Carbon Dots: The Newest Member of the Carbon Nanomaterials Family A. L. Himaja, P. S. Karthik, and Surya Prakash Singh* [a] [a] Inorganic and Physical Chemistry Division, CSIR-Indian Institute of Chemical Technology, Uppal Road Tarnaka, Hyderabad 500007 (India), E-mail: spsingh@iict.res.in Received: October 9, 2014 Published online: ËË ABSTRACT: Carbon nanomaterials have been extensively researched in the past few years owing to their interesting properties. The massive research efforts resulted in the emergence of carbon dots, which belong to the carbon nanomaterials family. Carbon dots (C-dots) have garnered the attention of researchers mainly due to their convenient availability from organic as well as inorganic materials and also due to the novel properties they exhibit. C-Dots have been said to overcome the era of quantum dots, referring to their levels of toxicity and biocompatibility. In this review, we focus on the discovery of C-dots, their structure and composition, surface passivation to enhance their optical properties, the various synthetic methods used, their applications in different areas, and future perspectives. Emphasis has been given to greener approaches for the synthesis of C-dots in order to make them cost effective as well as to improve their biocompatibility. Keywords: carbon, green chemistry, luminescence, nanoparticles, photocatalysis 1. Introduction Carbon dots (C-dots) are novel nanomaterials recently discov- ered in the year 2004. [1] They are best known for their fluores- cence ability. These nanoparticles belong to the carbon nanomaterials family and have sizes less than 10 nm. C-Dots have been gaining much more attention from researchers due to their easy availability and simple synthesis. Their important properties include water solubility, chemical inertness, easy functionalization, photoluminescence, reduced toxicity, bio- compatibility, and resistance to photobleaching. This has made them important in the fields of optoelectronics, bioimaging, biosensing, drug delivery, solar technology and photovoltaics. C-Dots are considered to be superior to quantum dots and organic dyes. [2,3] Quantum dots face the problem of the blinking effect, which can be overcome by surface passivation or core–shell formation. [4] Bioconjugation of quantum dots increases the size, which is undesirable and also makes their delivery into cells more difficult. [5] The composition of quantum dots is considered to be toxic for in vitro studies. [6] The major concern is with the bioaccumulation of these toxic materials in the body. The use of C-dots in place of quantum dots might overcome the above problems, as they are considered to be less toxic and have enhanced optical properties. Silicon is biocompatible, nontoxic and abundantly avail- able in nature; it belongs to the same group as carbon. Similar materials to C-dots have been developed with silicon, known as silicon quantum dots. These silicon quantum dots also possess optical properties similar to C-dots, and their prominent fea- tures include size tunability, fluorescence, upconversion pho- toluminescence, high water solubility and biocompatibility. THE CHEMICAL RECORD Personal Account Chem. Rec. 2015, ••, ••–•• Wiley Online Library 1 © 2015 The Chemical Society of Japan & Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/tcr.201402090