Nanoelectrochemical detection of single-molecule semiconducting polymers Daniel Felipe Duarte Sánchez , Serge G. Lemay Universiteit Twente, Netherlands
Despite the high attention that semiconducting polymers have received due to their impact in the evolution of organic electronics technologies, there is little insight into the electrical behavior of their constituting units (single polymer chains) as well as their potential applications as electrical labels for biochemical assays. Here we introduce an amperometry-based detection technique for electrolyte-gated single semiconducting polymer chains. 10 nm nanogap sensors were fabricated using standard microfabrication techniques and interfaced with fA-level current readout instrumentation. During each measurement, the current across the nanogap was recorded for several hours while being exposed to a polymer solution. A Pt reference/gate electrode set the solution potential so as to electrochemically dope the semiconducting molecules upon contact with the nanogap electrodes. When both electrodes were contacted by a molecule, sharp current steps were observed. This was followed by equally abrupt returns to the baseline current level once the polymer chains had diffused away. Time-varying, multi-step features also occurred, which we interpret as resulting from fluctuations in the internal conformation of the polymer chains. We have statistically evaluated the duration, current and noise levels of stochastic conduction events for three different alkyl-thiophenes to both characterize them as electrical labels and to assess their semiconducting properties. To achieve this we have developed an analysis technique based on the wavelet decomposition denoising of the current signals on the three (source, drain and gate) electrodes, thus enabling the detection of conduction events in a manner that is agnostic towards the SNR and background drift while also allowing the quasi-automated recognition of time overlapped events. Finally, we studied the coupled electronic-ionic transport occurring during the polymer doping process caused by electrochemical gating. This employed thin polymer films that are formed in the presence of higher concentrations of polymers in solution. The doping level and its variation in time were inferred from the source-drain conductivity, which could be disentangled from the charging current by simultaneously monitoring the liquid gate current. This revealed a doping process different from the intuitive “rolling-carpet" concept and that is dominated by the bulk resistance of the electrolyte solution. This may help optimize the design of electrolyte-gated devices. References 1. Chung, A. Khot, B. M. Savoie and B. W. Boudouris, ACS Macro Lett , 2020, 9 , 646–655. 2. Fahlman, S. Fabiano, V. Gueskine, D. Simon, M. Berggren and X. Crispin, Nature Reviews Materials 2019 4:10 , 2019, 4 , 627–650. 3. Abbasi, L. Bennet, A. J. Gunn and C. P. Unsworth, Int J Neural Syst , , DOI:10.1142/S0129065719500138. 4. H. Lee, D. W. Chang, J. Kim and J. Lee, Journal of the Korean Physical Society , 2023, 82 , 491–496.Roy, X. Chen, M. H. Li,
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