In contrast to one-photon microscopy, two-photon probe-based fluorescent imaging can provide improved three-dimensional spatial localization and increased imaging depth. Consequently, it has become one of the most attractive techniques for studying biological events in living cells and tissues. However, the quantitation of these probes is primarily based on single-emission intensity change, which tends to be affected by a variety of environmental factors. Ratiometric probes, on the other hand, can eliminate these interferences by the built-in correction of the dual emission bands, resulting in a more favorable system for imaging living cells and tissues. Herein, for the first time, we adopted a through-bond energy transfer (TBET) strategy to design and synthesize a small molecular ratiometric two-photon fluorescent probe for imaging living cells and tissues in real time. Specifically, a two-photon fluorophore (D-π-A-structured naphthalene derivative) and a rhodamine B fluorophore are directly connected by electronically conjugated bond to form a TBET probe, or Np-Rh, which shows a target-modulated ratiometric two-photon fluorescence response with highly efficient energy transfer (93.7%) and two well-resolved emission peaks separated by 100 nm. This novel probe was then applied for two-photon imaging of living cells and tissues and showed high ratiometric imaging resolution and deep-tissue imaging depth of 180 μm, thus demonstrating its practical application in biological systems.

Noble metals, especially gold, have been widely used in plasmon resonance applications. Although silver has a larger optical cross section and lower cost than gold, it has attracted much less attention because of its easy corrosion, thereby degrading plasmonic signals and limiting its applications. To circumvent this problem, we report the facile synthesis of superstable AgCu@graphene (ACG) nanoparticles (NPs). The growth of several layers of graphene onto the surface of AgCu alloy NPs effectively protects the Ag surface from contamination, even in the presence of hydrogen peroxide, hydrogen sulfide, and nitric acid. The ACG NPs have been utilized to enhance the unique Raman signals from the graphitic shell, making ACG an ideal candidate for cell labeling, rapid Raman imaging, and SERS detection. ACG is further functionalized with alkyne-polyethylene glycol, which has strong Raman vibrations in the Raman-silent region of the cell, leading to more accurate colocalization inside cells. In sum, this work provides a simple approach to fabricate corrosion-resistant, water-soluble, and graphene-protected AgCu NPs having a strong surface plasmon resonance effect suitable for sensing and imaging.

Alkaline phosphatases are a group of enzymes that play important roles in regulating diverse cellular functions and disease pathogenesis. Hence, developing fluorescent probes for in vivo detection of alkaline phosphatase activity is highly desirable for studying the dynamic phosphorylation in living organisms. Here, we developed the very first reaction-based near-infrared (NIR) probe (DHXP) for sensitive detection of alkaline phosphatase activity both in vitro and in vivo. Our studies demonstrated that the probe displayed an up to 66-fold fluorescence increment upon incubation with alkaline phosphatases, and the detection limit of our probe was determined to be 0.07 U/L, which is lower than that of most of alkaline phosphatase probes reported in literature. Furthermore, we demonstrated that the probe can be applied to detecting alkaline phosphatase activity in cells and mice. In addition, our probe possesses excellent biocompatibility and rapid cell-internalization ability. In light of these prominent properties, we envision that DHXP will add useful tools for investigating alkaline phosphatase activity in biomedical research.

Permissionless blockchains such as Bitcoin have excelled at financial services. Yet, adversaries extract monetary value from the mesh of decentralized finance (DeFi) smart contracts. Some have characterized the Ethereum peer-to-peer network as a dark forest, wherein broadcast transactions represent prey, which are devoured by generalized trading bots.While transaction (re)ordering and front-running are known to cause losses to users, we quantify how much value was sourced from blockchain extractable value (BEV). We systematize a transaction ordering taxonomy to quantify the USD extracted from sandwich attacks, liquidations, and decentralized exchange arbitrage. We estimate that over 2 years, those trading activities yielded 28.80M USD in profit, divided among 5, 084 unique addresses. While arbitrage and liquidations might appear benign, traders can front-run others, causing financial losses to competitors.To provide an example of a generalized trading bot, we show a simple yet effective automated transaction replay algorithm capable of replacing unconfirmed transactions without the need to understand the victim transactions' underlying logic. We estimate that our transaction replay algorithm could have yielded a profit of 51, 688.33 ETH (17.60M USD) over 2 years on past blockchain data.We also find that miners do not broadcast 1.64% of their mined transactions and instead choose to mine them privately. Privately mined and non-shared transactions, cannot be front-run by other traders or miners. We show that the largest Ethereum mining pool performs arbitrage and seemingly tries to cloak its private transaction mining activities. We therefore provide evidence that miners already extract Miner Extractable Value (MEV), which could destabilize the blockchain consensus security, as related work has shown.

In contrast to small molecules, DNA and RNA macromolecules can be accurately formulated with base “elements” abbreviated as A, T, U, C, and G. However, the development of functionally artificial bases can result in the generation of new biomaterials with unique properties and applications. Therefore, we herein report the design and synthesis of a photoresponsive base as a new functional or molecular “element” for constructing DNA nanomolecules. The new base is made by fusion of an azobenzene with a natural T base (zT). zT, a new molecular element, is not only the most size-expanded T analogue but also a photoresponsive base capable of specific self-assembly through hydrogen bonding. Our results showed that stable and selective self-assembly of double-stranded DNAs occurred through zT-A base pairing, but it could still be efficiently dissociated by light irradiation. The photoresponsive DNA bases will provide the versatility required for constructing desired DNA nanomolecules and nanodevices.