Michael Strano and colleagues at MIT have fabricated a novel Ni2+ chelating hydrogel and have shown that it can house a protein biosynthesis reaction. This reaction produces a so-called capture protein bound to a Ni2+ tether. The researchers then embed a fluorescent carbon nanotube into the system and watch how its photoluminescence changes when another protein then selectively binds to the capture protein. By measuring this change, they are able to perform label-free sensing of any type of protein.

“Our detection method is completely unique among those for any nanowire or nanotube sensor to date and quite incredibly allows detection even down to the single protein level,” Strano told nanotechweb.org. “The mechanism is fairly robust and we have already demonstrated its success by measuring over 1165 protein–protein interactions!”

The SWNT/protein microarray has many advantages when it comes to detecting protein–protein interactions compared to traditional techniques such as enzyme-linked immunosorbent assays (ELISA) and surface plasmon resonance. The new technology uses near-infrared florescence emitted from the SWNTs to work and so eliminates the need for any additional fluorescence labels on target proteins. It also avoids the use of secondary antibodies to recognize binding events – something that makes this method much simpler and more cost-effective.

Understanding how single proteins interact
“Our SWNT/protein microarray enables us to do high-throughput screening of many protein interactions in a short time,” added team member Jong-Ho Kim. “This capability is also very useful for understanding how single proteins interact with other proteins.”

The array can detect protein interactions using a single-molecule detection approach, something that has never been demonstrated before, he said. “Such a technique means much higher protein detection sensitivity.”

According to the team, the microarray will be very useful for investigating the weak interaction between proteins. And, since the technique is highly sensitive, smaller sample sizes will be needed. Large sample volumes have been a major limiting factor thus far when analysing protein–protein interactions in this way.

On the applications side, the array could screen for new biomarkers in blood, so allowing for early detection of certain diseases like cancer. Indeed, the researchers have already started to look at the exact role of glycosylation of proteins using their new technology and ultimately hope to discover the fundamental mechanism that leads to the onset and progression of some cancers.

The work was reported in Nano Letters.