There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

다중혈관 관상동맥 환자에서 y-문합을 이용하여 양쪽 내흉동맥만을 사용한 우회술의 조기 성적

抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Detection of chemical and biological agents plays a fundamental role in biomedical, forensic and environmental sciences1–4 as well as in anti bioterrorism applications.5–7 The development of highly sensitive, cost effective, miniature sensors is therefore in high demand which requires advanced technology coupled with fundamental knowledge in chemistry, biology and material sciences.8–13

In general, sensors feature two functional components: a recognition element to provide selective/specific binding with the target analytes and a transducer component for signaling the binding event. An efficient sensor relies heavily on these two essential components for the recognition process in terms of response time, signal to noise (S/N) ratio, selectivity and limits of detection (LOD).14,15 Therefore, designing sensors with higher efficacy depends on the development of novel materials to improve both the recognition and transduction processes. Nanomaterials feature unique physicochemical properties that can be of great utility in creating new recognition and transduction processes for chemical and biological sensors15–27 as well as improving the S/N ratio by miniaturization of the sensor elements.28

Gold nanoparticles (AuNPs) possess distinct physical and chemical attributes that make them excellent scaffolds for the fabrication of novel chemical and biological sensors (Figure 1).29–36 First, AuNPs can be synthesized in a straightforward manner and can be made highly stable. Second, they possess unique optoelectronic properties. Third, they provide high surface-to-volume ratio with excellent biocompatibility using appropriate ligands.30 Fourth, these properties of AuNPs can be readily tuned varying their size, shape and the surrounding chemical environment. For example, the binding event between recognition element and the analyte can alter physicochemical properties of transducer AuNPs, such as plasmon resonance absorption, conductivity, redox behavior, etc. that in turn can generate a detectable response signal. Finally, AuNPs offer a suitable platform for multi-functionalization with a wide range of organic or biological ligands for the selective binding and detection of small molecules and biological targets.30–32,36 Each of these attributes of AuNPs has allowed researchers to develop novel sensing strategies with improved sensitivity, stability and selectivity. In the last decade of research, the advent of AuNP as a sensory element provided us a broad spectrum of innovative approaches for the detection of metal ions, small molecules, proteins, nucleic acids, malignant cells, etc. in a rapid and efficient manner.37



Figure 1

Physical properties of AuNPs and schematic illustration of an AuNP-based detection system.



In this current review, we have highlighted the several synthetic routes and properties of AuNPs that make them excellent probes for different sensing strategies. Furthermore, we will discuss various sensing strategies and major advances in the last two decades of research utilizing AuNPs in the detection of variety of target analytes including metal ions, organic molecules, proteins, nucleic acids, and microorganisms.

/pdf/gold-nanoparticles-in-chemical-and-biological-sensing-5e2qojkdzn.pdf

Gold nanoparticles in chemical and biological sensing.

Over the past few decades, researchers have established artificial enzymes as highly stable and low-cost alternatives to natural enzymes in a wide range of applications. A variety of materials including cyclodextrins, metal complexes, porphyrins, polymers, dendrimers and biomolecules have been extensively explored to mimic the structures and functions of naturally occurring enzymes. Recently, some nanomaterials have been found to exhibit unexpected enzyme-like activities, and great advances have been made in this area due to the tremendous progress in nano-research and the unique characteristics of nanomaterials. To highlight the progress in the field of nanomaterial-based artificial enzymes (nanozymes), this review discusses various nanomaterials that have been explored to mimic different kinds of enzymes. We cover their kinetics, mechanisms and applications in numerous fields, from biosensing and immunoassays, to stem cell growth and pollutant removal. We also summarize several approaches to tune the activities of nanozymes. Finally, we make comparisons between nanozymes and other catalytic materials (other artificial enzymes, natural enzymes, organic catalysts and nanomaterial-based catalysts) and address the current challenges and future directions (302 references).

Nanomaterials with enzyme-like characteristics (nanozymes): next-generation artificial enzymes

Dispersing metal-organic framework (MOF) solids in stable colloids is crucial for their availability and processibility. Herein, we report a crown ether surface coordination approach for functionalizing the surface-exposed metal sites of MOF particles with amphiphilic carboxylated crown ether (CEC). The surface-bound crown ethers significantly improve MOF solvation without compromising the accessible voids. We demonstrate that CEC-coated MOFs exhibit exceptional colloidal dispersibility and stability in 11 distinct solvents and six polymer matrices with a wide range of polarities. The MOF-CEC can be instantaneously suspended in immiscible two-phase solvents as an effective phase-transfer catalyst and can form various uniform membranes with enhanced adsorption and separation performance, illustrating the effectiveness of crown ether coating.

Metal-Organic Framework Nanoparticles with Universal Dispersibility through Crown Ether Surface Coordination for Phase-Transfer Catalysis and Separation Membranes.

Enhancement of growth in Ulva prolifera by diurnal temperature difference combined with nitrogen enrichment.

Free radicals (ROS, NOS, etc.) play a vital role in the pathological process of many diseases from nerve and organ injury to cancer, tissue damage, and inflammatory disorders. Though moderate amount of free radicals helps maintain the normal body function and hamper the growth of bacteria, excessive amount of radicals will induce oxidative stress, resulting in damage to DNA, protein, lipid, and even the cell. Up to now, lots of nanozymes with free radical scavenging activities have been developed, including carbon nanozymes (such as fullerene, single-walled carbon nanotubes, and nitrogen-doped carbon nanodots) and metal oxide nanozymes (such as nanoceria, Fe3O4 nanoparticles, and V2O5 nanoparticles). These nanozymes have been used for radical-related therapeutics. This chapter highlights the interesting applications in therapeutics by free radical scavenging nanozymes, and discusses the related mechanisms.

Nanozymes for Therapeutics

Nanozymes are functional nanomaterials with enzyme-like activities, which have good stability and specific nanoscale properties. Among them, peroxidase-like (POD-like) nanozymes with two substrates are the biggest chunk and have been widely applied in biomedical and environmental fields. Maximum velocity (Vmax) is an essential kinetic parameter, accurate measurements of which can help in activity comparisons, mechanism studies, and nanozyme improvements. At present, the standardized assay determines the catalytic kinetics of POD-like nanozymes by a single fitting based on the Michaelis-Menten equation. However, the true Vmax cannot be confirmed by this method due to the test condition that the concentration of a fixed substrate is finite. Here, a double fitting method to determine the intrinsic Vmax of POD-like nanozymes is presented, which breaks through the limited concentration of the fixed substrate by an additional Michaelis-Menten fitting. Furthermore, a comparison of the Vmax among five typical POD-like nanozymes validates the accuracy and feasibility of our method. This work provides a credible method to determine the true Vmax of POD-like nanozymes, helping in activity comparisons and facilitating studies on the mechanism and development of POD-like nanozymes.

Determination of the Maximum Velocity of a Peroxidase-like Nanozyme.

The use of other nanomaterials beyond carbon-based nanomaterials, metal-based nanomaterials, and metal oxide-based nanomaterials for mimicking natural enzymes is discussed in this chapter. Prussian blue, metal-organic frameworks, metal chalcogenides, metal hydroxides, etc., have been selected as representative nanomaterials for mimicking peroxidase, superoxide dismutase, catalase, etc. The catalytic mechanisms are also discussed if they have been elucidated. Selected examples for in vitro biosensing, in vivo bioanalysis, and therapeutics are discussed to highlight the broad applications of these nanozymes.

Hui Wei

Papers

Metal-Organic Framework Nanoparticles with Universal Dispersibility through Crown Ether Surface Coordination for Phase-Transfer Catalysis and Separation Membranes.

Enhancement of growth in Ulva prolifera by diurnal temperature difference combined with nitrogen enrichment.

Nanozymes for Therapeutics

Determination of the Maximum Velocity of a Peroxidase-like Nanozyme.

Other Nanomaterials for Nanozymes