Ratiometric fluorescence detection of riboflavin based on fluorescence resonance energy transfer from nitrogen and phosphorus co-doped carbon dots to riboflavin

Aggregation-induced emission carbon dots as Al3+-mediated nanoaggregate probe for rapid and selective detection of tetracycline

Worldwide abuse of tetracycline (TC) seriously threatens environmental safety and human health. Metal-TC complexes formed by residual TC in the environment can also contribute to the spread of antibiotic resistance. Therefore, monitoring of TC residues is still required. Here, we report novel aggregation-induced emission carbon dots (AIE-Cdots) as nanoaggregate probes for the rapid and selective detection of TC residue. Riboflavin precursors with rotational functional groups led to the development of AIE-Cdots. The aggregation of AIE-Cdots was induced selectively for Al3+, amplifying the fluorescence signals owing to the restricted rotation of the side chains on the AIE-Cdot surface. The fluorescence signal of such Al3+-mediated nanoaggregates (Al3+-NAs) was further triggered by the structural fixation of TC at the Al3+ active sites, suggesting the formation of TC-coordinated Al3+-NAs. A linear correlation was observed in the TC concentration range of 0-10 μM with a detection limit of 42 nM. In addition, the strong Al3+ binding affinity of AIE-Cdots produced similar NAs and enhanced fluorescence signals in Al3+-TC mixtures. These AIE-Cdots-based nanoplatforms have a rapid response, good selectivity, and reliable accuracy for detecting TC or aluminum complexes, meeting the requirements for hazardous substance monitoring and removal in environmental applications.

Nanomaterials for fluorescent detection of vitamin B2: A review

Vitamin B2 plays vital roles in maintaining human health. It is of tremendous significance to construct sensitive sensors of VB2. In this review, we first briefly presented the sensing mechanisms of fluorescent nanomaterials for sensing VB2. Subsequently, the advances of nanomaterials for fluorescent determination of VB2 were highlighted. And sensing performance of traditional approaches and fluorescent nanosensors was further compared. In last section, the challenges and perspectives concerning the topic were discussed.

Rapid Pathogen Purge by Photosensitive Arginine-Riboflavin Carbon Dots without Toxicity

Photo-activatable antipathogenic carbon dots (CDs) were prepared by carbonization of citric acid and arginine (Arg) via 3 min microwave treatment for use in the eradication of common microorganisms. Nitrogen-doped Arg CDs were spherical in shape with a size range of 0.5 to 5 nm. The Arg CDs were modified with fluorescent dyes, such as fluorescein sodium salt (FSS, as Arg-FSS) and riboflavin (RBF, as Arg-RBF), to improve antimicrobial potency by enhancing their application in photodynamic therapy. The modified Arg CDs afforded fluorescence emission properties at 520 nm in the green region in addition to excellent blue fluorescence intensity at 420 nm under 345 nm excitation upon their FSS and RBF conjugation, respectively. Although the cytotoxicity of Arg CDs was decreased for Arg-RBF CDs to 91.2 ± 0.7% cell viability for fibroblasts, the Arg-based CDs could be safely used for intravenous applications at 1000 μg/mL concentration. The Arg CDs showed broad-spectrum antimicrobial activity against common pathogens and the minimum inhibitory concentration of Arg CDs was almost two-fold decreased for the modified forms without UV light. However, faster and more effective antibacterial activity was determined for photosensitive Arg-RBF CDs, with total bacterial eradication upon UV-A light exposure for 30 min.

Silicon Nanoparticle-Based Ratiometric Fluorescence Probes for Highly Sensitive and Visual Detection of VB2

In this work, blue fluorescent silicon nanoparticles (SiNPs) were prepared by a simple one-step hydrothermal method using (3-aminopropyl) triethoxy silane (APTES) and eriochrome black T as raw materials. The SiNPs showed favorable water solubility, thermal stability, pH stability, salt tolerance, and photobleaching resistance. At an excitation wavelength of 376 nm, the SiNPs emitted bright blue fluorescence at 460 nm. In the presence of vitamin B₂ (VB₂), the fluorescence intensity (FL intensity) of the SiNPs at 460 nm decreased obviously, and a new peak appeared at 521 nm. Based on this, a novel ratiometric fluorescence method was established for VB₂ detection. There was a good linear relationship between the fluorescence intensity ratio (F ₅₂₁/F ₄₆₀) and VB₂ concentration from 0.5 to 60 μM with a detection limit of 135 nM. This method was successfully applied to detect VB₂ content in the samples of vitamin B₂ drugs and beverages. Additionally, a simple paper sensor based on the SiNPs was designed to visualize detection of VB₂. With the support of color recognition software on a smartphone, the visual quantitative analysis of VB₂ was realized, ranging from 40 to 800 μM.

Dye-based dual-emission Eu-MOF synthesized by Post-modification for the sensitive ratio fluorescence visualization sensing of ClO. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2023;285:121863. [PMID: 36126623 DOI: 10.1016/j.saa.2022.121863]

As we all know, excessive hypochlorite will be transformed into highly toxic substances, while insufficient hypochlorite can not completely kill bacteria and viruses in water. Therefore, it is desirable to develop a new analytical method to detect ClO^- in environmental water. Here, a novel and simple fluorescence sensor was constructed for monitoring ClO^- by an effective strategy. An Acriflavine@lanthanide metal-organic framework (Acr@Eu(BTEC)) was designed by covalently integrating amino-rich dye (Acr) and carboxyl-rich Eu(BTEC) via post-synthesis method. The created fluorescence sensor has two emission centers originating from Acr and Eu(BTEC), respectively. In the presence of ClO^-, the strong green fluorescence derived from Acr was significantly quenched, while the invariant red emission from Eu³⁺ acted as the reference signal. Thus, Acr@Eu(BTEC) with two emissions was developed as a ratiometric fluorescence sensor for highly sensitive and selective detection of ClO^-. The limit of detection (LOD) was as low as 10.75 nM. Moreover, visual detection of ClO^- by the naked eyes is feasible with obvious fluorescent color changes from green to orange and then red. This method shows excellent performance in practical application, which suggests that it has great potential in water quality monitoring.

Catalytic nanozyme Zn/Cl-doped carbon quantum dots as ratiometric fluorescent probe for sequential on-off-on detection of riboflavin, Cu2+ and thiamine

A novel metal-doped Zn/Cl carbon quantum dots (Zn/Cl-CQDs) was developed successfully as ratiometric fluorescent probes for the sequential on-off-on detection of riboflavin, Cu²⁺ ion and thiamine. The excellent catalytic performance of the Zn/Cl-CQDs nanozyme serves as an ideal platform for sensitive detection of thiamine. Due to the addition of riboflavin to the Zn/Cl-CQDs, the blue emission peak of Zn/Cl-CQDs at 440 nm remains unaffected and used as an internal reference approach, while the green emission peak of riboflavin at 520 nm appeared and increased remarkably. Following the presence of Cu²⁺, a quenching blue fluorescence signal of Zn/Cl-CQDs was observed which resulted in consequent fluorescent 'turn-off' response toward Cu²⁺ ion. Finally, upon the addition of thiamine to the above solution under alkaline condition, the blue emission of Zn/Cl-CQDs was gradually recovered. The prepared Zn/Cl-CQDs could act as a nanozyme catalyst for directly catalyzing the oxidation of non-fluorescent substrate of thiamine to produce highly fluorescent substrate of thiochrome. As a result, the blue fluorescence emission peak at 440 nm was recovered. Eventually, the sequential detection properties of ratiometric probes for riboflavin, Cu²⁺ ion and thiamine were successfully applied in VB2 tablets, drinking water and VB1 tablet with good recoveries of 96.21%, 98.25% and 98.44%, respectively.

Ag NPs/PMMA nanocomposite as an efficient platform for fluorescence regulation of riboflavin

The fluorescence detection platform has broad application in many fields. In this paper, we report a simple and efficient fluorescence detection platform based on the synergistic effects of Ag nanoparticles (Ag NPs) and polymethylmethacrylate (PMMA). Ag NPs were introduced to realize the plasmon enhancement fluorescence and a thin PMMA layer was used to adjust the distance between Ag NPs and riboflavin. The thin PMMA layer not only enhances the fluorescence by enhancing adhesion of substrate, but also optimizes the plasmon enhancement fluorescence effect by serving as the spacer. The fluorescence enhancement factor based on this platform shows a trend of increasing with the decrease of the concentration of riboflavin, and the detection of riboflavin is realized based on this feature, the lowest detectable concentration is as low as 0.27 µM. In addition to the detection based on plasmon enhancement fluorescence, the detection of riboflavin at low concentrations can also be realized by the shift and broadening of the fluorescence peak due to the Ag NPs. The combination of the two ways of plasmon enhancement fluorescence and shift of the fluorescence spectra is used for the detection of riboflavin. These results show that the platform has great potential applications in the field of detection and sensing.

Uracil-Appended Fluorescent Sensor for Cu2+ and Hg2+ Ions: Real-Life Utilities Including Recognition of Vitamin B2 (Riboflavin) in Milk Products and Invisible Ink Applications

A simple uracil-appended fluorescent sensor (1) has been developed by one pot reaction and characterized by using common spectroscopic methods such as UV-vis, Fluorescence, HRMS and FT-IR analyses. Upon addition of various metal ions to the CH₃CN solution of sensor 1, the fluorescence was quenched in the presence of Cu²⁺ / Hg²⁺ ions. The limit of detection for Cu²⁺ and Hg²⁺ was calculated to be 3.31 and 0.316 µM, respectively. Further, the sensor was applied for real-life applications in the determination of Vitamin B₂ (riboflavin) and its presence in milk products. With the incorporation of different sources of vitamin-B to acetonitrile solution of it, there was discernible fluorescence enhancement only in the presence of vitamin B₂. Also, it has been successfully applied for the detection of Vitamin B₂ (riboflavin) in milk and curd. Moreover, based on the fluorescent color changes, the sensor was utilized for invisible ink applications.

A ratiometric fluorescent strategy based on copper nanoclusters/carbon dots for sensitive detection of doxorubicin

Sensitive detection of doxorubicin (DOX) is critical for clinical theranostics. A novel ratiometric fluorescence strategy based on inner filter effect (IFE) has been established for sensitive detection of DOX by designing a ratiometric fluorescence probe. In the presence of DOX, the fluorescence intensity of copper nanoclusters (CuNCs) at 485 nm decreases, and the fluorescence intensity of carbon dots (CDs) at 560 nm increases. Therefore, DOX can be quantitatively detected by measuring the ratio of the fluorescence intensities at 560 and 485 nm (F₅₆₀ /F₄₈₅ ). The F₅₆₀ /F₄₈₅ ratio exhibits a linear correlation to the DOX concentration in the range from 1.0×10^-8 M to 1.0×10^-4 M with the detection limit of 3.7 nM. Furthermore, this method is also successfully applied to analysis of DOX in human plasma samples, affording an effective platform for drug safety management.

Moxifloxacin detection based on fluorescence resonance energy transfer from carbon quantum dots to moxifloxacin using a ratiometric fluorescence probe

With an increase in the MOX concentration, the fluorescence intensity of CQDs decreases, whereas the fluorescence intensity of MOX increases gradually.

Optimizing the Efficiency of a Cytocompatible Carbon-Dots-Based FRET Platform and Its Application as a Riboflavin Sensor in Beverages

In this work, the Förster resonance energy transfer (FRET) between carbon dots (CDs) as energy donors and riboflavin (RF) as an energy acceptor was optimized and the main parameters that characterize the FRET process were determined. The results were successfully applied in the development of an ultrasensitive ratiometric fluorescent sensor for the selective and sensitive determination of RF in different beverages. Water-soluble CDs with a high quantum yield (54%) were synthesized by a facile and direct microwave-assisted technique. The CDs were characterized by transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), Zeta potential, and UV-visible and molecular fluorescence spectroscopy. The study of the FRET process at two donor concentrations showed that the energy transfer efficiency decreases as the donor concentration increases, confirming its dependence on the acceptor:donor ratio in nanoparticle-based systems. The results show the importance of optimizing the FRET process conditions to improve the corresponding output signal. The variation in the ratiometric signal with the concentration of RF showed linearity in a concentration range of 0 to 11 µM with R² = 0.9973 and a detection limit of 0.025 µM. The developed nanosensor showed good selectivity over other possible types of interference. The sensor was then applied for the determination of RF in beverage samples using the standard addition method with recoveries between 96% and 106%. Preliminary cytocompatibility tests carried out with breast cancer cells (MDA-MB-231) revealed the nanosensor to be cytocompatible in its working concentration regime, even after long incubation times with cells. Altogether, the developed RF determination method was found to be fast, low-cost, highly sensitive, and selective and can be extended to other samples of interest in the biological and food sectors. Moreover, thanks to its long-lasting cytocompatibility, the developed platform can also be envisaged for other applications of biological interest, such as intracellular sensing and staining for live cell microscopy.

A ratiometric fluorescent sensor based on g-CNQDs@Zn-MOF for the sensitive detection of riboflavin via FRET

A novel ratiometric fluorescent sensor based on Förster resonance energy transfer (FRET) platform was designed for riboflavin (RF) detection. The graphitic carbon nitrides quantum dots - Zn-MOF composite (g-CNQDs@Zn-MOF) was used as the fluorescent probe. In the FRET system, g-CNQDs@Zn-MOF and RF acted as donor and acceptor, respectively. The probe exhibited high sensitivity and good selectivity to RF, and had been successfully used for the detection of RF in milk and vitamin B₂ tablets. The detection limit of the sensor was 15 nM. The strategy expanded the application of MOF in sensing filed and provided a new method for the detection of RF.

Ratiometric fluorescent sensors for sequential on-off-on determination of riboflavin, Ag+ and l-cysteine based on NPCl-doped carbon quantum dots

The fluorescent sensor, especially ratiometric fluorescent sensor, is one of the most important applications for CQDs, which is becoming a research hotspot. Herein, carbon quantum dots co-doped with nitrogen, phosphorus and chlorine (NPCl-CQDs) were synthesized by acid-base neutralization reaction exothermic carbonization method. The as-fabricated NPCl-CQDs could emit blue fluorescence and possess excellent fluorescence properties. Based on the FRET, multifunctional and ratiometric fluorescent sensors for "on-off-on" sequential determination of riboflavin, Ag⁺, and Cys with good selectivity and high sensitivity were established. The linear range of riboflavin, Ag⁺, and Cys are 0.50-10.18 μM and 15.89-27.76 μM, 0.66-1.46 mM and 1.50-4.20 mM, and 0.01-0.15 μM and 0.15-0.36 μM with the limit of detection of 3.50 nM, 26.38 μM, and 0.96 nM, respectively. Furthermore, the sensors were successfully used to determine riboflavin, Ag⁺, and Cys in tablets, river water, and human urine with the recoveries of 95.2-104.0%, 95.6-102.0%, and 94.8-106.4%, respectively. More importantly, the as-constructed "on-off-on" NPCl-CQDs-based ratiometric fluorescent sensors were applied for detecting riboflavin, Ag⁺, and Cys in HeLa cells with satisfying results. The finding of this study shows the feasibility and effectiveness of the NPCl-CQDs as the available ratiometric fluorescent sensors for the determination of riboflavin, Ag⁺, and Cys in real samples and living cells.

Characterization of flavin binding in oxygen-independent fluorescent reporters

Fluorescent proteins based on light, oxygen, and voltage (LOV) sensing photoreceptors are among the few reporter gene technologies available for studying living systems in oxygen-free environments that render reporters based on the green fluorescent protein nonfluorescent. LOV reporters develop fluorescence by binding flavin mononucleotide (FMN), which they endogenously obtain from cells. As FMN is essential to cell physiology as well as for determining fluorescence in LOV proteins, it is important to be able to study and characterize flavin binding in LOV reporters. To this end, we report a method for reversibly separating FMN from two commonly used LOV reporters to prepare stable and soluble apoproteins. Using fluorescence titration, we measured the equilibrium dissociation constant for binding with all three cellular flavins: FMN, flavin adenine dinucleotide, and riboflavin. Finally, we exploit the riboflavin affinity of apo LOV reporters, identified in this work, to develop a fluorescence turn-on biosensor for vitamin B2.

N, S, I co-doped carbon dots for folic acid and temperature sensing and applied to cellular imaging

The application of fluorescent carbon dots in bio-imaging has huge positive significance in the field of biomedicine. By taking this advantage, herein we prepared nitrogen, sulfur and iodine doped carbon dots (N,S,I-CDs) by a facile hydrothermal reaction using C₃N₃S₃, potassium iodate (KIO₃) and ethylenediamine (EDA), and the obtained N,S,I-CDs show bright blue fluorescence with a high fluorescence quantum yield of about 32.4%. The prepared N, S, I-CDs could interact with the folic acid (FA) with high selectivity, lead to development of a high sensitive method for the FA detection from 0.1 to 175 μM wide linear range with a detection limit of 84 nM (S/N = 3) and also applied them in U-2 OS cells imaging. Moreover, this sensor possessed a good sensitivity, linearity and reversibility in the temperature range of 10-80 °C, and successfully applied for the temperature sensing in cell HT-29 samples. This investigation illustrates that as-prepared N, S, I-CDs probe may have great potential as a high-performance platform for the accurate recognition of temperature in cells and could provide a new tool for the detection of FA in cells.