Seccm-IRM: A New Tool for Quantitative in Situ Studies of Crystal Growth

Abstract

Scanning electrochemical cell microscopy (SECCM) is a versatile scanning probe imaging technique that allows for simultaneous elucidation of structure activity relationships at the nanoscale in defined electrolyte volumes and provides high resolution (nm length scale) information on the topography of surfaces and interfaces1. Since its inception in 2010 SECCM has improved understanding of model systems such as graphene, graphite, carbon nanotubes, nanoparticles and conductive diamond and provided electrochemists with a tool for true single entity measurements. Electrodeposition of microscale thin films has previously been reported2 but not of crystalline species, which is the focus of this work.SECCM can also be used as a tool for the precise delivery of nano to microscale solution droplets to surfaces. By using optically transparent yet conductive substrates (such as indium tin oxide (ITO), gold or graphene ) we can couple SECCM to highly surface-sensitive imaging modes such as interference reflectance microscopy (IRM)3 or traditional brightfield microscopy, allowing the evaporation and consequent precipitation of solutes to be monitored. The SECCM apparatus allows the deposition of large arrays, under well-defined conditions (deposition time, surface potential), with each droplet representing an individual and independent crystallisation experiment and provides statistical data based on single particle level. The emergence of precipitates within these arrays is tracked to investigate the effect of additives and also surface potential on crystallisation.SECCM can use capacitative response to examine minimally ionised systems, non-aqueous solvents etc allowing organic crystals to be studied. This work focuses on the precipitation of two such model organic systems: l-cystine and 5-methyl-2-[(2-nitrophenyl)amino]thiophene-3-carbonitrile (ROY). l-Cystine is of biological relevance due to its role in the formation of kidney stone’s which are resistant to traditional therapies4. The need therefore arises for l-cystine crystallisation inhibitors making it a prime candidate for testing additive screening procedures. ROY is investigated as a model system5 to identify the merits of SECCM-IRM as a polymorph screen method. We show how sensitive precipitation is to substrate, applied potential and solvent system. References Ebejer, N.; Güell, A. G.; Lai, S. C. S.; McKelvey, K.; Snowden, M. E.; Unwin, P. R., Scanning Electrochemical Cell Microscopy: A Versatile Technique for Nanoscale Electrochemistry and Functional Imaging. Annual Review of Analytical Chemistry 2013, 6 (1), 329-351. Aaronson, B. D. B.; Garoz-Ruiz, J.; Byers, J. C.; Colina, A.; Unwin, P. R., Electrodeposition and Screening of Photoelectrochemical Activity in Conjugated Polymers Using Scanning Electrochemical Cell Microscopy. Langmuir 2015, 31 (46), 12814-12822. Valavanis, D.; Ciocci, P.; Gabriel; Morris, P.; Lemineur, J.-F.; McPherson, I. J.; Kanoufi, F.; Unwin, P. R., Hybrid scanning electrochemical cell microscopy-interference reflection microscopy (SECCM-IRM): tracking phase formation on surfaces in small volumes. Faraday Discussions 2022. Rimer, J. D.; An, Z.; Zhu, Z.; Lee, M. H.; Goldfarb, D. S.; Wesson, J. A.; Ward, M. D., Crystal Growth Inhibitors for the Prevention of l -Cystine Kidney Stones Through Molecular Design. Science 2010, 330 (6002), 337-341. Lévesque, A.; Maris, T.; Wuest, J. D., ROY Reclaims Its Crown: New Ways To Increase Polymorphic Diversity. Journal of the American Chemical Society 2020, 142 (27), 11873-11883.