Molecular self-assembly is the spontaneous association of molecules under equilibrium conditions into stable, structurally well-defined aggregates joined by noncovalent bonds. Molecular self-assembly is ubiquitous in biological systems and underlies the formation of a wide variety of complex biological structures. Understanding self-assembly and the associated noncovalent interactions that connect complementary interacting molecular surfaces in biological aggregates is a central concern in structural biochemistry. Self-assembly is also emerging as a new strategy in chemical synthesis, with the potential of generating nonbiological structures with dimensions of 1 to 10(2) nanometers (with molecular weights of 10(4) to 10(10) daltons). Structures in the upper part of this range of sizes are presently inaccessible through chemical synthesis, and the ability to prepare them would open a route to structures comparable in size (and perhaps complementary in function) to those that can be prepared by microlithography and other techniques of microfabrication.

Molecular self-assembly and nanochemistry: A chemical strategy for the synthesis of nanostructures

As a new generation of artificial enzymes, nanozymes have the advantages of high catalytic activity, good stability, low cost, and other unique properties of nanomaterials. Due to their wide range of potential applications, they have become an emerging field bridging nanotechnology and biology, attracting researchers in various fields to design and synthesize highly catalytically active nanozymes. However, the thorough understanding of experimental phenomena and the mechanisms beneath practical applications of nanozymes limits their rapid development. Herein, the progress of experimental and computational research of nanozymes on two issues over the past decade is briefly reviewed: (1) experimental development of new nanozymes mimicking different types of enzymes. This covers their structures and applications ranging from biosensing and bioimaging to therapeutics and environmental protection. (2) The catalytic mechanism proposed by experimental and theoretical study. The challenges and future directions of computational research in this field are also discussed.

Recent Advances in Nanozyme Research

Nanozymes have advantages over natural enzymes, such as facile production on large scale, long storage time, low costs, and high stability in harsh environments. Carbon nanomaterials (CNMs), including fullerenes, carbon nanotubes, graphene, carbon quantum dots, and graphene quantum dots, have become a star family in materials science. As a new class of nanozymes, the catalytic activity of CNMs and their hybrids has been extensively reported. In this Minireview, recent progress of CNMs based artificial enzymes, focusing on those with peroxidase-like activity, has been summarized. The enzymatic properties, catalytic mechanisms, and novel applications of CNM nanozymes in sensing, therapy, and environmental engineering are discussed in detail. Additionally, we also highlight the remaining challenges and unsolved problems. With the fast development of bionanotechnology, the unique enzymatic properties and advantages of CNM nanozymes have received much attention and will continue to be an active and challenging field for the years to come.

Carbon Nanozymes: Enzymatic Properties, Catalytic Mechanism, and Applications.

The sol-gel process

Reduced graphene oxide has similar mechanical, optoelectronic or conductive properties to pristine graphene because it possesses a heterogeneous structure comprised of a graphene-like basal plane that is additionally decorated with structural defects and populated with areas containing oxidized chemical groups. The graphene-like properties make reduced graphene oxide a highly desirable material to be used in a plethora of sensorial, biological, environmental or catalytic applications as well as optoelectronic and storage devices. To further advance the development of the existent technologies and to design novel and better applications based on reduced graphene oxide, it is first necessary to understand which synthetic routes and processing strategies are suitable to significantly boost specific properties of this material alone or as a component in various composites. Therefore, in this work, we review the most important categories of recent applications based on reduced graphene oxide, with the emphasis on the relationship between the enhanced composite/device functionality and methods used to synthesize, to functionalize and/or to process and to structure reduced graphene oxide.

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Reduced graphene oxide today

Nanofabrication has been a critical area of research in the last two decades and has found wide-ranging application in improvising material properties, sensitive clinical diagnostics, and detection, improving the efficiency of electron transport processes within materials, generating high energy densities leading to pulse power, novel therapeutic mechanisms, environmental remediation and control. The continued improvements in the various fabrication technologies have led to realization of highly sensitive nanostructure-based devices. The fabrication of nanostructures is in principle carried out primarily using top-down or bottom-up approaches. This chapter summarizes the important bottom-up nanofabrication processes for realizing nanostructures and also highlights the recent research conducted in the domain of therapeutics and diagnostics.

Fabrication of Nanostructures with Bottom-up Approach and Their Utility in Diagnostics, Therapeutics, and Others

A novel paper-based device for colorimetric detection of uric acid was developed based on the peroxidase-like activity of gold nanoparticles–graphene conjugates (AuNPs–GO). Theoretical models were utilized for designing a device that was further verified by simulation and experimentation. Detection of uric acid was then carried out by initially soaking the paper in an AuNPs–GO solution and subsequently pipetting TMB–H2O2 solution on it. Detection was achieved by measuring the color change when uric acid interacted with AuNPs–GO. A significant reduction in the blue coloration of the paper to white color was observed in a brief time of 5 minutes. Moreover, a very low detection limit of 4 ppm for uric acid was obtained on paper by visualization with the naked eye. The assembly of AuNPs within the GO matrix resulted in many active sites, which were the reason for the low detection limit. The practicality of the device was also examined by testing it on several blood serum samples. The results were in agreement with clinical results and also showed a high selectivity towards uric acid. The device provides a real-time, rapid and easy-to-use platform for the detection of uric acid for clinical purposes.

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Development of a paper-based analytical device for colorimetric detection of uric acid using gold nanoparticles–graphene oxide (AuNPs–GO) conjugates

Dengue virus, a Flaviviridae family member, has emerged as a major worldwide health concern, making its early diagnosis imperative. Lateral flow immunoassays have been widely employed for point-of-care diagnosis of dengue because of their rapid naked eye readouts, ease of use, and cost-effectiveness. However, they entail a drawback of low sensitivity, limiting their usage in clinical applications. Herein, we report a novel lateral flow immunoassay for detection of dengue leveraging on the benefits of gold decorated graphene oxide sheets as detection labels and a tapered nitrocellulose membrane. The developed assay allows for rapid (10 min) and sensitive detection of dengue NS1 with a detection limit of 4.9 ng mL−1, ∼11-fold improvement over the previously reported values. Additionally, the clinical application of the developed assay has been demonstrated by testing it for dengue virus spiked in human serum. The reported lateral flow immunoassay shows significant promise for early and rapid detection of several target diseases.Dengue virus, a Flaviviridae family member, has emerged as a major worldwide health concern, making its early diagnosis imperative. Lateral flow immunoassays have been widely employed for point-of-care diagnosis of dengue because of their rapid naked eye readouts, ease of use, and cost-effectiveness. However, they entail a drawback of low sensitivity, limiting their usage in clinical applications. Herein, we report a novel lateral flow immunoassay for detection of dengue leveraging on the benefits of gold decorated graphene oxide sheets as detection labels and a tapered nitrocellulose membrane. The developed assay allows for rapid (10 min) and sensitive detection of dengue NS1 with a detection limit of 4.9 ng mL−1, ∼11-fold improvement over the previously reported values. Additionally, the clinical application of the developed assay has been demonstrated by testing it for dengue virus spiked in human serum. The reported lateral flow immunoassay shows significant promise for early and rapid detection of se...

Tapered lateral flow immunoassay based point-of-care diagnostic device for ultrasensitive colorimetric detection of dengue NS1.

Herein we report the facile synthesis of a quaternary nanocomposite material (hemin–silver coated gold–graphene oxide) and evaluate its efficacy as a novel peroxidase mimetic. A strong synergistic coupling between the various components involved results in an excellent catalytic performance of this nanocomposite. A comparison of the different morphologies of the silver coated gold particles strongly indicates a greater sensitivity of the nanostar morphology over the nanoparticle morphology owing to its high surface-to-volume ratio. Furthermore, the immobilization of hemin and silver coated gold nanostars on a graphene oxide sheet framework imposes a nanoscale confinement, effectively augmenting the overall catalytic performance of the composite. The nanocomposite followed typical Michaelis–Menten theory and electrochemical analysis suggested facilitation of accelerated electron transfer between TMB and H2O2. A KM value of 2.75 mM−1 suggested a high affinity of the nanocomposite towards TMB. Furthermore, a 2.8 times increase in the maximum reaction rate compared to HRP established the high catalytic activity of the nanocomposite. The nanocomposite demonstrates a nanomolar range sensitivity towards hydrogen peroxide and glucose (limit of detection = 1.26 nM and 425 nM). The nanocomposites have also been employed to develop a paper-based point-of-care diagnostic device. The device has been utilized for detection of glucose in human blood serum samples with satisfactory results.

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Facile synthesis of Au@Ag–hemin decorated reduced graphene oxide sheets: a novel peroxidase mimetic for ultrasensitive colorimetric detection of hydrogen peroxide and glucose

Acoustic metamaterials hold great potential for attenuation of low frequency acoustic emissions. However, a fundamental challenge is achieving high transmission loss over a broad frequency range. In this work, we report a double negative acoustic metastructure for absorption of low frequency acoustic emissions in an aircraft. This is achieved by utilizing a periodic array of hexagonal cells interconnected with a neck and mounted with an elastic membrane on both ends. An average transmission loss of 56 dB under 500 Hz and an overall absorption of over 48% have been realized experimentally. The negative mass density is derived from the dipolar resonances created as a result of the in-phase movement of the membranes. Further, the negative bulk modulus is ascribed to the combined effect of out-of-phase acceleration of the membranes and the Helmholtz resonator. The proposed metastructure enables absorption of low frequency acoustic emissions with improved functionality that is highly desirable for varied applications.

Pulak Bhushan

Papers

Fabrication of Nanostructures with Bottom-up Approach and Their Utility in Diagnostics, Therapeutics, and Others

Development of a paper-based analytical device for colorimetric detection of uric acid using gold nanoparticles–graphene oxide (AuNPs–GO) conjugates

Tapered lateral flow immunoassay based point-of-care diagnostic device for ultrasensitive colorimetric detection of dengue NS1.

Facile synthesis of Au@Ag–hemin decorated reduced graphene oxide sheets: a novel peroxidase mimetic for ultrasensitive colorimetric detection of hydrogen peroxide and glucose

Double negative acoustic metastructure for attenuation of acoustic emissions