Fluorescent carbon nanoparticles or carbon quantum dots (CQDs) are a new class of carbon nanomaterials that have emerged recently and have garnered much interest as potential competitors to conventional semiconductor quantum dots. In addition to their comparable optical properties, CQDs have the desired advantages of low toxicity, environmental friendliness low cost and simple synthetic routes. Moreover, surface passivation and functionalization of CQDs allow for the control of their physicochemical properties. Since their discovery, CQDs have found many applications in the fields of chemical sensing, biosensing, bioimaging, nanomedicine, photocatalysis and electrocatalysis. This article reviews the progress in the research and development of CQDs with an emphasis on their synthesis, functionalization and technical applications along with some discussion on challenges and perspectives in this exciting and promising field.

Carbon quantum dots and their applications

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

Taking advantage of exceptional attributes, such as being easy-to-operate, economical, sensitive, portable, and simple-to-construct, in recent decades, considerable attention has been devoted to the integration of recognition elements with electronic elements to develop electrochemical sensors and biosensors.Various electrochemical devices, such as amperometric sensors, electrochemical impedance sensors, and electrochemical luminescence sensors as well as photoelectrochemical sensors, provide wide applications in the detection of chemical and biological targets in terms of electrochemical change of electrode interfaces.

With remarkable achievements in nanotechnology and nanoscience, nanomaterial-based electrochemical signal amplifications have great potential of improving both sensitivity and selectivity for electrochemical sensors and biosensors. First of all, it is well-known that the electrode materials play a critical role in the construction of high-performance electrochemical sensing platforms for detecting target molecules through various analytical principles. Furthermore, in addition to electrode materials, functional nanomaterials can not only produce a synergic effect among catalytic activity, conductivity, and biocompatibility to accelerate the signal transduction but also amplify biorecognition events with specifically designed signal tags, leading to highly sensitive biosensing. Significantly, extensive research on the construction of functional electrode materials, coupled with numerous electrochemical methods, is advancing the wide application of electrochemical devices. For example, Walcarius et al. highlighted the recent advances of nano-objects and nanoengineered and/or nanostructured materials for the rational design of biofunctionalized electrodes and related (bio)sensing systems.1 The attractiveness of such nanomaterials relies on their ability to act as effective immobilization matrices and their intrinsic and unique features as described above. These features combined with the functioning of biomolecules contribute to the improvement of bioelectrode performance in terms of sensitivity and specificity. Our group recently presented a general overview of nanomaterial-enhanced paper-based biosensors including lateral-flow test-strip and paper microfluidic devices.2 With different kinds of nanoparticles (NPs), paper-based biosensor devices have shown a great potential in the enhancement of sensitivity and specificity of disease diagnosis in developing countries.

This Review focuses on recent advances in electrochemical sensors and biosensors based on nanomaterials and nanostructures during 2013 to 2014. The aim of this effort is to provide the reader with a clear and concise view of new advances in areas ranging from electrode engineering, strategies for electrochemical signal amplification, and novel electroanalytical techniques used in the miniaturization and integration of the sensors. Moreover, the authors have attempted to highlight areas of the latest and significant development of enhanced electrochemical nanosensors and nanobiosensors that inspire broader interests across various disciplines. Electrochemical sensors for small molecules, enzyme-based biosensors, genosensors, immunosensors, and cytosensors are reviewed herein (Figure ​(Figure1).1). Such novel advances are important for the development of electrochemical sensors that open up new avenues and methods for future research. We recommend readers interested in the general principles of electrochemical sensors and electrochemical methods to refer to other excellent literature for a broad scope in this area.3,4 However, due to the explosion of publications in this active field, we do not claim that this Review includes all of the published works in the past two years and we apologize to the authors of excellent work, which is unintentionally left out.



Figure 1

Schematic illustration of electrochemical sensors and biosensors based on nanomaterials and nanostructures, in which electrochemical sensors for small molecular, enzyme-based biosensors, genosensors, immunosensors, and cytosensors are demonstrated.

http://pubs.acs.org/doi/pdf/10.1021/ac5039863

Electrochemical Sensors and Biosensors Based on Nanomaterials and Nanostructures

The present review is devoted to summarizing the recent advances (2015-2017) in the field of metal-catalysed group-directed C-H functionalisation In order to clearly showcase the molecular diversity that can now be accessed by means of directed C-H functionalisation, the whole is organized following the directing groups installed on a substrate Its aim is to be a comprehensive reference work, where a specific directing group can be easily found, together with the transformations which have been carried out with it Hence, the primary format of this review is schemes accompanied with a concise explanatory text, in which the directing groups are ordered in sections according to their chemical structure The schemes feature typical substrates used, the products obtained as well as the required reaction conditions Importantly, each example is commented on with respect to the most important positive features and drawbacks, on aspects such as selectivity, substrate scope, reaction conditions, directing group removal, and greenness The targeted readership are both experts in the field of C-H functionalisation chemistry (to provide a comprehensive overview of the progress made in the last years) and, even more so, all organic chemists who want to introduce the C-H functionalisation way of thinking for a design of straightforward, efficient and step-economic synthetic routes towards molecules of interest to them Accordingly, this review should be of particular interest also for scientists from industrial R&D sector Hence, the overall goal of this review is to promote the application of C-H functionalisation reactions outside the research groups dedicated to method development and establishing it as a valuable reaction archetype in contemporary R&D, comparable to the role cross-coupling reactions play to date

/pdf/a-comprehensive-overview-of-directing-groups-applied-in-543u6d0g60.pdf

A comprehensive overview of directing groups applied in metal-catalysed C-H functionalisation chemistry.

Reactive oxygen (ROS) and nitrogen (RNS) species cause oxidative and nitrosative stresses, respectively. These stresses are implicated not only in diverse physiological processes but also in various pathological processes, including cancer and neurodegenerative disorders. In addition, some ROS and RNS in the environment are pollutants that threaten human health. As a consequence of these effects, sensitive methods, which can be employed to selectively monitor ROS and RNS in live cells, tissues and organisms as well as in environmental samples, are needed so that their biological roles can be understood and their concentrations in environmental samples can be determined. In this review, fluorescent, luminescent and colorimetric ROS and RNS probes, which have been developed since 2011, are comprehensively discussed.

Recent progress in the development of fluorescent, luminescent and colorimetric probes for detection of reactive oxygen and nitrogen species

Hydrothermal synthesis of highly fluorescent carbon nanoparticles from sodium citrate and their use for the detection of mercury ions

Fluorescent carbon nanoparticles for the fluorescent detection of metal ions.

Colorimetric detection of mercury, lead and copper ions simultaneously using protein-functionalized gold nanoparticles.

A simple and label-free colorimetric method for cadmium ions (Cd2+) detection using unmodified gold nanoparticles (AuNPs) is reported. The unmodified AuNPs easily aggregate in a high concentration of NaCl solution, but the presence of glutathione (GSH) can prevent the salt-induced aggregation of AuNPs. When Cd2+ is added to the stable mixture of AuNPs, GSH, and NaCl, Cd2+ can coordinate with 4× GSH as a spherical shaped complex, which decreases the amount of free GSH on the surface of gold nanoparticles to weaken the stability of AuNPs, and AuNPs will easily aggregate in high-salt conditions. On the basis of the mechanism, we design a simple, label-free colorimetric method using AuNPs accompanied by GSH in a high-salt environment to detect Cd2+ in water and digested rice samples.

Label-free colorimetric detection of cadmium ions in rice samples using gold nanoparticles.

The advances of nanomaterials have provided exciting technologies and novel materials for protein detection, based on the unique properties associated with nanoscale phenomena such as plasmon resonance, catalysis and energy transfer. This article reviews a series of nanomaterials including nanoparticles, nanofibers, nanowires, and nanosheets, and evaluates their performances in the application for protein detection, focusing on approaches that realize ultrasensitive detection. Many of these nanomaterials were used to analyze clinically relevant protein biomarkers. Their detection in the picomolar, femtomolar or even zeptomolar regime has been realized, sometimes even with naked-eye readout. We summarize the detection methods and results according to materials and targets, review the current challenges, and discuss the solution in the context of technological integration such as combining nanomaterials with microfluidics, and classical analytical technologies.

Yongming Guo

Papers

Hydrothermal synthesis of highly fluorescent carbon nanoparticles from sodium citrate and their use for the detection of mercury ions

Fluorescent carbon nanoparticles for the fluorescent detection of metal ions.

Colorimetric detection of mercury, lead and copper ions simultaneously using protein-functionalized gold nanoparticles.

Label-free colorimetric detection of cadmium ions in rice samples using gold nanoparticles.

Nanomaterials for Ultrasensitive Protein Detection