Physico-Chemical nanomaterials science

Carbon quantum dots for effective pH sensing with photoluminescence method
Dorosh T.S.1, Linnik R.P.1, Zaporozhets O.A.1, and Lisnyak V.V.1,2
1 Chemical Department, Taras Shevchenko University of Kyiv. Volodymyrska Str., 64, Kyiv-01601, Ukraine. 
E-mail: lisnyak@univ.kiev.ua
2 Presov University, 17 Novembra Str., 1, Presov-Lubotice, 01601 Presov, Slovakia. 

Carbon is most wide speared element in the nature. Carbon nanomaterials have unique optical properties and have attracted remarkable interest for their promising biomedical applications. Showing fluorescence properties, carbon nanoparticles that are so-called as carbon quantum dots have emerged as a new class of carbon bionanomaterials. Here we focused on the unique properties of carbon quantum dots, their synthesis, material and optical characterizations, the origin of fluorescence nature and applications in bioimaging. We examined the efficiency of carbon nanodots showed the dual emission with a long emission wavelength. Such unusual carbon quantum dots were synthesized via solvothermal method and green synthesis. The carbon nanodots possess relatively high photoluminescence and showed high quantum yield of about 47% towards near-infrared fluorescent peak up to 648 nm. We used the advanced characterization techniques of high resolution X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy; morphologic studies on nanoscaled noble metals were performed with SEM, HRTEM, AFM and STM methods. It is found that the doped nitrogen and sulfur atoms and organic groups used for surface functionalization play an important role in the formation of carbon quantum dots having high quantum yield. The functionalized carbon quantum dots showed distinct pH-sensitive features with reversible fluorescence in a good linear relationship with pH values in the range of 1.0–8.5 and 10–13.0. What is more, functionalized carbon quantum dots showed can be used as an ultrasensitive probe sensor for acidic and neutral pHs. This finding will expand the application of them for environmental sensors and in vivo biosensing. The kinetic aspect of photoluminescence was considered on the basis of the obtained alcohol and water solution. The case of PL signal blanking and the impact of dissolving were also considered. 
Acknowledgment
One of the authors, VVL gratefully acknowledges the financial support of the International Visegrad Found (grant No: 51810574).