Highly specific detection of biogenic amines using fluorescence-probe-modified silica nanoparticles

Abstract

A goal of this research is to design and synthesize chemosensors for detection of catecholamine and histidine in water solution. To enhance water solubility, silica nanosphere (SNPs) and mesoporous silica nanoparticles (MSNs) were applied as a solid support which was modified by o-phthalic hemithioacetal (OPTA) to detect primary amine and give high fluorescence emission of isoindole product as a donor fluorophore in the detection system. Moreover, CB and ZnC2 were designed and synthesized as acceptor fluorophores to specifically detect catecholamine and histidine, respectively. Studies on the specific detection of SNPs-OPTA and MSNs-OPTA toward various biogenic amines in phosphate buffer solution, pH 7.4 were found that all biogenic amines enable to form an isoindole product which displayed the emission band at 450 nm (λex = 345nm). Interestingly, histidine showed the highest fluorescence intensity of isoindole product. According to studies on the factors which influence on the binding ability of this system, it was proposed that the imidazole in histidine played important role as a self-catalyst in isoindole product formation. To discriminate the catecholamine, CB was applied to detect various biogenic amines in SNPs-OPTA solution. Interestingly, only dopamine and norepinephrine showed a significant influence on the fluorescence quenching of coumarin at 550 nm. Therefore, this new fluorescence sensor system to discriminate the catecholamine under photoinduced electron transfer (PET) process has been successfully developed. For detection of histidine, the fluorescence self-quenching of isoindole product and ZnC2 was observed as a hypothesis of orderly packing of napthalimide based ZnC2 on the surface of silica (SNPs-OPTA). To avoid this effect, the system consisting of CTAB (SNPs-OPTA_CTAB) was applied. The fluorescence responses of isoindole in SNPs-OPTA_CTAB by varying amount of ZnC2 exhibited the promoting of energy transfer and the system showed high fluorescence intensity at 550 nm belonging to ZnC2 in case of histidine. It was clear that SNPs-OPTA and MSNs-OPTA offered the highly promising selectivity for histidine detection without the assistant of the acceptor fluorophore. However, the Fluorescence Resonance Energy Transfer (FRET) process is an expected benefit for higher wavelength of emission band to avoid the interference from biological matrix in sensing purpose.