Arshak Poghossian

Penicillin detection by means of field-effect based sensors: EnFET, capacitive EIS sensor or LAPS?

Abstract Three types of semiconductor field-effect penicillin sensors, enzyme field-effect transistors (EnFETs), capacitive electrolyte–insulator–semiconductor (EIS) sensors and light-addressable potentiometric sensors (LAPS) have been developed and tested for the penicillin detection. For all sensor types the enzyme penicillinase was adsorptively immobilised directly onto a pH-sensitive Ta 2 O 5 surface. Some basic parameters of these sensors (e.g. sensitivity, linear range, detection limit, response time, hysteresis and life time) are investigated and their performances with regard to the respective measurement set-up as well as the sensor configuration are compared.

Constant-Current-Mode LAPS (CLAPS) for the Detectionof Penicillin

A software feedback control system for the constant-current-mode operation of the light-addressable potentiometric sensor (LAPS) was developed. The constant-current-mode LAPS (CLAPS) is suitable for online monitoring and recording of changes in the pH value or the ion concentration. An enzyme LAPS was fabricated by adsorptive immobilization of penicillinase on the pH-sensitive layer of Ta2O5. This sensor was operated in the constant-current-mode and the detection limit for penicillin G was found to be at least as low as 100 µM.

Multi-parameter detection of (bio-)chemical and physical quantities using an identical transducer principle

Abstract A multi-functional hybrid sensor module and multi-parameter measuring system for the detection of six (bio-)chemical and physical parameters (pH, penicillin concentration, diffusion coefficients of ions, temperature, flow velocity and flow direction) is realised using the same transducer principle. Here, an ion-sensitive field-effect transistor (ISFET), which is well known as a (bio-)chemical sensor, is also utilised as a physical sensor. Thus, more parameters can be determined than the number of sensors present in the modular system (so-called “high order” system). The multi-parameter detection is achieved by means of sequentially or simultaneously scheduling of different sensor arrangements and/or different operation modes. The results of testing of the developed hybrid module in different sensor configurations and basic characteristics of individual sensors, including an ISFET-based “time-of-flight”-type flow-velocity and flow-direction sensor employing the in situ electrochemical generation of chemical tracers, like H+- or OH−-ions, are presented and discussed. A novel diffusion-coefficient sensor that is based also on an ISFET is introduced and experimentally demonstrated.

(Bio-)chemical and physical microsensor arrays using an identical transducer principle

A new concept based on an identical transducer principle and structure for both (bio-)chemical and physical sensors is presented. For all sensors, the field effect is used as transducer principle. In this approach, the same chemical sensor is employed also as a physical sensor. A novel design of a temperature sensor on the basis of a differential arrangement of two identical ISFETs operating in different working points is demonstrated. A multifunctionality of the sensor system is achieved by means of different sensor arrangements and/or operation modes. Thus, the number of the obtained (bio-)chemical and physical quantities, like ion concentration, temperature, flow rate can be higher than the number of the sensors applied. A hybrid sensor module, for the pH, penicillin and temperature determination is realised and its performance has been investigated.

Application of ISFETs for pH measurement in rain droplets

Abstract The analysis of chemical components in single raindrops, including pH, is expected to give a new information about air pollution. This paper presents the first attempt of an ISFET application for the pH measurement in raindrops. The investigated rain samples are originated from 11 different rain events including even individually collected (using a liquid nitrogen) droplets. The results of pH measurements in raindrops with the pH ISFET are compared with the conventional glass electrode measurements in bulk rain samples. The observed raindrop size dependence of the pH value is discussed.

K+-selective field-effect sensors as transducers for bioelectronic applications

A K + -sensitive capacitive electrolyte-membrane-insulator-semiconductor (EMIS) sensor has been developed. The sensor utilizes a valinomycin-containing PVC-based membrane with different contents of plasticizer. This new type of sensor has been investigated in terms of its intrinsic characteristics, like impedance behavior, capacitance/voltage characteristics and frequency dependence. The optimized working conditions of the sensor and various membrane compositions have been studied with regard to the sensitivity performance in different electrolytes. The possibility of future applications for the measurement of extracellular potassium-ion concentrations are discussed.

Use of Information Visualization Methods Eliminating Cross Talk in Multiple Sensing Units Investigated for a Light-Addressable Potentiometric Sensor

The integration of nanostructured films containing biomolecules and silicon-based technologies is a promising direction for reaching miniaturized biosensors that exhibit high sensitivity and selectivity. A challenge, however, is to avoid cross talk among sensing units in an array with multiple sensors located on a small area. In this letter, we describe an array of 16 sensing units of a light-addressable potentiometric sensor (LAPS), which was made with layer-by-layer (LbL) films of a poly(amidomine) dendrimer (PAMAM) and single-walled carbon nanotubes (SWNTs), coated with a layer of the enzyme penicillinase. A visual inspection of the data from constant-current measurements with liquid samples containing distinct concentrations of penicillin, glucose, or a buffer indicated a possible cross talk between units that contained penicillinase and those that did not. With the use of multidimensional data projection techniques, normally employed in information visualization methods, we managed to distinguish the results from the modified LAPS, even in cases where the units were adjacent to each other. Furthermore, the plots generated with the interactive document map (IDMAP) projection technique enabled the distinction of the different concentrations of penicillin, from 5 mmol L(-1) down to 0.5 mmol L(-1). Data visualization also confirmed the enhanced performance of the sensing units containing carbon nanotubes, consistent with the analysis of results for LAPS sensors. The use of visual analytics, as with projection methods, may be essential to handle a large amount of data generated in multiple sensor arrays to achieve high performance in miniaturized systems.

DNA Immobilization and Hybridization Detection by the Intrinsic Molecular Charge Using Capacitive Field-Effect Sensors Modified with a Charged Weak Polyelectrolyte Layer.

Miniaturized setup, compatibility with advanced micro- and nanotechnologies, and ability to detect biomolecules by their intrinsic molecular charge favor the semiconductor field-effect platform as one of the most attractive approaches for the development of label-free DNA chips. In this work, a capacitive field-effect EIS (electrolyte-insulator-semiconductor) sensor covered with a layer-by-layer prepared, positively charged weak polyelectrolyte layer of PAH (poly(allylamine hydrochloride)) was used for the label-free electrical detection of DNA (deoxyribonucleic acid) immobilization and hybridization. The negatively charged probe single-stranded DNA (ssDNA) molecules were electrostatically adsorbed onto the positively charged PAH layer, resulting in a preferentially flat orientation of the ssDNA molecules within the Debye length, thus yielding a reduced charge-screening effect and a higher sensor signal. Each sensor-surface modification step (PAH adsorption, probe ssDNA immobilization, hybridization with complementary target DNA (cDNA), reducing an unspecific adsorption by a blocking agent, incubation with noncomplementary DNA (ncDNA) solution) was monitored by means of capacitance-voltage and constant-capacitance measurements. In addition, the surface morphology of the PAH layer was studied by atomic force microscopy and contact-angle measurements. High hybridization signals of 34 and 43 mV were recorded in low-ionic strength solutions of 10 and 1 mM, respectively. In contrast, a small signal of 4 mV was recorded in the case of unspecific adsorption of fully mismatched ncDNA. The density of probe ssDNA and dsDNA molecules as well as the hybridization efficiency was estimated using the experimentally measured DNA immobilization and hybridization signals and a simplified double-layer capacitor model. The results of field-effect experiments were supported by fluorescence measurements, verifying the DNA-immobilization and hybridization event.

Chemical sensor as physical sensor: ISFET-based flow-velocity, flow-direction and diffusion-coefficient sensor

Abstract An ion-sensitive field-effect transistor (ISFET), which is well known as a (bio-)chemical sensor is utilised for the development of a novel flow-velocity, flow-direction and diffusion-coefficient sensor. The proposed sensor presents a sensor-actuator system and consists of an ion generator and a pH ISFET that detects the in situ electrochemically generated H+- or OH−-ions. A good linearity between the measured flow-velocity with the ISFET and the delivered flow rate of the pump was observed. Since the ISFET has a short response time in the millisecond range, it can be utilised as an excellent detector for the measurement of flow-velocity in a wide range. The experimental results of the determination of the flow-direction and diffusion-coefficient of ions with the ISFET are presented, too.

Application of a (bio-)chemical sensor (ISFET) for the detection of physical parameters in liquids

Abstract An ion-sensitive field-effect transistor (ISFET), which is well known as a (bio-)chemical sensor, is utilised as transducer in a hybrid sensor module for the detection of four physical parameters (flow velocity, flow direction, diffusion coefficient of ions and liquid level). The experimental results of testing of the developed multi-parameter hybrid module in different sensor arrangements are presented. A novel ISFET-based liquid-level sensor as well as a “time-of-flight”-type ISFET-array-based flow-velocity sensor employing the in-situ ion-pulse generation are introduced and realised. An influence of the counter ions on the behaviour of the ISFET-based flow-direction sensor is discussed, too.