This presentation describes the use of microelectrodes and nanoelectrode patterns for precise electrodeposition of nanowire sensors made of charge-transfer complexes (CTCs). We use commercial gold microdisk electrodes as well as gold nanoelectrode patterns made by photolithography in this study. CTCs such as tetrathiafulvalene (TTF) and tetracyanoquinodimethane (TCNQ) salts are organic conductors with attractive structural and electronic characteristics for components in electronic devices such as nanowire sensors. Nanowires are widely recognized as the next generation building block for ultrasensitive and ultrafast chemical detection; however, scaling up nanowire assembly remains a bottleneck for nanosensor commercialization. We explore CTC nanoelectrochemistry as a scalable method for mass production of nanosensor devices. CTCs are nucleated at random sites and at different times on traditional electrodes. In contrast, using nanoelectrodes, nucleation and growth kinetics can be studied on one nucleation site at a time. We show that TTFBr0.76 crystals electrochemically grown on the gold microdisk electrode adopt a centrosymmetric orientation with aspect ratios increasing with increasing growth time. The number of TTFBr0.76 crystals scale with the size of the microelectrode. In the sawtooth gold lithographic nanopattern, we vary the tip angle and radius of the nanoelectrode to demonstrate controlled TTFBr0.76 nucleation and crystallization by nanoelectrochemistry. Cyclic voltammetry (CV) and current transient measurements show discrete, nano-sized molecular clusters forming and impinging on the micro/nanoelectrode. Scanning electron microscopy captures discrete morphological transitions, from irregular shaped clusters, crystalline cubes, elongated plates, to hollow tubes as the TTFBr0.76 nucleates and grows on the nanoelectrode. We show that CTC nanowires precisely deposited on nanoelectrode patterns exhibit much higher reproducibility in impedance sensing of ammonia and other chemicals. We aim to advance our TRL 4 nanosensor manufacturing technology towards real-time monitoring for food safety, mining safety, and national security applications.

Exploring nanoelectrochemistry of charge-transfer complexes for ultrasensitive chemical detection

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ACS Fall 2022

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