Synthesis of Fluorescent Sulfur Quantum Dots for Bioimaging and Biosensing

Abstract

The rapid industrialization has had a serious impact on the environment, leading to an increase in disease and healthcare problems. The development of simple and effective biosensors to achieve specific analyte detection and bioimaging can provide useful information for disease prevention and treatment. Sulfur quantum dots (SQDs), a new class of metal-free fluorescent nanomaterial, are being studied and applied in diagnostic fields such as bioimaging and biosensing due to their advantages of simple synthetic process, unique composition, ultrasmall size, adjustable fluorescence, and low toxicity. This minireview highlights the main synthetic methods to synthesize fluorescent SQDs and their recent progress in cell and tissue imaging, as well as detection of biomolecules, metal ions, and temperature. Finally, the future development and some critical challenges of SQDs as a fluorescent probe in the field of bioimaging and biosensing are also discussed.

Synthesis and Characterization of SCDs/TiO2 Composite

“…The synthesis of TiO 2 was carried out based on the method proposed by Aritonang et al [4], starting with the preparation of Ti(OH) 4 sol using solution B containing titanium tetraisopropoxide (TTIP) precursor in ethanol solvent. Acetylacetone was then added to the mixture [16], and it was refluxed at 55 o C, followed by calcination to form sol [17][18]. This process produced white TiO 2 crystals, as previously reported by Aritonang et al [19].…”

“…Based on observations of the luminescence properties of SCDs using UV light illumination (λ = 365 nm), a yellowishgreen color was produced during the process. The emergence of this color was due to competition between various emission centers (bright edge states) that dominate the optical properties of SCDs [18].…”

Visible Light-Mediated Photoactivated Sulfur Quantum Dots as Heightened Antibacterial Agents

“…It has been well reported that the chemical structure of Sdots contains the polymeric sulfur core, that is, polysulfide ions ( S x 2– ). − Recently, the polysulfide anion was employed as an excellent visible light photoredox catalyst for organic transformations. , The polysulfide anion induces the reactions via single-electron transfer-driven radical-mediated processes . Therefore, we anticipated that the generation of the ROS was one of the primary reasons for the inhibition of bacterial growth in the presence of sunlight.…”

“…The minimum inhibitory concentration (MIC) of Sdots was found to be 0.16 mg/mL (D1), 0.56 mg/mL (D2), and 1.13 mg/mL (D3). Generally, Sdots contain a relatively less amount of sulfur than a large amount of the surface-stabilizing agent poly­(ethylene glycol) (PEG). − Therefore, the effective MIC concentration of Sdots based on the sulfur concentration is 0.01 mg/mL (D1), 0.034 mg/mL (D2), and 0.068 mg/mL (D3). , At the abovementioned MIC concentrations, a comparative study of bacterial growth observed after 6 h under sunlight, dark, and SBGC along with the control (C) is given in Figure (Figure S4, Supporting Information). In the plot, the significant inhibition of the growth in the presence of sunlight compared to SBGC is clearly observed.…”

“…Non-metallic quantum dots such as Cdots are explored for photoactivated antibacterial effects. , Recently, another non-metallic quantum dot of the nanosulfur family named sulfur quantum dots (Sdots) has emerged as a new class of non-toxic (or less toxic) fluorescent material. − Sdots consist of a polymeric sulfur core and exhibit exciting photophysical properties . Sdots have been employed for photoluminescence-related versatile applications. − Nanoscale sulfur (not Sdots) is known for antibacterial, fungicides, and pesticide activities. − Zhang and Rhim groups have reported the promising antibacterial effect of Sdots in recent times. , However, Sdots have not been explored as a visible light-activated antibacterial agent. Herein, we report the sunlight-activated antibacterial activity of Sdots for the first time (Scheme ).…”