Andrey Bratov

Recent trends in potentiometric sensor arrays—A review

Nowadays there exists a large variety of ion sensors based on polymeric or solid-state membranes that can be used in a sensor array format in many analytical applications. This review aims at providing a critical overview of the distinct approaches that were developed to build and use potentiometric sensor arrays based on different transduction principles, such as classical ion-selective electrodes (ISEs) with polymer or solid-state membranes, solid-contact electrodes (SCE) including coated wire electrodes (CWE), ion-sensitive field-effect transistors (ISFETs) and light addressable potentiometric sensors (LAPS). Analysing latest publications on potentiometric sensor arrays development and applications certain problems are outlined and trends are discussed.

Enzyme semiconductor sensor based on butyrylcholinesterase

Abstract An enzyme field-effect transistor with a gelatin membrane containing butyrylcholinesterase (BCE) is investigated. The membrane formation procedure and experimental conditions are optimized. The sensor exhibits sensitivity to butyrylcholine in the range 10−4−10−2 mol/l with a response time 2 min. The influence of reversible and irreversible inhibitors on the sensor characteristics is studied.

Photosensitive polyurethanes applied to the development of CHEMFET and ENFET devices for biomedical sensing

Chemical microsensors based on ion-selective field effect transistor (ISFET) transducers with ion-selective and enzymatic membranes have been fabricated. In this case, photolithographically patterned membranes based on acrylated urethanes have been developed and applied onto the gate area of ISFET chips. Aliphatic urethane diacrylate has been used for K+ and NH+4 membranes, while a photocurable hydrogel formulation based on other type of acrylated urethane has been optimized for urea-FET sensors. Resulting potassium and ammonium sensors show similar performances to those found when PVC membranes are employed. An integrated packaging process for ISFET-based sensors has been developed giving the possibility of carrying out most of the encapsulation on wafer level. For this purpose, a photocurable polyurethane encapsulant formulation has been optimized to be microstructured by photolithography. Finally, a preliminary study of biocompatibility of photosensitive formulations containing urethane oligomers has been performed in order to examine future applications in biomedical and clinical analysis.

Three-dimensional interdigitated electrode array as a transducer for label-free biosensors.

A new transducer for biosensor applications has been developed based on a three-dimensional interdigitated electrode array (IDEA) with electrode digits separated by an insulating barrier. Binding of molecules to a chemically modified surface of the transducer induces important changes in conductivity between the electrodes. Three-dimensional sensor shows considerable improvement compared with a standard planar IDEA design. The potential of the developed device as a sensor transducer to detect immunochemical and enzymatic reactions, as well as DNA hybridization events is demonstrated. The immunosensor allows direct detection of the antibiotic sulfapyridine and shows the IC(50) parameter value of 5.6 microgL(-1) in a buffer. Immunochemical determination occurs under competitive configurations and without the use of any label. Each modified sensor is of a single use. Nevertheless, biochemical reagents can be easily cleaned off the sensor surface for its reuse. Layer-by-layer method of used to deposit polyethyleneimine and glucose oxidase showed that the sensor is also highly effective for detecting single and multilayered molecular assemblies.

Ion-selective field effect transistor (ISFET)-based calcium ion sensor with photocured polyurethane membrane suitable for ionised calcium determination in milk

Abstract Ca 2+ -ion-sensitive ISFETs with photocured polyurethane-based polymer membranes with alkylphosphate exchanger (DOPPCa) and three neutral carrier ionophores (ETH 1001, ETH 129 and ETH 5234) and dioctylsebacate as plasticizer have been studied in pure CaCl 2 solutions and in background solutions containing Na + , K + , Mg 2+ ions in concentrations normally found in milk. In case of DOPPCa and ETH 1001 the influence of Mg 2+ ions on the slope of the response curve is reported. ISFETs with membranes containing ETH 129 are shown to have high selectivity, more than 6 weeks life-time in constant contact with a solution and high precision of ionised calcium determination. Experimental results on determination of calcium ions in a whole milk are presented.

Planar Compatible Polymer Technology for Packaging of Chemical Microsensors

By applying special thick film photolithography it is possible to realize a highly automative ion-sensitive field effect transistor (ISFET) packaging at the wafer level. In this paper two approaches based on photolithographic processing of encapsulating layers are presented. A lift-off method of commercial thermocurable encapsulants has been investigated, as well as direct photopolymerization of ultraviolet-curable encapsulant compositions, containing either epoxy acrylate or polyurethane acrylate oligomers together with monomers and photoinitiators. Lift-off has been developed using either thin or thick photoresist sacrificial layers. The best compatibility implies thick photosensitive polyimide layers as a sacrificial photoresist together with the encapsulant material based on alumina-filled epoxy. However, better results are obtained by using photopatternable encapsulant polymers that permit application of thin or thick polymer layers on a wafer substrate containing ISFET chips. Windows over the gate region and contact pads are opened by exposure to ultraviolet light in a standard mask aligner system. Compositions based on epoxy acrylate oligomers are proved to be more reliable in a packaging process. Lifetime of encapsulated microsensors for pH measurements is presented.

Optimization of Photocurable Polyurethane Membrane Composition for Ammonium Ion Sensor

The composition of ammonium-ion sensitive membrane based on a photocurable aliphatic urethane diacrylate oligomer has been optimized. Membranes were prepared with exposure to UV and studied in a traditional ion-selective electrode configuration with liquid inner contact. The optimum composition is found to be: urethane diacrylate (45 to 50%), hexandiol diacrylate (10%), photoinitiator (0.8 to 1.2%), plasticizer (bis(2-ethylhexyl) sebacate or di-5-nonyladipate (35 to 40%), nonactin (2%), and KTpClPB (0.5%). The resulting ion-sensors show a sensitivity of 55.5 mV/decade, a range of linear response from 1 to 4.5 10 4 mol/liter of NH 4 Cl, a limit of detection around 10 5 mol/liter, and good selectivity in the presence of potassium ions. Introduction of 7% PVC into the membrane formulation gives a possibility to enhance the sensitivity up to 58 mV/decade but prevents application of photolithography for membrane patterning in case of ion sensitive field effect transistor-based sensors. The developed polymer composition was used to prepare ISFET-based ammonium sensors with the membrane deposited and structured on a wafer level.

Perchlorate-selective MEMFETs and ISEs based on a new phosphadithiamacrocycle

Abstract A new phosphadithiamacrocycle has been synthesized and used as neutral carrier in ion-selective PVC membranes. These membranes have been applied to the development of perchlorate-selective MEMFETs and ISEs. Both devices have shown Nernstian response and a wide working pH range. The response and selectivity found for perchlorate ions is better than those of conventional Cl O 4 − electrodes based on hydrophobic cations as electroactive species.

Application of an ion-selective field effect transistor with a photocured polymer membrane in nephrology for determination of potassium ions in dialysis solutions and in blood plasma

Application of a potassium ion sensor based on an ion sensitive field effect transistor (ISFET) for ion control of a dialysis solution in an artificial kidney and in blood plasma of patients treated by hemodialysis is presented. Sensors and their long-term stability were characterised in constant contact with test solutions. Test results are compared to those obtained with conventional ion-selective electrodes and commercial blood ion analyser. Tested ISFET sensors showed high reliability in potassium ion measurements in the physiologically significant concentration range which, along with low cost of their production, makes them promising for cited application.

ISE and ISFET microsensors based on a sensitive chalcogenide glass for copper ion detection in solution

Abstract All solid state ion microsensors based either on a potentiometric or a FET transducer with chalcogenide glass membranes sensitive to Cu 2+ -ions in solution have been developed. The membrane material was deposited by RF co-sputtering of Ge 28 Se 60 Sb 12 chalcogenide glass and metal copper. The resulting films highly doped with copper were characterised using electron microscopy and electron microprobe analysis. The method of photolithographic patterning of the chalcogenide membrane deposited on a wafer carrying the ISFET structures is presented. Analytical behavior of developed sensors were fully characterised in terms of sensitivity, selectivity, limit of detection, response time and time stability.