Fluorescent Turn-On Sensing of Zinc(II) and Alkaline Phosphatase Activity Using a Pyridoxal-5'-Phosphate Derived Schiff Base.

A novel Zn2+ ion and alkaline phosphatase (ALP) selective fluorescence turn-on sensor L was developed by reacting pyridoxal 5'-phosphate (PLP) with hydrazine. Sensor L shows significant flurescence enhancement at 476 nm due to the formation of a L-Zn2+ complex in 1:1 binding stoichiometry with the association constant of 3.1⋅104 M- 1. Using L, the concentration of Zn2+ can be detected down to 2.34 µM, and the practical utility of L was validated by quantifying Zn2+ in real water samples. Additionally, the receptor L was applied to mimic the dephosphorylation reaction catalysed by the enzyme ALP and the resulted fluorescence change was monitored to detect the ALP activity.

Tuning Zn(â ¡) selectivity by conjugating vitamin B6 cofactors over bovine serum albumin stabilized red-emitting silver nanoclusters.

The red-emitting bovine serum albumin stabilized silver nanoclusters (BSA-AgNCs) were conjugated with the vitamin B6 cofactors pyridoxal 5'-phosphate (PLP) and pyridoxal (PL). The deconvoluted bands in XPS revealed that the conjugation occurred due to the formation of imine-linkage between the vitamin B6 cofactors and the BSA functionalized over BSA-AgNCs. The TEM images supported the formation of pseudo-spherical shaped nano-aggregates upon conjugating vitamin B6 cofactor PLP over BSA-AgNCs. An emission band appeared at 532 nm after the conjugation of PLP or PL over the surface of BSA-AgNCs. The in situ formed nano-assembly PLP_BSA-AgNCs and PL_BSA-AgNCs showed a significant fluorescent enhancement, respectively, at 490 nm and 481 nm in the presence of Zn2+. The complexation-induced fluorescence enhancement from PLP_BSA-AgNCs and PL_BSA-AgNCs was reversed by adding a strong chelating agent EDTA. In addition, the fluorescence of PL_BSA-AgNCs was irreversibly quenched with the appearance of an emission band at 423 nm in the presence of Hg2+. The analytical performance and sensing mechanism of the developed nanoprobes PLP_BSA-AgNCs and PL_BSA-AgNCs were discussed, and the highly selective and sensitive nanoprobe PLP_BSA-AgNCs was applied for the quantification of Zn2+ in real samples.

Vitamin B6 cofactors guided highly selective fluorescent turn-on sensing of histamine using beta-cyclodextrin stabilized ZnO quantum dots.

Histamine, one of the most important biogenic amines (BAs) is considered as food hazard and therefore various agencies have fixed threshold in different food and beverages. In this manuscript, two novel fluorescent turn-on probes were developed for the instantaneous detection of histamine. The ß-cyclodextrin (ß-CD) capped ZnO quantum dots (QDs) were decorated with the vitamin B6 cofactors like pyridoxal 5'-phosphate (PLP) and pyridoxal (Py) by forming host-guest inclusion complexation between the capped ß-CD and PLP/Py. The cofactors decorated QDs (ZnO@PLP and ZnO@Py) were applied for the sensing of BAs. Addition of histamine to the ZnO@PLP and ZnO@Py solution resulted selective fluorescence enhancement at 473 nm and 460 nm, respectively. Without any interference from the other tested BAs, the fluorescence response of the probes ZnO@PLP and ZnO@Py showed good linearity to histidine concentration from 2.49 to 24.4 µM and 7.44 to 47.6 µM with the detection limit down to 0.59 µM and 0.97 µM, respectively.

Mimicking biological process to detect alkaline phosphatase activity using the vitamin B6 cofactor conjugated bovine serum albumin capped CdS quantum dots.

This manuscript presents a novel bioanalytical approach for the selective ratiometric fluorescent sensing of enzymatic activity of the alkaline phosphatase (ALP) in the biological samples. The probe was designed by conjugating the pyridoxal 5'-phosphate (PLP) over the surface of bovine serum albumin (BSA) stabilized CdS quantum dots (QDs) through the interaction of free amine present in BSA with the aldehyde group of PLP. The conjugation of PLP quenched the emission of QDs. Upon addition of the ALP, the emission of QDs was restored due to the dephosphorylation and the conversion of the functionalized PLP in to pyridoxal. With this probe, the ALP activity can be detected down to 0.05 U/L and also successfully applied for the detection of ALP activity in biological samples such as human serum and plasma.

Three-in-one type fluorescent sensor based on a pyrene pyridoxal cascade for the selective detection of Zn(ii), hydrogen phosphate and cysteine.

A novel fluorescent receptor L was synthesized by Schiff base condensation of 1-pyrenemethylamine with the vitamin B6 cofactor pyridoxal. The receptor L is highly selective and sensitive towards Zn2+ ions among other tested metal ions. Upon interaction with Zn2+, the receptor L showed a distinct fluorescence enhancement at 485 nm due to the excimer formation leading to the fluorescent colour change from blue to bluish-green. Subsequently, when the in situ generated ZnL2 complex interacted with various anions and amino acids, the addition of H2PO4- and cysteine reinstated the fluorescence of the receptor L due to the demetalation of Zn2+ from the ZnL2 complex. Accordingly, the receptor L was developed for the highly selective, specific and sensitive detection of three important bioactive analytes, i.e., Zn2+, H2PO4- and cysteine with a detection limit down to 2.3 × 10-6 M, 2.18 × 10-7 M and 1.59 × 10-7 M, respectively. Additionally, the receptor L was applied to the detection of intracellular Zn2+ ions in live HeLa cells.

Optical sensing of hydrogen sulphate using rhodamine 6G hydrazide from aqueous medium.

This communication reports the application of rhodamine 6G hydrazide (L) for the selective colorimetric and turn-on fluorescent sensing of hydrogen sulphate ions from aqueous medium. The ring opening of the colourless spirocyclic form of L was selectively triggered in the presence of HSO4- among the other tested anions (F-, Cl-, Br-, I-, AcO-, H2PO4-, NO3-, ClO4-, CN-, HO-, AsO33- and SO42-), which gives rise to a pink colour and strong fluorescence in the visible region. Sensor L showed a detection limit down to micromolar range without any interference from the other tested competitive anions. Sensor L was applied for the construction of two inputs (HO- and HSO4-) INHIBIT type molecular logic gate and naked-eye detection of HSO4- using test paper strips.

Chemically modified cellulose strips with pyridoxal conjugated red fluorescent gold nanoclusters for nanomolar detection of mercuric ions.

One-pot approach was adopted for the synthesis of highly luminescent near-infrared (NIR)-emitting gold nanoclusters (AuNCs) using bovine serum albumin (BSA) as a protecting agent. The vitamin B6 cofactor pyridoxal was conjugated with the luminescent BSA-AuNCs through the free amines of BSA and then employed for the nanomolar detection of Hg2+ in aqueous medium via selective fluorescence quenching of AuNCs. This nano-assembly was successfully applied for the real sample analysis of Hg2+ in fish, tap water and river water. The study also presents chemically-modified cellulosic paper strips with the pyridoxal conjugated BSA-AuNCs for detecting Hg2+ ion up to 1nM.

Applications of vitamin B6 cofactor pyridoxal 5'-phosphate and pyridoxal 5'-phosphate crowned gold nanoparticles for optical sensing of metal ions.

Vitamin B6 cofactor pyridoxal 5'-phosphate (PLP) and PLP crowned gold nanoparticles (PLP-AuNPs) was applied for the optical chemosensing of metal ions in aqueous medium. PLP showed a visually detectable colour change from colourless to yellow and 'turn-off' fluorescence in the presence of Fe3+. The fluorescence intensity of PLP at 433nm was also blue-shifted and enhanced at 395nm upon addition of Al3+. When the PLP was functionalized over AuNPs surface, the wine red colour of PLP-AuNPs was turned to purplish-blue and the SPR band at ~525nm was red-shifted upon addition of Al3+, Cd2+ and Pb2+ due to the complexation-induced aggregation of nanoparticles. The developed sensing systems exhibited good selectivity and specificity for the detected analytes (Fe3+, Al3+, Cd2+ and Pb2+).