Fluorescence Of Carbon Nanodots Research Articles

Fluorescence Turn‐On Analysis of Trace Protein Based on Carbon Nanodots and Hybridization Chain Reaction

AbstractIn this work, an ultrasensitive method for trace protein detection based on fluorescent carbon nanodots and hybridization chain reaction (HCR) is designed. Generally, the synthesized bright carbon nanodots are conjugated with two hairpin‐structured DNA probes, respectively, which act as subsequent HCR fuel strands. Since single‐stranded parts of DNA probes could be easily absorbed on graphene oxide (GO) nanosheets, fluorescence emission of carbon nanodots is effectively quenched via fluorescence resonance energy transfer. However, in the presence of target protein, the aptamer sequence in another hairpin‐structured DNA probe specially interacts with target and the hairpin is opened. A single‐stranded region is thus exposed, which initiates HCR by coupling with the DNA fuel strands on carbon nanodots. The formed HCR product displays a rigid, long double‐stranded structure, which facilitates the release of carbon nanodots from GO surface. As a result, fluorescence of carbon nanodots is recovered and initial concentration of target protein can be estimated. This protein detection method shows a favorable linear response with a low limit of detection (2.3 fg mL−1). Furthermore, it is highly selective and capable of detecting target in biological fluids like serum samples, which demonstrates the promising applications of this method.

Ultrafast spectroscopic investigation on fluorescent carbon nanodots: the role of passivation.

Disentangling the respective roles of the surface and core structures in the photocycle of carbon nanodots is a critical open problem in carbon nanoscience. While the need of passivating carbon dot surfaces to obtain efficiently emitting nanoparticles is very well-known in the literature, it is unclear if passivation introduces entirely new surface emitting states, or if it stabilizes existing states making them fluorescent. In this multi-technique femtosecond spectroscopy study, the relaxation dynamics of non-luminescent (non-passivated) carbon dots are directly compared with their luminescent (passivated) counterparts. Non-passivated dots are found to host emissive states, albeit very short-lived and practically incapable of steady-state fluorescence. In contrast, the passivation procedure gives birth to a distinctive new manifold of emitting states, localized on the surface of the dots, and capable of intense, tunable, long-lived fluorescence. It turns out that these surface states are instantaneously populated by photo-excitation, and their subsequent dynamics are entirely independent of core electronic transitions. The experiments reveal the lack of any crosstalk between core- and surface states, at least for certain common types of carbon dots, and open a new perspective on the mechanisms by which surface passivation governs the fluorescence properties of these nanoparticles.

Simultaneous Detection of Adenosine Triphosphate and Glucose Based on the Cu-Fenton Reaction

Both adenosine triphosphate (ATP) and glucose are important to human health, and their abnormal levels are closely related to angiocardiopathy and hypoglycaemia. Therefore, the simultaneous determination of ATP and glucose with a single test mode is highly desirable for disease diagnostics and early recognition. Herein, a new fluorescence on/off switch sensing platform is developed by carbon nanodots (CNDs) to detect ATP and glucose simultaneously. The fluorescence of CNDs can be quenched by Cu2+ and hydrogen peroxide (H2O2), due to the formation of hydroxyl radicals (·OH) produced in the Cu-Fenton reaction. Based on the high affinity of Cu2+ with ATP, the fluorescence of CNDs will recover effectively after adding ATP. Additionally, glucose can be efficiently catalyzed by glucose oxidase (GOx) to generate H2O2, so the platform can also be utilized to analyze glucose. Under optimum conditions, this sensing platform displays excellent sensitivity and the linear ranges are from 0.1 to 7 μM for ATP with a limit of detection (LOD) of 30.2 nM, and from 0.1 to 7 mM for glucose with a LOD 39.8 μM, respectively. Benefiting from the high sensitivity and selectivity, this sensing platform is successfully applied for simultaneous detection of ATP and glucose in human serum samples with satisfactory recoveries.

Effect of dark states on the fluorescence of carbon nanodots.

The nonlinear fluorescence properties of colloidal carbon dot solutions in glycerol were investigated at T = 298 K and 77 K. It was first found that the fluorescence intensity depended sublinearly on optical excitation intensity even at moderate excitation levels. With increasing excitation, the fluorescence signal shows a trend toward saturation, the latter being most pronounced at liquid nitrogen temperature. The relation between the fluorescence intensity and the excitation density was shown to be well approximated by the hyperbola equation. The behavior of the fluorescence intensity was theoretically described by a 3-level model that involves the singlet fluorescent state S1 and optically "dark" triplet state T1 of a carbon dot. The triplet states are almost inactive optically and manifest themselves in a very weak phosphorescence of the carbon dots that is several orders weaker than the fluorescence of the dots. The lifetimes of the triplet state were measured to be 0.75 ms at room temperature and 0.25 s at T = 77 K. Within the model used, the intersystem crossing (S1 → T1) lifetime in the carbon dots was estimated to be τIST ∼ 10-5 s at T = 77 K and τIST ∼ 10-6 s at T = 298 K.

Fluorescence-Converging Carbon Nanodots-Hybridized Silica Nanosphere.

Ultrabright carbon nanodots-hybridized silica nanospheres (CSNs) are synthesized through the Stöber process of silane functionalized C-dots. The fluorescence of carbon nanodots is converged intensely. A CSN is about 3800 times brighter than a single-carbon nanodot. Along with their high brightness and low cytotoxicity, CSNs also indicate their potential application in cellular labeling.