Organic electrochemical transistor device assesses presence of antibodies

STEPHEN RIFFLE: Welcome to MRS Bulletin’s Materials News Podcast, providing breakthrough news & interviews with researchers on the hot topics in materials research. My name is Stephen Riffle. Suppose for a minute that you’re developing a new vaccine that’s meant to give patients long-term immunity against a virus. One of the critical pieces of evidence that you’re going to need in order to prove that your vaccine works is to show that vaccinated patients start to produce what are known as neutralizing antibodies. As the name suggests, these are antibodies that help to neutralize pathogens. It’s easy to say, but proving that your vaccine does this is a little more difficult. You’re going to need an assay that allows you to analyze samples for the presence of neutralizing antibodies in the serum of patients. 

ALESSANDRA SCAGLIARINI: I know how long it takes, how difficult it is to interpret the results because it’s mainly subjective interpretation through a microscope. 

STEPHEN RIFFLE: That was Alessandra Scagliarini, a professor of infectious disease at the University of Bologna. Scagliarini has been working with her colleague, Beatrice Fraboni, to improve the safety, sensitivity and robustness of neutralizing antibody detection. Current tests work by collecting serum from patients or other test subjects. The serum will likely contain a mixture of antibodies, some of which may be neutralizing to the pathogen you’re studying. To test this, the serum is first going to be mixed with a potentially dangerous pathogen. That cocktail is then added on top of cultured cells. If there are neutralizing antibodies present, the pathogen will have a harder time infecting the cells and no changes will be observed. But if there are no neutralizing antibodies, the cells may become infected and change in either big or sometimes subtle ways. The assay then hinges on a researcher’s ability to recognize when cells have been infected. This, it turns out, can be very subjective and that’s not ideal when you’re trying to prove that something as important as a vaccine works. 

ALESSANDRA SCAGLIARINI: When you go to the microscope, you need to really be skilled in detecting a cytopathic effect. Sometimes, you don’t see anything. So, this is why this kind of tool that we are developing is so important for us—because it’s not my opinion. So, it’s not my opinion on what I was seeing with my eyes, but instead it’s just a machine that tells me that I was on the right way. 

STEPHEN RIFFLE: Scagliarini and Fraboni have developed a device that enables far more robust detection of the cellular changes that occurred during infection. The device is a type of organic electrochemical transistor, which means it is a transistor whose current is controlled by the injection of ions from an electrolyte solution. To help you imagine it, picture three tiny electrical terminals. Two of the terminals are physically connected by a semiconducting polymer, and across that physical bridge an electrical current will flow. We’ll call this physical bridge the “source–drain channel.” The third terminal is separated from the rest by an electrolyte fluid. When an electrical potential is applied to the third terminal, it affects the flow of ions in the fluid, which then interacts with and modulates the current flowing in the source–drain channel. Now, if something were to block the flow of ions to the source–drain channel, then the current would be considerably reduced. That's the basic premise behind Scagliarini and Fraboni’s device. Importantly, they built the device using a material known as poly(3,4-ethylenedioxythiophene) polystyrene sulfonate. If it sounds like a mouthful, it’s because it kind of is. So, for shorthand it’s often referred to as PEDOT:PSS or simply PDOT. Fraboni, who’s a professor of physics at the Department of Physics and Astronomy at the University of Bologna, describes the material a little more affectionately: 

BEATRICE FRABONI: So it’s a perfect material to be at the interface between biology and physics devices, and electronics. The key point is the material—this PEDOT:PSS—which is a good semiconductor. So, the material has, not only the capability of transferring the ion signals into electronic signals, but also being a transistor to amplify it. So, we have an intrinsic amplification of this very small signal, which is the ion-to-electron converted one. But, where does the signal come from? So the other good point is that with PDOT, you can grow cells on top of it because it’s nice—cells like it. So we can do cell cultures and grow, through tissue engineering procedures, a nice solid carpet of tissue on top of the transistor. 

STEPHEN RIFFLE: According to Fraboni, cells can be grown on top of the transistor where they prevent ions in the electrolyte solution from reaching the transistor. 

BEATRICE FRABONI: So, if you have your nice carpet of cells, and you have your serum with the antibodies that are able to grasp the virus, then the cells stay fine. There are no problems and you will still get the electrical signal that you got before you put anything on top of the cells. So. fine. If, on the other hand, there are no antibodies and the virus attacks the cells, then the carpet gets ruined. So, you start getting, not only macro cracks, but also minor disruptions in the tight junctions of the cells. So, it’s really minor effects that can be produced in the carpet. And now let’s say it breaks a bit—what happens to the electrical signal? Ions from the serum and from the top solution can go down, reach the polymer, are converted to electrons, and the current in the polymer will change. So the high sensitivity of this device is that it’s able to detect any small variation in transfer in contact between the top liquid and the bottom PDOT, which means that the carpet is ruined. 

STEPHEN RIFFLE: This is a key point: Unlike the limitations of human observation, this device is capable of detecting microscopic changes that cause a break in the carpet of cells on top of the transistor. This sensitivity is enabled by its use of a transistor, which works to amplify small signals up to detectable ranges. Scagliarini emphasized the importance of this point: 

ALESSANDRA SCAGLIARINI: But the amazing thing about this tool is that it is able to detect many different ways of cytopathic effects. So, not only just the cell lysis, but also others. And this is very important.

STEPHEN RIFFLE: This device gives researchers a sensitive, more robust way to assess cells for signs of an infection. This kind of data is an indirect way to then assess whether or not patient samples have neutralizing antibodies. And there’s no reason that this should be limited to just patients. Researchers often are interested in tracing viral outbreaks to their origins, which may mean tracing it back to animal reservoirs to identify which species the virus had been circulating in before hopping into humans. Researchers will need to test the serum of various animals for neutralizing antibodies. Currently, in order to do this, you need species-specific antibodies as well as other technically challenging materials to help you identify which species it is. However, this organic electrochemical transistor device is agnostic to the species you’re testing. It’s simply assessing whether a monolayer of cells is broken in response to an infectious agent. In short, they’ve created a device that allows for reliable, safer, and faster viral neutralization assays and potentially more in the future. Next steps for Scagliarini and Fraboni’s team is to look into downscaling the device to allow it to be used for smaller well formats, larger-scale applications, as well as use beyond viral neutralization assays. This work was published in Communications Materials. My name is Stephen Riffle from the Materials Research Society. For more news, log onto the MRS Bulletin website at mrsbulletin.org and follow us on twitter, @MRSBulletin. Don’t miss the next episode of MRS Bulletin Materials News – subscribe now. Thank you for listening.