Highly fluorescent carbon dots from Pseudo-stem of banana plant: Applications as nanosensor and bio-imaging agents
Introduction
Carbon dots (CDs) are carbon nano materials with sizes below 10 nm and consist of an amorphous or crystalline core with sp2 carbon and an oxidized carbon surface with carboxyl group [1], [2]. In recent years, CDs have emerged as potential eco-friendly fluorescent probes for visualizing structural and functional images of living systems. CDs can be considered as powerful fluorescent probes, as it holds a number of advantages over other fluorescent materials owing to their good solubility in water, high chemical stability, easy functionalization, resistance to photo bleaching, low toxicity and good biocompatibility [3], [4], [5], [6], [7], [8]. CDs can be prepared by various synthesis routes including arc discharge, combustion, hydrothermal preparation, microwave pyrolysis, laser ablation, and plasma treatment [9], [10], [11], [12]. CDs are not source-limited, small organic molecules [13], [14], egg [15], orange juice [2], garlic [4], cotton [16], oatmeal [17], coriander leaves [18], carbohydrate [19], onion [20], grape juice [21], apple juice [22], milk [23], rose-heart radish [24] and banana juice [25] have been reported as natural green sources for CDs. They have been explored in versatile applications such as bio-imaging [26], [27], chemosensors [28], [29], temperature sensors [30], drug carriers [31], [32], photocatalysts [33] and photothermal therapy [34]. Although this new category of nanomaterials is considered to be a potential candidate to substitute for quantum dots, some of the shortcomings should be eliminated, for instance, their inability to emit strong long-wavelength fluorescence and to dissolve in organic solvents other than water [35], [36].
Natural resources are found to be abundant in carbon, nitrogen and oxygen in the form of carbohydrate and proteins. Formation of CDs from these resources involves dehydration and carbonization of natural source followed by in situ surface passivation under high temperature and pressure conditions during hydrothermal treatment. Fluorescent CDs with ion-responsive properties that can selectively respond to specific ions are of extreme interest and importance amongst the smart sensors because of the crucial roles of ions in life processes and health [37], [38], [39]. Fe3+ ion is an important metal ion in life and plays significant roles in oxygen uptake, oxygen metabolism, and electronic transfer [40]. But excessive iron accumulate in body can lead to tissue damage, organ failures and eventually death. Development of effective sensing systems for qualitative and quantitative determination of Fe3+ is of great significance for clinical, medical and environmental concerns. Many efforts have been devoted to this topic and have produced a few carbon-based luminescence techniques for Fe3+ detection [37], [41], [42], [43]. In this work, we report the preparation of CDs by a facile, green, and low-cost hydrothermal method using pseudo-stem of banana plant as the precursor. The microstructures, chemical composition, cytotoxicity, stability and fluorescence properties of the CDs were investigated in detail. The application of the CDs as sensor towards Fe3+ detection and in cellular multi colour imaging was demonstrated. Besides, a detailed analysis of optical and physicochemical properties of CDs has been presented in detail. Apart from this, our study encompasses the multifunctional aspects of CDs such as selective ion detection probe and also as bio imaging agent.
Section snippets
Materials
Pseudo-stem of banana plant was purchased from the local market of Chennai, India. Metal chlorides/nitrates were purchased from Aldrich and ACROS. All commercially available organic and inorganic reagents were used without further purification. Ultrapure water (18.2 MΩ cm) was received by a Millipore water purification system.
Synthesis of carbon dots
CDs were synthesized from Pseudo-stem of banana plant (as carbon source) by using hydrothermal method [2]. In a typical procedure, the Pseudo-stem of banana plant was rinsed
Results and discussion
CDs were prepared by one-pot hydrothermal treatment (HT) using commercially available Pseudo-stem of banana plant as illustrated in Scheme 1. The main constituents of Pseudo-stem of banana plants were cellulose (43–50%), Hemi-cellulose (16–20%) and Lignin (12–16%). HT treatment is an appropriate method for the formation of CD since the formation process may involve dehydration, polymerization, and carbonization of the carbohydrates [44]. As shown in Scheme 1, the synthesized CDs suspension is
Conclusions
Simple approach to synthesize high quality water soluble fluorescent CDs of ∼2.5 nm size via hydrothermal treatment of cost effective Pseudo-stem of banana plant without any surface passivation and oxidizing agents. The CDs aqueous solution emits strong green light under UV irradiation with a fluorescent quantum yield of 48%, life time and the emission wavelength was red-shifted under excitation with longer wavelengths. Further studies showed that the CDs can be used as a fluorescent probe for
Acknowledgement
We acknowledge the Department of Science and Technology (DST), India, for funding National Centre for Catalysis Research (NCCR), Indian Institute of Technology Madras (IITM).
Somasundaram Anbu Anjugam Vandarkuzhali received her Ph.D from Seethalakshmi Ramaswami College affiliated to Bharathidasan University, Tiruchirappalli, India. She carried out her part of research work in Department of Inorganic Chemistry, Madras University, Chennai, India. Currently she is working as Research Associate in National Centre for Catalysis Research (NCCR), IIT Madras, India. Her field of interest is design and synthesis of nanostructured composites for real-time environmental
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Somasundaram Anbu Anjugam Vandarkuzhali received her Ph.D from Seethalakshmi Ramaswami College affiliated to Bharathidasan University, Tiruchirappalli, India. She carried out her part of research work in Department of Inorganic Chemistry, Madras University, Chennai, India. Currently she is working as Research Associate in National Centre for Catalysis Research (NCCR), IIT Madras, India. Her field of interest is design and synthesis of nanostructured composites for real-time environmental applications.
Velu Jeyalakshmi received Ph.D degree from Department of Chemistry, Thiagarajar College, Madurai Kamaraj University, India and conducted doctoral study at National Centre for Catalysis Research (NCCR), IIT Madras, India. She is currently Research Associate in NCCR, IIT Madras, India. Her research interest includes design and synthesis of photocatalyst for energy and environmental applications.
Gandhi Sivaraman received his B.Sc., (Chemistry) from thiyagarajar college (Madurai Kamaraj University) in 2007, M.Sc., (Chemistry) from The American college (Madurai Kamaraj University) in 2009. He received his Ph.d from the same university under the guidance of Prof. D. Chellappa in 2014. He is currently working as a bridging fellow in institute of stem cell biology and regenerative medicine (instem), Bangalore, India. His research interests are Chemosensors, Chemical Biology, and Computational Chemistry.
Subramanian Singaravadivel completed B. Sc. in 2004 and M.Sc. in chemistry in 2006 from G. T. N. Arts College Dindigul affiliated to Madurai Kamaraj University, Madurai. He joined for Ph. D. in 2006 under the supervision of Professor S. Rajagopal at Madurai Kamaraj University, Madurai and received doctoral degree in 2013. He worked as a postdoctoral fellow at Institute of Chemistry; Academia Sinica with Prof. Kuang-Lieh Lu in 2012–2013 in the field of Rhenium based supramolecular chemistry for sensor. He is currently working as assistant professor in chemistry at SSM Institute of Engineering and Technology. His field of interest is design and synthesis of fluorescent probes for sensing heavy metal ions, explosives and small molecules.
Prof. Konda Ramasamy Krishnamurthy is a chair professor of National Centre for Catalysis Research at Indian Institute of Technology Madras, India, with expertise in Catalysis, Analytical Chemistry, and Nanotechnology. He had been as a vice-president of Reliance Industries for 7 years (2002–2009). Before this, he was with R&D Centre, Indian Petrochemicals Corporation, Baroda from 1976 to 2002. He has published exclusively in many international journals and hold several patents in the field of expertise. His research interest lies in hydrogenation, carbon dioxide conversion and water splitting.
Prof. Balasubramanian Viswanathan is presently associated with the National Centre for Catalysis Research at the Indian Institute of Technology (IIT) Madras, India after his retirement from the Department of Chemistry in 2004. He has been in academic services since 1970 and has consistently introduced new frontier courses in educational curriculum at IIT Madras and has contributed more than 40 books published by national and international publishers including several e-books. He has published extensively in international journals and has been awarded numerous patents. His research publications have received more than 10 000 citations, and his H-index is 52. He is interested in the fields of catalysis, solid state materials and hydrogen energy.