Highly sensitive, low-cost integrated biosensors

Recently there has been an increasing interest in the development of electronic sensors for the detection and identification of biological species. For example, label-free DNA detection has been made possible by the use of field-effect sensors. In these sensor systems, the intrinsic charge of DNA molecules is detected through the use of metal-oxide-semiconductor field-effect transistors (MOSFETs) in which the gate electrode has been removed and the gate oxide area functionalized to make them sensitive to the species of interest. These modified transistors are called BioFETs because they are FETs that are modified to be sensitive to biological molecules. The feasibility of this BioFET approach has been demonstrated experimentally, but the sensitivity of these systems has to be significantly improved if they are to be used as a means to detect and identify biological species such as pathogen agents, quickly and at low cost. The sensitivity of biosensors is ultimately determined by their noise properties. While in principle it is possible to amplify an arbitrarily small electric signal, if this signal is embedded in noise, very little information can be recovered. In general, the noise performance of an electrical system is determined by the initial stages. In an instrumentation system, the transducer and the first amplifier connected to it have to add very little noise to the signal of interest. Also, the noise from the succeeding stages is less critical if the signal has been brought to reasonable levels by the first amplifier. For this reason, the noise properties of field-effect biosensors (BioFETs), as well as design techniques for very low-noise integrated amplifiers will be discussed. The detection of biological species is a relatively slow process, where the time constants typically range from minutes to hours; therefore, low-frequency noise is the main concern in integrated biosensors. In this presentation, we will discuss a BioFET sensor we have been developing for detecting specific pathogens. The noise properties of field-effect biosensors (BioFETs), as well as design techniques for very low-noise integrated amplifiers will be discussed in detail. Next, we will discuss the detailed modeling of all important parts of the electrolyte-sensor system and will show that by detailed analyses of both signal and noise characteristics of the integrated sensor system, that it is possible to optimize the BioFET's performance. Experimental results will also be described to show current state-of-the-art in these BioFET sensor systems. Finally, we will show how to create low-cost, highly integrated and parallel detection systems by integrating the sensor with fluidic and mechanical components, plus the processing electronics on the same chip, for real-world applications, and what are the resulting system's performance characteristics.