A Review on the Application of Carbon Quantum dots and Doped Carbon Quantum Dots in Fluorescent Sensors for the Detection of Metal Pollutants

Document Type : Review paper

Authors

Department of Environmental Research, Institute for Color Science and Technology, P.O.Box:16765-654, Tehran, Iran.

10.30509/jscw.2025.167510.1228

Abstract

Carbon quantum dots (CQDs) are zero-dimensional quasi-spherical nanoparticles smaller than 10 nm, composed of carbon and various surface groups. These compounds are utilized in applications such as metal ion detection, photodegradation of pollutants, bio-imaging, and drug delivery, due to their high solubility in water, optical stability, luminescence properties, and biocompatibility. Due to their fluorescent characteristics, carbon quantum dots can selectively respond to target molecules in environmental and biological samples. The fluorescence properties and color changes of carbon quantum dots serve as a key foundation for the performance of optical sensors in the accurate detection of metal pollutants. This article discusses the applications of carbon quantum dots across various fields, particularly their role as optical sensors for identifying one or more metal pollutants, either individually or simultaneously. It also explores the use of carbon quantum dots doped with one or more elements for detecting metal cations. Finally, the article examines the current challenges and prospects of using carbon quantum dots as sensors.
 

Keywords

Main Subjects


1.        Wang Y, Hu A. Carbon quantum dots: synthesis, properties and applications. J Mater Chem C. 2014;2(34):6921-39. https://doi.org/10.1039/C4TC00988F.
2.       Lim SY, Shen W, Gao Z. Carbon quantum dots and their applications. Chem Soc Rev. 2015;44(1):362-81. https:// doi.org/10.1039/C4CS00269E.
3.       Yousefi-Limaee N, Peik-Rayekan L, Seifpanahi-Shabani K. A review of ion-imprinted polymer for the removal and colorimetric detection of lead: preparation, mechanism and application. J stud color world. 2024;14:253-264. https://dorl .net/dor/10.30509/JSCW.2024.167332.1195 [In Persian].
4.       Jaishankar M, Tseten T, Anbalagan N, Mathew B, Beeregowda K. Toxicity, mechanism and health effects of some heavy metals. Interdiscip Toxicol. 2014;7:60–72. https://doi.org/10.2478/intox-2014-0009.
5.       Yousefi-Limaee N, Rouhani S. A review on the application of molecularly imprinted polymers in the detection of pollutants: A case study of optical sensors. J stud color world. 2021;10(4):53-68. https://dorl.net/dor/20.1001.1.22 517278.1399.10.4.5.2 [In Persian].
6.       Yousefi-Limaee N, Rouhani S, Kamandi R. Highly selective and sensitive colorimetric chemosensor using PVA/chitosan ion-imprinted nanofibers for copper ion detection and removal. Heliyon. 2024;10(15):e35193. https://doi.org/10. 1016/j.heliyon.2024.e35193.
7.       Yousefi-Limaee N, Rouhani S, Olya ME, Najafi F. Selective 2,4-dichlorophenoxyacetic acid optosensor employing a polyethersulfone nanofiber-coated fluorescent molecularly imprinted polymer. Polym. 2019;177:73-83. https://doi.org/ 10.1016/j.polymer.2019.05.067.
8.       Yousefi-Limaee N, Rouhani S, Olya ME, Najafi F. Selective Recognition of Herbicides in Water Using a Fluorescent Molecularly Imprinted Polymer Sensor. J Fluorescence. 2020;30(2):375-87. https://doi.org/10.1007/s10895-020-02 508-z.
9.       Devi P, Rajput P, Thakur A, Kim KH, Kumar P. Recent advances in carbon quantum dot-based sensing of heavy metals in water. TrAC, Trends Anal Chem. 2019;114:171-95. https://doi.org/10.1039/D3SU00375B.
10.    Lu Y, Liang X, Niyungeko C, Zhou J, Xu J, Tian G. A review of the identification and detection of heavy metal ions in the environment by voltammetry. Talanta. 2018;178:324-38.  https://doi.org/10.1016/j.talanta.2017.08. 033.
11.    Yousefi-Limaee N, Rezaei Y, CQDs-based optical sensors for the detection of metal ions: preparation and mechanism of detection. J stud color world. 2024;14:363-378. https:// dorl.net/dor/ 10.30509/jscw.2024.167400.1210 [In Persian].
12.    Kong J, Wei Y, Zhou F, Shi L, Zhao S, Wan M, et al. Carbon Quantum Dots: Properties, Preparation, and Applications. Molecules. 2024;29(9):2002. https://doi.org/10.3390/mole cules29092002.
13.    Rawat D, Singh RR. Fluorescent magnetic quantum dots in bioimaging. magnetic quantum dots for bioimaging: CRC Press; 2023.133-52. https://doi.org/10.1201/9781003 319870.
14.    Li J, Zhao H, Zhao X, Gong X. Boosting efficiency of luminescent solar concentrators using ultra-bright carbon dots with large Stokes shift. Nanoscale Horiz.2023;8(1):83-94. https://doi.org/10.1039/D2NH00360K.
15.    Li J, Gong X. The emerging development of multicolor carbon dots. Small. 2022;18(51):2205099. https://doi. org/10.1002/smll.202205099.
16.    Acharya B, Behera A, Behera S, Moharana S. Carbon quantum dots: A systematic overview of recent developments in synthesis, properties, and novel therapeutic applications. Inorg Chem Commun. 2024:112492. https://doi.org/ 10.1016/j.inoche.2024.112492.
17.    Ansari L, Hallaj S, Hallaj T, Amjadi M. Doped-carbon dots: Recent advances in their biosensing, bioimaging and therapy applications. Colloids Surf B Biointerfaces. 2021;203 :111743. https://doi.org/10.1016/j.colsurfb.2021.111743.
18.    Han Y, Li W, Lin J, Zhao H, Wang X, Zhang Y. Carbon quantum dots capped with metal ions for efficient optoelectronic applications. J Mater Chem C. 2024; 12(16):5818-25. https://doi.org/10.1039/D4TC00419A.
19.    Ozyurt D, Kobaisi MA, Hocking RK, Fox B. Properties, synthesis, and applications of carbon dots: A review. Carbon Trends. 2023;12:100276. https://doi.org/10.1016/j.cartre. 2023.100276.
20.    Selvaraj H, Bruntha G, Ilangovan A. Synthesis of carbon dots via microwave-assisted process: specific sensing of fe (iii) and antibacterial activity. J Fluoresc. 2024:1-11. https://doi.org/10.1007/s10895-024-03845-z.
21.    Zhao P, Zhang Q, Cao J, Qian C, Ye J, Xu S, et al. Facile and green synthesis of highly fluorescent carbon quantum dots from water hyacinth for the detection of ferric iron and cellular imaging. Nanomater. 2022;12(9):1528. https://doi. org/10.3390/nano12091528.
22.    Shabbir H, Tokarski T, Ungor D, Wojnicki M. Eco friendly synthesis of carbon dot by hydrothermal method for metal ions salt identification. Mater. 2021;14(24):7604. https:// doi.org/10.3390/ma14247604.
23.    Chen J, Wang Y, Wang L, Liu M, Fang L, Chu P, et al. Multi-applications of carbon dots and polydopamine-coated carbon dots for Fe3+ detection, bioimaging, dopamine assay and photothermal therapy. Discover Nano. 2023;18(1):30. https://doi.org/10.1186/s11671-023-03809-5.
24.    Yousefi-Limaee N, Tammari S. Preparation of a highly selective fluorescence sensor based on CQDs/PVA/Chitosan nanofiber. 16th International Seminar on Polymer Science & Technology (ISPST 2024), 7-9 September 2024, Sahand University of Technology, Tabriz, Iran.
25.    Das GS, Shim JP, Bhatnagar A, Tripathi KM, Kim T. Biomass-derived carbon quantum dots for visible-light-induced photocatalysis and label-free detection of Fe (III) and ascorbic acid. Sci Rep. 2019;9(1):15084. https://doi. org/10.1038/s41598-019-49266-y.
26.    Hu Y, Gao Z, Yang J, Chen H, Han L. Environmentally benign conversion of waste polyethylene terephthalate to fluorescent carbon dots for “on-off-on” sensing of ferric and pyrophosphate ions. J colloid Interface Sci. 2019;538:481-8. https://doi.org/10.1016/j.jcis.2018.12.016.
27.    Li W, Liu Y, Wang B, Song H, Liu Z, Lu S, et al. Kilogram-scale synthesis of carbon quantum dots for hydrogen evolution, sensing and bioimaging. Chin Chem Lett. 2019;30(12):2323-7. https://doi.org/10.1016/j.cclet.2019.0 6.040.
28.    Yan F, Zu F, Xu J, Zhou X, Bai Z, Ma C, et al. Fluorescent carbon dots for ratiometric detection of curcumin and ferric ion based on inner filter effect, cell imaging and PVDF membrane fouling research of iron flocculants in wastewater treatment. Sens Actuators B Chem. 2019;287:231-40. https://doi.org/10.1016/j.snb.2019.01.144.
29.    Li D, Wang S, Azad F, Su S. Single-step synthesis of polychromatic carbon quantum dots for macroscopic detection of Hg2+. Ecotoxicol Environ Saf. 2020; 190:110141. https://doi.org/10.1016/j.ecoenv.2019.110141.
30.    Zhang Q, Zhang X, Bao L, Wu Y, Jiang L, Zheng Y, et al. The application of green‐synthesis‐derived carbon quantum dots to bioimaging and the analysis of mercury (II). J anal methods chem. 2019;2019(1):8183134. https://doi.org/ 10.1155/2019/8183134.
31.    Kasinathan K, Samayanan S, Marimuthu K, Yim J-H. Green synthesis of multicolour fluorescence carbon quantum dots from sugarcane waste: Investigation of mercury (II) ion sensing, and bio-imaging applications. Appl Surf Sci. 2022;601:154266. https://doi.org/10.1016/j.apsusc.2022.15 4266.
32.    Ye Z, Zhang Y, Li G, Li B. Fluorescent determination of mercury (II) by green carbon quantum dots synthesized from eggshell membrane. Anal Lett. 2020;53(18):2841-53. https://doi.org/10.1080/00032719.2020.1759618.
33.    Dhandapani E, Maadeswaran P, Raj RM, Raj V, Kandiah K, Duraisamy N. A potential forecast of carbon quantum dots (CQDs) as an ultrasensitive and selective fluorescence probe for Hg (II) ions sensing. Mater Sci Eng B. 2023;287:116098. https://doi.org/10.1016/j.mseb.2022.116098.
34.    Jaison AMC, Vasudevan D, Ponmudi K, George A, Varghese A. One pot hydrothermal synthesis and application of bright-yellow-emissive carbon quantum dots in Hg2+ detection. J Fluoresc. 2023;33(6):2281-94. https:// doi.org/10.1007/s10895-023-03233-z.
35.    Duan Q, Wang X, Zhang B, Li Y, Zhang W, Zhang Y, et al. A fluorometric method for mercury (II) detection based on the use of pyrophosphate-modified carbon quantum dots. Mikrochim Acta. 2019;186:1-7. https://doi.org/10.1007/ s00604-019-3872-0.
36.    Huang Q, Bao Q, Wu C, Hu M, Chen Y, Wang L, et al. Carbon dots derived from Poria cocos polysaccharide as an effective “on-off” fluorescence sensor for chromium (VI) detection. J Pharm Anal. 2022;12(1):104-12. https://doi.org/ 10.1016/j.jpha.2021.04.004.
37.    Zhang Y, Dong Y, Zheng H, Yang X, Yao C. High Quantum Yield Fluorescent Chitosan-Based Carbon Dots for the Turn-On-Off-On Detection of Cr (VI) and H2O2. Nano. 2021;16(09):2150103. https://doi.org/10.1142/S1793292 021501034.
38.    Anpalagan K, Yin H, Cole I, Zhang T, Lai DT. Quantum Yield Enhancement of Carbon Quantum Dots Using Chemical-Free Precursors for Sensing Cr (VI) Ions. Inorgan. 2024;12(4):96. https://doi.org/10.3390/inorganics120400 96.
39.    He Z, Shen J, Zhang J, Lin W, Gu H. Cleaner, High-Efficiency, and High-Value Conversion of Chrome-Containing Leather Solid Waste into Carbon Quantum Dots as Renewable Bimetallic Ions Detection Sensors. ACS Sustain Chem Eng. 2023;11(35):13126-41. https://doi.org/ 10.1021/acssuschemeng.3c03382.
40.    Liu S, Wu Z, Nian N, Zhang P, Ni L. The Speciation of Heavy Metal Chromium in Water Environment by Carbon Quantum Dots System. Water Air Soil Pollut. 2024;235(7):449. https://doi.org/10.1007/s11270-024-072 22-1.
41.    Das P, Maruthapandi M, Saravanan A, Natan M, Jacobi G, Banin E, et al. Carbon dots for heavy-metal sensing, pH-sensitive cargo delivery, and antibacterial applications. ACS Appl. Nano Mater. 2020;3(12):11777-90. https://doi.org /10.1021/acsanm.0c02305.
42.    Ghosh B, Roy S, Bardhan S, Mondal D, Saha I, Ghosh S, et al. Biocompatible carbon dot decorated α-FeOOH nanohybrid for an effective fluorometric sensing of Cr (VI) in wastewater and living cells. J Fluoresc. 2022;32(4):1489-500. https://doi.org/10.1007/s10895-022-02962-x.
43.    Shen J, Gu H, He Z, Lin W. Wattle-bark-tannin-derived carbon quantum dots as multi-functional nanomaterials for intelligent detection of Cr6+ ions, bio-imaging, and fluorescent ink applications. Ind Eng Chem Res. 2023;62(8):3622-34. https://doi.org/10.1021/acs.iecr.2c04348.
44.    Luo J, Lei Y, Ge Q, Liu M, Jiang N, Huang Y-H, et al. Carbon quantum dots from hemicucur [6] bit and the application for the detection of Pb2+. Spectrochim. Acta A. 2024;317:124459. https://doi.org/10.1016/j.saa.2024.124459.
45.    Paydar S, Feizi F, Shamsipur M, Barati A, Chehri N, Taherpour AA, et al. An ideal ratiometric fluorescent probe provided by the surface modification of carbon dots for the determination of Pb2+. Sens Actuators B Chem. 2022; 369:132243. https://doi.org/10.1016/j.snb.2022.132243.
46.    Liu Q, Gao X, Liu Z, Gai L, Yue Y, Ma H. Sensitive and selective electrochemical detection of lead (ii) based on waste-biomass-derived carbon quantum dots@ zeolitic imidazolate framework-8. Mater. 2023;16(9):3378. https:// doi.org/10.3390/ma16093378.
47.    Chauhan P, Chaudhary S, Kumar R. Biogenic approach for fabricating biocompatible carbon dots and their application in colorimetric and fluorometric sensing of lead ion. J Clean Prod. 2021;279:123639. https://doi.org/10.1016/j.jclepro. 2020.123639.
48.    Rawat KS, Singh V, Sharma CP, Vyas A, Pandey P, Singh J, et al. Picomolar detection of lead ions (Pb2+) by functionally modified fluorescent carbon quantum dots from watermelon juice and their imaging in cancer cells. J Imaging. 2023;9(1):19. https://doi.org/10.3390/jimaging90 10019.
49.    Qian X, Wang Z, Chen Z, El-Bahy SM, Li D, Qin L, et al. Green-emitting carbon quantum dots as efficient fluorescent probes for Cu2+ and EDTA detection by “turn-on-off” strategy. Colloids Surf A Physicochem Eng Asp. 2024 ;693:134089. https://doi.org/10.1016/j.colsurfa.2024.1340 89.
50.    Zhang X, Hou X, Lu D, Chen Y, Feng L. Porphyrin functionalized carbon quantum dots for enhanced electrochemiluminescence and sensitive detection of Cu2+. Molecules. 2023;28(3):1459. https://doi.org/10.3390/ mole cules28031459.
51.    Huang S, Wang W, Cheng J, Zhou X, Xie M, Luo Q, et al. Amino-functional carbon quantum dots as a rational nanosensor for Cu2+. Microchem J. 2020;159:105494. https://doi.org/10.1016/j.microc.2020.105494.
52.    Murugan N, Prakash M, Jayakumar M, Sundaramurthy A, Sundramoorthy AK. Green synthesis of fluorescent carbon quantum dots from Eleusine coracana and their application as a fluorescence ‘turn-off’sensor probe for selective detection of Cu2+. Appl Sur Sci. 2019;476:468-80. https://doi.org/10.1016/j.apsusc.2019.01.090.
53.    Liu Y, Seidi F, Deng C, Li R, Xu T, Xiao H. Porphyrin derived dual-emissive carbon quantum dots: Customizable synthesis and application for intracellular Cu2+ quantification. Sens Actuators B Chem. 2021;343:130072. https://doi.org/10.1016/j.snb.2021.130072.
54.    Han Z, Nan D, Yang H, Sun Q, Pan S, Liu H, et al. Carbon quantum dots based ratiometric fluorescence probe for sensitive and selective detection of Cu2+ and glutathione. Sens. Actuators B Chem. 2019;298:126842. https:// doi.org/10.1016/j.snb.2019.126842.
55.    Liu G, Li B, Liu Y, Feng Y, Jia D, Zhou Y. Rapid and high yield synthesis of carbon dots with chelating ability derived from acrylamide/chitosan for selective detection of ferrous ions. Appl Surf Sci. 2019;487:1167-75. https://doi.org/ 10.1016/j.apsusc. 2019.05.069.
56.    Baragau I-A, Power NP, Morgan DJ, Lobo RA, Roberts CS, Titirici M-M, et al. Efficient continuous hydrothermal flow synthesis of carbon quantum dots from a targeted biomass precursor for on–off metal ions nanosensing. ACS Sustain Chem Eng. 2021;9(6):2559-69. https://doi.org/10.1021/ acssuschemeng.0c08594.
57.    Tejwan N, Sharma A, Thakur S, Das J. Green synthesis of a novel carbon dots from red Korean ginseng and its application for Fe2+ sensing and preparation of nanocatalyst. Inorg Chem Commun. 2021;134:108985. https://doi.org/ 10.1016/j.inoche.2021.108985.
58.    Pratap R, Hassan N, Yadav M, Srivastava SK, Chaudhary S, Verma AK, et al. Biogenic synthesis of dual-emission chlorophyll-rich carbon quantum dots for detection of toxic heavy metal ions–Hg (ii) and As (iii) in water and mouse fibroblast cell line NIH-3T3. Environ Sci Nano. 2024;11(4):1636-53. https://doi.org/10.1039/D3EN0078 9H.
59.    Liu F, Li H, Liao D, Xu Y, Yu M, Deng S, et al. Carbon quantum dots derived from the extracellular polymeric substance of anaerobic ammonium oxidation granular sludge for detection of trace Mn (vii) and Cr (vi). RSC Adv.2020;10(53):32249-58. https://doi.org/10.1039/D0R A06133F.
60.    Yan F, Bai Z, Zu F, Zhang Y, Sun X, Ma T, et al. Yellow-emissive carbon dots with a large Stokes shift are viable fluorescent probes for detection and cellular imaging of silver ions and glutathione. Mikrochim Acta. 2019;186:1-11. https://doi.org/10.1007/s00604-018-3221-8.
61.    Wu Y, Liu Y, Yin J, Li H, Huang J. Facile ultrasonic synthesized NH2-carbon quantum dots for ultrasensitive Co2+ ion detection and cell imaging. Talanta. 2019; 205:120121. https://doi.org/10.1016/j.talanta.2019.120121.
62.    Gong Y, Liang H. Nickel ion detection by imidazole modified carbon dots. Spectrochim. Acta A. 2019;211:342-7. https://doi.org/10.1016/j.saa.2018.12.024.
63.    Raja S, da Silva GT, Anbu S, Ribeiro C, Mattoso LH. Biomass-derived carbon quantum dot:“On–off-on” fluorescent sensor for rapid detection of multi-metal ions and green photocatalytic CO2 reduction in water. Biomass Convers. Biorefinery. 2023:1-13. https://doi.org/10.1007/ s13399-023-04247-0.
64.    Liu Y, Chen J, Xu Z, Liu H, Yuan T, Wang X, et al. Detection of multiple metal ions in water with a fluorescence sensor based on carbon quantum dots assisted by stepwise prediction and machine learning. Environ Chem Lett. 2022;20(6):3415-20. https://doi.org/10.1007/s10311-022-01475-0.
65.    Radhakrishnan K, Panneerselvam P, Marieeswaran M. A green synthetic route for the surface-passivation of carbon dots as an effective multifunctional fluorescent sensor for the recognition and detection of toxic metal ions from aqueous solution. Anal Methods. 2019;11(4):490-506. https://doi.org/10.1039/C8AY02451K.
66.    Arumugham T, Alagumuthu M, Amimodu RG, Munusamy S, Iyer SK. A sustainable synthesis of green carbon quantum dot (CQD) from Catharanthus roseus (white flowering plant) leaves and investigation of its dual fluorescence responsive behavior in multi-ion detection and biological applications. Sustain Mater Technol. 2020;23:e00138. https://doi.org /10.1016/j.susmat.2019.e00138.
67.    Park Y, Yoo J, Lim B, Kwon W, Rhee S-W. Improving the functionality of carbon nanodots: doping and surface functionalization. J Mater Chem. 2016;4(30):11582-603. https://doi.org/10.1039/C6TA04813G.
68.    Xie J, Wu Z, Sun J, Lv C, Sun Q. Green synthesis of carbon quantum dots derived from lycium barbarum for effective fluorescence detection of Cr (VI) sensing. J Fluoresc. 2024;34(2):571-8. https://doi.org/10.1007/s10895-023-033 00-5.
69.    Nguyen KG, Baragau I-A, Gromicova R, Nicolaev A, Thomson SA, Rennie A, et al. Investigating the effect of N-doping on carbon quantum dots structure, optical properties and metal ion screening. Sci Rep. 2022;12(1):13806. https://doi.org/10.1038/s41598-022-16893-x.
70.    Swathi R, Reddy GB, Rajkumar B, Ramakrishna D, Swamy PY. Jamun Seed-Derived Nitrogen-Doped Carbon Dots: A Novel Microwave-Assisted Synthesis for Ultra-Bright Fluorescence and Mn7+ Detection. J Fluoresc. 2023:1-12. https://doi.org/10.1007/s10895-023-03438-2.
71.    Liu R, Zhang Y, Piao Y, Meng L-Y. Development of nitrogen-doped carbon quantum dots as fluorescent probes for highly selective and sensitive detection of the heavy-ion Fe3+. Carbon Lett. 2021;31(4):821-9. https://doi.org/10. 1007/s42823-020-00222-1.
72.    Tadesse A, Hagos M, RamaDevi D, Basavaiah K, Belachew N. Fluorescent-nitrogen-doped carbon quantum dots derived from citrus lemon juice: green synthesis, mercury (II) ion sensing, and live cell imaging. ACS omega. 2020;5(8):3889-98. https://doi.org/10.1021/acsomega.9b03175.
73.    Cheng S, Zhang J, Liu Y, Wang Y, Xiao Y, Zhang Y. One-pot synthesis of nitrogen-doped carbon dots for sensing of Co2+ and tetracycline antibiotics, biological imaging, and fluorescent inks. J. Nanoparticle Res. 2022;24(2):44. https://doi.org/10.1007/s11051-022-05398-3.
74.    Tan A, Yang G, Wan X. Ultra-high quantum yield nitrogen-doped carbon quantum dots and their versatile application in fluorescence sensing, bioimaging and anti-counterfeiting. Spectrochim Acta A. 2021;253:119583. https://doi.org/ 10.1016/j.saa.2021.119583.
75.    Xing S, Zheng K, Shi L, Kang K, Peng Z, Zhang X, et al. Fluorescence detection of pb2+ in environmental water using biomass carbon quantum dots modified with acetamide-glycolic acid deep eutectic solvent. Molecules. 2024 ;29(7):1662. https://doi.org/10.3390/ molecules29071662.
76.    Zhang Y, Li Z, Sheng L, Meng A. Lemon juice-derived nitrogen-doped carbon quantum dots for highly sensitive and selective determination of ferrous ions and cell imaging. Colloids Surf A Physicochem Eng Asp. 2023;657:130580. https://doi.org/10.1016/j.colsurfa.2022.130580.
77.    Preethi M, Viswanathan C, Ponpandian N. Fluorescence quenching mechanism of P-doped carbon quantum dots as fluorescent sensor for Cu2+ ions. Colloids Surf A Physicochem Eng Asp. 2022;653:129942. https://doi.org/ 10.1016/j.colsurfa.2022.129942.
78.    Yadav A, Yadav R, Lahariya V, Singh AK. Versatile P-doped carbon quantum dots derived from green precursor: an efficient metal ion sensor and photocatalytic behaviour in aqueous environment. Res Chem Intermed. 2024; 50(4):1873-93. https://doi.org/10.1007/s11164-023-05225-x.
79.    Zhang L, Li B, Zhou Y, Wu Y, Sun Q, Le T. Preparation of phosphorus‐doped cow milk‐derived carbon quantum dots and detection of Au3+. J Food Process Eng. 2023;46(7): e14349. https://doi.org/10.1111/jfpe.14349.
80.    Kalaiyarasan G, Joseph J, Kumar P. Phosphorus-doped carbon quantum dots as fluorometric probes for iron detection. ACS omega. 2020;5(35):22278-88. https://doi .org/10.1021/acsomega.0c02627.
81.    Hao Y, Li T, Tian M, Dai Q, Zhang F, Chai F. A silicon-doped carbon dot-based multivariate fluorometric and colorimetric probe for the simultaneous detection of heavy metal ions and dopamine. New J Chem. 2024;48(4):1828-36. https://doi.org/10.1039/D3NJ04627C.
82.    Liao S, Zhang L, Li S, Yue S, Wang G. Selective detection of mercury ions via single and dual signals by silicon-doped carbon quantum dots. New J Chem. 2023;47(30):14242-8. https://doi.org/10.1039/D3NJ02521G.
83.    Desai ML, Basu H, Saha S, Singhal RK, Kailasa SK. Investigation of silicon doping into carbon dots for improved fluorescence properties for selective detection of Fe3+ ion. Opt Mater. 2019;96:109374. https://doi.org/ 10.1016/j.optmat.2019.109374.
84.    Zan M, Li C, Zhu D, Rao L, Meng Q-F, Chen B, et al. A novel “on–off–on” fluorescence assay for the discriminative detection of Cu (ii) and l-cysteine based on red-emissive Si-CDs and cellular imaging applications. J Mater Chem B. 2020;8(5):919-27. https://doi.org/10.1039/C9TB02681A.
85.    Hu A, Chen G, Huang A, Cai Z, Yang T, Ma C, et al. o-phenylenediamine Derived Fluorescent Carbon Quantum dots for Detection of Hg (II) in Environmental Water. J Fluoresc. 2024;34(2):905-13. https://doi.org/10.1007/ s10895-023-03331-y.
86.    Chen Y, Cui H, Wang M, Yang X, Pang S. N and S doped carbon dots as novel probes with fluorescence enhancement for fast and sensitive detection of Cr (VI). Colloids Surf A Physicochem Eng Asp. 2022;638:128164. https://doi.org/ 10.1016/j.colsurfa.2021.128164.
87.    Wu H, Tong C. Nitrogen-and sulfur-codoped carbon dots for highly selective and sensitive fluorescent detection of Hg2+ ions and sulfide in environmental water samples. J Agric Food Chem. 2019;67(10):2794-800. https://doi.org/10. 1021/acs.jafc.8b07176.
88.    Wang Y, Xu G, Zhang X, Yang X, Hou H, Ai W, et al. N-and S-codoped carbon quantum dots for enhancing fluorescence sensing of trace Hg2+. Phys Chem Chem Phys. 2023;25(41):28230-40. https://doi.org/10.1039/D3CP0292 4G.
89.    Yan Z, Yao W, Mai K, Huang J, Wan Y, Huang L, et al. A highly selective and sensitive “on–off” fluorescent probe for detecting cadmium ions and L-cysteine based on nitrogen and boron co-doped carbon quantum dots. RSC Adv. 2022;12(13):8202-10. https://doi.org/10.1039/D1RA0821 9A.
90.    Wang C, Sun Q, Li C, Tang D, Shi H, Liu E, et al. Biocompatible double emission boron nitrogen co-doped carbon quantum dots for selective and sensitive detection of Al3+ and Fe2+. Mater Res Bull. 2022;155:111970. https://doi.org/10.1016/j.materresbull.2022.111970.
91.    Wang Y, Hu X, Li W, Huang X, Li Z, Zhang W, et al. Preparation of boron nitrogen co-doped carbon quantum dots for rapid detection of Cr (VI). Spectrochim Acta A. 2020;243:118807. https://doi.org/10.1016/j.saa.2020.1188 07.
92.    Wu H, Pang L-F, Fu M-J, Guo X-F, Wang H. Boron and nitrogen codoped carbon dots as fluorescence sensor for Fe3+ with improved selectivity. J Pharm Biomed Anal. 2020;180:113052. https://doi.org/10.1016/j.jpba.2019.11 3052.
93.    John A, Roy RE, Hari H, Zachariah AK. Emerging stoke’s shift-based cr (vi) fingerprint sensor from intensely blue fluorescent, high quantum yield, pepitas-derived carbon dots. ACS Appl Opt Mater. 2024;2(2):291-300. https://doi. org/10.1021/acsaom.3c00411.
94.    Zhang J, Jing C, Wang B. A label-free fluorescent sensor based on Si, N-codoped carbon quantum dots with enhanced sensitivity for the determination of Cr (VI). Mater. 2022;15(5):1733. https://doi.org/10.3390/ma15051733.
95.    Mohandoss S, Khanal HD, Palanisamy S, You S, Shim J-J, Lee YR. Multiple heteroatom-doped photoluminescent carbon dots for ratiometric detection of Hg 2+ ions in cell imaging and environmental applications. Anal Methods. 2022;14(6):635-42. https://doi.org/10.1039/D1AY02077C.
96.    Karami C, Taher MA, Shahlaei M. A simple method for determination of mercury (II) ions by PNBS-doped carbon dots as a fluorescent probe. J Mater Sci Mater Electron. 2020;31:5975-83. https://doi.org/10.1007/s10854-020-031 57-5.
97.    Mondal TK, Mondal S, Ghorai UK, Saha SK. White light emitting lanthanide based carbon quantum dots as toxic Cr (VI) and pH sensor. J Colloid Interface Sci. 2019;553:177-85. https://doi.org/10.1016/j.jcis.2019.06.009.
98.    Vyas T, Joshi A. Chemical sensor thin film-based carbon quantum dots (CQDs) for the detection of heavy metal count in various water matrices. Analyst. 2024;149(4):1297-309. https://doi.org/10.1039/D3AN01571H.
99.    Torres Landa SD, Reddy Bogireddy NK, Kaur I, Batra V, Agarwal V. Heavy metal ion detection using green precursor derived carbon dots. iScience. 2022;25(2):103816. https://doi.org/10.1016/j.isci.2022.103816.
100. Yin Y, Huanhuan L, Weijun S, Xiaofeng H, and Sun C. Carbon quantum dot (cqd)-based composite fluorescent hydrogel for the isolation and determination of iron (iii). Anal Lett. 2024;57(10):1595-610. https://doi.org/10.108 0/00032719.2023.2262631.
101. Liu Y, Feng S, Zhu Q. The effect of CQDs’ particle size on its fluorescence behavior and Cu2+ detection. Spectrochim Acta A Mol Biomol Spectrosc. 2025;341:126408. https:// doi.org/10.1016/j.saa.2025.126408.
102. Che H, Tian X, Chen W, Dai C, Nie Y, Li Y, et al. Simultaneous visual detection of multiple heavy metal ions by a high-throughput fluorescent probe. Mikrochim Acta. 2023;190(8):311. https://doi.org/10.1007/s00604-023-0588 2-0.
103. Yang D, Ma C, Chen G, Li L, Hu A, Huang A, et al. Investigation of the application and mechanism of Nitrogen and Phosphorus co-doped Carbon dots for Mercury Ion Detection. J Fluoresc. 2024:1-9. https://doi.org/10.1007 /s10895-024-03594-z.
104. Chu C, Zou C, Qiu Y, Huo D, Deng Y, Wang X, et al. Synthesis of two nitrogen-doped carbon quantum dots to construct fluorescence probes for sensitive Hg2+ detection with dual signal output. Dalton Trans. 2023;52(23):7982-91. https://doi.org/10.1039/D3DT00663H.
105. Aladesuyi OA, Oluwafemi OS. ‘Off–On’ determination of lead (Pb2+) and fluoride (F−) ion in fish and wastewater samples using N, S co-doped carbon quantum dots (N, S-CQDs). Appl Water Sci. 2024;14(7):153. https://doi.org/ 10.1007/s13201-024-02191-6.
106. Yu J, Kalimuthu R, Liu X, Zhang W, Tan Y, Yan K, et al. Unveiling the quenching mechanism of metal ions using solvent-driven N, S-doped carbon quantum dots. Opt Mater. 2025;162:116948. https://doi.org/10.1016/j.optmat.2025.11 6948.