Functionalized carbon nanoparticles: Syntheses and applications in optical bioimaging and energy conversion

Modified facile synthesis for quantitatively fluorescent carbon dots

“…The latter with the carbon nanoparticles already in place before the dot synthesis is less ambiguous in terms of the formed dots being consistent with the general definition of CDots as surface-passivated carbon nanoparticles. 8,10 For referencing purpose in this study, the experimental protocols established in the literature on the carbonization processing were adopted and evaluated, including specifically the popular reaction conditions of heating a mixture of citric acid - oligomeric PEI (branched, molecular weight ~ 1,200) either in a gel-like morphology at 200 °C for 3 h under ambient pressure or hydrothermally in an autoclave at 150 – 200 °C. The somewhat different processing conditions yielded samples of rather similar absorption and fluorescence spectral features, which are also similar to those reported in the literature (Figure 2).…”

“…3–10 A wide variety of potential technological applications of CDots have been pursued, including bioimaging and sensing, 11–14 drug and gene delivery, 15,16 photodynamic therapy, 17 bactericidal functions, 18 photocatalytic energy conversion, 8,19 and others. 20–23 Most of these targeted applications mimic, compete, and/or go beyond those already derived from conventional semiconductor quantum dots (QDs).…”

“…8,10,24 In the original report on CDots, 1 specifically prepared carbon nanoparticles were chemically functionalized by oligomeric and polymeric molecules for the surface passivation purpose. Since then, such a synthesis, often referred to as the deliberate chemical functionalization method, 8,10 has yielded some of the best-performing CDots (with observed fluorescence quantum yields beyond 50% in the visible spectral region covered by green fluorescent proteins). 25,26 However, most of the reported syntheses of CDots in the literature have been based on the carbonization of organic molecules or other carbon-containing precursors, often in terms of "one-pot" processing.…”

“…25,26 However, most of the reported syntheses of CDots in the literature have been based on the carbonization of organic molecules or other carbon-containing precursors, often in terms of "one-pot" processing. 3–10,27–30 While a variety of molecules and materials as precursors have been studied in the literature, the use of citric acid - polyethyleneimine (PEI) binary mixtures have been particularly popular in many publications. 27,31–36 The popularity is probably due to the facile nature of the synthetic protocol, such as simply the heating of a precursor mixture of citric acid and PEI up to 200 °C for a few hours.…”

Real-time monitoring of the UV-induced formation of quantum dots on a milliliter, microliter, and nanoliter scale

“…However, potential toxicity of heavy metals attracted a great attention to safety concerns for health and environment [7]. For this reason, QDs made from less toxic materials, such as zinc [8] and carbon [9] were developed. The photo-physical properties, which make QDs interesting compared to classic organic dyes include very narrow emission spectra, broad absorption spectra, long fluorescence lifetime, high quantum yield, high molar extinction coefficient, large effective Stokes shift, and high stability against photobleaching [10].…”