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    Topic review

    Quantum Dots

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    Submitted by: Atiqah Salleh


    Quantum dots (QDs) are an advanced nanomaterial technology deem to be useful in clinical and biomedical applications. QDs have given a big impact in biomedical application due to their imaging potential which significantly improved the clinical diagnostics test. Meanwhile, QDs also have the potential to become the nanocarrier for the drug.

    1. Characteristics of Quantum Dots

    Quantum Dots (QDs) were first discovered by Ekimov and Onushenko in 1981, and are nanoscale semiconductor crystals and first nanotechnologies to be applied in biological science made of heavy metals [1][2]. QDs have shown great potential in several biomedical types of research including fluorescence imaging, disease detection, fluorescence assays for single protein track, drug discovery and intracellular reporting due to their mechanical and physicochemical properties [3]. QDs have five distinct properties that ameliorate tremendous research interest including (1) the nano size ranges from 4 until 12 nm in diameter, (2) narrow and size-tunable Gaussian emission spectra which excite to the near-infrared (NIR); lower than 650 nm, (3) self-luminescence due to their absorption extinction coefficients and high fluorescence quantum yields, (4) QDs are photochemically robust due to its inorganic composition and the fluorescence intermittency with observation of single dot event, (5) observing a single protein compound [4].

    The synthesis of QDs results in organic capping ligands that make them biocompatible, and a biological targeting development which achieved by surface modification and linking with antibodies, peptides or small molecules [4][5]. QDs also have been applied in biomedical applications such as delivery of drug, bio-sensing and also tissue engineering [6]. QDs are ideal nano-carriers for the drug due to their high surface area to interact with other molecules especially their strong interactions with organic molecules and specific compounds [7]. Application of QDs in drug delivery has increased drug stability, prolonged in vivo circulation time, improve the distribution and metabolism process of drugs and enhance absorption [3]. The optical properties of QDs have been used for bio-imaging applications in various biological research for deep-tissue imaging with reduced light scattering and low tissue absorption [8]. Researchers worldwide used the QDs as fluorescence labeling for both in vivo cellular imaging and in vitro assay detection due to photoluminescence properties [9].

    There have been increasing research on QDs in wound healing as these nanoparticles equip the same properties as their bulk counterparts and more stable due to their large surface area [10]. The unique physicochemical characteristics of QDs are highly beneficial in tissue engineering applications especially their antibacterial properties as these aspects are important in development of biomaterials. QDs also can enhance the mechanical strength of tissue scaffolds and hydrogels for wound healing, or for regenerative medicine [11]. Due to its nano-scale size (less than 20 nm), QDs have low toxicity towards the cells and have enzymatic functions such as oxidase which make it suitable to be incorporated into a bioscaffold [12]. The large surface area of QDs could bind to the ligands which involved in wound healing process. For example, carbon quantum dots proven to involve in angiogenesis process as these nanoparticles able to enhance the anti-angiogenic factors expression which is crucial to avoid overexpression of pro-angiogenic factors expression [13]. QDs also involve in signaling pathway which enhance the inflammation phase of wound healing as it increases the interleukin-6 expression [14].

    2. Wound Healing Properties of QDs

    The outcomes from the review highlighted the advantageous of quantum dots (QDs) in wound healing. There are various reports on the application of QDs in wound healing and it has been tested in vivo, in vitro and in ovo model. The overall result of QDs seems to be beneficial towards wound healing as the treatment group obtains better results compared to the control group. However, the combination of QDs with polymer e.g., carbon quantum dots with hybrid tannic acid and keratin (CQDs-TA/KA) hydrogel yields a more appealing result compared to QDs itself [15].

    2.1. Wound Closure

    The in vivo studies were used to study the biological effect of QDs in a dynamic and complex biosystem e.g., the wound closure. Apart from having QDs derived from various types of heavy metals, the papers were primary aim to assess their biological effect in selected wound model in each study. Most of the studies inflict a cutaneous incisional wound and there only one study that inflicts burn wound on the animal. The wound healing assessments were performed by gross morphology of the wound, the size of wounds and the histological evaluation using hematoxylin and eosin (H & E) staining to determine the condition of the regenerated tissue [16]. The in vivo studies reporting the effects of QDs on wound healing were simplified in Table 1.

    Table 1. In vivo study on wound healing.

    Based on the results obtained, the QDs supports the wound healing process in vivo. The histological assessment shows the regeneration of tissue and formation of blood vessel when treated with QDs. Xiang et al., 2019 show even disposition of collagen and dense collagen fibers when treated with QDs [17]. Haghshenas et al., 2019 show that QDs involve the formation or regeneration of tissue at the wound site are faster in treated compare with non-treated model [18]. In the context of wound healing, progression in the inflammatory stage depends on the suitable microenvironment at the wound site. Infection is also one of the factors which affect the healing process where it is important for the removal of micro-organisms before advancing to the next stage of wound healing process [19]. Microbial infections may prolong the inflammatory stage and causing high expression of pro-inflammatory cytokines (interleukin 1 alpha, interleukin 1 beta and tumor necrosis factor alpha) that not only harmful towards infected cells but also healthy cells [20].

    The entry is from 10.3390/polym13020191


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