Carbon Dot Based, Naphthalimide Coupled FRET Pair for Highly Selective Ratiometric Detection of Thioredoxin Reductase and Cancer Screening

Abstract

The fluorescence resonance energy transfer (FRET) mechanism has been established between carbon dots (CDs) and naphthalimide to monitor the activity of thioredoxin reductase (TrxR), which is often overexpressed in many cancer cells. The naphthalimide moiety was covalently attached to the surface of CDs through a disulfide linkage. In normal cell conditions (when devoid of high concentrations of TrxR), the CDs act as an energy donor and naphthalimide acts as an acceptor, which establishes the FRET pair as interpreted from the emission at λ = 565 nm, when excited at λ = 360 nm. However, contrary to this, the elevated levels of TrxR cause the breakage of disulfide bonds and consequently abolishes the FRET pair through the release of the naphthalimide moiety from the surface of CDs. This process was studied by monitoring of fluorescence intensity at λ = 565 and 440 nm, when excited at the same wavelength (λ = 360 nm). The TrxR based ratiometric quenching and enhancement of fluorescence intensity offers an interesting opportunity to monitor the enzyme activities and has many advantages over conventional monitoring of fluorescence intensity at a single wavelength to avoid interference of external factors. Fluorescence images of cancer cells in response to the nanosensor were visualized under a confocal microscope. Cytotoxicity study of nanosensor retards the growth of HeLa and MCF-7 cell lines in the presence of visible light. Therefore, the nanosensor also acts as a theranostic agent to diagnose as well as killing of cancer cells.

Synthesis of a 3,4-Disubstituted 1,8-Naphthalimide-Based DNA Intercalator for Direct Imaging of Legionella pneumophila

“…Compound 1 was synthesized according to the procedure reported in the literature. 71 243 mg (1 mmol) of compound 1 was dissolved in 5 mL of ethanol and 3 mmol of hydrazine hydrate was added into it. The reaction mixture was refluxed for 6 h, and yellow precipitates were collected after filtration.…”

Ratiometric optical nanoprobes enable accurate molecular detection and imaging

“…In addition, Singh and co-workers employed Cdot and naphthalimide-based FRET pair to build a selective ratiometric nanosensor for cancer screening by sensing thioredoxin reductase (TrxR) activity, which is overexpressed in numerous cancer cells. 182…”

Carbon Dots for In Vivo Bioimaging and Theranostics

“…Additionally, thioredoxin reductase (TrxR) often overexpresses in cancer cells and mainly maintains the redox homeostasis between the thiol group and the disulfide reaction. Based on a Föster resonance energy transfer (FRET) mechanism, CDs with emission at 450 nm were developed as donors, coupled with a matchable FRET acceptor (3‐aminonaphthalimide with emission at 565 nm) via a linker of disulfide bonds . In the cancer cells, the overexpressed TrxR reduced the disulfide bond and released naphthalimide, which was used for sensing TrxR activity and screening cancer cells (Figure b).…”

“…b) Schematic representation of the sensing mechanism of thioredoxin reductase. Reproduced with permission . Copyright 2017, American Chemical Society.…”