Materials Today Chemistry
Volume 12, June 2019, Pages 282-314
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Progress in microwave-assisted synthesis of quantum dots (graphene/carbon/semiconducting) for bioapplications: a review

https://doi.org/10.1016/j.mtchem.2019.03.001Get rights and content

Highlights

  • This review article provides knowledge about microwave-assisted synthesis and some selected bio applications.

  • Microwave-assisted heating is a simple, fast and inexpensive process to produce large quantity of quantum dots.

  • MW-assisted synthesis approach provides QDs formation in various media.

  • MW-assisted approach provides uniform distribution of energy, shorter reaction times and high reproducibility.

Abstract

Quantum dots (QDs) are small nanometer-sized (<10 nm) pure or composite materials with excellent novel properties, thus making them interesting and emerging candidates for new and exceptional applications in biomaterials research fields. As emerging members of QDs, carbon (especially, carbon QDs and graphene QDs) and semiconducting QDs have attracted greater attention owing to their excellent properties, unique size, versatile surface, and biocompatibility with nanotechnology. In this work, a comprehensive overview on the possibilities and achievements in the field of carbon and semiconducting QDs obtained by only microwave (MW)-assisted for biomedical purposes is provided. This specific literature review provides knowledge about MW-assisted synthesis and some selected bioapplication of carbon and semiconducting QDs. Currently, the MW-assisted fabrication of QDs represents a growing research field in nanomaterial research. MW-assisted approach for QD synthesis has been studied in details as this approach has several advantages such as uniform distribution of energy inside the reaction vessel, shorter reaction times, environmentally friendly and energy-saving technique, high reproducibility, and excellent control over experimental parameters. Also, a comprehensive overview is provided in this review, which contains the possibilities and achievements using MW-assisted heating approaches. This article updates the latest synthesis progress as well as applications and also comments all the challenges and perspective in this emerging research area.

Introduction

Quantum dot (QD) materials have high potential for the development of novel analytical methodologies for device applications owing to their small nanosizes usually < 10 nm and better to be < 5 nm for several specific applications [1], [2], [3], [4], [5]. Over the past few decades, QDs obtained from different materials have attracted increasing attentions in many research fields, such as solar cells, optoelectronic transistor components, and fluorescent biological labels because of their unique size-tunable optical and electronic properties [6], [7], [8], [9], [10], [11], [12], [13], [14], [15], [16], [17]. Carbon-based QDs such as graphene QDs (GQDs), carbon QDs (CQDs), and several types of semiconducting QDs become a potential new platform in designing and tuning fluorescent probes [18], [19], [20], [21]. The zero-dimensional GQDs, a new type of QD system, represent an active area of great interest and are produced using top–down approaches such as chemical ablation from graphene, electrochemical synthesis, oxygen plasma treatment, and so on [22], [23], [24], [25], [26], [27], [28], [29], [30], [31], [32]. The semiconductor QDs, especially cadmium selenide (CdSe), cadmium telluride (CdTe), and cadmium sulfide (CdS) among others, have been researched extensively because of their fluorescent properties in infrared, near-infrared, and visible regions [33], [34], [35], [36], [37], [38], [39], [40], [41], [42], [43], [44], [45], [46], [47]. Recently, several works are devoted to the synthesis of excellent selective and size-sensitive QD structures [41], [48], [49]. Various methods have been used for the preparation of these QD structures using different chemicals; however, the adopted synthesis approaches are time consuming and require sophisticated high-valued equipment [50], [51], [52], [53], [54]. Therefore, there is a need for the development of a rapid, simple, sensitive and selective method for large-scale synthesis of various kinds of QDs.

Rapid and facile synthetic approaches are extremely essential for scientists to perform more accurate experiments within a short time period without releasing much heat in the environment. Microwave (MW)-assisted synthesis fulfills the promise of being a rapid and facile technique as an alternative energy input source and has been widely used because of its control for internal and volumetric heating of materials [55], [56]. Currently, research studies are focused on the MW-assisted preparation of organic/inorganic nanostructured materials in various media (liquid and gaseous) as there is of great importance and significance for future rapid development of the academic and industrial related research fields. Also, researchers are constantly challenged to consider more environmentally friendly methods for the fabrication of new material structures, components, and devices. For the last few years, several research articles have been published on MW-assisted synthesis of nanostructured materials, such as metal [57], [58], [59], nanoporous materials [60], [61], colloidal nanocrystals [62], inorganic nanomaterials [63], [64], semiconducting nanomaterials [65], [66], [67], and polymer nanocomposites [68]. The MW-assisted synthesis is highly used in the field of carbon research as carbon materials interact strongly with MW radiation producing fast heating rates and localized heating. Thus, nanostructured carbon materials [69], [70], [71], [72], [73], [74], [75], [76], [77], [78], metal oxide nanoparticles supported on graphene [79], [80], [81], [82], [83], [84], [85], [86], [87], [88], [89], [90], [91], [92], [93], [94], [95], and metal oxide supported on carbon nanotubes (CNTs) have been obtained by MW-assisted synthesis [86], [96], [97], [98], [99]. Besides metal oxide supported CNTs and graphene, other types of carbon materials have been synthesized and investigated for various applications, e.g. three-dimensional (3D) carbon composite, activated carbons, and carbon nanocapsules (CNCs) [100]. The MW-assisted synthesis is an effective method for QD preparation, and several reports confirm the feasibility and potential of this technique [101], [102], [103], [104], [105], [106], [107], [108].

This review article is mainly focused on the possibilities and accomplishments of latest advances in MW-assisted synthesis method of organic and semiconducting QDs used for bioapplications. The MW-assisted route is one of the most promising clean, low-temperature, and economic synthesis routes. One of the supreme and noteworthy advantages of this method, which constraints on specific shape and size of QD dependence on the experimental parameters, is also brought to focus. We have also reviewed some selected application of QDs relating to biocompatible devices. These MW-assisted formations of QDs are rapidly being applied to existing and emerging technologies and have significant role in many research areas. The QDs synthesized by MW using either top–down or bottom–up approaches are broadly adopted for various research applications, including drug delivery, biosensors, bioimaging, fuel cells, supercapacitors, photocatalyst, photovoltaics and so on as shown in schematic Fig. 1.

Section snippets

MW-assisted synthesis: rapid, facile, and cost-effective approach

The MW consists of synchronized perpendicular oscillations of electric and magnetic fields [109]. These MW energy absorbed by carbon materials and transformed in the form of heat is called dielectric heating [110]. Dielectric heating can take place either using resonance modes of absorption or using relaxation mechanisms as a result of phase lag between the motion of the polar species in the material and the alternating MW field [111], [112]. This heating differs from the conventional heating,

GQDs and CQDs

The approaches used for synthesizing GQDs and CQDs with tunable size and shape can be classified into two major groups: top–down and bottom–up approaches. For the top–down approach, it is essential to carve up a large size particle into its compositional subsystems in a reverse engineering fashion [149]. Some of the methods used are electrochemical oxidation [150], [151], [152], [153], hydrothermal route [154], [155], [156], laser ablation [86], [157], [158], [159], electrochemical and plasma

Semiconducting QDs

Recently, luminescent semiconductor QDs (sizes < 10 nm) have gained attention owing to their unique properties that arise due to the quantum confinement of electrons and large surface area. Various kinds of semiconducting QD materials (combination of II-VI, III-V, and IV-VI group elements) such as Si, PbS, CdS, CdSe, CdTe, InAs, In2S3, PbSeS, copper indium sulfide (CuInS2), AgBiS2, CdSexTe1-x, CdS/CdSe, CdTe/CdSe, and so on have been rigorously explored [31], [191], [216], [217], [218], [219],

Multifunctional bioapplications of various types of QDs synthesized by MW approach

Various types of QDs obtained by different methods, including MW irradiation, either in their pure or functionalized form or having their surface capped/tagged with some biological molecules are tested for nanomarker applications in biology and medicine [306], [307], [308], [309], [310], [311], [312]. They are used as biosensors, in vivo imaging/mapping of the cell, early cancer diagnostics, drug delivery, gene therapy, attaching other biomolecules, and so on. Some of these applications are

Conclusions

The QD-based materials contain small pieces of organic/inorganic materials whose physical dimensions are so confined that they have a quantum-induced finite band gap. This review illustrates the MW-assisted heating for synthesis of various organic and inorganic QDs, which are highly used in bio-related application as biosensors, bioimaging, drug delivery, and cancer treatment. The properties of the MW-assisted synthesized QDs can be changed and more sensitively tuned by changing/modifying their

Acknowledgments

R.K. acknowledges the Japan Society for the Promotion of Science (JSPS; Standard) for international postdoctoral fellowship (P18063), and financial support (JSPS KAKENHI Grant No. 18F18063). D.P.S. acknowledges financial support from Millennium Institute for Research in Optics (MIRO). R.S. and S.A.M. would like to acknowledge CNPq and FAPESP (Brazil) for financial support. R.K. would like to dedicate this research work to the memory of late Prof. Yoshiyuki Suda, Toyohashi University of

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