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2190-4286-8-188

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2190-4286-8-188

Abstract

  • Carbon nano-onions (CNOs) are highlighted as promising agents for bioimaging due to their low toxicity and ability to penetrate cells.

  • This study details the functionalization of CNOs with a specific BODIPY dye, enabling fluorescent activity that can switch on/off in response to pH changes.

  • The switching mechanism is attributed to the photoinduced electron transfer (PET) attributes of the BODIPY dye.

Introduction

  • Diagnostic applications increasingly rely on nanomaterials that can sense physiological changes in cells.

  • Fluorescent nanosensors are cost-effective and simple to operate, capable of generating optical responses to stimuli.

  • Intracellular pH is critical to cell health, with fluctuations indicating various cellular processes.

Properties of CNOs

  • CNOs are an attractive class of carbon nanomaterials for imaging due to:

    • Low density and high surface area to volume ratio

    • Spherical shape allowing versatile functionalization

  • CNOs show low inflammatory response and cytotoxicity, with successful internalization into cancer cells.

Functionalization Process

  • The procedure includes:

    • Oxidation of CNOs using nitric acid to create carboxylic groups.

    • Reaction of oxidized CNOs with BODIPY dye to create fluorescently labeled CNOs (fluo-CNOs).

Mechanism of Action

  • The modulation of fluorescence in fluo-CNOs is linked to protonation states of the dimethylamino group in the BODIPY:

    • Non-protonated form (BODIPY 3) exhibits lower fluorescence at 737 nm when pH is neutral or basic.

    • Protonated form (BODIPY 4) leads to enhanced fluorescence at 637 nm in acidic conditions.

  • The fast and reversible nature of the on/off fluorescence switching is ideal for pH-sensing applications.

Results and Discussion

Synthesis

  • Synthetic Schemes:

    • Scheme 1: Details the BODIPY synthesis.

    • Scheme 2: Illustrates the preparation of oxidized CNOs.

Characterization

  • Photophysical Properties:

    • Emission spectra confirm the switching between different BODIPY states upon changing pH.

  • Dynamic Light Scattering (DLS) indicated effective hydrodynamic diameters of oxi-CNOs and fluo-CNOs.

  • Confocal Microscopy studies demonstrate successful internalization and pH-triggered fluorescence in HeLa cells.

Cytotoxicity Studies

  • Fluo-CNOs showed moderate toxicity, with cell viability above 80% across various concentrations.

    • Impacts on HeLa cells further emphasize the materials' suitability for use as intracellular sensors.

Conclusion

  • BODIPY-CNO probes were synthesized and demonstrated rapid fluorescence modulation based on pH changes.

  • The potential applications of these probes in biological sensing highlight their relevance in diagnostics.

Experimental Techniques

  • Characterization Techniques: Include TGA, Raman spectroscopy, fluorescence spectroscopy, DLS, and NMR spectroscopy to assess the compounds.

  • Cell Culture: HeLa cells were maintained and assessed for cytotoxicity using standard protocols.