Professional Education


  • Diplom, Universitat Karlsruhe (2012)
  • Master of Science, Imperial College of Science, Technology & Medicine (2014)
  • Doctor of Philosophy, Imperial College of Science, Technology & Medicine (2018)

Current Research and Scholarly Interests


I am interested in the development of recyclable batteries based on solution-processable organic polymers. The materials used for the battery will be solution processable which is a key factor for recycling electrodes and electrolytes.

All Publications


  • Direct metabolite detection with an n-type accumulation mode organic electrochemical transistor SCIENCE ADVANCES Pappa, A., Ohayon, D., Giovannitti, A., Maria, L., Savva, A., Uguz, I., Rivnay, J., McCulloch, L., Owens, R. M., Inal, S. 2018; 4 (6): eaat0911

    Abstract

    The inherent specificity and electrochemical reversibility of enzymes poise them as the biorecognition element of choice for a wide range of metabolites. To use enzymes efficiently in biosensors, the redox centers of the protein should have good electrical communication with the transducing electrode, which requires either the use of mediators or tedious biofunctionalization approaches. We report an all-polymer micrometer-scale transistor platform for the detection of lactate, a significant metabolite in cellular metabolic pathways associated with critical health care conditions. The device embodies a new concept in metabolite sensing where we take advantage of the ion-to-electron transducing qualities of an electron-transporting (n-type) organic semiconductor and the inherent amplification properties of an ion-to-electron converting device, the organic electrochemical transistor. The n-type polymer incorporates hydrophilic side chains to enhance ion transport/injection, as well as to facilitate enzyme conjugation. The material is capable of accepting electrons of the enzymatic reaction and acts as a series of redox centers capable of switching between the neutral and reduced state. The result is a fast, selective, and sensitive metabolite sensor. The advantage of this device compared to traditional amperometric sensors is the amplification of the input signal endowed by the electrochemical transistor circuit and the design simplicity obviating the need for a reference electrode. The combination of redox enzymes and electron-transporting polymers will open up an avenue not only for the field of biosensors but also for the development of enzyme-based electrocatalytic energy generation/storage devices.

    View details for DOI 10.1126/sciadv.aat0911

    View details for Web of Science ID 000443175500063

    View details for PubMedID 29942860

    View details for PubMedCentralID PMC6014717

  • The Role of the Side Chain on the Performance of N-type Conjugated Polymers in Aqueous Electrolytes CHEMISTRY OF MATERIALS Giovannitti, A., Maria, I. P., Hanifi, D., Donahue, M. J., Bryant, D., Barth, K. J., Makdah, B. E., Savva, A., Moia, D., Zetek, M., Barnes, P. F., Reid, O. G., Inal, S., Rumbles, G., Malliaras, G. G., Nelson, J., Rivnay, J., McCulloch, I. 2018; 39 (9): 2945–53

    Abstract

    We report a design strategy that allows the preparation of solution processable n-type materials from low boiling point solvents for organic electrochemical transistors (OECTs). The polymer backbone is based on NDI-T2 copolymers where a branched alkyl side chain is gradually exchanged for a linear ethylene glycol-based side chain. A series of random copolymers was prepared with glycol side chain percentages of 0, 10, 25, 50, 75, 90, and 100 with respect to the alkyl side chains. These were characterized to study the influence of the polar side chains on interaction with aqueous electrolytes, their electrochemical redox reactions, and performance in OECTs when operated in aqueous electrolytes. We observed that glycol side chain percentages of >50% are required to achieve volumetric charging, while lower glycol chain percentages show a mixed operation with high required voltages to allow for bulk charging of the organic semiconductor. A strong dependence of the electron mobility on the fraction of glycol chains was found for copolymers based on NDI-T2, with a significant drop as alkyl side chains are replaced by glycol side chains.

    View details for PubMedID 29780208

    View details for PubMedCentralID PMC5953566

  • Redox-Stability of Alkoxy-BDT Copolymers and their Use for Organic Bioelectronic Devices ADVANCED FUNCTIONAL MATERIALS Giovannitti, A., Thorley, K. J., Nielsen, C. B., Li, J., Donahue, M. J., Malliaras, G. G., Rivnay, J., McCulloch, I. 2018; 28 (17)
  • Controlling the mode of operation of organic transistors through side-chain engineering. Proceedings of the National Academy of Sciences of the United States of America Giovannitti, A., Sbircea, D., Inal, S., Nielsen, C. B., Bandiello, E., Hanifi, D. A., Sessolo, M., Malliaras, G. G., McCulloch, I., Rivnay, J. 2016; 113 (43): 12017-12022

    Abstract

    Electrolyte-gated organic transistors offer low bias operation facilitated by direct contact of the transistor channel with an electrolyte. Their operation mode is generally defined by the dimensionality of charge transport, where a field-effect transistor allows for electrostatic charge accumulation at the electrolyte/semiconductor interface, whereas an organic electrochemical transistor (OECT) facilitates penetration of ions into the bulk of the channel, considered a slow process, leading to volumetric doping and electronic transport. Conducting polymer OECTs allow for fast switching and high currents through incorporation of excess, hygroscopic ionic phases, but operate in depletion mode. Here, we show that the use of glycolated side chains on a thiophene backbone can result in accumulation mode OECTs with high currents, transconductance, and sharp subthreshold switching, while maintaining fast switching speeds. Compared with alkylated analogs of the same backbone, the triethylene glycol side chains shift the mode of operation of aqueous electrolyte-gated transistors from interfacial to bulk doping/transport and show complete and reversible electrochromism and high volumetric capacitance at low operating biases. We propose that the glycol side chains facilitate hydration and ion penetration, without compromising electronic mobility, and suggest that this synthetic approach can be used to guide the design of organic mixed conductors.

    View details for PubMedID 27790983

  • N-type organic electrochemical transistors with stability in water NATURE COMMUNICATIONS Giovannitti, A., Nielsen, C. B., Sbircea, D., Inal, S., Donahue, M., Niazi, M. R., Hanifi, D. A., Amassian, A., Malliaras, G. G., Rivnay, J., McCulloch, I. 2016; 7

    Abstract

    Organic electrochemical transistors (OECTs) are receiving significant attention due to their ability to efficiently transduce biological signals. A major limitation of this technology is that only p-type materials have been reported, which precludes the development of complementary circuits, and limits sensor technologies. Here, we report the first ever n-type OECT, with relatively balanced ambipolar charge transport characteristics based on a polymer that supports both hole and electron transport along its backbone when doped through an aqueous electrolyte and in the presence of oxygen. This new semiconducting polymer is designed specifically to facilitate ion transport and promote electrochemical doping. Stability measurements in water show no degradation when tested for 2 h under continuous cycling. This demonstration opens the possibility to develop complementary circuits based on OECTs and to improve the sophistication of bioelectronic devices.

    View details for DOI 10.1038/ncomms13066

    View details for Web of Science ID 000385587100001

    View details for PubMedID 27713414

    View details for PubMedCentralID PMC5059848

  • Molecular Design of Semiconducting Polymers for High-Performance Organic Electrochemical Transistors. Journal of the American Chemical Society Nielsen, C. B., Giovannitti, A., Sbircea, D., Bandiello, E., Niazi, M. R., Hanifi, D. A., Sessolo, M., Amassian, A., Malliaras, G. G., Rivnay, J., McCulloch, I. 2016; 138 (32): 10252-10259

    Abstract

    The organic electrochemical transistor (OECT), capable of transducing small ionic fluxes into electronic signals in an aqueous environment, is an ideal device to utilize in bioelectronic applications. Currently, most OECTs are fabricated with commercially available conducting poly(3,4-ethylenedioxythiophene) (PEDOT)-based suspensions and are therefore operated in depletion mode. Here, we present a series of semiconducting polymers designed to elucidate important structure-property guidelines required for accumulation mode OECT operation. We discuss key aspects relating to OECT performance such as ion and hole transport, electrochromic properties, operational voltage, and stability. The demonstration of our molecular design strategy is the fabrication of accumulation mode OECTs that clearly outperform state-of-the-art PEDOT-based devices, and show stability under aqueous operation without the need for formulation additives and cross-linkers.

    View details for DOI 10.1021/jacs.6b05280

    View details for PubMedID 27444189

    View details for PubMedCentralID PMC4991841

  • Nanoscale Ion-Doped Polymer Transistors. Nano letters Thiburce, Q., Giovannitti, A., McCulloch, I., Campbell, A. J. 2019

    Abstract

    Organic transistors with submicron dimensions have been shown to deviate from the expected behavior due to a variety of so-called "short-channel" effects, resulting in nonlinear output characteristics and a lack of current saturation, considerably limiting their use. Using an electrochemically doped polymer in which ions are dynamically injected and removed from the bulk of the semiconductor, we show that devices with nanoscale channel lengths down to 50 nm exhibit output curves with well-defined linear and saturation regimes. Additionally, they show very large on-currents on par with their microscale counterparts, large on-to-off ratios of 108, and record-high width-normalized transconductances above 10 S m-1. We believe this work paves the way for the fabrication of high-gain, high-current polymer integrated circuits such as sensor arrays operating at voltages below |1 V| and prepared using simple solution-processing methods.

    View details for PubMedID 30720280

  • Influence of Water on the Performance of Organic Electrochemical Transistors CHEMISTRY OF MATERIALS Savva, A., Cendra, C., Giugni, A., Torre, B., Surgailis, J., Ohayon, D., Giovannitti, A., McCulloch, I., Di Fabrizio, E., Salleo, A., Rivnay, J., Inal, S. 2019; 31 (3): 927–37
  • Role of the Anion on the Transport and Structure of Organic Mixed Conductors ADVANCED FUNCTIONAL MATERIALS Cendra, C., Giovannitti, A., Savva, A., Venkatraman, V., McCulloch, I., Salleo, A., Inal, S., Rivnay, J. 2019; 29 (5)
  • Double doping of conjugated polymers with monomer molecular dopants NATURE MATERIALS Kiefer, D., Kroon, R., Hofmann, A. I., Sun, H., Liu, X., Giovannitti, A., Stegerer, D., Cano, A., Hynynen, J., Yu, L., Zhang, Y., Nai, D., Harrelson, T. F., Sommer, M., Moule, A. J., Kemerink, M., Marder, S. R., McCulloch, I., Fahlman, M., Fabiano, S., Mueller, C. 2019; 18 (2): 149-+

    Abstract

    Molecular doping is a crucial tool for controlling the charge-carrier concentration in organic semiconductors. Each dopant molecule is commonly thought to give rise to only one polaron, leading to a maximum of one donor:acceptor charge-transfer complex and hence an ionization efficiency of 100%. However, this theoretical limit is rarely achieved because of incomplete charge transfer and the presence of unreacted dopant. Here, we establish that common p-dopants can in fact accept two electrons per molecule from conjugated polymers with a low ionization energy. Each dopant molecule participates in two charge-transfer events, leading to the formation of dopant dianions and an ionization efficiency of up to 200%. Furthermore, we show that the resulting integer charge-transfer complex can dissociate with an efficiency of up to 170%. The concept of double doping introduced here may allow the dopant fraction required to optimize charge conduction to be halved.

    View details for DOI 10.1038/s41563-018-0263-6

    View details for Web of Science ID 000456325600016

    View details for PubMedID 30643236

  • Subthreshold Operation of Organic Electrochemical Transistors for Biosignal Amplification ADVANCED SCIENCE Venkatraman, V., Friedlein, J. T., Giovannitti, A., Maria, I. P., McCulloch, I., McLeod, R. R., Rivnay, J. 2018; 5 (8): 1800453

    Abstract

    With a host of new materials being investigated as active layers in organic electrochemical transistors (OECTs), several advantageous characteristics can be utilized to improve transduction and circuit level performance for biosensing applications. Here, the subthreshold region of operation of one recently reported high performing OECT material, poly(2-(3,3'-bis(2-(2-(2-methoxyethoxy)ethoxy)ethoxy)-[2,2'-bithiophen]-5-yl)thieno[3,2-b]thiophene), p(g2T-TT) is investigated. The material's high subthreshold slope (SS) is exploited for high voltage gain and low power consumption. An ≈5× improvement in voltage gain (AV) for devices engineered for equal output current and 370× lower power consumption in the subthreshold region, in comparison to operation in the higher transconductance (gm), superthreshold region usually reported in the literature, are reported. Electrophysiological sensing is demonstrated using the subthreshold regime of p(g2T-TT) devices and it is suggested that operation in this regime enables low power, enhanced sensing for a broad range of bioelectronic applications. Finally, the accessibility of the subthreshold regime of p(g2T-TT) is evaluated in comparison with the prototypical poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), and the role of material design in achieving favorable properties for subthreshold operation is discussed.

    View details for DOI 10.1002/advs.201800453

    View details for Web of Science ID 000441869400040

    View details for PubMedID 30128254

    View details for PubMedCentralID PMC6097142

  • Lipid bilayer formation on organic electronic materials JOURNAL OF MATERIALS CHEMISTRY C Zhang, Y., Wustoni, S., Savva, A., Giovannitti, A., McCulloch, I., Inal, S. 2018; 6 (19): 5218–27

    View details for DOI 10.1039/c8tc00370j

    View details for Web of Science ID 000432599600016

  • Enhanced n-Doping Efficiency of a Naphthalenediimide-Based Copolymer through Polar Side Chains for Organic Thermoelectrics ACS ENERGY LETTERS Kiefer, D., Giovannitti, A., Sun, H., Biskup, T., Hofmann, A., Koopmans, M., Cendra, C., Weber, S., Koster, L., Olsson, E., Rivnay, J., Fabiano, S., McCulloch, I., Muller, C. 2018; 3 (2): 278–85

    Abstract

    N-doping of conjugated polymers either requires a high dopant fraction or yields a low electrical conductivity because of their poor compatibility with molecular dopants. We explore n-doping of the polar naphthalenediimide-bithiophene copolymer p(gNDI-gT2) that carries oligoethylene glycol-based side chains and show that the polymer displays superior miscibility with the benzimidazole-dimethylbenzenamine-based n-dopant N-DMBI. The good compatibility of p(gNDI-gT2) and N-DMBI results in a relatively high doping efficiency of 13% for n-dopants, which leads to a high electrical conductivity of more than 10-1 S cm-1 for a dopant concentration of only 10 mol % when measured in an inert atmosphere. We find that the doped polymer is able to maintain its electrical conductivity for about 20 min when exposed to air and recovers rapidly when returned to a nitrogen atmosphere. Overall, solution coprocessing of p(gNDI-gT2) and N-DMBI results in a larger thermoelectric power factor of up to 0.4 μW K-2 m-1 compared to other NDI-based polymers.

    View details for PubMedID 29457139