Graphene quantum dot

Graphene quantum dots (GQDs) consist of one or a few layers of graphene and are smaller than 100 nm in size.{{Cite journal |last1=Campbell |first1=Elizabeth |last2=Hasan |first2=Md Tanvir |last3=Gonzalez-Rodriguez |first3=Roberto |last4=Truly |first4=Tate |last5=Lee |first5=Bong Han |last6=Green |first6=Kayla N. |last7=Akkaraju |first7=Giridhar |last8=Naumov |first8=Anton V. |date=October 2021 |title=Graphene quantum dot formulation for cancer imaging and redox-based drug delivery |url=https://pubmed.ncbi.nlm.nih.gov/34015513/ |journal=Nanomedicine: Nanotechnology, Biology and Medicine |volume=37 |pages=102408 |doi=10.1016/j.nano.2021.102408 |issn=1549-9642 |pmid=34015513|s2cid=235075216 }} They are chemically and physically stable, have a large surface to mass ratio and can be dispersed in water easily due to functional groups at the edges.{{cite journal |doi=10.1016/j.mtchem.2018.09.007 |title= Graphene quantum dots from chemistry to applications |journal= Materials Today Chemistry|volume=10 |pages=221–258 |year=2018 |last1=Tian |first1=P. |last2=Tang |first2=L. |last3=Teng |first3=K.S. |last4=Lau |first4=S.P.|doi-access=free |hdl=10397/80356 |hdl-access=free }}{{cite journal |doi=10.1002/ppsc.201400219 |title= Recent Advances in Graphene Quantum Dots for Fluorescence Bioimaging from Cells through Tissues to Animals |journal=Particle & Particle Systems Characterization |volume=32 |issue= 5 |pages=515–523 |year=2014 |last1=Wang |first1=Dan |last2=Chen |first2=Jiang-Fen |last3=Dai |first3=Liming|s2cid= 53120598 }} The fluorescence emission of GQDs can extend across a broad spectral range, including the UV, visible, and IR. The origin of GQD fluorescence emission is a subject of debate, as it has been related to quantum confinement effects, defect states and functional groups{{cite journal |doi=10.1002/adma.200902825 |pmid=20217780

|title=Hydrothermal Route for Cutting Graphene Sheets into Blue‐Luminescent Graphene Quantum Dots

|journal=Advanced Materials |volume=22 |issue=6 |pages=734–738 |year=2010 |last1=Pan|first1=Dengyu |last2=Zhang |first2=Jingchun |last3=Li |first3=Zhen|last4=Wu |first4=Minghong |bibcode=2010AdM....22..734P

|s2cid=39981399

}}{{cite journal |last1=Wang |first1=Shujun |last2=Cole |first2=Ivan S. |last3=Zhao |first3=Dongyuan |last4=Li |first4=Qin |title=The dual roles of functional groups in the photoluminescence of graphene quantum dots |journal=Nanoscale |date=2016 |volume=8 |issue=14 |pages=7449–7458 |doi=10.1039/C5NR07042B |pmid=26731007 |bibcode=2016Nanos...8.7449W |hdl=10072/142465 |hdl-access=free }} that might depend on the pH, when GQDs are dispersed in water.{{cite journal |doi=10.1039/C3NR06353D |pmid= 24589665 |title= A general quantitative pH sensor developed with dicyandiamide N-doped high quantum yield graphene quantum dots |journal=Nanoscale |volume=6 |issue= 7 |pages=3868–3874 |year=2014 |last1=Wu|first1=Zhu Lian |last2=Gao |first2=Ming Xuan |last3=Wang |first3=Ting Ting |last4=Wan |first4=Xiao Yan |last5=Zheng |first5=Lin Ling|last6=Huang |first6=Cheng Zhi |bibcode= 2014Nanos...6.3868W}} Their electronic structure depends sensitively on the crystallographic orientation of their edges, for example zigzag-edge GQDs with 7-8 nm diameter show a metallic behavior.{{cite journal |doi=10.1038/nmat2378 |pmid=19219032 |title=The influence of edge structure on the electronic properties of graphene quantum dots and nanoribbons |journal=Nature Materials |volume=8 |issue=3 |pages=235–42 |year=2009 |last1=Ritter |first1=Kyle A |last2=Lyding |first2=Joseph W |bibcode=2009NatMa...8..235R }} In general, their energy gap decreases, when the number of graphene layers or the number of carbon atoms per graphene layer is increased.{{cite journal |doi=10.1016/j.spmi.2019.106171 |title=Single-particle energy – and optical absorption – spectra of multilayer graphene quantum dots |journal=Superlattices and Microstructures |volume=132 |pages=106171|year=2019 |last1=Wimmenauer|first1=Christian |last2=Scheller |first2=Julienne |last3=Fasbender |first3=Stefan|last4=Heinzel |first4=Thomas |s2cid=198435346 }}

{{Main|Health and safety hazards of nanomaterials|Nanotoxicology}}

The toxicity of graphene-family nanoparticles is a matter of ongoing research.{{cite journal |last1=Ou |first1=Lingling |last2=Song |first2=Bin |last3=Liang |first3=Huimin |last4=Liu |first4=Jia |last5=Feng |first5=Xiaoli |last6=Deng |first6=Bin |last7=Sun |first7=Ting |last8=Shao |first8=Longquan |title=Toxicity of graphene-family nanoparticles: a general review of the origins and mechanisms |journal=Particle and Fibre Toxicology |date=31 October 2016 |volume=13 |issue=1 |pages=57 |doi=10.1186/s12989-016-0168-y |pmid=27799056 |pmc=5088662 |doi-access=free }} The toxicity (both in vivo and cytotoxicity) of GQDs are related to a variety of factors including particle size, methods of synthesis, chemical doping and so on.{{cite journal |last1=Wang |first1=Shujun |last2=Cole |first2=Ivan S. |last3=Li |first3=Qin |title=The toxicity of graphene quantum dots |journal=RSC Advances |date=2016 |volume=6 |issue=92 |pages=89867–89878 |doi=10.1039/C6RA16516H |bibcode=2016RSCAd...689867W }} Many authors claim, that GQDs are biocompatible and cause only low toxicity{{cite journal |doi=10.1039/C2CC00110A |pmid= 22410424|title= Graphene quantum dots: emergent nanolights for bioimaging, sensors, catalysis and photovoltaic devices|journal=Chemical Communications |volume=48 |issue= 31|pages=3686–3699|year=2012 |last1=Shen|first1=Jianhua |last2=Zhu |first2=Yihua |last3=Yang |first3=Xiaoling|last4=Li |first4=Chunzhong }} as they are just composed of organic materials, which should lead to an advantage over semiconductor quantum dots. Several in vitro studies, based on cell cultures, show only marginal effects of GQDs on the viability of human cells.{{cite journal |last1=Shang |first1=Weihu |last2=Zhang |first2=Xiaoyan |last3=Zhang |first3=Mo |last4=Fan |first4=Zetan |last5=Sun |first5=Ying |last6=Han |first6=Mei |last7=Fan |first7=Louzhen |title=The uptake mechanism and biocompatibility of graphene quantum dots with human neural stem cells |journal=Nanoscale |date=2014 |volume=6 |issue=11 |pages=5799–5806 |doi=10.1039/c3nr06433f |pmid=24740121 |bibcode=2014Nanos...6.5799S }}{{cite journal |last1=Fasbender |first1=Stefan |last2=Allani |first2=Sonja |last3=Wimmenauer |first3=Christian |last4=Cadeddu |first4=Ron-Patrick |last5=Raba |first5=Katharina |last6=Fischer |first6=Johannes C. |last7=Bulat |first7=Bekir |last8=Luysberg |first8=Martina |last9=Seidel |first9=Claus A. M. |last10=Heinzel |first10=Thomas |last11=Haas |first11=Rainer |title=Uptake dynamics of graphene quantum dots into primary human blood cells following in vitro exposure |journal=RSC Advances |date=2017 |volume=7 |issue=20 |pages=12208–12216 |doi=10.1039/C6RA27829A |bibcode=2017RSCAd...712208F |doi-access=free }}{{cite journal |last1=Zhu |first1=Shoujun |last2=Zhang |first2=Junhu |last3=Qiao |first3=Chunyan |last4=Tang |first4=Shijia |last5=Li |first5=Yunfeng |last6=Yuan |first6=Wenjing |last7=Li |first7=Bo |last8=Tian |first8=Lu |last9=Liu |first9=Fang |last10=Hu |first10=Rui |last11=Gao |first11=Hainan |last12=Wei |first12=Haotong |last13=Zhang |first13=Hao |last14=Sun |first14=Hongchen |last15=Yang |first15=Bai |title=Strongly green-photoluminescent graphene quantum dots for bioimaging applications |journal=Chemical Communications |date=2011 |volume=47 |issue=24 |pages=6858–60 |doi=10.1039/c1cc11122a |pmid=21584323 }} An in-depth look at the gene expression changes caused by GQDs with a size of 3 nm revealed that only one, namely the selenoprotein W, 1 out of 20 800 gene expressions was affected significantly in primary human hematopoietic stem cells.{{cite journal |last1=Fasbender |first1=Stefan |last2=Zimmermann |first2=Lisa |last3=Cadeddu |first3=Ron-Patrick |last4=Luysberg |first4=Martina |last5=Moll |first5=Bastian |last6=Janiak |first6=Christoph |last7=Heinzel |first7=Thomas |last8=Haas |first8=Rainer |title=The Low Toxicity of Graphene Quantum Dots is Reflected by Marginal Gene Expression Changes of Primary Human Hematopoietic Stem Cells |journal=Scientific Reports |date=19 August 2019 |volume=9 |issue=1 |pages=12028 |doi=10.1038/s41598-019-48567-6 |pmid=31427693 |pmc=6700176 |bibcode=2019NatSR...912028F }} On the contrary, other in vitro studies observe a distinct decrease of cell viability and the induction of autophagy after exposure of the cells to GQDs{{cite journal |last1=Xie |first1=Yichun |last2=Wan |first2=Bin |last3=Yang |first3=Yu |last4=Cui |first4=Xuejing |last5=Xin |first5=Yan |last6=Guo |first6=Liang-Hong |title=Cytotoxicity and autophagy induction by graphene quantum dots with different functional groups |journal=Journal of Environmental Sciences |date=March 2019 |volume=77 |pages=198–209 |doi=10.1016/j.jes.2018.07.014 |pmid=30573083 |s2cid=58555272 }} and one in vivo study in zebrafish larvae observed the alteration of 2116 gene expressions.{{cite journal |last1=Deng |first1=Shun |last2=Jia |first2=Pan-Pan |last3=Zhang |first3=Jing-Hui |last4=Junaid |first4=Muhammad |last5=Niu |first5=Aping |last6=Ma |first6=Yan-Bo |last7=Fu |first7=Ailing |last8=Pei |first8=De-Sheng |title=Transcriptomic response and perturbation of toxicity pathways in zebrafish larvae after exposure to graphene quantum dots (GQDs) |journal=Journal of Hazardous Materials |date=September 2018 |volume=357 |pages=146–158 |doi=10.1016/j.jhazmat.2018.05.063 |pmid=29883909 |s2cid=47013910 }} These inconsistent findings may be attributed to the diversity of the used GQDs, as the related toxicity is dependent on particle size, surface functional groups, oxygen content, surface charges and impurities.{{cite journal |last1=Guo |first1=Xiaoqing |last2=Mei |first2=Nan |title=Assessment of the toxic potential of graphene family nanomaterials |journal=Journal of Food and Drug Analysis |date=March 2014 |volume=22 |issue=1 |pages=105–115 |doi=10.1016/j.jfda.2014.01.009 |pmid=24673908 |pmc=6350507 }} Currently, the literature is insufficient to draw conclusions about the potential hazards of GQDs.

Presently, a range of techniques have been developed to prepare GQDs. These methods are normally classified into two groups top down and bottom up. Top down approaches applied different techniques to cut bulk graphitic materials into GQDs including graphite, graphene, carbon nanotubes, coal, carbon black and carbon fibres. These techniques mainly include electron beam lithography, chemical synthesis, electrochemical preparation, graphene oxide (GO) reduction, C60 catalytic transformation, the microwave assisted hydrothermal method (MAH),{{cite journal |doi=10.1021/nn300760g |pmid=22559247 |title=Deep Ultraviolet Photoluminescence of Water-Soluble Self-Passivated Graphene Quantum Dots |journal=ACS Nano |volume=6 |issue=6 |pages=5102–10 |year=2012 |last1=Tang |first1=Libin |last2=Ji |first2=Rongbin |last3=Cao |first3=Xiangke |last4=Lin |first4=Jingyu |last5=Jiang |first5=Hongxing |last6=Li |first6=Xueming |last7=Teng |first7=Kar Seng |last8=Luk |first8=Chi Man |last9=Zeng |first9=Songjun |last10=Hao |first10=Jianhua |last11=Lau |first11=Shu Ping |hdl=10397/28413 |hdl-access=free }}{{cite journal |doi=10.1021/nn501796r |pmid=24848545 |title=Deep Ultraviolet to Near-Infrared Emission and Photoresponse in Layered N-Doped Graphene Quantum Dots |journal=ACS Nano |volume=8 |issue=6 |pages=6312–20 |year=2014 |last1=Tang |first1=Libin |last2=Ji |first2=Rongbin |last3=Li |first3=Xueming |last4=Bai |first4=Gongxun |last5=Liu |first5=Chao Ping |last6=Hao |first6=Jianhua |last7=Lin |first7=Jingyu |last8=Jiang |first8=Hongxing |last9=Teng |first9=Kar Seng |last10=Yang |first10=Zhibin |last11=Lau |first11=Shu Ping |url=https://cronfa.swan.ac.uk/Record/cronfa21239 }} the Soft-Template method,{{cite journal |doi=10.1002/ppsc.201200131 |title=Size-Dependent Structural and Optical Characteristics of Glucose-Derived Graphene Quantum Dots |journal=Particle & Particle Systems Characterization |volume=30 |issue=6 |pages=523–31 |year=2013 |last1=Tang |first1=Libin |last2=Ji |first2=Rongbin |last3=Li |first3=Xueming |last4=Teng |first4=Kar Seng |last5=Lau |first5=Shu Ping |hdl=10397/32222 |s2cid=96410135 |hdl-access=free }} the hydrothermal method,{{cite journal |doi=10.1039/C3TC31473A |title=Multicolour light emission from chlorine-doped graphene quantum dots |journal=Journal of Materials Chemistry C |volume=1 |issue=44 |pages=7308–13 |year=2013 |last1=Li |first1=Xueming |last2=Lau |first2=Shu Ping |last3=Tang |first3=Libin |last4=Ji |first4=Rongbin |last5=Yang |first5=Peizhi |hdl=10397/34810 |hdl-access=free }}{{cite journal |doi=10.1039/C3NR33849E |pmid=23579482 |title=Focusing on luminescent graphene quantum dots: Current status and future perspectives |journal=Nanoscale |volume=5 |issue=10 |pages=4015–39 |year=2013 |last1=Li |first1=Lingling |last2=Wu |first2=Gehui |last3=Yang |first3=Guohai |last4=Peng |first4=Juan |last5=Zhao |first5=Jianwei |last6=Zhu |first6=Jun-Jie |bibcode=2013Nanos...5.4015L }}{{cite journal |doi=10.1039/C4NR00693C |pmid=24699893 |title=Sulphur doping: A facile approach to tune the electronic structure and optical properties of graphene quantum dots |journal=Nanoscale |volume=6 |issue=10 |pages=5323–8 |year=2014 |last1=Li |first1=Xueming |last2=Lau |first2=Shu Ping |last3=Tang |first3=Libin |last4=Ji |first4=Rongbin |last5=Yang |first5=Peizhi |bibcode=2014Nanos...6.5323L |hdl=10397/34914 |hdl-access=free }} and the ultrasonic exfoliation method.{{cite journal |doi=10.1063/1.4896278 |bibcode=2014ApPhL.105k1116Z |title=Chlorine doped graphene quantum dots: Preparation, properties, and photovoltaic detectors |journal=Applied Physics Letters |volume=105 |issue=11 |pages=111116 |year=2014 |last1=Zhao |first1=Jianhong |last2=Tang |first2=Libin |last3=Xiang |first3=Jinzhong |last4=Ji |first4=Rongbin |last5=Yuan |first5=Jun |last6=Zhao |first6=Jun |last7=Yu |first7=Ruiyun |last8=Tai |first8=Yunjian |last9=Song |first9=Liyuan }} Top down methods usually need intense purification as strong mixed acids are used in these methods. On the other hand, bottom up methods assemble GQDs from small organic molecules such as citric acid{{cite journal |last1=Wang |first1=Shujun |last2=Chen |first2=Zhi-Gang |last3=Cole |first3=Ivan |last4=Li |first4=Qin |title=Structural evolution of graphene quantum dots during thermal decomposition of citric acid and the corresponding photoluminescence |journal=Carbon |date=February 2015 |volume=82 |pages=304–313 |doi=10.1016/j.carbon.2014.10.075 |hdl=10072/69171 |hdl-access=free }} and glucose. These GQDs have better biocompatibility.

Graphene quantum dots are studied as an advanced multifunctional material due to their unique optical, electronic, spin,{{cite journal |doi=10.1103/PhysRevB.84.035425 |title=Electric-field controlled spin in bilayer triangular graphene quantum dots |journal=Physical Review B |volume=84 |issue=3 |pages=035425 |year=2011 |last1=Güçlü |first1=A. D |last2=Potasz |first2=P |last3=Hawrylak |first3=P |arxiv=1104.3108 |bibcode=2011PhRvB..84c5425G |s2cid=119211816 }} and photoelectric properties induced by the quantum confinement effect and edge effect. They have possible applications in treatment of Alzheimer's disease, bioimaging,{{Cite journal |last1=Lu |first1=Huiting |last2=Li |first2=Wenjun |last3=Dong |first3=Haifeng |last4=Wei |first4=Menglian |date=September 2019 |title=Graphene Quantum Dots for Optical Bioimaging |url=https://pubmed.ncbi.nlm.nih.gov/31304647/ |journal=Small |volume=15 |issue=36 |pages=e1902136 |doi=10.1002/smll.201902136 |issn=1613-6829 |pmid=31304647|s2cid=196617689 }} photothermal therapy,{{cite journal |doi=10.1039/C6RA25976F |title=Multifunctional graphene quantum dots for combined photothermal and photodynamic therapy coupled with cancer cell tracking applications |journal=RSC Advances |volume=7 |issue=9 |pages=5251–61 |year=2017 |last1=Thakur |first1=Mukeshchand |last2=Kumawat |first2=Mukesh Kumar |last3=Srivastava |first3=Rohit |bibcode=2017RSCAd...7.5251T |doi-access=free }} temperature sensing,{{cite journal |doi=10.1021/acssuschemeng.6b01893 |title=Graphene Quantum Dots from Mangifera indica: Application in Near-Infrared Bioimaging and Intracellular Nanothermometry |journal=ACS Sustainable Chemistry & Engineering |volume=5 |issue=2 |pages=1382–91 |year=2017 |last1=Kumawat |first1=Mukesh Kumar |last2=Thakur |first2=Mukeshchand |last3=Gurung |first3=Raju B |last4=Srivastava |first4=Rohit }} drug delivery,{{cite journal |last1=Kersting |first1=David |last2=Fasbender |first2=Stefan |last3=Pilch |first3=Rabea |last4=Kurth |first4=Jennifer |last5=Franken |first5=André |last6=Ludescher |first6=Marina |last7=Naskou |first7=Johanna |last8=Hallenberger |first8=Angelika |last9=Gall |first9=Charlotte von |last10=Mohr |first10=Corinna J |last11=Lukowski |first11=Robert |last12=Raba |first12=Katharina |last13=Jaschinski |first13=Sandra |last14=Esposito |first14=Irene |last15=Fischer |first15=Johannes C |last16=Fehm |first16=Tanja |last17=Niederacher |first17=Dieter |last18=Neubauer |first18=Hans |last19=Heinzel |first19=Thomas |title=From in vitro to ex vivo: subcellular localization and uptake of graphene quantum dots into solid tumors |journal=Nanotechnology |date=27 September 2019 |volume=30 |issue=39 |pages=395101 |doi=10.1088/1361-6528/ab2cb4 |pmid=31239418 |bibcode=2019Nanot..30M5101K |doi-access=free }}{{cite journal |doi=10.1016/j.msec.2016.05.007 |pmid=27287144 |title=Milk-derived multi-fluorescent graphene quantum dot-based cancer theranostic system |journal=Materials Science and Engineering: C |volume=67 |pages=468–477 |year=2016 |last1=Thakur |first1=Mukeshchand |last2=Mewada |first2=Ashmi |last3=Pandey |first3=Sunil |last4=Bhori |first4=Mustansir |last5=Singh |first5=Kanchanlata |last6=Sharon |first6=Maheshwar |last7=Sharon |first7=Madhuri }} LEDs lighter converters, photodetectors, OPV solar cells, and photoluminescent material, biosensors fabrication.{{cite journal |doi=10.1021/acsomega.9b00858 |pmid=31460168 |pmc=6648105 |title=Nitrogen-Doped Graphene Oxide Dots-Based "Turn-OFF" H2O2, Au(III), and "Turn-OFF–ON" Hg(II) Sensors as Logic Gates and Molecular Keypad Locks |journal=ACS Omega |volume=4 |issue=6 |pages=10702–10713 |year=2019 |last1=Bogireddy |first1=Naveen Kumar Reddy |last2=Barba |first2=Victor |last3=Agarwal |first3=Vivechana }}

• Cadmium-free quantum dot
• Carbon quantum dot
• Carbon nanotube quantum dot

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Category:Graphene

Category:Quantum dots