Fluorescent and Electrochemical Sensor Based on Basic Red 9 Dye Functionalised Graphene Oxide-Montmorillonite Composite for Selective Detection of Cerium (III) Ion.

In this work, graphene oxide (GO) has been prepared from used dry cells using modified Hummer's method and encapsulated with montmorillonite clay. To enhance its electrical property, the GO-MMT composite has been functionalised with Basic Red 9 dye. The sensor was characterized by various spectroscopic techniques like FT-IR spectroscopy, PXRD, SEM analysis, etc. Basic Red 9 dye functionalised GO-MMT composite has been employed for fluorescent and electrochemical detection of Ce3+ ion. The fluorescent turn-on sensing is sensitive, reversible and free from interference from other metal ions. The detection of Ce3+ ion by the sensor was also conducted in bovine serum albumin (BSA) medium. Pt electrode modified with the hybrid sensor produces excellent electrochemical change in presence of Ce3+ ion through cyclic voltammetry and square wave voltammetry technique. The limit of detection (LOD) from fluorescence spectroscopy, cyclic voltammetry and square wave voltammetry were calculated to be 0.6556 × 10- 9 M, 1.232 × 10- 9 M and 1.923 × 10- 9 M respectively.

Rosaniline Hydrochloride Encapsulated MCM-48: Fluorescent and Electrochemical Sensor for Dopamine.

The dye Rosaniline hydrochloride (RANH) has been successfully incorporated in MCM-48 (designated as RANH@MCM-48) and characterized by various spectroscopic methods including FT-IR, SEM, EDX and N2 adsorption-desorption isotherm. RANH@MCM-48 in aqueous medium acts as fluorescence "on" sensor for neurotransmitter dopamine (DA) in presence of its main biological interfering agent ascorbic acid or vitamin c (AA) along with Glucose, Cholesterol and Uric acid (UA). The limits of detection (LOD) were found to be 65 nM and 51 nM respectively in absence and in presence of AA. The interaction of DA to RANH@MCM-48 is found to be reversible with respect to EDTA2-. The fluorescence intensity vs. pH plot shows a narrow fluorescence window of 7.2 to 8.8. RANH@MCM-48 has been successfully applied for DA detection in artificial cerebrospinal fluid (ACF) and bovine serum albumin (BSA) with LOD values 27 nM and 22.5 nM respectively. Platinum disc electrode has been modified with RANH@MCM-48 which showed distinct oxidation peaks with a separation of 0.188 V in cyclic voltammetry (CV). The LOD for DA in presence of AA determined from oxidation current is 77.5 nM. The voltammetric detection of DA is found to be free from common interfering species Na+, K+, Ca2+, Fe2+, UA, Cholesterol and Glucose. RANH@MCM-48 has been found to be a very effective fluorescence and voltammetric sensor for DA with very low  LOD.

Condensation Product of 1-Naphthaldehyde and 3-Aminophenol: Fluorescent "on" Probe for Ce3+and "off" Probe for Dichromate (Cr2O72-).

A new probe (Z)-3-((naphthalen-1-ylmethylene)amino)phenol has been synthesized by condensation reaction between 1-naphthaldehyde and 3-aminophenol for the fluorescent sensing of Ce3+ by "on" mode and dichromate (Cr2O72-) by "off" mode. Metal ions-Ag+, Al3+, As3+, Ba2+, Ca2+, Cd2+, Ce4+, Co2+, Cr3+, Cr6+, Cu2+, Fe2+, Fe3+, Hg2+, K+, La+, Li+, Mg2+, Mn2+, Na+, Ni2+, Pb2+, Zn2+and anions Br-, C2O42-, CH3COO-, Cl-, CO32-, F-, H2PO4-, HCO3-, HF2-, HPO42-, I-, MnO4-, NO3-, OH-, S2-, S2O32-, SCN-, SO42- do not interfere. The limit of detection (LOD) for sensing Ce3+ and Cr2O72- ions are 1.286 × 10-7 M and 6.425 × 10-6 M, respectively.

Fluorescent Sensors for Hg2+ and Cu2+ Based on Condensation Products of 4H-1,2,4 Triazole-4-Amine and Carboxylated Benzoic Acids.

Mercury (Hg) causes serious health issues in its all forms. Deficiency as well as excess of copper ion (Cu2+) in human body is hazardous. A series of four compounds have been derived from carboxylated benzoic acids (benzoic acid, isophthalic acid, terephthalic acid and phthalic acid) and 4H-1,2,4 triazole-4-amine and characterized. Fluorescence detection of Hg2+ was recorded by the derivates with benzoic acid and isophthalic acid while the derivatives of terephthalic acid and phthalic acid detect Cu2+ by fluorescence "off" mode. Metal ions like Li+, Na+, K+, Zn2+, Al3+, Mg2+, Mn2+, Co2+, Ni2+, Cu2+, Cd2+, Pb2+ and Hg2+ found not to interfere. The stoichiometry of binding is 1:1 for the benzoic acid derivative with Hg2+ while it is 1:2 for the other three derivatives. The binding constants are ca. 10-4.5 between the sensors and Hg2+ or Cu2+ and detection limits are around 10-5.5 M. DFT calculation provided optimized geometries of the sensors and confirmed the stoichiometry of binding with Hg2+/Cu2+.

Condensation Product of p-anisaldehyde and L-phenylalanine: Fluorescent "on-off" Sensor for Cu2+ and IMPLICATION Logic Gate.

(Z)-2-(4-methoxybenzylideneamino)-3-phenylpropanoic acid (L) synthesized by condensation of p-anisaldehyde and L-phenylalanine acts as selective fluorescent as well as voltammetric sensor for Cu2+ in 2:1 (v/v) CH3OH:H2O. The fluorescence intensity of L (λmax 425 nm) is quenched ca. 65% by Cu2+. Metal ions - Li+, Na+, K+, Al3+, Cu2+, Zn2+, Cd2+, Hg2+, Mn2+, Ni2+ and Pb2+ do not interfere. The binding constant and the detection limits were calculated to be 0.56 × 102 M-1 and 10-6 M respectively. DFT and TDDFT calculations confirmed 2:1 binding stoichiometry between L and Cu2+ obtained from fluorescence data. The interaction between L and Cu2+ is reversible for many cycles with respect to ethylenediamine tetraacetate anion (EDTA2-) which results in IMPLICATION logic gate.

A New Schiff Base Based Fluorescent Sensor for Al(III) Based on 2-Hydroxyacetophenone and o-Phenylenediamine.

A simple Schiff base (L) based on 2-hydroxyacetophenone and o-phenylenediamine was prepared which acts as an effective fluorescent sensor for Al3+ with ca. 9.0 fold enhancement in fluorescence intensity and detection limit 10-4.3 M. L can quite clearly distinguish Al3+ over other metal ions Zn2+, Hg2+, Cd2+, Pb2+, Mn2+, Mg2+, Co2+, Ni2+, Cu2+, Ca2+, K+, Li+, Na+ and Fe3+. Cyclic voltammogram and square wave voltammogram of L shows a significant change on interaction with Al3+. Spectroscopic data and DFT calculations confirm 1:1 interaction between L and Al3+ which is reversible with respect to Na2EDTA.

Schiff Base Derived from 4,4'-methylenedianiline and p-anisaldehyde: Colorimetric Sensor for Cu2+, Paper Strip Sensor for Al3+ and Fluorescent Sensor for Pb2.

The condensation product (L) of 4,4'-methylenedianiline and p-anisaldehyde acts as colorimetric sensor for Cu2+ and Pb2+ ions. On interaction with Cu2+, ethanolic solution of L changes its color to brown while it becomes light pink on interaction with Pb2+. Interaction of Al3+ with L coated paper strip emits bright blue fluorescence. Metal ions like Mg2+, Cu2+, Li+, K+, Na+, Mn2+, Al3+, Hg2+, Co2+, Pb2+, Ni2+, Cd2+, Zn2+, Fe3+ do not interfere the paper strip sensor. The fluorescent intensity of L in ethanol is quenched 25 times by Pb2+ ion. The interaction between L and Pb2+ is reversible and the detection limit of Pb2+ is 10-6 M. The binding constant and stoichiometry of binding between L and Pb2+ was calculated to be 104.8 and 1:2. Theoretical calculations show that the binding of the metal ions to L are favorable and the fluorescence of L is due to π → π* transition.

Condensation Product of 4-Methoxybenzaldehyde and Ethylenediamine: "Off-On" Fluorescent Sensor for Cerium(III).

The condensation product (L) of 4-methoxybenzaldehyde and ethylenediamine has been synthesised and characterised. L showed a 21 times enhancement in fluorescence intensity on interaction with Ce3+ in CH3OH at λmax = 360 nm when excited with 270 nm photons. Metal ions K+, Na+, Al3+, Co2+, Hg2+, Cd2+, Ni2+, Zn2+, Mn2+, Mg2+ and Ca2+ do not interfere. The stoichiometry of binding and the binding constants were determined from spectroscopic data and found to be 1:1 and 104.8 M respectively. The detection limit was found to be 10-5.2 M. The protonation/de-protonation of water molecules coordinated to Ce3+ was found to show interesting behaviour on the fluorescence of L:Ce3+.

Condensation Product of Phenylalanine and Salicylaldehyde: Fluorescent Sensor for Zn(2.).

The condensation product of phenylalanine and salicylaldehyde (L) was synthesised and characterised which was found to be selective fluorescent "off-on" sensor for Zn(2+) ion with the detection limit 10(-5) M. The sensor is free of interferences from metal ions - Na(+), K(+), Al(3+), Mn(2+), Co(2+), Ni(2+), Cu(2+), Pb(2+), Cd(2+) and Hg(2+). The Fluorescence and the UV/visible spectral data reveals a 1:1 interaction between the sensor and Zn(2+) ion with binding constant 10(8). The DFT and TDDFT calculations confirm the structures of the sensor and the sensor-Zn(2+) complex.

Surfactant Dependent pH Controlled "off-on", "off-on-off" and "on-off" Fluorescent Switches Exhibited by N-Benzylidenenaphthalen-1-Amine.

N-benzylidenenaphthalen-1-amine (L) acts as pH dependent "off-on", "off-on-off" and "on-off" fluorescent switch in 1:1 (v/v) CH3CN:H2O depending on the presence of anionic sodiumdocdecyl sulphate (SDS), neutral triton X-100 (TX-100) and cationic cetyltrimethylammonium bromide (CTAB) surfactants respectively. DFT calculation shows the possibility of formation of L.H(+) due to protonation at immine N and L.OH(-) due to introduction of OH(-) group at immine C. The relative stability of these two cationic and anionic species depends on the charge environment provided by surfactants. This influences the photoinduced electron transfer (PET) processes involved and results in different switch behaviour.

A New Fluorescent "Off-On" Sensor for Al(3+) Derived from L-alanine and Salicylaldehyde.

The condensation product of L-alanine and salicylaldehyde was synthesised and characterised which was found to be selective fluorescent "on" sensor for Al(3+) ion with the detection limit 10(-6) M. The sensor is free of interferences from metal ions - Na(+), K(+), Ca(2+), Mn(2+), Co(2+), Ni(2+), Cu(2+), Pb(2+), Cd(2+), Hg(2+) and Fe(3+). The Fluorescence and the UV/visible spectral data reveals a 1:1 interaction between the sensor and Al(3+) ion with binding constant 10(4.5). The DFT and TDDFT calculations confirm the structures of the sensor and the sensor-Al(3+) complex.

Structurally simple ferrocene derivatives for selective cadmium sensing.

Three new ferrocene based Schiff bases 4-{[(E)-ferrocenylmethylidene] amino}benzenethiol (1b), 3-{[(E)-ferrocenylmethylidene]amino} benzenethiol (1c), 2-{[(E)-ferrocenylmethylidene]amino} benzenethiol (1d) have been synthesized to study their sensor property to various metal ions. It has been observed that 1b is highly fluorescent and its fluorescence changes in presence of metal ions. It was further observed that compound 1b is highly selective towards Cd(2+) ion in solution.

N-benzoate-N' salicylaldehyde ethynelediamine: a new fluorescent sensor for Zn2+ ion by "off-on" mode.

Imbalance of zinc ion (Zn(2+)) in human body causes diseases like Alzheimer's and Parkinson's and therefore Zn(2+) estimation in biological fluids has diagnostic values. Fluorescence "off-on" sensors have advantages of high sensitivity and in situ application over other sensors. A new fluorescent "off-on" Zn(2+) sensor, N-benzoate-N' salicylaldehyde ethynelediamine (L), has been synthesisied. In 1:1(v/v) CH3OH:PBS (PBS = phosphate buffer solution), L shows ca. 20 times enhancement in fluorescence intensity on interaction with Zn(2+), due to snapping of photoinduced electron transfer (PET) process, which is selective over metal ions - Na(+), K(+), Ca(2+), Ni(2+), Cu(2+), Cd(2+), Hg(2+) and Pb(2+). These metal ions either individually or all together does not interfere the sensing ability of L towards Zn(2+). A 1:1 interaction between L and Zn(2+) ion with binding constant 10(4.25) has been established from spectroscopic data.

The first bifluoride sensor based on fluorescent enhancement.

The first fluorescent sensor for HF2(-) anion, N(1), N(3)-di(naphthalene-1-yl)isophthalamide (L) has been derived from α-Napthylamine and isopthaloyl chloride. In 1:1 (v/v) DMSO:H2O, L exhibits high selectivity towards HF2(-) anion with a 4-fold enhancement in fluorescent intensity. Very little enhancement in fluorescence intensity is observed for F(-), Cl(-), Br(-), I(-), SCN(-), PO4(3-), SO4(2-), and CH3COO(-) anions. The stoichiometry interaction between L and HF2 (-) is found to be 1:1 from fluorescence and UV/Visible spectral data. DFT calculation shows that binding between HF2(-) and L is 1:1 and increases the relative planarity between the two naphthyl rings causing fluorescence enhancement. A shift of 0.080 V in oxidation potential of L is observed on interaction with HF2(-) by cyclic voltammetry and square wave voltammetry.

A new on-fluorescent probe for manganese (II) ion.

A new fluorescent probe for Mn(2+) ion, (6E)-N-((E)-1,2-diphenyl-2-(pyridin-2-ylimino)ethylidene)pyridin-2-amine (L), has been synthesized from benzil and 2-amino pyridine and characterized. In 1:1 (v/v) CH3CN:H2O (pH 4.0, universal buffer) L exhibits fluorescent intensity with emission peak at λmax 360 nm on excitation with photons of 310 nm. Fluorescent intensity of L increases distinguishingly on interaction with Mn(2+) ion compared to metal ions--Na(+), K(+), Ca(2+), Mg(2+), Ba(2+), Fe(2+), Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+), Hg(2+), Pb(2+) and Ag(+) individually or all together. The enhancement in fluorescent intensity is due to snapping of photoinduced electron transfer (PET) prevailed in free L. Fluorescence and UV/visible spectral data analysis shows that binding stoichiometry between Mn(2+) and L is 1:1 with log ß ≈ 3.0. Both L and its Mn(2+) complex were optimised using density functional theory (DFT) and vibrational frequency calculations confirm that both are at local minima on the potential energy surfaces.

Salicylaldehyde phenylhydrazone: a new highly selective fluorescent lead (II) probe.

The fluorescence intensity of salicylaldehyde phenylhydrazone (L), in 1:1 (v/v) CH3OH:H2O was enhanced by ca. 100 times with a blue shift in emission maximum, on interaction with Pb(2+) ion. No enhancement in fluorescent intensity of L was observed on interaction with metal ions - Na(+), K(+), Ca(2+), Cu(2+), Ni(2+), Zn(2+), Cd(2+) and Hg(2+). This signal transduction was found to occur via photoinduced electron transfer (PET) mechanism. A 1:1 complexation between Pb(2+) and L with log ß = 7.86 has been proved from fluorescent and UV/Visible spectroscopic data. The detection limit of Pb(2+) was calculated to be 6.3 × 10(-7) M.

N,N,N,N-tetradentate macrocyclic ligand based selective fluorescent sensor for zinc (II).

N,N,N,N-tetradentate macrocyclic ligand (L) has been synthesized by the condensation of benzil and semicarbazide and characterized. On excitation by light of wavelength 350 nm, L exhibited a fluorescent peak at λ(max) = 454 nm, which showed ca 6 times enhancement in intensity with a blue shift on interaction with Zn(2+). L has been found to act as a selective fluorescent sensor for zinc(2+) ion over a host of other metal ions such as- Cd(2+), Pb(2+), Hg(2+), Ca(2+), Fe(2+), Na(2+), Co(2+), Mn(2+), Cu(2+) and Ni(2+), in 1:1 CH(3)OH:H(2)O. A 1:1 complex formation between L and Zn(2+) was proved. The enhancement in the fluorescence could be explained on the basis of Photo induced electron transfer (PET) mechanism with log ß = 1.86.

A new highly sensitive and selective fluorescent cadmium sensor.

Condensation product (L) of salicylaldehyde and semicarbazide behaves as a fluorescent sensor for Cd(2+) ion, in 1:1 DMSO:H(2)O, over Mn(2+), Fe(2+), Ni(2+), Co(2+), Cu(2+), Pb(2+) and Hg(2+) ions. The emission peak of L at λ(max) = 520 nm, on excitation with 420 nm wavelength photons, showed an enhancement in intensity of ca 60-fold when interacted with Cd(2+) ion. The intensity was however found to remain unaltered when interacted with metal ions--Mn(2+), Fe(2+), Ni(2+), Co(2+), Cu(2+), Pb(2+) and Hg(2+). The intensity increases by approximately 20 fold on interaction with Zn(2+) ion. The increase in the fluorescent peak can be explained on the basis of photo induced electron transfer (PET) mechanism. A 1:1 complexation between Cd(2+) and L with log ß = 4.25 has been proved.

New duel fluorescent "on-off" and colorimetric sensor for Copper(II): Copper(II) binds through N coordination and pi cation interaction to sensor.

Schiff base derived from naphthylamine and benzil (L) binds to two Cu(2+) ions, one by coordination through N of the Schiff base and another by pi cation interaction through benzil rings. This bonding pattern determined by DFT calculation has been proved by matching electronic spectrum obtained from TDDFT calculation to the experimental one. L acts as "on-off" fluorescent and bare eye detectable colorimetric (purple color) sensor for Cu(2+) ion over the metal ions - Na(+), K(+), Ca(2+) Mn(2+), Co(2+) Ni(2+), Zn(2+), Pb(2+), Cd(2+), Hg(2+), Ag(+), Hg(2+) and Al(3+) in 1:1 v/v CH3CN:H2O. These metal ions do not interfere the fluorescent/colorimetric sensing. As fluorescent sensor the linear range of detection is 5×10(-5) to 3×10(-4)M and detection limit 10(-5)M.

A new simple Schiff base fluorescence "on" sensor for Al3+ and its living cell imaging.

The simple Schiff base (Z)-N-benzylidenenaphthalen-1-amine (L) acts as an effective fluorescence sensor for Al(3+) by "off-on" mode, and ca. 42 times enhancement in fluorescence intensity is observed. The detection limit of L towards Al(3+) is observed to be 5 × 10(-5) M. UV/Visible and fluorescence data as well as DFT calculations confirm 1:3 coordination between Al(3+) and L through N atoms in a pyramidal shape. L is employed for imaging the Al(3+) ion in living biological cells and for the determination of the Al(3+) ion in bovine serum albumin.