WO2015168556A1

WO2015168556A1 - Magnetically-modified conducting polymer composites and methods of preparation thereof

Info

Publication number: WO2015168556A1
Application number: PCT/US2015/028799
Authority: WO
Inventors: Shelley D. Minteer; Garett G.W. Lee
Original assignee: The University Of Utah Research Foundation
Priority date: 2014-05-01
Filing date: 2015-05-01
Publication date: 2015-11-05

Abstract

Magnetically-modified conducting polymer composites and methods of preparing magnetically-modified conducting polymer composites are disclosed. Conducting polymers may be magnetically modified by polymerizing the conducting polymer in the presence of magnetic particles in a composite, matrix, or a suspension. Magnetic modification of conducting polymers may increase the conductivity of conducting polymers. The magnetically-modified conducting polymer composites may be used in technologies including, but not limited to, organic light-emitting diodes, biofuel cells, biosensors, and batteries.

Description

MAGNETICALLY-MODIFIED CONDUCTING POLYMER COMPOSITES AND METHODS OF PREPARATION THEREOF

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of United States Provisional Application No. 61/987,310, filed May 1 , 2014, which is hereby incorporated by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH

[0002] This invention was made with government support under Grant No. 1 158943 awarded by the National Science Foundation (NSF). The government has certain rights in the invention.

TECHNICAL FIELD

[0003] The present disclosure is directed to magnetically-modified conducting polymer composites and to methods of preparing magnetically-modified conducting polymer composites.

BACKGROUND

[0004] Biofuel cells are electrochemical devices that convert chemical potential energy to electrical energy. Like the electrochemical processes of traditional fuel cells, biofuel cells rely on a heterogeneous catalyst to make the conversion of fuel to electrical power more kinetically favorable. Yet, unlike traditional fuel cells {e.g., proton exchange membrane (PEM) fuel cells) that rely on precious metal platinum and platinum group metal (PGM) catalysts, biofuel cells make use of naturally occurring biological catalysts (i.e., enzymes) for catalysis.

[0005] The enzymes used in biofuel cells come from both naturally occurring and cultured sources. Depending on which fuel is utilized, a specific enzyme, or a series of enzymes is chosen, for fuel oxidation. For example, glucose dehydrogenase (GDH) can be used for the oxidation of the sugar glucose to D-glucono-1 ,5-lactone, a process that produces two electrons. For further oxidation (beyond D-glucono-1 , 5- lactone), additional enzymes are needed from the pentose phosphate pathway.

[0006] Magnetic field effects have been studied sporadically over the last 25 years. This research has identified a variety of effects in electrochemical systems. These effects have been produced by both large, external permanent magnets and small, microparticulate magnets embedded at electrode surfaces. Large magnets are able to drive charged, solution-based particles on a magnetic field, an effect called magnetohydrodynamics. Magnetic fields also effect the spins of particles {e.g., bosons and fermions), whereby the spin of particles are aligned with the external field. This process, called adiabatic magnetization, is commonly utilized in techniques such as nuclear magnetic resonance (NMR) and electron paramagnetic resonance (EPR). Given the sporadic nature of magnetic field effect research in electrochemical systems, no single theory yet exists to explain the effect. Gradient effects {e.g., transport effects) play a large role in some of the measurements made, but in systems where transport is slowed {e.g., fuel cells), gradient effects are less.

[0007] Additionally, over the last decade, increased sales of consumer electronics have driven the demand for thinner and more power-efficient display devices. Organic light-emitting diode (OLED) technology stands poised to meet this demand. Because OLED displays do not require a backlight, they can be produced thinner than many other technologies. OLEDs also have the potential to be flexible, an attractive quality for curved lighting applications or lighting on textiles. Traditionally, OLED displays have utilized a transparent oxide ceramic electrode known as indium tin oxide (ITO) (see Kim M et al., Synth Met 161 , 2318-2322 (201 1 ), incorporated by reference herein). ITO, although optically transparent and conductive, is brittle in nature and costly to manufacture (see Tait JG et al., Sol Energy Mat Sol Cells 1 10, 98-106 (2013), incorporated by reference herein). As such, current research focusing on conducting polymers looks to replace ITO anodes with flexible conducting polymers. Conducting polymer based devices, however, are currently less efficient than devices made with ITO anodes. This reduced efficiency has limited their practical use and stands as a barrier towards the commercialization of flexible anode technologies (see Mu H et al., J Lumin 126, 225-229 (2007), incorporated by reference herein).

[0008] Much of the research involving conducting polymers as OLED anodes is based around poly(3,4-ethylenedioxythiophene), more commonly known as PEDOT. PEDOT has a relatively high conductivity while maintaining good optical transparency (>80%), both of which are ideal anode properties. While PEDOT is conductive, its conductivity is lower than that of ITO, causing a decrease in OLED efficiency (see Kim M et al., 201 1 , supra). Research has shown ways in which the conductivity of PEDOT can be increased, however, making it more viable for use as an OLED anode (see Wang GF et al., Nanotechnology 19, 145201 (2008), incorporated by reference herein).

[0009] Conducting polymers may also be utilized for a variety of other technologies, including, but not limited to, biofuel cells, biosensors, organic solar cells, fuel cells, and batteries.

[0010] Standard light-emitting diodes (LEDs) operate by utilizing a p-n junction composed of semiconducting materials. A p-n junction operates by separating positive and negative charge carriers (i.e., electrons and holes) by a region that is depleted of charge carriers. An energy barrier prevents the charge carriers from entering this depleted region and recombining. Applying a forward bias voltage to the p-n junction reduces the energy barrier, allowing for charge carriers to enter the depleted region and recombine. Electrons from the conduction band recombine with holes from the valence band and in so doing a photon is emitted. Applying a reverse voltage will only increase the energy barrier and no charge injection will occur (see Kasap SO, Principles of Electronic Materials and Devices, Vol. 3, New York, NY: McGraw-Hill (2006), incorporated by reference herein). OLEDs operate by a similar mechanism. In OLEDs, organic molecules or polymers replace semiconductors as the material which creates both the energy barrier and the region in which charge carriers recombine to produce light (see Ke L et al., IEEE Trans Electron Dev 53, 1483-1486 (2006), incorporated by reference herein). The highest occupied molecular orbital (HOMO) functions as the valence band and the lowest unoccupied molecular orbital (LUMO) functions as the conduction band. For an OLED to function properly, the anodic contact must have a work function that is similar in energy to the HOMO of the adjacent layer through which current will flow; a mismatch will limit efficiency. In addition, the anode must be conductive and optically transparent (see Ke L et al., 2006, supra). In a simple single-layer device, electrons are injected from the cathode into the LUMO of the organic emissive layer and recombine with holes that have been inserted from the anode into the HOMO. Utilizing a double layer or other structures can fine tune the energy levels at which injection occurs and lower the resistance of the device (see Anikeeva P, Physical Properties and Design of Light-Emitting Devices Based on Organic Materials and Nanoparticles, Massachusetts Institute of Technology (2009), incorporated by reference herein).

[0011] It has been shown that the conductivity of polymer electrolytes can be increased by casting them in the presence of a magnetic field (see Kovarsky R et al., Electrochim Acta 57, 27-35 (201 1 ), incorporated by reference herein). In its application to OLEDs, the work of Kalinowski et al. has shown that the electroluminescent output and quantum efficiency of tris(8- hydroxyquinoline)aluminum (AIQ₃) based devices can be improved when the OLED is operated within a magnetic field (see Kalinowski J et al., Chem Phys Lett 380, 710-715 (2003), incorporated by reference herein), but this is not generally practical.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The embodiments disclosed herein will become more fully apparent from the following description and appended claims, taken in conjunction with the accompanying drawings. These drawings depict only typical embodiments, which will be described with additional specificity and detail through use of the accompanying drawings in which:

[0013] FIG. 1 is a graph depicting cyclic voltammetry (CV) of polymerization of methylene green at Toray^® carbon paper electrodes (light gray), Toray^®|tetrabutylammonium bromide (TBAB) modified Nafion^® electrodes (medium gray), and magnetic composite electrodes (black) in a polymerization solution comprising of pH 8.95 50 mM PBS, 10 mM borate, and 0.4 mM methylene green, scan rate = 50 mV/sec.

[0014] FIG. 2 is a graph comparing voltammetric polymerization of methylene green at Toray^®|TBAB modified Nafion^® electrodes (gray) and magnetic composite electrodes (black) in a polymerization solution comprising pH 6.04 50 mM PBS and 0.4 mM methylene green dashed lines, pH 8.95 solid lines, scan rate = 50 mV/sec.

[0015] FIG. 3 is a graph depicting average voltammetric response of poly(methylene green) (PMG) modified Toray^® electrodes in 50 mM PBS and 0.1 M nitrate, pH 7, scan rate = 20 mV/sec.

[0016] FIG. 4 is a graph depicting peak potentials and current responses for reductive (red) and oxidative (ox) sweeps from the CV data of FIG. 3; error bars indicate relative standard deviation. [0017] FIG. 5 is a graph depicting ultraviolet-visible spectroscopy (UV-Vis) of PMG films on ITO-coated polyethylene terephthalate (PET) electrodes.

[0018] FIG. 6 is a graph depicting CV overlay of NADH oxidation at Toray^® control electrodes (light gray), Toray^®|PMG electrodes (medium light gray), Toray^®|TBAB|PMG electrodes (medium dark gray), and Toray^®|MagComp|PMG electrodes (black) in 15 mM NADH, pH 7 50 mM PBS, and 0.1 M NaNO₃, scan rate = 20 mV/sec.

[0019] FIG. 7 is a graph depicting an amperometric-/t curve for the oxidation of NADH at Toray^® paper (TP)|TBAB|PMG (gray) and TP|MagComp|PMG (black) at 0.3 V vs saturated calomel (SCE) applied; 500 μΙ_ additions of 50 mM NADH in pH 7 50 mM PBS and 0.1 M NaNO₃.

[0020] FIG. 8 is a graph depicting amperometric-/t curve data for the oxidation of NADH at TP|TBAB|PMG (gray) and TP|MagComp|PMG (black) at 0.3 V vs SCE applied; 500 μΙ_ additions of 50 mM NADH in pH 7 50 mM PBS and 0.1 M NaNO₃.

[0021] FIG. 9 is a graph depicting amperometric-/t curve data for the oxidation of NADH at TP|TBAB|PMG (gray) and TP|MagComp|PMG (black) at 0.3 V vs SCE applied; 500 μΙ_ additions of 50 mM NADH in pH 7 50 mM PBS and 0.1 M NaNO₃.

[0022] FIG. 10 is a graph depicting an amperometric-/t curve for the oxidation of glucose at GDH-modified electrodes; TP|TBAB|PMG (gray) and TP|MagComp|PMG (black), potential applied 0.3 V vs SCE; 500 μΙ_ additions of 0.15 M glucose solution in pH 7, 50 mM PBS and 0.1 M NaNO₃ solution.

[0023] FIG. 1 1 is a graph depicting amperometric-/t curve data for the oxidation of glucose at GDH modified electrodes; TP|TBAB|PMG (gray) and TP|MagComp|PMG (black), potential applied 0.3 V vs SCE; 500 μΙ_ additions of 0.15 M glucose solution in pH 7, 50 mM PBS and 0.1 M NaNO₃ solution.

[0024] FIG. 12 is a graph depicting the voltammetric response of laccase, anthracene-modified multi-walled carbon nanotubes (An-MWCNT) modified Toray^® electrodes, control electrodes (gray) and magnetic composite electrodes (black); in pH 4.5 0.15 M citrate buffer solution, scan rate = 10 mV/sec, gas (O2 or N₂) saturation achieved via 15 minute purge.

[0025] FIG. 13 is a schematic depiction of an embodiment of an OLED design.

[0026] FIG. 14 is an image of PEDOT film with 5 wt. % Fe₃O₄. DETAILED DESCRIPTION

[0027] This disclosure is related to magnetically-modified conducting polymer composites and methods of preparing magnetically-modified conducting composites. It will be readily understood that the embodiments, as generally described herein, are exemplary. The following more detailed description of various embodiments is not intended to limit the scope of the present disclosure, but is merely representative of various embodiments. Moreover, the order of the steps or actions of the methods disclosed herein may be changed by those skilled in the art without departing from the scope of the present disclosure. In other words, unless a specific order of steps or actions is required for proper operation of the embodiment, the order or use of specific steps or actions may be modified.

[0028] Unless specifically defined otherwise, the technical terms, as used herein, have their normal meaning as understood in the art. The following terms are specifically defined with examples for the sake of clarity.

[0029] The term "conducting polymer" refers herein to a polymer that can conduct electricity. Examples of conducting polymers include, but are not limited to, PEDOT, polyacetylenes, polyanilines, poly(p-phenylene vinylene), poly(methylene green), poly(methylene blue), polyphenylene sulfides, polypyrroles, polythiophenes, and others known to those skilled in the art.

[0030] The term "ionomer" refers herein to a polymer with ionic properties. Most ionomers are classified as anion exchange polymers containing cation functional groups or cation exchange polymers containing anionic functional groups. Examples of ionomers include, but are not limited to, Nafion^®, polyallylammonium, Flemion^®, polystyrene sulfonate, and others known to those skilled in the art..

[0031] The term "magnetic particles" refers herein to magnetic particles, magnetic microparticles, and/or magnetic nanoparticles.

[0032] Herein, the magnetic field effect at bioanodes has been considered. Magnetic composites with an ionomer but without a conducting polymer have previously been analyzed for their effects on a traditional nickel electrocatalyst (see Lee GG et a/., Chem Commun 48, 1 1972-1 1974 (2012), incorporated by reference herein). Described below are experimental protocols and results of the effects of magnetic composite bioanodes containing the conducting polymer poly(methylene green).

[0033] Magnetic composites can have a substantial and/or significant effect on oxidation of both NADH and glucose, and bioanodes containing NADH electrocatalysis PMG and the enzyme glucose dehydrogenase. The enhancement may be due, at least in part, to the effect of magnetic fields on transport of changed species (i.e., magnetohydrodynamics), interfacial transport effects, and increased film conductivity. Other effects may also play a role in the enhancement.

[0034] Disclosed herein are a variety of methods that may enhance or improve the performance of conducting polymers via the formation of magnetically-modified conducting polymer composites. Enhancement or improvement in the performance of conducting polymers may be achieved by forming a magnetic composite with an ionomer and electropolymerizing the conducting polymer in a matrix. Magnetically- modified conducting polymer composites can also be formed from suspensions of a conducting polymer with added magnetic particles and an applied magnetic field. In some embodiments, the applied magnetic field may only be applied during formation.

EXAMPLES

[0035] To further illustrate these embodiments, the following examples are provided. These examples are not intended to limit the scope of the claimed invention, which should be determined solely on the basis of the attached claims.

Example 1 - Preparation of enzyme-modified electrodes

[0036] Enzyme-modified electrodes were prepared. The preparation protocol comprised multiple steps, including drop casting and an electropolymerization procedure. Enzyme immobilization may occur within a bromide-modified Nafion^® membrane, tetrabutylammonium bromide modified Nafion^® (TBAB-Nafion^®). This membrane can act to stabilize the enzyme, and has been shown to prolong the lifetime of bio-modified electrodes.

[0037] Electrochemical electrode preparation and evaluation occurred using a Digi-lvy^® DY2000 or DY2300 model bipotentiostat using a personal computer (PC) interface. These techniques comprised both cyclic voltammetry (CV) and amperometry, which are both examples of potential (voltage) controlled methods. Deposition and evaluations used a platinum (Pt) mesh counter electrode and a saturated calomel (SCE) reference electrode. The analytical solutions were prepared with Milli-Q^® 18 ΜΩ water.

[0038] Magnetic composite electrodes were compared to two, non-magnetic analogues: 1 ) Toray^®|PMG electrodes and 2) Toray^®|TBAB|PMG electrodes. The second electrodes, Toray^®|TBAB|PMG electrodes, were used as the magnetic composite was drop cast before the polymerization of methylene green, and as such, a non-magnetic film was used as a control.

[0039] The preparation of control electrode 1 proceeded as follows: Toray^® paper electrodes were templated and cut to 1 cm², and a wax coating was used to confine the working area of the electrode to 1 cm². The electrodes were then coated with PMG via an electropolymerization procedure in an aqueous solution of 0.1 M sodium nitrate, 10 mM sodium borate, and 0.4 mM methylene green. In solution, the electrodes were polymerized via CV at a scan rate of 50 mV/sec, over a potential window of -0.3 to 1 .3 V vs. an SCE reference electrode for six cycles. The electrodes were then removed from solution, rinsed, and allowed to dry before use.

[0040] The preparation of control electrode 2 was preceded by an initial drop casting of TBAB-Nafion^®, wherein a standard concentration TBAB-Nafion^® solution was first mixed in a 50:50 ratio with ethyl alcohol (this was done to mimic the decreased Nafion^® concentration of the magnetic composite casting solution described below). The electrodes were then coated with the polymer film by drop casting 12 μΙ_ of solution onto one side of the Toray^® paper electrodes. The electrodes were allowed to dry for at least four hours. Polymerization of PMG then occurred as with control electrode 1 .

[0041] Magnetic composite electrodes were prepared analogously to control electrodes 2; however, the composite electrodes were formed with a drop casting a solution of magnetic microparticles (Bangs Laboratories, Inc.™) that were combined with ethyl alcohol and TBAB-Nafion^® in a ratio of 15:35:50, respectively. The composite casting solution was also drop cast on Toray^® paper electrodes at 12 L/cm².

[0042] PMG electrodes were assessed in both buffer and NADH solutions before the immobilization of enzyme-containing films. These assessments were used for control of the PMG layer at the various electrodes. The procedures and results of both CV and amperometric analyses, both current-response measurements, are discussed below.

[0043] Enzyme containing films were similarly drop-cast onto the PMG-Toray^® electrodes. A standard solution of lyophilized glucose dehydrogenase (GDH) was combined in a pH 7, 50 mM phosphate buffer (PBS) and 0.1 M NaNO3 solution to a concentration of 2 mg enzyme/mL. To the enzyme solution, was then added 83 μΙ_ of the standard TBAB-Nafion^® solution. The GDH/TBAB-Nafion^® solution was then drop-cast on top of the PMG electrodes at 15 L/cm². The electrodes were then again allowed to dry for at least four hours (overnight drying may also be acceptable as immobilized enzyme stability can be on the order of weeks to months).

[0044] The heterocyclic, aromatic dye, methylene green, was used herein as a catalyst for the oxidation of NAD⁺ to NADH. Glucose dehydrogenase (GDH) can be an NAD⁺ dependent enzyme, and as such can require NAD⁺ to complete the oxidation of glucose to D-glucono-1 ,5-lactone. NAD⁺ can be reduced in the process of glucose oxidation to NADH; NADH can then be oxidized back to NAD⁺ at the working electrode in a reversible reduction/oxidation cycle. The reduction and oxidation of NAD7NADH may require overpotential, or substantial overpotential, (i.e., -0.56 V vs. SCE) at planar electrode surfaces. The application of PMG as an electrocatalyst for NADH oxidation can lower the required potential to -0.3 V vs. SCE at pH 7. Lowered overpotential may translate into increased efficiency for electrochemical processes.

[0045] FIG. 1 depicts the polymerization of methylene green in the three separate systems as described above. As is shown, the magnetic composites can demonstrate both increased current response during deposition, as well as peak shifts during the deposition. For example, the prevalent peak at approximately -0.1 V for the magnetic composites is shifted nearly + 50 mV for the TBAB composite control. In the Toray^® control, the single peak is actually two features for the first cycle. The oxidative feature, or shoulder, near + 1 .0 V is also shifted in the case of the magnetic composite to more negative potentials. To further explore this effect, a polymerization solution at pH 6 was utilized to determine if the features were proton dependent. [0046] FIG. 2 shows the initial sweep for the polymerization of PMG at TBAB and magnetic composite Toray^® paper electrodes as an overlay with the same electrodes in pH 8.95 borate solution. There is a viable shift to more positive potentials (consistent with a change to more negative pH values) for the features at negative potentials. More negative pH values also make apparent the two electron transfer process involved for the reduction steps (at -0.1 V and -0.2 V vs SCE).

Example 2 - Analysis of magnetic composite effects

[0047] PMG can be utilized in a system of the present disclosure as a catalyst for the oxidation of NADH to NAD⁺. To conduct an analysis of magnetic composite effects on the systems, the three electrode systems were first analyzed via CV in pH 7 PBS buffer. From the deposition voltammograms, it was assumed that more PMG was deposited in the case of the magnetic composite than in the case of the control electrodes; however, CVs of the resulting polymers in buffer indicated that more PMG existed on Toray^® electrodes (see FIG. 3).

[0048] The PMG CVs in buffer also exhibited a shift of the oxidative and reductive features to more negative potentials for the magnetic composite versus the control electrodes. The potentials of these features have been extracted and plotted in FIG. 4 and tabulated in Tables 1 and 2 below.

Table 1. Values of peak shifts (difference from TP|PMG controls)

TBAB-Nafion^® Potential Shift (V) Tcalc Difference (n = 3)

ΔΕ_ρ red 0.018 3.4 95 %

Magnetic Potential Shift (V) Tcalc Difference (n = 3)

Composite

AEp ox 0.1 16 24.5 99.9 %

Table 2. Values of peak splittings (difference from TP|PMG controls)

Composition ΔΕρ (V) Tcalc Difference (n = 3)

TP control 0.151 (± 0.024)

TBAB-Nafion^® 0.082 (± 0.01 1 ) 4.45 97 %

Mag Composite 0.084 (± 0.06) 4.54 98 %

[0049] To further analyze the relationship between PMG deposition current and the current of the PMG in buffer, PMG films were deposited on indium tin oxide (ITO) coated polyethylene terephthalate (PET) slides, analogously to the process described above, which were then analyzed via UV-Vis spectroscopy. The overlay depicted in FIG. 5 indicates that more PMG was deposited on magnetic composite electrodes.

Example 3 - Analysis of catalytic ability of Torav^® electrodes

[0050] The catalytic ability of the Toray^® electrodes were analyzed in a NADH control solution comprising 15 mM NADH in pH 7 PBS with 0.1 M NaNO₃. The electrodes were analyzed first by CV. As is depicted in FIG. 6, the current response of magnetic composite electrodes is nearly double that of Toray^®|PMG electrodes, and more than five times greater than TBAB|PMG electrodes.

[0051] The data corresponding to the current responses in FIG. 6 for both the first and second sweeps are given in Table 3. The solution is not stirred (non-steady state) which produces a decrease in current response for the second sweep.

Table 3. Current response of NADH oxidation at 0.3 V vs SCE, average of n = 3 electrodes

1 -94 (± 25) μΑ -450 (± 97) μΑ -170 (± 45) μΑ -970 (± 280) μΑ

2 -71 (± 10) μΑ -390 (± 61 ) μΑ -130 (± 24) μΑ -700 (± 140) μΑ

[0052] Amperometric analysis, a constant potential technique, was also used to analyze the electrodes for NADH catalysis. Here, standard addition was used over a range of zero to 14 mM NADH. A potential of 0.3 V was applied and 500 μΙ_ additions of 50 mM NADH were added to a stirring solution every 120 seconds. The average current response of NADH oxidation at pH 8.95 deposited electrodes is shown in FIG. 7.

[0053] The corresponding data for the standard additions that correlates current response to concentration of NADH is depicted in FIG. 8. The fits for the pH 6.04 buffer and PMG electrode system are control fits of y = - 5 x 10^"6x - 2 x 10^"4 and y = - 2 x 10^"5x - 2 x 10^"4for the magnetic composites.

[0054] An identical amperometric analysis was run for PMG electrodes prepared in pH 6.04 buffer. The result of this analysis is shown in FIG. 9. No substantial difference in the electrocatalytic behavior exists between the two data sets. The fits for the pH 6.04 buffer and PMG electrode system are control fits of y = - 4 x 10^"6x - 2 x 10^"5, and y = -3 x 10^"5x - 6 x 10^"5 for the magnetic composites.

Example 4 - Analysis of glucose oxidation at the bioanodes

[0055] Analysis of the bioanodes also included the immobilization of glucose dehydrogenase (GDH) in TBAB-Nafion^® and the oxidation of glucose via amperometry. Here, electrodes deposited in a pH 6.04 buffer were modified with the previously described GDH casting solution and were allowed to dry for four hours before analysis.

[0056] The corresponding data for the standard additions that correlates current response to concentration of glucose is depicted in FIG. 1 1 . Though not truly a linear response, linear fits to the data for glucose oxidation give returns control fits of y = - 5 x 10^"8x - 3 x 10^"8, and y = -6 x 10^"7x - 8 x 10^"8 for the magnetic composites. This increase in response is nearly 1 .6 times more sensitive than the amperometric response of NADH oxidation alone.

[0057] The oxidation of glucose at magnetic composite electrodes produces over ten-time greater current response at 30 mM glucose than at the TBAB-Nafion^® analogues. This current response is significantly better than the improvement of NADH oxidation alone. Rise time and voltammetric behavior are similar between the two species, indicating occurrence of an effect in addition to transport effects, for example, an effect on kinetic behavior. Additionally, glucose oxidation at TP|PMG electrodes may give current response between magnetic composite and TBAB- Nafion^® analogues. Example 5 - Analysis of transport effects in a bio-electrode system

[0058] Another bio-electrode system was prepared with magnetic composites to determine if transport effects are the predominate effects benefiting bio- electrochemical systems. Magnetic microparticles were incorporated in a composite mixture of the oxygen reducing enzyme laccase, anthracene-modified multi-walled carbon nanotubes (An-MWCNT), and TBAB-Nafion^®, prepared as in Lee GG et ai, 2012, supra. This composite was cast on Toray^® paper electrodes, and the oxygen reduction capabilities were examined in pH 4.5 PBS oxygen-saturated solutions.

[0059] As can be seen in FIG. 12, the incorporation of magnetic microparticles statistically reduced the efficiency at which oxygen reduction occurred. The magnetic composites here were also compared to near identical non-magnetic analogues that contain the same loading of enzyme, nanotubes, and TBAB-Nafion^®.

[0060] Analysis of another electropolymer, neutral red, revealed that the magnetic field does not increase the amount of polymerization in all polymer systems. This may indicate that magnetic transport is not the predominant method of current enhancement; if transport on the magnetic gradient predominated in these systems then enhancement would likely be observed for each electrodeposited film.

Example 6 - Preparation of an PLED comprising a magnetically-modified conducting polymer composite

[0061] Tris(8-hydroxyquinoline)aluminum (AIQ₃) was selected as an emissive layer of a device and N,N-Bis(3-methylphenyl)-N,N'-diphenylbenzidine (TPD) was selected as a hole transport layer of the device. While a standard practice for depositing these organic solids is the use of a thermal evaporation technique, thermal evaporation may not be conducive to the addition of nanoparticles and therefore a solution processing technique was utilized. The AIQ₃ and TPD were mixed into a single solution to avoid the dissolution of any previously deposited layers upon spin coating of a second organic layer. A schematic of the design is depicted in FIG. 13.

[0062] Organic solutions were prepared by dissolving an AIQ₃/TPD mixture (1 .33 wt. ratio) in chloroform. Both the AIQ₃ and TPD were purchased from Sigma-Aldrich^® ( Product numbers 444561 , 443263) and used as received. The organic solids composed 1 % wt. of the total solution mixture. Poly(3,4-ethylenedioxythiophene)- poly(styrenesulfonate); 3.0-4.0% in water (Product number 655201 , Sigma-Aldrich ) was also used as received.

[0063] Glass microscope slides were used as the substrate material and were cut to an area of roughly 2 cm² using a diamond scorer. Slides were rinsed three times each with deionized water and methanol sequentially.

[0064] Before the spin coating procedure, a selected area for the anode was masked off using Kapton^® tape (roughly 1 cm²). PEDOT was pipetted onto the substrate and spin coated at RPM values ranging from 1500-2500 RPM (see Table 4). The PEDOT solution was dried on a hot plate at 1 10 °C for 15 minutes. After drying the PEDOT film, an additional masking layer was applied to cover a portion of the PEDOT for use as the anodic contact. Following this second masking, the AIQ3/TPD solution was spin coated at values ranging from 1500-2500 RPM (see Table 4) and dried on a hot plate at 1 10 °C for 15 minutes. Aluminum was deposited using a Denton^® Discovery 18 sputtering system with an argon pressure of 7.28 mTorr and an operating voltage of 357 V. A pre-sputter of one minute was followed by a four minute deposition time at a rate of 22.5 nm/min. After each unsuccessful device, variations in the masking procedure were used in an attempt to eliminate observed edge effects. The variations can be found in Table 4. Film thicknesses were measured using a Tencor^® P-20H profilometer. Sheet resistance was measured using a Magnetron Instruments^® Microtech RF-1 four point probe.

Table 4. Fabrication procedures for PEDOT films

Samples Spin Speed & Sheet PEDOT Film Masking Procedure

Time Resistance Thickness

(RPM-S) -M

Sample 1 1500-30 225 558 -Masked anode area

-Masked contact after spin coating PEDOT

Sample 2 2000-30 227 507 -Masked anode area

-Removed mask and re- masked before each layer

Sample 3 2500-30 221 466 -Same as sample 1 Sample 4 2400-40 224 250 -Masked anode area

-Re-masked before Al sputter

Sample 5 2600-30 300 -Masked after

deposition of anode [0065] Spin coating of the PEDOT films resulted in film thicknesses varying from 1 13 nm to 500 nm. The film thicknesses corresponding to their spin coating speeds can be found in Table 4. The average sheet resistance of the films was found to be 224 ± 2 Ω/sq. The conductivity of the films was consistent with other PEDOT films used in the fabrication of similar devices (see Kim M et al., 201 1 , supra). The increase in the conductivity may be attributed to dispersion of the Fe3O₄ (see FIG. 14). The iron oxide (Fe₃O ) magnetic particles were added to the PEDOT solution before spin coating.

[0066] It will be apparent to those having skill in the art that many changes may be made to the details of the above-described embodiments without departing from the underlying principles of the invention. The scope of the present invention should, therefore, be determined only by the following claims.

Claims

CLAIMS:

1 . A method of making a magnetically-modified conducting polymer composite, comprising the steps of:

combining a plurality of magnetic particles with an ionomer to form a matrix; adding the matrix to a solution comprising monomers of a conducting polymer; and

polymerizing the conducting polymer.

2. The method of claim 1 , wherein the polymerization comprises electropolymerization .

4. The method of claim 1 , wherein the plurality of magnetic particles are selected from at least one of magnetic microparticles or magnetic nanoparticles.

5. The method of claim 1 , wherein the ionomer comprises Nafion^®.

6. The method of claim 1 , wherein the conducting polymer is selected from at least one of poly(3,4-ethylenedioxythiophene), a polyacetylene, a polyaniline, poly(p-phenylene vinylene), a polyphenylene sulfide, poly(methylene green), poly(methylene blue), a polypyrrole, or a polythiophene.

7. The method of claim 1 , wherein the conducting polymer comprises poly(3,4-ethylenedioxythiophene).

8. The method of claim 1 , further comprising the step of:

casting a suspension of the magnetic particles and the ionomer in the presence of a magnetic field;

drying the cast suspension; and

removing the magnetic field.

9. A method of making a magnetically-modified conducting polymer composite, comprising the steps of:

forming a suspension of a conducting polymer;

adding a plurality of magnetic particles to the suspension; and

applying a magnetic field to the suspension comprising the plurality of magnetic particles.

10. The method of claim 9, further comprising the step of:

drying the conducting polymer composite.

1 1 . The method of claim 9, wherein the magnetic field is cylindrical.

12. A method of making an organic light-emitting diode (OLED), comprising the steps of:

coating at least a portion of a substrate with a layer of a solution comprising a conducting polymer and a plurality of magnetic particles;

covering at least a portion of the conducting polymer layer with a masking layer;

coating at least a portion of the conducting polymer layer with a layer of a mixture of a first organic solid and a second organic solid; and

depositing a metal on at least a portion of the layer of the first organic solid and the second organic solid.

13. The method of claim 12, wherein the first organic solid comprises tris(8-hydroxyquinoline)aluminum.

14. The method of claim 12, wherein the second organic solid comprises N,N-Bis(3-methylphenyl)-N,N'-diphenylbenzidine.

15. The method of claim 12, wherein the first organic solid and the second organic solid comprise up to one percent weight of the total solution mixture.

16. The method of claim 12, wherein the substrate is coated with the solution comprising the conducting polymer and the plurality of magnetic particles via spin coating.

17. The method of claim 16, wherein the spin coating is conducted at a revolutions per minute (RPM) value between 1 ,500 RPM and 2,500 RPM.

18. The method of claim 12, wherein the conducting polymer layer is coated with the mixture of the first organic solid and the second organic solid via spin coating.

19. The method of claim 18, wherein the spin coating is conducted at a revolutions per minute (RPM) value between 1 ,500 RPM and 2,500 RPM.

20. The method of claim 12, wherein the metal comprises aluminum.

21 . A method of making a magnetic composite bioanode, comprising the steps of:

coating an electrode with a first solution comprising a plurality of magnetic particles, an ionomer, and a solvent;

further coating the coated electrode with a conducting polymer; and polymerizing the conducting polymer.

22. The method of claim 21 , wherein the polymerization of the conducting polymer comprises electropolymerization.

23. The method of claim 21 , wherein the coating of the electrode with the first solution is conducted via drop casting.

24. The method of claim 21 , wherein the plurality of magnetic particles are selected from at least one of magnetic microparticles or magnetic nanoparticles.

25. The method claim 21 , wherein the ionomer comprises Nafion^®.

26. The method of claim 21 , wherein the conducting polymer is selected from at least one of poly(3,4-ethylenedioxythiophene), a polyacetylene, a polyaniline, poly(p-phenylene vinylene), a polyphenylene sulfide, a polypyrrole, or a polythiophene.

27. The method of claim 21 , wherein the conducting polymer comprises poly(3,4-ethylenedioxythiophene).

28. A conducting polymer composite, comprising:

a plurality of magnetic particles;

an ionomer; and

a conducting polymer.

29. The conducting polymer composite of claim 28, wherein the plurality of magnetic particles are selected from at least one of magnetic microparticles or magnetic nanoparticles.

30. The conducting polymer composite of claim 28, wherein the ionomer comprises Nafion^®.

31 . The conducting polymer composite of claim 28, wherein the conducting polymer is selected from at least one of poly(3,4-ethylenedioxythiophene), a polyacetylene, a polyaniline, poly(p-phenylene vinylene), a polyphenylene sulfide, a polypyrrole, or a polythiophene.

32. The conducting polymer composite of claim 28, wherein the conducting polymer comprises poly(3,4-ethylenedioxythiophene).