Nanotube sensors can detect single molecules

ENGINEERS at MIT, US, have developed carbon nanotube-based sensors which are sensitive enough to detect a single protein molecule.

Chemical engineering professor Michael Strano says that the sensor arrays, which are the most sensitive ever created, could be used to look for the “needle in a haystack”. Potential uses include tracking virus infections, monitoring the production of living cells, or testing for food contamination. The nanotubes can be functionalised in different ways.

Carbon nanotubes naturally fluoresce in laser light. Strano and the team coat the nanotubes with molecules which can bind to the desired target molecule. When the coated nanotubes bind to the target molecule, the fluorescence changes, and this can be detected. In this case, the team used short DNA chains called aptamers. Previously, it was difficult to make aptamers bind to carbon nanotubes whilst maintaining their configuration and functionality, but researcher Markita Landry found a way to solve the problem. She added a so-called “spacer sequence” of DNA between the section of the aptamer that attaches to the carbon nanotube and the section that binds to the target protein. This allows the binding end to maintain its configuration.

The researchers tested the nanosensors in an array on a microscope slide and added a single bacterial, human or yeast cell. When the cell secretes even just one molecule of the target protein, the sensors can detect it. Strano and the team have so far tested the nanosensors with two proteins, RAP1, a signalling protein and HIV1 integrase, found in HIV, but they believe the technique will work with other proteins.

“This platform will open a new path to detect trace amounts of proteins secreted by microorganisms. It will advance biological research [on] the generation of signal molecules, as well as the biopharmaceutical industry's [efforts to monitor] microorganism health and product quality,” said researcher Juyao Dong.

It could also help to test genetically engineered cells to ensure that they are performing as expected. This would be particularly important of an experimental technique where a patient’s own cells are modified to produce a therapeutic protein before being put back into the patient.

Nature Nanotechnology DOI: 10/bxsg

Strano and his laboratory have been working on fluorescent nanotube sensors for some time. In 2013, the team used synthetic antibodies to functionalise the nanotubes, having previously demonstrated sensors using natural antibodies.