Many scientific papers have been written concerning gas sensors for different sensor applications using several sensing principles. This review focuses on sensors and sensor systems for gaseous ammonia. Apart from its natural origin, there are many sources of ammonia, like the chemical industry or intensive life-stock. The survey that we present here treats different application areas for ammonia sensors or measurement systems and different techniques available for making selective ammonia sensing devices. When very low concentrations are to be measured, e.g. less than 2 ppb for environmental monitoring and 50 ppb for diagnostic breath analysis, solid-state ammonia sensors are not sensitive enough. In addition, they lack the required selectivity to other gasses that are often available in much higher concentrations. Optical methods that make use of lasers are often expensive and large. Indirect measurement principles have been described in literature that seems very suited as ammonia sensing devices. Such systems are suited for miniaturization and integration to make them suitable for measuring in the small gas volumes that are normally available in medical applications like diagnostic breath analysis equipment.

/pdf/ammonia-sensors-and-their-applications-a-review-35hg34lbf3.pdf

Ammonia sensors and their applications - a review

The gas sensors fabricated by using conducting polymers such as polyaniline (PAni), polypyrrole (PPy) and poly (3,4-ethylenedioxythiophene) (PEDOT) as the active layers have been reviewed. This review discusses the sensing mechanism and configurations of the sensors. The factors that affect the performances of the gas sensors are also addressed. The disadvantages of the sensors and a brief prospect in this research field are discussed at the end of the review.

/pdf/gas-sensors-based-on-conducting-polymers-4l6i49715q.pdf

Gas Sensors Based on Conducting Polymers

Using a new interfacial polymerization method for the synthesis of polyaniline nanofibers, we have developed nanofiber sensors and compared them to conventional polyaniline sensors. Five different response mechanisms are explored:  acid doping (HCl), base dedoping (NH3), reduction (with N2H4), swelling (with CHCl3), and polymer chain conformational changes (induced by CH3OH). In all cases, the polyaniline nanofibers perform better than conventional thin films. Their high surface area, porosity and small diameters enhance diffusion of molecules and dopants into the nanofibers.

Polyaniline Nanofiber Gas Sensors: Examination of Response Mechanisms

Molecularly imprinted polymers are synthetic receptors for a targeted molecule. As such, they are analogues of the natural antibody–antigen systems. In this review, after a recounting of the early history of the general field, we specifically focus on the application of these polymers as sensors. In these applications, the polymers are paired with a reporting system, which may be electrical, electrochemical, optical, or gravimetric. The presence of the targeted molecule effects a change in the reporting agent, and a calibrated quantity of the target is recorded. In this review, we describe the imprinted polymer production processes, the techniques used for reporting, and the applications of the reported sensors. A brief survey of recent applications to gas-phase sensing is included, but the focus is primarily on the development of sensors for targets in solution. Included among the applications are those designed to detect toxic chemicals, toxins in foods, drugs, explosives, and pathogens. The application...

Molecularly Imprinted Polymers

Glucose detection is of great significance in biomedical applications. Principles, methods and recent developments in electrochemical glucose sensors are reviewed here. Special attention is given to the discussion on some problems and bottlenecks in areas of nonenzymatic and enzymatic (glucose oxidase-based) amperometric glucose sensing.

/pdf/recent-advances-in-electrochemical-glucose-biosensors-a-4zf5h9p6ys.pdf

Recent advances in electrochemical glucose biosensors: a review

We propose a new type of ammonia sensor with polyaniline (electroconducting polymer) as the sensitive element. Such sensors are characterized by high sensitivity, wide range of measured concentrations (1–2000 ppm) and high stability of electrical parameters. The use of polyaniline ensures high chemical stability of the sensors in oxidizing ambients. A sensor design based on a silicon chip custom-packed into a linear plastic case is presented. The chip is provided with a system of heaters and thermometers to check the temperature regime of sensor operation. We have studied I – V curves, temperature, concentration and kinetic characteristics of the sensors, as well as their ageing. The possibility for thermoregeneration of the sensor parameters after long-term functioning in an ammonia ambient is emphasized.

Ammonia sensors based on sensitive polyaniline films

The use of thin conducting polymer films (polyaniline, polypyrrole and poly-3-methylthiophene doped with ordinary mineral acids or monovalent anions, as well as heteropolyacids of Keggin type or corresponding heteropolyanions) as sensitive layers in the sensor arrays for chemical recognition of volatile organic analytes is investigated. The discrimination ability of various sensor subsets is evaluated by statistical analysis of the data retrieved from responses of 20 different polymer sensors to the vapors of nine volatile organic solvents. An approach for constructing optimal sensor array is developed and the method for systematic selection of separate sensors from the given set to achieve the required analyte recognition reliability is proposed.

Application of sensor arrays based on thin films of conducting polymers for chemical recognition of volatile organic solvents

A multienzyme electrochemical sensor array is developed. It is based on capacitance pH-sensitive electrolyte–insulator–semiconductor (EIS) sensors with silicon nitride ion-sensitive layers and different forms of cholinesterase, urease and glucose oxidase as sensitive elements. With this sensor array, we used a multienzyme analysis to recognize the heavy metal ions in solutions containing a mixture of different metal ions, as well as for determination of their content in the analysed samples. The content of toxic elements was determined by estimation of the residual activity of enzymatic membranes after the injection of analysed samples. The conditions for enzyme sensors operation, such as buffer capacity, substrate concentration, time of incubation and time of response signal measurement, were optimised to reach the maximal sensitivity of multisensor for analysis of heavy metal ions in the investigated solutions. It was shown that multienzyme analysis followed by mathematical processing is an efficient approach to develop sensor arrays for toxic substrates detection.

Multienzyme electrochemical sensor array for determination of heavy metal ions

Multi-enzymatic electrochemical sensor: field measurements and their optimisation

A comparative analysis of responses of thin films of various conducting polymers (polyaniline, polypyrrole and poly-3-methylthiophene) to the vapors of polar as well as low- and nonpolar organic solvents was performed. Conductivity measurements, infra-red and electron paramagnetic resonance spectroscopy were used to characterize responses of the polymer films doped with different dopants. Main physical and chemical factors which define the magnitude of the response to the studied analytes were determined. It was shown that the differences in response of conducting polymer films are conditioned by the influence of chemical structure of the polymer and its dopant, and also by different nature of their doping.

A.L. Kukla

Papers

Ammonia sensors based on sensitive polyaniline films

Application of sensor arrays based on thin films of conducting polymers for chemical recognition of volatile organic solvents

Multienzyme electrochemical sensor array for determination of heavy metal ions

Multi-enzymatic electrochemical sensor: field measurements and their optimisation

Comparative analysis of sensor responses of thin conducting polymer films to organic solvent vapors