).
Reference may be made to the patent by Skotheim, Terje; Okamoto, Yoshiyuki; Gorton, Lo G.; Lee, Hung Sui; Hale, Paul U.S. Pat. No. 5,264,092A; 23 Nov. 1993 where the enzyme modified carbon paste electrode was used for making biosensor.
Reference may be made to the patent by Don N. Gray; George G. Guilbault, U.S. Pat. No. 3,929,609, A, 30 Dec. 1975 where a solid sensor electrode versatile than conventional noble-metal electrodes was fabricated by screen printing a mixture of the noble metal and a low-alkali glass on an inert substrate.
Reference may be made to the patent by Joseph, Wang; Ziad H. Taha, WO 9218857, A1 29 Oct. 1992, where trace metal testing was performed over the screen printed electrode by electrochemical flow injection method.
Reference may be made to the patent by Rebecca Y. Lai; Weiwei Yang, US 20110139636, A1; 16 Jun. 2011, where screen printed sensor cartridge comprising working, counter and reference electrode on a single chip for electrochemical sensor has been reported.
Reference may be made to the patent by Vijaywant, Mathur; Chander Raman Suri; Priyanka Sharma, IN 2010CH00236, A, 25 May 2012, where screen printed biochip is reported.
Reference may be made to the patent by J. Yu, Y. Zheng, H. Li, J. Li; CN 103448308 A 20131218, where biodegradable flexible conductive substrate and its manufacturing method is reported.
Reference may be made to the patent by Q. Liu, B. Deng; CN 102943315 A 20130227, where production of poly(lactic acid)-based conductive fibers is reported.
Reference may be made to the patent by T. Suzuki, Y. Hirabayashi, M. Yoneda, A. Maruyama; JP 2005032633 A 20050203, where coating of conducting composite of biodegradable polymers like polybutylene succinate, polybutylene succinate adipate, polyethylene succinate, polylactic acid, poly-ε-caprolactone, poly-3-hydroxybutyrate, poly (3-hydroxybutyrate-3-hydroxyvalerate), and/or polyglycolic acid is reported. The coated electrodes were then used as cathode and anode in Li batteries.
Reference may be made to the article by R. P. Pawar, S. U. Tekale, S. U. Shisodia, J. T. Totre, A. J. Domb; Recent Patents on Regenerative Medicine (2014), 4(1), 40-51, where various Biomedical Applications of Poly(Lactic Acid) is discussed.
Reference may be made to the patent by Y. Fukuhira, E. Kitazono, H. Kaneko, Y. Sumi, Y. Narita, H. Kagami, Y. Ueda, M. Ueda; WO 2006115281 A1 20061102, where application of poly(Lactic Acid) in cardiac pacemaker is reported.
Reference may be made to the article by S. Peng, P. Zhu, Y. Wu, S. G. Mhaisalkar, S. Ramakrishna; RSC Advances (2012), 2(2), 652-657, where polyaniline-polylactic acid composite nano-fibers were used as counter electrodes in dye-sensitized solar cells.
The main object of this present invention is to develop low cost, portable and bulk conducting electrodes which can be presented as a superior alternative for the conventional and expensive electrodes such as gold, platinum or other noble metal electrodes and coated electrodes like screen printed electrodes by a simple fabrication steps.
Another object of the present invention is to develop disposable and self-standing polymer composite electrodes which can be used directly after fabrication without any template or support (as in carbon paste electrodes) or thermal curing steps (as in screen printed electrodes).
Yet another object of the present invention is to adopt simple technique (solution casting method) for the fabrication of electrodes.
Yet another object of the invention is to develop a protocol for fabrication of electrodes withreproducible physical dimensions and conductivity.
Yet another object of the present invention is to try various polymers in combination with graphite for the formation of plastic chip electrode.
Yet another objective of this investigation is to incorporate environment-friendly and greener aspect in the plastic chip electrodes by using biodegradable polymer.
Yet another objective of the present investigation is to study the kinetics of biodegradability of the BPCE and compare it with the pristine poly (lactic acid).
Another object of the present investigation is to test PCE and BPCE in various electrochemical processes.
Accordingly, the present invention provides a self-standing polymer chip electrode comprising graphite and polymer in the weight ratio ranging between 70:30 to 40:60, wherein the polymer used is selected from the group consisting of poly (methyl methacrylate) (PMMA), polystyrene (PS) and polyvinyl chloride (PVC) for non-biodegradable electrodes; or poly (lactic acid) (PLA) for biodegradable electrodes.
In an embodiment, present invention provides a process for the preparation of electrode comprising the steps of:
In yet another embodiment of the present invention, the thickness of the film having graphite: polymer weight ratio in the range from 70:30 to 40:60 is in the range of 0.5 mm to 0.42 mm for 48.99 cm2 casting area and 3 gm total mass.
In yet another embodiment of the present invention, electrical conductivity of the electrode having graphite: polymer weight ratio in the range from 70:30 to 40:60, when various polymer are used is in the range of 2.3×10−2 S/cm to 1.1×10−11 S/cm.
In yet another embodiment of the present invention, the thermal stability of the electrode is up to 300° C.
In yet another embodiment of the present invention, the polymer used is selected from the group consisting of poly (methyl methacrylate) (PMMA), polystyrene (PS), polyvinyl chloride (PVC) and poly (lactic acid) (PLA).
In yet another embodiment of the present invention, the solvent used is selected from the group consisting of chloroform and tetrahydrofuran.
Another embodiment of the present invention provides an electrode for use in electrochemistry and electroanalysis in aqueous media.
In yet another embodiment of the present invention, the electrodeis useful as a working electrode in cyclic voltammetry of various redox couples in aqueous medium, electropolymerization of aniline and 3,4-ethylenedioxythiophene in aqueous medium, electrowinning of zinc, amperometric sensing of hydrogen peroxide and anodic stripping voltammetry of Pb (II) ion.
In yet another embodiment of the present invention, the electrode is useful as a working electrode for electrodeposition of zinc and copper aniline and 3,4-ethylenedioxythiophene.
In yet another embodiment of the present invention, other plasticizing or biodegradable plasticizing polymers can be used in place of poly (methyl methacrylate) (PMMA), polystyrene (PS), polyvinyl chloride (PVC) and poly (lactic acid) (PLA).
In yet another embodiment of the present invention, the electrode can be used for any electrochemical process in aqueous media.
In yet another embodiment of the present invention, the electrode is useful as working electrode in cyclic voltammetry of various redox couples such as Ru2+/3+, ferrocene/ferrocenium, and Fe2+/3+in aqueous system.
In yet another embodiment of the present invention, the electrode is useful for amperometric sensing of hydrogen peroxide in a wide concentration window (9 μM to 400 μM) with sensitivity of 0.42 μA μM−1.
In yet another embodiment of the present invention, the electrodes is used for detection of various heavy metals via stripping voltammetry with a lower detection limit 100 ppb.
Present invention relates to a cost effective, self-standing and bulk conducting disposable electrode fabricated from the composite of graphite and polymer. This invention also relates to the introduction of environment-friendly and greener aspect in these electrodes by using biodegradable polymer. The invention recognized that graphite is very cheap and easily available conducting material suitable for the purpose of electrode fabrication. In order to obtain self-standing, bulk conducting electrodes, the graphite was composited with plasticizing polymer in suitable ratio. Solution casting method was chosen for making electrode film recognizing its ease and simplicity. The electrode was cut in required shape. The biodegradability of the electrode was checked through enzymatic and hydrolytic degradation processes and its kinetics was studied with gel permeation chromatography.The electrodes were applied successfully in various electrochemical techniques such as cyclic voltammetry, electrochemical polymerization, amperometric sensing and stripping voltammetry.
In current invention a flat, self-standing, two dimensional and bulk conducting polymer composite sheet was fabricated by simple solution casting method and used as electrode.
Accordingly, a self-standing, bulk conducting and cost effective electrode materials is disclosed. The detail description of the invention is given in following points.
The novel inventive steps related to the present invention are as follows:
Following examples are given by way of illustration and should not be construed to limit the scope of the invention.
Material and methods
Poly (methyl methacrylate) (PMMA) was taken as representative polymer for preparing Plastic Chip Electrode (PCE) in different weight ratios of graphite:polymer viz. 70:30, 60:40, 40:60 and 20:80 denoted as PCE-PMMA-I, PCE-PMMA-II, PCE-PMMA-III and PCE-PMMA-IV respectively. The thickness and conductivity of the film of different graphite:PMMA weight ratio is given in table 1. Various other polymers suchas polystyrene, polyvinyl chloride and poly (lactic acid) were used for fabrication of electrodesby maintaining graphite:polymer weight ratio 60:40 which are denoted as PCE-PS, PCE-PVC and BPCE respectively. The thickness, conductivity, total mass of materials, casting area and the solvent used for making of electrode using various polymers are shown in table 2.
1.1 × 10−11
1.0 × 10−11
Current-voltage (I-V) measurements were performed using a Keithley 2635A source meter unit (SMU) by applying a range of bias voltage and measuring corresponding current. For this purpose, the film was cut into 1 cm×1 cm size and sandwiched between two platinum foils and placed in a spring loaded brass holder. The holder was connected to the source meter unit (SMU) through a crocodile clip. Bias voltage inthe range ±100 mV was applied for PCE-PMMA-I, PCE-PMMA-II, PCE-PS, PCE-PVC and BPCE while ±1.0 V for PCE-PMMA-III and ±10.0 V for PCE-PMMA-IV.The data were collected and plotted to obtain the I-V curve. The electrical conductance of the films was calculated from the slope of the curve. The specific conductance was calculated by using the formula, σ=G×1/A, where 1 is thickness, A is area and G is the electrical conductance of the film respectively. The pH measurements of solutions were carried out using Thermo Scientific (ORION VERSASTAR) pH meter at room temperature calibrated every time before use. All electrochemical experiments were performed on Princeton Applied Research potentiostat (PARSTAT 2273) at room temperature (24±2° C.). A three-electrode assembly was used during electrochemical measurements where composite film (0.8 cm width and 3 cm length) was used as working electrode, while platinum foil and Ag/AgCl (saturated KCl) were used as auxiliary and reference electrode respectively. The working length on working electrode was maintained at 0.5 cm by applying Teflon tape over the unused area. The electrical contact in the working electrode was made through a crocodile clip, which was suitably modified for the purpose. PCEs and BPCE were characterized for the surface morphology by a scanning electron microscope (SEM) (LEO 1430 VP) after thin coating of conducting Au—Pd alloy, and by an atomic force microscope (AFM) (NT-MDT Ntegra Aura) without any pre-treatment over a 0.8×2 cm-sized sample. Tensile tests of the electrodes were carried out using a universal testing machine (Zwick Roell, type X force P, Ser. No. 756,324), applying a preload of 0.01 N at 0.2 mm/min.
The specimen dimensions for the tensile test were 8×0.45×35 mm (w×t×l). The thermal stability of the electrodes were examined by thermogravimetric analysis (TGA) (NETZSCH, TG 209 F1, libra), taking 30 mg of sample. The measurements were performed from 25° C. to 600° C. at a heating rate of 10° C./min in nitrogen atmosphere.
Enzymatic degradation of biodegradable plastic chip electrode was studied using protease enzyme in 0.1M Tris-HCl buffer (pH 8). The BPCE was kept in the buffer solution at 37° C. and residual mass was taken after every 2 days. For this purpose sample was removed from solution, carefully washed with milli-Q water and dried in vacuum desiccators. Weight of dried sample was taken with a balance (readability 0.001 mg) and percentage loss in mass (% Δm) was calculated by the formula: % Δm=[(mi−mf)/mi]×100. Where mi is initial mass and mf (at time t) is final mass of BPCE. % Δm was plotted with respect to time which is given in
Hydrolytic degradation of BPCE and PLA film were measured in Milli-Q water thermostated at 58° C. Several pieces of PLA and BPCE film of same thickness weighing around 50 mg were placed in separate beakers having 25 gm of water (weight ratio of water:film 500:1). In every 48 hours, pH of liquids in each beaker was measured and then water was removed by sucking with a syringe. All other beakers were filled with fresh Milli-Q water and kept thermostated (58° C.) for further hydrolytic degradation, except one each of PLA films and BPCE. The spared chips were dried at 58° C. for 2.5 hours and stored in air tight plastic pouches for further analysis. A definite portion of degraded films were cut and dissolved in tetrahydrofuran (THF) at 58° C. The graphite was removed from the solution by centrifugation process and supernatant was taken out for analysis. The molecular weight distribution measurements were carried out by HPLC using Waters 2695 separations module coupled with Waters 2414 RI Detectors.
The kinetics (rate constant and half-life) of hydrolytic degradation of PLA and BPCE films was studied by the help of Gel Permeation Chromatography (GPC) by measuring the decrease in molecular weight of the polymer. The following formulas were used to calculate rate constant and half-life considering that the degradation follows first order kinetics:
Where, ‘k’ is the rate constant of the hydrolysis process. ‘Mn’ is number average molecular mass at time ‘t’ during hydrolysis process, ‘M’ is the molecular weight of the repeating unit which is 72 g/mol and t1/2 is half-life.
9 ml of 10% (w/v) poly (methyl methacrylate) (PMMA) solution (made by dissolving PMMA in chloroform) was taken in a beaker and 2.1 gm of graphite was added to it. The graphite:polymer weight ratio was 70:30 (PCE-PMMA-I). The mixture was stirred and sonicated for 10 minutes. The suspension was spread over modified glass mould of area 48.99 cm2. The system was kept for drying for 24 hours at room temperature (25° C.). The thickness and conductivity of the film was 0.5 mm and 2.2×10−2 S/cm respectively.
3 ml of 10% (w/v) PMMA solution (made by dissolving PMMA in chloroform) was taken in a beaker and 0.7 gm of graphite was added to it. The graphite:polymer weight ratio was 70:30 (PCE-PMMA-I). The mixture was stirred and sonicated for 10 minutes. The suspension was spread over modified glass mold of area 15.89 cm2. The system was kept for drying for 24 hours at room temperature (27° C.). The thickness and conductivity of the film was 0.5 mm and 2.3×10−2 S/cm respectively, which is same to the film formed in experiment-1, within the limits of experimental errors.
12 ml of 10%(w/v) PMMA(made by dissolving PMMA in chloroform) solution was taken in a beaker and 1.8 gm of graphite was added to it. The graphite:polymer weight ratio was 60:40 (PCE-PMMA-II). The mixture was stirred and sonicated for 10 minutes. The suspension was spread over modified glass mold of area 48.99 cm2.
The system was kept for drying for 24 hours at room temperature. The thickness and conductivity of the film was 0.42 mm and 1.6×10−2 S/cm respectively.
4 ml of 10% (w/v) PMMA(made by dissolving PMMA in chloroform) solution was taken in a beaker and 0.6 gm of graphite was added to it. The graphite:polymer weight ratio was 60:40 (PCE-PMMA-II). The mixture was stirred and sonicated for 10 minutes. The suspension was spread over modified glass mold of area 15.89 cm2. The system was kept for drying for 24 hours at room temperature. The thickness and conductivity of the film was 0.42 mm and 1.6×10−2 S/cm respectively, which is same to the film formed in experiment-3, within the limits of experimental errors.
18 ml of 10% (w/v) PMMA(made by dissolving PMMA in chloroform) solution was taken in a beaker and 1.2 gm of graphite was added to it. The graphite:polymer weight ratio was 40:60 (PCE-PMMA-III). The mixture was stirred and sonicated for 10 minutes. The suspension was spread over modified glass mold of area 48.99 cm2. The system was kept for drying for 24 hours at room temperature. The thickness and conductivity of the film was 0.45 mm and 1.0×10−5 S/cm respectively.
6 ml of 10% (w/v) PMMA(made by dissolving PMMA chloroform) solution was taken in a beaker and 0.4 gm of graphite was added to it. The graphite:polymer weight ratio was 40:60 (PCE-PMMA-III). The mixture was stirred and sonicated for 10 minutes. The suspension was spread over modified glass mold of area 15.89 cm2. The system was kept for drying for 24 hours at room temperature. The thickness and conductivity of the film was 0.46 mm and 1.0×10−5 S/cm respectively, which is same to the film formed in experiment-5, within the limits of experimental errors.
24 ml of 10% (w/v) PMMA (made by dissolving PMMA chloroform) solution was taken in a beaker and 0.6 gm of graphite was added to it. The graphite:polymer weight ratio was 20:80 (PCE-PMMA-IV). The mixture was stirred and sonicated for 10 minutes. The suspension was spread over modified glass mold of area 48.99 cm2. The system was kept for drying for 24 hours at room temperature. The thickness and conductivity of the film was 0.44 mm and 1.1×10−11 S/cm respectively.
8 ml of 10% (w/v) PMMA (made by dissolving PMMA chloroform) solution was taken in a beaker and 0.2 gm of graphite was added to it. The graphite:polymer weight ratio was 20:80 (PCE-PMMA-IV). The mixture was stirred and sonicated for 10 minutes. The suspension was spread over modified glass mold of area 15.89 cm2. The system was kept for drying for 24 hours at room temperature. The thickness and conductivity of the film was 0.43 mm and 1.0×10−11 S/cm respectively, which is same to the film formed in experiment-7, within the limits of experimental errors.
12 ml of 10% (w/v) polystyrene (made by dissolving polystyrene in chloroform) solution was taken in a beaker and 1.8 gm of graphite was added to it. The graphite:polymer weight ratio was 60:40 (noted as PCE-PS). The mixture was stirred and sonicated for 10 minutes. The suspension was spread over modified glass mold of area 48.99 cm2. The system was kept for drying for 24 hours at room temperature. The thickness and conductivity of the film was 0.41 mm and 3.1×10−2 S/cm respectively, which is same to the film formed in experiment-3 & 4, within the limits of experimental errors.
1.52 gm polyvinyl chloride dissolved in 20 ml of hot tetrahydrofuranwith continuous stirring. 2.28 gm of graphite then added to it and mixed with the help of glass rod. The graphite:polymer weight ratio was 60:40 (noted as PCE-PVC). The mixture was sonicated for 10 minutes by maintaining the temperature at around 60° C. The suspension was spread over modified glass mold of area 62.18 cm2. The thickness and conductivity of the film was 0.43 mm and 1.2×10−3 S/cm respectively.
20 ml of 10% (w/v) poly (lactic acid) (made by dissolving PLA in chloroform) was taken in a beaker and 3 gm of graphite was added to it. The graphite:polymer weight ratio was 60:40(noted as BPCE). The mixture was stirred and sonicated for 10 minutes. The suspension was spread over modified glass mold of area 100 cm2. The system was kept for drying for 24 hours at room temperature. The thickness and conductivity of the film was 0.38 mm and 2.0×10−3 S/cm respectively.
PCE-PMMA-II was used as working electrode for the measurement of cyclic voltammogram of ferrocyanide/ferricyanide(
This example demonstrates that the electrode shows super Nernstian behavior (ΔE larger than 59 mV/s for one electron transfer and Ipa>Ipc) for all three redox couples which is characteristics of graphite composite electrodes.
Effort was made for anodic oxidation of aniline to form polyaniline via electropolymerization using PCE-PMMA-II and BPCEas working electrode. For this purpose, asulphatemonomer of aniline was prepared by dissolving 0.1M aniline in 0.5 M H2SO4 followed by sonication for 4-5 minutes. Freshly prepared aniline monomer was taken in 10 ml beaker and polymerization was carried out by cycling the potential in −0.2V to 0.8 V range for 9 cycles at 50 mV/s scan rate. The cyclic voltammograms for the electropolymerization of aniline overboth the electrodes are given in
This example demonstrates that the PCE & BPCEcan be used effectively for the electropolymerization.
PCE-PMMA-II was used as working electrode for the non-enzymatic amperometric sensing of hydrogen peroxide. For this purpose, a stock solution of 1 mM H2O2 was prepared in 0.1 M phosphate buffer (pH 5.2). A constant potential −0.2V was applied and responses were recorded by successive addition of 100 □L of stock solution under stirring condition. The addition of stock solution was started after attainment of steady state (constant current) at an interval of 1 minute. The chronoamperometric graph for H2O2 sensing is given
This example shows that non enzymatic amperometric detection of hydrogen peroxide can be performed using PCE. The responses were found to be instantaneous linear (R2=0.998) in wide concentration window (9 μM to 400 μM). The sensitivity was found to be 0.42 μA/μM and lower detection limit was 9 μM.
Galvenostatic electrowinning of zinc was tried on the PCE-PMMA-II electrode using a solution having zinc (167.5 g/L), manganese (5.5 g/L), and iron (7 g/L). Three different current densities viz. 0.25, 1.25 and 2.25 mA/cm2 were examined for the zinc deposition (
This example demonstrates that these electrodes can be effectively used for the electrowinning purpose.
Anodic stripping voltammetric (ASV) for the detection of lead was attempted on PCE-PMMA-II using it as working electrode. A stock solution (1 mM) of lead nitrate was prepared in acetate buffer (0.1M) pH 4.5 for this purpose. Several solutions of lead ranging from 0.5 □M to 40 □M were prepared by successive dilution of stock solution with same buffer. Electrodeposition was carried out by applying −1.2V for 5 minutes with continuous stirring. The voltammogram (
The advantages of the present invention are
| Number | Date | Country | Kind |
|---|---|---|---|
| 1254/DEL/2014 | May 2014 | IN | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/IN2015/000202 | 5/8/2015 | WO | 00 |
