Selective recognition of Fe3+ and Cr3+ in aqueous medium via fluorescence quenching of graphene quantum dots

Water-soluble graphene quantum dot-based polymer nanoparticles with internal donor/acceptor heterojunctions for efficient and selective detection of cancer cells

We present a new, insightful donor-acceptor (D-A) energy transfer-based strategy for the preparation and development of water-soluble multifunctional pH-responsive heterojunction nanoparticles. Hydrophilic tertiary amine-grafted polythiophene (WPT) as a donor and blue fluorescent graphene quantum dots (GQD) as an acceptor spontaneously form co-assembled nanoparticles that function as a highly pH-sensitive and efficient biosensor appropriate for the detection of cancer cells. These WPT/GQD nanoparticles exhibit a number of unique physical characteristics-such as broad-range, tunable GQD-loading contents and particle sizes, extremely low cytotoxicity in normal and cancer cells, and highly sensitive pH-responsiveness and rapid acid-triggered fluorescent behavior under aqueous acidic conditions. We show these features are conferred by self-aggregation of the GQD within the nanoparticles and subsequent aggregation-induced fluorescence of GQD after disassembly of the nanoparticles and dissociation of the D-A interactions under acidic conditions. Importantly, in vitro fluorescence imaging experiments clearly demonstrated the WPT/GQD nanoparticles were gradually taken up into normal and cancer cells in vitro. Selective formation of GQD aggregates subsequently occurred in the acidic microenvironment of the cancer cells and the interior of the cancer cells exhibited strong blue fluorescence; these phenomena did not occur in normal cells. In contrast, pristine WPT and GQD did not exhibit cellular microenvironment-triggered fluorescence transitions in cancer or normal cell lines. Therefore, this newly discovered water-soluble heterojunction system may represent a strongly fluorescent highly pH-sensitive bioprobe for rapid detection of cancer cells.

Green-synthesized, pH-stable and biocompatible carbon nanosensor for Fe3+: An experimental and computational study

Brightly fluorescent Carbon Dots (CDs) were synthesized by green hydrothermal method using commonly available biomass (Aloe vera) as carbon precursor. Their physiochemical and optical characterization was done by standard microscopic and spectroscopic techniques. Photophysical features of their aqueous dispersion were investigated in detail. The influence of wide pH range (2–12), high ionic load (2M) and temperature on their photoluminescence behavior was investigated. Their in-vitro cytotoxicity examination was conducted on Human Cervical Cancer Cells (HeLa) using MTT assay. Testing of their ion-recognition property for common metal ions was done in aqueous medium. These CDs exhibited preferential interaction with Fe³⁺ over other tested metal ions, without any functionalization. Interaction between CDs and Fe³⁺ was analyzed in the light of Density Functional Theory (DFT). The work demonstrates that these CDs are acting as nanoprobe for Fe³⁺ and sensing it at ultra-trace level (5 nM).

Synthesis of highly fluorescent and water soluble graphene quantum dots for detection of heavy metal ions in aqueous media

Fluorescent graphene quantum dots (GQDs) are nanomaterials which possess unique properties that show great potential in different applications. In this work, GQDs were synthesized using graphene oxide (GO) as precursor via thermal treatment at high temperature. The obtained GQDs were highly fluorescent and were suitable for the determination of heavy metal ions. X-ray diffraction, FTIR spectroscopy, and UV visible spectroscopy confirm the formation of GQDs. TEM images show that formed GQDs have size ranging from 2 to 10 nm. Emission profile of aqueous GQDs was taken by exciting GQDs at different wavelength. The intensity of GQDs remains the same for 4-5 months. Furthermore, as prepared, GQDs were used for selective recognition of Fe³⁺, Pb⁺², and Cr³⁺ from the bunch of different metal ions in aqueous media. Lower limit of detection obtained for Fe³⁺, Cr³⁺ and Pb²⁺ using GQDs were 50, 100 and 100 nM, respectively, which indicates that the GQDs can be utilized as a promising material for sensing of the heavy metal ions. Graphical abstract.