Capacitive field-effect sensors modified with a multi-enzyme membrane have been applied for an electronic transduction of biochemical signals processed by enzyme-based AND-Reset and OR-Reset logic ...gates. The local pH change at the sensor surface induced by the enzymatic reaction was used for the activation of the Reset function for the first time.
Integration of enzyme-based AND-Reset and OR-Reset logic gates with a field-effect electronic transducer modified with a multi-enzyme membrane.
► A biosensor chip with integrated microfluidic channel and enzyme-based sensors was developed. ► The chip was successfully used for measurement of glucose, glutamate and glutamine. ► Cost-effective ...and small-sized analysis tool with opportunity to integrate further sensors.
A microfluidic chip integrating amperometric enzyme sensors for the detection of glucose, glutamate and glutamine in cell-culture fermentation processes has been developed. The enzymes glucose oxidase, glutamate oxidase and glutaminase were immobilized by means of cross-linking with glutaraldehyde on platinum thin-film electrodes integrated within a microfluidic channel. The biosensor chip was coupled to a flow-injection analysis system for electrochemical characterization of the sensors. The sensors have been characterized in terms of sensitivity, linear working range and detection limit. The sensitivity evaluated from the respective peak areas was 1.47, 3.68 and 0.28μAs/mM for the glucose, glutamate and glutamine sensor, respectively. The calibration curves were linear up to a concentration of 20mM glucose and glutamine and up to 10mM for glutamate. The lower detection limit amounted to be 0.05mM for the glucose and glutamate sensor, respectively, and 0.1mM for the glutamine sensor. Experiments in cell-culture medium have demonstrated a good correlation between the glutamate, glutamine and glucose concentrations measured with the chip-based biosensors in a differential-mode and the commercially available instrumentation. The obtained results demonstrate the feasibility of the realized microfluidic biosensor chip for monitoring of bioprocesses.
We present a label-free method for the detection of DNA hybridization, which is monitored by non-metallized silicon field-effect transistors (FET) in a microarray approach. The described method ...enables a fast and fully electronic readout of ex situ binding assays. The label-free detection utilizing the field-effect is based on the intrinsic charge of the DNA molecules and/or on changes of the solid–liquid interface impedance, when biomolecules bind to the sensor surface. With our sensor system, usually a time-resolved, dc readout is used. In general, this FET signal suffers from sensor drift, temperature drift, changes in electrolyte composition or pH value, influence of the reference electrode, etc. In this article, we present a differential ac readout concept for FET microarrays, which enables a stable operation of the sensor against many of these side-parameters, reliable readout and a possibility for a quick screening of large sensor arrays. We present the detection of point mutations in short DNA samples with this method in an ex situ binding assay.
The semiconductor field-effect platform represents a powerful tool for detecting the adsorption and binding of charged macromolecules with direct electrical readout. In this work, a capacitive ...electrolyte–insulator–semiconductor (EIS) field-effect sensor consisting of an Al-p-Si-SiO
2
structure has been applied for real-time in situ electrical monitoring of the layer-by-layer formation of polyelectrolyte (PE) multilayers (PEM). The PEMs were deposited directly onto the SiO
2
surface without any precursor layer or drying procedures. Anionic poly(sodium 4-styrene sulfonate) and cationic weak polyelectrolyte poly(allylamine hydrochloride) have been chosen as a model system. The effect of the ionic strength of the solution, polyelectrolyte concentration, number and polarity of the PE layers on the characteristics of the PEM-modified EIS sensors have been studied by means of capacitance–voltage and constant-capacitance methods. In addition, the thickness, surface morphology, roughness and wettabilityof the PE mono- and multilayers have been characterised by ellipsometry, atomic force microscopy and water contact-angle methods, respectively. To explain potential oscillations on the gate surface and signal behaviour of the capacitive field-effect EIS sensor modified with a PEM, a simplified electrostatic model that takes into account the reduced electrostatic screening of PE charges by mobile ions within the PEM has been proposed and discussed.
Figure
Label-free electrical monitoring of polyelectrolyte multilayer formation by means of a capacitive field-effect sensor consisting of Al-p-Si-SiO
2
structure. The consecutive adsorption of oppositely charged polyelectrolyte layers leads to alternating shifts of the capacitance-voltage and constant-capacitance curves, whereas the direction of these shifts correlates with the charge sign of the terminating polyelectrolyte layer
► Enzyme-based AND/OR logic gates are integrated with a capacitive field-effect sensor. ► The AND/OR logic gates compose of multi-enzyme system immobilised on sensor surface. ► Logic gates were ...activated by different combinations of chemical inputs (analytes). ► The logic output (pH change) produced by the enzymes was read out by the sensor.
The integration of biomolecular logic gates with field-effect devices – the basic element of conventional electronic logic gates and computing – is one of the most attractive and promising approaches for the transformation of biomolecular logic principles into macroscopically useable electrical output signals. In this work, capacitive field-effect EIS (electrolyte–insulator–semiconductor) sensors based on a p-Si–SiO
2–Ta
2O
5 structure modified with a multi-enzyme membrane have been used for electronic transduction of biochemical signals processed by enzyme-based
OR and
AND logic gates. The realised
OR logic gate composes of two enzymes (glucose oxidase and esterase) and was activated by ethyl butyrate or/and glucose. The
AND logic gate composes of three enzymes (invertase, mutarotase and glucose oxidase) and was activated by two chemical input signals: sucrose and dissolved oxygen. The developed integrated enzyme logic gates produce local pH changes at the EIS sensor surface as a result of biochemical reactions activated by different combinations of chemical input signals, while the pH value of the bulk solution remains unchanged. The pH-induced charge changes at the gate-insulator (Ta
2O
5) surface of the EIS transducer result in an electronic signal corresponding to the logic output produced by the immobilised enzymes. The logic output signals have been read out by means of a constant–capacitance method.
The integration of living cells together with silicon field-effect devices challenges a new generation of biosensors and bioelectronic devices. Cells are representing highly organised complex ...systems, optimised by millions of years of evolution and offering a broad spectrum of bioanalytical receptor “tools” such as enzymes, nucleic acids proteins, etc. Their combination with semiconductor-based electronic chips allows the construction of functional hybrid systems with unique functional and electronic properties for both fundamental studies and biosensoric applications. This review article summarises recent advances and trends in research and development of cell/transistor hybrids (cell-based field-effect transistors) as well as light-addressable potentiometric sensors.
Bonding of polymer-based microfluidics to polymer substrates still poses a challenge for Lab-On-a-Chip applications. Especially, when sensing elements are incorporated, patterned deposition of ...adhesives with curing at ambient conditions is required. Here, we demonstrate a fabrication method for fully printed microfluidic systems with sensing elements using inkjet and stereolithographic 3D-printing.
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 350nm. 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 ∼120mV 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.
A critical evaluation of the possibilities and limitations of the label-free detection of deoxyribonucleic acid (DNA) hybridization by means of field-effect-based devices is discussed. A new ...DNA-detection method is introduced, which utilizes an ion-sensitive field-effect device as transducer. The upon the DNA hybridization induced redistribution of the ion concentration within the intermolecular spaces and/or the alteration of the ion sensitivity of the device is proposed as detection mechanism. The theoretical calculations predict a substantial change in the average ion concentration within the intermolecular spaces induced upon hybridization that are enough to obtain a detectable sensor signal.
Field-effect-based capacitive electrolyte–insulator–semiconductor (EIS) sensors have been utilised for the deoxyribonucleic acid (DNA) immobilisation and hybridisation detection as well as for ...monitoring the layer-by-layer adsorption of polyelectrolytes (anionic poly(sodium 4-styrene sulfonate) (PSS) and cationic poly(allylamine hydrochloride) (PAH)). The EIS sensors with charged macromolecules have been systematically characterised by capacitance–voltage, constant-capacitance, impedance spectroscopy and atomic-force microscopy methods. The effect of the number and polarity of the polyelectrolyte layers on the shift of the capacitance–voltage curves has been investigated. Alternating potential shifts of about 30–90
mV have been observed after the adsorption of each polyanion and polycation layer, respectively. The DNA immobilisation and hybridisation signals were 35–55 and 24–33
mV, respectively. The possible mechanisms for the sensor responses are discussed.
