Microsystem-assisted synthesis of carbon dots with fluorescent and colorimetric properties for pH detection

Abstract

Chamarro, J. (2014). Microsystem-assisted synthesis of carbon dots with fluorescent and colorimetric properties for pH detection. Nanoscale, 6, pp. 6018-6024. The present paper describes the use of a microfluidic system to synthesize carbon dots (Cdots) and their use as optical pH sensors. The synthesis is based on the thermal decomposition of ascorbic acid in dimethyl sulfoxide. The proposed microsystem is composed of a fluidic and a thermal platform, which enable proper control of synthesis variables. Uniform and monodispersed 3.3 nm-sized Cdots have been synthesized, the optical characterization of which showed their down/upconversion luminescence and colorimetric properties. The obtained Cdots have been used for pH detection with down and upconverison fluorescent properties as excitation sources. The naked eye or a photographic digital camera has also been implemented as detection systems with the hue parameter showing a linear pH range from 3.5 to 10.2. On the other hand, experiments on the cytotoxicity and permeability of the Cdots on human embryonic kidney cells revealed their adsorption on cells without causing any impact on the cellular morphology.The recent application of uorescent nanoparticles (NPs) such as quantum dots, dye-doped NPs and rare earth-based NPs in biomedical sensing and imaging has become a major subject of research over the last few years. Although a wide range of diverse photoluminescent NPs have been developed from new materials, an increased concern about their potential environmental and human health toxicity exists.1 Moreover, there are some NP-associated drawbacks such as modication of their surface for a particular function which involves highly timeconsuming processes.At the moment, one of the most attractive NPs are carbon dots (Cdots), which have recently had a major relevance in analytical and bioanalytical chemistry mainly due to their excellent luminescent properties and high biocompatibility as well as their low cost synthesis.2 However, although these Cdots are very promising NPs in nanotechnology and nanobiomedicine, much research needs to be done either to investigate their potential in sensor development or to identify novel synthesis approaches. In addition, Cdots show size dependent photoluminescence and upconversion luminescence properties leading to anti-Stokes type emissions.

Carbon Based Dots and Their Luminescent Properties and Analytical Applications

“…Accordingly, some pH sensors have been developed based on the PL of CDs. The PL intensities of CDs obtained by the thermal decomposition of ascorbic acid in dimethyl sulfoxide decreased linearly as the pH value increased from pH 4.5 to 11.5, based on which a pH sensor could be used directly for environmental monitoring applications [244]. CDs synthesized by refluxing CHCl 3 and diethylanime were modified with a pH-sensitive dye, fluorescein isothiocyanate (FITC), and used as a pH probe [156].…”

Development of microscopic time‐domain dual lifetime referencing luminescence detection for pH monitoring in microfluidic free‐flow isoelectric focusing

“…These are favorable tools due to their sensitivity, selectivity, and capability of spatially resolved analyte and parameter monitoring. Fluorescent pH sensor layers were incorporated into microfluidic platforms using various methods such as photolithography, inkjet printing, dip, blade spin coating and used for chemical reaction and bioprocess engineering [7][8][9][10][11][12][13][14][15][16][17][18]. Because of its simplicity and sensitivity, fluorescence intensity detection is widely used in miniaturized systems.…”

Highly luminescent nitrogen‐doped carbon dots for simultaneous determination of chlortetracycline and sulfasalazine

“…The surface functional groups and structure of N‐CDs were explored by FT‐IR spectrometry. As shown in Figure d, the broad absorption bands in the 3100–3500 cm −1 range are attributed to the stretching vibrations of O‐H and N‐H bonds . Two sharp peaks of 1672 and 1399 cm −1 are assigned to the characteristic absorption bands of ‐CONH‐ and C‐N, respectively, indicating the successful adulteration of nitrogen atoms in the CDs .…”