NIST, NRL focus on lab-on-a-chip shelf life

Researchers are working on many fronts to remove technical roadblocks to effective lab-on-a-chip technology. One roadblock is limited sensor shelf life. Now, researchers at NIST and the Naval Research Laboratory have patented a concept that could extend sensor life for months or more.

According to NIST, NIST researcher John Kasianowicz has discovered an approach that involves building arrays of nanopores, each small enough that only one protein or DNA molecule at a time can pass through and be identified. A membrane peppered with such nanopores arranged to support real-time chemical analysis could give doctors a snapshot of health status, but to support the analysis, the membrane would need to be mounted on an electronics-compatible biochip.

“But these chips need to have a long shelf life,” said Kasianowicz in a press release. “As it stands, we make nanopore membranes from fatty lipids that aren’t robust—the membranes only last a week or so. We wanted to extend that lifetime substantially.”

Kasianowicz team at NIST worked with Devanand Shemoy’s team at NRL to explore the possibility of turning the lipids into polymers to make them tougher but without rendering the nanopores ineffective at trapping and identifying blood serum proteins—perhaps by excessive squeezing or stretching of the membrane holes. Fortunately, tests at NIST showed the nanopores performed just as well as before.

“Conceivably, chips made with polymerized membranes could last a year, perhaps much longer,” Kasianowicz said. “The nanopores still allow molecules to flow through for characterization.”

Kasianowicz said the teams are optimistic that the membranes will continue to exhibit long shelf life when attached to a biochip. “Based on observations we’ve made in previous research, it should work in principle,” he said. “We hope this is the next step toward allowing medical professionals to judge health conditions based on immediate blood analysis, which should be more accurate than using day-old samples.”

NIST reported that the technique could ultimately be applied to applications such as an inexpensive DNA sequencing method, such as one explored by NIST and Columbia University's School of Engineering and Applied Science. That method, described last fall, determines DNA sequences by attaching molecular tags to each of A, G, C, and T bases of a DNA strand. Each of these polymer tags could be cut from the strand and passed through a nanopore, one tag at a time. Being different sizes, the tags would result in altered electrical current flow in accordance with which DNA base pair they represent.

Kasianowicz estimated that the technique could identify a DNA building block with an error rate of less than one in 500 million, and the necessary equipment would be within any medical provider reach. “The heart of the sequencer would be an operational amplifier that would cost much less than $1,000 for a one-time purchase,” he said, “and the cost of materials and software should be trivial.”

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