Controlled Synthesis Of Heteroatom-Doped Carbon Dots And Their Applications In Biochemical Analysis

Carbon dots(CDs), which generally refer to carbon nanomaterials less than 10 nm in size, have been attracting enormous attention due to their unique and desirable properties. Because of their chemical stability, low photobleaching, low toxicity and biocompatibility, CDs have become a new generation of photoluminescent(PL) nanomaterials. Their excellent optical properties are superior to those conventionally used PL chromophores such as fluorescent organic small molecules(OSMs) and quantum dots(QDs). CDs have been demonstrated to be good optical probes, and have been found to have wide applications in bioimaging, photocatalysis and energy conversion. However, to date, there is still limited research publications regarding the origin of PL emission in CDs, the synthesis of CDs with different optical properties, or the functionalization of CDs. These research directions need to be further explored in order to extend the applications of CDs. In this paper, we used citric acid(CA) as the carbon source to complete a series of CD synthesis. In addition, we investigated the PL emission origin in CDs and do researches as follows.(1) Germanium-doped carbon dots as a new type of fluorescent probe forvisualizing the dynamic invasions of mercury(II) ions into cancer cellsFor the first time, this paper took citric acid and Bis(2-carboxyethylgermanium(IV) sesquioxide, Ge-132) as carbon source and germanium source respectively. And we fabricated the germanium doped GeCDs using an easy bottom-up route, which only required 15 min. The as-prepared GeCDs demonstrate excitation-independent PL emissions behavior which is much different from most of the previous reported CDs. The as-prepared GeCDs have low cell toxicity, good biocompatibility, high intracellular delivery efficiency and stability. And the GeCDs could be unitized to the detection of mercury(II) ions, providing a particularly useful platform in complex conditions such as honeysuckle dew samples and cells. Especially, taking GeCDs as a novel cellular probe for imaging and monitoring Hg~ (2+) in HEp-2 cells is interesting, which makes it possible for rapid visualizing and monitoring significant physiological changes caused by Hg~ (2+) in living cells.(2) Synthesis of nitrogen-doped carbon dots with different photoluminescentproperties by controlling the surface statesA series of CDs are prepared by using citric acid(CA) and guanidine hydrochloride as precursors, and the as-prepared CDs display either excitation-dependent emission(EDE) property or excitation-independent emission(EIE) property, along with low cell toxicity, stability, and excellent optical properties. By tuning of the nitrogen content, we revealed that the EDE and QY of CDs could be governed by the surface states of CDs and the different optical properties of CDs originate from different surface states, and if the as-prepared CDs are fully surface-passivized with adequate proportion of guanidine hydrochloride, they will display EIE features, with high quantum yield up to 60.5%. The as-prepared CDs have specific binding ability with Hg~ (2+). As a consequence, the photoluminescence will be quenched, which is caused by electrons transfer overlapping mechanism from the LUMO levels of CDs to Hg~ (2+). Furthermore, the specific binding of CDs to mercury(II) ion shows that the CDs can serve as an effective fluorescent probe for specifically visual monitoring of intracellular mercury(II) ions.