Covalent inorganic complexes enabled zinc blende to wurtzite phase changes in CdSe nanoplatelets.

Phase changes in colloidal semiconductor nanocrystals (NCs) are essential in material design and device applications. However, the transition pathways have yet to be sufficiently studied, and a better understanding of the underlying mechanisms is needed. In this work, a complete ligand-assisted phase transition from zinc blende (ZB) to wurtzite (WZ) is observed in CdSe nanoplatelets (NPLs). By monitoring with in situ absorption spectra along with electrospray ionization mass spectrometry (ESI-MS), we demonstrated that the transition process is a ligand-assisted covalent inorganic complex (CIC)-mediated phase transition pathway, which involves three steps, ligand exchange on ZB CdSe NPLs (Step 1), dissolution of NPLs to form CICs (Step 2), and conversion of CdSe-CIC assemblies to WZ CdSe NPLs (Step 3). In particular, CICs can be directly anisotropically grown to WZ CdSe NPL without other intermediates, following pseudo-first-order kinetics (kobs = 9.17 × 10-5 s-1). Furthermore, we demonstrated that CICs are also present and play an essential role in the phase transition of ZnS NPLs from WZ to ZB structure. This study proposes a new crystal transformation pathway and elucidates a general phase-transition mechanism, facilitating precise functional nanomaterial design.

Coupling a Wireless Bipolar Ultramicroelectrode with Nano-electrospray Ionization Mass Spectrometry: Insights into the Ultrafast Initial Step of Electrochemical Reactions.

We report a new mass spectrometric method for detecting electrogenerated intermediates. This approach is based on simultaneous activation of electrospray ionization and redox reaction on a wireless bipolar ultramicroelectrode, which is fabricated in the tip of a quartz nanopipette. The hollow structure of the ultramicroelectrode permits rapid transferring the transient species from electrode-electrolyte interfaces into the gas phase for mass spectrometric identification on the time scale of microseconds. The long-sought fleeting intermediates including TPrA.+ , whose lifetime in solution is only 200 µs, and catecholamine o-semiquinone radicals, the second-order rate constant of which is typically 109 m-1 s-1 , were successfully identified, helping clarify the previously hidden reaction pathways. Accordingly, our method may have wide applicability in exploring the dynamics of many electrochemical reactions, especially their ultrafast initial steps.

Three-dimensional CdS nanosheet-enwrapped carbon fiber framework: Towards split-type CuO-mediated photoelectrochemical immunoassay.

This work reports a customized methodology for the fabrication of 3D CdS nanosheet (NS)-enwrapped carbon fiber framework (CFF) and its utilization for sensitive split-type CuO-mediated PEC immunoassay. Specifically, the 3D CdS NS-CFF was fabricated via a solvothermal process, while the sandwich immunocomplexing was allowed in a 96 well plate with CuO nanoparticles (NPs) as the signaling labels. The subsequent release of the Cu2+ ions was directed to interact with the CdS NS, generating trapping sites and thus inhibiting its photocurrent generation. In such a protocol, the 3D CdS NS-CFF photoelectrode could not only guarantee its sufficient contact with the Cu2+-containing solution but also supply plenty CdS surface for the Cu2+ ions. Because of the target-dependent release of the Cu2+ ions and its proper coupling with the 3D CdS NS-CFF photoelectrode, a sensitive split-type PEC immunoassay was achieved for the detection of brain natriuretic peptide (BNP). This proposed system exhibited good stability and selectivity, and its applicability for real sample analysis was also demonstrated via comparison with the commercial BNP enzyme-linked immunosorbent assay (ELISA) kit. We expect this work could stimulate more interest in the design and utilization of 3D photoelectrodes for novel PEC bioanalysis.

An improvement in scanning electrochemical microscopy based on a plasmon-accelerated electrochemical reaction.

We demonstrate an approach using a plasmon-accelerated electrochemical reaction to improve the performance of scanning electrochemical microscopy.

Three-Dimensional CdS@Carbon Fiber Networks: Innovative Synthesis and Application as a General Platform for Photoelectrochemical Bioanalysis.

This Letter reports a novel synthetic methodology for the fabrication of three-dimensional (3D) nanostructured CdS@carbon fiber (CF) networks and the validation of its feasibility for applications as a general platform for photoelectrochemical (PEC) bioanalysis. Specifically, 3D architectures are currently attracting increasing attention in various fields due to their intriguing properties, while CdS has been most widely utilized for PEC bioanalysis applications because of its narrow band gap, proper conduction band, and stable photocurrent generation. Using CdS as a representative material, this work realized the innovative synthesis of 3D CdS@CF networks via a simple solvothermal process. Exemplified by the sandwich immunoassay of fatty-acid-binding protein (FABP), the as-fabricated 3D CdS@CF networks exhibited superior properties, and the assay demonstrated good performance in terms of sensitivity and selectivity. This work features a novel fabrication of 3D CdS@CF networks that can serve as a general platform for PEC bioanalysis. The methodology reported here is expected to inspire new interest for the fabrication of other 3D nanostructured Cd-chalcogenide (S, Se, Te)@CF networks for wide applications in biomolecular detection and beyond.

Copper-catalyzed C-H/N-H cross-coupling reactions for the synthesis of 3-heteroaryl quinoxalin-2(1H)-ones.

An effective copper-catalyzed direct C-H/N-H cross-coupling of quinoxalin-2(1H)-ones with diverse unprotected 2-quinoxalinones and 2-quinolinones has been developed. This protocol provides a convenient route, with broad substrate scope, good functional group tolerance, and high atom economy, to various important quinoxalin-2(1H)-one-containing biheteroaryls, which are privileged structures in many biologically active compounds.

Plasmon-enhanced Raman spectroscopic metrics for in situ quantitative and dynamic assays of cell apoptosis and necrosis.

Apoptosis and necrosis are distinct cell death processes related to many cellular pathways. In situ, quantitatively and dynamically monitoring such processes may provide vitally important information for cell studies. However, such a method still remains elusive, even though current immunochemical methodologies have developed extremely valuable tools. Herein, we demonstrate Raman spectroscopic metrics for validating and quantifying apoptotic and necrotic cells based on their distinct molecular vibrational fingerprints. It not only allows us to quantify apoptotic and necrotic cell populations in situ in adherent cell samples, but also to be capable of continuously monitoring the dynamical processes of apoptosis and necrosis at the same time in one sample. This method provides comparable results with the "gold standard" of flow cytometry, moreover, with several incomparable advantages. Our work offers a powerful new tool for cell apoptosis and necrosis assays and is expected to become a benchmark technology in biological and medical studies.

Synchronized Polarization Induced Electrospray: Comprehensively Profiling Biomolecules in Single Cells by Combining both Positive-Ion and Negative-Ion Mass Spectra.

In this work, a synchronized polarization induced electrospray ionization (SPI-ESI) method is developed and applied for the analysis of single-cell samples. In SPI-ESI, periodic alternating current square wave voltage (AC-SWV) is applied to induce the bipolar spray and both positive-ion and negative-ion mass spectra are obtained through one measurement by synchronizing the mode of mass analyzer with the bipolar spray process. Compared with conventional nanoelectrospray ionization (nESI, flow rate < 1000 nL/min), ultralow spray flow rate (pico-electrospray ionization, pESI, flow rate < 1000 pL/min) is achieved in SPI-ESI without loss of its sensitivity. The decrease of flow rate prolongs the MS signal duration from single-cell samples to acquire ms(2) data for components determination. To our knowledge, this is the first time to successfully achieve comprehensive analysis of single-cell samples by combining both positive-ion and negative-ion mass spectra. Ultimately, 86 components are profiled from single Allium cepa cells and 94 components are profiled from single PC-12 cells.