An aniline trimer-based multifunctional sensor for colorimetric Fe3+, Cu2+ and Ag+ detection, and its complex for fluorescent sensing of L-tryptophan

Highly Sensitive and Selective Detection of L-Tryptophan by ECL Using Boron-Doped Diamond Electrodes

L-tryptophan is an amino acid that is essential to the metabolism of humans. Therefore, there is a high interest for its detection in biological fluids including blood, urine, and saliva for medical studies, but also in food products. Towards this goal, we report on a new electrochemiluminescence (ECL) method for L-tryptophan detection involving the in situ production of hydrogen peroxide at the surface of boron-doped diamond (BDD) electrodes. We demonstrate that the ECL response efficiency is directly related to H2O2 production at the electrode surface and propose a mechanism for the ECL emission of L-tryptophan. After optimizing the analytical conditions, we show that the ECL response to L-tryptophan is directly linear with concentration in the range of 0.005 to 1 µM. We achieved a limit of detection of 0.4 nM and limit of quantification of 1.4 nM in phosphate buffer saline (PBS, pH 7.4). Good selectivity against other indolic compounds (serotonin, 3-methylindole, tryptamine, indole) potentially found in biological fluids was observed, thus making this approach highly promising for quantifying L-tryptophan in a broad range of aqueous matrices of interest.

Pyridine-2,6-Dicarboxylic Acid As a Facile and Highly Selective "Turn-Off" Fluorimetric Chemosensor for Detection of Cu (II) Ions in Aqueous Media

Copper metal is third most abundant trace element in human body. Determination of Cu (II) ions is a burning topic in field of environment protection and food safety because of its significant impact on ecosystem. In this study, 2,6-pyridine dicarboxylic acid (PDA) has been explored as "turn-off" florescent probe for florescent detection of Cu (II) ions. This sensor showed highly selective complexing ability towards Cu (II) ions. Addition of aqueous solution of Cu (II) ions remarkably quenched the fluorescence intensity of PDA while, on contrary, there was no any prominent fluorescence quenching interference on addition of various metal ions. The binding mode of PDA and Cu (II) ions was determined as stoichiometry of 1:1 and it was further confirmed by single crystal XRD analysis. Mechanisms of static and dynamic quenching were confirmed by stern-volmer plot. Limit of detection (LOD) and limit of quantification (LOQ) for Cu (II) ions was calculated as 3.6 µM and 1.23 µM respectively, which is far below the acceptable value (31.5µM) according to the World Health Organization. The use of the sensor for detection of Cu (II) ions in real samples in aqueous media was also performed.

Development of a label-free impedimetric aptasensor based on Zr-MOF and titaniom carbide nanosheets for detection of L-tryptophan

This study primarily focuses on the L-Tryptophan (Trp) biomarker assay, with particular attention given to its objectives. The investigation centers on the potential implications of imbalanced Trp levels and its associated metabolites, which have been attributed to the spectrum of both psychological and physiological disorders, encompassing conditions such as cancer. Therefore, the swift and accurate detection of this amino acid is of paramount importance in cancer monitoring, as it plays a crucial role in preventing the metastasis and spread of cancer cells. Thus, an electrochemical aptasensor was designed based on nanocomposite of AgNPs@UiO-66/Ti3C2 (MXene) as immobilization strategy for the ultrasensitive detection of Trp. Zirconium metal-organic frameworks (Zr-MOFs) were employed as carriers for silver nanoparticles to facilitate subsequent binding with aptamers. Markedly, the obtained results show that the constructed aptasensor can specifically detect Trp in the two concentration range from 1fM to 1 nM and 1 nM to 200 nM and with a low detection limit of 0.35 fM. When applied to real samples, the experimental results demonstrated positive recovery rates. Consequently, a discerning and sensitive electrochemical aptasensor devoid of labeling agents was successfully fabricated for the explicit purpose of Trp detection.

Recent Advances in Organic Sensors for the Detection of Ag+ Ions: A Comprehensive Review (2019-2023)

Recently, organic sensors for the detection of Ag+ and other metal ions have experienced significant advancements. This is because there is a growing demand for reliable and sensitive tools to monitor various environmental pollutants. Organic sensors have O-, S-, and N-donor atoms, which can act as a ligand and coordinate with different metal ions, hence stabilizing them in a variety of oxidation states. This interaction gives colorimetric and fluorescence changes, which are used to monitor Ag+ and other metal ions. This comprehensive review highlights the latest developments in organic sensors for the recognition of Ag+. We present an in-depth analysis of the underlying principles and mechanisms governing Ag+ ion recognition. Various organic sensing platforms, such as fluorescent and colorimetric sensors, are discussed, shedding light on their unique advantages and limitations. Special attention is given to the diverse range of organic ligands, receptors, and functional materials used to achieve high sensitivity, selectivity, and quantification accuracy. Additionally, we delve into real-world applications of organic sensors for Ag+ ion detection, examining their performance in complex matrices such as biological, environmental, industrial and agricultural matrices.

A Simple Schiff Base Probe for Quintuplicate-Metal Analytes with Four Emission-Wavelength Responses

A versatile mono-Schiff compound consisting of o-aminobenzene-hydroxyjulolidine (ABJ-MS) has been easily synthesized using a one-step reaction. ABJ-MS displays four diverse fluorescence responses to the addition of Zn2+/Al3+/Fe3+/Ag+, with the maximum fluorescence emission at 530 nm undergoing a hypsochromic shift to 502/490/440/430 nm, synchronously with the discriminating fluorescence enhancement being 10.6/22.8/2.6/7.1-fold, respectively. However, the addition of Cu2+ into ABJ-MS leads to an opposite behavior, namely, fluorescence quenching. Meanwhile, ABJ-MS also displays distinct absorption changes after adding these five metal ions due to different binding affinities between them and ABJ-MS, which gives ABJ-MS quite a versatile detecting nature for Cu2+/Zn2+/Al3+/Fe3+/Ag+. Moreover, ABJ-MS can mimic a series of versatile AND/OR/INH-consisting logic circuits on the basis of the Cu2+/Zn2+/Al3+/Fe3+/Ag+-mediated diverse optical responses. These will endow the smart ABJ-MS molecule and potential applications in the multi-analysis chemosensory and molecular logic material fields.

Semicarbazide-based fluorescent probe for detection of Cu2+ and formaldehyde in different channels

Two fluorescent sensors with the receptor semicarbazide respectively at 7- (CAA) and 3-position (CAB) of coumarin were designed and synthesized. CAA exhibits fluorescence turn-on response to Cu²⁺ by triggering the intramolecular charge transfer (ICT) process via Cu²⁺-catalyzed hydrolysis, and can detect formaldehyde (FA) at different channel by inhibiting the photo-induced electron transfer (PET). However, CAB displays quite different responses: the photophysical properties hardly changed in the presence of FA; while a three-stage fluorescence response of fast quenching, steady increasing and slowly decreasing was found upon addition of Cu²⁺. The high selectivity enabled CAA a good candidate for quantification of Cu²⁺ and formaldehyde as well as bioimaging Cu²⁺ in living cells. Good linear relationships between the fluorescence intensity and analyte concentration were observed in the range of 0.1-30 μM for Cu²⁺ and 1.0-50 μM for FA, and their detection limits (LOD) were calculated to be 0.43 μM and 1.92 μM (3δ/k), respectively.

A novel highly selective FRET sensor for Fe(III) and DFT mechanistic evaluation

A novel FRET-based sensor has been designed and developed through the conjugation of naphthyl and rhodamine via propylamine spacer, Naph-Rh. The naphthyl moiety serves as a FRET donor due to its emission spectrum overlapping with the rhodamine B absorption band. Naph-Rh exhibited a selectivity for sensing Fe³⁺ over other metal ions with a visual color change and fluorescent enhancement. The ratio of the Naph-Rh and Fe³⁺ was determined to be 1:1 based on Job's plot analysis with a detection limit of 83 nM. The probe exhibited a linear response to Fe³⁺ in the range of 0-120 μM. Furthermore, the density functional theory (DFT) calculations of Naph-Rh were carried out to rationalize the design and portray the plausible Fe³⁺ sensing mechanism.

Novel selective "on-off" fluorescence sensor based on julolidine hydrazone-Al3+ complex for Cu2+ ion: DFT study

A hydrazone (T1) was synthesized by reacting 8-hydroxyjulolidine-9-carboxaldehyde with 2-furoic hydrazide and then modified with Al³⁺ ion to form a novel hydrazone Al³⁺ complex (T1-Al³⁺) in an aqueous solution (8% propylene glycol in 10 mM HEPES pH 5.5). The T1-Al³⁺ complex was studied as a Cu²⁺ selective sensor due to its highly efficient capacibility of paramagnetic quenching. The results showed that the T1-Al³⁺ complexed sensor possesses remarkable sensitivity and selectivity for Cu²⁺ ion in 8% propylene glycol in 10 mM HEPES pH 5.5 as compared with other tested analytes. Notably, this sensor has a broad linear detection range of 10-110 µM for Cu²⁺ ion and a detection limit level of 0.62 µM, which is lower than the Cu²⁺ concentration threshold in drinking water designated by the United States Environmental Protection Agency (EPA). Additionally, it was detectable for the presence of Cu²⁺ ion in mineral water and tap water samples. The selectivity of T1-Al³⁺ complexed sensor with Cu²⁺ ion could be explained by the basis of computation with Gaussian software complied with the basis sets of B3LYP/6-31 G(d,p)/LANL2DZ. Furthermore, only T1 exhibited anticancer efficacy against HeLa and U251 cells with MTT assay.

A highly selective silver ion optical chemosensor based on isoxazolyl-azo pyrimidine: synthesis, spectroscopy, DFT calculations and applications

In this work, an isoxazolyl-azo pyrimidine optical chemosensor (PICS) was efficiently synthesized and applied for naked-eye detection of Ag⁺ ions in solution. The chemical formula of the PICS was recognized by UV-vis, FTIR and NMR analyses. The detection ability of PICS toward various ions was assessed. The results revealed the excellent selectivity and sensitivity of the chemosensor PICS to Ag⁺ ions in aqueous DMSO solutions. The PICS displayed an obvious color change from yellow to dark red in the presence of silver ions. The PICS could efficiently detect Ag⁺ ions over a wide pH range of 6-11, which makes it suitable for detection of Ag⁺ under physiological conditions. PICS also binds Ag⁺ ions to form a 1 : 1 stoichiometry complex (PICS-Ag⁺), resulting in a bathochromic shift in the absorption maximum from 372 to 410 nm. The detection limit of the probe PICS towards Ag⁺ was calculated to be 1.78 μM. Furthermore, the probe PICS shows excellent detection performance in the solid state, and PICS-based test strips were fabricated and applied as efficient Ag⁺ test kits for detection of silver ions in water samples. In addition, the sensing mechanism of PICS-Ag⁺ was completely evaluated using the density functional theory (DFT) calculations. Results indicated that the calculated energy gap between the HOMO and LUMO (3.41 eV) of PICS-Ag is lower than that of the free PICS (3.57 eV). This suggests that a red shift occurred upon addition of the Ag⁺ ion to PICS.

A dimedone-phenylalanine-based fluorescent sensor for the detection of iron (III), copper (II), L-cysteine, and L-tryptophan in solution and pharmaceutical samples

The development of fluorescence molecules for the fast and effective detection of L-tryptophan (L-Trp) has attracted a lot of attention because it is an important amino acid for baby growth, nitrogen equilibrium in adults, improving sleep, and mood regulation. A dimedone-phenylalanine-based chiral sensor (SDPA) was synthesized and exhibited a strong fluorescence quenching by Fe³⁺ and Cu²⁺ in a water/DMSO (3/7) solution with a detection limit of 2.29 × 10^-6 M and 6.37 × 10^-6 M, respectively. The factors affecting fluorescence sensings, such as the pH and competing cations, were studied. The sensor can be reused at least five times after being treated with EDTA. The Job plot, ESI-MS spectra, ¹H NMR spectra, absorbance, and fluorescence titration experiments were investigated to study the mechanism of SDPA-Fe³⁺ and SDPA-Cu²⁺ complexation. The SDPA-Cu²⁺ complex can detect L-tryptophan and L-cysteine at trace levels by turn-on fluorescence with a detection limit of 9.35 × 10^-6 M and 8.86 × 10^-6 M, respectively. Moreover, applying the SDPA-Cu²⁺ complex for quantitative analysis of L-tryptophan in real sleep-improving capsules resulted in good recovery. The L-tryptophan level of the Elining capsule was determined at 190.8 ± 10.5 mg/g (mg L-tryptophan/g medicine), which is close to the announced quantity of 180 mg/g. Besides, the SDPA-Cu²⁺ complex can selectively detect free L-Try molecules and L-Try residues in proteins.

An effective long-wavelength fluorescent sensor for Cu2+ based on dibenzylidenehydrazine-bridged biphenylacrylonitrile

Although numerous fluorescence sensors for Cu²⁺ have been presented, a long-wavelength sensor in aqueous media has rarely been reported as expected due to practical application requirements. In this work, a novel AIE molecule (DHBB) containing two biphenylacrylonitrile units bridged by dibenzylidenehydrazine was prepared. It possessed the merits of long-wavelength emission, good emission in aqueous media, and multiple functional groups for binding Cu²⁺. It exhibited good sensing selectivity for Cu²⁺ among all kinds of tested metal ions. The detection limit was as low as 1.08 × 10^-7 M. The sensing mechanism was clarified as 1:1 stoichiometric ratio based on the binding cooperation of O and N functional groups of DHBB. The selective sensing ability for Cu²⁺ remained stable at pH = 5-9 and was influenced little by other metal ions. The Cu²⁺ sensing ability of DHBB was applied in real samples with 96% recovery rate. The bio-imaging experiment of living cells suggested that DHBB possessed not only good bio-imaging performance but also sensing ability for Cu²⁺ in living environments. This work suggested the good application prospect of DHBB to sense Cu²⁺ in real samples and living environment.

Solvothermal synthesis of 3D hierarchical Cu2FeSnS4 microspheres for photocatalytic degradation of organic pollutants

In this work, we prepared Cu₂FeSnS₄ (CFTS) microspheres via solvothermal method and studied their photocatalytic performance towards the degradation of organic pollutants. With increasing solvothermal temperature from 160 °C to 180 °C, the morphology of CFTS changes from irregular 2D to hierarchical 3D shapes. Hierarchical 3D CFTS microspheres packed with 2D nanosheets were successfully prepared at 180 °C. During the solvothermal process, octadecyl amine (ODA) acts as a capping agent to prevent the aggregation of particles, while L-cystine functions as an environmentally friendly sulfur source and complexing reagent. The large surface area and mesoporous structure of the as-prepared 3D hierarchical CFTS microspheres provide more active sites, enhance visible light absorption and promote charge separation and transfer, leading to the improved photodegradation performance for RhB and MB compared to the samples prepared at the temperature lower than 180 °C. This work provides a simple and low-cost method for the synthesis of 3D hierarchical CFTS towards photocatalytic applications.

Naked-eye colorimetric and turn-on fluorescent Schiff base sensor for cyanide and aluminum (III) detection in food samples and cell imaging applications

A new efficient Schiff base sensor SB3 for fluorescent and colorimetric "naked-eye" "turn-on" sensing of cyanide anion (CN^-) with excellent sensitivity and selectivity was developed. The 4,4'-(perfluoropropane-2,2-diyl)bisphenol group and two phenyl groups were covalently linked by two C = N bonds to extend the conjugation length. The four hydroxyl groups can improve the water solubility of the SB3 sensor. The SB3 sensor exhibited high specificity towards CN^- by interrupting its intramolecular charge transfer, resulting in a color change and remarkable "turn-on" green fluorescence emission. The sensing mechanism is caused by the nucleophilic addition of CN- toward imine groups of the SB3 sensor, leading to breaks of the conjugation, fluorescent spectral changes, and color change. It was confirmed by ¹H NMR titration and Mass spectra. The detection limits for CN^- and Al³⁺obtained by fluorescence spectrum are 0.80 µM and 0.25 µM, respectively. The SB3 sensor can act as an efficient chemical sensor for detecting the CN^- and Al³⁺ ions under common environmental and physiological conditions (pH 5-12). Besides, the sensor can also detect CN^- in food materials (such as sprouting potatoes and cassava flour) and imaging CN^-in living cells with strong "turn-on" fluorescence at 490 nm. SB3 is an excellent CN^- sensor that exhibits some advantages, including easy synthesis, distinct fluorescence and color change, high selectivity, low detection limit, and good anti-interference ability to analyze solution and food samples, together with fluorescence cell imaging.

A novel turn-on fluorogenic aldehyde-appended salamo-like copper(ii) complex probe for the simultaneous detection of S2O32− and GSH

A novel salamo-like copper(ii) complex probe (ASC) behaves as a two-pronged sensor of S₂O₃²⁻ ions and GSH by a ‘turn-on’ fluorescence mechanism.