Prasad Taranekar

Electrochemical Surface Plasmon Resonance and Waveguide-Enhanced Glucose Biosensing with N-Alkylaminated Polypyrrole/Glucose Oxidase Multilayers

In this work, we report an electrochemical surface plasmon resonance/waveguide (EC-SPR/waveguide) glucose biosensor that could detect enzymatic reactions in a conducting polymer/glucose oxidase (GO(x)) multilayer thin film. In order to achieve a controlled enzyme electrode and waveguide mode, GO(x) (negatively charged) was immobilized with a water-soluble, conducting N-alkylaminated polypyrrole (positively charged) using the layer-by-layer (LbL) electrostatic self-assembly technique. The electrochemical and optical signals were simultaneously obtained from the composite LbL enzyme electrode upon the addition of glucose as mediated by the electroactivity and electrochromic property of the polypyrrole layers. Signal enhancement in EC-SPR detection is obtained by monitoring the doping-dedoping events on the polypyrrole. The real-time optical signal could be distinguished between the change in the dielectric constant of the enzyme layer and other nonenzymatic reaction events such as adsorption of glucose and the change of the refractive index of the solution. This was possible by correlation of both the SPR mode and the m = 0 and 1 modes of the waveguide in an SPR/waveguide spectroscopy experiment.

Carbazole peripheral poly(benzyl ether) dendrimers at the air-water interface: electrochemical cross-linking and electronanopatterning.

A Langmuir film of a third-generation carbazole-terminated poly(benzyl ether) (G3-CtPBE) dendrimer was investigated at the air-water interface. Langmuir-Blodgett (LB) films were deposited on gold substrates and investigated by atomic force microscopy (AFM), followed by electrochemical and electronanopatterning studies. For the G3-CtPBE dendrimer aggregates, variable concentration and surface pressure gave control over aggregate size and shape at the air-water interface. At a lower concentration C1, aggregate-spherical nanoparticles were observed with a face-on or overlapped orientation with increasing surface pressure. However, at a higher concentration C2, their surface morphologies exhibited circular and rod-shaped aggregates with respect to increasing surface pressure attributed to an edge-on configurational change. Moreover, in situ simultaneous interfacial potentiostatic electrodeposition with LB transfer at the air-water interface was employed for the first time with the G3-CtPBE dendrimers onto a hydrophilic surface under constant voltage (i.e., close to the oxidation potential of G3-CtPBE for electrochemical cross-linking). Electrochemical cross-linking on G3-CtPBE dendrimer LB films was also performed ex situ to investigate electrochemical and optical properties. Finally, as an application of a cross-linkable LB film, electronanolithography was carried out to prepare nanopatterns using the current sensing atomic force microscopy (CS-AFM) technique.

Polythiophene precursor electrochemical nanolithography: highly local thermal and morphological characterization

We describe the formation of nanopatterns on an electroactive polythiophene precursor (polyterthiophene methylmethacrylate, P3T) film using a current-sensing atomic force microscopy (CS-AFM) technique. Patterning parameters such as applied bias voltages, sweep duration, and scan rate were adapted for the nanolithographic electrochemical patterning process. The formation of nanopatterns on the film was mainly attributed to the electrochemical cross-linking and oxidation process of the terthiophene units. This is related to the electron transport process under an applied electric field and mass transfer due to Joule heating generated in a localized area from the tip. To further highlight the role of Joule heating, thermal AFM lithography of various blend film compositions (P3T:PMMA) was made using the heated tip AFM (HT-AFM) method. The thermal effects on local morphology were then studied not only as a function of sequential increase in local temperature, but also by nano-scale direct thermal-writing.

Conjugated Polymer Network Ultrathin Films on Metal Interfaces using the Precursor Polymer Approach: Design, Synthesis and In-situ Characterization

We have reported recently a novel method for cross-linking conjugated polymers involving a “precursor polymer” route, where the electrochemical method can be used to prepare ultrathin films on conducting metal and metal oxide surfaces. In this paper, we present the design, synthesis, protocol, and recent results in the application of these thin film materials. An emphasis will be given on how these films are characterized in-situ by a combined surface plasmon spectroscopy (SPS) and electrochemical approach. As a methodology, the concept can be extended to new methods of electrodeposition, patterning, and grafting of conjugated polymers on electrochemically addressable metal surfaces. Compared to spin-cast or electropolymerized monomer films, they are very robust both thermally and mechanically. Other applications of these films to sensors, dielectric materials, non-lithographic patterning, etc. are currently being investigated.

The Precursor Polymer Approach to Electrodeposition and Patterning of Conjugated Polymer Ultrathin Films

In this paper, we report strategies for electrodepositing and patterning ultrathin films of conjugated polymers on flat electrode surfaces using the precursor polymer approach. This involves a rational synthesis design of the precursor polymer followed by careful electrodeposition and characterization of ultrathin films on conducting substrates. This has resulted in the preparation of smooth, high optical quality films, which should be important for applications involving flat electrode surfaces in devices. Characterization was made using surface sensitive spectroscopic and microscopic techniques. Copolymerization with monomers, polymer backbone design, and grafting on modified surfaces are key points in this strategy. Novel methods of in-situ characterization techniques have also been developed combing electrochemistry and surface plasmon resonance techniques.