Single-atom-sized catalysts (often called single atom catalysts) are highly desired for maximizing the efficiency of metal atom use. However, their synthesis is a major challenge that largely depends on finding an appropriate supporting substrate to achieve a well-defined and highly dispersed single atom. This work demonstrates, based on density functional theory (DFT) predictions and experimental validations, that graphdiyne is a good substrate for anchoring Fe atoms through the formation of covalent Fe–C bonds to produce graphdiyne-supported single-atom-sized Fe catalysts (Fe–graphdiyne catalysts); moreover, this catalyst shows high catalytic activity to oxygen reduction reactions (ORRs) similar to or even slightly better than the precious metal benchmark (commercial 20 wt % Pt/C catalyst). DFT predicts that the O2 molecule can bind with an Fe atom, and the electron transformation process of ORRs occurs through a 4e– pathway. To validate the theoretical predictions, the Fe–graphdiyne catalyst was then synthesized by a reduction of Fe3+ ions adsorbed on a graphdiyne surface in aqueous solution, and its electrocatalytic activities toward ORR were experimentally evaluated in alkaline electrolytes (0.1 M KOH). The electrochemical measurements indicate that the Fe–graphdiyne catalyst can facilitate the 4e– ORR while limiting the 2e– transfer reaction, showing a high 4e– selectivity for ORRs and a good agreement with DFT predictions. The results presented here demonstrate that graphdiyne can provide a unique platform for synthesizing well-defined and uniform single-atom-sized metal catalysts with high catalytic activity toward ORRs.

An electrochemical approach for measuring the dynamic process of H(2)O(2) (a major ROS) release from living cells is reported. This approach, which is based on enhanced reduction of H(2)O(2) by nitrogen-doped graphene, could be potentially useful in the study of downstream biological effects of various stimuli in physiology and pathology.

Nitrogen-doped graphene quantum dots (N-GQDs) are synthesized at low temperature as a new catalyst allowing electrochemical detection of 2,4,6-trinitrotoluene (TNT). N-GQDs are made by an oxidative ultrasonication of graphene oxide (GO) forming nanometer-sized species, which are then chemically reduced and nitrogen doped by reacting with hydrazine. The as-synthesized N-GQDs have an average diameter of ∼2.5 nm with an N/C atomic ratio of up to ∼6.4%. To detect TNT, TNT is first accumulated on N-GQDs modified glassy carbon (N-GQDs/GC) electrode by holding the electrode at a 0 V versus Ag/AgCl for 150 s in an aqueous TNT solution. Next, the N-GQDs/GC electrode with accumulated TNT is transferred to a fresh PBS solution (0.1 M, pH 7.0, without TNT), where the TNT reduction current at -0.36 V versus Ag/AgCl in a linear scan voltammogram (LSV) shows a linear response to TNT concentration in the aqueous solution from 1 to 400 ppb, with a correlation coefficient of 0.999, a detection limit of 0.2 ppb at a signal/noise (S/N) of 3, and a detection sensitivity of 363 ± 7 mA mM(-1) cm(-2). The detection limit of 0.2 ppb of TNT for this new method is much lower than 2 ppb set by the U.S. Environmental Protection Agency for drinking water. Therefore, N-GQDs allow an electrochemical method for assaying TNT in drinking water to determine if levels of TNT are safe or not.

The four-electron (4e‒) oxygen reduction reaction (ORR) is a basic reaction in fuel cells and metal-air batteries, but its wide use needs the development of efficient and inexpensive catalysts. This...

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Multibranched gold nanoparticles (M-AuNPs) can serve as photothermal agents for near-infrared (NIR) photothermal therapy (PTT) of cancer, but a major shortcoming is that they tend to strongly scatter NIR light, causing a significant reduction in absorption. This work addresses this issue, based on theoretical simulations and experimental determinations, to enhance the absorption and reduce the scattering of these materials by screening their structural parameters. Our finite-difference time-domain simulations predict that M-AuNPs with a core size of ∼25 nm, a tip number of 5, and a tip height of ∼40 nm (i.e., an aspect ratio of ∼2) are optimal for trapping NIR light and yielding the highest light-to-heat conversion efficiency (η) and for trapping NIR light of various polarization and incident directions. The predicted M-AuNPs were synthesized by a seed-mediated growth method, and the measured optical properties agreed well with the simulation results. The M-AuNPs were further used as photothermal agents for in vitro killing of MCF-7 cells and in vivo ablation of tumors constructed on nude mice. Nearly all cells died after they were incubated with M-AuNPs and irradiated under an 808 nm laser at a 1.0 W cm–2 for 10 min. The tumors on the nude mice were also effectively ablated without regrowth during the observation period (20 days) after PTT.

Plasmonic nanoparticle (NP)-mediated photothermal therapy (PPTT) has been explored as a minimally invasive approach to cancer therapy and has progressed from concept to the early stage of clinical trials. Better understanding of the cellular and molecular response to PPTT is crucial for improvement of therapy efficacy and advancement of clinical application. However, the molecular mechanism underlying PPTT-induced apoptosis is still unclear and under dispute. In this work, we used nuclear-targeting Au nanostars (Au NSs) as both a photothermal agent to specifically induce apoptosis in cancer cells and as a surface enhanced Raman spectroscopy (SERS) probe to monitor the time-dependent SERS spectra of MCF-7 cells which are undergoing apoptosis. Through SERS spectra and their synchronous and asynchronous SERS correlation maps, the occurrence and dynamics of a cascade of molecular events have been investigated, and a molecular signaling pathway of PPTT-induced apoptosis, including release of cytochrome c, protein degradation, and DNA fragmentation, was revealed, which was also demonstrated by metabolomics, agarose gel electrophoresis, and western blot analysis, respectively.These results indicated that PPTT-induced apoptosis undergoes an intrinsic mitochondria-mediated apoptosis pathway. Combined with western blot results, this intrinsic mitochondria-mediated apoptosis pathway was further demonstrated to be initiated by a BH3-only protein, BID. This work is beneficial for not only improving the fundamental understanding of the molecular mechanism of apoptosis induced by PPTT but also for guiding the modulation of PPTT to drive forward its clinical application.

Constructing graphdiyne-supported transition metal double-atom catalysts to address the challenges of activity and selectivity in the electrochemical nitrogen reduction reaction.