Fabrication of optically responsive microstructures via direct laser writing Teodora Faraone 1 , Jing Qiang 2 , A. Louise Bradley 2 , Colm Delaney 1 , Larisa Florea 1 . 1 School of Chemistry & AMBER, The SFI Research Centre for Advanced Materials and BioEngineering Research, Trinity College Dublin, Dublin 2, Ireland. 2 School of Physics and AMBER, Trinity College Dublin, College Green, Dublin 2, Ireland. Nature has showcased a plethora of structural colour varieties for over 500 million years (1). This type of colouration is often achieved by controlling structural organisation across several orders of magnitude. Many insects, such as Adscita statices , Dynastes tityus , and Tmesisternus isabellae , have displayed a fascinating ability to show dynamic structural colour in response to certain stimuli (2,3,4). Drawing inspiration from these fascinating creatures, we exploit direct laser writing (DLW) of composite nanomaterials to exhibit dynamic structural colour on the microscale. DLW by 2-photon polymerisation (2PP) is a lithography technique for material photo-polymerisation within a determined volume element, known as ‘voxel’. This technique allows for the fabrication of 3D structures with a resolution of ~ 100 nm (5) and feature sizes of a few hundred nanometres (6). In this work, a range of polymer nanoparticles was synthesised and characterised using DLS, AFM, SEM, and TEM. These nanoparticles were then incorporated into DLW photoresists. Optimisation of the latter (monomer composition, volume fraction, particle size) with functional monomers and multi-arm crosslinkers, yielded dispersions with tuneable structural colour, which were suitable for 3D fabrication using DLW. The resulting microstructures displayed structural colour and also retained the inherent hydrophilic nature of the polymer matrix. This work demonstrates the effect of fabrication parameters on the response of the structures to different stimuli, such as solvents, vapours, and humidity changes. Characterisation of the microstructures using optical microscopy, SEM, and AFM will also be presented. This approach presents a viable route to making rapid-response photonic sensors that can be tuned optically and chemically to generate sensors and switches for the biomedical, environmental monitoring, and food quality control fields. References 1. A. R. Parker J. Opt. A: Pure Appl. Opt. 2 (2000) R15 2. B. D. Wilts, K. Mothander, A. Kelber Biol. Lett. (2019) 15: 20190516 3. K.D.L. Umbers, S.A. Fabricant, F.M. Gawryszewski, A.E. Seago, and M.E. Herberstein, Biol Rev (2014) 89: 820-848. 4. F. Liu, B. Q. Dong, X. H. Liu, Y. M. Zheng, J. Zi. Opt Express. (2009); 17(18):16183-91 5. L. Zheng, K. Kurselis, A. El-Tamer et al. Nanoscale Res Lett 14 (2019), 134 6. C. Delaney, J. Qian, Xia Zhang, R. Potyrailo, A. L. Bradley, L. Florea J. Mater. Chem. C (2021), 9, 11674-11678
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