According to IDTechEx’s, biosensors is the biggest market segment of printed sensors simply because of the multi-billion dollar market that represent blood glucose sensors shipping as billions of disposable test strips used every year for diabetes monitoring. But gas sensors are expected to become the second largest segment according to the market research firm. And there is much more to blood glucose monitoring or environmental sensing, as the speakers revealed in their presentations.
Jean-Luc Wojkiewicz from IMT-Université de Lille sees environmental sensing and pollution monitoring as a huge market for printed biosensors, his lab being very active in the development of hybrid nano-compounds and biopolymers for electronic gas sensors.
Wojkiewicz cited an OMS estimate that about 7 million death per year can be attributed to air contamination, with ammonia (NH3) being one of the most underreported contaminants coming mostly from agriculture (for 93.7%) and industrial processes. But many other contaminants including H2S,
amines, volatile organic compounds (VOCs), O3, CO, CO2 to name a few also need to be monitored outdoor and indoor in real time, calling for compact and cheap sensors. This is where printed biosensors, which can be formulated with conductive polymers to detect many gases, can give a very fine monitoring mesh (in the meter pitch compared to kilometre-wide satellite observations).
“With one litre of solution, you can fabricate several millions of sensors, the cost of the active surface of the sensor becomes negligible”, Wojkiewicz highlighted, sharing the details of a typical resistance-based sensor layout with comb electrodes and a tiny drop of tuned polymer whose conductivity is impacted by the adsorption of analytes.
In an experimental setup, the researcher and his team were able to characterize 400 sensors (with different compositions) held in a tiny controlled cylinder, in less than a minute. The researchers used doped polyaniline (PANI) and PANI/TiO2 hybrid nanocomposites to detect ammonia levels between 0.2 and 30ppm, with a quantification limit at about 10ppb. Further investigation showed that the response of the hybrids (blending TiO2 nanoparticles with the conductive doped polyaniline are 10 or 35 times superior than the pure form of doped PANI.
This was due to the formation of p-n heterojunctions at the PANI TiO2 nanoparticle interfaces, Wojkiewicz explained. The sensors boast fast response and recovery times (fully reversible when fresh air is restored). For the low-cost and non-toxicity aspect, the researcher turned to blending PANI with Chitosan, an abundant and biodegradable polymer found in crustacean shells. Sensors built with the new blend offered a good response to ammonia too.
Since the polyaniline can be doped to respond to different gas, sensors can be fabricated to detect known disease biomarkers in breath, providing non-invasive screening tools to diagnose a disease at an early stage. Wojkiewicz cited renal diseases as being characterized by an increase of ammonia concentration in breath, but the single-digit ppm variations that differentiate a healthy subject from an unhealthy one require the design of multiple sensing layers and further characterization, with new signal processing algorithms. Wojkiewicz expects to see his results published in the Sensors and Actuators B: Chemical journal. In future investigation, the researcher hopes to be able to apply his biosensors to the early detection of lung cancer, breast cancer and even neurological diseases.
“We are undergoing a patenting process, but there is still a lot of work to do before this can be commercialized” admitted Wojkiewicz. Again the researcher emphasized that such sensors could be designed to detect hundreds of different pollutants, some of which may be carcinogenic. In a research collaboration with car maker Peugeot, the Wojkiewicz and his team were tasked to monitor VOCs in new cars. “Generally when it smells of new, it is bad news for your health” he concluded jokingly.
Other promising printed biosensors include Electrolyte-Gated Organic Field-Effect Transistors (EGOFETs) and Organic Electro-Chemical Transistors (OECT), as presented by Benoît Piro and Vincent Noël, both researchers at the Université Paris Diderot ITODYS lab. Although their operating mechanisms are different, both organic transistors present a similar layout that is very simple to print out, consisting of three PEDOT:PSS electrodes (source, drain and gate made) and two conductive layers including an electrolyte and an organic semiconducting polymer.
For the OECT, as an enzyme-based analyte indirectly transfers an electron to the gate, the organic semiconductor is reduced which decreases its conductivity and lowers the detected drain-source current. For the EGOFET, polarizing the gate generates an accumulation of ions at the gate/electrolyte and semiconductor/electrolyte interfaces, creating a charge accumulation in the organic semiconductor. For a p-type semiconductor, this leads to a conductive channel when VGS is negative. Both implementations operate under 1V to detect target analytes.
In the second part of their joint presentation, Vincent Noël focused on the emerging markets for printed biosensors, highlighting two large but very differently regulated fields of application, health and cosmetics.
For health applications, the trends are point-of-care diagnostics and personalized therapy enabled through portable and disposable sensors to be used by the patient directly, doing away with large and costly lab equipment. Now, a bigger trend that Noel sees is the convergence of point-of-care diagnostics sensors with the identification of biomarkers for personalized care. Ideally, the pharmaceutical industry would like to associate companion auto-diagnostics biosensors with every pharmaceutical, enabling the patient to ensure that the treatment is relevant to his/her condition, out-of-the-box. This may be happening within the next 10 years, anticipates the researcher.
“Printed bioelectronics is right at the convergence point of that hypertrend” Noël said, notably thanks to EGOFETs. One drawback though, is that the health market is very competitive and heavily regulated, making it difficult and costly to get any product certification.
On the other hand, many active molecules and administration modes could easily be transferred to cosmetics for so-called skin point-of-care, under much less scrutiny. Cosmetics is largely marketing driven and Luxury brands in particular are very good at adding value out of virtually nothing, he noted jokingly.
Some luxury brands already offer basic tools, sometimes as smartphone add-ons or standalone devices that measure basic skin parameters such as hydration, UV exposure, fat content or roughness. Here printed biosensors could be delivered with standalone promotional samples or integrated in the packaging of cosmetics for skin auto-diagnostics.
“Next could come personalized skin-care based on the analysis of your microbiome, the blend of living bacteria on your skin that is truly unique to you” envisioned Noel.
“The good thing with cosmetics is that this is a rather novel market for biosensors, highly value-added and still to be defined” concluded the researcher, noting that France with its Cosmetic Valley is well placed to become a leader in this field.
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