Photophysical properties and fluorescence lifetime imaging of exfoliated near-infrared fluorescent silicate nanosheets

Gabriele Selvaggio; Milan Weitzel; Nazar Oleksiievets; Tabea A Oswald; Robert Nißler; Ingo Mey; Volker Karius; Jörg Enderlein; Roman Tsukanov; Sebastian Kruss

doi:10.1039/d1na00238d

Photophysical properties and fluorescence lifetime imaging of exfoliated near-infrared fluorescent silicate nanosheets

Nanoscale Adv. 2021 Jun 24;3(15):4541-4553. doi: 10.1039/d1na00238d. eCollection 2021 Jul 27.

Authors

Gabriele Selvaggio^{1

2}, Milan Weitzel², Nazar Oleksiievets³, Tabea A Oswald⁴, Robert Nißler^{1

2}, Ingo Mey⁴, Volker Karius⁵, Jörg Enderlein^{3

6}, Roman Tsukanov³, Sebastian Kruss^{1

2

7}

Affiliations

¹ Physical Chemistry II, Bochum University Bochum 44801 Germany Sebastian.Kruss@rub.de.
² Institute of Physical Chemistry, University of Göttingen Göttingen 37077 Germany.
³ Third Institute of Physics, University of Göttingen Göttingen 37077 Germany.
⁴ Institute of Organic and Biomolecular Chemistry, University of Göttingen Göttingen 37077 Germany.
⁵ Department of Sedimentology and Environmental Geology, Geoscience Center, University of Göttingen Göttingen 37077 Germany.
⁶ Cluster of Excellence "Multiscale Bioimaging: from Molecular Machines to Networks of Excitable Cells" (MBExC), University of Göttingen Germany.
⁷ Fraunhofer Institute for Microelectronic Circuits and Systems Duisburg 47057 Germany.

Abstract

The layered silicates Egyptian Blue (CaCuSi₄O₁₀, EB), Han Blue (BaCuSi₄O₁₀, HB) and Han Purple (BaCuSi₂O₆, HP) emit as bulk materials bright and stable fluorescence in the near-infrared (NIR), which is of high interest for (bio)photonics due to minimal scattering, absorption and phototoxicity in this spectral range. So far the optical properties of nanosheets (NS) of these silicates are poorly understood. Here, we exfoliate them into monodisperse nanosheets, report their physicochemical properties and use them for (bio)photonics. The approach uses ball milling followed by tip sonication and centrifugation steps to exfoliate the silicates into NS with lateral size and thickness down to ≈ 16-27 nm and 1-4 nm, respectively. They emit at ≈ 927 nm (EB-NS), 953 nm (HB-NS) and 924 nm (HP-NS), and single NS can be imaged in the NIR. The fluorescence lifetimes decrease from ≈ 30-100 μs (bulk) to 17 μs (EB-NS), 8 μs (HB-NS) and 7 μs (HP-NS), thus enabling lifetime-encoded multicolor imaging both on the microscopic and the macroscopic scale. Finally, remote imaging through tissue phantoms reveals the potential for bioimaging. In summary, we report a procedure to gain monodisperse NIR fluorescent silicate nanosheets, determine their size-dependent photophysical properties and showcase the potential for NIR photonics.