Abstract
Herein, we demonstrate a new concept of chemical sensing for the construction of pH-mediated magnetic sensors. The strategy is based on the notion that the oxidation of paramagnetic Mn2+ ions to insoluble Mn(IV)O(OH)2 by dissolved oxygen under alkaline conditions can lead to a significant decrease in the transverse relaxation rate (1/T2) of water protons. Crucially, the conversion of Mn2+ ions to MnO(OH)2 correlates with the amount of NaOH, that is, the reaction is pH-dependent. Thus, by combining this reaction with enzymatic reactions that cause pH changes, we can construct pH-mediated chemical sensors based on magnetic relaxation principles. In this work, we selected glucose and urea as model substrates to verify the feasibility of this strategy, since the oxidation of glucose by glucose oxidase and the hydrolysis of urea by urease lead to a notable decrease and increase of pH, respectively, thereby causing a change in the 1/T2 of the solution. Experimental results showed that the linear detection range was 20–2000 µM with a detection limit of 10 µM for glucose, and 50–1000 µM with a detection limit of 20 µM for urea, validating the proof of concept and potential broad applicability of this strategy.
Published Version
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