Ioannis Kymissis

Nitroaromatic explosive vapor detection using a digitally printed sensor array (Conference Presentation)

We report on a fluorescent optoelectronic nose for the trace detection of nitroaromatic explosive vapors. The sensor arrays, fabricated by aerosol-jet printing, consist of six different polymers as transducers. We demonstrate the nose’s ability to discriminate between several nitroaromatics including nitrobenzene, 1,3-dinitrobenzene and 2,4-dinitrotoluene at three different concentrations using linear discriminant analysis (LDA). We assess the within-batch reproducibility of the printing process and we report that the sensor polymers show efficient fluorescence quenching capabilities with detection limits of a few parts-per-billion in air. Our approach enables the realization of highly integrated optical sensor arrays in optoelectronic noses for the sensitive and selective detection of nitroaromatic explosive trace vapors using a potentially low-cost digital printing technique suitable for high-volume fabrication. An important challenge is temperature-dependence which is often neglected even though organic emitters are strongly affected by temperature. For some materials, even small changes of a few Kelvin can lead to large changes in the emission intensity making a temperature-control for sensing applications inevitable. Therefore, the temperature-dependence of these sensors is investigated via a heated transparent thin film on the back of such sensors allowing the active layer to be temperature controlled. All of these led to the development of a portable system.

Characterization of the waterstable CNT based field-effect transistors for sensing applications (Conference Presentation)

There is a big need for electronic biosensors that can be operated in water for biomedical applications and environmental monitoring. Devices based on organic materials are currently attracting great attention for applications where low-cost, large area coverage and flexibility are required. Water is an aggressive medium and due to its chemical activity the operational voltage window for stable sensor operation is limited. Related to that, in the past, degradation under both ambient and aqueous environments have limited their application in bio sensors for portable, label-free detection in the field of healthcare and environmental monitoring. Quite recently, our group has demonstrated stable FET device operation based on organic active materials directly exposed to water and more interestingly, even sea water.[1-3] By pattering an array of gold nano-particles on top of the organic semiconductor but close to the transistor channel, the developed structure was able to sense low concentrations of mercury ions in sea water.[2,3] Here we would like to present the second generation of this highly sensitive bio-sensor platform based on organic field-effect transistors developed in our group able to operate at even lower voltages which is a necessary condition for stable device operation in water based environments.[4,5] Functionalization is a powerful tool to attach receptor units close to the transistor channel which are able to detect its corresponding analytes. This methodology allows preparing a scalable, easy producible and high performing sensor platform suitable for portable biosensing in aqueous media. [1] M. E. Roberts et. al., PNAS, 105, 12134 –12139, 2008. [2] M. L. Hammock et al., ACSNano, 6, 3100-3108, 2012. [3] O. Knopfmacher et. al. Nature Communications, 5, 2954, 2014. [4] C. Wang, et al. Scientific Reports, 5, 17849, 2015. [5] D. Kong, et al. Advanced Functional Materials, 26, 4680–4686, 2016.

Graphene electronic tattoo sensors (Conference Presentation)

Tattoo-like epidermal sensors are an emerging class of truly wearable electronics owing to their thinness and softness. While most of them are based on thin metal films, silicon membrane, or nanoparticle-based printable inks, we report the first demonstration of sub-micron thick, multimodal electronic tattoo sensors that are made of graphene. The graphene electronic tattoo (GET) is designed with filamentary serpentines and fabricated by a cost- and time-effective “wet transfer, dry patterning” method. It has a total thickness of 463 ± 30 nm, an optical transparency of ~85%, and a stretchability of more than 40%. GET can be directly laminated on human skin just like a temporary tattoo and can fully conform to the microscopic morphology of the surface of skin via just van der Waals forces. The open mesh structure of GET makes it breathable and its stiffness negligible. Bare GET is able to stay attached to skin, for several hours, without fracture or delamination. With liquid bandage coverage, GET may stay functional on skin up to several days. As a dry electrode, GET-skin interface impedance is on par with medically used silver/silver-chloride (Ag/AgCl) gel electrodes, while offering superior comfort, mobility and reliability. GET has been successfully applied to measure electrocardiogram (ECG), electromyogram (EMG), electroencephalogram (EEG), skin temperature, and skin hydration. Graphene represents a new facile route for ultra-conformable multifunctional electronic tattoos, and paves the path for the introduction of other two dimensional materials for future advanced tattoo systems.

Characterization of novel organic short wavelength infrared photosensors (Conference Presentation)

Short wavelength infrared (SWIR) sensors are important to applications in environmental monitoring, medical diagnosis and optical communications, but there are only a few organic semiconductors that show optoelectronic response in the SWIR region. Recently we demonstrated a family of novel donor-acceptor polymers with narrow bandgap responsive in the SWIR region, and the bulk heterojunction photodiodes based on these polymers show detectivity up to 1E11 Jones at a wavelength of 1.37 micron, with absorption edge extending out to 1.7 micron. A SWIR photodiode was incorporated into the etalon-array reconstructive spectroscopy system to demonstrate its imaging capabilities. As the initial performance is very promising, we proceed to investigate the stability of the encapsulated devices and to infer the degradation mechanisms. The performance of photodiodes were monitored by IV measurement, external quantum efficiency (EQE) and electrochemical impedance spectroscopy. The IV measurement and electrochemical impedance spectroscopy were conducted both in the dark and under illumination, to track over several weeks the change in charge generation and recombination processes under the short circuit and open circuit conditions. The characteristics from band-to-band absorption and from absorption in charge-transfer states were compared to quantify the lifetime and recombination losses of photogenerated carriers in these devices.

Sulphonated mesoporous silica as proton exchanging layer in solid state organic transistors for bio-sensing (Conference Presentation)

Electronic devices that can interface with the human body are highly desirable for sensing of physiological parameters and for smart prosthetics. This is particularly challenging since the mechanism of signalling in most electronic materials is different from the mechanism of signalling in the human body. Most electronic devices in our daily life send signals through flow of electrons while body signals are carried via the exchange of ions and protons. There is a considerable interest in developing bioinspired proton conducting materials and solid-state devices for bio-electronic applications [1, 2, 3]. In this work, we will present a new class of proton conducting gate materials, sulphonated mesoporous silica nanoparticles (SMSN) [4], that are able to sense conduction of protons in all solid state, low voltage operating organic thin film transistors (OTFTs). Ordered mesoporous silica nanoparticles with various functional groups have been investigated for applications in catalysis, gas adsorption and drug delivery. SMSN have also been successfully investigated for applications in fuel cell membranes [4]. In this presentation, we will describe the OTFT operation of solution processable SO3H-MCM-41 films that have highly ordered pore structures. The OTFTs fabricated maintained low voltage transistor output characteristics for operating source-drain voltages 0 > Vds > -1.25 V. We will also present results that demonstrate the application of our low voltage operating OTFTs in sensing proton exchange, where a drop of H2O2 dropped on top of the SO3H-MCM-41 gate electrode captures strong modulation in the current flow. H2O2 breaks down to oxygen, protons and electrons when a voltage above a threshold voltage is applied between source and drain. The Ids increases immediately by ~ 3-fold and continues to increase to a maximum value of ~ 5-fold, demonstrating that these OTFTs are highly applicable in advanced biomedical sensing applications. 1. L. Herlogsson, X. Crispin, N.D. Robinson, M. Sandberg, O.-J. Hagel, G. Gustafson, M. Berggren, Adv. Mater. 19, 97-101 (2007). 2. C.J. Wan, L.Q. Zhu, Y. H. Liu, P. Feng, Z.P. Liu, H.L. Cao, P. Xiao, Y. Shi, Q. Wan, Adv. Mater. 28, 3557-3563 (2016). 3. C. Zhong, Y. Deng, A.F. Roudsari, A. Kapetanovic, M.P. Anantram, M. Rolandi, Nature Comm. 2, 476 (2011). 4. R. Marschall, I. Bannat, A. Feldhoff, L. Wang, G.Q. Lu, M. Wark, Small 5 (7), 854-859 (2009).

Low voltage organic charge modulated FETs: A flexible approach for the fabrication of high sensitive biosensors (Conference Presentation)

Charge Modulated OTFTs represent a versatile tool for the realization of a wide range of sensing applications. The architecture is based on a floating gate organic transistor whose sensitivity to a specific target is obtained by properly functionalizing a part of the floating gate with a sensing layer that can be chosen according to the specific external stimulus to be sensed. In this work we will show that such devices can be routinely fabricated on highly flexible, ultra-conformable thin films and that they can be employed, with no need of any chemical modification of the sensing area, for monitoring pH variations featuring a super-nernstian sensitivity. Interestingly, we will also show that the proposed approach has been applied for monitoring cell metabolic activity, demonstrated with a preliminary validation. In addition this device can be used for monitoring electrical activity of excitable cells, thus giving rise to a new family of highly sensitive, reference-less, and low-cost devices for a wide range of bio-sensing applications. Finally, we will also demonstrate that using a different sensing layer it is possible to employ the same device architecture for the realization of matrices of multimodal tactile transducers capable to detect at the same time temperature and pressure stimuli, and that being fabricated on sub-micrometer thin film can be conformably transferred on whatever kind of surface allowing the reproduction of the sense of touch.