Highly selective and sensitive fluorescence sensing of nanomolar Zn2+ ions in aqueous medium using Calix[4]arene passivated Carbon Quantum Dots based on fluorescence enhancement: Real-time monitoring and intracellular investigation

N-doped carbon nanomaterials as fluorescent pH and metal ion sensors for imaging

Herein we describe the facile synthesis of new N-doped carbon nanoparticles (CNPs) obtained from 1,10-phenanthroline by the solvothermal method. Characterization of CNPs were carried out with transmission electron microscope (TEM), X-ray photoelectron spectra (XPS), Fourier transform infrared spectra (FTIR), UV-vis absorption spectra, and luminescence spectra. CNPs were pH sensitive and exploited as fluorescent chemosensors and imaging agents for Al(III) and Zn(II) ions in real-life samples. Remarkably, we show that CNPs can be used for the detection of Al(III) and Zn(II) ions in water samples. Accordingly, the results indicate that CNPs are highly effective in detecting Zn(II) content of cosmetic creams. We also demonstrated that the CNPs could be used for in vitro imaging of Al(III) and Zn(II) in Human Larynx Squamous Cell Carcinoma (Hep-2). Finally, Al(III) imaging in Angelica Officinalis root tissue was also achieved successfully. The CNPs are promising as luminescent multianalyte (pH, Al(III) and Zn(II)) sensors.

A sensitive and rapid determination of zinc ion (Zn2+) using electrochemical sensor based on f-MWCNTs/CS/PB/AuE in drinking water

An electrochemical method for detecting the presence of zinc (Zn²⁺) ions in drinking water was developed using functionalized multi-walled carbon nanotubes (f-MWCNTs) and chitosan (CS). Numerous cylinder-shaped graphene molecules make up f-MWCNTs, which have a high mechanical and electrical conductivity. CS benefits from nanomaterials include biocompatibility, biodegradability, and low toxicity, which are excellent in capacity absorption of metal ions. Dangerous levels of metal ions such as zinc are currently present in drinking water as a result of human and natural activity. Zinc toxicity is associated with a variety of disorders, including Alzheimer's, Parkinson's, diabetes, and cancer. This study incorporated f-MWCNTs and CS with Prussian blue (PB) immobilised on a gold electrode (AuE). Several parameters, including as buffers, pH, scan rate, redox indicator, accumulation time, and volume, were optimised using the cyclic voltammetry (CV) method. According to the CV method, the optimal parameters were phosphate buffered saline (0.1 M, pH 2), 5 mM Prussian blue, 200 mVs^-1 scan rate, and 5 s accumulation time. Under ideal circumstances, the differential pulse voltammetry (DPV) method was used to determine the Zn²⁺ ions concentration range of 0.2-7.0 ppm. The limit of detection (LOD) was 2.60 × 10^-7 mol L^-1 with a correlation coefficient of R² = 0.9777. The recovery rate of the developed sensor (f-MWCNTs/CS/PB/AuE) ranged from 95.78 to 98.96%. The developed sensor showed a variety of advantages for detecting Zn²⁺ in drinking water, including a quick setup process, quick detection, high sensitivity, and mobility. This study developed the essential sensor for monitoring Zn²⁺ levels in drinking water in the future.

Sensitive visual detection of intracellular zinc ions based on signal-on polydopamine carbon dots

The concentration of intracellular zinc ions is a significant clinical parameter for diagnosis. However, it is still a challenge for direct visual detection of zinc ions in cells at single-cell level. To address this issue, herein, water-soluble amino-rich polydopamine carbon quantum dots (PDA-CQDs) were successfully synthesized, with strong blue-green fluorescence as the probes for zinc ions detection in cells. The structure and properties of PDA-CQDs were confirmed by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transformed infrared (FT-IR), UV-visible spectrophotometry (UV-vis), and fluorescence spectroscopy. Importantly, by successfully linking salicylaldehyde (SA) to PDA-CQDs via nucleophilic reaction, the FL quenching and Zn ions induced FL-recovering system was built up, thus offering a signal-on platform for the detection of zinc ions. This PDA-CQDs-SA nanoprobe can be applied for the detection of Zn²⁺with a detection limit of 0.09μM, with good biocompatibility confirmed using cytotoxicity assay. Of significance, the results of fluorescence bioimaging showed that PDA-CQDs-SA is able to detect Zn²⁺in single-cell visually, with the detection limit of Zn ions in cells as low as 0.11μM per cell, which was confirmed using flow cytometry. Therefore, this work offers a potential probe for Zn²⁺detection in cells at single-cell level, towards the precise diagnosis of zinc ions related diseases.

Red-emission carbon dots-quercetin systems as ratiometric fluorescent nanoprobes towards Zn2+ and adenosine triphosphate

Carbon dots (CDs) emitting red fluorescence (610 nm) were synthesized by solvent thermal treatment of p-phenylenediamine in toluene. Upon 440 nm excitation, quercetin (QCT) alone endowed slight effects on the red fluorescence of CDs. Once Zn²⁺ was further introduced, the QCT-Zn²⁺ complex was quickly formed. This complex absorbs excitation light and emits bright green fluorescence at 480 nm. The red fluorescence of CDs was greatly quenched owing to the inner-filter effect. The ratio of fluorescence intensity at 480 nm and 610 nm (I₄₈₀/I₆₁₀) gradually increases with increasing concentration (c) of Zn²⁺. Al³⁺ exhibits the same phenomen like Zn²⁺. Fluoride ions form a more stable complex with Al³⁺ than QCT-Al³⁺ complex but have a negligible effect on the QCT-Zn²⁺ complex. The possible interference of Al³⁺ on Zn²⁺ can thus be avoided by adding certain amount of F^-. The CD-QCT-F^- system was constructed as a ratio-metric fluorescent nanoprobe toward Zn²⁺ with determination range of 0.14-30 μM and limit of detection (LOD) of 0.14 μM. Due to the stronger affinity of adenosine triphosphate (ATP) to Zn²⁺ than QCT, the I₄₈₀/I₆₁₀ value of CD-QCT-F^--Zn²⁺ system gradually decreases with increasing c_ATP. The ratiometric fluorescent nanoprobe toward ATP was established with detection ranges of 0.55-10 and 10-35 μM and a LOD of 0.55 μM. The above two probes enable the quantitative determination of Zn²⁺ and ATP in tap and lake water samples with satisfactory recoveries. Graphical abstract Schematic representation of the ratiometric fluorescent nanoprobes based on the carbon dots (CDs)-quercetin (QCT) system towards Zn²⁺ and adenosine triphosphate (ATP) with high selectivity and sensitivity.

Synthesis of folic acid conjugated photoluminescent carbon quantum dots with ultrahigh quantum yield for targeted cancer cell fluorescence imaging

Folic acid functionalized carbon quantum dots (FA-CQDs) with ultrahigh quantum yield (50 %) were synthesized by one-pot hydrothermal route using citric acid. The synthesized CQDs were characterized by fluorescence spectroscopy, transmission electron microscopy (TEM), dynamic light scattering (DLS) and X-ray diffraction. The cell viability of about 95 % and 97 % were obtained for MTT assay of the CQDs and FA-CQDs toward MCF-7 cells after 24 h of incubation respectively. The FA-CQDs were successfully applied for targeted imaging of ovarian cancer (type HeLa) and human breast adenocarcinoma (type MCF7) cells using fluorescence microscope.

Vinyl Phosphate-Functionalized, Magnetic, Molecularly-Imprinted Polymeric Microspheres' Enrichment and Carbon Dots' Fluorescence-Detection of Organophosphorus Pesticide Residues

The rapid detection of organophosphorus pesticide residues in food is crucial to food safety. One type of novel, magnetic, molecularly-imprinted polymeric microsphere (MMIP) was prepared with vinyl phosphate and 1-octadecene as a collection of dual functional monomers, which were screened by Gaussian09W molecular simulation. MMIPs were used to enrich organic phosphorus, which then detected by fluorescence quenching in vinyl phosphate-modified carbon dots (CDs@VPA) originated from anhydrous citric acid. MMIPs and CDs@VPA were characterized by TEM, particle size analysis, FT-IR, VSM, XPS, adsorption experiments, and fluorescence spectrophotometry in turn. Through the fitting data from experiment and Gaussian quantum chemical calculations, the molecular recognition properties and the mechanism of fluorescence detection between organophosphorus pesticides and CDs@VPA were also investigated. The results indicated that the MMIPs could specifically recognize and enrich triazophos with the saturated adsorption capacity 0.226 mmol g^-1, the imprinting factor 4.59, and the limit of recognition as low as 0.0006 mmol L^-1. Under optimal conditions, the CDs@VPA sensor has shown an extensive fluorescence property with a LOD of 0.0015 mmol L^-1 and the linear range from 0.0035 mmol L^-1 to 0.20 mmol L^-1 (R² = 0.9988) at 390 nm. The mechanism of fluorescence detection of organic phosphorus with CDs@VPA sensor might be attributable to hydrogen bonds formed between heteroatom O, N, S, or P, and the O-H group, which led to fluorescent quenching. Meanwhile, HN-C=O and Si-O groups in CDs@VPA system might contribute to cause excellent blue photoluminescence. The fluorescence sensor was thorough successfully employed to the detection of triazophos in cucumber samples, illustrating its tremendous value towards food sample analysis in complex matrix.

Quantum Dot-Based Simultaneous Multicolor Imaging

Quantum dots have attracted a great deal of attention among researchers in optical imaging because of their unique physicochemical properties. Their adjustable size allows quantum dots to emit visible fluorescence with different wavelengths excited by a single light source, allowing them to play an unmatched role in multitarget simultaneous multicolor imaging of tissues and cells compared with other molecular biotechnologies and traditional fluorescent materials. This technology affords real-time observation in situ of multiple biomarkers, allowing us to quantify their expression levels, and helping us to gain a deeper understanding of the interactions among biomolecules and the relationship between biomolecules and disease occurrence, progression, and prognosis. This has potential to aid in clinical diagnosis and treatment decision making.

A novel and simple imidazo[1,2-a]pyridin fluorescent probe for the sensitive and selective imaging of cysteine in living cells and zebrafish

Cysteine (Cys), homocysteine (Hcy) and glutathione (GSH) play many crucial physiological roles in organisms. Their abnormal levels can cause and indicate various diseases. In the present study, a small-molecule fluorescent probe 2-(imidazo[1,2-a]pyridin-2-yl)phenyl acrylate (IPPA) was designed, synthesized and characterized by NMR, FT-IR and HRMS. IPPA can selectively detect Cys over other analytes because of an approximately 76 times enhancement in fluorescence intensity. The limit of detection of IPPA for Cys was 0.33 μM. The pseudo-first-order rate constant of the reaction between IPPA and Cys was approximately 10 times that of the reaction between IPPA and Hcy (KCys 3.18 × 10-3 S-1vs KHcy 4.92 × 10-4 S-1), indicating that Cys can be distinguished from Hcy. In addition, IPPA exhibits strong anti-interference ability, small molecular weight, high efficiency, low toxicity and good cell permeability. It was successfully used in imaging HepG2 cells and zebrafish. The fluorescence response of IPPA for calf serum are powerful proofs for practical application. Therefore, IPPA has high potential for bioassay applications.

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.