An Integrated Microelectronic Device for Label-Free Nucleic Acid Amplification and Detection

While there have been extensive advances in miniaturized polymerase chain reaction (PCR) systems, progress on integrated microfabricated readout mechanisms has been rather limited, and most systems rely on off-chip optical detection modules to mea¬ure the final product. Existing optical detection platforms typically include CCD cameras, photodiodes, and photomultiplier tubes. While such hardware has adequate sensitivity for detecting PCR products in sample volumes significantly lower than that of bench-top systems, most are difficult to miniaturize and integrate into a compact analytical system. For example, some portable systems incorporating external LEDs and photodetectors can weigh between 1 kg and 4 kg each. To address these limitations, several groups have successfully embedded photodetectors within integrated PCR platforms. However, these devices still rely on external excitation sources.

To address this limitation, we have developed an integrated microelectronic device for amplification and label-free detection of nucleic acids. Amplification by PCR is achieved with on-chip metal resistive heaters, temperature sensors, and microfluidic valves. We demonstrate a rapid thermocycling with rates of up to 50 degrees C/s and a PCR product yield equivalent to that of a bench-top system. Amplicons within the PCR product are detected by their intrinsic charge with a silicon field-effect sensor. Similar to existing optical approaches with intercalators such as SYBR Green, the sensing approach can directly detect standard double-stranded PCR products while in contrast our sensor occupies a micron-scale footprint, dissipates only nano-watt power during operation, and does not require labeling reagents. By combining amplification and detection on the same device, we show that the presence or absence of a particular DNA sequence can be determined by converting the analog surface potential output of the field-effect sensor to a simple digital true/false readout.