Ultra-bright green carbon dots with excitation-independent fluorescence for bioimaging

Abstract

Current and future diagnostics urgently need imaging agents that are non-toxic and superior to clinically used small molecule dyes. Herein, we have developed luminescent green light-emitting carbon dots (GCDs) via a single-step hydrothermal reaction using a low-cost chemical precursor, p-toluenesulfonic acid. The GCDs exhibit excitation-independent fluorescence (FL) emission with the photoluminescence quantum yield of 70% and no FL quenching up to 1.25 mg/mL. The GCDs exhibit negligible cytotoxicity up to 250 µg/mL concentration in RAW 264.7 cells. Interestingly, GCDs exhibit an excitation-independent and concentration-dependent fluorescence emission behaviour. In vitro, the peak emission was obtained at 520 nm using the excitation at 430 nm. Whereas FL intensity increased with increasing concentration up to 1.25 mg/mL and a sharp decrease in FL intensity is observed upon further increasing the concentration of GCDs. Upon subcutaneously injecting the GCDs into a euthanized mouse, a similar concentration-dependent FL behaviour is evident. Background autofluorescence hinders the use of the GCDs at 420 nm excitation, however, a strong FL emission at 520 nm can be obtained by exciting subcutaneously injected GCDs at 465 nm—demonstrating excitation-independent emission characteristics. The above results indicate the potential of the non-toxic, low-cost carbon dots for diverse bioimaging applications. Graphical abstract Ultra-bright green-emitting carbon dots (GCDs) with photoluminescence quantum yield of 70% were synthesized using p-toluenesulfonic acid and ethylenediamine as precursors. The GCDs were subcutaneously injected into fresh mouse cadaver for fluorescence (FL)bioimaging, showing dose-dependent FL intensity behaviour.

Biomass-Based Carbon Dots for Fe3+ and Adenosine Triphosphate Detection in Mitochondria

“…These data demonstrated that GB-CDs have long shelf-life stability and great preparation reproducibility, great merits for commercial use. Similarly, green light-emitting CDs prepared by hydrothermal treatment of p -toluenesulfonic acid and ethylenediamine showed a good stability with a charge of −18 mV …”

“…Similarly, green light-emitting CDs prepared by hydrothermal treatment of p-toluenesulfonic acid and ethylenediamine showed a good stability with a charge of −18 mV. 62 2.6. Fe 3+ Detection in Mitochondria Using GB-CDs.…”

Facile synthesis of graphene quantum dots with red emission and high quantum yield

“…Therefore, the solution concentration has a great influence on the QY of red light emission. 51 Considering the featured GQDs with long-wavelength emission and high QY, the as-prepared GQDs have been proposed to serve as an intracellular imaging probe. Hence, the properties of aqueous the GQD solutions have been studied.…”

A Carbon Nanodot Based Near-Infrared Photosensitizer with a Protein-Ruthenium Shell for Low-Power Photodynamic Applications

“…29 However, these bioconjugates can only be activated by 470 nm light irradiation, thus limiting deep tissue penetration. Carbon nanodots (Cdots) have attracted major interest as fluorescent sub 10 nm carbon nanomaterials for biomedical applications due to their ease of synthesis, 30,31 facile surface functionalization, 32 biocompatibility, 33 chemical stability and photostability, 34 photoluminescence (PL), 35 and efficient twophoton absorption even at low irradiation power. 36,37 Several of their photophysical and biological properties are comparatively better than those of easily photobleachable fluorescent organic dyes and conventional toxic semiconductor nanomaterials such as heavy-metal-containing quantum dots.…”

“…Carbon nanodots (Cdots) have attracted major interest as fluorescent sub 10 nm carbon nanomaterials for biomedical applications due to their ease of synthesis, , facile surface functionalization, biocompatibility, chemical stability and photostability, photoluminescence (PL), and efficient two-photon absorption even at low irradiation power. , Several of their photophysical and biological properties are comparatively better than those of easily photobleachable fluorescent organic dyes and conventional toxic semiconductor nanomaterials such as heavy-metal-containing quantum dots . Recently, conjugates composed of carbon nanodots and a PS have been reported for NIR two-photon activated PDT, including (a) carbon quantum dot–protoporphyrin IX sensitizers that were activated at 800 nm irradiation (80 mW femtosecond (fs) laser power) by a two-photon excitation process, (b) carbon nanodot–5,10,15,20-tetrakis­(1-methyl-4-pyridinio)­porphyrin tetra­( p -toluenesulfonate) conjugates that were excited with fs lasers (160 mW/cm 2 ) at 700 nm, (c) a noncovalent nanocomposite from single-walled carbon nanotubes and Ru­(II) complexes for efficient dual phototherapy employing an 808 nm diode laser (0.25 W/cm 2 ), and (d) a nanohybrid composed of carbon nanodots and a Ru­(II) complex for lysosome-targeted PDT using an 810 nm laser (100 mW, 100 fs) .…”