Md. Azahar Ali

Bio: Md. Azahar Ali is an academic researcher from Iowa State University. The author has contributed to research in topics: Biosensor & Indium tin oxide. The author has an hindex of 29, co-authored 77 publications receiving 2038 citations. Previous affiliations of Md. Azahar Ali include National Physical Laboratory & Council of Scientific and Industrial Research.

Microfluidic-integrated biosensors: prospects for point-of-care diagnostics.

Abstract: There is a growing demand to integrate biosensors with microfluidics to provide miniaturized platforms with many favorable properties, such as reduced sample volume, decreased processing time, low cost analysis and low reagent consumption. These microfluidics-integrated biosensors would also have numerous advantages such as laminar flow, minimal handling of hazardous materials, multiple sample detection in parallel, portability and versatility in design. Microfluidics involves the science and technology of manipulation of fluids at the micro- to nano-liter level. It is predicted that combining biosensors with microfluidic chips will yield enhanced analytical capability, and widen the possibilities for applications in clinical diagnostics. The recent developments in microfluidics have helped researchers working in industries and educational institutes to adopt some of these platforms for point-of-care (POC) diagnostics. This review focuses on the latest advancements in the fields of microfluidic biosensing technologies, and on the challenges and possible solutions for translation of this technology for POC diagnostic applications. We also discuss the fabrication techniques required for developing microfluidic-integrated biosensors, recently reported biomarkers, and the prospects of POC diagnostics in the medical industry.

Microfluidic Immuno-Biochip for Detection of Breast Cancer Biomarkers Using Hierarchical Composite of Porous Graphene and Titanium Dioxide Nanofibers.

Abstract: We report on a label-free microfluidic immunosensor with femtomolar sensitivity and high selectivity for early detection of epidermal growth factor receptor 2 (EGFR2 or ErbB2) proteins. This sensor utilizes a uniquely structured immunoelectrode made of porous hierarchical graphene foam (GF) modified with electrospun carbon-doped titanium dioxide nanofibers (nTiO2) as an electrochemical working electrode. Due to excellent biocompatibility, intrinsic surface defects, high reaction kinetics, and good stability for proteins, anatase nTiO2 are ideal for electrochemical sensor applications. The three-dimensional and porous features of GF allow nTiO2 to penetrate and attach to the surface of the GF by physical adsorption. Combining GF with functional nTiO2 yields high charge transfer resistance, large surface area, and porous access to the sensing surface by the analyte, resulting in new possibilities for the development of electrochemical immunosensors. Here, the enabling of EDC–NHS chemistry covalently immobil...

Carboxylated multiwalled carbon nanotubes based biosensor for aflatoxin detection

Abstract: We report results of studies relating to the development of an electrochemical immunosensor based on carboxylated multiwalled carbon nanotubes (c-MWCNTs) electrophoretically deposited onto indium tin oxide (ITO) glass. This c-MWCNTs/ITO electrode surface has been functionalized with monoclonal aflatoxin B1 antibodies (anti-AFB1) for the detection of aflatoxin-B1 using electrochemical technique. Electron microscopy, X-ray diffraction and Raman studies suggest successful synthesis of c-MWCNTs and the Fourier transform infra-red spectroscopic (FT-IR) studies reveal its carboxylic functionalized nature. The proposed immunosensor shows high sensitivity (95.2 μA ng−1 mL cm−2), improved detection limit (0.08 ng mL−1) in the linear detection range of 0.25–1.375 ng mL−1. The low value of association constant (0.0915 ng mL−1) indicates high affinity of immunoelectrode towards aflatoxin (AFB1).

Highly sensitive biofunctionalized mesoporous electrospun TiO(2) nanofiber based interface for biosensing.

Abstract: The surface modified and aligned mesoporous anatase titania nanofiber mats (TiO2-NF) have been fabricated by electrospinning for esterified cholesterol detection by electrochemical technique. The electrospinning and porosity of mesoporous TiO2-NF were controlled by use of polyvinylpyrrolidone (PVP) as a sacrificial carrier polymer in the titanium isopropoxide precursor. The mesoporous TiO2-NF of diameters ranging from 30 to 60 nm were obtained by calcination at 470 °C and partially aligned on a rotating drum collector. The functional groups such as -COOH, -CHO etc. were introduced on TiO2-NF surface via oxygen plasma treatment making the surface hydrophilic. Cholesterol esterase (ChEt) and cholesterol oxidase (ChOx) were covalently immobilized on the plasma treated surface of NF (cTiO2-NF) via N-ethyl-N0-(3-dimethylaminopropyl carbodiimide) and N-hydroxysuccinimide (EDC-NHS) chemistry. The high mesoporosity (∼61%) of the fibrous film allowed enhanced loading of the enzyme molecules in the TiO2-NF mat. The ChEt-ChOx/cTiO2-NF-based bioelectrode was used to detect esterified cholesterol using electrochemical technique. The high aspect ratio, surface area of aligned TiO2-NF showed excellent voltammetric and catalytic response resulting in improved detection limit (0.49 mM). The results of response studies of this biosensor show excellent sensitivity (181.6 μA/mg dL(-1)/cm(2)) and rapid detection (20 s). This proposed strategy of biomolecule detection is thus a promising platform for the development of miniaturized device for biosensing applications.

Microfluidic impedimetric sensor for soil nitrate detection using graphene oxide and conductive nanofibers enabled sensing interface

Abstract: This paper reports on a microfluidic impedimetric nitrate sensor using a graphene oxide (GO) nanosheets and poly(3,4-ethylenedioxythiophene) nanofibers (PEDOT-NFs) enabled electrochemical sensing interface. The sensor has demonstrated the ability to accurately detect and quantify nitrate ions in real samples extracted from soil. The PEDOT NFs-GO composite serves as an effective matrix for immobilization of nitrate reductase enzyme molecules. The oxygenated functional groups available at GO allows an increased charge transfer resistance of the electrochemical electrode. Microscopic, spectroscopic, and electrochemical studies were systematically conducted to illustrate synergic interactions between the GO and PEDOT NFs. The sensor provides a sensitivity of 61.15 Ω/(mg/L)/cm 2 within a wide concentration range of 0.44–442 mg/L for nitrate ions in agricultural soils. The detection limit of the sensor is 0.135 mg/L with good specificity, reliability, and reproducibility.

Electrospinning and Electrospun Nanofibers: Methods, Materials, and Applications

Abstract: Electrospinning is a versatile and viable technique for generating ultrathin fibers. Remarkable progress has been made with regard to the development of electrospinning methods and engineering of electrospun nanofibers to suit or enable various applications. We aim to provide a comprehensive overview of electrospinning, including the principle, methods, materials, and applications. We begin with a brief introduction to the early history of electrospinning, followed by discussion of its principle and typical apparatus. We then discuss its renaissance over the past two decades as a powerful technology for the production of nanofibers with diversified compositions, structures, and properties. Afterward, we discuss the applications of electrospun nanofibers, including their use as "smart" mats, filtration membranes, catalytic supports, energy harvesting/conversion/storage components, and photonic and electronic devices, as well as biomedical scaffolds. We highlight the most relevant and recent advances related to the applications of electrospun nanofibers by focusing on the most representative examples. We also offer perspectives on the challenges, opportunities, and new directions for future development. At the end, we discuss approaches to the scale-up production of electrospun nanofibers and briefly discuss various types of commercial products based on electrospun nanofibers that have found widespread use in our everyday life.

Micromachining a miniaturized capillary electrophoresis-based chemical analysis system on a chip

Abstract: Micromachining technology was used to prepare chemical analysis systems on glass chips (1 centimeter by 2 centimeters or larger) that utilize electroosmotic pumping to drive fluid flow and electrophoretic separation to distinguish sample components. Capillaries 1 to 10 centimeters long etched in the glass (cross section, 10 micrometers by 30 micrometers) allow for capillary electrophoresis-based separations of amino acids with up to 75,000 theoretical plates in about 15 seconds, and separations of about 600 plates can be effected within 4 seconds. Sample treatment steps within a manifold of intersecting capillaries were demonstrated for a simple sample dilution process. Manipulation of the applied voltages controlled the directions of fluid flow within the manifold. The principles demonstrated in this study can be used to develop a miniaturized system for sample handling and separation with no moving parts.

Electrochemical Sensors and Biosensors Based on Nanomaterials and Nanostructures

Abstract: Taking advantage of exceptional attributes, such as being easy-to-operate, economical, sensitive, portable, and simple-to-construct, in recent decades, considerable attention has been devoted to the integration of recognition elements with electronic elements to develop electrochemical sensors and biosensors.Various electrochemical devices, such as amperometric sensors, electrochemical impedance sensors, and electrochemical luminescence sensors as well as photoelectrochemical sensors, provide wide applications in the detection of chemical and biological targets in terms of electrochemical change of electrode interfaces. With remarkable achievements in nanotechnology and nanoscience, nanomaterial-based electrochemical signal amplifications have great potential of improving both sensitivity and selectivity for electrochemical sensors and biosensors. First of all, it is well-known that the electrode materials play a critical role in the construction of high-performance electrochemical sensing platforms for detecting target molecules through various analytical principles. Furthermore, in addition to electrode materials, functional nanomaterials can not only produce a synergic effect among catalytic activity, conductivity, and biocompatibility to accelerate the signal transduction but also amplify biorecognition events with specifically designed signal tags, leading to highly sensitive biosensing. Significantly, extensive research on the construction of functional electrode materials, coupled with numerous electrochemical methods, is advancing the wide application of electrochemical devices. For example, Walcarius et al. highlighted the recent advances of nano-objects and nanoengineered and/or nanostructured materials for the rational design of biofunctionalized electrodes and related (bio)sensing systems.1 The attractiveness of such nanomaterials relies on their ability to act as effective immobilization matrices and their intrinsic and unique features as described above. These features combined with the functioning of biomolecules contribute to the improvement of bioelectrode performance in terms of sensitivity and specificity. Our group recently presented a general overview of nanomaterial-enhanced paper-based biosensors including lateral-flow test-strip and paper microfluidic devices.2 With different kinds of nanoparticles (NPs), paper-based biosensor devices have shown a great potential in the enhancement of sensitivity and specificity of disease diagnosis in developing countries. This Review focuses on recent advances in electrochemical sensors and biosensors based on nanomaterials and nanostructures during 2013 to 2014. The aim of this effort is to provide the reader with a clear and concise view of new advances in areas ranging from electrode engineering, strategies for electrochemical signal amplification, and novel electroanalytical techniques used in the miniaturization and integration of the sensors. Moreover, the authors have attempted to highlight areas of the latest and significant development of enhanced electrochemical nanosensors and nanobiosensors that inspire broader interests across various disciplines. Electrochemical sensors for small molecules, enzyme-based biosensors, genosensors, immunosensors, and cytosensors are reviewed herein (Figure ​(Figure1).1). Such novel advances are important for the development of electrochemical sensors that open up new avenues and methods for future research. We recommend readers interested in the general principles of electrochemical sensors and electrochemical methods to refer to other excellent literature for a broad scope in this area.3,4 However, due to the explosion of publications in this active field, we do not claim that this Review includes all of the published works in the past two years and we apologize to the authors of excellent work, which is unintentionally left out. Figure 1 Schematic illustration of electrochemical sensors and biosensors based on nanomaterials and nanostructures, in which electrochemical sensors for small molecular, enzyme-based biosensors, genosensors, immunosensors, and cytosensors are demonstrated.