▎ 摘　　要

NOVELTY - Preparing platinum micro-electrode comprises boiling platinum wires in concentrated nitric acid, ultrasonically washing with acetone and double-distilled water respectively, subjecting to cyclic voltammetry in a solution of potassium chloride-containing potassium ferricyanide until the desired cyclic voltammogram is obtained, dissolving graphene oxide (GO) and acidified multi-walled carbon nanotubes (MWCNT) in ultrapure water, adding thionin, ultrasonically processing to form nanoclusters of sulfur/GO/MWNT, purifying by centrifugation, washing with ultrapure water, re-suspending the pellet in ultrapure water to form a dispersion of thionin/GO/MWNT, placing the platinum microfilament into the dispersion of thionin/GO/MWNT, spin-drying, immersing in the nafion solution, taking out, drying and repeating the above process multiple times to obtain platinum microfilament electrode modified with nafion/thionin/GO/MWNT. USE - The platinum micro-electrode is useful for detecting salicylic acid. The micro-ratio sensor is useful for detection of plant salicylic acid in vivo living body (all claimed). ADVANTAGE - The miniature ratio type sensor: provides dual signal output, hence applied to the living body research of plants; improves the stability and reproducibility of the sensor, thus achieving the accuracy and reliability of the plant SA detection. DETAILED DESCRIPTION - Preparing platinum micro-electrode comprises (a) boiling platinum wires in concentrated nitric acid, ultrasonically washing with acetone and double-distilled water respectively, subjecting platinum microwires to cyclic voltammetry in a solution of potassium chloride-containing potassium ferricyanide until the desired cyclic voltammogram is obtained, (b) dissolving graphene oxide (GO) and acidified multi-walled carbon nanotubes (MWCNT) in ultrapure water, adding thionin to the solution, ultrasonically processing to form nanoclusters of thionin/GO/MWNT, purifying by centrifugation, washing with ultrapure water, re-suspending the pellet in ultrapure water to form a dispersion of thionin/GO/MWNT, and (c) placing the platinum microfilament obtained in the step (a) in the dispersion of thionin/GO/MWNT, spin-drying at room temperature, immersing in the nafion solution, taking out, drying and repeating the above process multiple times to obtain platinum microfilament electrode modified with nafion/thionin/GO/MWNT. INDEPENDENT CLAIMS are also included for: (1) a micro-ratio sensor, comprising The platinum micro-electrode sealed in a glass capillary, and copper wire, where one end of the glass capillary exposes a specific length of copper wire as a wire and the other end exposes a specific length of the platinum microwire electrode as a working electrode, sealing both ends of the glass capillary with an insulation material; and (2) on-line detection of plant salicylic acid, comprising (a) taking platinum microwire electrode or a platinum microwire electrode of micro ratio type sensor as a working electrode, silver/silver chloride wire as reference electrode and platinum wire is as counter electrode, testing a series of phosphate buffer saline (PBS) standard solutions containing different concentrations of salicylic acid (SA) by electrochemical method in an electrochemical workstation, establishing a standard curve line using the oxidation current of SA and the concentration of SA corresponding to sulfur oxide oxidation, inserting the working electrode, silver/silver chloride wire reference electrode and the platinum wire counter electrode of the step (a) into the plant tissue to be tested, electrochemical detection, and obtaining the content of SA in the plant to be tested according to the above standard curve.