Determination of cholic acid in body fluids by β‑cyclodextrin-modified N-doped carbon dot fluorescent probes

Research progress of fluorescent composites based on cyclodextrins: Preparation strategies, fluorescence properties and applications in sensing and bioimaging

Fluorescence analysis has been regarded as one of the commonly used analytical methods because of its advantages of simple operation, fast response, low cost and high sensitivity. So far, various fluorescent probes, with noble metal nanoclusters, quantum dots, organic dyes and metal organic frameworks as representatives, have been widely reported. However, single fluorescent probe often suffers from some deficiencies, such as low quantum yield, poor chemical stability, low water solubility and toxicity. To overcome these disadvantages, the introduction of cyclodextrins into fluorescent probes has become a fascinating approach. This review (with 218 references) systematically covers the research progress of fluorescent composites based on cyclodextrins in recent years. Preparation strategies, fluorescence properties, response mechanisms and applications in sensing (ions, organic pollutants, bio-related molecules, temperature, pH) and bioimaging of fluorescent composites based on cyclodextrins are summarized in detail. Finally, the current challenges and future perspectives of these composites in relative research fields are discussed.

Diethylenetriamine-β-CD-modified carbon quantum dots for selective fluorescence sensing of Hg2+ and Fe3+ and cellular imaging

Diethylenetriamine-β-cyclodextrin-modified carbon quantum dots (3 N-CQDs) were synthesized via a one-step hydrothermal method using citric acid as the carbon source and diethylenetriamine-β-cyclodextrin (3 N-β-CD) as the nitrogen source. The successful preparation of 3 N-CQDs were revealed by infrared absorption spectroscopy, ultraviolet (UV)-visible absorption spectroscopy, fluorescence spectroscopy, XRD, XPS, TEM, and TG. Further spectroscopic studies showed that the synthesized carbon quantum dots offered good anti-interference capability. The relative fluorescence quantum yield was 67.2 %. The limits of detection for Hg²⁺ and Fe³⁺ were 0.25 µM and 0.57 μM, respectively. Cytotoxicity and imaging studies showed that the prepared carbon quantum dots had low cytotoxicity, good biocompatibility, and good cellular imaging capability for HeLa cells. They offered fluorescent sensing of Hg²⁺ and Fe³⁺ in live cells. Therefore, 3 N-CQDs were ideal fluorescent probes for the detection of Hg²⁺ and Fe³⁺ in water.

Construction of mitochondria targeted and FRET based ratiometric sensing nanoplatform for sulfur dioxide accurate detection in vitro and in vivo

Sulfur dioxide (SO₂) is a key molecule in organisms that is involved in the regulation of different physiological procedures. Aberrant SO₂ causes a variety of diseases, such as cancer and neurodegeneration. Thus, sensitive and selective detection of SO₂ is of great importance. Based on the Förster resonance energy transfer (FRET) between green fluorescence carbon dots (GCDs) donor and amide-linked near-infrared fluorescence emissive organic small molecular dye (CDDBT) acceptor, one ratiometric fluorescent nano platform, Mito-GCDs-CDDBT for mitochondria SO₂ sensing was constructed. In this FRET sensing system, CDDBT served as the receptor for SO₂, and the presence of SO₂ enhanced GCDs green fluorescence signal and quenched CDDBT near-infrared fluorescence signal due to the disruption of FRET. Mito-GCDs-CDDBT could sensitively detect SO₂ with a detection limit of as low as 0.701 μM. Meanwhile, Mito-GCDs-CDDBT achieved fluorescence imaging to measure the response of cellular exogenous and endogenous SO₂ with remarkable mitochondrial targeting. Moreover, Mito-GCDs-CDDBT also realized SO₂ sensing in vivo including zebrafish and mice. The as-prepared versatile nanoplatform displayed several advantages, such as mitochondria targeting, FRET-based sensitive detection, and sensing capabilities in biological milieu. Potentially, it could be applied in the diagnostics of SO₂ involved diseases.

Novel β-cyclodextrin doped carbon dots for host-guest recognition-assisted sensing of isoniazid and cell imaging

In the present study, novel β-cyclodextrin doped carbon dots (CCDs) were prepared via a simple one-pot hydrothermal method at a mild temperature (140 °C), using mixtures of β-cyclodextrin and citric acid as precursors. By characterizing the chemical properties of CCDs prepared at 140 °C and 180 °C, the importance of low-temperature reaction for preservation of the specific structure of β-CD was elucidated. The CCDs showed excellent optical properties and were stable to changes in pH, ionic strength and light irradiation. Since the fluorescence of the CCDs could be selectively quenched by isoniazid (INZ) through specific host-guest recognition effects, a convenient isoniazid fluorescence sensor was developed. Under the optimal conditions, the sensor exhibited a relatively low detection limit of 0.140 μg mL^-1 and a wide detection range from 0.2 μg mL^-1 to 50 μg mL^-1 for INZ detection. Furthermore, the sensor was employed successfully for the determination of INZ in urine samples with satisfactory recovery (91.1-109.5%), displaying potential in clinical applications. Finally, low cytotoxicity of the prepared CCDs was confirmed using the CCK-8 method, followed by application in HepG2 cell imaging.

Photoinduced Electron Transfer in Encapsulated Heterocycles by Cavitands

Host-guest complexation of small heterocyclic (guest) and macrocyclic cavitands (hosts) organic molecules is still to date a very popular, inexpensive approach that bypasses the burdens of conventional covalent synthesis. Understanding the selection criteria of these chemicals is crucial to the design and potential applications of their supramolecular assemblies. This review surveys examples within the last 15 years (2005-2020) of supramolecular complexes in which the interacting photoinduced electron transfer (PET)-based chromophore and quencher fragments are commonly used in the market with reported CAS numbers. It appears from this survey that the supramolecular effects can be directed to specifically disrupt PET when the nonemissive macrocycles separately encapsulate the fluorescent acceptor or donor molecules, among other specific factors, such as when inducing conformational changes or pK_a shift of the donor. On the contrary, synergetic encapsulation of both donor and acceptor molecules, formation of ternary self-assembly at the rim or encapsulation of one component while grafting the other onto the macrocycle, among other specific factors such as the modulation of the excited-state structure of donor, will lead to the enhancement of PET process. In the event the donor or acceptor molecules have multitopic structures, the PET process can repeatedly be switched on and off. It is generally concluded that understanding the criteria for the combination of these available products for the purpose of manipulating their PET efficiency should pave the way for the facile alternative generation of new noncovalently bonded host-guest supramolecular assemblies with a more specific design tailored for more advanced, diverse and economic applications such as chemical sensing, molecular gates, drug delivery and biolabeling.

Determination of melamine in milk based on β-cyclodextrin modified carbon nanoparticles via host-guest recognition

Illegal addition of melamine (MEL) to milk has caused serious food safety accident. It is urgent to develop a highly sensitive method for detecting MEL in milk. β-Cyclodextrin with inner hydrophobic and outer hydrophilic cavities have been widely used in smart sensors design. In this study, an "ON-OFF-ON" sensor for MEL detection was constructed based on β-cyclodextrin modified carbon nanoparticles (β-CD-CNPs). The sensor is switched "OFF" when Fe³⁺ interacts with β-CD-CNPs and switched "ON" when MEL replaces Fe³⁺. Fluorescence recovery of β-CD-CNPs exhibits good linear correlations with MEL concentration ranging from 10.00 ng/mL ~ 180.00 ng/mL and 180.00 ~ 1000.00 ng/mL, the detection limit is 6.82 ng/mL. The sensor was applied to analysis melamine in milk samples with recovery between 94.80% ~ 102.05%, and RSD bellow 12.61%. The results show that this method can meet the requirements of real sample analysis.

4-aminoantipyrine modified carbon dots and their analytical applications through response surface methodology

A sensitive and selective nanoprobe for detection of hypochlorite (OCl^-) based on 4-aminoantipyrine (AAP) modified carbon dots (CDs-AAP) has been prepared. The CDs-AAP exhibit an emission peak at 484 nm when the excitation wavelength is 370 nm, accompanying 36 nm red shift compare with the pristine CDs. The addition of OCl^- lead to the AAP on the surface of CDs experience a process of hydrazide hydrolysis and double bond addition, causing the singlet and triplet electrons of the excited state more closer in energy (ie, the energy difference between the two is reduced), eventually quenching the fluorescence of CDs due to heavy atomic effects. Central composite design (CCD) and response surface method (RSM) were used to optimize the detection variables of pH, incubation time and temperature. The designed model study indicated that the optimum detection conditions was pH 7.0, temperature 30 °C and incubation time 20 min, respectively. Under optimal conditions, the fluorescent intensity of the nanoprobe linearly responded to the OCl^- concentration from 3 μM to 36 μM and the limit of detection was 40 nM. The proposed nanoprobe was successfully used to the detection of OCl^- in tap water and pool water, and the recovery were in the range of 94% - 103%. In addition, the nanoprobe was also applied in imaging of VMSCs cells and labeling E.coli.