Contents

Cover

Title page

Copyright page

Preface

Chapter 1: Carbon Dots: Discovery, Synthesis and Characterization

1.1 Background
1.2 Introduction to QD
1.3 Carbon QD and Graphene QD
1.4 Various Methods of Synthesis of Carbon Dots
1.5 Characterization of Carbon Dots
1.6 Summary

Chapter 2: Properties of Carbon Dots

2.1 Introduction
2.2 Optical Properties
2.3 Chemically Inert
2.4 Easy Functionalization
2.5 Water Solubility
2.6 Low Toxicity
2.7 Biocompatibility
2.8 Summary

Chapter 3: Carbon Dots and Conjugates

3.1 Introduction
3.2 Why Conjugation of Carbon Dots?
3.3 Types of Carbon Dot Conjugates and Their Applications
3.4 Summary

Chapter 4: CD as Drug Delivery Vehicle

4.1 Introduction
4.2 Considerations in Using CD as Drug Delivery Vehicle
4.3 Designs of CD-Based Drug Delivery System
4.4 Carbon Dots for Delivery of Anti-Cancer Drug
4.5 CD for Drug Delivery to Neurodegenerative Disease
4.6 CD for Gene Therapy
4.7 CD to Monitor Delivery of SiRNA
4.8 Challenges in Using CD as Drug Delivery Vehicle
4.9 Suitability of CD-Conjugated Drugs
4.10 Summary

Chapter 5: Carbon Dots for Cell Imaging and Diagnostics

5.1 Introduction
5.2 Bioimaging
5.3 CDs as Sensor
5.4 Concluding Remarks

Chapter 6: Suitability of Carbon Dots as Payload for Plants

6.1 Introduction
6.2 Suitability of Carbon Dots as a Payload for Plant
6.3 Carbon Dots and Plant Fertilizer
6.4 Need for Sensor to Detect
6.5 Carbon Dots and Foliar Application of Drugs on Plants
6.6 Carbon Dots as Trojan Horse to Penetrate Foliar Surface for Therapeutic Molecule Delivery
6.7 Concluding Remarks

References

Index

End User License Agreement

List of Illustrations

Chapter 1

Figure 1.1: Band gap and exciton.
Figure 1.2: Schematic diagram of electron occupancy of allowed energy bands for given materials.
Figure 1.3: Density of states and their dimensions.
Figure 1.4: The four stages of CDs formation using glycine as a model precursor molecule: dehydration, polymerization, carbonization, and passivation. (Reprinted with permission from [45]; Copyright © 2010 John Wiley and Sons)
Figure 1.5: Pulsed laser irradiation of nanocarbon source dispersed in solvent to synthesize CD. (Reproduced with permission from [29])
Figure 1.6: Schematic representation of the synthesis of CDs in reverse micelles: (a) formation of water-in-oil reverse micelles, (b) hydrolytic polymerization, (c) carbonization and (d) in-situ passivation by hexadecylamine. (Reproduced with permission from [75])
Figure 1.7: Schematic representation of synthesis of CDs using mesoporous silica as host particles. (Reproduced with permission from [76])
Figure 1.8: Schematic representation of (a) CD coated with metal film and (b) corresponding secondary electron profile.
Figure 1.9: TEM image of CDs. Inset shows HRTEM image of a single dot. (Reproduced with permission from [82])
Figure 1.10: (a) TEM image of CDs obtained from neem gum and (b) SAED image of neem gum CDs (Reproduced with permission from [83])
Figure 1.11: AFM image of CDs.
Figure 1.12: Schematic diagram of a spectrophotometer.
Figure 1.13: (a) UV-Vis absorption spectra of CD and (b) Emission spectra when excited from 300–400 nm. Inset is normalized emission spectra. (Reproduced with permission from [85])
Figure 1.14: Absorption and fluorescence spectra of (a) Bare CDs, (b) Passivated CDs and (c) Plot of fluorescence intensity of bare CDs (π) and modified CDs (■) vs. concentration. (Reproduced with permission from [86])
Figure 1.15: FTIR spectra of (a) Biological CDs and (b) Ciprofloxacin attached CDs. (Reproduced with permission from [72])
Figure 1.16: A typical XRD graph of CDs.
Figure 1.17: (a) XPS, (b) C1s and (c) O1s spectra of as-prepared CDs. (Reproduced with permission from [44])
Figure 1.18: Schematic representation of DPI. (Reproduced with permission from [87])
Figure 1.19: Raman spectra of CDs displaying its defective nature based on D-band and G-band intensities. (Reproduced with permission from [50])

Chapter 2

Figure 2.1: CD powder synthesized in Sharon’s wcRnb Lab.
Figure 2.2: Aqueous solution of CDs under visible light and under UV (365 nm) light showing fluorescence [synthesized in Sharon’s wcRnb Lab].
Figure 2.3: UV-Vis spectra of CDs showing characteristic absorption peak between 210–300 nm.
Figure 2.4: (a) Absorption of a photon causing an electron to move o an excited state, (b) the electron moves down in energy due to non-radiative processes, and (c) the electron recombines with the hole and gives off a photon.
Figure 2.5: Photoluminescence of CDs.
Figure 2.6: Jablonski energy diagram.
Figure 2.7: Quantum size effect and increase in quantum dot size. (Source: Physics Open Lab; Modern DIY Physics Laboratory for Science Enthusiast, English Post; Quantum Dots: A True “Particle in a Box” System)
Figure 2.8: The electronic transitions observed in one-photon or two-photon excitation for multiphoton bioimaging.
Figure 2.9: Upconversion photoluminescence by CDs. Facile preparation and upconversion luminescence of graphene QD. (Reproduced with permission from [109]; Copyright © 2012, Royal Society of Chemistry)
Figure 2.10: Electronic energy states of a semiconductor when it goes from (a) the single molecule to (c) the bulk material, passing through (b) the nanomaterial stage where quantum confinement is observed. (d) The effect of the existence of surface-defect states in the electronic energy state of the bulk material. (Adapted from [111])
Figure 2.11: (a) The on-off switching observed by alternating 401 nm and 639 nm laser excitation. (b) Photon counts in a hybrid photomultiplier detector show photo decay and subsequent gain in intensity (photoswitch) using a 401 laser. The blue arrow shows the 401 nm pulses (detected in channel 1) and the red bars show the photo decay with a 639 nm laser (detected in channel 2). The 4th and 6th cycles, with a slightly higher exposure time of blue light, result in a better recovery of fluorescence. (Reproduced with permission from [114])
Figure 2.12: Possible catalytic mechanism for TiO₂/CDs under visible light. (Reproduced with permission from [118])

Chapter 3

Figure 3.1: Examples of conjugated systems.
Figure 3.2: NH₂ functionalized carbon dot; here, NH₂ can act as a linker.
Figure 3.3: Carbon dots synthesized from folic acid as precursor by acid (H₃PO₄(H₂O) and alkali (NaOH) treatment. (Adapted with permission from [162])
Figure 3.4: SEM image of CDs/SiO₂ nanocomposites. Insert is the corresponding SEM image of a typical single particle. (Adapted with permission from [183])
Figure 3.5: UV-Vis spectra of meso-SiO₂/CD synthesized using rice husk. Inset shows photoluminescence spectra excited at (a) 250, (b) 350, and (c) 450 nm. (Adapted with permission from [184])
Figure 3.6: Layer-by-layer assembled silver/CD plasmonic luminescent nanoparticles. (Adapted from [185])
Figure 3.7: Schematic representation of the preparation of the CDs-adsorbed Ag@SiO2 composite nanoparticles. (Adapted with permission from [186])
Figure 3.8: Schematic representation of Pi detection based on the off–on fluorescence probe of CDs adjusted by Eu³⁺. (Adapted with permission from [199])
Figure 3.9: Multistimuli-responsive CDs prepared by Yin et al. [189].
Figure 3.10: Covalent conjugation of Rhodamine B dyes with CD. (Adapted with permission from [140])
Figure 3.11: (a) SWCNT and (b) MWCNT.
Figure 3.12: Schematic diagram of hydrogen peroxide detection by CD decorated MWCNT.
Figure 3.13: UV-Vis spectra of (i) Ciprofloxacin, (ii) CD, (iii) Cipro-CDs conjugate, (iv) Post dialysis Cipro-CD conjugate and (b) PL spectra of respective samples. (Adapted with permission from [72])
Figure 3.14: (b-i and b-ii) SEM images and (b-iii) HRTEM image of carbon dot synthesized using gum arabic. (Adapted with permission from [72])
Figure 3.15: Chemical bonds between CDs and streptomycin conjugate proposed by Sharon.
Figure 3.16: UV-Visible spectra of (a) CDs synthesized from phenylalanine, showing sharp peak at 232 nm and a broad peak at 276 nm, confirming the formation of CDs and (b) CD-CysHCl and CD-CysHCl-HP complex, with respect to peaks observed in the case of CD-CysHCl complex, there was a slight blue shift of 1 nm (from 224 to 223 nm) and altered humps at 273, 330 and 375 nm specific to HP and CD-CysHCl-HP complex. The peak intensity is elevated, which is due to masking of functional groups and attachment of HP onto the surface of CDs. (c) Photoluminescence spectra of CDs, CDs-CysHCl and CDsCysHCl haloperidol complex; labeled as i, ii and iii respectively. Inset showing the same under UV light. (Adapted with permission from [71])
Figure 3.17: FTIR spectra of (a) CDs, (b) Cysteamine-HCl, (c) Haloperidol, (d) Conjugate of CD and Cysteamine-HCl, (e) Conjugate of CD+ Cysteamine-HCl + Haloperidol. (Adapted with permission from [71])
Figure 3.18: Schematic diagram showing quenching of CDs fluorescence due to FRET between CDs and curcumin. (Adapted with permission from [244])
Figure 3.19: Schematic diagram of the intracellular release behavior of doxorubicin from the CDs–Hep/DOX drug delivery system. (Adapted with permission from [251])

Chapter 4

Figure 4.1: Schematic representation of targeting cancer cells using folic acid-conjugated CDs. (Adapted from [50])
Figure 4.2: Formation of CD-PEI and CD-PEI/pDNA complex. (Adapted with permission from [260])

Chapter 5

Figure 5.1: (a) UV–Vis absorption and normalized photoluminescence spectra of the CDs and t-CDs. Inset: photograph of the CD (left) and t-CD (right) aqueous solutions under visible light and 365 nm UV light, respectively. (b) Emission spectra of the CDs with excitation at different wavelengths. (Reproduced from [283])
Figure 5.2: Proposed mechanism of environment-dependent blue emission of CDs (Reproduced with permission from [291]; Copyright © 2014 The Royal Society of Chemistry)
Figure 5.3: In-vivo fluorescence imaging. (a) In vivo fluorescence images of a CDs-injected mouse. The images were taken under various excitation wave length at 455, 523, 595, 605, 635, 661, and 704 nm. Red and green represent the fluorescent signals of CDs and the tissue autofluorescence, respectively. (b) Signal-to-background separation of the spectral image taken under the NIR (704 nm) excitation. The fluorescence of CDs was well separated from the tissue autofluorescence background. (Reproduced with permission from [288]; Copyright © 2012 John Wiley and Sons)
Figure 5.4: Images of cells taken in (left panel) Bright field and (right panel) epifluorescence microscope. (a-b) HeLa cells treated with functionalized CD with FA complex; (c-d) HeLa cells treated with only functionalized CD-dots (without FA); (e-f) Vero cells with functionalized CD-FA complex. (Adapted with permission from [50])
Figure 5.5: PL images of MCF-10A cells treated with CDs (0.5x, 0.18 mg mL–¹) under (b) blue (360–380 nm), (c) green (460–480 nm), and (d) red (510–530 nm) light excitation. Insets to (b), (c), and (d): amplified PL images of single cells. (Reproduced with permission from [296]; Copyright © 2013 Royal Society of Chemistry)
Figure 5.6: Schematic of the synthesis and structure of HA-Cds. (Reproduced from [299]; Copyright © 2017 The Royal Society of Chemistry)
Figure 5.7: C6 glioma cells exhibiting fibroblast morphology.
Figure 5.8: In-vivo and ex-vivo imaging of glioma-bearing mice after tail intravenous injection of CD-Asp. (a) Whole body distribution of CD-Asp as a function of time after injection. (b) Three-dimensional reconstruction of CD-Asp distribution in the brain 20 min after injection. (c) Ex-vivo imaging of the brain 90 min after the injection of CD Asp. (Reproduced from [305])
Figure 5.9: Graphic representation of CD-BSA-Dox delivering doxorubicin in cytopkasm and nucleus. (Adapted with permission from [50])
Figure 5.10: (a) Schematic representation of the self-assembly process of graphene oxide-cationic quaternized carbon dots (GOQCD) hybrid materials in water. (b) Transmission electron microscopy image of the hybrid material GO-QCD (with a GO:QCDs ratio of 0.5, coded as GO250QCD500). The scale bar in (b) corresponds to 1 mm, the inset (top right) shows the high-resolution transmission electron microscopy image. Fluorescence images of mouse fibroblast NIH/3T3 cells containing: (c) quaternized carbon dots (QCDs); hybrid materials GO-QCD with a GO:QCDs ratios of (d) 0.5; (e) 1. Concentration used: 100 g/mL, time of incubation with cells: 1 day. Scale bars: 200_m. (Modified with permission from [307]; Copyright © 2014 Royal Society of Chemistry.)
Figure 5.11: Amphiphilic CDs for bacteria labeling. (a) Schematic representation of the labeling methodology of bacteria with fluorescent CDs; (b) Multicolor fluorescence microscopy images of E. coli incubated with amphiphilic CDs at different excitation/emission wavelengths. Blue: excitation at 365 nm, emission filter 420 LP; green: excitation at 470 nm, emission filter 510 LP; magenta: excitation at 510 nm, emission filter 545 nm; red: excitation at 540 nm, emission filter 605 nm. Scale bar corresponds to 5_m. Exposure time was 0.5 s in all experiments. (Reproduced with permission from [161]; Copyright © 2015 Royal Society of Chemistry)
Figure 5.12: Nitrogen-doped CDs with high fluorescence as an active site, selectively and sensitively detects pH values, Ag^I, Fe^III, and H₂O₂. (Adapted from [315])
Figure 5.13: Schematic representation of the fluorescence of the branched poly(ethylenimine) (BPEI)-functionalized CDs (BPEI-CDs) quenched by Cu²⁺ ions. (Reproduced with permission from [316]; Copyright © 2012 The American Chemical Society)
Figure 5.14: Schematic representation of the ratiometric fluorescent Cu2⁺ nanosensor based on CDs@Rhodamine B-doped silica nanoparticles. (Reproduced with permission from [318]; Copyright © 2014 The American Chemical Society)
Figure 5.15: Sensing principle of the N-doped CDs-based probe for Fe³⁺. (Adapted with permission from [322])
Figure 5.16: Diagram for sensing of phosphate based on the modified CDs mediated by Eu³⁺ ion. (Reproduced with permission from [199]; Copyright © 2011 Royal Society of Chemistry)
Figure 5.17: Schematic representations of the sensing of H₂S (Reprinted with permission from [330]; Copyright © 2013 Royal Society of Chemistry)
Figure 5.18: Graphical abstract of a facile method based on CDs for sensitive detection of H₂Q as proposed by Ni et al. (Reproduced with permission from [333]; Copyright © 2015 Elsevier)
Figure 5.19: Stokes effect. (Source: Wikipedia)
Figure 5.20: Schematic diagram of the electrons’ migration routes. (Adapted with permission from [335])
Figure 5.21: Laser scanning confocal microscopy images of ethylenediamine-carbon dots-labeled L929 cells. (Reproduced with permission from [347]; Copyright © 2012 Royal Society of Chemistry)
Figure 5.22: (a) UV-Vis absorption spectrum of levodopachrome; the inset is the corresponding digital photograph under visible light. (b) Superposed graphs of the UV spectrum of levodopachrome and photoluminescence spectrum of CDs. (c) Schematic illustration of the mechanism of detection of L-DOPA by CDs. (Reproduced with permission from [352]; Copyright © 2015 Royal Society of Chemistry.

Chapter 6

Figure 6.1: Possible applications and uses of carbon dots in agriculture.
Figure 6.2: Tomato seedlings germinated in vitro with (in black culture media) and without CNT in the culture media. (Reproduced from [371])
Figure 6.3: (a) Raman spectra of carbon nanodots (CND) showing the characteristic D and G band; (b) FTIR of the water-soluble CND; (c) SEM images of water-soluble CND; (d) EDX of CND showing the major presence of carbon and small amount of oxygen. (Reproduced with permission from [372]; Copyright © 2014 Springer)
Figure 6.4: XPS survey scan of N-doped CDs. (a) XPS scanning spectra show three major peaks of carbon, nitrogen and oxygen. XPS high resolution survey scan of (b) C1s, (c) N1s and (d) O1s region of N-doped CDs. (Reproduced from [70])
Figure 6.5: (a) Green beans were added into solution; bean sprouts photo under (b) daylight and (c) 365 nm UV beam after a few days growth. From left to right: pure water, N-doped CDs solution (our method), N-doped CDs solution (citric acid and urea). (Reproduced from [373])
Figure 6.6: Schematic of cell wall structure.
Figure 6.7: Schematic representation of plasmodesma.
Figure 6.8: TEM image of nanoparticles taken up into ryegrass root (Reproduced from [375])
Figure 6.9: Mechanisms of phosphorus (P) solubilization by phosphate-solubilizing bacteria.
Figure 6.10: Graphical illustration of monitoring plant water status using a microfluidic-printed electro-mechanical sensor of stomata. (Reproduced from [395])
Figure 6.11: Graphical illustration of monitoring free chlorine in water. (Reproduced from [313])
Figure 6.12: (a) Epidermal cuticular layer of a leaf showing open stomata and (b) schematic diagram showing details of the stomata.
Figure 6.13: (a) Epidermal layer of a leaf showing trichomes and (b) schematic diagram showing details of trichome.
Figure 6.14: Possible proposed sites of attachment of streptomycin to carbon dot.
Figure 6.15: A rod-shaped Erwinia amylovora bacterium.

Scrivener Publishing
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Advances in Nanotechnology & Applications

Series Editor: Madhuri Sharon

The unique properties of nanomaterials encourage the belief that they can be applied in a wide range of fields, from medical applications to electronics, environmental sciences, information and communication, heavy industries like aerospace, refineries, automobile, consumer and sports good, etc.

This book series will focus on the properties and related applications of nanomaterials so as to have a clear fundamental picture as to why nanoparticles are being tried instead of traditional methods. Since nanotechnology is encompassing various fields of science, each book will focus on one topic and will detail the basics to advanced science for the benefit of all levels of researchers.

Series Editor: Madhuri Sharon, Director, Walchand Centre for Research in Nanotechnology & Bionanotechnology
W.H. Marg, Ashok Chowk, Solapur 413 006
Maharashtra,
India

E-mail:sharonmadhuri@gmail.com

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Library of Congress Cataloging-in-Publication Data

ISBN 978-1-119-46010-7

Preface

I would like to begin this preface with a quote from Sir Isaac Newton, which justifies our efforts in writing this book i.e. “What we know is a drop, what we don’t know is an ocean”. Carbon Dots (CD) is an emerging luminescent nanomaterial, to which scientists have employed tremendous efforts to study its use in health care systems, as a nontoxic alternative to replace traditional heavy metal-based Quantum Dots (QD). In this book, we have tried to compile the knowledge available for basic understanding of quantum mechanics and concepts related to the phenomenon, the discovery, properties, applications, as well as the present drawbacks of QD. CDs have many advantages, including low toxicity, chemical inertness, biocompatibility and no photobleaching that makes it a suitable theranostic agent for humans. In addition, typical CDs contain a large amount of hydrophilic carboxyl and hydroxyl groups, imparting them with excellent water solubility and multi-functionality. For enhancing the efficacies of CD for various applications, during synthesis, CDs have been conjugated with inorganic, organic, biogenic and synthesized drugs and antibiotics. Moreover, efforts are devoted to the surface passivation of CD with different molecules, so as to make it stable and at the same time also help in increasing the quantum yield, which is one of the most important aspects for biological applications. We have also explored the possibility of use of CD as a payload for plants nutrients/fertilizers and therapeutic agents, especially through foliar application. The importance of the physical and chemical properties attributed to bioapplications (high photostability and chemical stability, low cytotoxicity and high quantum yield) is also touched upon in this book. Various other aspects such as characterization techniques, product characteristics, bioavailability, pharmacokinetics, stability, drug use, and toxicity in humans have also been systematically introduced.

However, CDs prepared from diverse methods exhibit large size distribution and photoluminescence non-uniformity, and the complex and time-consuming separation and purification severely limit their further applications, impeding further bioapplications of CDs. Moreover, the mechanism of photoluminescence is still unclear. This demands that an effective synthesis method with a high yield should be developed to fabricate CDs with a high quantum yield in a small size distribution, meaning that an understanding of CDs’ photoluminescence phenomenon, especially their bright multiphoton emission, should be explored to facilitate their in-vivo applications.

We hope that this book will suffice the need of those who want to enter into the magnificent field of carbon dots for various applications in the health care system.

Madhuri Sharon
Ashmi Mewada
Mumbai
31^st May 2018