Biosensor Listens to Cellular Monologues in Real Time

Cells are the ultimate ensemble cast members, but they can also deliver soliloquies – if the cells ever get the chance to have the stage to themselves. To give individual cells their turn in the spotlight, an international team of scientists has built a sort of microfluidic theatre, complete with a gold-coated glass stage and a nanoplasmonic lighting system.

With the right stage management, individual cells can be induced to reveal their innermost motivations, the signals they would transmit to other cells while playing their parts – heroic or otherwise – in dramas as varied as infection, immune disorders, inflammation, sepsis, and cancer. By listening intently to cells and designing the appropriate therapeutic interventions, scientists may be able to direct cellular actors toward happier endings.

That’s the hope that has been expressed by scientists based at RMIT University in Australia, École polytechnique fédérale de Lausanne (EPFL), and Ludwig Institute for Cancer Research in Lausanne. These scientists reported that they have developed an optofluidic device that contains a chamber that is around one one-thousandth the size of a raindrop.

The chamber accepts a single cell, which may then be observed in real time while its environment remains undisturbed by molecular labels, which are common in other venues such as fluorescence- and colorimetric-based systems, and which tend to interfere with cell integrity and compromise temporal resolution. Without these distractions, a cell’s chemical secretions come through more clearly and continuously.

Details appeared in the journal small, in an article entitled “Label-Free Optofluidic Nanobiosensor Enables Real-Time Analysis of Single-Cell Cytokine Secretion.” This article describes what happened after the cellular casting call went out to single lymphoma cells, which were evaluated for cytokine secretion, which the scientists noted, must be monitored if the heterogeneity of cellular functionalities is to be understood, and if novel therapies for multiple diseases are to be developed.

“An innovative label-free optofluidic nanoplasmonic biosensor is introduced for single-cell analysis in real time,” the article’s authors wrote. “The nanobiosensor incorporates a novel design of a multifunctional microfluidic system with small volume microchamber and regulation channels for reliable monitoring of cytokine secretion from individual cells for hours.”

The biosensor was shown to work for 12 hours straight, but it could, the authors argued, function much longer, offering researchers a powerful and innovative selection tool.

“Different interleukin-2 secretion profiles are detected and distinguished from single lymphoma cells,” the article continued. “The sensor configuration combined with optical spectroscopic imaging further allows us to determine the spatial single-cell secretion fingerprints in real time.”

The nanophotonic biosensor developed by the researchers is a glass slide coated with a thin gold film, perforated with billions of nanopores arranged in a precise pattern. A small chamber, whose walls are made of porous membranes, is placed above the slide. The chamber receives a steady flow of water and nutrients through tiny microfluidic channels. Temperature and humidity are carefully regulated. The device contains valves that let scientists insert a cell into the chamber, in which ligands or antibodies are positioned to recognize and capture specific molecules secreted by the cell.

A broadband light source shines on the chamber. Thanks to an optical phenomenon called plasmons, the nanopores let only one light-wave frequency or color through. When a cell secretes a molecule, it attaches to the antibodies, thereby changing the frequency transmitted by the nanopores. This is how minutes of specific molecules can be identified.

Developed by the Australian-Swiss research team, the technology offers researchers unprecedented insights into how individual cells behave – something that scientists are discovering is far more complex than previously thought.

“We know a lot about how groups of cells communicate to fight disease or respond to infections but we still have a lot to learn about individual cells,” said Arnan Mitchell, Ph.D., director of RMIT’s MicroNano Research Facility. “Studies have recently shown that you can take two cells of the same type and give them the same treatment, but they will respond very differently.

“We don’t know enough about the underlying mechanisms to understand why this happens and we don’t have the right technologies to help scientists figure it out. Our solution to this challenge is a complete package – an integrated optofluidic biosensor that can isolate single cells and monitor the chemicals they produce in real-time over at least 12 hours.

“It’s a powerful new tool that will give us a deeper fundamental understanding of cell communication and behavior. These insights will open the way to develop radically new methods for diagnosing and treating disease.”

Human cells communicate that something is wrong in complex and dynamic ways, producing various chemical substances that signal to other cells what they need to do. When an infection is detected, for example, white blood cells will spring into action and release special proteins to fight and eliminate the intruders.

Understanding how individual cells interact and communicate is critical to developing new therapies for serious diseases, to better harness the power of the body’s own immune system or precisely target defective cells.

The new biosensor has many potential applications. For example, it could be used to identify the most aggressive cancer cells in a tumor and decide exactly which treatment to administer to the patient.