Synthesis, characterisation and application of inherently conducting polymer nanoparticles

Synthesis of inherently conducting polymers (ICPs) nanoparticles is an option to improve the processability and conductivity of ICPs. In this thesis, the synthesis and application of ICPs nanoparticles has been demonstrated. Various polymerisation methods, such as emulsion polymerisation, use of steric stabiliser and synthesis in ionic liquid (IL) media, have been used to synthesise polymer nanoparticles. These synthesis methods render the ICPs nanoparticles stable as dispersions which are more processable and contain peculiar and fascinating properties superior to their bulk counterparts. These nanoparticles are further applied as mediators for biosensors. They have been fabricated into sensors using electrodeposition, evaporative casting, or ink-jet printing methods. Electrodeposition method results in formation of ultra thin nanostructured polymeric films that enhance sensor performance. Evaporative casting method is an easy one-step method, but precision is hard to achieve and dense films with rough morphology are formed. Ink-jet printing can be used to produce precise and accurate patterns and also this approach is amenable to mass production. Polyaniline (PANI) nanoparticles; nanoPANI-dodecylbenzene sulphonic acid (DBSA) have been synthesised using emulsion polymerisation (Chapter 3). The nanoPANI-DBSA obtained has a conductivity of 34±7 S/cm with particle size in the range of 10±2 nm. The nanoPANI-DBSA has been used as a mediator layer in biosensor applications as demonstrated in Chapter 7. These nanoparticles were fabricated onto the conductive electrode using an electrodeposition method with subsequent immobilisation of the enzyme horseradish peroxidase (HRP). Sensor performance was examined using amperometric method and HRP/hydrogen peroxide (H2O2) configuration as a model system. The nanodomain of the nanoPANI-DBSA particles contributed to highly ordered nanostructure patterning on the electrode surface. This uniform surface showed improved enzyme deposition characteristics, a lower background signal and better sensor performance at a lower HRP loading when compared to the sensors fabricated from electropolymerisation of the bulk monomer. NanoPANI-DBSA particles aggregate at high concentrations; hence they are not amenable to ink-jet printing. sPANI-DBSA was prepared from centrifugation of the nanoPANI-DBSA dispersions and used as a material for ink-jet printing. HRP was premixed with the sPANI-DBSA nanodispersions before fabrication onto ITO-coated mylar using ink-jet printing. The print quality from the sPANI-DBSA nanodispersions was inconsistent and the catalytic signal of this biosensor was very low. These resulted in no further ink-jet printing work for this material. The PANI-DBSA-rapid mixing (RM) nanodispersions were synthesised using a RM method. These dispersions contained nanometre size PANI particles dispersed in aqueous media. These nanoparticles have been successfully printed using ink-jet printing as outline in Chapter 9. This work has demonstrated the ink-jet printability of conducting polymer nanoparticles and their use as working electrodes for biosensors. The sensor response from these ink-jet printed PANI-DBSA-RM was higher than the sensor response from evaporative casting of poly(2-methoxyaniline-5-sulphonic acid) (PMAS) in Chapter 8. The addition of functional group into PANI nanoparticles was also investigated. Carbolan Blue (CB) dye was incorporated into the PANI backbone using emulsion polymerisation method as demonstrated in Chapter 4. The dye was proved to have strong interaction with PANI backbone using Raman spectroscopy and centrifugation test. The distinct solution colour after a reduction process could lead the PANI-DBSA-CB to be a potential candidate of the material for electrochromic devices. Synthesis of polypyrrole (PPy) nanoparticles is demonstrated in Chapter 5. Poly(vinyl alcohol) (PVA) was used as the steric stabiliser to produce PPy-DS-PVA nanoparticles. These nanoparticles were well dispersed in water with particle size in the order of 52±5 nm. Aggregation was obvious in concentrated solutions and leaded to poor ink-jet printed quality of the PPy-DS-PVA nanoparticles. The water soluble polymer, PMAS, was also used to fabricate biosensors using evaporative casting method in Chapter 8 and ink-jet printing in Chapter 9. In chapter 8, its solubility enabled PMAS to pre-mix with the HRP enzyme prior to complexing with the polycations poly(L-lysine) hydrochloride (PLL) and subsequently casting onto ITO coated mylar substrate. This biosensor format has proven ability to easily fabricate the conducting polymer nanoparticles by one-step evaporative casting. The optimised sensors exhibited good sensor response, high selectivity and very good long-term stability. The ink-jet printed films from PMAS and PLL solutions (Chapter 9) showed better electroactivity compared to the evaporative cast films which could lead to better sensor performance. However, the problem of PLL blocking the print head resulted in the discontinuation of its use. The polyterthiophene (PTTh) aqueous dispersed nanoparticles were also successfully synthesised in the presence of surfactant (DBSA) and in ionic liquid; 1-ethyl- 3-methylimidazolium bis(trifluoromethane-sulfonyl)amide (emiTFSA) as demonstrated in Chapter 6. The dispersion of PTTh-DBSA nanoparticles has shown poor colloidal stability and poor electroactivity. Although the PTTh nanoparticles synthesised in emiTFSA needed 2-3 minutes sonication to be dispersed in water, they have shown good electrochemistry and being test in another study in our laboratories for its use in photovoltaic devices. These processable ICPs nanoparticles are promising materials for biosensor applications, electrochromic devices and solar cells. Assembly of these nanoparticles on to conductive substrates leads to highly ordered nanostructured ICPs on the surface and improves the biosensor performances. Also these nanoparticles prove their ability to be processable in mass production scale

Application of nanoparticulate conducting polyaniline in nanofilm biosensor technology

This biosensor uses a novel aqueous-based nanoparticulate polyaniline (PANI), synthesised using dodecylbenzenesulphonic acid (DBSA) and aniline as starting material. These polymer nanoparticles have been electrodeposited on to the surface of carbon electrodes resulting in conductive nano-films, which were examined by electrochemistry, scanning electron microscopy (SEM), atomic force microscopy (AFM), profilometry and spectroelectrochemistry. Biomolecules were then electrostatically adsorbed onto this surface and physical techniques have shown that the nanofilm possesses properties which allow for uniform adsorption of protein to take place. This effective biosensor format has been characterised using a horseradish peroxidase (HRP) and H2O2 format. This sensor exhibits higher signal/noise (S/N) ratios and quicker response times than previous PANI biosensor formats developed by our group, due to its nanofilm characteristic

Novel biosensor fabrication methodology based on processable conducting polyaniline nanoparticles

This work investigates polyaniline (PANI) nanoparticles, (synthesised using dodecylbenzenesulphonic acid (DBSA) as a dopant), as a novel, highly processable, non-diffusional mediating species in an enzyme biosensing application. These nanoparticles are readily dispersed in aqueous media which helps overcome some of the processability issues traditionally associated with polyaniline. Modification of screen-printed electrodes was readily achieved with these aqueous nanoparticle dispersions, where the nanoparticles were simply cast by a drop-coating method onto the surface. After suitable pH adjustment, it was shown that horseradish peroxidase (HRP) enzyme could be added to the dispersion, and cast simultaneously with the conducting polyaniline. This effective fabrication method involves no electrochemical steps, and as such is easily amenable to mass production. The feasibility of casting enzyme with polyaniline nanoparticles is demonstrated in this short communication. More accurate deposition of protein-containing inks onto screen-printed carbon working electrodes could in the future transfer the drop-coating protocol from manual deposition to largescale production by mechanical methods such as ink-jet printing

Incorporation of dye into conducting polyaniline nanoparticles

Synthesis of polyaniline (PANi) nanodispersions with and without the presence of a reactive dye has been performed via micellar chemical oxidative polymerisation using dodecylbenzene sulfonic acid (DBSA) as the dispersant. The dye used was a textile reactive dye (Carbolan Blue – CB) which was chosen due to it’s structural similarity to DBSA. The polymers formed were PANi · DBSA and PANi · DBSA · CB. The inclusion of the CB dye appeared to facilitate the polymerisation process as observed from open circuit potential measurements during polymerisation. Using transmission electron microscopy, PANi · DBSA · CB was shown to have an average particle size larger than that observed for PANi · DBSA. The CB dye was shown to be incorporated into the polymer by Raman spectroscopy. The CB containing polymer was amenable to protonation/deprotonation as well as redox switching

Conducting polymers with fibrillar morphology synthesized in a biphasic ionic liquid/water system

The synthesis of poly(pyrrole), poly(terthiophene), and poly(3,4-ethylenedioxythiophene) with unusual fibrillar morphologies has been achieved by chemical polymerization in a biphasic ionic liquid/water system. Use of aqueous gold chloride as the oxidant, with the monomers dissolved in a hydrophobic ionic liquid, allows the polymerization to occur at the ionic liquid/water interface. The resultant conducting polymer fibrils are, on average, 50−100 nm wide and can be thousands of nanometers long. The polymers produced in this ionic liquid system are compared to those synthesized in a biphasic chloroform/water system

Journal of Sichuan University : medical science edition = Sichuan-daxue-xuebao : yixue ban

The engineered addition of hexa-histidine sequences to biomolecules such as antibody fragments has been found to be an excellent means of purifying these materials. This tagging methodology has also been extended to its use as a tool for immobilization and orientation of antibodies on transducer surfaces. Polyvinyl sulfonate-doped polyanilne (PANI/PVS) can be used as a mediator in amperometric biosensors. This short communication looks at the effect of nickel chelate materials and nickel chelation on this conducting polymer and evaluates it as a potential surface for the immobilization of his-tagged biomolecules. N-nitrilotriacetic acid (NTA) was doped into the electropolymerized PANI/PVS at a screen-printed carbon paste electrode. The resulting NTA-PANI/PVS film was shown to have comparable electrochemical properties of polymer without the chelating agent. When Ni2+ was applied to the electrode, the incorporated NTA was found to efficiently chelate the metal ions at the electrode surface

Inkjet printable polyaniline nanoformulations

Aqueous polyaniline (PANI) nanodispersions doped with dodecylbenzenesulfonic acid (DBSA) were synthesized and successfully inkjet-printed using a piezoelectric desktop printer. This paper examines the optimization and characterization of the nanoparticulate formulation for optimal film electrochemistry and stability. PANI nanoparticle synthesis was optimized in terms of the ratio of monomer (aniline) to oxidant (ammonium persulphate, APS) and dopant (DBSA). Particle size, UV−vis spectroscopy, electrochemical, and conductivity analyses were performed on all materials. Optimal synthesis conditions were found to be at a molar ratio of 1.0:0.5:1.2 aniline/APS/DBSA. This resulting nanodispersion showed a uniform particle size distribution of ∼82 nm, and UV−vis analysis indicated a high doping level. These synthetic conditions resulted in the highest conductivity, and the electrochemistry of the resulting films was well-defined and stable. Surface tension analysis and rheological studies demonstrated that the aqueous nanodispersions were suitable for inkjet printing. Successful inkjet printing of these polyaniline nanoparticulate formulations is demonstrated

Journal des économistes et des études humaines : JEEH ; a bilingual journal of interdisciplinary studies

The properties of poly (2-methoxyaniline-5-sulfonic acid) (PMAS), a water-soluble polymer, has been investigated as a potential mediator for biosensors. Addition of poly (L-Lysine) (PLL) to the PMAS renders this material water-insoluble; an important feature for aqueous based biosensors. Characterisation of various PMAS/PLL mixtures showed that a uniform and stable film could reproducibly be fabricated on ITO coated Mylar using 0.1% (w/v) PMAS and 0.05% (w/v) PLL. Immobilisation of enzyme horseradish peroxidase (HRP) onto the PMAS/PLL film was also investigated. Amperometric detection (-0.1 V vs. Ag/AgCl reference electrode) of hydrogen peroxide was investigated using the PMAS/PLL/HRP electrode as the working electrode in a three electrode cell containing phosphate buffer saline (pH 6.4) solution. Amperometric responses were observed upon the addition of hydrogen peroxide. HRP immobilised concentration was optimised to be 0.35% (w/v) at 35 μL. Loading volume was also studied and optimised to be 35 μL. The optimal condition for amperometric test was using constant applied potential at -100 mV. Detection limit of the sensor in PBS solution was 0.01 mM H[2]O[2]. Calibration curve in PBS pH 6.4 shows a linear response range between 0.01 and 0.1 mM H[2]O[2] with a sensitivity of 24.91 μA/cm[2] mM[-1] and correlation coefficient of 0.9966