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Portable and low-cost analytical devices are essential for rapid detection of bioactive substrates in agricultural products. This study presents the first highly integrated microelectrochemical sensor based on pencil graphite for rapid and sensitive detection of hesperidin in Citrus reticulate 'Chachi' peel. The surface morphology and characterization as well as the electrochemical property of pencil graphite was investigated and discussed. A high electrocatalytic efficiency of hesperidin has been found at used pencil graphite-based microelectrodes. Kinetic analysis was carried out to further understand the electrochemical process of hesperidin at a pencil graphite microelectrode. Consequently, a portable and highly-integrated microelectrochemical sensor exhibits a sensitivity of 0.7251 μA cm−2 μM−1 and a detection limit as low as 25 nM (S/N = 3), and high selectivity was fabricated. Proposed microelectrochemical sensors were applied to electrochemically determinate the hesperidin content in the extract of Citrus reticulata "chachi" peel. As a result, the concentration of hesperidin in the actual real sample detected electrochemically with the proposed portable and low-cost microelectrochemical sensors is highly consistent to that obtained with a common chromatographic method, thus indicating the good reliability and that it can be used in practical applications. [ABSTRACT FROM AUTHOR]

• Characterizing distinct metabolic and transcriptional profiles associated with raw materials of Geqingpi, Sihuaqingqi and Citri Reticulatae Pericarpium. • The relative content of flavonoids in the pericarp of Citrus reticulata 'Chachi' is the most abundant, with polymethoxyflavonoids (PMFs) being the main component of flavonoids. • A set of seven biomarkers were identified that demonstrated the ability to clearly distinguish between the three stages, and nobiletin possessed the most significant contribution. • A total of 93 O -methyltransferase genes were identified in Citrus reticulata 'Chachi', and 28 of them were potentially responsible for catalyzing the biosynthesis of PMFs (i.e., sinensetin, nobiletin and 3,5,6,7,8,3',4'- heptemthoxyflavone). The dried pericarp of Citrus reticulata 'Chachi' (CRC) is commonly utilized in Traditional Chinese Medicine (TCM) and food consumption. Geqingpi (GQP), Sihuaqingpi (SHQP) and Guangchenpi (CRP) are TCM materials derived from different developmental stages of CRC pericarp, each possessing distinct medicinal properties. However, there is currently limited study on the active substances in these three stages. Metabolome data suggested that the discrepancies in flavonoid content, particularly polymethoxyflavonoids (PMFs), predominantly contribute to the variations across the three periods. Additionally, through multivariate statistical analysis, 7 potential biomarkers were identified and nobiletin (NOB) possessed the most significant contribution. O -methyltransferases (OMTs) play a crucial role to catalyze the formation of -OCH 3 in PMFs. The analysis of transcriptome and genome data revealed the presence of 93 CrOMTs in CRC and 43 were expressed on pericarp. Further investigation identified that 28 of these genes were potentially responsible for catalyzing the biosynthesis of important PMFs such as NOB, sinensetin (SIN), and 3,3′,4′,5,6,7,8-heptamethoxyflavone (HEP). Our results may provide a new perspective for the study of GQP, SHQP and CRP, as well as the regulatory mechanism of PMFs in CRC. [ABSTRACT FROM AUTHOR]