Synthesis of red photoluminescent nickel doped self-assembled copper nanoclusters and their application in biothiol sensing
Introduction
Metal based photoluminescent (PL) nanomaterials, such as metal nanoclusters (NCs) [1], [2], [3], [4], [5], semiconductor quantum dots (QDs) [6], [7], [8], [9], perovskite QDs [10], [11], [12], etc., have been used as nanoprobes for PL sensors due to their controllable synthesis, high PL intensity and photobleaching resistance. For those nanodots, II-VI CdSe/ZnS QDs, I-III-VI AgInSe QDs, II-III-VI CuInS QDs, and perovskite QDs contain Cd, In, and Pb, which is highly toxic and harmful to environment. Thus, we chosen Cu NCs as nanoprobe because of the metal Cu is inexpensive, abundant, and widely used in industries. The Cu NCs consist of a few or dozens of Cu atoms protected with surface ligands possess discrete electronic states and exhibit molecule-like properties [13], [14]. The PL property of Cu NCs mainly originates from a metal-centered triplet state caused by the ligand-to-metal charge transfer (LMCT) or ligand-to-metal−metal charge transfer (LMMCT) between metal core and surface capping ligands [15], [16], [17]. However, the vibration and rotation of protected ligands of individual NCs induce nonradiative relaxation of excited states, resulting in weak emission intensity of individual NCs.
Recently, the studies of the aggregation induced emission (AIE) and self-assembly induced emission (SAIE) of metal NCs provide a way to optimize and adjust the PL property of metal NCs. For aggregated metal NCs or assembled metal NCs, the restrain of the molecular motion of capping ligands facilitates radiative relaxation of the excited states electrons, leading to significant enhancement of emission intensity [18], [19], [20], [21]. Compared with aggregated metal NCs, assembled metal NCs are capable of further controlling the spatial arrangement of individual NCs in assembly, as well as the inter-NC interactions [22], [23], [24]. Thus, the emission intensity and wavelength are possibly tailored. To date, various studies for enhancing the emission intensity of metal NCs have been reported by inhibiting the molecular motion of ligands. As it is known, the PL of metal NCs depends not only on the character of surface ligands but also on metal core [25], [26], [27]. The metal atoms doped is a conventional strategy for adjusting the PL property of metal-based PL nanomaterials [28], [29], [30], [31]. Using Au, Ag, and Cu elements both as fundamental metal compositions and doped atoms, many individual doped and alloyed metal NCs are synthesized [32], [33], [34]. Yang’s group reported that Au(I) was doped into self-assembled Cu NCs, which give rise to Cu-Au metallophilic interaction and then affect the LMMCT approach [35]. Considering the similar chemical property between Cu and Ni, Ni may be suitable to serve as the doped heteroatom and then affect the LMCT and LMMCT process. As a result, the relaxation process of excited electrons changed.
Biothiols, such as cysteine (Cys), homocysteine (Hcy) and glutathione (GSH), are crucial biological molecules consisting of thiol group, which are widespread in heart, liver, and brain [36]. Cys, Hcy, and GSH play vital roles in many physiological approaches, for instance, providing nutrition for cells and organisms, maintaining structure and function of protein, and keeping the reductive environment of cells [37]. Moreover, the levels of Cys, Hcy, and GSH in physiological environment are closely related to many diseases. Enhanced level of biothiols is connected with cardiovascular and neurotoxicity diseases, while lack of biothiols is also associated with lethargy, weakness, edema, skin lesions, and liver damage [38], [39]. Thus, determination of biothiols in blood, urine, and other physiological environments is very significant for human healthy.
Herein, using 4-(trifluoromethyl) thiophenol (TTP) as reducing agent and protecting ligand, the self-assembled Cu NCs were prepared by a one-step synthesis method. The Cu NCs were assembled to nanoribbons architecture without Ni doping, while the Cu NCs were assembled to nanowires after doped with Ni. The PL intensity of Cu NWs with 3% Ni-doped showed a 3-fold emission enhancement than Cu NRs, and the absolute QY was increased from 4.53% to 19.76%. The morphology, composition, geometric structure, arrangement and PL property of assembled Cu NCs were studied. Both the PL of Cu NRs and Cu NWs was sensitive and selective to the existence of Cys, Hcy, and GSH. So, a sensing system for detection of biothiol was proposed and the PL test strips based on assembled Cu NCs were prepared by dropping Cu NWs dispersed solution on cellulose paper. The as-prepared PL probe and test strip was successfully applied to measure the Cys and Hcy in fetal bovine serum sample.
Section snippets
Preparation of Cu NRs
12.1 mg of Cu(NO3)2·3H2O was dissolved in 0.5 mL of ethanol and then added into 3 mL of dichloromethane. Then, 20 µL of TTP was added and the mixture was stirred at room temperature. After 3 h, the prepared product was isolated by centrifugation. The precipitate was washed three times with ethanol and finally dispersed in ethanol.
Preparation of Ni-doped Cu NWs
1.2 mg NiCl2.6H2O and 12.1 mg of Cu(NO3)2·3H2O were both dissolved in 0.5 mL of ethanol and added into 3 mL of dichloromethane. Then, 20 µL of TTP was added and the
Self-assembled Cu NRs
The self-assembled Cu NCs were synthesized in dichloromethane using TTP as the capping ligand cum reductant. After stirring at room temperature for 3 h, a light yellow product was obtained, which exhibited red emission under 365 nm UV light (inset of Fig. 1E). TEM and SEM images show that the as-prepared Cu NCs were self-assembled to nanoribbons architectures with average length about 300–400 nm and width about 10–15 nm (Fig. 1A, S1). The composition of Cu NCs was investigated by MALDI-TOF MS,
Conclusion
In summary, the Cu NRs and Ni-doped Cu NWs were prepared with a one-step synthesis method by mixing TTP ligand and metal ions precursor in dichloromethane. The Cu NRs exhibited red emission at 615 nm with a QY of 4.53%. After Ni doping, the PL intensity of the Cu NCs assembly obviously enhanced. When added Ni amount increased to 3%, the PL intensity showed a 3-fold emission enhancement with absolute QY as high as 19.76%. The doped Ni atom homogeneous distributed within the nanowires through
CRediT authorship contribution statement
Ailing Han: Conceptualization, Methodology, Investigation, Writing – original draft, Writing – review & editing. Xiaoyu Luo: Data curation, Writing – review & editing. Sijia Hao: Writing – review & editing. Yayu Yang: Writing – review & editing. Jianan Chen: Writing – review & editing. Guozhen Fang: Supervision. Jifeng Liu: Conceptualization, Supervision. Shuo Wang: Supervision.
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.
Acknowledgment
This work was supported by Natural Science Foundation of China (Funding, 21575102) and the National Key Research and Development Program of China (project No. 2020YFF0305002).
Ailing Han is presently pursuing for her doctor degree in food science in Tianjin University of Science and Technology.
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2022, Materials CharacterizationCitation Excerpt :Adjacent precipitates sharing the same crystallographic orientation spontaneously assemble, and then they would join at the interface [49]. The precipitates with different orientations assemble by atomic motion in the solidification [50–52]. The motion of atoms causes the transition region between sphere-like precipitates to go from disordered, dislocated to coherent atomic arrangement.
Ailing Han is presently pursuing for her doctor degree in food science in Tianjin University of Science and Technology.
Xiaoyu Luo is presently pursuing for his doctor degree in food science in Tianjin University of Science and Technology.
Sijia Hao is presently pursuing for her doctor degree in food science in Tianjin University of Science and Technology.
Yayu Yang is presently pursuing for her doctor degree in food science in Tianjin University of Science and Technology.
Jianan Chen is presently pursuing for her doctor degree in food science in Tianjin University of Science and Technology.
Guozhen Fang is a professor at College of Food Engineering and Biotechnology, Tianjin University of Science and Technology. Her main research interests focus on food nutrition and safety.
Jifeng Liu is a professor at College of Food Engineering and Biotechnology, Tianjin University of Science and Technology. His main research interests focus on food nutrition and safety.
Shuo Wang is a professor at Research Center of Food Science and Human Health, Nankai University. His main research interests focus on food nutrition and safety.