Aoife Morrin

The application of conducting polymer nanoparticle electrodes to the sensing of ascorbic acid.

An ascorbic acid sensor was fabricated via the drop-casting of dodecylbenzene sulphonic acid (DBSA)-doped polyaniline nanoparticles onto a screen-printed carbon-paste electrode. The modified electrode was characterised with respect to the numbers of drop cast layers, optimum potential and operating pH. The sensor was found to be optimal at neutral pH and at 0V vs. Ag/AgCl. Under these conditions, the sensor showed good selectivity and sensitivity in that it did not respond to a range of common interferents such as dopamine, acetaminophen, uric acid and citric acid, but was capable of the detection of ascorbic acid at a sensitivity of 0.76 microA mM(-1) or 10.75 microA mM(-1) cm(-2) across a range from 0.5 to 8mM (r2=0.996, n=6), and a limit of detection of 8.3 microM (S/N=3). The sensor was compared to a range of other conducting polymer-based ascorbate sensors and found to be comparable or superior in terms of analytical performance.

Fabrication of Polyaniline-Based Gas Sensors Using Piezoelectric Inkjet and Screen Printing for the Detection of Hydrogen Sulfide

This work describes a fully printable polyaniline-copper (II) chloride sensor for the detection of hydrogen sulfide gas. The sensing device is composed of screen printed silver interdigitated electrode (IDE) on a flexible PET substrate with inkjet printed layers of polyaniline and copper (II) chloride. The sensor is employed as a chemiresistor with changes in measured current being correlated with concentration. On exposure to hydrogen sulfide, 2.5 ppmv (parts per million by volume) is clearly detectable with a linear relationship between measured current and concentration over the 10-100 ppmv region. The detection mechanism is discussed with respect to the hydrogen sulfide response, the choice of electrode materials in addition to UV-vis and surface enhanced Raman spectroscopy (SERS) characterization.

Electrochemical Characterization of Commercial and Home-Made Screen-Printed Carbon Electrodes

Abstract Screen-printing technology is widely used for the mass-production of disposable electrochemical sensors. The practical utility of carbon screen-printed electrodes has been exploited, despite the fact that little is known about the nature of the electrode reactions. (Wang, J.; Pedrero, M.; Sakslumd, H.; Hammerich, O.; Pingarron, J. Electrochemical activation of screenprinted carbon strips. The Analyst 1996, 121 (3), 345–350). Given the complexity of carbon electrodes in general, and differences in the composition of commercial carbon inks, the question arises as to how such differences and complexity affect their electrochemical reactivity. The aim of this work was to compare the electroactivity of both commercial electrodes and electrodes fabricated in-house from various commercial inks, in order to find the electrode most suited to amperometric sensor work. Methods of analysis include cyclic voltammetry, amperometry and linear sweep voltammetry. It was found that the commercial working electrodes were not suited to the high current work of interest, due to their poor charge transfer properties. The in-house electrode had less resistive properties, and was more suited for high current amperometric sensing. Utilizing this electrode configuration, an optimal carbon paste was chosen for the working electrode.

Reactive inkjet printing

Functional materials can be synthesised at the same time as their final device geometries are patterned.

Characterisation of horseradish peroxidase immobilisation on an electrochemical biosensor by colorimetric and amperometric techniques

This study presents the use of complementary colorimetric and amperometric techniques to measure the quantity of protein or enzyme immobilised onto a carbon paste electrode modified with a layer of electrodeposited polyaniline. By applying a solution of bovine serum albumin at 0.75 mg/ml, efficient blocking of the electrode from electroactive species in the bulk solution could be achieved. When the horseradish peroxidase was immobilised on the electrode, optimal amperometric responses from hydrogen peroxide reduction were achieved at approximately the same concentration. The mass of enzyme immobilised at this solution concentration was determined by a colorimetric enzyme assay to be equivalent to the formation of a protein monolayer. Under these conditions, amperometric responses from the immobilised layer are maximised and non-specific bulk solution interactions are minimised. At higher immobilised protein concentrations, diminished amperometric responses may be due to inhibited diffusion of hydrogen peroxide to enzyme which is in electronic communication with the electrode surface, or impeded electron transfer.

Printing polyaniline for sensor applications

In recent years, much research has focused on the development of low-cost, printed electrochemical sensor platforms for environmental monitoring and clinical diagnostics. Much effort in this area has been based on utilising the redox properties of conducting polymers, particularly polyaniline (PANI). In tackling the inherent lack of processability exhibited by these materials, several groups have examined various mass-amenable fabrication approaches to obtain suitable thin films of PANI for sensing applications. Specifically, the approaches investigated over the years include the in situ chemical synthesis of PANI, the use of sulphonated derivatives of PANI and the synthesis of aqueousbased nano-dispersions of PANI. Nano-dispersions have shown a great deal of promise for sensing applications, given that they are inkjet-printable, facilitating the patterning of conducting polymer directly to the substrate. We have shown that inkjet-printed films of PANI can be finely controlled in terms of their two-dimensional pattern, thickness, and conductivity, highlighting the level of precision achievable by inkjet printing. Utilising these nanomaterials as inkjet-printable inks opens novel, facile, and economical possibilities for conducting polymer-printed electronic applications in areas of sensing, but also many other application areas such as energy storage, displays, organic light-emitting diodes. Given that inkjet-printing is a scalable manufacturing technique, it renders possible the large-scale production of devices such as sensors for a range of applications. Several successes have emerged from our work and from the work of others in the area of applying PANI in low-cost sensor applications, which is the focus of this review.

Wholly printed polypyrrole nanoparticle-based biosensors on flexible substrate

Printing has been widely used in the sensor industry for its speed, low cost and production scalability. In this work we present a wholly-printed polypyrrole (PPy) based biosensor produced by inkjet printing bioinks composed of dispersions of PPy nanoparticles and enzymes onto screen-printed carbon electrodes. Two enzymes, horseradish peroxidase (HRP) or glucose oxidase (GoD) were incorporated into the PPy nanoparticle dispersions to impart biosensing functionality and selectivity into the conducting polymer ink. Further functionality was also introduced by deposition of a permselective ethyl cellulose (EC) membrane using inkjet printing. Cyclic voltammetry (CV) and chrono-amperometry were used to characterize the response of the PPy biosensors to H2O2 and glucose. Results demonstrated the possibility of PPy based biosensor fabrication using the rapid and low cost technique of inkjet printing. The detection range of H2O2 was found to be 10 μM-10 mM and for glucose was 1-5 mM.

Determination of inorganic mercury using a polyaniline and polyaniline-methylene blue coated screen-printed carbon electrode

Inorganic mercury ions (Hg2+) in laboratory prepared solutions were determined with a screen-printed carbon electrode (SPCE) coated with a polyaniline-methylene blue (PANI-MB) polymer layer. The structure and properties of the PANI-MB polymer layer were compared to that of normal polyaniline (PANI) in order to elucidate the structure of the PANI-MB layer. The electrically-conducting polymers were prepared by electrochemical polymerisation of monomer solutions of aniline, and mixed solutions of aniline with methylene blue onto respective screen-printed carbon electrodes (SPCEs). Scanning Electron Microscopy (SEM) analyses of the SPCE polymer coated electrodes have shown that nanostructured materials have formed with the diameters of the PANI nanoclusters and PANI-MB nanorods at approximately 200 nm. Anodic stripping voltammetry (ASV) was used to evaluate a solution composed of 1 × 10−6 M Hg2+, in the presence of the SPCE/PANI-MB polymer sensor electrode. The Hg2+ ions were determined as follows: (i) pre-concentration and reduction on the modified electrode surface and (ii) subsequent stripping from the electrode surface during the positive potential sweep. The experimental conditions optimised for Hg2+ determination included the supporting electrolyte concentration and the accumulation time. The results obtained have shown that the SPCE/PANI-MB polymer sensor electrode operates optimally at a pH 2, with the supporting electrolyte concentration at 0.5 M HCl. A linear calibration curve was found to be in the range of 1 × 10−8 M to 1 × 10−5 M Hg2+ after 120 s of pre-concentration. The detection limit was calculated and found to be 54.27 ± 3.28 µg L−1 of Hg2+. The results have also shown that a conducting polymer modified SPCE sensor electrode can be used as an alternative transducer for the voltammetric stripping and analysis of inorganic Hg2+ ions.

Electro-stimulated release from a reduced graphene oxide composite hydrogel

Electro-stimulated release was established using a novel, electro-conductive hydrogel system comprising Jeffamine polyetheramine and polyethylene glycol diglycidyl ether (PEGDGE) that was composited with reduced graphene oxide (rGO). The swelling response, morphology, mechanical and electrochemical properties of the composite hydrogel were investigated. Enhanced mechanical and electrical properties were observed with increased rGO content. Passive and electro-stimulated release of methyl orange (MO) from these gels was examined. A significant reduction in passive release of the dye was observed by incorporating rGO. Upon electrical stimulation, the release rate and dosage could be tuned through variation of the % w/w rGO, as well as the polarity and amplitude of the applied electric potential. A high level of control and flexibility was achieved demonstrating the applicability of this system for localised drug delivery applications.

Chronocoulometric determination of urea in human serum using an inkjet printed biosensor

A biosensor for the determination of urea in human serum was fabricated using a combination of inkjet printed polyaniline nanoparticles and inkjet printed urease enzyme deposited sequentially onto screen-printed carbon paste electrodes. Chronocoulometry was used to measure the decomposition of urea via the doping of ammonium at the polyaniline-modified electrode surface at -0.3 V vs. Ag/AgCl. Ammonium could be measured in the range from 0.1 to 100 mM. Urea could be measured by the sensor in the range of 2-12 mM (r(2)=0.98). The enzyme biosensor was correlated against a spectrophotometric assay for urea in 15 normal human serum samples which yielded a correlation coefficient of 0.85. Bland-Altman plots showed that in the range of 5.8-6.6 mM urea, the developed sensor had an average positive experimental bias of 0.12 mM (<2% RSD) over the reference method.