Tailored fluorescence traits of pulse laser ablated Gold-Cinnamon nanocomposites
Introduction
Various organic, inorganic, and hybrid nanoparticles with unique attributes (size below 100 nm, large surface area, stability, non-toxic, high biocompatibility, ferromagnetic, paramagnetic, strong fluorescence (FL), chemical inertness and so forth) that are absent in their bulk/macro-scale counterparts are excellent candidates for diverse applications [1], [2], [3], [4]. Particularly, the essential physiochemical properties of gold (Au)/cinnamon (Ci) nanocomposite particles (Au-Ci NCPs) that are advantageous for different nanobiomedicinal applications can be customized by controlling their morphology and chemical surface structure [5], [6]. These novel NCPs as nanovehicles became promising for the bio-molecular vectorization with extensive relevance (for example targeted drug delivery). The strong surface plasmon resonance (SPR) enabled several emergent properties Au-NPs make them potential for diverse technological applications [7].
The colloidal Au-Ci NCPs are versatile due to their outstanding biocompatibility, sustainability, easy reproducibility, excellent chemical stability, and admirable optical properties [5], [6], [7]. The large scale fabrication of the Au/Ci NPs following the wet chemistry approaches is limited because of the requirement of extra purifications, precursors, toxic materials, and external conditions to control their morphology [5], [4]. To surmount these problems, the eco-friendly (as the green chemistry route) nanosecond pulse laser ablation in liquid (PLAL) technique has emerged as an alternative strategy to synthesis varieties of agglomerated NPs without requiring any surfactant and strong reducing agent that typically poison the active surface areas of NPs [8]. The PLAL technique is preferred for making different organic/inorganic NPs because of its easy experimental protocols, economy, high productivity, capability to produce the in-situ dispersion of the NPs in diverse liquids, and long-term stability [8], [9].
Different strategies have recently been adopted to enhance the FL gain and stability of the Au-NPs by customizing their physiochemical properties, wherein the morphology was altered by coating their surfaces with inert shells of organic structures [1], [7], [10]. The mechanism of the SPR enabled enhanced FL from Au-NPs was mainly attributed to the increased excitation rate mediated by the local field enhancement (LFE) effect. Effectively, the observed SPR assisted improved emission rate in these NPs was ascribed to the enrichment of the plasmonic quantum yield [11]. Li et al. [11] argued that the lifetime modification of the fluorescent molecules is related to the SPR mediated LFE effect of the single metal NP. Furthermore, the decrease in the FL lifetime of the fluorophores close to the metal NPs was shown to be strongly dependent on the SPR bands and physical properties of the NPs [7], [10], [11], [12], [13], [14].
Considering the immense benefits of the inorganic-organic nanocomposites, some Au-Ci NCPs were prepared using PLAL technique and characterized for the first time. These Au-Ci NCPs were shown to be fundamentally interesting due to their extended miscibility gaps and differing crystal structures than their bulk counterparts, indicating diverse applications potential.
Section snippets
Preparation and characterisations
First, the Au and Ci NPs were prepared disjointedly using the PLA of the Au/Ci target immersed in 8 mL liquid ethanol (C2H5OH of 96% purity, Sigma-Aldrich) without any precursors. A Q-switched Nd:YAG pulse laser (wavelength of 1064 nm, pulse duration of 10 ns and frequency of 1 Hz) was focused (spot size of 2 mm) vertically through a planoconvex lens (focal length of 8 cm) onto the gold target (purity >99.9%, dimension of 25 mm × 25 mm) and natural cinnamon stick (purchased from local
Results and discussion
Fig. 1 (a–c) shows the HR-TEM images of the as-synthesised Au-NPs, Ci-NPs and Au–Ci NCPs. The insets of each figure reveal the crystallinity, size distribution, EDX spectra and maps (elemental compositions) of the corresponding sample. Table 1 summarizes the samples codes, laser fluence, different properties, mean sizes of the NPs ± standard deviation (SD) and quantum efficiency (η). Uniformly dispersed nearly spherical NPs were achieved (Insets a1, b1, and c1). The SAED patterns of samples
Conclusions
The simple and novel PLAL technique was used to produce high quality Au-Ci NCPs for the first time. Through laser parameters optimization it was possible to lessen the FL lifetime of the Au-Ci NCPs (acted as fluorophores) very close to the Au-NPs. This tailored FL properties of the Au-Ci NCPs was essentially decided by the synergistic spectral overlap between the FL emission and SPR bands. Based on these findings, it was established that the proposed Au-Ci NCPs may contribute towards the
Credit author statement
All authors discussed the results and contributed to the final manuscript, provided critical feedback and helped shape the research, analysis and manuscript. Authors contributed to the design and implementation of the research, to the analysis of the results and to the writing of the manuscript.
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
The authors appreciate the financial support from RMC-UTM 04E86 and MOHE FRGS 5F050.
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