Nanomolar Fluorescent Detection of Guanine Using Tin Porphyrin.

5,10,15,20-tetramethoxyphenylporphyrinatotin (IV) (SnTMPP) was synthesised. SnTMPP exhibited Soret band at 432 nm and emission peaks at 629 and 682 nm. The fluorescence intensity of SnTMPP was quenched in the presence of guanine linearly in the range 4 × 10-9 M to 7.2 × 10-8 M and the quenching response was found to be stable even in the presence of other nucleosides such as adenine, cytosine, uracil, thymine, alanine, aspartic acid and ascorbic acid. The detection limit was found to be 0.17 nM and the mechanism behind the decrease in the fluorescence intensity of SnTMPP in the presence of guanine is due to dynamic quenching, which was confirmed by cyclic voltammetric studies and life time studies. The CV studies illustrates the possibilty for an electron transfer between the guanine and the electron deficient metal core of SnTMPP.

A novel benzothiophene incorporated Schiff base acting as a "turn-on" sensor for the selective detection of Serine in organic medium.

A novel fluorogenic sensor N-benzo[b]thiophen-2-yl-methylene-4,5-dimethyl-benzene-1,2-diamine (BTMPD) was synthesized and characterized by using spectroscopic methods including UV-visible, FT-IR, 1H NMR, 13C NMR, and mass spectrometry. The designed fluorescent probe, owing to its remarkable properties, behaves as an efficient turn-on sensor for the sensing of amino acid Serine (Ser). Also, the strength of the probe enhances upon the addition of Ser via charge transfer, and the renowned properties of the fluorophore were duly found. The sensor BTMPD shows incredible execution potential with respect to key performance indicators such as high selectivity, sensitivity, and low detection limit. The concentration change was linear ranging from 5 × 10-8 M to 3 × 10-7 M, which is an indication of the low detection limit of 1.74 ± 0.02 nM under optimal reaction conditions. Interestingly, the Ser addition leads to an increased intensity of the probe at λ = 393 nm which other co-existing species did not. The information about the arrangement and the features of the system and the HOMO-LUMO energy levels was found out theoretically using DFT calculations which is fairly in good agreement with the experimental cyclic voltammetry results. The fluorescence sensing using the synthesized compound BTMPD reveals the practical applicability and its application in real sample analysis.

Selective Fluorescent Sensing of Adenine Via the Emissive Enhancement of a Simple Cobalt Porphyrin.

Porphyrins absorb strongly in the visible region and are also excellent fluorophores that emit in the visible region that make them excellent candidates for fluorescence sensing and in vivo imaging. This work describes the fluorescence determination of adenine using cobalt complex of a simple porphyrin. Tetraphenylporphyrin (TPP) and tetraphenylpophyrinatocobalt(II) (CoTPP) were synthesized and characterised. TPP on metallation with cobalt resulted in the red shift of fluorescence emission in the region 652 nm and 716 nm and showed an enhancement in the emission peaks with the addition of the nucleobase, adenine. CoTPP is found to be an efficient fluorescent sensor for adenine in DMF solvent. The fluorescence enhancement is due to the formation of the ground state complex formation between adenine and CoTPP, which is supported by experimental evidences from UV- visible spectra, time resolved fluorescence life time measurements etc. The detection limit of adenine was found to be 4.2 µM using the CoTPP fluorescent probe. The proposed sensor is found to be highly selective for adenine in presence of other nitrogen bases like guanine, cytosine, uracil, thymine, alanine, histidine etc. in 1:1 concentration.

Water Soluble Porphyrin for the Fluorescent Determination of Cadmium Ions.

Porphyrins are highly conjugated molecules that perform wide variety of functions in biological systems. They absorb strongly in the visible region and they are excellent fluorophores that emit in the visible region. If the meso or ß positions of porphyrins are properly substituted, emission in the NIR region is facilitated. The fluorescence property of porphyrins can be used in sensing applications. Here, we report the synthesis of a water soluble porphyrin that emits in the NIR region and this molecule is used in the fluorescent determination of cadmium ion, which is an environmental pollutant and affects the health of living organisms adversely. 5,10,15,20-tetrakis(4-hydroxy-3,5-dimethoxyphenyl)porphyrin (THMPP), which is water soluble was synthesised from 5,10,15,20-tetrakis(3,4,5-trimethoxyphenyl)porphyrin (TMPP) by partial demethylation, which in turn was synthesized by mixture acid method. The donor-acceptor interaction of THMPP-Cd2+ system displays a dynamic fluorescence quenching through the electron transfer (ET) mechanism. Developed method showed a linear response toward Cd2+ in the concentration range of 0.25 µM to 2 µM. The limit of detection was found to be 0.1499 µM. THMPP exhibited excellent selectivity towards Cd (II) in presence of other metal ions like Hg2+, Mn2+, Mg2+, Co2+ in 1:100, Zn2+, Cu2+, Ni2+ in 1:10 and Na+, K+ in 1:1 M ratio.