A new green technology for direct synthesis of carbon nanodots with narrow size distribution

Fluorescence turn-off sensing of TNT by polyethylenimine capped carbon quantum dots

In recent years, the determination of 2,4,6-trinitrotoluene (TNT) explosive residues in various matrices has attracted great interest from the perspective of national security and public health. Here, a fluorescent polyethylenimine capped carbon quantum dots (PEI-C-dots) probe was synthesized by a microwave-assisted technique using polyethylenimine and citric acid precursors and used to detect TNT. The sensing mechanism of TNT is based on fluorescence quenching as a result of the donor-acceptor interaction between Meisenheimer anion form of TNT and PEI on the PEI-C-dots surface. The fluorescence quantum yield of the synthesized PEI-C-dots was 54% and the detection limit for TNT was 93 μg/L. It was observed that neither the nitramine group (HMX and RDX) explosives with similar structures nor common soil ions and camouflage agents interfered with the determination of TNT. The interference effect of picric acid was eliminated by removing it with a basic anion exchanger before the determination. This nanosensor allows rapid, simple, selective, and sensitive determination of TNT residues in complex matrices and has the potential to be converted into a kit format.

Plasmonic enhancement of nitric oxide generation

While the utility of reactive oxygen species in photodynamic therapies for both cancer treatments and antimicrobial applications has received much attention, the inherent potential of reactive nitrogen species (RNS) including nitric oxide (NO˙) for these applications should not be overlooked. In recent years, NO˙ donor species with numerous-including photodynamic-mechanisms have been classified with efficacy in antimicrobial and therapeutic applications. While properties of NO˙ delivery may be tuned structurally, herein we describe for the first time a method by which photodynamic NO˙ release is amplified simply by utilizing a plasmonic metal substrate. This is a process we term "metal-enhanced nitric oxide release", or ME-NO˙. Using donor agents known as brominated carbon nanodots (BrCND), also the first carbon nanodot variation classified to release NO˙ photodynamically, and the fluorescence-on probe DAF-FM, we report metal-enhanced release of NO˙ 2- to 6-fold higher than what is achieved under classical conditions. Factors affecting the plasmon-amplified photodynamic system are subsequently studied, including exposure times, excitation powers, and surface area, and consistent ME-NO˙ factors are reported from BrCND across these tunable conditions. Only probe concentration is determined to impact the detected ME-NO˙ factor, with higher concentrations resulting in improved detectability of "actual" NO˙ release enhancement. Further, principles of metal-enhanced fluorescence (MEF) are applied to achieve a faster, high-throughput experimental method with improved data resolution in ME-NO˙ detection. The results have significant implications for the improvement of not just carbon nanodot NO˙ donor agents, but a wide spectrum of photoactivated NO˙ donor systems as well.

Construction of FeCo2O4@N-Doped Carbon Dots Nanoflowers as Binder Free Electrode for Reduction and Oxidation of Water

Electrochemical water splitting is known as a potential approach for sustainable energy conversion; it produces H₂ fuel by utilizing transition metal-based catalysts. We report a facile synthesis of FeCo₂O₄@carbon dots (CDs) nanoflowers supported on nickel foam through a hydrothermal technique in the absence of organic solvents and an inert environment. The synthesized material with a judicious choice of CDs shows superior performance in hydrogen and oxygen evolution reactions (HER and OER) compared to the FeCo₂O₄ electrode alone in alkaline media. For HER, the overpotential of 205 mV was able to produce current densities of up to 10 mA cm⁻², whereas an overpotential of 393 mV was needed to obtain a current density of up to 50 mA cm⁻² for OER. The synergistic effect between CDs and FeCo₂O₄ accounts for the excellent electrocatalytic activity, since CDs offer exposed active sites and subsequently promote the electrochemical reaction by enhancing the electron transfer processes. Hence, this procedure offers an effective approach for constructing metal oxide-integrated CDs as a catalytic support system to improve the performance of electrochemical water splitting.