Multiple spectroscopies of carbon dots synthesized by laser ablation in biocompatible liquids

Carbon dots (CDs) are quantum particles of carbon-based nanomaterials with a size lower than 10 nm. They can be synthesized by the laser ablation of different types of carbon targets placed in liquids. They have particular properties, such as high penetration of biological membranes, high luminescence induced by UV excitation, and high biocompatibility, which confer special interest for bioimaging, diagnosis, photodynamic therapy, photocatalysis, solar cells, and other interesting applications. The technique for preparing CDs dispersion using an ns pulsed Nd:YAG laser operating at the fundamental frequency is presented and described in detail. Four different green targets producing high-luminescent CD dispersions were investigated: graphite, vegetal carbon (charcoal), bay leaves, and Saccharina latissima algae. The CD dispersions in phosphate-buffered saline (PBS) biocompatible solution, with a neutral pH, have been investigated using various optical spectroscopic techniques, including luminescence detection, UV–visible absorbance and transmittance measurements, Raman spectroscopy, Fourier transform infrared spectroscopy, and others. TEM investigations were also presented to provide information about the carbon nucleus size and shape, as well as the types of molecules that can be bonded to functionalize the synthesized CDs. Some biological and medical applications and potential future developments of the CD-based devices will be presented and discussed.