An imidazo[1,5-α]pyridine-derivated fluorescence sensor for rapid and selective detection of sulfite

CdTe based water-soluble fluorescent probe for rapid detection of zilpaterol in swine urine and pork

Zilpaterol hydrochloride (zilpaterol) is used in animal feed as it can increase the lean meat mass. However, consuming zilpaterol-containing animal products may damage human health. Therefore, rapid detection of zilpaterol is attracting increasing research attention. This study aimed to developed a fast, accurate, and ultrasensitive fluorescence immunoassay based on CdTe quantum dots (QDs). A CdTe QD fluorescence sensor was synthesized from thioglycolic acid using a simple hydrothermal method. The morphology and structure of the CdTe QDs were characterized using transmission electron microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier-transform infrared spectroscopy. The detection limits of our method in swine urine and pork samples were 0.5 μg/L and 1.2 μg/kg, respectively. A wide linear range of 0.1-10000 μg/L (R2 = 0.996) was achieved. Both within-run precision (CVw) and between-run precision (CVb) were ≤ 10 %. The method was then successfully applied for the analysis of zilpaterol contents in swine urine and pork samples.

A novel 2-(2-aminophenyl) imidazo [1,5-a] pyridine-based fluorescent probe for rapid detection of phosgene

Phosgene is a highly concealed and highly toxic gas that seriously threatens human health and public security. Therefore, the detection of phosgene is of great significance to world security. Herein, a new type of fluorescent probe based on 2-(2-aminophenyl) imidazo [1,5-a] pyridine is reported for the rapid detection of phosgene. The probe itself only emits a faint green fluorescence, while phosgene allows it to produce a strong blue fluorescence. During the recognition process, phosgene interacts simultaneously with both amino site and imidazole moiety in the probe molecule, resulting in a four-ring-fused rigid structure with high fluorescence quantum yield. The probe not only has the characteristics of high efficiency, high sensitivity (detection limit 2.68 nM), and high selectivity, but also has remarkable spectral changes. Finally, a portable test strip is used to detect phosgene in the gas phase, and the fluorescent color change of the test strip can be easily observed. The most exciting thing is that the portable test strip with the probe PMPY-NH2 can produce a strong fluorescence response to 1 ppm of phosgene, which is far lower than the level of phosgene that seriously threatens to human health.

Mono-, Bis-, and Tris-Chelate Zn(II) Complexes with Imidazo[1,5-a]pyridine: Luminescence and Structural Dependence

New mono-, bis-, and tris-chelate Zn(II) complexes have been synthesized starting from different Zn(II) salts and employing a fluorescent 1,3-substituted-imidazo[1,5-a]pyridine as a chelating ligand. The products have been characterized by single-crystal X-ray diffraction; mass spectrometry; and vibrational spectroscopy. The optical properties have been investigated to compare the performances of mono-, bis-, and tris-chelate forms. The collected data (in the solid state and in solution) elucidate an important modification of the ligand conformation upon metal coordination; which is responsible for a notable increase in the optical performance. An intense modification of the emission quantum yield along the series in the solid state is observed comparing mono-, bis-, and tris-chelate adducts; independently from the anionic ligand introduced by ionic exchange.

Coordination of Distal Carboxylate Anion Alters Metal Ion Specific Binding in Imidazo[1,2-a]pyridine Congeners

Imidazo[1,2-a]pyridine derivatives have excellent potential for chelation with transition metal ions. Two new imidazo[1,2-a]pyridine-8-carboxylates were synthesized and characterized by ¹H NMR, ¹³C NMR, HRMS, and single crystal-XRD techniques. Methyl carboxylate (probe 1) turns on fluorescence upon coordination with Zn²⁺, while sodium carboxylate (probe 2) turns off its fluorescence upon coordination with Co²⁺ or Cu²⁺ ions present in aqueous acetonitrile medium. ¹³C NMR study revealed that the change in metal ion specific binding was due to the involvement of carboxylate anion in complex formation with Co²⁺ or Cu²⁺ ions. The carboxylate anion at 8-position also enhanced the sensitivity of detection of probe 2 by an order of magnitude (detection limits: 3.804 × 10^-7 M, probe 1/Zn²⁺; 0.420 × 10^-7 M, probe 2/Co²⁺ and 0.304 × 10^-7 M, probe 2/Cu²⁺). The detection limits of probes 1 and 2 comply well with the World Health Organization (WHO) and US Environmental Protection Agency (US-EPA) guidelines for detection of heavy metal ions present in drinking water and ground water. Both the probes form a 1:1 complex with Zn²⁺, Co²⁺ or Cu²⁺, and the stoichiometry was verified by Job plot and ESI-mass analysis. The sensing mechanism is explained using ¹³C NMR experiments, ESI-mass analytical data and theoretical DFT calculations. The suitability of probes 1 and 2 for on-site detection and quantitative determination of Zn²⁺, Co²⁺ and Cu²⁺ ions present in biological, environmental and industrial samples is demonstrated. In addition, both 1 and 2 are used for detection of intracellular contamination of Zn²⁺, Co²⁺ or Cu²⁺ ions in onion epidermal cells.

Progress in the Development of Imidazopyridine-Based Fluorescent Probes for Diverse Applications

Different classes of Imidazopyridine i.e., Imidazo[1,2-a]pyridine, Imidazo[1,5-a] pyridine, Imidazo[4,5-b]pyridine, have shown versatile applications in various fields. In this review, we have concisely presented the usefulness of the fluorescent property of imidazopyridine in different fields such as imaging tools, optoelectronics, metal ion detection, etc. Fluorescence mechanisms such as excited state intramolecular proton transfer, photoinduced electron transfer, fluorescence resonance energy transfer, intramolecular charge transfer, etc. are incorporated in the designed fluorophore to make it for fluorescent applications. It has been widely employed for metal ion detection, where selective metal ion detection is possible with triazole-attached imidazopyridine, β-carboline imidazopyridine hybrid, quinoline conjugated imidazopyridine, and many more. Also, other popular applications involve organic light emitting diodes and cell imaging. This review shed a light on recent development in this area especially focusing on the optical properties of the molecules with their usage which would be helpful in designing application-based new imidazopyridine derivatives.

An imidazo[1,5-α]pyridines-based ratiometric fluorescent probe for sensing sulfur dioxide derivatives in real samples based on a FRET mechanism

A novel fluorescence resonance energy transfer (FRET)-based ratiometric emission fluorescent probe AT was designed and developed in which the imidazo[1,5-α]pyridine was served as a FRET donor and tricyanofuran (TCF) as the FRET acceptor to detect SO₃^2-/HSO₃^- based on the Michael addition reaction. Probe AT had a high energy transfer efficiency (95%) and a large pseudo-Stokes shift (259 nm) in EtOH/PBS buffer (5/5, v/v). It also possessed good selectivity and quick response to SO₃^2-/HSO₃^-. There was good linearity between the ratio of fluorescence intensity (F₄₉₉/F₆₄₅) and the concentrations of SO₃^2-/HSO₃^- in the ranges of 1.5-7.5 μM and 9-20 μM, with calculated detection limits (LOD) of 55 nM. In addition, the probe could also detect the concentrations of SO₃^2-/HSO₃^- in real samples such as environmental water and sugar, allowing the probe to be used in a variety of applications.

A stable and sensitive Au metal organic frameworks resonance Rayleigh scattering nanoprobe for detection of SO3 2- in food based on fuchsin addition reaction

A stable Au metal organic frameworks (AuMOF) nanosol was prepared. It was characterized by electron microscopy and molecular spectral techniques. In pH 6.8 PBS buffer solution, AuMOF nanoprobes exhibit a strong resonance Rayleigh scattering (RRS) peak at 330 nm. After basic fuchsin (BF) adsorbing on the surface of AuMOF, the RRS energy of the nanoprobe donor can be transferred to BF receptor, resulting in a decrease in the RRS intensity at 330 nm. Both sulfite and BF taken place an addition reaction to form a colorless product (SBF) that exhibit weak RRS energy transfer (RRS-ET) between AuMOF and SBF, resulting in the enhancement of the RRS peak. As the concentration of SO3 2-increases, the RRS peak is linearly enhanced. Thus, a new and sensitive RRS-ET method for the detection of SO3 2- (0.160-5.00 μmol/L) was developed accordingly using AuMOF as nanoprobes, with a detection limit of 0.0800 μmol/L. This new RRS method was applied to determination of SO3 2- in food and SO2 in air samples. The recoveries of food and air samples were 97.1-106% and 92.9-106%, and the relative standard deviation (RSD) was 2.10-4.80% and 2.10-4.50%, respectively.

A novel ratiometric sensor prepared based aggregation-induced emission for ultrafast detection of SO2 derivatives in food samples and living cells

As one of the gaseous signaling molecules, aberrant levels of SO₂ are usually associated with many diseases. it is of great significance to develop sensitive methods for detection SO₂ on real. In this paper, a D-π-A near-infrared aggregation-induced fluorescent probe (DPA-CN) was built using diphenylamino-4-benzaldehyde and malononitrile for sensing SO₂. The DPA-CN exhibit AIE characterization that can quickly recognize SO₂ via the Michael addition mechanism. The DPA-CN displayed emission blue drift from 650 nm to 560 nm after adding SO₂, thereby realizing rapid and sensitive colorimetric detection of SO₂. The mechanism for recognition of SO₂ was verified via magnetic resonance imaging ⁽¹H NMR), electrospray ionization mass spectrometry (ESI-MS), scanning electron microscopy (SEM) and dynamic light scattering (DLS). The DPA-CN realized rapid and sensitive recognition of SO₂ with high specificity in 10 s within the concentration range of 0-100 μM. The limit of detection (LOD) is as low as 0.31 μM. Owing to its high sensitivity and low toxicity, the DPA-CN can be applied in monitoring of SO₂ in living cells and food analysis. Furthermore, the DPA-CN was used to prepare a visible and ultrafast semiquantitative paper-based SO₂ sensor with low cost and easy operation.

Fluorescent Imaging Probe Targeting Mitochondria Based on Supramolecular Host-Guest Assembly and Disassembly

Fluorescent dyes and probes play an indispensable role in bioimaging. The mitochondrion is one of the crucial organelles which takes charge of energy production and is the primary site of aerobic respiration in the cell. To illuminate mitochondria, a series of supramolecular fluorescent imaging probes were developed based on the host-guest assembly of 1,4-bis[2-(4-pyridyl)ethenyl]-benzene (BPEB) derivatives and cucurbituril[6] (CB[6]). These host-guest conjugates can be efficiently internalized into cells due to their water solubility and target mitochondria according to their positive charges. In response to the intracellular microenvironments, these conjugates start dynamic disassembly. The released BPEBs show a highly hydrophobic feature, which can crystallize to form fluorescent solids that illuminate the mitochondria. The intracellular disassembly of the host-guest probes was evidenced by fluorescence lifetime imaging in situ. These smart mitochondrion-targeting fluorescent imaging probes can be available to investigate the structures and functions of mitochondria, which are of great significance in the intracellular dynamic transformation of supramolecular assemblies.

Application of 2,4,5-Tris(2-pyridyl)imidazole as "Turn-Off" Fluorescence Sensor for Cu (II) and Hg (II) ions and in vitro Cell Imaging

The 2,4,5-tris(2-pyridyl)imidazole (L) molecule has been evaluated as a probe for dual sensing of Hg²⁺ and Cu²⁺ ions in EtOH/HEPES buffer medium (5mM, pH=7.34, 1:1, v/v). Probe L shows a good sensitive and selective turn-off response in the presence of both Hg²⁺ and Cu²⁺ ions, which is comprehensible under long UV light. The probe can detect Cu²⁺ ion in the pH range of 3-11 and Hg²⁺ ion in 6-8. The limit of detection for Cu²⁺ (0.77 μM) is well under the allowable limit prescribed by the United States Environmental Protection Agency. Two metal (Cu²⁺ /Hg²⁺ ) ions are needed per L for complete fluorescence quenching. The probe shows remarkable reversibility on treatment with Na₂ EDTA, making the protocol more economical for practical purposes. Paper strip coated with the L solution of EtOH can detect the presence of Cu²⁺ and Hg²⁺ ions in the sample by visible quenching of the fluorescence intensity. DFT-TDDFT calculations support experimental observations, and d-orbitals of Cu²⁺ /Hg²⁺ provide a non-radiative decay pathway. Cell imaging study using HDF and MDA-MB-231 cells also supported the viability of L in detecting Cu²⁺ and Hg²⁺ ions in living cells.

Optimizing the framework of indolium hemicyanine to detect sulfur dioxide targeting mitochondria

Endogenous sulfur dioxide (SO₂) is mainly produced by the enzymatic reaction of sulfur-containing amino acids in mitochondria, which has unique biological activity in inflammatory reaction, regulating blood pressure and maintaining the homeostasis of biological sulfur. It is more and more common to detect monitor SO₂ levels by fluorescence probe. In recent years, the indolium hemicyanine skeleton based on the D-π-A structure has been widely used in the development of fluorescent sensors for the detection of SO_2. However, subtle changes in the chemical structure of indolium may cause significant differences in SO₂ sensing behavior. In this article, we designed and synthesized two probes with different lipophilicities to further study the relationship between the structure and optical properties of hemicyanine dyes. On the basis of previous studies, the structure of indolium hemicyanine skeleton was optimized by introducing -OH group, so that MC-1 and MC-2 had the best response to SO₃^2- in pure PBS system. In addition, the lipophilicity of MC-2 was better than that of MC-1, which enabled it to respond quickly to SO₃^2- and better target mitochondria for SO₂ detection. Most importantly, the low detection limits of MC-1 and MC-2 conducive to the detection of endogenous SO₂. This work provided an idea for developing SO₂ fluorescent sensors with excellent water solubility and low detection limit.

A benzophenoxazine-based NIR fluorescent probe for the detection of hydrogen sulfide and imaging in living cells

Fluorescence probe NRDNP exhibits excellent sensing performance toward H2S with about 80-fold fluorescence enhancement. The excellent sensitivity and a detection limit of 19 nM make it application for fluorescence imaging of H2S in living cells.

Determination of sulfite in food and beverages using a reliable ratiometric AIE probe

The feasibility of using an “AIE + ICT” probe for a highly accurate and reliable determination of the sulfite level in food and beverages is demonstrated.