Amino acid functionalized blue and phosphorous-doped green fluorescent carbon dots as bioimaging probe

Abstract

Thermal coupling between citric acid and Na-salt of glycine, L-valine and L-isolucine produced amino acid surface functionalized fluorescent blue emitting carbon dots (CDs). The same precursor in presence of NaH 2 PO 4 , produced phosphorous doped amino acid functionalized carbon dots which are green emitting. These blue and green emitting carbon dots were utilized for cell imaging.Abstract: Amino acid functionalized carbon dots (CDs) were synthesized in a simple and cost effective bottom up approach. Citric acid was used as the source of carbon core and three amino acids L-isoleucine, L-valine and glycine were used for the surface fabrication of CDs to produce CD iso , CD val and CD gly , respectively. Interestingly these CDs were found to be fluorescent with blue emission. Doping of phosphorus to these CDs (PCDs) tuned the photoemission properties and produced green emitting PCDs. The doping of phosphorous (P) to these CDs improved their fluorescence intensity as well as quantum yields. Both doped and non-doped CDs were characterized by spectroscopic and microscopic techniques. These highly stable CDs were biocompatible in nature and did not exhibit any photobleaching property over a long span of time even under UV exposure. Subsequently, these CDs were exploited as excellent bioimaging probe. Importantly CDs and PCDs illuminated cells in two completely different spectral regions blue and green, respectively in accordance with their fluorescence spectral behaviour. Hence, amino acid functionalized carbon dots based bioimaging probes of different fluorescence character were developed that are widely applicable for cellular imaging in both blue and green spectral regions. Fig. 7 Percentage cell viability of Hela cells incubated with varying concentrations of (a) CDs and (b) PCDs after 24 h incubation. The experimental errors were in the range of 3-5% in triplicate experiments.

Carbon Nanodots: A Review—From the Current Understanding of the Fundamental Photophysics to the Full Control of the Optical Response

“…In fact, bottom-up methods have allowed for obtaining the CDs with the highest emission efficiencies reported in the literature so far. The most common doping agent by far is nitrogen [6,8,9,21,53,[65][66][67][68][69], sulphur [22,[70][71][72], but also boron [73][74][75][76] and phosphorous [77,78] have been used. It seems, in fact, that the introduction of these doping agents substantially modifies the structure and increases the fluorescence quantum efficiency of the nanosystem, although the physical mechanisms behind this is still unclear, and recently very debated [8,9,68,79].…”

Improving the functionality of carbon nanodots: doping and surface functionalization

“…6,7,[27][28][29] The paper showed that the temperature generally employed for C-dot synthesis is not high enough to form a fully graphitized nanostructure, leading to the formation of graphitic clusters with ca. 5-8 aromatic rings instead.…”

“…Toxicity and bioimaging experiments showed that P-doped C-dots have low cell toxicity and excellent biolabeling ability. 29 Doping the non-doped C-dots with phosphorus caused a red shift of the maximum emission wavelength from 420 to 470 nm and enhanced their fluorescence intensity as well as quantum yields by up to 10%.…”

Recent Advancements in Doped/Co-Doped Carbon Quantum Dots for Multi-Potential Applications

“…In another study, Shi et al (2015) have prepared P-doped CQDs with blue emission and QY of 21.8% by hydrothermal treatment (5 h at 200 • C) of sucrose and phosphoric acid [92]. However, Sarkar et al (2015) have synthesized P-doped CQDs with green emission by using thermal coupling between citric acid and Na-salt of glycine, L-valine, and L-isolucine in the presence of sodium dihydrogen phosphate (as P source) [93]. Moreover, these P-doped CQDs using glycine, L-valine, and L-isolucine displayed higher QYs (i.e., 15.2%, 11.0% and 19.7%) as compared to their un-doped CQDs (i.e., 8%, 8.9% and 3.7%), respectively.…”