(250m) Unamplified and Sensitive DNA Sensor for MRSA Detection by Capacitive Sensing and Low Voltage AC Dielectrophoresis

Methicillin-resistant Staphylococcus aureus (MRSA) is one of the most prevalent causes of nosocomial and community-acquired infections with worst clinic consequences. MRSA-colonized patients face significantly higher mortality and morbidity rates than patients infected with methicillin-susceptible S aureus. Therefore, fast and reliable methods for detection of MRSA are warranted to limit the spread of infection. This work presents a low-cost, highly sensitive, and specific DNA sensor as a screening tool for rapid detection of MRSA.

Mechanism:

The sensing mechanism for our bacterium DNA detection is based on alternating current (AC) electrokinetics-enhanced capacitive sensing. A special AC measuring signal is applied between a pair of functionalized interdigitated microelectrodes (IDMEs). Innovation includes (1) low voltage dielectrophoresis (DEP) enrichment of DNA molecules for rapid hybridization and high sensitivity; (2) Use of interfacial capacitance (C_int) as the indicator of specific binding, and the direct measurement of C_int for robust operation and minimal matrix effects; (3) Simultaneous execution of (1) and (2) during assay to achieve a single step operation.

Experiments:

Voltage optimization: The measuring AC signal was carefully chosen. As such, it will induce sufficiently strong DEP attraction of DNA molecules and yet not so strong for the detection to be non-specific. 7 mV, 10 mV and 15 mV was tested, and 10 mV was found to be the best of three.

Electrodes and probe density: Two types of electrode materials were tested, electroplated gold on printed-circuit-based IDMEs and aluminum IDMEs. The plated gold electrodes were shown to immobilize more probe than aluminum electrodes, and yielded larger responses. However, their capacitive responses cannot distinguish between positive and negative samples. Aluminum electrodes had lower probe density, which allows target DNAs to approach the IDME to exhibit a decreasing capacitance change, while non-targets lead to an increasing capacitance change. So aluminum IDMEs were adopted.

Results and conclusions:

This sensor is capable of direct DNA detection with a response time of 30 s. The LOD was calculated to be 8 pg/mL in standard buffer. The dose response was found to be, where x is DNA concentration in pg/mL. The sensor is specific against MRSA. The detection does not need any signal amplification, which considerably simplifies the sensor operation and makes it highly suitable for point of care disease diagnosis.