Innam Lee

Highly sensitive single polyaniline nanowire biosensor for the detection of immunoglobulin G and myoglobin.

A single polyaniline (PANI) nanowire-based biosensor was established to detect immunoglobulin G (IgG) and myoglobin (Myo), which is one of the cardiac biomarkers. The single PANI nanowires were fabricated via an electrochemical growth method, in which single nanowires were formed between a pair of patterned electrodes. The single PANI nanowires were functionalized with monoclonal antibodies (mAbs) of IgG or Myo via a surface immobilization method, using 1-ethyl-3-(3-dimethyaminopropyl) carbodiimide (EDC), and N-hydroxysuccinimde (NHS). The functionalization was then verified by Raman spectroscopy and fluorescence microscopy. The target proteins of IgG and Myo were detected by measuring the conductance change of functionalized single PANI nanowires owing to the capturing of target proteins by mAbs. The detection limit was found to be 3 ng/mL for IgG and 1.4 ng/mL for Myo. No response was observed when single nanowires were exposed to a non-specific protein, demonstrating excellent specificity to expected target detection. Together with the fast response time (a few seconds), high sensitivity, and good specificity, this single PANI nanowire-based biosensor shows great promise in the detection of cardiac markers and other proteins.

Detection of Cardiac Biomarkers Using Single Polyaniline Nanowire-Based Conductometric Biosensors

The detection of myoglobin (Myo), cardiac troponin I (cTnI), creatine kinase-MB (CK-MB), and b-type natriuretic peptide (BNP) plays a vital role in diagnosing cardiovascular diseases. Here we present single site-specific polyaniline (PANI) nanowire biosensors that can detect cardiac biomarkers such as Myo, cTnI, CK-MB, and BNP with ultra-high sensitivity and good specificity. Using single PANI nanowire-based biosensors integrated with microfluidic channels, very low concentrations of Myo (100 pg/mL), cTnI (250 fg/mL), CK-MB (150 fg/mL), and BNP (50 fg/mL) were detected. The single PANI nanowire-based biosensors displayed linear sensing profiles for concentrations ranging from hundreds (fg/mL) to tens (ng/mL). In addition, devices showed a fast (few minutes) response satisfying respective reference conditions for Myo, cTnI, CK-MB, and BNP diagnosis of heart failure and for determining the stage of the disease. This single PANI nanowire-based biosensor demonstrated superior biosensing reliability with the feasibility of label free detection and improved processing cost efficiency due to good biocompatibility of PANI to monoclonal antibodies (mAbs). Therefore, this development of single PANI nanowire-based biosensors can be applied to other biosensors for cancer or other diseases.

Rapid Real-time Electrical Detection of Proteins Using Single Conducting Polymer Nanowire-Based Microfluidic Aptasensor

Single polypyrrole (PPy) nanowire-based microfluidic aptasensors were fabricated using a one-step electrochemical deposition method. The successful incorporation of the aptamers into the PPy nanowire was confirmed by fluorescence microscopy image. The microfluidic aptasensor showed responses to IgE protein solutions in the range from 0.01 nM to 100 nM, and demonstrated excellent specificity and sensitivity with faster response and rapid stabilization times (~20 s). At the lowest examined IgE concentration of 0.01 nM, the microfluidic aptasensor still exhibited ~0.32% change in the conductance. The functionality of this aptasensor was able to be regenerated using an acid treatment with no major change in sensitivity. In addition, the detection of cancer biomarker MUC1 was performed using another microfluidic aptasensor, which showed a very low detection limit of 2.66 nM MUC1 compared to commercially available MUC1 diagnosis assay (800 nM).

Highly reproducible single polyaniline nanowire using electrophoresis method

Site-specific single polyaniline nanowires were fabricated through electrophoresis growth with acetone wetting. After growing the nanowires, the post-process of acetone wetting of the nanowires improved morphology, topology, and electrical conductivity with coagulation and substitution in polyaniline. They showed resistance changes of 39.57 ± 11.57% and presented 2.38 × 10-4 ± 3 × 10-5 Ω · cm, 133.77 ± 13.82 nm thickness, and 133.17 ± 13.01 nm width in 1 μm to 5.5 μm length. The new combined growth process of electrophoresis and acetone wetting significantly improved reproducibility, reliability, and controllability in the fabrication of single polymer nanowires.

Anomalous schottky barriers and contact band-to-band tunneling in carbon nanotube transistors

Devices incorporating nanoscale materials, particularly carbon nanotubes (CNTs), offer exceptional electrical performance. Absent, however, is an experimentally backed model explaining contact-metal work function, device layout, and environment effects. To fill the void, this report introduces a surface-inversion channel model based on low temperature and electrical measurements of a distinct single-walled semiconducting CNT contacted by Hf, Cr, Ti, and Pd electrodes. Anomalous barrier heights and metal-contact dependent band-to-band tunneling phenomena are utilized to show that, dependent upon contact work function and gate field, transport occurs either directly between the metal and CNT channel or indirectly via injection of carriers from the metal-covered CNT region to the CNT channel. The model is consistent with previously contradictory experimental results, and the methodology is simple enough to apply in other contact-dominant systems.

Thermionic Field Emission Transport in Carbon Nanotube Transistors

With experimental and analytical analysis, we demonstrate a relationship between the metal contact work function and the electrical transport properties saturation current (Isat) and differential conductance (σsd=∂Isd/∂Vsd) in ambient exposed carbon nanotubes (CNT). A single chemical vapor deposition (CVD) grown 6 mm long semiconducting single-walled CNT is electrically contacted with a statistically significant number of Hf, Cr, Ti, Pd, and Au electrodes, respectively. The observed exponentially increasing relationship of Isat and σsd with metal contact work function is explained by a theoretical model derived from thermionic field emission. Statistical analysis and spread of the data suggest that the conduction variability in same CNT devices results from differences in local surface potential of the metal contact. Based on the theoretical model and methodology, an improved CNT-based gas sensing device layout is suggested. A method to experimentally determine gas-induced work function changes in metals is also examined.

Current anisotropy of carbon nanotube diodes: Voltage and work function dependence

Here, we report a performance analysis on carbon nanotube (CNT) Schottky diodes using source-drain current anisotropy. An analytical model is derived based on thermionic field emission and used to correlate experimental data from Pd–Hf, Ti–Hf, Cr–Hf, Ti–Cr, and Pd–Au mixed metal devices fabricated on one single 6 mm long CNT. Results suggest that the difference in work functions of the two contact-metals, and not a dominant Schottky contact, determines diode performance. Results are further applied and demonstrated in a reversible polarity diode.Here, we report a performance analysis on carbon nanotube (CNT) Schottky diodes using source-drain current anisotropy. An analytical model is derived based on thermionic field emission and used to correlate experimental data from Pd–Hf, Ti–Hf, Cr–Hf, Ti–Cr, and Pd–Au mixed metal devices fabricated on one single 6 mm long CNT. Results suggest that the difference in work functions of the two contact-metals, and not a dominant Schottky contact, determines diode performance. Results are further applied and demonstrated in a reversible polarity diode.

Materialization of single multicomposite nanowire: entrapment of ZnO nanoparticles in polyaniline nanowire

We present materialization of single multicomposite nanowire (SMNW)-entrapped ZnO nanoparticles (NPs) via an electrochemical growth method, which is a newly developed fabrication method to grow a single nanowire between a pair of pre-patterned electrodes. Entrapment of ZnO NPs was controlled via different conditions of SMNW fabrication such as an applied potential and mixture ratio of NPs and aniline solution. The controlled concentration of ZnO NP results in changes in the physical properties of the SMNWs, as shown in transmission electron microscopy images. Furthermore, the electrical conductivity and elasticity of SMNWs show improvement over those of pure polyaniline nanowire. The new nano-multicomposite material showed synergistic effects on mechanical and electrical properties, with logarithmical change and saturation increasing ZnO NP concentration.

Single metal and conducting polymer nanowires used as chemical/bio molecular sensors

We present the fabrication of single nanowires composed of different materials including Palladium (Pd), Polyaniline (PANI) and Polypyrrole (PPy) via electrochemical deposition. The individual nanowires have diameters within 100 nm and lengths from 3 to 10 µm. A gate-assisted growth further improves the growth and limits the size of the nanowires. Single Pd, PPy and PANI nanowires are used as sensors to detect multiple chemical gases, including hydrogen (H2), methanol (CH3OH), and nitrogen dioxide (N02). Each nanowire shows repeatable and reproducible sensing signals, with very low detection limits. Single PPy nanowire entrapped with anti-IgE aptamers is also fabricated with good morphology for biosensor applications. This aptamer-doped single nanowire is used to detect IgE and shows good performance in this report.