Design of novel anthracene-based fluorescence sensor for sensitive and selective determination of iron in real samples

Highly-fluorescent extracts from Pterocarpus wood for Fe3+ ion detection

At present, excessive Fe3+ in daily water has become a threat to human health. Among the conventional detection methods for Fe3+, fluorescent probes have been applied on a large scale due to their simplicity and efficiency. However, the currently available fluorescent probes are difficult to synthesize, costly and environmentally unfriendly, limiting their applications. In this work, a fluorescent extract of Pterocarpus wood was successfully obtained, and the structure of some coumarin-based molecules in this extract was determined by 2D-NMR. Subsequently, the intensity of this fluorescence was optimized using response surface methodology (RSM), resulting in a high-intensity fluorescent probe. The probe was sensitive to the concentrations of Fe3+ and MnO4-, and could efficiently detects Fe3+ in the range of 2.7 μM-8.0 μM, with LOD and LOQ reaching 1.06 μM and 3.20 μM, respectively. Moreover, based on the strong complexation property of EDTA on Fe3+, this work designed the "switch-on" fluorescent probes. The experiment shows that both static and dynamic quenching exist in this system. The mechanism of complexation and oxidation of fluorescent molecules by the quencher is interpreted in the quenching reaction. In addition, the fluorescent probe has a high yield and low cost, it also performs well in actual water sample tests. This method is expected to be developed as a new way on Fe3+ detection.

Synthesis, Crystal Structure and Fluorimetric Study of 2-phenylphthalazin-1(2H)-one: a Highly Selective Florescent Chemosensor for Detection of Fe3+ and Fe2+ Metal Ions

A ligand, 2-phenylphthalazin-1(2H)-one (K), was synthesized by refluxing 2-formylbenzoic acid with phenyl hydrazine in presence of ethanol. FTIR, elemental analysis and single crystal XRD techniques were used to elucidate the structure. Fluorimetric turn-off response was recorded when solution of ligand (K) in DMF was treated with aqueous solution of Fe3+ and Fe2+ metal ions. No specific changes were observed on addition of other metal ions (Pb2+, Cd2+, Mn2+, Zn2+, Ba2+, Ni2+, Al3+, Ag1+, Co2+, Ca2+, Cu2+, Mg2+, Cr3+). Limit of Detection (LOD) was calculated for Fe2 and Fe3+as 2.4 µM and 2.5µM respectively, which is quite below to the recommended value 5.4 µM of the Environment Protection Agency of USA. Association constants for Fe3+ and Fe2+ metal ions were determined as 6 × 10-4 M-1 and 3.6 × 10-4 M-1 respectively. Benesi-Hildebrand plot confirmed 1:1 binding ratio between metal ions and ligand.

Fluorescence "Turn OFF-ON" detection of Fe3+ and propiconazole pesticide using blue emissive carbon dots from lemon peel

In this study, water-soluble carbon dots (CDs) were employed as a novel fluorescence "turn OFF-ON" sensor to detect Fe³⁺ ions in pharmaceutical sample and propiconazole (PC) in food samples. Blue fluorescent "LPCDs" are synthesized from the lemon peel that exhibited emission at 468 nm when excited at 378 nm. The average size of the as-prepared LPCDs is 2.03 nm, displaying a quantum yield of 32 %. Fluorescence "turn OFF-ON" strategy was developed for sensing of Fe³⁺ ion and PC, demonstrating favorable linearity in the range of 0.5-180 μM and 0.1-40 μM with the detection limits of 0.18 μM and 0.054 μM for Fe³⁺ and PC, respectively. Further, LPCDs-loaded cellulose paper was used as visual reader to detect Fe³⁺ and PC. This approach was effectively applied to detect Fe³⁺ and PC in pharmaceutical and vegetable samples.

Oxadiazole Schiff Base as Fe3+ Ion Chemosensor: "Turn-off" Fluorescent, Biological and Computational Studies

Compound, (E)-5-(4-((thiophen-2-ylmethylene)amino)phenyl)-1,3,4-oxadiazole-2-thiol (3) was synthesized via condensation reaction of 5-(4-aminophenyl)-1,3,4-oxadiazole-2-thiol with thiophene-2-carbaldehyde in ethanol. For the synthesis and structural confirmation the FT-IR, ¹H, ¹³C-NMR, UV-visible spectroscopy, and mass spectrometry were carried out. The long-term stability of the probe (3) was validated by the experimental as well as theoretical studies. The sensing behaviour of the compound 3 was monitored with various metal ions (Ca²⁺, Cr³⁺, Fe³⁺, Co²⁺, Mg²⁺, Na⁺, Ni²⁺, K⁺) using UV- Vis. and fluorescence spectroscopy techniques by various methods (effect of pH and density functional theory) which showing the most potent sensing behaviour with iron. Job's plot analysis confirmed the binding stoichiometry ratio 1:1 of Fe³⁺ ion and compound 3. The limit of detection (LOD), the limit of quantification (LOQ), and association constant (K_a) were calculated as 0.113 µM, 0.375 µM, and 5.226 × 10⁵ respectively. The sensing behavior was further confirmed through spectroscopic techniques (FT-IR and ¹H-NMR) and DFT calculations. The intercalative mode of binding of oxadiazole derivative 3 with Ct-DNA was supported through UV-Vis spectroscopy, fluorescence spectroscopy, viscosity, cyclic voltammetry, and circular dichroism measurements. The binding constant, Gibb's free energy, and stern-volmer constant were find out as 1.24 × 10⁵, -29.057 kJ/mol, and 1.82 × 10⁵ respectively. The cleavage activity of pBR322 plasmid DNA was also observed at 3 × 10^-5 M concentration of compound 3. The computational binding score through molecular docking study was obtained as -7.4 kcal/mol. Additionally, the antifungal activity for compound 3 was also screened using broth dilution and disc diffusion method against C. albicans strain. The synthesized compound 3 showed good potential scavenging antioxidant activity against DPPH and H₂O₂ free radicals.

Compact Fluorescence Detection System Based on a Monolithic DBR-Integrated III-Nitride LED Chip

Portable applications of fluorescence detection systems have gained much attention in various fields and require system components to be small and compact. In this work, we report on a compact fluorescence detection system and demonstrate its application for fluorescence sensing and imaging. The light source and filter are integrated on a single chip for the proposed system, which not only realizes the separation between excitation and fluorescent lights but also improves the light-emitting diode (LED) light extraction efficiency. Furthermore, the detection system allows for a removable sample unit. The results indicate that the performance of the distributed Bragg reflector (DBR) filter based on an amorphous dielectric film is excellent with selection ratios larger than 4600:1. The peak emission wavelength of the LED is 528 nm. The influence of green light leakage can be neglected, and the fluorescent red light is dominant when the fluorescence detection system is used for sensing and imaging. The low-cost and monolithic DBR-integrated III-nitride LED chip makes the proposed architecture a competitive candidate for portable fluorescence detection applications.

Aryl-Phenanthro[9,10-d]imidazole: A Versatile Scaffold for the Design of Optical-Based Sensors

Fluorescent and colorimetric sensors are important tools for investigating the chemical compositions of different matrices, including foods, environmental samples, and water. The high sensitivity, low interference, and low detection limits of these sensors have inspired scientists to investigate this class of sensing molecules for ion and molecule detection. Several examples of fluorescent and colorimetric sensors have been described in the literature; this Review focuses particularly on phenanthro[9,10-d]imidazoles. Different strategies have been developed for obtaining phenanthro[9,10-d]imidazoles, which enable modification of their optical properties upon interaction with specific analytes. These sensing responses usually involve changes in the fluorescence intensity and/or color arising from processes like photoinduced electron transfer, intramolecular charge transfer, intramolecular proton transfer in the excited state, and Förster resonance energy transfer. In this Review, we categorized these sensors into two different groups: those bearing formyl groups and their derivatives and those based on other molecular groups. The different optical responses of phenanthro[9,10-d]imidazole-based sensors upon interaction with specific analytes are discussed.

Can machine learning methods accurately predict the molar absorption coefficient of different classes of dyes?

In this article, we provide a convenient tool for all researchers to predict the value of the molar absorption coefficient for a wide number of dyes without any computer costs. The new model is based on RFR method (ALogPS, OEstate + Fragmentor + QNPR) and is able to predict the molar absorption coefficient with an accuracy (5-fold cross-validation RMSE) of 0.26 log unit. This accuracy was achieved due to the fact that the model was trained on data for more than 20,000 unique dye molecules. To our knowledge, this is the first model for predicting the molar absorption coefficient trained on such a large and diverse set of dyes. The model is available at https://ochem.eu/article/145413. We hope that the new model will allow researchers to predict dyes with practically significant spectral characteristics and verify existing experimental data.

Pyrene Substituted Phthalonitrile Derivative As a Fluorescent Sensor For Detection of Fe3+ Ions in Solutions

In this current study, the novel bis[4,5-(pyrene-2-yl)-3,6-(hexyloxy)] phthalonitrile (SPN) fluorophore has been successfully synthesized. Structural characterization of this novel compound was performed by different spectroscopic methods such as FT-IR, MALDI-TOF, ¹H-NMR, ¹³C-NMR and elemental analyses as well. In addition, the photophysical properties were determined using UV-vis absorption, steady-state fluorescence, time-resolved fluorescence spectroscopic methods and quantum chemical calculations. The metal sensing behavior of the SPN was determined in the presence of various metals (Li⁺, Na⁺, K⁺, Mg²⁺, Ca²⁺, Ba²⁺, Mn²⁺, Fe³⁺, Cr³⁺, Co²⁺, Ni²⁺, Ag⁺, Cd²⁺, Al³⁺, Hg⁺ and Zn²⁺) using fluorescence spectroscopy. The novel pyrene based phthalonitrile (SPN) showed high sensitivity and selectivity towards Fe³⁺ ion over other examined metal ions. In order to perform the determination of Fe³⁺ ion in environmental samples, experimental conditions such as selectivity, stability, precision, sensitivity, accuracy and recovery were optimized. Also, the complex stoichiometry of the novel pyrene based phthalonitrile (SPN) and Fe³⁺ ions was determined by a Job's plot. The compound was also studied via density functional theory calculations revealing the interaction mechanism of the molecule with Fe³⁺ ions.

Recent advances in the highly sensitive determination of zearalenone residues in water and environmental resources with electrochemical biosensors

Zearalenone (ZEN), a significant class of mycotoxin which is considered as a xenoestrogen, permits, similar to natural estrogens, it's binding to the receptors of estrogen resulting in various reproductive diseases especially, hormonal misbalance. ZEN has toxic effects on human and animal health as a result of its teratogenicity, carcinogenicity, mutagenicity, nephrotoxicity, genotoxicity, and immunotoxicity. To ensure water and environmental resources safety, precise, rapid, sensitive, and reliable analytical and conventional methods can be progressed for the determination of toxins such as ZEN. Different selective nanomaterial-based compounds are used in conjunction with different analytical detection approaches to achieve this goal. The current review demonstrates the state-of-the-art advances of nanomaterial-based electrochemical sensing assays including various sensing, apta-sensing and, immunosensing studies to the highly sensitive determination of various ZEN families. At first, a concise study of the occurrence, structure, toxicity, legislations, and distribution of ZEN in monitoring has been performed. Then, different conventional and clinical techniques and procedures to sensitive and selective sensing techniques have been reviewed and the efficient comparison of them has been thoroughly discussed. This study has also summarized the salient features and the requirements for applying various sensing and biosensing platforms and diverse immobilization techniques in ZEN detection. Finally, we have defined the performance of several electrochemical sensors applying diverse recognition elements couples with nanomaterials fabricated using various recognition elements coupled with nanomaterials (metal NPs, metal oxide nanoparticles (NPs), graphene, and CNT) the issues limiting development, and the forthcoming tasks in successful construction with the applied nanomaterials.

Preparative Production of Functionalized (N- and O-Heterocyclic) Polycyclic Aromatic Hydrocarbons by Human Cytochrome P450 3A4 in a Bioreactor

Polycyclic aromatic hydrocarbons (PAHs) and their N- and O-containing derivatives (N-/O-PAHs) are environmental pollutants and synthetically attractive building blocks in pharmaceuticals. Functionalization of PAHs can be achieved via C-H activation by cytochrome P450 enzymes (e.g., P450 CYP3A4) in an environmentally friendly manner. Despite its broad substrate scope, the contribution of CYP3A4 to metabolize common PAHs in humans was found to be small. We recently showcased the potential of CYP3A4 in whole-cell biocatalysis with recombinant yeast Komagataella phaffii (Pichia pastoris) catalysts for the preparative-scale synthesis of naturally occurring metabolites in humans. In this study, we aimed at exploring the substrate scope of CYP3A4 towards (N-/O)-PAHs and conducted a bioconversion experiment at 10 L scale to validate the synthetic potential of CYP3A4 for the preparative-scale production of functionalized PAH metabolites. Hydroxylated products were purified and characterized using HPLC and NMR analysis. In total, 237 mg of fluorenol and 48 mg of fluorenone were produced from 498 mg of fluorene, with peak productivities of 27.7 μmol/L/h for fluorenol and 5.9 μmol/L/h for fluorenone; the latter confirmed that CYP3A4 is an excellent whole-cell biocatalyst for producing authentic human metabolites.

Development of dipodal fluorescence sensor of iron for real samples based on pyrene modified anthracene

A novel pyrene modified anthracene dipodal sensor was prepared by a simple synthetic method for the sensitive determination of iron ions in real samples. The chemical characterization analyses including nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry were carried out to characterize the target fluorescent sensor. Photophysical and electrochemical behaviors of the sensor were studied by the absorption, excitation-emission matrix analysis, steady-state fluorescence, three-dimensional fluorescence, and cyclic and square wave voltammetry, respectively. The fluorescent sensor properties were evaluated via Ultraviolet-visible and fluorescence spectroscopies. According to obtained results, the fluorescence signal of the sensor was selectively quenched with interaction with Fe³⁺ ions. The spectrofluorimetric determination of iron, in real water and medicine samples were successfully carried out under optimized experimental conditions. A detection limit and linear working range were calculated as 0.265 μM and 0.275-55.000 μM, respectively which demonstrated the ability of the simple and sensitive sensor for slight amounts of iron. The obtained detection limit for iron determination with the presented novel fluorescent sensor was less than nearly 20 times the tolerance limit (5.40 µM) in drinking water that was determined by the United States Environmental Protection Agency. The accuracy of the newly developed method was evaluated by Inductively coupled plasma optical emission spectroscopy and spike/recovery test which demonstrated that the developed fluorescent sensor has high accuracy for fast, easy and accessible determination of iron at 95% confidence level.

A facile colorimetric method for the quantification of labile iron pool and total iron in cells and tissue specimens

Quantification of iron is an important step to assess the iron burden in patients suffering from iron overload diseases, as well as tremendous value in understanding the underlying role of iron in the pathophysiology of these diseases. Current iron determination of total or labile iron, requires extensive sample handling and specialized instruments, whilst being time consuming and laborious. Moreover, there is minimal to no overlap between total iron and labile iron quantification methodologies-i.e. requiring entirely separate protocols, techniques and instruments. Herein, we report a unified-ferene (u-ferene) assay that enables a 2-in-1 quantification of both labile and total iron from the same preparation of a biological specimen. We demonstrate that labile iron concentrations determined from the u-ferene assay is in agreement with confocal laser scanning microscopy techniques employed within the literature. Further, this assay offers the same sensitivity as the current gold standard, inductively coupled plasma mass spectrometry (ICP-MS), for total iron measurements. The new u-ferene assay will have tremendous value for the wider scientific community as it offers an economic and readily accessible method for convenient 2-in-1 measurement of total and labile iron from biological samples, whilst maintaining the precision and sensitivity, as compared to ICP-MS.

Multi-anthracene containing fluorescent probe for spectrofluorimetric iron determination in environmental water samples

An anthracene-based fluorescence (FL) system was synthesized via a general synthetic procedure. Fourier transform infrared spectroscopy (FTIR), MALDI-MS, and nuclear magnetic resonance spectroscopy (¹³C and ¹H NMR) were carried out to characterize the multi-anthracene containing probe. The photophysical properties of the probe were illustrated via 3D-FL analysis and excitation-emission matrix (EEM) measurements. Density-functional theory (DFT) was applied to optimize the structure of the prepared probe and investigate its molecular interactions with Fe³⁺. The FL proficiency of the probe was appraised by spectroscopic measurements like Ultraviolet-Visible (UV-Vis) and FL spectroscopies. The simple and highly sensitive probe was able to diagnose ferric ions' low concentrations and detection limit reached upto 0.223 µM with linear working range between 0.22 and 92.00 µM for Fe³⁺ ions. The efficacy of this fluorescent probe was confirmed by testing for iron determination in environmental samples. Various fluorophores or ionophores could be applied for achieving novel probes by the proposed procedures and for diagnosing diverse metal ions.

Enzyme-free and label-free detection of Staphylococcus aureus based on target-inhibited fluorescence signal recovery

In this work, a one-step fluorometric strategy based on nanometal surface energy transfer (NSET) between carbon dots (CDs) and gold nanoparticles (AuNPs) was developed for facile detection of Staphylococcus aureus (S. aureus). The fluorescence of CDs was quenched up to 63.5% by AuNPs due to nucleic acid hybridization in the presence of linker DNA, which contained the complementary sequences of S. aureus-specific aptamer, and the fluorescence signal was in the "off" state. Upon aptamer addition, the CDs was released from linker DNA through the strong competitiveness of aptamer, leading to the notable fluorescence recovered. Once S. aureus is introduced, aptamer preferentially bind to the bacterial surface and cannot hybridize with complementary sequences in the linker DNA, resulting in the fluorescence signal with "off" state. Based on these findings, the performance and reliability of the fluorescence-based assay were evaluated. Compared to direct hybridization of complementary DNA on the surface of CDs and AuNPs, our sensing strategy has enhanced detection limit (10 cfu⋅mL^-1) and improved linear range (10 to 10⁶ cfu⋅mL^-1) for S. aureus. Therefore, our proposed enzyme-free and label-free strategy may become a promising method for ease of operation, sensitive and selective S. aureus detection.

A “turn-on” small molecule fluorescent sensor for the determination of Al3+ ion in real samples: theoretical calculations, and photophysical and electrochemical properties

The fluorescence sensing properties of a naphthalene-based acetohydrazide (3) were investigated. A highly selective “turn-on” response was obtained towards Al3+ ions, and this was used for real sample analysis and development of paper test strips.

Red-fluorescent graphene quantum dots from guava leaf as a turn-off probe for sensing aqueous Hg(ii)

In this work, we have prepared red-fluorescent graphene quantum dots and utilized as a highly selective and sensitive fluorescence turn-off probe for detection of the toxic metal ion Hg²⁺ from guava leaf extract.

A hybrid nanosensor based on novel fluorescent iron oxide nanoparticles for highly selective determination of Hg2+ ions in environmental samples

Novel fluorescent iron oxide nanoparticles were prepared for the determination of Hg²⁺ in real samples. The fluorescence behaviors of the sensor were examined using absorption and fluorescence (steady-state, time-resolved, 3-D, EEM) spectroscopies.

ESIPT on/off switching and crystallization-enhanced emission properties of new design phenol-pyrazole modified cyclotriphosphazenes

Cyclophosphazene-based high-efficiency excited state intramolecular proton transfer (ESIPT) active and inactive molecules were prepared depending on the different bonding patterns of the difunctional phenol-pyrazol reagent.

Fluorescence determination of trace level of cadmium with pyrene modified nanocrystalline cellulose in food and soil samples

Cadmium is one of the most toxic metal that accumulates in the human body via food chain, industrial/agricultural activites. It also has negative effects in organs such as the brain, liver and central nervous system. Therefore, International Agency for Research on Cancer is classified cadmium as "carcinogenic to humans" (group 1). In this work, novel pyrene modified nanocrystalline cellulose (NP-1) was designed as a fluorescence sensor for selective determination of Cd²⁺ in food and soil samples. FTIR, UV-Vis, SEM, TEM and TGA were used for structural, morphological characterizations and thermal properties of NP-1. The experimental conditions such as selectivity, pH, sensor concentration, photostability, time and interaction mechanism were examined and optimized. The LOD was determined as 0.09 μM (10.70 μg/L) which was lower than WHO's permissible limit of cadmium in plant with 0.10-60.00 μM linear working range. Validation of the present method was performed by spike/recovery test and ICP-MS, then fluorescence determination of Cd²⁺ in food and soil samples was succesfully applied. The results indicated that the proposed method based on "turn-on" fluorescence of NP-1 was a simple, sensitive and reliable for rapid determination of Cd²⁺ in real samples with high applicability and stability.