Maryam H. Abouzar

Penicillin biosensor based on a capacitive field-effect structure functionalized with a dendrimer/carbon nanotube multilayer

Silicon-based sensors incorporating biomolecules are advantageous for processing and possible biological recognition in a small, reliable and rugged manufactured device. In this study, we report on the functionalization of field-effect (bio-)chemical sensors with layer-by-layer (LbL) films containing single-walled carbon nanotubes (SWNTs) and polyamidoamine (PAMAM) dendrimers. A capacitive electrolyte-insulator-semiconductor (EIS) structure modified with carbon nanotubes (EIS-NT) was built, which could be used as a penicillin biosensor. From atomic force microscopy (AFM) and field-emission scanning electron microscopy (FESEM) images, the LbL films were shown to be highly porous due to interpenetration of SWNTs into the dendrimer layers. Capacitance-voltage (C/V) measurements pointed to a high pH sensitivity of ca. 55 mV/pH for the EIS-NT structures. The biosensing ability towards penicillin of an EIS-NT-penicillinase biosensor was also observed as the flat-band voltage shifted to lower potentials at different penicillin concentrations. A dynamic response of penicillin concentrations, ranging from 5.0 microM to 25 mM, was evaluated for an EIS-NT with the penicillinase enzyme immobilized onto the surfaces, via constant-capacitance (ConCap) measurements, achieving a sensitivity of ca. 116 mV/decade. The presence of the nanostructured PAMAM/SWNT LbL film led to sensors with higher sensitivity and better performance.

An array of field-effect nanoplate SOI capacitors for (bio-)chemical sensing.

An array of individually addressable nanoplate field-effect capacitive (bio-)chemical sensors based on an SOI (silicon-on-insulator) structure has been developed. The isolation of the individual capacitors was achieved by forming a trench in the top Si layer with a thickness of 350 nm. The realized sensor array allows addressable biasing and electrical readout of multiple nanoplate EISOI (electrolyte-insulator-silicon-on-insulator) capacitive biosensors on the same SOI chip as well as differential-mode measurements. The feasibility of the proposed approach has been demonstrated by realizing sensors for the pH and penicillin concentration detection as well as for the label-free electrical monitoring of polyelectrolyte multilayers formation and DNA (deoxyribonucleic acid)-hybridization event. A potential change of ∼ 120 mV has been registered after the DNA hybridization for the sensor immobilized with perfectly matched single-strand DNA, while practically no signal changes have been observed for a sensor with fully mismatched DNA. The realized examples demonstrate the potential of the nanoplate SOI capacitors as a new basic structural element for the development of different types of field-effect biosensors.

Characterisation of capacitive field-effect sensors with a nanocrystalline-diamond film as transducer material for multi-parameter sensing.

The feasibility of a capacitive field-effect EDIS (electrolyte-diamond-insulator-semiconductor) platform for multi-parameter sensing is demonstrated by realising EDIS sensors with an O-terminated nanocrystalline-diamond (NCD) film as transducer material for the detection of pH and penicillin concentration as well as for the label-free electrical monitoring of adsorption and binding of charged macromolecules, like polyelectrolytes. The NCD films were grown on p-Si-SiO(2) substrates by microwave plasma-enhanced chemical vapour deposition. To obtain O-terminated surfaces, the NCD films were treated in an oxidising medium. The NCD-based field-effect sensors have been characterised by means of constant-capacitance method. The average pH sensitivity of the O-terminated NCD film was 40 mV/pH. A low detection limit of 5 microM and a high penicillin G sensitivity of 65-70 mV/decade has been obtained for an EDIS penicillin biosensor with the adsorptively immobilised enzyme penicillinase. Alternating potential changes, having tendency to decrease with increasing the number of adsorbed polyelectrolyte layers, have been observed after the layer-by-layer deposition of polyelectrolyte multilayers, using positively charged PAH (poly (allylamine hydrochloride)) and a negatively charged PSS (poly (sodium 4-styrene sulfonate)) as a model system. The response mechanism of the developed EDIS sensors is discussed.

A Semiconductor-based Field-effect Platform for (Bio-)Chemical and Physical sensors: From Capacitive EIS Sensors and LAPS over ISFETs to Nano-scale Devices

The coupling of semiconductor field-effect devices (FED) together with chemical and biological recognition elements, like functional intelligent materials, biomolecules and living cells, represents an attractive platform for the creation of different (bio-)chemical sensors, multi-parameter analysis systems and bio-chips. This paper summarises recent developments and current research activities in the field of (bio-)chemically modified FEDs, scaling down from capacitive EIS (electrolyte-insulator-semiconductor) sensors and LAPS (light-addressable potentiometric sensor) to ISFETs (ion-sensitive field-effect transistor) that have been realised in our laboratory. Selected examples of application of ISFETs for the detection of physical parameters in liquids are presented, too. With the aim of future development of nano-devices for the detection of single biomolecules, the possibility of a simple preparation of different self-aligned nano-structures by using conventional photolithography and pattern-size reduction technique has been experimentally demonstrated.

Capacitive field-effect (bio-)chemical sensors based on nanocrystalline diamond films

Capacitive field-effect electrolyte-diamond-insulator-semiconductor (EDIS) structures with Oterminated nanocrystalline diamond (NCD) as sensitive gate material have been realized and investigated for the detection of pH, penicillin concentration, and layer-by-layer adsorption of polyelectrolytes. The surface oxidizing procedure of NCD thin films as well as the seeding and NCD growth process on a Si-SiO 2 substrate have been improved to provide high pH-sensitive, non-porous thin films without damage of the underlying SiO 2 layer and with a high coverage of O-terminated sites. The NCD surface topography, roughness, and coverage of the surface groups have been characterized by SEM, AFM and XPS methods. The EDIS sensors with O-terminated NCD film treated in oxidizing boiling mixture for 45 min show a pH sensitivity of about 50 mV/pH. The pH-sensitive properties of the NCD have been used to develop an EDIS-based penicillin biosensor with high sensitivity (65-70 mV/decade in the concentration range of 0.252.5 mM penicillin G) and low detection limit (5 µM). The results of label-free electrical detection of layer-by-layer adsorption of charged polyelectrolytes are presented, too.

Markierungsfreie DNA-Detektion mit Silizium-Feldeffekt-Sensoren – Messeffekte oder Artefakte? (Label-free DNA Detection with Silicon Field-Effect Sensors – Real Effects or Artefacts?)

Die Entwicklung von diagnostischen Methoden auf der Basis von DNA-Mikroarrays, bekannt als DNA- oder Gen-Chips, wird in Zukunft in vielen Bereichen neue Möglichkeiten eröffnen. Zurzeit basieren die meisten DNA-Chips auf Fluoreszenzmarkierung oder radioaktiver Markierung der zu analysierenden DNA in Verbindung mit entsprechenden Nachweismethoden für die jeweiligen Marker. In diesem Artikel stellen wir eine markerfreie und voll-elektronische Messmethode vor, die auf der Detektion der DNA mittels Feldeffekt-Sensoren beruht. The development of diagnostic methods based on DNA microarrays, so-called DNA- or gene chips, offers many promising future applications. At the moment, most DNA chips are based on fluorescence or radioactive marker assays, where the DNA molecules of interest are sensed by probing these markers with different methods. In this article we introduce a direct, label-free, and fully-electronic detection method for DNA, which is based on field-effect sensors.

Nanocrystalline Diamond-Based Field-Effect Capacitive pH Sensor

The pH-sensitive properties of field-effect capacitive electrolyte-diamond-insulator- semiconductor (EDIS) sensors with undoped nanocrystalline diamond (NCD) thin films (100-500 nm) having hydrogen (H)- and oxygen (O)-terminated surfaces have been investigated. The NCD films were grown on p-Si-SiO2 substrates by a microwave plasma-enhanced chemical vapour deposition from a mixture of methane and hydrogen. The EDIS sensors have been characterised by means of capacitance- voltage spectroscopy, constant-capacitance and impedance-spectroscopy method. The developed EDIS sensors with O-terminated and H-terminated NCD surfaces show an average pH sensitivity of 38 mV/pH and 34-36 mV/pH, respectively. A possible mechanism of the pH sensitivity is discussed.

Towards label-free detection of charged macromolecules using field-effect-based structures: Scaling down from capacitive EIS sensor over ISFET to nano-scale devices

The possibility of a label-free electrical detection of charged macromolecules using semiconductor field-effect sensors offers a new approach for the development of DNA chips with fast and direct electrical readout. A deep understanding of the adsorption and interaction of charged biomolecules onto charged surfaces is of great interest also for the fundamental understanding of many key physiological processes. In the present work, two types of field-effect sensors, namely a capacitive EIS (electrolyte-insulator-semiconductor) structure and an ISFET (ion-sensitive field-effect transistor) have been utilised for monitoring layer-by-layer adsorption of polyelectrolytes as well as for the DNA immobilisation and hybridisation detection.