title: Graphene flakes enhance the detection of TiO2-enriched catechins by SALDI-MS after microwave-assisted enrichment.
abstract: In this study, we describe a novel method for the rapid detection of catechins in tea leaves using surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS). The method involves incubating catechins in a mixture of titanium dioxide (TiO2) nanoparticles and graphene flakes (GF) and then subjecting the mixture to microwave irradiation to facilitate the enrichment of analytes. In this approach, TiO2 nanoparticles serve as probes to enrich catechins while GF serve to increase the desorption/ionization efficiency. The use of the TiO2-GF mixture as matrix provides a number of advantages over TiO2 nanoparticles alone, including higher desorption/ionization efficiency, enhanced analyte enrichment and reduced run time (less 10min). We demonstrate that the addition of GF to nanoparticles of TiO2 improves the detection of catechins by SALDI-MS. At a signal-to-noise ratio of 3, the limits of detection were 0.04pmole for (+)-catechin (C), 0.17pmole for (-)-epigallocatechin (EGC), 0.35pmole for (-)-epicatechin gallate (ECG), and 0.50pmole for (-)-epigallocatechin gallate (EGCG). This method was further applied to determine the catechin content in several tea samples and the results showed good shot-to-shot and sample-to-sample reproducibility (less than 10% and 13%, respectively) as well as good quantitative linearity for the four analytes (R(2)>0.995). The precision calculated as percent relative standard derivation (%RSD), ranged from 3.6% to 12.4%. Overall, we show that this method is a sensitive, simple and high-throughput technique for the detection of catechins in tea.
authors.affiliation: Institute of Molecular Biology, National Chung Hsing University, Taichung, 40227, Taiwan. Electronic address: g9555012@gmail.nchu.edu.tw.
authors.forename: Yu-Min
authors.initials: YM
authors.lastname: Juang
authors.affiliation: Institute of Molecular Biology, National Chung Hsing University, Taichung, 40227, Taiwan. Electronic address: ru0300618@hotmail.com.
authors.forename: Han-Ju
authors.initials: HJ
authors.lastname: Chien
authors.affiliation: Proteomics Core Lab, Department of Medical Research, China Medical University Hospital, Taichung 40407, Taiwan; Graduate Institute of Integrated Medicine, China Medical University, Taichung 40402 Taiwan. Electronic address: ironmanchen@yahoo.com.tw.
authors.forename: Chao-Jung
authors.initials: CJ
authors.lastname: Chen
authors.affiliation: Institute of Molecular Biology, National Chung Hsing University, Taichung, 40227, Taiwan; Graduate institute of Chinese Medical Science, China Medical University, Taichung 40402, Taiwan; Rong Hsing Reasearch Center for Translational Medicine, National Chung Hsing University, Taichung 40227, Taiwan. Electronic address: lailai@dragon.nchu.edu.tw.
authors.forename: Chien-Chen
authors.initials: CC
authors.lastname: Lai
mesh_terms: D002392:Catechin; D006108:Graphite; D008872:Microwaves; D015203:Reproducibility of Results; D013662:Tea; D014025:Titanium
chemical_list: D013662:Tea; C009495:titanium dioxide; D006108:Graphite; D002392:Catechin; D014025:Titanium
keywords: Catechins; Graphene flakes; Microwave irradiation; SALDI-MS; Titanium dioxide (TiO(2)) nanoparticles