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Nanowires for Biosensing
The fast development of point-of-care diagnostics and personalized medicine raises new requirements to future biosensors in terms of limit of detection, throughput, materials and miniaturization. Within this framework we are currently involved in developing two parallel sensor architectures implemented as either ion-sensitive field-effect transistors (ISFETs) or extended-gate field-effect transistors (EGFETs). These devices are aimed at facilitating real-time measurements of various metal ions, pH and proteins in complex fluids. Our expertise ranges from surface functionalization with highly specific groups and molecules, to micro- and nanofabrication, microfluidics as well as electrochemistry and the interfacial double layer. The central focus of this research activity is to demonstrate the operation of these sensors in arrays of multiple sensing units for multiplexed sensing applications.
Figure 1: Design of an ISFET device for pH sensing. Detecting changes in the surface potential gives an opportunity to use wide range of receptor-target combinations with ISFET. ISFETs are sensing devices based on metal oxide semiconductor field-effect transistors. Thereby the gate metal is replaced by the solution carrying the analyte species. The electrical potential of the solution affects the output of the ISFET. Reactions of charged analytes with corresponding ligand groups at the sensor surface contribute to a surface charge which leads to an additional surface potential. This change in surface potential is monitored and can be related to the number of adsorbed analytes. Using differential treated surfaces, the sensitivity to specific target analytes can be tuned. We achieved ideal pH sensitivity and specific alkaline ion detection using arrays of silicon nanowires in a differential setup. Potentiometric detection, realized with such devices, has a great potential for precise detection of various analytes as well as understanding of the processes, happening at the surface. Currently we focus on detection of copper, which is essential element for human organism, but at too high or too low concentrations leads to numerous diseases. For detection we use peptide Gly-Gly-His, which is a model of copper-binding site of human serum albumin – main path of transporting copper in blood.
Figure 2: Schematic of the structure of EGFET biosensor where the transducer architecture is separated from the sensing surface. The EGFETs sensors are fabricated on various substrates, including transparent materials which are compatible with optical methods of investigation of biological systems and molecular interactions. Our expertise ranges from surface functionalization with highly specific groups and molecules, to micro- and nanofabrication, microfluidics as well as electrochemistry and the interfacial double layer. Compared to ISFETs, extended-gate field-effect transistors offer higher flexibility in surface geometry and substrate material. Therefore, they are ideal for potentiometric sensing with strict requirements on shape and substrate properties (transparency, flexibility and bonding).
Transport at Nanoscale Interfaces Laboratory