Detection of GSH with a dual-mode biosensor based on carbon quantum dots prepared from dragon fruit peel and the T-Hg(II)-T mismatch.

Glutathione (GSH) is commonly used as a diagnostic biomarker for many diseases. In this study, based on carbon quantum dots prepared from dragon fruit peel (D-CQDs) and the T-Hg(II)-T mismatch, a dual-mode biosensor was developed for the detection of GSH. This system consists of two single-stranded DNA (ssDNA). DNA1 was the T-rich sequence; DNA2 was attached to streptavidin-coated magnetic beads and consisted of T-rich and G-rich fragments. Due to the presence of Hg(II), the T-Hg(II)-T mismatch was formed between T-rich fragments of two ssDNA. In the presence of GSH, Hg(II) detached from dsDNA and bound with GSH to form a new complex. The G-rich fragment assembled with the hemin shed from D-CQDs to form the G-quadruplex/hemin complex. At this time, in fluorescence mode, the fluorescence of D-CQDs quenched by hemin could be restored. In colorimetric mode, after the magnetic beads separate, a visual signal could be produced by catalyzing the oxidation of ABTS using the peroxide-like activity of the G-quadruplex/hemin complex. This biosensor in both fluorescence mode and colorimetric mode had excellent selectivity and sensitivity, and the limit of detection was 0.089 µM and 0.26 µM for GSH, respectively. Moreover, the proposed dual-mode biosensor had good application prospects for detection of GSH.

A Fluorescence Biosensor Based on Carbon Quantum Dots Prepared from Pomegranate Peel and T-Hg2+-T Mismatch for Hg2+ Detection.

Mercury ions (Hg2+) can cause damage to human health, and thus, the study of the detection of Hg2+ is extraordinarily important in daily life. This work reported a fluorescence biosensor for the detection of Hg2+. The key point of this strategy was that the fluorescence of carbon quantum dots made from pomegranate peel (P-CQDs) was quenched by hemin, and restored after G-quadruplex binding with hemin. The presence of Hg2+ caused thymine (T)-rich DNA fragments to form T-Hg2+-T mismatches, and this change allowed the release of G-quadruplex. G-quadruplex could change the fluorescence of hemin/P-CQDs. P-CQDs exhibited excellent properties through characterization analysis, such as transmission electron microscope, X-ray photoelectron spectroscopy and Fourier transform infrared. This proposed fluorescence detection strategy established the linear ranges of Hg2+ from 1 nM to 50 nM. In conclusion, this simple biosensor had the advantages of strong sensitivity, high selectivity, and low cost for Hg2+ detection in environmental water samples.

The discrepancy of NH3 oxidation mechanism between SAPO-34 and Cu/SAPO-34.

The difference of NH3 oxidation mechanism over SAPO-34 and Cu-SAPO-34 was studied. XRD (X-ray diffraction), SEM (scanning electron microscopy) and H2-TPR (H2-temperature programmed desorption) were conducted to estimate the Cu species distribution. The quantity of individual Cu2+ ions escalated with the elevation of silicon content in the Cu/SAPO-34 catalysts, leading to an enhancement in the activity of the NH3-SCR (ammonia-selective catalytic reduction) process. This augmentation in activity can be attributed to the increased presence of isolated Cu2+ species, which are pivotal in facilitating the catalytic reaction. In addition, the kinetic test of NH3 oxidation indicated that the CuO species were the active sites for NH3 oxidation. Specifically, the strong structural Brønsted acid sites were the NH3 oxidation active sites over the SAPO-34 support, and the NH3 reacted with the O2 on the Brønsted acid sites to produce the NO mainly. While the NH3 oxidation mechanism over Cu/SAPO-34 consisted of two steps: firstly, NH3 reacted with O2 on CuO sites or residual Brønsted acid sites to form NO as the product; subsequently, the generated NO was reduced by NH3 into N2 on isolated Cu2+ sites. Simultaneously, the isolated Cu2+ sites might demonstrate a significant function in the NH3 oxidation process to form N2. The identification of active sites and corresponding mechanism could deepen the understanding of excellent performance of NH3-SCR over the Cu/SAPO-34 catalyst at high temperature.

Mechanochemical coordination self-assembly for Cobalt-based metal-organic framework-derived bifunctional oxygen electrocatalysts.

The exploration and preparation of inexpensive, high-performance and stable catalysts for oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is of significant imperativeness, yet is still on the way. In this study, a facile operation protocol is presented for constructing an exquisite three-dimensional coral reef-like carbon nanotube assembly bridged with N-doped graphene (assigned as 3D CNTAs-NG, which represented carbonization products at 900℃) as highly efficient and durable ORR/OER electrocatalysts. It does not require the introduction of reductive atmosphere. In this tactic, the dicyanamide ligand on the Co-MOF not only was instrumental in the introduction of nitrogen but also acted as the inducer of carbon nanotubes (CNTs) to lock the metallic Co in graphitic carbon layers. Graphene oxide (GO) is chosen as a matrix to pin the CNTs and ensure the uniform distribution of CNTs. The obtained CNTAs-NG structure possesses 3D open porous texture, abundant defects, desired nitrogen bonding type and high specific surface area, providing them with excellent ORR and OER properties. As such, the optimized 3D CNTAs-NG sample shows high onset potential (Eonset = 0.97 V vs. RHE) and half-wave potential (E1/2 = 0.85 V vs. RHE) for ORR and overpotential of 340 mV at 10 mA∙cm-2 for OER. Meanwhile, the prepared optimum catalyst exhibited outstanding durability for ORR and OER in alkaline solutions. This work may pave significant concepts for the synthesis of highly active bifunctional electrocatalysts with intriguing architectures and compositions.