Emily Oblath, Hampton Henley, J.P. Alarie and Professor Michael Ramsey describe in Lab on a Chip, a microfluidic chip integrating DNA extraction, amplification, and detection for the identification of bacteria in saliva. The chip design integrates a monolithic aluminum oxide membrane (AOM) for DNA extraction with seven parallel reaction wells for real-time polymerase chain reaction (rtPCR) amplification of the extracted DNA.
Samples were first heated to lyse target organisms and then added to the chip and filtered through the nanoporous AOM to extract the DNA. PCR reagents were added to each of the wells and the chip was thermocycled. Identification of Streptococcus mutans in a saliva sample was demonstrated along with the detection of 300 fg (100–125 copies) of both methicillin-susceptible Staphylococcus aureus (MSSA) and methicillin-resistant S aureus (MRSA) genomic DNA (gDNA) spiked into a saliva sample. Multiple target species and strains of bacteria can be simultaneously identified in the same sample by varying the primers and probes used in each of the seven reaction wells. In initial tests, as little as 30 fg (8–12 copies) of MSSA gDNA in buffer has been successfully amplified and detected with this device.
Researchers in the Ramsey Group, published in ACS NANO, describe a nanofluidic device that is capable of electrically monitoring the driven translocation of DNA molecules through a nanochannel. This is achieved by intersecting a long transport channel with a shorter orthogonal nanochannel. The ionic conductance of this transverse nanochannel is monitored while DNA is electrokinetically driven through the transport channel. When DNA passes the intersection, the transverse conductance is altered, resulting in a transient current response. In 1 M KCl solutions, this was found to be a current enhancement of 5–25%, relative to the baseline transverse ionic current.
The group investigated two different device geometries. In one device, the DNA was detected after it was fully inserted into and translocating through the transport nanochannel. In the other device, the DNA was detected while it was in the process of entering the nanochannel. It was found that these two conditions are characterized by different transport dynamics. Simultaneous optical and electrical monitoring of DNA translocation confirmed that the transient events originated from DNA transport through the nanochannel intersection.