On-line Gold Nanoparticle-catalyzed Luminol Chemiluminescence And Its Applications In The Design Of Detector For High-performance Liquid Chromatography

Chemiluminescence (CL) is defined as the emission of electromagnetic radiationproduced by chemical reactions which yield one of the reaction products in anelectronic excited state producing light on falling to the ground state. Because theemission intensity is a function of the concentration of the chemical species involvedin the CL reaction, measurement of emission intensities can be used for analyticalpurposes. Although the theory and the application of CL have been investigated formany years，the study of CL was limited to molecular and ion systems. Recently，metal nanoparticle-involved CL became one of the most attractive developments inthese fields,in which metal nanoparticles can participate in CL reactions as catalyst，reductant, naonosized, platform and energy acceptor. However, nanoparticle-involvedCL system has been rarely reported yield for application in analysis.The design ofnew nanoparticle-involved CL system were valuable to gain a better understanding ofthe fundamental studies of CL and also to extend the analytical applications of CL.HPLC coupled to CL (HPLC CL) detection has become in the last years quite auseful detecting tool due to its high selectivity, high sensitivity, simplicity, and lowcost. A wide variety of HPLC CL methods have been developed for the clinical,pharmaceutical, environmental and food analysis. However, only one article reportedthat the nanoparticle-involved CL system couple with HPLC application in analysis.Therefore, in the present dissertation, Au nanoparticle (AuNPs) was employed to todesign a new, online AuNPs-involved CL system. The CL behavior and mechanism ofthe CL system was investigated. Meanwhile, an ultrasensitive HPLC coupled to on-line AuNPs-catalyzed luminol CL method was established. The research work wasillustrated in detailed as follows:Part I. A novel on-line gold nanoparticle-catalyzed luminol chemiluminescencedetector for high-performance liquid chromatographyA novel on-line AuNPs-catalyzed Luminol CL syetem was established, in whichAuNPs were formed by on-line mixing luminol prepared in buffer solution ofNaHCO3Na2CO3, HAuCl4and H2O2. It was found that phenolic compounds canintensively enhance the intensities of the novel CL system. The CL and UV-visibleabsorption spectra and transmission electron microscopy studies were carried out, andthe CL enhancement mechanism was ascribed to that the presence of phenoliccompound promoted the on-line formation of38-nm-diameter AuNPs, which bettercatalyzed the luminol–H2O2CL reaction. A novel on-line gold nanoparticle-catalyzedluminol–H2O2chemiluminescence (CL) detector for high-performance liquidchromatography (HPLC) was established, in which gold nanoparticles were producedby the on-line reaction of H2O2, NaHCO3Na2CO3(buffer solution of luminol), andHAuCl4.8phenolic compounds (gallic acid, protocatechuic acid, protocatechuicaldehyde,2,5-dihydroxybenzoic acid, caffeic acid,2,3-dihydroxybenzoic acid,(+)-catechin, and ()-epicatechin) were chosen as the model compounds. Everyseparated phenolic compound in the column eluent strongly enhanced the CL signalof on-line gold nanoparticle-catalyzed luminol system. The effects of methanol andphosphoric acid in the proposed HPLC configuration were performed by two gradientelution programs, and the baseline profile revealed that on-line goldnanoparticle-catalyzed luminol–H2O2CL detector had better compatibility than38nmgold colloids-luminol-H2O2CL detector. The proposed CL detector exhibits excellentanalytical performance with the low detection limit (S/N=3) of0.53–0.97ng/mL(10.6-19.4pg) phenolic compounds, and offers a new strategy for developing on-linenanoparticle-catalyzed CL detector for HPLC with sensitive analysis. The analytical application of the proposed on-line AuNP-catalyzed luminol CL detector was testedby determining phenolic compounds in “Cabernet Sauvignon” dry red wine.Part II. Pharmacokinetics and blood-brain barrier penetration of (+)-catechinand (–)-epicatechin in rats by microdialysis sampling coupled tohigh-performance liquid chromatography with on-line goldnanoparticle-catalyzed luminol chemiluminescence detection(+)-Catechin (C) and ()-epicatechin (EC) as the basic monomer unit of flavanols,can be widely present in natural products or medicinal herbs. To investigate thepharmacokinetics and blood-brain barrier (BBB) penetration of C and EC in rats, aultrasensitive method using high-performance liquid chromatography (HPLC) withchemiluminescence (CL) detection was developed. Good separations of C and ECwere achieved with an isocratic elution using the mixture of methanol and aqueous0.2%phosphoric acid (27:73, v/v) within10min. The limits of detection for C andEC in Ringer’s solution were1.0and1.2ng/mL, respectively. The accuracies for Cand EC in Ringer’s solution ranged from–3.0to4.4%. The relative standarddeviations of intra-day and inter-day precision were below5.2%. Microdialysisprobes were inserted into jugular vein and brain hippocampus under anesthesia,respectively. The mean in vivo recoveries of C and EC in microdialysis probes were33.7%and26.5%in blood while38.3%and29.1%in brain. C and EC could bedetected in both blood and brain microdialysates after i.v. administration (C and EC,20mg/kg of body weight). Pharmacokinetic parameters were estimated usingstatistical moment method. Brain-to-blood (AUCbrain/AUCblood) distribution ratioswere0.0726±0.0376and0.1065±0.0531for C and EC. The results indicated that Cand EC could pass through the BBB. It is a further evidence of C and EC havingneuroprotective effects in brain.