(Invited) Silicon Nanowire and Graphene Field-Effect Transistors for Sensing Applications

Ion-sensitive field-effect transistors (ISFETs)[1] offer a promising set of features for integrating sensor and readout electronics on the same chip, providing a portable and cost-effective sensing solution. Such sensors are label-free and convert chemical reactions into electrical signals via electrostatic gating of the FET by adsorbed chemical or biological species. During the past decade, the ISFET concept has been applied to nanoscale devices such as carbon nanotubes, graphene[2] or Si nanowires.[3, 4] Even though many exciting biosensing experiments have been reported, several key challenges are still limiting their wide-spread application. In particular, the miniaturization of the reference electrode[5] and resolving the stability and drift issues proved to be difficult tasks. Also, competing reactions at the sensor surface have to be taken into account as they limit the sensing performance and might lead to misreading.[6]  Here, we discuss these and other issues related to sensing in an electrolyte environment based on our results using silicon nanowires[4-11] and graphene FETs[2, 12] as transducers. Several examples of specific detection of pH,[5, 6] sodium,[9] potassium,[12] and biomolecules in a reliable differential setup will be presented along with a new quantitative model for describing the competing reactions in an electrolyte environment.[6, 13]  The application of these devices in the animal health sector for the diagnosis of bovine respiratory disease (BRD), which is a major cause of calf death, will also be addressed.

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2.            Fu, W., et al., Graphene transistors are insensitive to pH changes in solution. Nano Lett., 2011. 11(9): p. 3597-3600.

3.            Cui, Y., et al., Nanowire Nanosensors for Highly Sensitive and Selective Detection of Biological and Chemical Species. Science, 2001. 293(5533): p. 1289-1292.

4.            Knopfmacher, O., et al., Nernst Limit in Dual-Gated Si-Nanowire FET Sensors. Nano Lett., 2010. 10: p. 2268-2274.

5.            Tarasov, A., et al., True reference nanosensor realized with silicon nanowires. Langmuir, 2012. 28(25): p. 9899-9905.

6.            Tarasov, A., et al., Understanding the electrolyte background for biochemical sensing with ion-sensitive field-effect transistors. ACS Nano, 2012. 6(10): p. 9291-9298.

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8.            Knopfmacher, O., et al., Silicon‐Based Ion‐Sensitive Field‐Effect Transistor Shows Negligible Dependence on Salt Concentration at Constant pH. ChemPhysChem, 2012. 13(5): p. 1157-1160.

9.            Wipf, M., et al., Selective sodium sensing with gold-coated silicon nanowire field-effect transistors in a differential setup. ACS Nano, 2013. 7(7): p. 5978-5983.

10.          Bedner, K., et al., pH response of silicon nanowire sensors: impact of nanowire width and gate oxide. Sensors and Materials, 2013. 25(8): p. 567-576.

11.          Bedner, K., et al., Investigation of the dominant 1/f noise source in silicon nanowire sensors. Sens. Actuators B, 2014. 191: p. 270-275.

12.          Fu, W., et al., High mobility graphene ion-sensitive field-effect transistors by noncovalent functionalization. Nanoscale, 2013. 5(24): p. 12104-12110.

13.          Stoop, R.L., et al., Competing Surface Reactions Limiting the Performance of Ion-Sensitive Field-Effect Transistors. ACS Appl. Mater. Interfaces, 2014. submitted.