Bi-component sensing platform for the detection of Cd2+, Fe2+and Fe3+ ions

The ability of N-(1,3-dioxo-1H-benzo[de]isoquinolin-2(3H)-yl)isonicotinamide (naphydrazide) or 2,6-pyridinedicarboxylic acid (2,6-H2pdc) individually or as a bi-component system in distinguishing and detecting Fe3+ or Fe2+ and Cd2+ ions was investigated. The use of these molecules as single or bi-component analytes in absorption or emission spectroscopy studies showed that under specific conditions each had their own merits for specific purposes. UV-visible spectroscopic studies of 2,6-H2pdc for assessing the interactions with ferrous and ferric ions showed characteristic distinctions. The detection limit for Fe3+ analysed through UV-visible spectroscopy using naphydrazide was 0.46 μM, whereas it was 1.28 μM using 2,6-H2pdc. Naphydrazide together with Fe3+ allowed distinguishing Cd2+ ions from Zn2+ and Fe2+ ions. The bi-component system was useful for the selective detection of Cd2+ ions using fluorescence spectroscopy, with a detection limit for Cd2+ ions of 18.31 μM. The presence of Fe2+ and Cd2+ ions in a solution of the bi-component had resulted white-light emission. An analogous compound N,N'-(1,3,6,8-tetraoxobenzo[lmn][3,8]phenanthroline-2,7(1H,3H,6H,8H)-diyl)diisonicotinamide (binaphydrazide) was found unsuitable for such detections. Two 2,6-pyridinedicarboxylate Fe3+ complexes possessing protonated naphydrazide or binaphydrazide were prepared and characterised. These complexes were also found unsuitable for the detection of the said ions in solution. Electrochemical studies with the bi-component system showed that cyclic voltammograms could distinguish Fe3+ or Fe2+ from Cd2+ ions.

Sumanene-carbazole conjugate with push-pull structure and its chemoreceptor application

The first-of-its-kind tetra-substituted sumanene derivative, featuring the push-pull chromophore architecture, has been successfully designed. The inclusion of both strong electron-withdrawing (CF3) and electron-donating (carbazole) moieties in this buckybowl compound has enhanced the charge transfer characteristics of the molecule. This enhancement was supported by ultraviolet-visible (UV-Vis) and emission spectra analyses along with density functional theory (DFT) calculations. The application of the title sumanene-carbazole push-pull chromophore as a selective recognition material for cesium cations (Cs+) was also presented. The title compound exhibited effective and selective Cs+-trapping ability, characterized by a high apparent binding constant value (at the level of 105) and a low limit of detection (0.09-0.13 μM). Owing to the tuned optical properties of the title push-pull chromophore, this study marks the first time in sumanene-tethered chemoreceptor chemistry where efficient tracking of Cs+ binding was possible with both absorption and fluorescence spectroscopies. This work introduces a new approach toward tuning the structure of bowl-shaped optical chemoreceptors.

Sustainable and reusable probe-encapsulated porous poly(AMST-co-TRIM) monolithic sensor for the selective and ultra-sensitive detection of toxic cadmium(II) from industrial/environmental wastewater

This study focuses on a new type of fast responsive solid-state visual colorimetric sensor, custom engineered with dual-entwined porous polymer imbued with chromoionophoric 4-(sec-butyl)- 2-((5-mercapto-1,3,4-thiadiazol-2-yl)diazenyl)phenol (SMDP) probe for selective and ultra-sensitive colorimetric sensing of Cd(II). The polymer monolith, i.e., poly(aminostyrene-co-trimethylolpropanetrimethacrylate) denoted as poly(AMST-co-TRIM), is designed through a stoichiometric blending of monomer, crosslinker, and porogens leading to superior surface area, pore and adsorption properties for the voluminous incorporation of SMDP probe for target specific ion sensing. The porosity, surface and structural characteristics of the poly(AMST-co-TRIM)monolith and poly(AMST-co-TRIM)SMDP sensor are investigated using p-XRD, XPS, TG-DTA, FT-IR, BET/BJH, FE-SEM, HR-TEM, EDAX, and SAED techniques. The poly(AMST-co-TRIM)SMDP sensor reveals a frozen geometrical orientation of SMDP molecules to bind selectively with Cd(II), forming stable charge-transfer complexes by exhibiting transitional visible color shifts from light yellow to dark green (λmax 608 nm). The sensor imposes a linear response from 0-200 ppb, with quantification and detection limits of 0.95 and 0.28 ppb. The fabricated sensor material is cost-effective and versatile in its solid-state naked-eye sensing, with excellent reusability. The sensor performance has been verified using various environmentally contaminated water and commercial cigarette samples, with a recovery of ≥ 99.12% and an RSD of ≤ 1.95%, thus reflecting exceptional data reproducibility/reliability.

Grind, shine and detect: mechanochemical synthesis of AIE-active polyaromatic amide and its application as molecular receptor of monovalent anions or nucleotides

A mechanochemical synthesis of novel polyaromatic amide consisting of 1,3,5-triphenylbenzene and 1,1',2,2'-tetraphenylethylene skeletons has been established. The designed mechanochemical approach using readily available and low-cost equipment allowed a twofold increase in reaction yield, a 350-fold reduction in reaction time and a significant reduction in the use of harmful reactants in comparison to the solution synthesis method. The parameters of Green Chemistry were used to highlight the advantages of the developed synthesis method over the solution-based approach. The title compound was found to exhibit attractive optical properties related to the Aggregation-induced emission (AIE) behaviour. Taking the advantage of AIE-active properties of the synthesized polyaromatic amide, its application as effective and versatile molecular receptor towards detection of monovalent anions, as well as bio-relevant anions - nucleotides, has been demonstrated. The values of the binding constants were at the satisfactory level of 104, the detection limit values were low and ranged from 0.2 μM to 19.9 μM.

Application of Monoferrocenylsumanenes Derived from Sonogashira Cross-Coupling or Click Chemistry Reactions in Highly Sensitive and Selective Cesium Cation Electrochemical Sensors

This paper reports the synthesis and characterization of novel monoferrocenylsumanenes obtained by means of the Sonogashira cross-coupling or click chemistry reaction as well as their application in cesium cation electrochemical sensors. A new synthetic protocol based on Sonogashira cross-coupling was developed for the synthesis of monoferrocenylsumanene or ethynylsumanene. The click chemistry reaction was introduced to the sumanene chemistry through the synthesis of 1,2,3-triazole containing monoferrocenylsumanene. The designed synthetic methods for the modification of sumanene at the aromatic position proved to be efficient and proceeded under mild conditions. The synthesized sumanene derivatives were characterized by detailed spectroscopic analyses of the synthesized sumanene derivatives. The supramolecular interactions between cesium cations and the synthesized monoferrocenylsumanenes were spectroscopically and electrochemically investigated. Furthermore, the design of the highly selective and sensitive cesium cation fluorescence and electrochemical sensors comprising the synthesized monoferrocenylsumanenes as receptor compounds was analyzed. The tested cesium cation electrochemical sensors showed excellent limit of detection values in the range of 6.0-9.0 nM. In addition, the interactions between the synthesized monoferrocenylsumanenes and cesium cations were highly selective, which was confirmed by emission spectroscopy, laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), and cyclic voltammetry.

Synthesis of π-extended and bowl-shaped sumanene-ferrocene conjugates and their application in highly selective and sensitive cesium cations electrochemical sensors

Carbon-carbon bond formation, condensation or click chemistry reactions were used to synthesize novel bowl-shaped sumanene-ferrocene conjugates, along with the extended π-electron framework in good yields. For the first time, the present study uses sumanene derivatives tris-substituted at the benzylic positions as the materials to begin the study on the click chemistry or the metal-catalyzed coupling reactions, Suzuki-Miyaura or Sonogashira couplings. The synthesized conjugates exhibited the property of selective recognizing cesium cations. As a result, this led to the development of highly sensitive and selective fluorescent or electrochemical sensors dedicated to the recognition of cesium cations (Cs⁺) in water. We successfully designed the Cs⁺ electrochemical sensors, which exhibited an acceptable limit of detection (LOD) values at 0.05-0.38 μM. Spectrofluorimetry, voltammetry, and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) were used to perform the selectivity studies. The results revealed that the designed sensors are highly Cs⁺-selective. This work significantly contributes to the design of new methods of sumanene modification. It also provides further information on the electrochemical properties and innovative applications of metallocene-tethered sumanene derivatives.

Plasma-assisted in-situ preparation of L-cystine functionalized silver nanoparticle: An intelligent multicolor nano-sensing of cadmium and paracetamol from environmental sample

L-cystine (L-cys) functionalized plasmonic silver nanomaterial (Ag NPs) was fabricated toward the selective and sensitive detection of paracetamol and cadmium. The prepared L-cys-Ag nanoparticles (NPs) were characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray diffraction spectroscopy (XRD) and fourier transform infrared spectroscopy (FTIR) analyses. SEM imaging show that Ag NPs was decorated on the surface of L-cysteine 3D cubic nanosheet. L-cys-Ag NPs showed selective and sensitive detection towards paracetamol and cadmium. The interference study confirms that the presence of other metal ions didn't inhibit the detection of cadmium by L-cys-Ag NPs. The limit of detection of paracetamol and cadmium by L-cys-Ag NPs was calculated to be 1.2 and 2.82 nM respectively. In addition, the real sample detection of paracetamol on blood serum and urine, and cadmium on STP were performed and the recovery percentage was above 97%. Further, the real sample analysis was performed in tap and drinking water and the recovery percentage was more than 98%. The analytic logic gate on the multicolour detection of cadmium and paracetamol was performed for the semi-quantitative monitoring of paracetamol and cadmium by L-cys-Ag NPs. The developed L-cys-Ag NPs were found to be an effective tool for the monitoring of cadmium in environmental water bodies and paracetamol in blood and urine.

An excited state intramolecular proton transfer induced phosphate ion targeted ratiometric fluorescent switch to monitor phosphate ions in human peripheral blood mononuclear cells

Detection of biological phosphate is very important for environmental and health care applications. In this study, a new ratiometric fluorescent probe (E)-N'-(3-(benzo[d]thiazol-2-yl)-2-hydroxybenzylidene) picolinohydrazide (BTP) is developed and exhibits a prominent excited-state intramolecular proton-transfer (ESIPT) mechanism. The probe BTP undergoes a unique phosphate induced hydrolytic reaction in mixed aqueous solution which produces a colorimetric change associated with a huge red-shift of ∼130 nm in the UV-visible absorption spectrum. Initially, BTP exhibits a strong fluorescence emission as the ESIPT process is 'on' and the tautomeric hydrogen remains flexible and is free to give two tautomeric forms. Eventually, after the addition of PO₄^3-, the two tautomeric forms break and thereby shift the equilibrium towards the 'enol' form. The phosphate ion binds with BTP which is associated with a ratiometric change and accounts for an enhancement in the fluorescence intensity with a large blue shift and the limit of detection value of 8.33 × 10^-8 M in a mixed aqueous medium. The binding constant (1.92 × 10⁵ M^-1) proportionally reflects the stability of the complexation between the binding sites of BTP with the guest PO₄^3- anion. The probable mechanism is supported by the NMR spectroscopy studies. The sensing phenomenon is found to be reversible towards Zn²⁺ and thus the sensor beautifully mimics the INHIBIT logic gate. Observations have been made in fluorescence imaging studies with human peripheral blood mononuclear cells (PBMCs) which indicates that BTP can be employed to successfully monitor the phosphate ion in human PBMCs.

Tuning the sumanene receptor structure towards the development of potentiometric sensors

Herein, we report for the first time the application of a sumanene derivative in potentiometric recognition of caesium cations. The structure of the sumanene receptor was carefully tuned to obtain its compatibility with polyvinyl chloride plasticized membranes of potentiometric sensors. The developed ion-selective electrodes based on membranes doped with octyloxybenzene sumanene exhibited a near theoretical sensitivity towards caesium cations, with a detection limit of 4 μM Cs⁺.

Disaggregation of a sumanene-containing fluorescent probe towards highly sensitive and specific detection of caesium cations

A sumanene derivative functionalized with triphenylbenzene units was found to exhibit aggregation-induced emission enhancement (AIEE). A disaggregation process after the addition of caesium cations (Cs+) was observed. This feature was employed for the design of the first sumanene-containing disaggregation-based fluorescent probe for specific, efficient and fast Cs+ recognition.

FRET based ratiometric switch for selective sensing of Al3+ with bio-imaging in human peripheral blood mononuclear cells

FRET based ratiometric switch for selective sensing of Al³⁺ with bio-imaging in human peripheral blood mononuclear cells (PBMCs).

A novel fluorescent sensor for specific recognition of GSH based on the copper complex and its bioimaging in living cells

Given the important role of biothiols in various physiological processes, there is a need to develop novel fluorescent sensors for detecting them. Herein, a novel "on-off-on" fluorescent sensor (E)-N'-((7-(diethylamino)-2-oxo-2H-chromen-3-yl)methylene)-6-((quinolin-8-yloxy)methyl)picolinohydrazide (PQC) was synthesized and its absorbance and fluorescence properties were characterized. The sensor PQC could form a stable complex and showed a significant fluorescence quenching response to Cu²⁺ with a quenching efficiency of approximately 100%, and the PQC-Cu²⁺ complex showed a fluorescence enhancement response to GSH with a higher recovery rate of above 80% in a CH₃OH/HEPES (9:1 v/v, pH = 7.23) buffer system. Its detection limits were determined to be 0.17 μM for Cu²⁺ and 0.20 μM for GSH, and the binding stoichiometry of PQC-Cu²⁺ was determined to be 1: 1 by Job's plot method. Importantly, the sensor PQC can be used for filter paper strip tests and bioimaging in living cells.

Switching of Fluorescent Zn/Cd Selectivity in N,N,N',N'-Tetrakis(6-methoxy-2-quinolylmethyl)-1,2-diphenylethylenediamine by One Asymmetric Carbon Atom Inversion

A quinoline-based hexadentate ligand, (S,S)-N,N,N',N'-tetrakis(6-methoxy-2-quinolylmethyl)-1,2-diphenylethylenediamine ((S,S)-6-MeOTQPh₂EN), exhibits fluorescence enhancement at 498 nm upon addition of 1 equiv of Zn²⁺ (I_Zn/I₀ = 12, φ_Zn = 0.047) in aqueous DMF solution (DMF/H₂O = 2:1). Addition of 1 equiv of Cd²⁺ affords a much smaller fluorescence increase at the same wavelength (I_Cd/I₀ = 2.5, I_Cd/I_Zn = 21%). The trivalent metal ions such as Al³⁺, Cr³⁺, and Fe³⁺ also exhibit fluorescence enhancement at 395 nm (I_Al/I₀ = 22, I_Cr/I₀ = 6 and I_Fe3+/I₀ = 13). In contrast, meso-6-MeOTQPh₂EN exhibits a Cd²⁺-selective fluorescence increase at 405 nm in the presence of 1 equiv of metal ion (I_Cd/I₀ = 11.5, φ_Cd = 0.022), while Zn²⁺ induces a smaller fluorescent response under the same experimental conditions (I_Zn/I₀ = 3.3, I_Zn/I_Cd = 29%). In this case, the fluorescence intensities of meso-6-MeOTQPh₂EN in the presence of a large amount of Zn²⁺ and Cd²⁺ become similar. This diastereomer-dependent, fluorescent metal ion specificity is derived from the Zn²⁺-specific intramolecular excimer formation in (S,S)-6-MeOTQPh₂EN-Zn²⁺ complex and higher binding affinity of meso-6-MeOTQPh₂EN with Cd²⁺ in comparison to Zn²⁺. The more conformationally restricted diastereomeric pair, namely, cis- and trans-TQDACHs (cis- and trans-N,N,N',N'-tetrakis(2-quinolylmethyl)-1,2-diaminocyclohexanes), both exhibit Zn²⁺-specific fluorescence enhancement because of the high metal binding affinity and intramolecular excimer forming property derived from the rigid DACH backbone.

Efficient and very selective dual mode chemosensor for Cd(II) ions in live cells

A sensitive dual mode chemosensor NS-1 comprising Nitrobenzoxadiazole and salicylhydrazide conjugate has been synthesized via single step reaction. The probe NS-1 is characterized by analytical techniques such as multi nuclear NMR techniques and Mass spectrometry. The probe is showing a strong change in color from yellow to red on treatment of Cd(II) ions, interestingly its shows bright "Switch-ON" fluorescence state upon binding of Cd²⁺ ions in buffer solution whereas other cations did not showed any color change as well as fluorescent change. Interestingly the probe NS-1 did not results in the any color and fluorescence change with the adding together of Zn(II) ions, hence the probe is able to differentiate between Cd(II) ions from Zn(II). Further the color change and turn-on fluorescence can be rationalized by the interruption of internal charge transfer upon binding of Cd(II) ions with NS-1. The Internal charge transfer disturbance led to fluorescence change of the receptor NS-1 upon addition of Cd²⁺ has been further supported by TD-DFT calculations. The limit of detection was found to be 6.31 nano molar. The association constant was found to be 7.97*10⁴ M^-1 using Benesi-Hildebrand plot method. MTT assay suggesting that the probe NS-1 is least toxic to cells and it will be widely applicable to image Cd(II) ions in living cells via fluorescence imaging.

Rhodamine-Appended Benzophenone Probe for Trace Quantity Detection of Pd2+ in Living Cells

Designing a fluorogenic probe for the determination of Pd²⁺ is a challenging analytical task. Pd²⁺ is a potentially toxic and harmful substance even at a very low level of contamination in the end product. Herein, a promising spirolactam-functionalized chemosensor, rhodamine-appended benzophenone (HBR), is designed and characterized by spectroscopic (¹H NMR, ¹³C NMR, ESI-MS, and FT-IR) data along with the single-crystal X-ray diffraction technique. It acts as a highly sensitive and selective fluorogenic chemosensor for Pd²⁺ ions over other environmentally relevant cations in aqueous ethanol (1:1, v/v) at pH 7.4. The limit of detection (LOD) is 34 nM that is far below the WHO recommended Pd uptake (47 μM). The plausible mechanism involves the specific binding of HBR with Pd²⁺ and the formation of 1:1 stoichiometry of the complex, which has been supported by ESI-MS, FT-IR data, Job plot, and association constant data (Benesi-Hildebrand plot). The computation study has been attempted to explain the ring cleavage fluorescence enhancement scheme of HBR upon binding with Pd²⁺. Furthermore, this "turn-on" probe has successfully applied to image the Pd²⁺ ion in cultured MDA-MB-231 cells.

A nanomolar detection of mercury(II) ion by a chemodosimetric rhodamine-based sensor in an aqueous medium: Potential applications in real water samples and as paper strips

A new promising rhodamine based colorimetric and fluorometric chemosensor, RDV has been designed and synthesized for specific detection of Hg²⁺ ion. It acts as highly selective "turn-on" fluorescent chemosensor for Hg²⁺ ion without interference from other competitive metal ions in aqueous acetonitrile medium. The drastic color change with addition of Hg²⁺, from colorless to pink, indicates RDV can acts as "naked-eye" indicator for Hg²⁺. The Hg²⁺ promoted selective hydrolysis of appended vinyl ether group in RDV followed by Hg²⁺ chelated complex formation with concomitant opening of spirolactam ring is the plausible sensing mechanism. The detailed absorption, fluorescence, ¹H NMR, ¹³C NMR and mass spectrometry confirms the proposed sensing mechanism. The limit of detection (LOD) of Hg²⁺ by RDV is 136 nM indicating the high sensitivity towards Hg²⁺. The RDV shows consistent spectroscopic response in biological pH range 4-10. In addition to explore practical applicability of RDV, its paper strips have been made and used to detect Hg²⁺ in pure water solution up to 10 ppm level. Furthermore, the potential application of RDV for the sensing of Hg²⁺ in real water samples (tap water and drinking waters from different sources) were also monitored and demonstrated.

A water-soluble BODIPY based 'OFF/ON' fluorescent probe for the detection of Cd2+ ions with high selectivity and sensitivity

A water-soluble dilithium salt BODIPY derivative (LiBDP) with appended dicarboxylate pseudo-crown ether [NO4] coordinating sites has been designed, synthesized and characterized successfully for the selective and sensitive recognition of Cd2+ in aqueous media. The chemosensor exhibits a remarkable increase in fluorescence intensity as well as a distinct color change upon the addition of Cd2+ over other environmentally and biologically relevant metal ions in H2O. The fluorometric response of LiBDP is attributed to the metal chelation-enhanced fluorescence (MCHEF) effect which has been confirmed by a strong association constant of 2.57 ± 1.06 × 105 M-1 and Job's plot, indicating 1 : 1 binding stoichiometry between LiBDP and Cd2+. Frontier molecular orbital analysis (obtained from DFT studies) also illustrates the turn-on fluorescence of the probe by blocking photoinduced electron transfer (PET) after coordination to Cd2+. The probe can detect Cd2+ in a competitive environment up to a submicromolar level in a biologically significant pH range. The sensor is proved to be reversible and reusable by the alternative addition of Cd2+ followed by S2-. The OFF/ON/OFF sensing behavior is utilized to construct an INHIBIT molecular logic gate based on the two inputs of Cd2+ and S2- and a fluorescence intensity at 512 nm as an output. The test paper experiment demonstrates the practical utility of LiBDP to monitor Cd2+ in an aqueous sample. Finally, the sensing probe was utilized to monitor Cd2+ in living cells.

Methoxy-substituted tetrakisquinoline analogs of EGTA and BAPTA for fluorescence detection of Cd2+

A 5,6,7-trimethoxyquinoline-based octadentate ligand with a BAPTA (1,2-bis(2-aminophenoxy)ethane-N,N,N′,N′-tetraacetic acid) structure exhibits Cd²⁺-specific fluorescence enhancement.

A multifunctional fluorescence sensor for Cd2+, PO43- and Cr3+ in different system and the practical application

A fluorescence probe based on thiosemicarbazide has been synthesized and well characterized by ¹H NMR, ¹³C NMR, Elemental analysis, Electrospray ionization mass spectra. The probe 1 functions as a multitarget ion sensor, detect biologically and ecologically important Cd²⁺, PO₄^3- and Cr³⁺. Meanwhile, probe 1 displays selectivity for Cd²⁺ over other metal ions and anions in DMF by emission spectrum. Interestingly, probe 1 has been explored to recognize PO₄^3- in CH₃OH-H₂O (v:v = 1:9). The binding stoichiometry of probe 1 with Cd²⁺ and PO₄^3- are 2:1 and 1:1, respectively, which are confirmed by Electrospray ionization mass spectra. Probe 1 is selective, sensitive and reversibility/reusability to Cd²⁺ and PO₄^3- with the detection limit as low as 0.035 μM and 0.011 μM respectively. Besides, the designed probe 1 has shown potential applications in the area of photo-printing.

A highly selective and sensitive fluorescent chemosensor for distinguishing cadmium(ii) from zinc(ii) based on amide tautomerization

A naphthalimide-derived fluorescent sensor termed L2 was designed and synthesized.

A tricorn-rhodamine fluorescent chemosensor for detection of Co2+ ions

A novel chemosensor TrisRh based on tris(2-aminoethyl)amine and rhodamine 6G is designed and synthesized as a fluorescence turn-on probe for Co²⁺ ions that is paramagnetic with a property of quenching fluorescence. Rhodamine spirolactam forms are nonfluorescent, whereas, ring-opening of corresponding spirocyclic induced by Co²⁺ results in strong fluorescence emission. Upon the addition of Co²⁺ ions, TrisRh can display significant enhancements in absorbance and fluorescence intensity as well as evident colorific transformation, which can be perceived by the naked eye. The association stoichiometry of TrisRh to Co²⁺ ions was inferred to be 1:1 through Job's plot and electrospray ionization mass spectrometry analysis. The binding model was speculated from Fourier transform infrared spectra and ¹ H-nuclear magnetic resonance technologies. Significantly, the limit of detection was determined to be as low as 1.22 nmol. Furthermore, TrisRh can exhibit robust anti-jamming ability against other interference metal ions.

Rhodamine Diaminomaleonitrile Conjugate as a Novel Colorimetric Fluorescent Sensor for Recognition of Cd2+ Ion

Rhodamine diaminomaleonitrile linked probe (RD-1) shows highly sensitive colorimetric and selective turn-on fluorescent response to Cd²⁺ over other metal ions. The fluorescence intensity and absorbance of the probe RD-1 showed a good linearity, with very low detection limits of 18.5 nm. The probe RD-1 was preliminarily applied to the determination of Cd²⁺ ion in water samples from river and tap water with satisfying results. The live cell image confocal microscopy, HeLa cell demonstrated that RD-1 had low cytotoxicity with good membrane permeable property is successfully applied to fluorescence microscopic imaging for the detection of Cd²⁺ ions.

A novel Hg2+-selective fluorescent chemprobe based on thiooxorhodamine-B and β-C-glycoside

In this paper, two novel easily available probes based on rhodamine B and β-C-glycoside were synthesized and characterized by ¹H NMR, ¹³C NMR and elemental analysis. Sensor 1 exhibited very high sensitivity and selectivity toward Hg²⁺ over other metal ions, due to the opening of the spiro ring in thiooxorhodamine B caused by Hg²⁺ through desulfurization. The binding analysis using Job's plot suggested 1:1 stoichiometry for the complexes formed for Hg²⁺. The fluorescent probe is pH independent in medium condition and common interferent ions do not show any interference with the Hg²⁺ determination. It is anticipated that 1 could be a good candidate probe and has potential application for Hg²⁺ determination.

A coumarin–chalcone hybrid used as a selective and sensitive colorimetric and turn-on fluorometric sensor for Cd2+ detection

A chalcone-based naked-eye colorimetric chemical sensor, (E)-4-hydroxy-3-(3-(4-methoxyphenyl)acryloyl)-2H-chromen-2-one 1a, was developed for selective and sensitive recognition of Cd²⁺ in mixed aqueous–organic media.

A FRET-based fluorescent probe for mercury ions in water and living cells

On the basis of fluorescence resonance energy transfer (FRET), a new rhodamine derivative (DRh) was synthesized as a ratiometric fluorescent probe for detecting Hg(2+) in water and living cells samples. The recognition properties of the probe DRh with metal ions had been investigated in H2O/CH3CN (9:1, v/v; Tris-HCl 50mmolL(-1); pH=7.0) solution by the UV-Vis spectrophotometry and the fluorescence spectrophotometry. The results showed that the probe DRh exhibited the selective recognition of Hg(2+). Upon the addition of Hg(2+), the spirolactam ring of probe DRh was opened. The 1:1 stoichiometric structure between DRh and Hg(2+) were supported by Job's plot, MS and DFT theoretical calculations. The linearly fluorescence intensity ratio (I582/I538) is proportional to the concentration of Hg(2+) in the range 0-30μmolL(-1). The limit of detection (LOD) of Hg(2+) is 0.008μmolL(-1) (base on S/N=3). The present probe was applied to the determination of Hg(2+) in neutral water samples and gave recoveries ranging from 104.5 to 107.9%. Furthermore, the fluorescent probe also can be applied as a bioimaging reagent for Hg(2+) detection in HeLa cells.

A Naphthalimide-Based Cd(2+) Fluorescent Probe with Carbamoylmethyl Groups Working as Chelators and PET-Promoters under Neutral Conditions

We have developed a novel naphthalimide-based Cd(2+) fluorescent probe (1), featuring almost no background response, high sensitivity and selectivity toward Cd(2+) through its high association constant [K=(2.10±0.423)×10(6) ], and a practical working pH range. Membrane-permeability was conferred on 1 by replacing the imide and amide substituents with n-butyl groups, and hence the derivative (4) has found practical utility on fluorescent imaging of Cd(2+) in HeLa cells. Comparison of fluorescent properties between various compounds derived from 1 has demonstrated that the carbamoylmethyl groups in 1 function not only as Cd(2+) chelators but also as promoters for photoinduced electron transfer (PET) by lowering the basicity of the two tertiary amino groups. As a result, 1 and 4 exhibited highly practical performance as Cd(2+) probes under neutral conditions.

Alizarin Dye based ultrasensitive plasmonic SERS probe for trace level Cadmium detection in drinking water

Alizarin functionalized on plasmonic gold nanoparticle displays strong surface enhanced Raman scattering from the various Raman modes of Alizarin, which can be exploited in multiple ways for heavy metal sensing purposes. The present article reports a surface enhanced Raman spectroscopy (SERS) probe for trace level Cadmium in water samples. Alizarin, a highly Raman active dye was functionalized on plasmonic gold surface as a Raman reporter, and then 3-mercaptopropionic acid, 2,6-Pyridinedicarboxylic acid at pH 8.5 was immobilized on the surface of the nanoparticle for the selective coordination of the Cd (II). Upon addition of Cadmium, gold nanoparticle provide an excellent hotspot for Alizarin dye and Raman signal enhancement. This plasmonic SERS assay provided an excellent sensitivity for Cadmium detection from the drinking water samples. We achieved as low as 10 ppt sensitivity from various drinking water sources against other Alkali and heavy metal ions. The developed SERS probe is quite simple and rapid with excellent repeatability and has great potential for prototype scale up for field application.

A ratiometric lysosomal pH probe based on the imidazo[1,5-a]pyridine–rhodamine FRET and ICT system

A new pH-activatable ratiometric fluorescent probe (RhMP) has been developed based on FRET. This probe displayed good selectivity, and excellent reversibility. In addition, RhMP has low cytotoxicity and has been successfully applied in HeLa cells.

Dual anion colorimetric and fluorometric sensing of arsenite and cyanide ions

A naphthalene appended probe, 2-((2-hydroxynaphthalen-1-yl)methylene)hydrazine carbothioamide, was synthesized and found to recognize AsO₂⁻ and CN⁻ ions with turn-on emission fluorescence over different anions in DMF–H₂O (HEPES buffer, 7.2 pH) (9 : 1, v/v solution) medium.

Carbazole–benzimidazole based dyes for acid responsive ratiometric emissive switches

Three carbazole conjugated benzimidazole dyes have been synthesized and their acid/base induced photophysical properties have been studied.