Microwave-assisted synthesis of carbon dots and its potential as analysis of four heterocyclic aromatic amines
Graphical abstract
Introduction
The International Agency for Research on Cancer (IARC) regards some of the heterocyclic aromatic amines (HAAs) as possible human carcinogens such as (2-amino-3,4-dimethyl-imidazo [4,5-f]-quinoline, 2-amino-3,8-dimethyl-imidazo [4,5-f] quinoxaline and 2-amino-3,4,8-trimethylimidazo [4,5-f]-quinoxaline, 2-amino-3,7,8-trimethyl-imidazo [4,5-f]-quinoxaline (class 2B) and 2-amino-3-methylimidazo [4,5-f]-quinoline (class 2A) [1], [2], [3]. Therefore, an important issue in Analytical Chemistry as the main source is the cooked food when the proteins are converted at high temperatures due to the incomplete their combustion process.
Chromatographic methods are the most widely used when analyzed grilled, barbecued or fried meat and fish and urine samples, being HPLC–MS the main analytical technique used previous micro-extraction procedure [4], [5], [6], [7], [8], [9], [10], [11], [12], [13]. HPLC with different detection systems such as UV [14], [15], [16] and fluorescence [17], [18]; GC–MS [19], [20], [21], [22], [23] and by electrophoresis capillary (CE) [24], [25], [26], [27], [28], an extensive revision of all this techniques and compared can be found in literature [29]. Very few references to other techniques have been found in the literature for the analysis of these harmful metabolites, except for improvements in the processes of extraction prior to chromatographic analysis such as the used of supercritical fluids [27] and ionic liquids [30], making interesting the development of new alternatives as the sensitive luminescent techniques for their analysis is an important and interesting challenge in the analysis of HAAs [31].
Nanotechnology offers the best alternative, which combines the easiest design of nanoparticles with their cheap cost and luminescent properties, being the emerging system based in carbon dots (CDs) the best candidates to be applied as a detection system of any analyte to study due to its application in many other areas of analysis. These systems are the one of the lasts discover where heavily functionalized carbon networks are involved, which were firstly discovered by simple purification of carbon nanotubes and nowadays can be obtained by means a great variety of simple process [32], [33], [34], [35], [36], [37].
This work shows the photoluminescent characteristics of CDs prepared from lactose using microwave process. The advantages of this treatment include faster preparation method, good fluorescence efficiency, reproducibility and stability of the obtained nanoparticles. Furthermore, the exploitation of the sensorial ability of these CDs gives rise to an excellent tool for the quantification, and without any further functionalization, of four different HAAs, by the quenching effect on the fluorescence of CDs.
Section snippets
Chemicals
Lactose monohydrate (99%) and hydrochloric ( 37%) were purchased from Panreac S.A.U. (Barcelona, Spain), 2-amino-3,4-dimethyl-imidazo [4,5-f]-quinoline (MeIQ), 2-amino-3,8-dimethyl-imidazo [4,5-f]-quinoxaline(8-MeIQx), 2-amino-3,4,8-trimethylimidazo [4,5-f]-quinoxaline (4,8-DiMeIQx), 2-amino-3,7,8-trimethyl-imidazo [4,5-f]-quinoxaline (7,8-DiMeIQx), 2-Amino-1-methyl-6-phenyilimidazo [4,5-b]-pyridine (PhIP) and 2-amino-1-methyl-imidazo [4,5-f]-quinoline (iso-IQ) (Fig. 1), were supplied from
Results and discussion
An easiest, rapid and hydrothermal procedure, assisted by microwave treatment, previous purification process, was chosen to obtain CDs from lactose which exhibited a strong emission. The most attractive feature of this method is that the surface passivation step is not necessary, since the starting material. Fig. 2A and B shows the TEM images of CDs at different magnifications revealing, that the synthesis procedure without any modification, could easily disperse in water with a narrow size
Conclusions
In summary, a fluorescent analytical method based on the quenching of the un-functionalized carbon fluorescent nanoparticles, obtained by the assisted microwave treatment of lactose by HCl, and was used as potential system to quantify heterocyclic aromatic amines at μM range of concentration static quenching effect was demonstrated, after analysis of the fluorescence lifetime decay curves, no effect was detected when used 4,8-DiMeIQx as heterocyclic aromatic amine probe at different
Acknowledgements
Authors are gratefully to Grant SFRH/BD/84318/2012 to FCT (Lisbon, Portugal) and Andalucía Tech Program from Univ Málaga (Spain). Financial support from the Spanish Ministry of Economy and Competitiveness (CTQ2013-48411-P) is gratefully acknowledged. The support given through an “INCRECYT” research contract to M. Zougagh is also acknowledged.
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