Ebtisam Wilkins

Biosensors for detection of pathogenic bacteria

Abstract This paper presents an overview of different physicochemical instrumental techniques for direct and indirect identification of bacteria such as: infrared and fluorescence spectroscopy, flow cytometry, chromatography and chemiluminescence techniques as a basis for biosensor construction. A discussion of publications dealing with emerging biosensors for bacterial detection is presented. The review presents recent advances in the development of alternative enzyme- and immunosensors for detection of pathogenic bacteria in a variety of fields (e.g. clinical diagnostics, food analysis and environmental monitoring). Depending on the biological element employed: enzyme; nucleic acid and antibody based biosensors are discussed. Depending on the basic transducer principles, recent advances in biosensing technologies that use electrochemical, piezoelectric, optical, acoustic and thermal biosensors for detection of pathogenic bacteria are overviewed. Special attention is paid to methods for improving the analytical parameters of biosensors including sensitivity and analysis time as well as automation of assay procedures. Recent developments in immunofiltration, flow-injection and flow-through biosensors for bacterial detection are overviewed from the system’s engineering point of view. Future directions for biosensor development and problems related to the commercialization of bacterial biosensors are discussed in the final part of this review.

Immunosensors: electrochemical sensing and other engineering approaches.

This article overviews the engineering approaches and the recent trends in the development of alternative immunoassay systems. A brief description of the main principles and limitations of conventional immunoassay is given. Immunosensing approaches overcoming these limitations are discussed. Alternatives to traditional immunoassay systems are discussed in terms of the enhancement of immunointeraction processes and in terms of the various detection principles. Applications of flow-injection techniques to the development of immunosensing systems are presented. Immunosensors are categorized based on the detection principle employed, as immunoelectrodes (electrochemical immunosensors), piezoelectric immunosensors, or as sensors based on optical detection of the immunointeraction. The discussion focuses on electrochemical immunosensors. In conclusion, the engineering issues involved in immunosensor development are outlined and trends towards practical applications are discussed.

Glucose monitoring: state of the art and future possibilities

This article reviews the development of glucose monitoring techniques and approaches during the last decade. The predominance of the electrochemical measuring principles reported in the literature makes them a focus of this work. Biosensors are still in the main stream of the research interest of most teams due to their high selectivity for glucose determination. Systematization and classification of the glucose monitoring principles and types of glucose sensors is shown. The review gives a brief description of the basic operational principles of the most popular types of glucose biosensors, providing an enhanced bibliography of the original works of the main groups in establishing or significantly contributing to the development of the particular type of glucose biosensor. Different design approaches are overviewed including needle-type sensors, sensors for chronical implantation and the combination of the glucose biosensors with microdialysis sampling technique. The authors approach for replacing of the spent enzyme and thus recharging the sensor in situ while implanted is widely discussed. This approach provides a way to increase the lifespan of the system and ultimately, it could lead to rare transcutaneous interventions for refilling of the implanted sensor.

Application of Electrochemical Biosensors for Detection of Food Pathogenic Bacteria

Current practices for preventing microbial diseases rely upon careful control of various kinds of pathogenic bacteria in food safety and environmental monitoring. The main disadvantages of conventional bacterial detection methods are the multistep procedure and long time requirements. This article gives an overview of alternative electrochemical biosensors for detection of pathogenic bacteria in the food industry. Focus has been on new microbial metabolism-based, antibody-based and DNA-based biosensors. The underlying principles and applications of these biosensors are discussed. Recent developments in flow-injection biosensor systems with an electrochemical detection are also presented.

Flow-through immunofiltration assay system for rapid detection of E. coli O157 :H7

A flow-through amperometric immunofiltration assay system based on disposable porous filter-membranes for rapid detection of Escherichia coli O157:H7 has been developed. The analytical system utilizes flow-through, immunofiltration and enzyme immunoassay techniques in conjunction with an amperometric sensor. The parameters affecting the immunoassay such as selection of appropriate filter membranes, membrane pore size, antibody binding capacity and the concentrations of immunoreagents were investigated and optimized. Non-specific adsorption of the enzyme conjugate was investigated and minimized. A sandwich scheme of immunoassay was employed and the immunofiltration system allows to specifically and directly detect E. coli cells with a lower detection limit of 100 cells/ml. The working range is from 100 to 600 cells/ml with an overall analysis time of 30 min. No pre-enrichment was needed. This immunosensor can be easily adapted for assay of other microorganisms and may be a basis for a new class of highly sensitive bioanalytical devices for rapid quantitative detection of bacteria.

A Telemetry-Instrumentation System for Long-Term Implantable Glucose and Oxygen Sensors

Abstract This paper describes the development of a compact, low power, implantable system for in vivo monitoring of oxygen and glucose concentrations. The telemetry-instrumentation system consists of two amperometric sensors: one oxygen and one glucose biosensor and two potentiostats for biasing the sensors, an instrumentation amplifier to subtract and amplify sensor output signals, and a signal transmitter subunit to convert and transmit glucose dependent signal from the sensors to a remote data acquisition system. The system produces a unipolar glucose dependent voltage in the range of 1 to 3.6 V which is converted to a frequency and then transmitted using a frequency-modulated (FM) oscillator. Initial tests were performed on an open model electronic circuit using resistors to simulate sensor outputs in the 10 to 1000 nA range. Further in vitro evaluation of the system was conducted with a compact printed circuit board embedded in silicone elastomer, entirely submerged in buffer solution using actual se...

Development of needle-type glucose sensor with high selectivity

Abstract An amperometric needle-type glucose biosensor employing rhodium as electrocatalyst for hydrogen peroxide detection is described. A novel transducer design is based on electrodeposition of rhodium particles on the external wall of the needle which serves as the working electrode and an external Ag/AgCl reference/counter electrode. Electropolymerized 1,3-diaminobenezene (1,3-phenylenediamine) is employed as a protective layer for the rhodium particles as well as an interference eliminating layer. This configuration uses the rhodium electrocatalyst in its most active dispersed form and ensure good mechanical rigidity. At the same time, because of the large working surface area, it provides a large sensitivity for the sensor response. The use of rhodium electrocatalyst allows detection of H 2 O 2 at low working potential of +0.25 V. Electrophoretic deposition of enzyme on the needle surface followed by cross-linking with glutaraldehyde was chosen for the immobilization of glucose oxidase (GOD) on the needle surface. Nafion was used as external diffusion control and additional interference eliminating layer, which extend the linear range of the sensor response to over 25 mM glucose concentration. These biosensors demonstrated diminished response to interference from oxidizable compounds present in body fluids and a life time of at least 3 months.

Integrated implantable device for long-term glucose monitoring

In this study we report the development of an integrated implantable device for glucose monitoring. The dimensions of the device (5.0 x 7.0 x 1.5 cm) allow implantation under the abdominal skin of a large animal for in vivo evaluation of sensor performance. The experimental set-up includes amperometric glucose biosensor, a miniature potentiostat, an FM signal transmitter, a power supply and an antenna and receiver linked to a computer-based data acquisition system. The device performance was evaluated in vitro using a ten-day continuous test and other long-term operation experiments. The biosensor was tested in different model solutions that simulated the physiological environment in which it will be ultimately used. A linear response to glucose concentration was obtained up to 25 mM glucose, with a sensitivity of less than 0.5 microA/mM. The ability of the biosensor to measure glucose levels in serum was also tested, and a good correlation demonstrated between glucose serum levels measured by routine technique and those measured using the biosensor (R2 = 0.993; slope = 0.996). Initial results obtained from the short-term subcutaneous implantation of the sensor demonstrate its potential for the monitoring of glucose concentration in vivo.

Heavy metal removal by caustic-treated yeast immobilized in alginate

Abstract Saccharomyces cerevisiae yeast biomass was heated in 0.75 M NaOH at 70–90°C for 10–15 min to increase its biosorption for heavy metals, and then immobilized in alginate gel. Biosorption for Cu2+, Cd2+ and Zn2+ on alginate gel, native yeast, native yeast immobilized in alginate gel, and caustic-treated yeast immobilized in alginate gel, were all compared. Immobilized yeasts (native yeast and caustic-treated yeast) could be reactivated and reused in a manner similar to ion-exchange resins. Immobilized caustic-treated yeast has high heavy metal biosorption capacity and high metal removal efficiency over a rather wide pH region. The biosorption isotherm of immobilized caustic-treated yeast was studied and empirical equations were obtained. The initial pH of polluted water affected the metal removal efficiency in extreme pH regions, and the biosorption capacity almost remained constant over a wide pH range. The equilibrium biosorption appeared to be temperature independent in the range from 7°C to 45°C at low initial metal concentration.

Highly sensitive flow-injection immunoassay system for rapid detection of bacteria☆

A flow-injection amperometric immunofiltration assay system for the rapid detection of total Escherichia coli and Salmonella was developed. The system is based on the use of disposable porous nylon membranes which act as a support for the immobilization of anti-E. coli or anti-Salmonella antibodies. The assay system consists of a flow-injection system, a disposable filter-membrane and an amperometric sensor. Parameters affecting the performance of the immunofiltration assay system such as membrane pore size, non-specific binding, conjugate concentration and sample volume were studied and optimized. A sandwich scheme of immunoassay was employed and the immunofiltration system was able to specifically and directly detect 50 cells/ml of total E. coli or 50 cells/ml of Salmonella with an overall analysis time of 35 min. This immunosensor can be easily adapted for the assay of other microorganisms and may be a basis for a new class of highly sensitive and automated bioanalytical devices for the rapid quantitative detection of bacteria.