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.

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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

The invention relates to an unmarked colorimetric method for determining thrombin based on gold nano-probe and nucleic acid aptamer, which belongs to the technical field of analytical chemistry. The nucleic acid aptamer uncombined with the thrombin is in a free stretching state, the single-chain nucleic acid aptamer can stabilize gold nano-particles to protect the gold nano-particles from being aggregated by added salts, and the gold nano-particles are claret red at that time; and on the contrary, the nucleic acid aptamer combined with the thrombin has a 'quadripole/duplex helix' structure, cannot react with the gold nano-particles and then cannot protect the salt-induced gold nano-particles from being aggregated, and the gold nano-particles are sky blue at that time. Thus, the detection of the thrombin can be achieved through the color changes of the gold nano-particles. The detection limit on the thrombin by the method is 0.83 nano-mole per liter, and the linearity range is between 0and 167 nano-mole per liter. The colorimetric method for detecting the thrombin has the advantages of high selectivity, high sensitivity, simple operation and no need of complex instruments.

Unmarked colorimetric method for determining thrombin based on gold nano-probe and nucleic acid aptamer

Designing metal-metal oxide heteronanostructures with synergistic and superior activities (unattainable in the case of a single entity) is of great interest for a wide range of technological applications. Traditional synthetic strategies typically require reducing agents, stabilizing ligands, or high temperature reductive treatment to produce oxide-supported metals. Herein, a facile noble metal deposition strategy is developed to produce silver, gold, and platinum nanocrystals on the surface of hollow mesoporous cerium oxide nanospheres without any pretreatment. Unlike the galvanic replacement reaction, the developed protocol employs the innate reductive potential of CeO2 to produce a high density of ultrafine noble metal nanocrystals homogeneously immobilized onto the surface of CeO2 nanospheres. The multienzyme-like activities (i.e., superoxide dismutase-like and catalase-like) of CeO2@metal nanostructures, originating from CeO2 and metal nanoparticles, were effectively utilized for anti-inflammatory therapies in two in vivo models. This oxygen vacancy-mediated reduction strategy can be generalized to produce diverse metal-metal oxide nanostructures for a wide range of applications.

Nanoceria as an Electron Reservoir: Spontaneous Deposition of Metal Nanoparticles on Oxides and Their Anti-inflammatory Activities.

The field of nanobiocatalysis focuses on improving catalytic efficiency of biocatalysts or developing artificial enzymes using nanotechnology and nanomaterials, broadening their applications in an unfriendly environment, and in vitro and in vivo disease diagnosis and treatment. Nanobiocatalysis typically contains enzyme immobilization on nanocarriers and artificial enzymes based on nanomaterials (nanozymes). The latter is one of the representative interdisciplinary fields in nanobiology. On one hand, natural enzymes can be immobilized on nanocarriers to improve catalytic efficiency and stability. On the other hand, nanomaterials themselves may exhibit intrinsic enzyme-like properties which catalyze the biochemical reactions of the substrates of natural enzymes, providing a new generation of artificial enzymes. Nanobiocatalysis has been successfully explored, and has identified great potential in many important fields, including biomedicine, chemical industry, pharmacy, and environment engineering. In this review, we briefly summarize recent progress and developing trend for both enzyme immobilization on nanocarriers and nanozymes.

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Current developments and trends in nanobiocatalysis

While an in-depth understanding of the biological behavior of engineered nanoparticles (NPs) is of great importance for their various applications, it remains challenging to quantitatively characterize NP-protein interactions in a simple and high-throughput manner. In the present work, we propose a new, colorimetric approach capable of quantitatively analyzing the adsorption of proteins onto the surface of NPs by their distinct peroxidase-mimic properties. Taking cationic AuNPs as an example, we demonstrate that this colorimetric method is capable of evaluating NP-protein interactions in a simple and high-throughput manner in multiwell plates. Important binding parameters (e.g., the binding affinity) of three different serum proteins (bovine serum albumin, transferrin, and lysozyme) as well as human serum to AuNPs with three different sizes (average diameters of 5, 10, and 15 nm) have been obtained. Based on a quantitative analysis of NP-protein interactions, we observe that the binding affinity and the inhibition efficiency of the nanozyme activity of AuNPs are strongly affected by the characteristics of proteins as well as the sizes of NPs. These results illustrate the great potential of the present colorimetric method as a simple, low-cost, and high-throughput platform for quantitatively investigating NP-protein interactions.

Hui Wei

Papers

Unmarked colorimetric method for determining thrombin based on gold nano-probe and nucleic acid aptamer

Nanoceria as an Electron Reservoir: Spontaneous Deposition of Metal Nanoparticles on Oxides and Their Anti-inflammatory Activities.

Current developments and trends in nanobiocatalysis

High-Throughput Colorimetric Analysis of Nanoparticle-Protein Interactions Based on the Enzyme-Mimic Properties of Nanoparticles.

Correction to 2D-Metal-Organic-Framework-Nanozyme Sensor Arrays for Probing Phosphates and Their Enzymatic Hydrolysis.