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.