Regular ArticleHand-ground fullerene-nanodiamond composite for photosensitized water treatment and photodynamic cancer therapy
Graphical abstract
Introduction
The capability of C60 in absorbing broadband light and mediating photosensitized reactions was recognized soon after its discovery [1] and has been exploited to enhance light harvesting in applications including organic solar cell [2], photodynamic therapy (PDT) [3], [4], [5], [6], [7], [8], [9], and water treatment [10], [11], [12], [13], [14]. The production of reactive oxygen species (ROS) such as 1O2 and O2•- through energy and electron transfer, respectively, to molecular oxygen [15], [16] has been the primary goal of using C60 as a photosensitizer in some aqueous phase applications. For example, 1O2 can oxidatively degrade organic pollutants [13] and inactivate microorganisms [17], [18], [19], as well as induce cancer cell apoptosis when localized at cancer sites [20]. However, the hydrophobic nature of C60, which prevents molecular dispersion and leads to the formation of less reactive colloidal clusters, is a well-recognized, inherent limitation. Strategies developed so far to enable aqueous dispersion without altering its spherical conjugated structure and intrinsic photophysical property include encapsulation with surface active agents such as poly(ethylene glycol) [20], [21], poly(vinyl alcohol) [22], [21], poly(N-vinylpyrrolidone) [22], γ-cyclodextrin [23], dendrimers [24] , sugars [25], and amino acid [26], [27] as well as immobilization onto colloidal substrates such as graphene [28] and silica [29], [11], [13].
We here present a strikingly simple approach to make C60 available to these applications by hand-grinding dry C60 powder with nanodiamond (ND) using a mortar and pestle. This newly-developed method is highly scalable and does not require any organic solvents nor complex synthetic procedures. Despite what the name might imply, ND is a relative inexpensive and biocompatible material [13], [30] and has been explored for the development of both biomedical [30], [31], [32] and environmental remediation technologies [33]. ND is distinguished from other carbonaceous nanomaterials by its unique all-carbon core–shell structure. Inner diamond core sp3 carbons are surrounded by the shells of sp2 carbons. We hypothesize that these highly conjugated carbons of ND shell strongly interact with conjucated carbons in C60 to enable strong binding between these materials. A fraction of ND shell carbons are oxygen functionalized, endowing hydrophilicity and allowing this composite (referred to herein as ND-C60) to be dispersed in water and the physicological media. Accordingly, this study examines whether ND can function like a surfactant to stablize C60 in aqueous phase applications such as visible-light-driven PDT and pollutant destruction.
Section snippets
Photochemical and photoelectrochemical experiments
See Text S1 for the specifications of chemicals and water used in this study. Batch photochemical experiments were performed using a magnetically stirred cylindrical quartz reactor under air-equilibrated conditions at ambient temperature (20 ± 1 °C). The reaction solution (50 mL) was prepared by adding the powder (0.5 or 1 gL-1) and the target organic compound (0.02 mM). pH of the solution was adjusted at 7 with 1 mM phosphate buffer. The reactor was illuminated by six 4 W fluorescent lamps
Characterization
We first mildly oxidized ND (Carbodeon Co.; 5 wt% aqueous suspension) by annealing at 430 °C for 5 h in a muffle furnace under ambient atmosphere [33], [35], [36]. Then we mixed the dried ND with dry powder of C60 (SES Research; purity > 99.75%) at varying mass ratios (ND:C60 at 5:1, 2:1, 1:1, 1:2, and 1:5) and hand-ground the mixture using a mortar and pestle for 5 min. Control experiments confirmed that 5 min (approximately 500 times of circular grinding motion) was sufficient to result in
Conclusions
Fullerene is known to generate reactive oxygen species under visible light illumination, and has recently attracted attention for applications in water purification and cancer therapy. However, these applications often face challenges due to limited dispersibility of C60 in water and physiological solution. In this study, we discovered that composites prepared by simply hand-grinding C60 with nanodiamonds in mortar can be readily dispersed in water. The availability in water was enhanced by the
CRediT authorship contribution statement
Hongshin Lee: Conceptualization, Investigation, Writing - original draft. Jung Seok Lee: Conceptualization, Investigation, Writing - original draft. Kyle J. Moor: Methodology, Validation. Hyoung-il Kim: Methodology, Validation. Sang-Ryoung Kim: Methodology, Validation. Geondu Gim: Formal analysis. Jaesang Lee: Formal analysis. Hak-Hyeon Kim: Formal analysis. Tarek M. Fahmy: Conceptualization, Supervision. Jae-Hong Kim: Conceptualization, Writing - original draft, Writing - review & editing,
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This work was supported by a National Research Foundation of Korea (NRF) Grant (NRF-2017R1A2B3006827 and NRF-2016R1A6A3A11933788).
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These authors contributed equally to this work.