Abstract
Imaging of complex (biological) samples in the near-infrared (NIR) is beneficial due to reduced light scattering, absorption, phototoxicity, and autofluorescence. However, there are few NIR fluorescent materials known and suitable for biomedical applications. Here we exfoliate the layered pigment CaCuSi4O10 (Egyptian Blue, EB) via ball milling and facile tip sonication into NIR fluorescent nanosheets (EB-NS). The size of EB-NS can be tailored to diameters <20 nm and heights down to 1 nm. EB-NS fluoresce at 910 nm and the fluorescence intensity correlates with the number of Cu2+ ions. Furthermore, EB-NS display no bleaching and high brightness compared with other NIR fluorophores. The versatility of EB-NS is demonstrated by in-vivo single-particle tracking and microrheology measurements in Drosophila melanogaster embryos. EB-NS can be uptaken by plants and remotely detected in a low-cost stand-off detection setup. In summary, EB-NS have the potential for a wide range of bioimaging applications.
Highlights
Imaging of complex samples in the near-infrared (NIR) is beneficial due to reduced light scattering, absorption, phototoxicity, and autofluorescence
We first reduced the size of Egyptian Blue (EB) by planetary ball (PB) milling and exfoliated EB nanosheets (EB-NS) via tip sonication, which allowed for the controlled decrease in height and diameter with sonication time (Fig. 1a and Supplementary Fig. 1)
Milling techniques such as PB are routinely employed for silicates[36], whereas tip sonication is a widely used method to disperse nanomaterials such as carbon nanotubes[37]
Summary
Imaging of complex (biological) samples in the near-infrared (NIR) is beneficial due to reduced light scattering, absorption, phototoxicity, and autofluorescence. SWCNTs have been used as building blocks for NIR imaging and as fluorescent sensors that detect small signaling molecules, proteins, or lipids[13,14,15,16,17,18,19] They can be chemically tailored and have been used to reveal spatiotemporal release patterns of neurotransmitters from single cells[2,15,20,21,22]. There is a major need for novel NIR fluorescent and biocompatible nanomaterials for sophisticated applications such as long-time single-particle tracking in organisms or multiscale bioimaging such as stand-off detection in plants[23,24]. We use a facile tip sonication technique to exfoliate CaCuSi4O10 (EB) nanosheets (EB-NS) This procedure allows one to control the nanomaterial size/thickness and retain the unique NIR fluorescent properties of macroscopic CaCuSi4O10. We demonstrate the use of this material for in-vivo NIR microscopy and stand-off detection
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