As a biomarker of several diseases, the activity of acid phosphatase (ACP) is generally used to assistantly diagnose these diseases. Thus, developing reliable ACP activity analytical methods becomes quite significant. Herein, we recommend a one-step sampling filtration-free electrochemical method for ACP activity determination based on the target-induced synergetic modulation of tag concentration and surface passivation . Mn 3 O 4 microspheres with favorable oxidase-mimicking activity are synthesized to catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to its product TMBox, resulting in a remarkable re-reduction signal of TMBox to TMB recorded by an integrated electrochemical system consisting of screen-printed electrode (SPE) and 3D-printed holder. When hexametaphosphate ions (HMPi) with rich negative charges are employed to interact positively charged TMBox, the formed flocculent precipitate TMBox-HMPi automatically sedimentates onto SPE surface, and both the decreased concentration of free TMBox in solution and the increased electrode surface passivation triggered by TMBox-HMPi sedimentation synergistically reduce the re-reduction signal of TMBox. When ACP is present, it hydrolyzes the HMPi substrate, greatly relieving the formation of the TMBox-HMPi precipitate and its sedimentation onto SPE surface. As a result, the electrochemical re-reduction signal of TMBox becomes remarkable again. With the strategy of using one stimulus to generate two-fold signal change, highly sensitive ACP activity detection was realized, with a wide linear range from 0.05 to 50 U/L and a limit of detection down to 0.024 U/L. Reliable monitoring of ACP activity in clinical serum was also demonstrated.
Lithium-sulfur (Li-S) batteries are considered to be promising candidates for next-generation storage systems. However, the practical applications are still hindered by the severe capacity decay, mainly caused by the large volume change, polysulfide shuttle and sluggish sulfur conversion kinetics. Herein, hollow urchin-like Mn 3 O 4 (HU-Mn 3 O 4 ) microspheres as sulfur hosts have been synthesized by the hydrothermal method and calcination treatment, aiming to prevent the polysulfide dissolution (benefiting from the strong polysulfide anchoring effect of Mn 3 O 4 ) and alleviate the volume expansion of sulfur (benefiting from the special hollow structure). Meanwhile, the urchin-like thorny surface also facilitates the rapid ion/electron transfer and the abundant active sites for the fast sulfur redox kinetics. When used as the sulfur host in Li-S batteries, the S@HU-Mn 3 O 4 cathode delivers a high initial capacity of 1137.4 mAh g −1 with a slow capacity decay of 0.042% after 200 cycles at 0.2 C. Even under the conditions of lean electrolyte (E/S = 7 mL g −1 ) and low N/P ratio (N/P = 2.1), the S@HU-Mn 3 O 4 cathode still enables a stable cycling performance with a high gravimetric energy density (202 Wh kg cell −1 ), demonstrating its great potential in the development of future practical Li-S battery materials.
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