Cooperative Amplification of Au@FeCo as Mimetic Catalytic Nanozymes and Bicycled Hairpin Assembly for Ultrasensitive Electrochemical Biosensing

Exploring the cooperative amplification of peroxidase-like metal nanocomposites and cycled hairpin assembly is intriguing for sensitive bioanalysis. Herein, we report the first design of a unique electrochemical biosensor based on mimicking Au@FeCo nanozymes and bicycled hairpin assembly (BHA) for synergistic signal amplification. By loading the enzyme-like FeCo alloy in Au nanoparticles (AuNPs), the as-synthesized Au@FeCo hybrids display great improvement of electronic conductivity and active surface area and excellent mimic catalase activity to H2O2 decomposition into •OH radicals. The immobilization of Au@FeCo in an electrode sensing interface is stabilized via the resulting electrodeposition in HAuCl4 while efficiently accelerating the electron transfer of electroactive ferrocene (Fc). Upon the immobilization of a helping hairpin (HH) via Au–S bonds, a specific DNA trigger (T*) is introduced to activate BHA operation through competitive strand displacement reactions among recognizing hairpin (RH), signaling hairpin (SH), and HH. T* and RH are rationally released to catalyze two cycles, in which the transient depletion of dsDNA intermediates rapidly drives the progressive hairpin assemblies to output more products SH·HH. Thus, the efficient amplification of Au@FeCo mimic catalase activity combined with BHA leads to a significantly increased current signal of Fc dependent on miRNA-21 analogous to T*, thereby directing the creation of a highly sensitive electrochemical biosensor having applicable potential in actual samples

In Situ Electrodeposited Synthesis of Electrochemiluminescent Ag Nanoclusters as Signal Probe for Ultrasensitive Detection of Cyclin-D1 from Cancer Cells

Metal nanoclusters (NCs) as a new type of electrochemiluminescence (ECL) nanomaterials have attracted great attention, but their applications are limited due to relatively low luminescent efficiency and a complex preparation process. Herein, an ultrasensitive ECL biosensor for the detection of Cyclin-D1 (CCND1) was designed by utilizing in situ electrogenerated silver nanoclusters (AgNCs) as ECL emitters and Fe₃O₄–CeO₂ nanocomposites as a coreaction accelerator. The ECL luminous efficiency of AgNCs on the electrode could be significantly enhanced with the use of the Fe₃O₄–CeO₂ for accelerating the reduction of S₂O₈^2– to generate the strong oxidizing intermediate radical SO₄^•–. As a result, the assay for CCND1 detection achieved excellent sensitivity with a linear range from 50 fg/mL to 50 ng/mL and limit of detection down to 28 fg/mL. Impressively, the efficiency of Traditional Chinese Medicines (TCM), sophorae, toward MCF-7 cells was successfully investigated due to the overexpression of CCND1 in relation to the growth and metastasis of MCF-7 human breast cancer cells. In general, the proposed strategy provided an effective method for anticancer drug screening and expanded the application of metal NCs in ultrasensitive biodetection

Homoadamantane-Fused Tetrahydroquinoxaline as a Robust Electron-Donating Unit for High-Performance Asymmetric NIR Rhodamine Development

Rhodamines have emerged as a useful class of dye for bioimaging. However, intrinsic issues such as short emission wavelengths and small Stokes shifts limit their widespread applications in living systems. By taking advantage of the homoadamantane-fused tetrahydroquinoxaline (HFT) moiety as an electron donor, we developed a new class of asymmetric NIR rhodamine dyes, NNR1–7. These new dyes retained ideal photophysical properties from the classical rhodamine scaffold and showed large Stokes shifts (>80 nm) with improved chemo/photostability. We found that NNR1–7 specifically target cellular mitochondria with superior photobleaching resistance and improved tolerance for cell fixation compared to commercial mitochondria trackers. Based on NNR4, a novel NIR pH sensor (NNR4M) was also constructed and successfully applied for real-time monitoring of variations in lysosomal pH. We envision this design strategy would find broad applications in the development of highly stable NIR dyes with a large Stokes shift

Fluorescent Features and Applicable Biosensing of a Core–Shell Ag Nanocluster Shielded by a DNA Tetrahedral Nanocage

The DNA frame structure as a natural shell to stably shield the sequence-templated Ag nanocluster core (csAgNC) is intriguing yet challenging for applicable fluorescence biosensing, for which the elaborate programming of a cluster scaffold inside a DNA-based cage to guide csAgNC nucleation might be crucial. Herein, we report the first design of a symmetric tetrahedral DNA nanocage (TDC) that was self-assembled in a one-pot process using a C-rich csAgNC template strand and four single strands. Inside the as-constructed soft TDC architecture, the template sequence was logically bridged from one side to another, not in the same face, thereby guiding the in situ synthesis of emissive csAgNC. Because of the strong electron-repulsive capability of the negatively charged TDC, the as-formed csAgNC displayed significantly improved fluorescence stability and superb spectral behavior. By incorporating the recognizable modules of targeted microRNAs (miRNAs) in one vertex of the TDC, an updated TDC (uTDC) biosensing platform was established via the photoinduced electron transfer effect between the emissive csAgNC reporter and hemin/G-quadruplex (hG4) conjugate. Because of the target-interrupted csAgNC switching in three states with the spatial proximity and separation to hG4, an “on–off–on” fluorescing signal response was executed, thus achieving a wide linear range to miRNAs and a limit of detection down to picomoles. Without complicated chemical modifications, this simpler and more cost-effective strategy offered accurate cell imaging of miRNAs, further suggesting possible therapeutic applications