Fluorescent carbon nanoparticles obtained from charcoal via green methods and their application for sensing Fe3+ in an aqueous medium

Single Step Solid State Synthesis of Carbon Nanoparticles for Instantaneous Detection of Fe (III) in Water Samples

Though iron is one of the vital micronutrients in biological systems excess of which is associated with various illness. Consumption of contaminated water and crops because of its extensive industrial utility is one of the major sources for excess iron in living beings. Hence, we have designed a sensor based on carbon nanoparticles for the detection of Fe (III) and we have also attempted to estimate Fe (III) in spiked water samples. Carbon nanoparticles (CNP) with quantum yield of 40.2 % was synthesized by solid state synthesis from aromatic molecular precursors unlike conventional synthesis methodology. The particle size, stability and optical properties of CNP were investigated by microscopic and spectroscopic techniques. CNP manifested a naked color change from colorless to yellow in presence of Fe (III) and 72 % of CNP's emission was quenched at 487 nm on excitation at 377 nm by Fe (III). The detection time was less than a second and limit of detection was calculated as 0.248 µM. The mechanistic aspect of detection was investigated and applicability of CNP was examined in spiked water samples.

What makes carbon nanoparticle a potent material for biological application?

Carbon materials are generally utilized in the form of carbon allotropes and their characteristics are exploited as such or for improving the thermal, electrical, optical, and mechanical properties of other biomaterials. This has now found a broader share in conventional biomaterial space with the generation of nanodiamond, carbon dot, carbon nanoparticles (CNPs), and so forth. With properties of better biocompatibility, intrinsic optical emission, aqueous suspendability, and easier surface conjugation possibilities made CNPs as one of the fore most choice for biological applications especially for use in intracellular spaces. There are various reports available presenting methods of preparing, characterizing, and using CNPs for various biological applications but a collection of information on what makes CNP a suitable biomaterial to achieve those biological activities is yet to be provided in a significant way. Herein, a series of correlations among synthesis, characterization, and mode of utilization of CNP have been incorporated along with the variations in its use as agent for sensing, imaging, and therapy of different diseases or conditions. It is ensembled that how simplified and optimized methods of synthesis is correlated with specific characteristics of CNPs which were found to be suitable in the specific biological applications. These comparisons and correlations among various CNPs, will surely provide a platform to generate new edition of this nanomaterial with improvised applications and newer methods of evaluating structural, physical, and functional properties. This may ensure the eventual use of CNPs for human being for specific need in near future. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Diagnostic Tools > Biosensing Diagnostic Tools > In Vitro Nanoparticle-Based Sensing Therapeutic Approaches and Drug Discovery > Emerging Technologies.

Optical properties and photoactivity of carbon nanodots synthesized from olive solid wastes at different carbonization temperatures

Carbon nanodots (CNDs) have many fascinating properties, such as optical properties (UV-Visible absorption and fluorescence emission), which make them good candidates in many applications, such as photocatalysts for the degradation of several organic pollutants. This study aims to synthesize CNDs from olive solid wastes at different carbonization temperatures from 300 to 900 °C and study the effect on the optical properties of the CNDs, such UV-Vis, fluorescence, quantum yield, and energy bandgap, in addition to the influence on the photoactivity of the CNDs as photocatalysts for the degradation of methylene blue (MB). CNDs were prepared from olive solid wastes (OSWs) by pyrolysis at different temperatures (300-900 °C) for conversion to carbonized material, and then oxidized chemically in the presence of hydrogen peroxide (H2O2). It was found that an increase in the carbonization temperature of the OSWs leads to an increase in the product yield with a maximum value at 500 °C, and it then decreased dramatically. On the other hand, a decrease in fluorescence due to the diminishment of oxygen groups and the destruction of the surface of the CNDs was observed. The higher quantum yield (5.17%) and bandgap (2.77 eV) were achieved for CNDs prepared from OSWs that carbonized at 300 °C. The rate and degradation efficiency of MB were studied with the different synthesized CNDs, and it was found that an increase in the carbonization temperature leads to a decrease in the rate and degradation efficiency of MB, with the highest degradation rate of 0.0575 min-1 and degradation efficiency of 100% after 120 minutes of light irradiation being realized for the sample carbonized at 300 °C.

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.

Carbon Dots for Intracellular pH Sensing with Fluorescence Lifetime Imaging Microscopy

The monitoring of intracellular pH is of great importance for understanding intracellular trafficking and functions. It has various limitations for biosensing based on the fluorescence intensity or spectra study. In this research, pH-sensitive carbon dots (CDs) were employed for intracellular pH sensing with fluorescence lifetime imaging microscopy (FLIM) for the first time. FLIM is a highly sensitive method that is used to detect a microenvironment and it can overcome the limitations of biosensing methods based on fluorescence intensity. The different groups on the CDs surfaces changing with pH environments led to different fluorescence lifetime values. The CDs aqueous solution had a gradual change from 1.6 ns to 3.7 ns in the fluorescence lifetime with a pH range of 2.6-8.6. Similar fluorescence lifetime changes were found in pH buffer-treated living cells. The detection of lysosomes, cytoplasm, and nuclei in living cells was achieved by measuring the fluorescence lifetime of CDs. In particular, a phasor FLIM analysis was used to improve the pH imaging. Moreover, the effects of the coenzymes, amino acids, and proteins on the fluorescence lifetime of CDs were examined in order to mimic the complex microenvironment inside the cells.

High Quantum Yield Fluorescent Carbon Nanodots for detection of Fe (III) Ions and Electrochemical Study of Quenching Mechanism

Carbon nanodots (CNDs) offer potential applications in photocatalysis, optoelectronics, bio-imaging, and sensing due to their excellent photoluminescence (PL) properties, biocompatibility, aqueous solubility, and easy functionalization. Recent emphasis on CNDs in the selective detection of metal ions is due to the growing concern for human and environmental safety. In this work, two types of fluorescent carbon nanodots (CNDs) are synthesized economically from ethylene diamine (E-CNDs) or urea (U-CNDs) in a single step microwave process. The as-prepared CNDs exhibit excellent PL at an excitation wavelength of 350 nm with a quantum yield of 64% for E-CNDs and 8.4% for U-CNDs with reference to quinine sulfate. Both E-CNDs and U-CNDs demonstrate high selectivity towards Fe (III) ions among different metal ions, by fluorescence quenching in a dose dependent manner. The limit of detection of E-CNDs and U-CNDs is observed to be 18 nM and 30 nM, respectively, in the linear response range of 0-2000 μM with a short response time (seconds). The CNDs detect Fe (III) ions in tap water and serum sample with no spiking and the recovery was ~100% with the Fe (III) samples. Cellular internalization studies confirm the localization of the CNDs and the optical imaging sensing of Fe (III) ions inside living cells. A charge transfer fluorescence quenching mechanism, specifically between the CNDs and Fe (III), is proposed and examined using cyclic voltammetry. The overall characteristics of the E-CNDs provides a potential sensing platform in highly sensitive and selective detection of Fe (III) ions.

Silicon nanoparticles synthesized using a microwave method and used as a label-free fluorescent probe for detection of VB12

A simple and rapid detection strategy for vitamin B₁₂ (VB₁₂ ) was established based on label-free silicon quantum dots (SiQDs); the detection mechanism was additionally investigated. SiQDs were synthesized using a one-step microwave method, and their fluorescence was stronger than that synthesized using the hydrothermal method. SiQDs fluorescence was quenched using VB₁₂ due to the inner filter effect (IFE), which was demonstrated using ultraviolet (UV) absorption spectra, fluorescence lifetime, transmission electron microscopy and zeta potential analysis. Subsequently, quercetin (Que) and doxorubicin (Dox) with absorption peaks that overlapped the excitation or emission peaks of SiQDs respectively were used as control groups to investigate the quenching mechanism. Results showed that quenching efficiency was related to the level of overlap between the adsorption peak of the quencher and the excitation or emission peaks of SiQDs. A greater level of overlap caused a higher quenching efficiency. Therefore, the sensitive quenching of VB₁₂ for SiQDs was due to the synergistic effect of the synchronous overlap between the absorption peak of VB₁₂ with the excitation and emission peaks of SiQDs. Fluorescence quenching efficiency increased linearly in the 0.5 to 16.0 μmol·L^-1 VB₁₂ concentration range, and the detection limit was 158 nmol·L^-1 . In addition, SiQDs were applied to determine VB₁₂ in tablets and human urine samples with satisfactory recoveries ranging from 97.7 to 101.1%.