Phenanthroline-Derivative Functionalized Carbon Dots for Highly Selective and Sensitive Detection of Cu2+ and S2- and Imaging inside Live Cells

Detection of Ferric Ion by Fluorescent Carbon Nano Dots Synthesized from Forsythia Residue

To fully utilize the wastes of the traditional Chinese herbs, a highly functionalized fluorescent carbon nano dots (CDs) based ferric ion sensor was prepared from forsythia residue via a one-step hydrothermal method. Under transmission electron microscope (TEM), the CDs were observed to be spherical with the diameter in the range of 5-20 nm. Comprehensive analyses documented the CDs' favorable morphology, diverse functional groups, high water solubility, remarkable optical properties, and exceptional stability under various environmental conditions. Moreover, the CDs exhibited good optical properties with vivid green photoluminescence (PL) when they were exposed to ultraviolet (UV) light. Furthermore, the prepared CDs demonstrated selective fluorescence quenching behavior towards ferric ions with satisfactory sensitivity and a low limit of detection (LOD) of 4.3 µM. Additionally, the CDs displayed good selectivity towards Fe3+ and the least interference with several other metal ions. Consequently, this strategy could be effectively applied to real water samples, demonstrating its potential for broader applications.

Detection of sulphur(II) of carbon dots synthesized from Gardenia residue

The detection of anions using carbon dots (CDs) has received less attention compared to cations. Therefore, the present study aimed to develop a fluorescence sensor based on carbon dots (CDs) capable of detecting S2- in real water samples. The CDs were successfully prepared from the residues of a traditional Chinese herb, Gardenia, which emitted green photoluminescence (PL) under ultraviolet light irradiation. The as-prepared CDs were quasi-spherical in shape and ranged in size from 10 to 30 nm. Different detailed analyses proved that the CDs had good morphology, various functional groups, high water solubility, great optical features, and excellent stability under diverse environmental conditions. The ion detection showed that only Ag+ had the strongest fluorescence quenching effect on the CDs, however, the addition of S2- could recover their fluorescence. Based on these results, an "off-on" fluorescence sensor was achieved to selectively detect the concentration of S2- in real water samples with a limit of detection (LOD) of 39 μM, which further expanded the application of residues from traditional Chinese herbal medicine.

Peptide-based probe for colorimetric and fluorescent detection of Cu2+ and S2- in environmental and biological systems

Pollution caused by Copper and hydrogen sulfide pollution has severe adverse effects on the environment and organisms. Real-time, fast and accurate monitoring of Cu2+ and S2- faces serious challenges. In this study, we designed a novel biosensor and synthesized it by mimicking the structure of the main Cu(II)-binding site on bovine serum albumin. As a peptide-based sensor, FGGH (FITC-Gly-Gly-His-NH2) can perform the sequential detection of Cu2+ and S2- by fluorescence and colorimetry. The high water solubility and selectivity make it suitable for monitoring Cu2+ and S2- in environmental water samples with high sensitivity; its limit of detection (LOD) is as low as 1.42 nM for Cu2+ and 22.2 nM for S2-. The paper-based sensing platform of this probe was found to be a promising tool for the on-site visualization of real-time quantitative analysis of Cu2+ and S2- due to its rapid response and recyclable detection characteristics. Additionally, FGGH was successfully used to image Cu2+ and S2- in living cells and zebrafish models with adequate fluorescence stability and low cytotoxicity, providing the first visual evidence of the effect of the interactions between Cu2+ and S2- on the redox homeostasis of organisms.

Fluorescent carbon dots from water hyacinth as detection sensors for ferric ions: the preparation and optimisation using response surface methodology

The search for alternatives to chemicals from natural products as precursors for the preparation of highly doped carbon dots (CDs) remains challenging. Novel CDs (W-CDs) were synthesised using a one-step pyrolysis method with wastewater hyacinth as the sole carbon and nitrogen source at a mild temperature without using any surface-activating reagents or salt. The obtained W-CDs emitted strong blue fluorescence under 365 nm UV light excitation, with a quantum yield of 15.12%. The Box-Behnken design of the response surface methodology was applied to optimize the W-CD preparation conditions, including the reaction temperature, reaction time and weight of water hyacinths. The temperature was found to be the most important factor affecting the fluorescence intensity of the W-CDs. Additionally, the fluorescence sensor based on W-CDs demonstrated excellent selectivity towards ferric (Fe) ions, with a limit of detection of 2.35 μM. The fluorescent sensor was successfully applied for detecting Fe³⁺ in real water samples with a recovery of 97.80-103.10%. Hence, the pyrolysis of water hyacinth is proven to be a rapid, effective and green approach for CDs and provides a novel method for recycling water hyacinth.

Bifunctional Nitrogen and Fluorine Co-Doped Carbon Dots for Selective Detection of Copper and Sulfide Ions in Real Water Samples

Copper ions (Cu²⁺) and sulfur ions (S²⁻) are important elements widely used in industry. However, these ions have the risk of polluting the water environment. Therefore, rapid and quantitative detection methods for Cu²⁺ and S²⁻ are urgently required. Using 2,4-difluorobenzoic acid and L-lysine as precursors, nitrogen and fluorine co-doped dots (N, F-CDs) were synthesized in this study via a hydrothermal method. The aqueous N, F-CDs showed excellent stability, exhibited satisfactory selectivity and excellent anti-interference ability for Cu²⁺ detection. The N, F-CDs, based on the redox reactions for selective and quantitative detection of Cu²⁺, showed a wide linear range (0–200 μM) with a detection limit (215 nM). By forming the N, F-CDs@Cu²⁺ sensing platform and based on the high affinity of S²⁻ to Cu²⁺, the N, F-CDs@Cu²⁺ can specifically detect S²⁻ over a linear range of 0–200 μM with a detection limit of 347 nM. In addition, these fluorescent probes achieved good results when used for Cu²⁺ and S²⁻ detection in environmental water samples, implying the good potential for applications.

A Review of Off-On Fluorescent Nanoprobes: Mechanisms, Properties, and Applications

With the development of nanomaterials, fluorescent nanoprobes have attracted enormous attention in the fields of chemical sensing, optical materials, and biological detection. In this paper, the advantages of "off-on" fluorescent nanoprobes in disease detection, such as high sensitivity and short response time, are attentively highlighted. The characteristics, sensing mechanisms, and classifications of disease-related target substances, along with applications of these nanoprobes in cancer diagnosis and therapy are summarized systematically. In addition, the prospects of "off-on" fluorescent nanoprobe in disease detection are predicted. In this review, we presented information from all the papers published in the last 5 years discussing "off-on" fluorescent nanoprobes. This review was written in the hopes of being useful to researchers who are interested in further developing fluorescent nanoprobes. The characteristics of these nanoprobes are explained systematically, and data references and supports for biological analysis, clinical drug improvement, and disease detection have been provided appropriately.

Facile and Efficient Fabrication of Bandgap Tunable Carbon Quantum Dots Derived From Anthracite and Their Photoluminescence Properties

Low-cost and earth-abundant coal has been considered to have a unique structural superiority as carbon sources of carbon quantum dots (CQDs). However, it is still difficult to obtain CQDs from raw coal due to its compactibility and lower reactivity, and the majority of the current coal-based CQDs usually emit green or blue fluorescence. Herein, a facile two-step oxidation approach (K₂FeO₄ pre-oxidation and H₂O₂ oxidation) was proposed to fabricate bandgap tunable CQDs from anthracite. The K₂FeO₄ pre-oxidation can not only weaken the non-bonding forces among coal molecules which cause the expansion of coal particles, but also form a large number of active sites on the surface of coal particles. The above effects make the bandgap tunable CQDs (blue, green, or yellow fluorescence) can be quickly obtained from anthracite within 1 h in the following H₂O₂ oxidation by simply adjusting the concentration of H₂O₂. All the as-prepared CQDs contain more than 30 at% oxygen, and the average diameters of which are <10 nm. The results also indicate that the high oxygen content only can create new energy states inside the band gap of CQDs with average diameter more than 3.2 ± 0.9 nm, which make the as-prepared CQDs emit green or yellow fluorescence.

"On-off-on" detection of Fe3+ and F-, biological imaging, and its logic gate operation based on excitation-independent blue-fluorescent carbon dots

A fluorescent nanoprobe based on carbon dots (CDs) has been facilely synthesized by a one-step hydrothermal pyrolysis of salicylic acid and utilized for the sequential detection of Fe³⁺ and F^- in vitro. The fluorescence of CDs can be extinguished dramatically by Fe³⁺ based on static quenching and subsequently recovery upon addition of F^- due to the formation of stabler FeF₃. The probe exhibits high selectivity and sensitivity toward Fe³⁺ and F^- with a good linearity in the range of 10-300 μM and 0.1-200 μM, respectively, and a low detection limit of 52 nM and 8.5 nM, respectively. More importantly, as-prepared CDs with exceedingly fluorescence stability, negligible toxicity and superior biocompatibility have been expanded for detection Fe³⁺ and F^- in living cell and Escherichia coli. Furthermore, an "AND" logic gate based on as-obtained CDs has been constructed.

Terbium Functionalized Schizochytrium-Derived Carbon Dots for Ratiometric Fluorescence Determination of the Anthrax Biomarker

Efficient and instant detection of biological threat-agent anthrax is highly desired in the fields of medical care and anti-terrorism. Herein, a new ratiometric fluorescence (FL) nanoprobe was elaborately tailored for the determination of 2,6-dipicolinic acid (DPA), a biomarker of anthrax spores, by grafting terbium ions (Tb³⁺) to the surface of carbon dots (CDs). CDs with blue FL were fabricated by a simple and green method using schizochytrium as precursor and served as an FL reference and a supporting substrate for coordination with Tb³⁺. On account of the absorbance energy transfer emission effect (AETE), green emission peaks of Tb³⁺ in CDs-Tb nanoprobe appeared at 545 nm upon the addition of DPA. Under optimal conditions, good linearity between the ratio FL intensity of F₅₄₅/F₄₄₅ and the concentrations of DPA was observed within the experimental concentration range of 0.5–6 μM with the detection limit of 35.9 nM, which is superior to several literature studies and significantly lower than the infectious dosage of the Bacillus anthracis spores. Moreover, the CDs-Tb nanoprobe could sensitively detect DPA in the lake water sample. This work offers an efficient self-calibrating and background-free method for the determination of DPA.

Bioimaging Applications of Carbon Nanodots: A Review

Carbon nanodots (CNDs) is the newest member of carbon-based nanomaterials and one of the most promising for the development of new, advanced applications. Owing to their unique and unparalleled physicochemical and photoluminescent properties, they are considered to be a rising star among nanomaterials. During the last decade, many applications have been developed based on CNDs. Among others, they have been used as bioimaging agents to label cells and tissues. In this review, we will discuss the advancements in the applications of CNDs in in the field of imaging, in all types of organisms (i.e., prokaryotes, eukaryotes, and animals). Selective imaging of one type of cells over another, imaging of (bio)molecules inside cells and tumor-targeting imaging are some of the studies that will be discussed hereafter. We hope that this review will assist researchers with obtaining a holistic view of the developed applications and hit on new ideas so that more advanced applications can be developed in the near future.