In this study, the investigation of surface-treatment of chemically inert graphitic carbon microelectrodes (derived from pyrolyzed photoresist polymer) for improving their attachment chemistry with DNA molecular wires and ropes as part of a bionanoelectronics platform is reported. Polymer microelectrodes were fabricated on a silicon wafer using standard negative lithography procedures with negative-tone photoresist. These microelectrode structures were then pyrolyzed and converted to a form of conductive carbon that is referred to as PP (pyrolyzed polymer) carbon throughout this paper. Functionalization of the resulting pyrolyzed structures was done using nitric, sulfuric, 4-amino benzoic acids (4-ABA), and oxygen plasma etching and the surface modifications confirmed with Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and electron dispersion x-ray spectroscopy (EDS). Post surface-treatment analysis of microelectrodes with FTIR and Raman spectroscopy showed signature peaks characteristics of carboxyl functional groups while EDS showed an increase in oxygen content in the surface-treatment procedures (except 4-ABA) indicating an increase in carboxyl functional group. These functional groups form the basis for peptide bond with aminated oligonucleotides that in turn could be used as molecular wires and interconnects in a bionanoelectronics platform. Post-pyrolysis analysis using EDS showed relatively higher oxygen concentrations at the edges and location of defects compared to other locations on these microelectrodes. In addition, electrochemical impedance measurements showed metal-like behavior of PP carbon with high conductivity (|Z| <1 KΩ) and no detectable detrimental effect of oxygen plasma surface-treatment on electrical characteristic. In general, characterization results—taken together—indicated that oxygen plasma surface-treatment produced more reliable, less damaging, and consistently repeatable generation of carboxyl functional groups than diazonium salt and strong acid treatments.

In this study, the investigation of attachment of DNA molecular wires and ropes to high aspect-ratio three-dimensional (3D) metal microelectrodes and their subsequent electrical characterization as part of a bionanoelectronics platform is reported. The 3-D microelectrode architecture consists of mainly high aspect-ratio microelectrode structures (75 μm height and above) patterned from relatively thick layers of negative tone photoresist and covered by sputtered gold on their top surface. DNA attachments on 3-D microelectrode structures was demonstrated using oligonucleotide-DNA self-assembly and thiol-gold covalent bonding. Further, DC and AC electrical characterization of double-stranded λ-DNA molecular wires in a dry environment and suspended between high aspect-ratio 3D microelectrodes 75 μm away from the substrate (to heights unprecedented so far in the literature which thereby eliminate interference of substrate) is presented. Electrical characterizations based on I-V and AC impedance analysis of several repeatable data points of attachment with varying λ-DNA concentration (500 ng/μL to 1.5 ng/μL) showed measurable and significant conductivity of λ-DNA molecular wires with some band-gap; thereby establishing it as semi-conductor at low-frequencies (<100 Hz) and a very good conductor at high-frequencies (∼1 MHz). We believe that the research presented here represents a significant departure from previous studies and makes unique contributions through (i) more accurate direct conductivity measurement of DNA molecular wires facilitated by suspension of the DNA away from the substrate, and (ii) AC impedance measurement of DNA molecular wires in dry-state attachment (relevant for long-term viability studies) that suggest metal-type low impedance at high-frequencies. The significant conductivity of λ-DNA molecular wires (similar to metals) observed at high-frequencies (|Z| < 5 KΩ) opens up substantial opportunities.

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In this study, the surface-treatment of pyrolyzed carbon microelectrodes -which are otherwise chemically inert -for improving their attachment chemistry with double-stranded DNA molecular wires as part of a bio-nanoelectronics platform is investigated. Pyrolyzed carbon microelectrodes were fabricated using standard negative lithography procedures with SU-8 (10) negative-tone photoresist on a silicon wafer. These microelectrode structures were then pyrolyzed and converted to a form of conductive carbon that we refer to as PSU-8. Functionalization of the resulting pyrolyzed structures was done using oxygen plasma etching and the results confirmed with Fourier Transform Infrared Spectroscopy (FTIR). Post-pyrolysis analysis using Electron Dispersion X-ray Spectroscopy (EDS) showed a decrease in oxygen content after pyrolysis and higher oxygen concentrations at the edges and location of defects. FTIR results confirmed the presence of carboxyl and hydroxyl groups in both untreated pyrolyzed carbon (PSU-8) and plasma-treated PSU-8 structures.

Carbon nanotubes/polymer composite are recently opening new dimension for researchers. We report, the fabrication of nanocomposite of polyaniline (PANI) with functionalized CNTs (f-CNTs) by in-situ chemical polymerization using a novel approach of polymerization of monomers directly over the surface of the CNTs by taking oxidizing agent adsorbed CNTs. In this process of composite formation, CNTs were functionalized with carboxyl group using potassium permanganate (KMnO 4 ) and sulphuric acid (H 2 SO 4 ) as an oxidizing agent. The deposition of oxidizing agent on the surface of CNTs induces the growth of a uniform layer of PANI on CNTs, which leads the formation of homogeneous nanocomposite of CNTs/PANI. We have studied thermal stability (TGA) and electrochemical behavior of CNTs/PANI nanocomposite. In the nanocomposite, the PANI degradation temperature shifted to higher temperature upto 600 C. Cyclic Voltammetry of CNTs/PANI composite suggests the catalytic effect of CNTs for fast electron transfer. In this novel synthesis procedure, nanotubes act as a template for the formation of nanocomposite. The formation of f-CNTs coated with oxidizing agent and CNTs/PANI composite were characterized by XRD, SEM and TEM studies. A feasible model for the formation of composite has also been discussed. The processible nanocomposite showed its potential for wide applications.