A. J. Saleh Ahammad

A Comprehensive Review of Glucose Biosensors Based on Nanostructured Metal-Oxides

Nanotechnology has opened new and exhilarating opportunities for exploring glucose biosensing applications of the newly prepared nanostructured materials. Nanostructured metal-oxides have been extensively explored to develop biosensors with high sensitivity, fast response times, and stability for the determination of glucose by electrochemical oxidation. This article concentrates mainly on the development of different nanostructured metal-oxide [such as ZnO, Cu(I)/(II) oxides, MnO2, TiO2, CeO2, SiO2, ZrO2, and other metal-oxides] based glucose biosensors. Additionally, we devote our attention to the operating principles (i.e., potentiometric, amperometric, impedimetric and conductometric) of these nanostructured metal-oxide based glucose sensors. Finally, this review concludes with a personal prospective and some challenges of these nanoscaled sensors.

Electrochemical Sensors Based on Carbon Nanotubes

This review focuses on recent contributions in the development of the electrochemical sensors based on carbon nanotubes (CNTs). CNTs have unique mechanical and electronic properties, combined with chemical stability, and behave electrically as a metal or semiconductor, depending on their structure. For sensing applications, CNTs have many advantages such as small size with larger surface area, excellent electron transfer promoting ability when used as electrodes modifier in electrochemical reactions, and easy protein immobilization with retention of its activity for potential biosensors. CNTs play an important role in the performance of electrochemical biosensors, immunosensors, and DNA biosensors. Various methods have been developed for the design of sensors using CNTs in recent years. Herein we summarize the applications of CNTs in the construction of electrochemical sensors and biosensors along with other nanomaterials and conducting polymers.

Electrochemical Impedance Spectra of Dye-Sensitized Solar Cells: Fundamentals and Spreadsheet Calculation

Electrochemical impedance spectroscopy (EIS) is one of the most important tools to elucidate the charge transfer and transport processes in various electrochemical systems including dye-sensitized solar cells (DSSCs). Even though there are many books and reports on EIS, it is often very difficult to explain the EIS spectra of DSSCs. Understanding EIS through calculating EIS spectra on spreadsheet can be a powerful approach as the user, without having any programming knowledge, can go through each step of calculation on a spreadsheet and get instant feedback by visualizing the calculated results or plot on the same spreadsheet. Here, a brief account of the EIS of DSSCs is given with fundamental aspects and their spreadsheet calculation. The review should help one to develop a basic understanding about EIS of DSSCs through interacting with spreadsheet.

Hydrogen Peroxide Biosensors Based on Horseradish Peroxidase and Hemoglobin

Hydrogen peroxide (H2O2) plays a pivotal role in various industrial applications [1]. It is an essential mediator in pharmaceutical, clinical, and environmental research. In addition, it is a byproduct of highly selective oxidases and an important contaminant in several industrial products and wastes [2]. Therefore, a reliable and economical method for the determination of H2O2 is of great significance. Several methods, such as titrimetry [3], spectrometry [4], chemiluminescence [5], fluorimetry [6], chromatography [7], and electrochemical techniques [8,9], have been reported for this purpose. Among these techniques, the electrochemical techniques are preferable because of their simplicity, low cost, high sensitivity, and selectivity [10-16]. In particular, an amperometric biosensor is an attractive tool for the detection of H2O2. Other electrochemical methods such as cyclic voltammetry, linear sweep voltammetry and differential pulse voltammetry are also used for the development of H2O2 biosensor. In the electrochemical methods, different types of modified electrodes have been used. Horseradish Peroxidase (HRP) enzyme is one of the mostly used materials for the modification of electrode. Different mediator such as ferrocene, hydroquinone, catechol, methylene blue, methylene green, nile blue, potassium hexacyanoferrate, thionine, toluidine blue etc. have been used with the enzyme modified electrodes. However, mediator-free HRP based biosensor was also reported. In this case, the direct electrochemistry of HRP enzyme plays vital role. Hemoglobin (Hb) protein is also used for the modification of electrodes. In most case, mediator is not necessary for protein modified electrodes. Enzyme free or protein free modified electrodes were also reported for the electrochemical method based H2O2 biosensor. Some other materials such as nanomaterials, conducting polymers, metal oxides, quantum dots, dendrimer, bilayer lipid membrane, kieselguhr membrane, ionic liquid, liquid crystal, etc. have been used with enzyme and protein modified electrodes. The sensitivity and selectivity of the H2O2 biosensor depends on how the electrodes are modified by different materials.

Metal Oxides and Their Composites for the Photoelectrode of Dye Sensitized Solar Cells

Nowadays, solar energy is one of the most promising future energy resources in concerns to the sustenance of life on Earth and the depletion of fossil fuels. It is projected that the fossil fuel related CO2 emissions rise from 32 to 42 billion metric tons in 2007 and 2035 (EIA., 2010). This enormous amount of CO2 emission will leads to a severe climatic change of the world and therefore a greatest anxieties for the scientific era of 21st century. This rigorous apprehension leads the scientist for the development of solar cell that utilizes solar energy, a renewable and carbon free energy source. The solar energy strike to the earth in one hour is about 4.3x1020 J, which is higher than all the energy consumed in the planet (4.1x1020 J). Therefore, covering 0.1% of the earth’s surfaces with solar cell of 10% efficiency would satisfy the current energy demand (Gratzel., 2001). In general, solar cells can be classified as p-n junction semiconductor solar cells and organicbased exitonic solar cells (OESCs), in which polymer solar cell (PSC), dye sensitized solar cell (DSSC) and hybrid solar cell are included. In 1991, O’Regan & Gratzel first reported the dye sensitized nanocrystalline TiO2 solar cell (DSSC) based on the mechanism of a first regenerative photoelectrochemical processes with an efficiency of 7.1-7.9 %(under simulated solar light) (O’Regan & Gratzel., 1991). Since then, extensive researches have continued to increase the power conversion efficiency (PCE) of DSSC by incorporating n-type metal oxide semiconductors such as TiO2, ZnO, SnO2, Nb2O5, SrTiO3 etc and their composites as photoelectrode materials to achieve a reasonable efficiency of DSSCs of low cost, being therefore a promising alternative to conventional p-n junction solar cell. The wide band gap (Eg > 3eV) metal oxide semiconductors having suitable band position relative to sensitizer has been employed for the fabrication of DSSCs. The high surface area of nanoporous metal oxides facilitates the improvement of light absorption with improved dye loading for improved performance of DSSC. It is evident that the metal oxides employed for the fabrication of DSSCs has solar absorption below a threshold wavelength, ┣g (where, ┣g = 1240/Eg), i.e., they have absorption at ultraviolet region. On the other hand, dye is only responsible for the absorption of light at visible and near-infrared region. The strong absorption of light is attributed to the intramolecular charge transfer transition (ICT) from electron donating group to the anchoring acceptor group of dye. Therefore, the anchored

Fermi energy level tuning for high performance dye sensitized solar cells using sp2 selective nitrogen-doped carbon nanotube channels

Here, we find that doping sp(2) selective nitrogen, N sp(2), into carbon nanotube (CNT) channels induces a positive shift in the Fermi level of TiO(2) photoelectrodes. It is found that this results in the large diffusion coefficient of solar driven electrons for increasing the photocurrent as well as in the low recombination rate for improving open circuit voltage with 0.74 V, which could not be overcome by using pristine CNT channels with 0.66 V.

Interference-Free Determination of Dopamine at the Poly(thionine)-Modified Glassy Carbon Electrode

A highly selective and sensitive electrochemical method, based on a poly(thionine)-modified glassy carbon electrode (PTH-GCE), was developed for the determination of dopamine (DA). The modified electrode was characterized by electrochemical techniques and an atomic force microscope (AFM). The modified GCE exhibited catalytic behavior towards the oxidation of DA in 0.1 M pH 7.0 phosphate buffer solution (PBS). In differential pulse voltammetry (DPV) measurements, the oxidation peak potential of ascorbic acid (AA), uric acid (UA) and serotonin (5-HT) overlapped with that of DA at the bare GCE. However, the oxidation peak of 5-HT was separated from that of DA at the PTH-GCE while the oxidation of AA and UA were suppressed at the same time. The peak potential separation of ca. 0.2 V was large enough for selective determination of DA from the interference of 5-HT. A linear range of 5.0―35.0 μM and a detection limit (S/N = 3) of 0.2 μM were obtained for DA detection in PBS (pH 7.0). This approach provides a simple and easy method to detect DA selectively from the interferences of AA, UA and 5-HT.

Pyrolytic preparation of gold nanoparticle-coated taro carbon and its application for the selective detection of dopamine

A highly selective and sensitive electrochemical method was developed for the detection of dopamine (DA), based on a gold nanoparticle (AuNP)-coated taro carbon (TC)-modified glassy carbon electrode (AuNP-TC/GCE). This novel AuNP-TC material was simply prepared by carrying out a pyrolysis of a composite material obtained by treatment of an acid-treated taro stem powder with HAuCl4. Transmission electron microscopy (TEM), Raman spectroscopy, field-emission scanning electron microscopy (FESEM), energy dispersive spectroscopy (EDS), and X-ray diffraction (XRD) were employed to characterize the AuNP-TC material. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) were used to characterize the modified electrode. The modified GCE exhibited a well-defined current response only toward the electrochemical oxidation of DA in a mixture solution of ascorbic acid (AA), DA, and uric acid (UA). This designed electrochemical sensor showed a linear response in the concentration range of 0.5 μM to 250 μM DA and a sensing limit (S/N = 3) of 0.25 μM was found. The sensor was also able to successfully detect DA in a dopamine hydrochloride injection (DAI). Moreover, the sensor exhibited excellent stability and reproducibility.

Characterization of Carboxylated-SWCNT Based Potentiometric DNA Sensors by Electrochemical Technique and Comparison with Potentiometric Performance

Aptasensors for detection of thrombin were produced by covalently linking aptamer (ssDNA) to cSWCNT. Those biosensors were fully characterized by cyclic voltammetry to evaluate the electrode surface charge/ligand density. We performed the CV studies of electrostatically bound [Ru(NH3)6]3+ redox markers on aptamer surfaces and calculated aptamer surface charge density from the CV data. Potentiometric detection of thrombin allows then the correlation with the CV results. The electrode surfaces containing higher amount of aptamers exhibited better performance in potentiometric measurements. These investigations will introduce the pathway to build reusable and regenarable aptasensors including a simple, accurate and precise estimation of aptemer surface charge density to characterize the surface and hence to ensure the quality of apatsensors.