Synthesis of multicolor silver nanostructures for colorimetric sensing of metal ions (Cr3+, Hg2+ and K+) in industrial water and urine samples with different spectral characteristics

In this work, we have synthesized four different color (yellow, orange, green, and blue (multicolor)) silver nanostructures (AgNSs) by chemical reduction method where silver nitrate, sodium borohydride and hydrogen peroxide were used as reagents. The as-synthesized multicolor AgNSs were successfully functionalized with bovine serum albumin (BSA) and applied as a colorimetric sensor for the assaying of metal cations (Cr³⁺, Hg²⁺, and K⁺). The addition of metal ions (Cr³⁺, Hg²⁺, and K⁺) into BSA functionalized AgNSs (BSA-AgNSs) causes the aggregation of BSA-AgNSs, and are accompanied by visual color changes with red or blue shift in the surface plasmon resonance (SPR) band of BSA-AgNSs. The BSA-AgNSs show different SPR characteristic for each metal ions (Cr³⁺, Hg²⁺, and K⁺) with exhibiting different spectral shift and color change. The yellow color BSA-AgNSs (Y-BSA-AgNSs) act as a probe for sensing Cr³⁺, orange color BSA-AgNSs (O-BSA-AgNSs) act as probe for Hg²⁺ ion assay, green color BSA-AgNSs (G-BSA-AgNSs) act as a probe for the assaying of both K⁺ and Hg²⁺, and blue color BSA-AgNSs (B-BSA-AgNSs) act as a sensor for colorimetric detection of K⁺ ion. The detection limits were found to be 0.26 μM for Cr³⁺ (Y-BSA-AgNSs), 0.14 μM for Hg²⁺ (O-BSA-AgNSs), 0.05 μM for K⁺ (G-BSA-AgNSs), 0.17 μM for Hg²⁺ (G-BSA-AgNSs), and 0.08 μM for K⁺ (B-BSA-AgNSs), respectively. Furthermore, multicolor BSA-AgNSs were also applied for assaying of Cr³⁺, and Hg²⁺ in industrial water samples and K⁺ in urine sample.

Mo(vi) complexes of amide-imine conjugates for tuning the selectivity of fluorescence recognition of Y(iii) vs. Pb(ii)

Two amide-imine conjugates, viz. 3-methyl-benzoic acid (4-diethylamino-2-hydroxy-benzylidene)-hydrazide (L1) and 3-methyl-benzoic acid (2-hydroxy-naphthalen-1-ylmethylene)-hydrazide (L2), have been prepared and used for a further synthesis of Mo(vi) complexes (M1 and M2, respectively). Single crystal X-ray diffraction analysis confirmed their structures. Interestingly, M1 selectively recognizes Y3+ and Pb2+ at two different wavelengths, whereas M2 selectively interacts with Y3+ with a significantly high binding constant, 1.3 × 105 M-1. The proposed sensing mechanism involves the displacement of Mo(vi) by Y3+/Pb2+ from respective Mo(vi) complexes. The TCSPC experiment also substantiates the "turn-on" fluorescence process. A logic gate has been constructed utilizing the fluorescence recognition of cations by M1. DFT studies corroborated the cation-probe interactions and allowed exploring the orbital energy parameters.

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.

Acridine-2,4-Dinitrophenyl Hydrazone Conjugated Silver Nanoparticles as an Efficient Sensor for Quantification of Mercury in Tap Water

Excretion of heavy metals especially mercury (Hg2+) from the industries into the environment becomes a major global problem. In this context, mercury is a highly dangerous metal which poses serious impact on human health. In the present study, acridine- (ACR-) based silver nanoparticles (ACR-AgNPs) were prepared and employed as a nanosensor for effective detection and quantification of Hg2+ in tap water. Conjugation between ACR-based coating agent and silver was examined by UV-visible and FT-IR spectroscopy, while morphology and particle size were determined through atomic force microscopy (AFM), dynamic light scattering (DLS), and scanning electron microscopy (SEM). Furthermore, sensing behavior of nanosensor for metal ions was evaluated by mixing different metals such as Mn2+, Ni2+, Ba2+, Mg2+, Cr3+, Pb2+, Pd2+, Al3+, Sn2+, Fe2+, Co2+, Cu2+, Fe3+, Cd2+, and Hg2+with ACR-AgNPs. Among all the added metal ions, only Hg2+resulted in significant quenching in the absorption intensity of ACR-AgNPs. The limit of detection of the ACR-AgNP-based nanosensor was found to be 1.65 μM in a wide pH range (1-14). The proposed mercury sensor worked efficiently in the presence of other interfering agents such as other metal ions. Therefore, the synthesized ACR-AgNPs have proved to be an efficient and robust nanosensor for quantitative detection of Hg2+ in real sample analysis such as tap water. The proposed method does not require expensive instrumentation and trained manpower.

An AIE active BODIPY based fluorescent probe for selective sensing of Hg2+ via dual mechanism PET and CHEF

A pyrazole appended BODIPY ligand (L) is synthesized and thoroughly characterized by various spectroscopic studies (1H, [Formula: see text]C, [Formula: see text]B, [Formula: see text]F, ESI–MS, UV-vis and fluorescence). The ligand (L) displays aggregation induced emission (AIE) in solution (a mixture of CH3OH and water) and solid state. The vital role of the restriction of intramolecular rotation (RIR) in AIE is supported by viscosity experiments and fluorescence lifetime studies. Photophysical behaviour and aggregate morphology is investigated by UV-vis, emission and scanning electron microscopy (SEM). Multiple strong intermolecular hydrogen bonds (C–H[Formula: see text]N and C–H[Formula: see text]F) play a significant role in the AIE response. In addition, L shows strong sensitivity toward Hg[Formula: see text]ion via chelation induced enhanced fluorescence (CHEF) mechanism. Job’s plot analysis suggested a 1:1 binding stoichiometry between L and Hg[Formula: see text], which has been further supported by electrospray ionization mass spectrometry and density functional theory.

Fluorescent chemosensors for Hg2+ ions based on a pyridine-attached phenanthridine probe

The sensor probe detects selectively Hg2+ ions in semi-aqueous medium. Probe showed ratiometric response with low detection limit. We observed that 1 : 1 binding mode between probe and Hg2+ ions. Additionally, this probe was utilized for various practical applications.

Synthesis and characterization of a plant growth regulator based silver nanoparticles for the ultrasensitive detection of environmentally toxic Hg2+ ions in tap water

Herein, we report the synthesis and characterization of a plant growth regulator based silver nanoparticles and its application as a sensor for the ultrasensitive detection of toxic metal ions (Hg2+) in tapwater.

Phenanthroimidazole derivatives showing mild intramolecular charge transfer and high quantum yields and their applications in OLEDs

Phenanthroimidazole derivatives showing bipolar characters, strong emissions in the blue region and their applications in OLED is presented.

A New Highly Selective Colorimetric and Fluorometric Coumarin-based Chemosensor for Hg2

A novel colorimetric and fluorometric method based on coumarin as signalling unit was developed for Hg²⁺ recognition and quantification. Initially, the alkyne functionality was incorporated into a coumarin system and the resulting molecule showed higher specificity and sensitivity for Hg²⁺ over other cations in both absorption and emission sensing assays. The Hg²⁺ recognition was detected as visible colour change from colourless to yellow and as fluorescence quenching. The colour change was assigned to the increased intramolecular charge transfer (ICT) in the signalling unit upon Hg²⁺ binding whereas a decline in the fluorescence intensity was ascribed to the heavy atom effect from Hg²⁺. In order to generate a material with high sensing performance level, alkyne-functionalized molecule was hosted into a polymeric material. The resulting functionalized polymer showed higher sensitivity and selectivity for Hg²⁺ over its corresponding coumarin molecule. The investigation of the possible binding modes for Hg²⁺ suggested both alkyne and triazole functionalities as potential binding sites for Hg²⁺. The limit of detection (LOD) and limit of quantification (LOQ) of the proposed method were evaluated and values less than a recommended maximum level of Hg²⁺contaminant in drinking water (2.00 μg/L) were obtained (LOD = 0.44 μg/L and LOQ = 1.33μg/L). The real-life application of the method was investigated using natural water samples containing Hg²⁺ levels equivalent to the maximum tolerable concentration of Hg²⁺ in drinking water. The outcomes suggested that the method could be used in the sensing and determination of Hg²⁺ level of contaminant in the environment.

Fluorescent, colourimetric, and ratiometric probes based on diverse fluorophore motifs for mercuric(II) ion (Hg2+) sensing: highlights from 2011 to 2019

Though it has not been shown to deliver any biological importance, mercuric(II) ion (Hg²⁺) is a deleterious cation which poses grievous effects to the human body and/or the ecosystem, hence, the need for its sensitive and selective monitoring in both environmental and biological systems. Over the years, there has been a great deal of work in the use of fluorescent, colourimetric, and/or ratiometric probes for Hg²⁺ recognition. Essentially, the purpose of this review article is to give an overview of the advances made in the constructions of such probes based on the works reported in the period from 2011 to 2019. Discussion in this review work has been tailored to the kinds of fluorophore scaffolds used for the constructions of the probes reported. Selected examples of probes under each fluorophore subcategory were discussed with mentions of the typically determined parameters in an analytical sensing operation, including modulation in fluorescence intensity, optimal pH, detection limit, and association constant. The environmental and biological application ends of the probes were also touched where necessary. Important generalisations and conclusions were given at the end of the review. This review article highlights 196 references.

Synthesis, optical, and structural properties of bisphenol-bridged aromatic cyclic phosphazenes

Phenoxy- and naphthoxy-substituted bisphenol-bridged cyclic phosphazenes were synthesized in 2 steps and their thermal, photophysical, and electrochemical properties were investigated. The structures of the cyclic phosphazene compounds were determined by ESI-MS mass spectrometry and 1 H, 13 C, and 31 P NMR spectroscopies. The photophysical studies of phenoxy- and naphthoxy-substituted bridged cyclophosphazenes were investigated by means of absorption and fluorescence spectroscopies in different solvents. Thermal and electrochemical properties of the target compounds were also studied. Furthermore, the excimer emissions through intramolecular interactions in solution and in solid state were investigated by fluorescence spectroscopy and the theoretical calculations were performed in detail using DFT.

Synthetic ratiometric fluorescent probes for detection of ions

Metal cations and anions are essential for versatile physiological processes. Dysregulation of specific ion levels in living organisms is known to have an adverse effect on normal biological events. Owing to the pathophysiological significance of ions, sensitive and selective methods to detect these species in biological systems are in high demand. Because they can be used in methods for precise and quantitative analysis of ions, organic dye-based ratiometric fluorescent probes have been extensively explored in recent years. In this review, recent advances (2015-2019) made in the development and biological applications of synthetic ratiometric fluorescent probes are described. Particular emphasis is given to organic dye-based ratiometric fluorescent probes that are designed to detect biologically important and relevant ions in cells and living organisms. Also, the fundamental principles associated with the design of ratiometric fluorescent probes and perspectives about how to expand their biological applications are discussed.

Theoretical Design of Near-Infrared Fluorescent Sensor for F Anion Detection Based on 10-Hydroxybenzo[h]quinoline Backbone

Proper design and development of near-infrared (NIR) fluorescent sensors is very important for applications in vivo. In this work, we theoretically designed a ratiometric and NIR fluorescent sensor based on the 10-hydroxybenzo[h]quinoline (HBQ) backbone via systematically investigating the substituent effects of electron-donating groups (-NH₂, -CH₃, -C(CH₃)₃) and electron-withdrawing groups (-NO₂, -CN, -F, -Cl, -CF₃) at the proton donor site on the proton transfer process in HBQ in both the S₀ and the S₁ states. According to the calculated potential energy profiles along the proton transfer as well as the photophysical properties among all the derivatives, we successfully screened out that 7NH₂-HBQ is a promising fluorescent sensor exhibiting the near IR emission spectra accompanied by the large Stokes shift. The potential use of 7NH₂-HBQ for F^- detection among anions (F^-, Cl^-, and Br^-) was further studied, and the results showed that 7NH₂-HBQ is very sensitive and selective toward F^- based on the intermolecular hydrogen bonding interaction between F^- and OH bond, forming a new complex FAC_S0 . The ratiometric change in the fluorescence intensity could be induced by the H-F bond transfer from the O atom to the N atom in the S₁ state.

Visualization of mercury(ii) accumulation in vivo using bioluminescence imaging with a highly selective probe

Mercury is a highly toxic environmental pollutant that negatively affects human health. Thus, an in vivo method for noninvasive imaging of mercury(ii) and visualization of its accumulation within living systems would be advantageous. Herein, we describe a reaction-based bioluminescent probe for detection of mercury(ii) in vitro and accumulation in vivo. The application of this probe would help to shed light on the intricate contributions of mercury(ii) to various physiological and pathological processes.

A highly selective and sensitive ESIPT-based coumarin–triazole polymer for the ratiometric detection of Hg2+

A reversible ESIPT based system for the detection of Hg²⁺ was developed. The system exhibited better properties compared to that of recently developed ratiometric fluorescent systems.

Photophysics of proton transfer in hydrazides: a combined theoretical and experimental analysis towards OLED device application

Effect of conjugation to support ESIPT with impossible double proton transfer in structurally favored species.

A two-photon fluorescent probe for colorimetric and ratiometric monitoring of mercury in live cells and tissues

Owing to the extreme toxicity of mercury, methods for its selective and sensitive sensing in solutions, and in live cells and tissues are in great demand.

An ultra-sensitive and ratiometric fluorescent probe based on the DTBET process for Hg2+ detection and imaging applications

In this article, we present an ultra-sensitive and ratiometric fluorescent probe (TR-Hg) for Hg²⁺ detection based on the mechanism of aggregation induced emission (AIE) and dark through-bond energy transfer (DTBET). The probe was constructed using tetraphenylethene as the dark donor and rhodamine B thiolactone as the acceptor. By exploiting the advantages of DTBET, which eliminates emission leakage from dark donors and provides nearly 100% energy transfer efficiency, TR-Hg exhibits more than a 30 000-fold fluorescence ratio enhancement after reacting with Hg²⁺. TR-Hg demostrates (i) a detection limit of 43 pM, which is the lowest among the reported ratiometric Hg²⁺ probes, (ii) excellent selectivity, fast response-time (<10 s) and a wide pH application range, (iii) strong applicability for paper-based colorimetric assay, where readout can be performed by the naked eye, and (iv) fluorescent imaging of Hg²⁺ in onion epidermal tissues, indicating its potential use in living organisms.

A simple fluorescent probe for the fast sequential detection of copper and biothiols based on a benzothiazole derivative

A simple benzothiazole fluorescent chemosensor was developed for the fast sequential detection of Cu²⁺ and biothiols through modulating the excited-state intramolecular proton transfer (ESIPT) process. The compound 1 exhibits highly selective and sensitive fluorescence "on-off" recognition to Cu²⁺ with a 1:1 binding stoichiometry by ESIPT hinder. The in situ generated 1-Cu²⁺ complex can serve as an "on-off" fluorescent probe for high selectivity toward biothiols via Cu²⁺ displacement approach, which exerts ESIPT recovery. It is worth pointing out that the 1-Cu²⁺ complex shows faster for cysteins (within 1min) than other biothiols such as homocysteine (25min) and glutathione (25min). Moreover, the compound 1 displays 160nm Stoke-shift for reversibly monitoring Cu²⁺ and biothiols. In addition, the probe is successfully used for fluorescent cellular imaging. This strategy via modulation the ESIPT state has been used for determination of Cu²⁺ and Cys with satisfactory results, which further demonstrates its value of practical applications.

Excited-state intramolecular proton-transfer (ESIPT) based fluorescence sensors and imaging agents

We review recent advances in the design and application of excited-state intramolecular proton-transfer (ESIPT) based fluorescent probes. These sensors and imaging agents (probes) are important in biology, physiology, pharmacology, and environmental science.

Novel Cu2+-specific “Turn-ON” fluorescent probe based on [5]helicene with very large Stokes shift and its potential application in living cells

The sensor provides Cu²⁺-sensitive with low detection limit and very large Stokes shift, and can induce the emission in the HepG2 cellular system.

A highly sensitive naked-eye fluorescent probe for trace hydrazine based on ‘C-CN’ bond cleavage

The ‘C–CN’ bond cleavage was applied to the recognition of N₂H₄ for the first time; the obvious change in color could be used for “naked-eye” detection; the corresponding detection limit was found to be 5.81 × 10⁻⁸ M (1.65 ppb); the probe could be applied for N₂H₄ detection in real water samples.

A new simple phthalimide-based fluorescent probe for highly selective cysteine and bioimaging for living cells

A new turn-on phthalimide fluorescent probe has designed and synthesized for sensing cysteine (Cys) based on excited state intramolecular proton transfer (ESIPT) process. It is consisted of a 3-hydroxyphthalimide derivative moiety as the fluorophore and an acrylic ester group as a recognition receptor. The acrylic ester acts as an ESIPT blocking agent. Upon addition of cystein, intermolecular nucleophilic attack of cysteine on acrylic ester releases the fluorescent 3-hydroxyphthalimide derivative, thereby enabling the ESIPT process and leading to enhancement of fluorescence. The probe displays high sensitivity, excellent selectivity and with large Stokes shift toward cysteine. The linear interval range of the fluorescence titration ranged from 0 to 1.0×10^-5M and detection limit is low (6×10^-8M). In addition, the probe could be used for bio-imaging in living cells.

A novel label-free fluorescence assay for one-step sensitive detection of Hg2+ in environmental drinking water samples

A novel label-free fluorescence assay for detection of Hg²⁺ was developed based on the Hg²⁺-binding single-stranded DNA (ssDNA) and SYBR Green I (SG I). Differences from other assays, the designed rich-thymine (T) ssDNA probe without fluorescent labelling can be rapidly formed a T-Hg²⁺-T complex and folded into a stable hairpin structure in the presence of Hg²⁺ in environmental drinking water samples by facilitating fluorescence increase through intercalating with SG I in one-step. In the assay, the fluorescence signal can be directly obtained without additional incubation within 1 min. The dynamic quantitative working ranges was 5–1000 nM, the determination coefficients were satisfied by optimization of the reaction conditions. The lowest detection limit of Hg²⁺ was 3 nM which is well below the standard of U.S. Environmental Protection Agency. This method was highly specific for detecting of Hg²⁺ without being affected by other possible interfering ions from different background compositions of water samples. The recoveries of Hg²⁺ spiked in these samples were 95.05–103.51%. The proposed method is more viable, low-costing and simple for operation in field detection than the other methods with great potentials, such as emergency disposal, environmental monitoring, surveillance and supporting of ecological risk assessment and management.

A fluorescence “turn-on” chemosensor for Hg2+and Ag+based on NBD (7-nitrobenzo-2-oxa-1,3-diazolyl)

A fluorescence “turn-on” chemosensor for the simultaneous detection of Hg²⁺and Ag⁺was developed and practically applied with test strips.

Bioluminescent Probe for Detecting Mercury(II) in Living Mice

A novel bioluminescence probe for mercury(II) was obtained on the basis of the distinct deprotection reaction of dithioacetal to decanal, so as to display suitable sensitivity and selectivity toward mercury(II) over other ions with bacterial bioluminescence signal. These experimental results indicated such a probe was a novel promising method for mercury(II) bioluminescence imaging in environmental and life sciences ex vivo and in vivo.

A dual-mode turn-on fluorescent BODIPY-based probe for visualization of mercury ions in living cells

A novel turn-on fluorescent 8-amino BODIPY-based probe carrying a thiourea unit as the mercury ion recognition unit has been developed. Due to the cascade reaction processes, consecutive color changes reflecting the electronic absorption and emission responses were observed upon addition of increased concentrations of mercury(ii) ions. The likely sensing mechanism was proposed as mercury ion-promoted cyclization and subsequent hydrolysis. The probe displayed a selective response to mercury ions over other metal ions. Additionally, experiments with living Human Hepatoma SMMC-7721 cells to visualize intracellular mercury ions in biological systems were carried out with the probe.

A novel 2-(2′-aminophenyl)benzothiazole derivative displays ESIPT and permits selective detection of Zn2+ ions: experimental and theoretical studies

Synthesis of a novel 2-(2′-aminophenyl)benzothiazole based probe (1) and demonstration of excited state intramolecular proton transfer (ESIPT) with a large Stokes shift (∼246 nm) are presented.

Single excited state intramolecular proton transfer (ESIPT) chemodosimeter based on rhodol for both Hg2+ and OCl−: ratiometric detection with live-cell imaging

We have synthesised a ratiometric fluorescence chemodosimeter, STBR, for the detection of Hg²⁺ and OCl⁻ in one platform over other cations, anions and oxidants in aqueous solution.

A facile, fast responsive and highly selective mercury(ii) probe characterized by the fluorescence quenching of 2,9-dimethyl-1,10-phenanthroline and two new metal–organic frameworks

A fast responsive and highly selective mercury(ii) sensor was developed using the fluorescence quenching mechanism of 2,9-dimethyl-1,10-phenanthroline (2,9-DMP) towards mercury(ii).

Highly sensitive and selective fluorescence detection of Hg(ii) ions based on R-phycoerythrin from Porphyra yezoensis

R-Phycoerythrin (R-PE) is a kind of natural fluorescent protein from marine Porphyra yezoensis.

Pyrano[3,2-c]julolidin-2-ones: a novel class of fluorescent probes for ratiometric detection and imaging of Hg2+ in live cancer cells

A novel pyrano[3,2-c]julolidin-2-one based fluorescent molecular rotor PYJO4 has been designed and developed for selective ratiometric detection, quantification and imaging of intracellular Hg²⁺ in live cells.

Proton donor modulating ESIPT-based fluorescent probes for highly sensitive and selective detection of Cu2+

Two novel ESIPT-based fluorescent probes for Cu²⁺ detection were developed. Altering the linker in probe molecules reversed their sensing behavior. Both probes exhibited high selectivity and sensitivity to Cu²⁺, and can be used for cell imaging.