Design and fabrication of new anticancer sensor for monitoring of daunorubicin using 1-methyl-3-octylimidazolinium chloride and tin oxide/nitrogen-doped graphene quantum dot nanocomposite electrochemical sensor

In this study, a novel tin oxide/nitrogen-doped graphene quantum dot nanocomposite (SnO₂-NDGQD) and 1-methyl-3-octylimidazolinium chloride (1M3OICl) ionic liquid amplified carbon paste electrode (CPE) was fabricated as an efficient and fast-response sensor to determine daunorubicin, an anticancer drug. The electrochemical characteristics of daunorubicin at the surface of the 1M3OICl/SnO₂-NDGQD/CPE was explored via various voltammetric methods. The high-resolution transmission electron microscope (HR-TEM) images were recorded to examine the morphological structure of the as-synthesized nanocomposites. The 1M3OICl/SnO₂-NDGQD/CPE offered a wide linear concentration of 0.001-280.0 μM with a low detection limit of 0.40 nM at the optimized experimental conditions using square wave voltammetric (SWV) method. In a nutshell, the developed electrode illustrated outstanding selectivity in the presence of interfering agents and long-term stability. The1M3OICl/SnO₂-NDGQD/CPE was used as new and powerful analytical tool for determination of daunorubicin in real samples with recovery range 98.75%-104.8%.

Design and construction of Z-scheme Bi2S3/nitrogen-doped graphene quantum dots: Boosted photoelectric conversion efficiency for high-performance photoelectrochemical aptasensing of sulfadimethoxine

Rational design and fabrication of Z-scheme visible-light-driven photoactive materials have drawn much attention owing to their great potential in handling environment and energy crisis. In this work, Z-scheme Bi₂S₃/nitrogen-doped graphene quantum dots (NGQDs) with superior photoelectric conversion efficiency were designed and fabricated, which demonstrated enhanced photoactivity compared with Bi₂S₃ owing to the improved separation efficiency of photogenerated electron and hole pairs. The emphasis was put on designing Z-scheme Bi₂S₃/NGQDs, and then the mechanism of Z-scheme charge transfer mode was verified by the electron spin resonance (ESR) technique. On this basis, the proposed sensor exhibited a wide linear range of 0.1-120 nM and a detection limit of 0.03 nM (S/N = 3) for SDM, with high sensitivity (0.075 μA nM ^-1), good selectivity and stability. Moreover, the proposed PEC aptasensor using Bi₂S₃/NGQDs as the photoelectrode achieved sensitive and selective determination of sulfadimethoxine in milk samples. This work could provide some ideas for designing other Z-scheme photoactive species and insights into the charge transfer mechanism of Z-scheme. Furthermore, the promising applicability of PEC aptasensor using photoactive species could be extended to other accurate monitoring for contaminants.

A novel electrochemiluminescence resonance energy transfer system of luminol-graphene quantum dot composite and its application in H2O2 detection

Luminol-nitrogen doped graphene quantum dot (luminol-NGQDs) nanocomposite was synthesized and a novel electrochemiluminescence resonance energy transfer (ECL-RET) process occurred between luminol as the donor and NGQDs as the acceptor in the composite. This ECL-RET effect helped luminol-NGQDs composite produced an anodic ECL signal without coreactants. The ECL-RET mechanism was also studied based on the fluorescence spectra, the ultraviolet-visible absorption spectra and the electrochemiluminescence (ECL) spectra. Based on the significant sensitization effect of hydrogen peroxide on luminol-NGQDs ECL signal, an ECL method for the sensitive determination of hydrogen peroxide was established and then applied to the detection of hydrogen peroxide in water samples.

Nitrogen-doped graphene quantum dot for direct fluorescence detection of Al3+ in aqueous media and living cells

Graphene quantum dot (GQD) has been attractive in analytical science field due to its low toxicity, stable photoluminescence. Herein, nitrogen-doped GQD (N-GQD) was prepared by a facile solvothermal treatment of GO using dimethylformamide, and exhibited a green emission with 23.1% quantum yield. The N-GQD probe showed a selective and sensitive fluorescence enhancement response to Al³⁺, the mechanism might be the formation of a complex between Al³⁺ and N-GQD constrained the photo-induced electron transfer (PET) process of N-GQD itself. With Benesi-Hildebrand equation, the binding constant and molar ratio between N-GQD and Al³⁺ was calculated to be 4.6 × 10⁴Lmol^-1 and 1:1 respectively. The pK_a value of N-GQD was also determined to be 4.4 by capillary electrophoresis. In pH 4.0 PBS solution, there was a good linear relation between the fluorescence intensity and the logarithm of concentration of Al³⁺ in the range of 2.5-75μmolL^-1, the limit of detection (3σ) was 1.3μmolL^-1. This "Off - On" fluorescence method had been applied to accurate quantification of aluminum in hydrotalcite tablets. What's more, the fluorescence switch property of N-GQD was explored by alternate addition of Al³⁺ and EDTA. The probe was also utilized for detection Al³⁺ in living cells due to its excellent biocompatibility.