Accessing the spatiotemporal heterogeneities of single nanocatalysts by optically imaging gas nanobubbles

Catalysts that catalyze the generation of products in the gas phase, especially those involved in the hydrogen evolution reaction (HER), hold great promise for ecofriendly and sustainable energy development. In general, gas chromatography is widely used to measure catalytic activity. Unfortunately, it gives an averaged output that washes out the heterogeneities among individuals. To assess the unique catalytic properties at the single nanoparticle level, various methods based on single particle catalysis have been proposed. Over the past fifteen years, tremendous breakthroughs have been achieved, which uncovered hidden spatial and temporal heterogeneities. Although powerful, effectively quantifying the activities of single HER nanocatalysts remains challenging because of the fast diffusion of hydrogen (H₂). In 2017, a novel approach based on a nanobubble indicator was proposed to correlate the kinetics of gas bubble evolution with the catalytic activities of individual nanoentities during the HER process. Since then, a plethora of optical microscopy techniques have been utilized to monitor dynamically evolved nanobubbles and to measure the catalytic activities of single HER catalysts. In this minireview, we summarized state-of-the-art optical microscopy for in operando imaging of dynamic nanobubbles involved in gas-generating reactions while highlighting some important discoveries, including the blinking photocatalytic activity and heterogeneous distribution of active sites. Finally, challenges and future perspectives in this promising field were identified.     

单颗粒光散射显微成像技术在生化医药分析中的应用

等离子体纳米颗粒(PNPs)具有体积小、易表面修饰、生物相容性好、毒性低等优点,在生物传感、生物成像、疾病诊断、肿瘤治疗、材料科学等领域得到了广泛的应用。PNPs的光散射光学性质可以通过调节其大小、组成、形貌和微环境来控制,可用于生化和药物分析。此外,由于单粒子散射显微技术具有高空间分辨率和高灵敏度,借助PNPs具有的独特局域表面等离子体共振(LSPR)特性,可在单颗粒水平进行实时成像。根据PNPs的大小、组成、形态、微环境或耦合变化引起的信号变化,研究人员发展了多种显微成像分析方法,主要分为4种,包括散射光谱的波长位移、单粒子散射强度的变化、高通量RGB分析和计数方法。基于纳米颗粒LSPR散射光谱位移变化的方法准确、灵敏,但需要昂贵的单颗粒散射光谱仪和复杂的操作。基于纳米颗粒散射强度变化的方法简单可行,但易受纳米颗粒粒径和曝光时间等因素的影响。高通量RGB分析方法灵敏度高、成本低,但不适用于颜色变化不明显的单颗粒分析,且重复性差。单粒子计数法灵敏度高,但有时粒子分布不均匀,背景杂质的干扰限制了方法的准确度。因此,这4种定量方法各有优缺点。此外,近年来逐渐发展了一些新的定量方法。例如,研究人员开发了新的时间分辨分析定量方法,并将暗场显微镜与偏振器、滤光片等光学器件相结合以消除背景干扰,以及与电化学、拉曼等仪器相结合以扩大应用范围。此外,为提高分析方法的准确度和灵敏度,暗场显微镜与深度学习、云计算、人工智能等现代计算机科学技术的结合,越来越受到人们的欢迎。基于以上原因,该文重点介绍了单粒子光散射显微镜在生化和药物分析领域的应用,总结了近年来的最新研究进展,讨论了单粒子光散射显微镜在定量分析中的几种主要定量方法,提出了未来的发展趋势,以期为相关研究领域的新人提供一定的学术参考。     

Donor-Acceptor Typed AIE Luminogens with Near-infrared Emission for Super-resolution Imaging

Aggregation-induced emission(AIE)luminogens(AIEgens)with high brightness in aggregates exhibit great potentials in biological imaging,but these AIEgens are seldom applied in super-resolution biological imaging,especially in the imaging by using the structural illumination microscope(SIM).Based on this consideration,we synthesized the donor-acceptor typed AIEgen of DTPA-BTN,which not only owns high brightness in the near-infrared(NIR)emission region from 600 nm to 1000 nm(photoluminescence quantum yield,PLQYs=11.35%),but also displays excellent photo-stability.In addition,AIE nanoparticles based on 4,7-ditriphenylamine-[1,2,5]-thiadiazolo[3,4-c]pyridine(DTPA-BTN)were also prepared with highly emissive features and excellent biocompatibility.Finally,the developed DTPA-BTN-based AIE nanoparticles were applied in the super-resolution cellular imaging via SIM,where much smaller full width at half-maximum values and high signal to noise ratios were obtained,indicating the superior imaging resolution.The results here imply that highly emissive AIEgens or AIE nanoparticles can be promising imaging agents for super-resolution imaging via SIM.     

激活型有机光声造影剂的应用

光声(PA)成像作为一种结合了光学和声学成像优势的新型成像方式,具有深层组织穿透和高空间分辨率等优点,在重大疾病的早期影像诊断方面有着巨大的应用前景。然而传统的PA造影剂依然存在信噪比低、选择性及特异性差等不足,容易产生假阳性诊断结果。激活型PA造影剂可以有效的降低背景噪声,并提升成像的灵敏度和特异性,是目前PA造影剂设计与构筑的主要趋势。本综述首先简单介绍了PA成像的原理,然后结合近几年在金属离子、酶、活性氮和活性氧等相关方面的生物成像应用,梳理了可激活探针在不同微环境中的响应方式。最后,对激活型探针在PA成像中的应用进行了总结和展望。     

Organic Nanocrystals Based on a Solid-emission-tunable AIEgen for Cell Imaging

The development of fluorescent nanocrystals based on organic small molecules is of great importance in bioimaging due to the merits of easy modification,high brightness and excellent photostability,however suffering from the emission-detrimental aggregation-caused quenching(ACQ)effect.Herein,we successfully designed and synthesized an AIE-active di(N,N-dimethylaniline)-dibenzofulvene(named as NFTPE),which exhibits the crystallization-induced emission enhancement(CIEE)effect.Interestingly,two types of yellow-and orange-emissive crystals for NFTPE were obtained,exhibiting aggregation microenvironment-dependent emission tuning in the solid state.Single-crystal analysis and density functional theory(DFT)calculations reveal that different aggregation microenvironments result in the distinct molecular conformation for various emission.Excitingly,the crystallization of NFTPE in an aqueous solution under the assistance of amphiphilic PEG polymer matrices could be monitored in situ by the fluorescence changes,facilitating the preparation of NFTPE nanocrystals(NFTPE-NCs)by adjusting the aggregation microenvironment.The obtained NFTPE-NCs exhibit the superior performance in cell imaging in respect to high brightness,photostability,and biocompatibility,thus demonstrating the potential in bioimaging applications.     

Advanced Nanomaterials for Multimodal Molecular Imaging

The development of multimodal molecular imaging contrast agents based on versatile nanomaterials has recently attracted much attention in disease diagnosis and therapeutic delivery. Contrast agents made from nanoparticles and used for multimodal imaging in vivo provide a multidimensional pathophysiological overview of diseases. This review summarizes recently developed advanced nanomaterials for multimodal molecular imaging. We comprehensively discuss these nanoparticle contrast agents in terms of their targeting modalities, limitations in clinical translation and future directions.     

Expanding the Ligand Classes Used for Mn(II) Complexation: Oxa-aza Macrocycles Make the Difference

We report two macrocyclic ligands based on a 1,7-diaza-12-crown-4 platform functionalized with acetate (tO2DO2A²⁻) or piperidineacetamide (tO2DO2AM^Pip) pendant arms and a detailed characterization of the corresponding Mn(II) complexes. The X−ray structure of [Mn(tO2DO2A)(H₂O)]·2H₂O shows that the metal ion is coordinated by six donor atoms of the macrocyclic ligand and one water molecule, to result in seven-coordination. The Cu(II) analogue presents a distorted octahedral coordination environment. The protonation constants of the ligands and the stability constants of the complexes formed with Mn(II) and other biologically relevant metal ions (Mg(II), Ca(II), Cu(II) and Zn(II)) were determined using potentiometric titrations (I = 0.15 M NaCl, T = 25 °C). The conditional stabilities of Mn(II) complexes at pH 7.4 are comparable to those reported for the cyclen-based tDO2A²⁻ ligand. The dissociation of the Mn(II) chelates were investigated by evaluating the rate constants of metal exchange reactions with Cu(II) under acidic conditions (I = 0.15 M NaCl, T = 25 °C). Dissociation of the [Mn(tO2DO2A)(H₂O)] complex occurs through both proton− and metal−assisted pathways, while the [Mn(tO2DO2AM^Pip)(H₂O)] analogue dissociates through spontaneous and proton-assisted mechanisms. The Mn(II) complex of tO2DO2A²⁻ is remarkably inert with respect to its dissociation, while the amide analogue is significantly more labile. The presence of a water molecule coordinated to Mn(II) imparts relatively high relaxivities to the complexes. The parameters determining this key property were investigated using ¹⁷O NMR (Nuclear Magnetic Resonance) transverse relaxation rates and ¹H nuclear magnetic relaxation dispersion (NMRD) profiles.     

一种用于活细胞中检测Zn2+的萘酚席夫碱类荧光探针

设计合成了1种基于C=N异构化和螯合荧光增强机理（CHEF）的Zn²⁺荧光探针BMO和NBMO,其结构经¹H NMR,¹³C NMR,¹H-¹H COSY,HSQC,IR和HRMS进行了表征。光谱分析实验结果显示,探针对Zn²⁺均具有较好的选择性和灵敏度,检出限分别为30和21 nmol·L^-1。在0~20 μmol·L^-1浓度的范围内,BMO和NBMO的荧光强度与Zn²⁺浓度可呈良好的线性关系。NBMO-Zn²⁺配合物单晶结构和Job曲线证实该探针与Zn²⁺以1：1配位。NBMO被成功应用于活细胞中Zn²⁺的检测。     

A Rhodamine-based fluorescent sensor for chromium ions and its application in bioimaging

A rhodamine-based sensor (1) has been developed for the detection of chromium ions. Cr³⁺-induced opening of the rhodamine spirocycle in sensor (1) led to the distinct colorimetric and fluorescence responses. Among all the tested ions, only Cr³⁺ generated a significant fluorescence enhancement of up to 13-fold, which indicated the high selectivity of 1. Sensor (1) was successfully applied in the in vivo fluorescence imaging of Cr³⁺ in C. elegans. The results provided solid evidences for the future estimation of Cr³⁺ in environmental applications and tobacco samples.     

Polyethylene glycol phospholipids encapsulated silicon 2,3-naphthalocyanine dihydroxide nanoparticles (SiNcOH-DSPEPEG(NH2) NPs) for single NIR laser induced cancer combination therapy

Currently, the combination of photothermal therapy (PTT) and photodynamic therapy (PDT) has emerged as a powerful technique for cancer treatment. However, most examples of combined PTT and PDT reported use multi-component nanocomposites under excitation of separate wavelength, resulting in complex treatment process. In this work, a novel theranostic nanoplatform (SiNcOH-DSPE-PEG(NH₂) NPs) has been successfully developed by coating silicon 2,3-naphthalocyanine dihydroxide (SiNcOH) with DSPE-PEG and DSPE-PEG-NH₂ for photoacoustic (PA) imaging-guided PTT and PDT tumor ablation for the first time. The as-prepared single-agent SiNcOH-DSPE-PEG(NH₂) NPs not only have good water solubility and biocompatibility, but also exhibit high photothermal conversion efficiency and singlet oxygen generation capability upon 808 nm NIR laser irradiation. In addition, owing to their high absorption at NIR region, the SiNcOH-DSPE-PEG(NH₂) NPs can also be employed as an effective diagnostic nanoagent for photoacoustic (PA) imaging. In vitro and in vivo experimental results clearly indicated that the simultaneously combined PTT and PDT under the guidance of PA imaging with single NIR laser excitation can effectively kill cancer cells or eradicate tumor tissues. Taking facile synthesis and high efficiency in cancer treatment by SiNcOH-DSPE-PEG(NH₂) NPs into consideration, our study provides a promising strategy to realize molecular imaging-guided combination therapy.