Hydrogen peroxide (H2O2) is a key molecule in biology. As a byproduct of many enzymatic reactions, H2O2 is also a popular biosensor target. Recently, interfacing H2O2 with inorganic nanoparticles has produced a number of nanozymes showing peroxidase or catalase activities. CeO2 nanoparticle (nanoceria) is a classical nanozyme. Herein, a fluorescently labeled DNA is used as a probe, and H2O2 can readily displace adsorbed DNA from nanoceria, resulting in over 20-fold fluorescence enhancement. The displacement mechanism instead of oxidative DNA cleavage is confirmed by denaturing gel electrophoresis and surface group pKa measurement. This system can sensitively detect H2O2 down to 130 nM (4.4 parts-per-billion). When coupled with glucose oxidase, glucose is detected down to 8.9 μM in buffer. Detection in serum is also achieved with results comparable with that from a commercial glucose meter. With an understanding of the ligand role of H2O2, new applications in rational materials design, sensor development, and drug delivery can be further exploited.

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Despite high-energy density and low cost of the lithium-sulfur (Li-S) batteries, their commercial success is greatly impeded by their severe capacity decay during long-term cycling caused by polysulfide shuttling. Herein, a new phase engineering strategy is demonstrated for making MXene/1T-2H MoS 2 -C nanohybrids for boosting the performance of Li-S batteries in terms of capacity, rate ability, and stability. It is found that the plentiful positively charged S-vacancy defects created on MXene/1T-2H MoS 2 -C, proved by high-resolution transmission electron microscopy and electron paramagnetic resonance, can serve as strong adsorption and activation sites for polar polysulfide intermediates, accelerate redox reactions, and prevent the dissolution of polysulfides. As a consequence, the novel MXene/1T-2H MoS 2 -C-S cathode delivers a high initial capacity of 1194.7 mAh g −1 at 0.1 C, a high level of capacity retention of 799.3 mAh g −1 after 300 cycles at 0.5 C, and reliable operation in soft-package batteries. The present MXene/1T-2H MoS 2 -C becomes among the best cathode materials for Li-S batteries.

Adsorption of a fluorophore-labeled DNA probe by graphene oxide (GO) produces a sensor that gives fluorescence enhancement in the presence of its complementary DNA (cDNA). While many important analytical applications have been demonstrated, it remains unclear how DNA hybridization takes place in the presence of GO, hindering further rational improvement of sensor design. For the first time, we report a set of experimental evidence to reveal a new mechanism involving non-specific probe displacement followed by hybridization in the solution phase. In addition, we show quantitatively that only a small portion of the added cDNA molecules undergo hybridization while most are adsorbed by GO to play the displacement role. Therefore, it is possible to improve signaling by raising hybridization efficiency. A key innovation herein is using probes and cDNA with a significant difference in their adsorption energy by GO. This study offers important mechanistic insights into the GO/DNA system. At the same time, it provides simple experimental methods to study biomolecular reaction dynamics and mechanism on surface, which may be applied for many other biosensor systems.3

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