Enzyme assays using sensor arrays based on ion-selective carbon nanotube field-effect transistors.

In the fields of clinical diagnostics and point-of-care diagnosis as well as food and environmental monitoring there is a high demand for reliable high-throughput, rapid and highly sensitive assays for a simultaneous detection of several analytes in complex and low-volume samples. Sensor platforms based on solution-processable electrolyte-gated carbon nanotube field-effect transistors (CNT-FETs) are a simple and cost-effective alternative for conventional assays. In this work we demonstrate a selective as well as direct detection of the products of an enzyme-substrate interaction, here the for metabolic processes important urea-urease system, with sensors based on spray-coated CNT-FETs. The selective and direct detection is achieved by immobilizing the enzyme urease via certain surface functionalization techniques on the sensor surface and further modifying the active interfaces with polymeric ion-selective membranes as well as pH-sensitive layers. Thereby, we can avoid the generally applied approach for a field-effect based detection of enzyme reactions via detecting changes in the pH value due to an on-going enzymatic reaction and directly detect selectively the products of the enzymatic conversion. Thus, we can realize a buffering-capacity independent monitoring of changes in the substrate concentration.

Photoluminescence Efficiency of Substituted Quaterthiophene Crystals.

The photoluminescence (PL) efficiency of substituted alpha-conjugated quaterthiophene crystals shows marked differences depending on crystal packing and molecular geometry. This effect is studied by evaluating the role of the intermolecular interactions and the effects of the single molecule conformation on the intersystem crossing (ISC) rate. The comparison of these calculations with absolute quantum efficiency measurements and with the experimental temperature dependence of the PL decay time, indicates that the differences in PL efficiency are not inherent to crystal packing effects but they are determined by the ISC rate.

Back-gated spray-deposited carbon nanotube thin film transistors operated in electrolytic solutions: an assessment towards future biosensing applications.

We report on back-gated carbon nanotube (CNT) thin-film transistors (CNTFETs) and their performance in electrolytic solutions to assess their suitability for future application as biosensors. Spray-deposited CNT networks were used as the sensitive active layer which offers the opportunity for integration on flexible sensing platforms at low-cost. We characterized the transistors' behavior in electrolytes by analyzing the response to different KCl solutions and buffers over a wide pH range. We observed a linear response of the drain current upon changing the pH in low molarity buffers and obtained an exponential dependence on the salt concentration of the electrolyte. These responses can be attributed to electrostatic gating effects that go along with shifts in the threshold voltage. Even though a lot of effort has been put into understanding the biosensing mechanism a detailed theory is still missing. Back-gated CNTFETs operated in electrolytic solutions can be a further tool to investigate and clarify the existing unsolved phenomena.