Chip-based provides control over individual molecules

The researchers at UC Santa Cruz have used the device to control the delivery of individual biomolecules - including ribosomes, DNA, and proteins - into a fluid-filled channel on the chip. The device can also be used to sort different types of molecules, providing selective analysis of target molecules from a mixture. The team’s findings are published in Nature Communications.

The capabilities of the programmable nanopore-optofluidic device point the way toward a novel research tool for high-throughput single-molecule analysis on a chip, said Holger Schmidt, the Kapany Professor of Optoelectronics at UC Santa Cruz and corresponding author of the paper.

"We can bring a single molecule into a fluidic channel where it can then be analysed using integrated optical waveguides or other techniques," Schmidt said in a statement. "The idea is to introduce a particle or molecule, hold it in the channel for analysis, then discard the particle, and easily and rapidly repeat the process to develop robust statistics of many single-molecule experiments."

Nanopore technology has been successfully used in DNA sequencing applications, and Schmidt and other researchers have been exploring new ways to exploit the information in the signals produced as molecules or particles translocate through a nanopore.

With the feedback control system - a microcontroller and solid-state relay - in the new device, real-time analysis of the current turns the nanopore into a so-called "smart gate" that can be programmed to deliver molecules into the channel. The gate can be closed as soon as a single molecule (or any number set by the user) has passed through, then opened again after a set time.

"The use of nanopores as 'smart gates' is a key step toward a single-molecule analysis system that is user-friendly and can work at high throughput," Schmidt said. "It allows user-programmable control over the number of molecules that are being delivered to a fluidic channel for further analysis or processing, selective gating of different types of single molecules, and the ability to deliver single molecules into a chip at record rates of many hundreds per minute."

Using bacterial (70S) ribosomes, the researchers are said to have demonstrated controlled delivery of over 500 ribosomes per minute. They also used a mixture of DNA and ribosomes to show the device's capacity to selectively activate the gating function for a target molecule (in this case, DNA). In use, this could be used in fluorescence experiments on a controlled number of target molecules, while unlabelled particles are ignored and discarded.

Selective gating could also be used for purification or sorting of different particles downstream from the nanopore, based on the signals as the particles pass through the nanopore, Schmidt said. The programmable system allows flexibility for a wide range of potential applications, he added.

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