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Hydrogen peroxide (H 2 O 2 ) has been reported to mediate a variety of physiological and pathological processes in living systems. In this work, a biosensor for determination of H 2 O 2 was prepared by using an HRP/Ti 3 C 2 /Nafion film-modified glassy carbon electrode (GCE). Ti 3 C 2 nanosheets with remarkable conductivity and high specific surface area were chosen as carriers for HRP. Moreover, this biosensor modified with HRP has a specific catalytic effect on H 2 O 2 . The difference in peak current could reflect the quantitative change of H 2 O 2 . The linear range of the biosensor is 5-8000 μM, and the detection limit is 1 μM ( S / N = 3). This biosensor was used to detect H 2 O 2 in clinical serum samples of normal controls and patients with acute myocardial infarction (AMI) before and after percutaneous coronary intervention (PCI). The results showed that the difference between normal controls and patients is significant ( P < 0.05), as well as the difference for patients before and after PCI ( P < 0.01), but no significant difference existed between postoperative patients and normal controls. This biosensor has the advantages of simple preparation, high sensitivity, and quick detection, showing potential application in clinical diagnosis.

Titanium carbide quantum dots (Ti 3 C 2 QDs) derived from two-dimensional (2D) Ti 3 C 2 T x (MXene) are the rising-star material recently. Herein, nitrogen-doped Ti 3 C 2 QDs (N-Ti 3 C 2 QDs) were synthesized via a solvothermal method. The obtained N-Ti 3 C 2 QDs exhibited excitation-dependent photoluminescence, antiphotobleaching, and dispersion stability. Furthermore, by combining the N-Ti 3 C 2 QDs and DAP (2,3-diaminophenazine, the oxidative product of o -phenylenediamine) as a composite nanoprobe (N-Ti 3 C 2 QDs@DAP), we developed a dual-emission reverse change ratiometric sensor to quantitatively monitor H 2 O 2 based on photoinduced electron-transfer effects, where N-Ti 3 C 2 QDs acted as the donor and DAP as the acceptor. On the basis of the xanthine converting into H 2 O 2 through the catalysis of xanthine oxidase, the N-Ti 3 C 2 QDs@DAP nanoprobe was also exploited for xanthine sensing. As a result, the proposed assay was demonstrated to be highly sensitive for H 2 O 2 and xanthine with detection limits of 0.57 and 0.34 μM, respectively. In a word, we have investigated the application of N-Ti 3 C 2 QDs in H 2 O 2 and xanthine sensing and opened a new and exciting avenue for the N-Ti 3 C 2 QDs in biosensing.

In this research, we attempted to develop a sensitive colorimetric sensing strategy for the detection of acid phosphatase (ACP) based on MnO 2 nanosheets and explored its applications in screening and evaluating inhibitors of ACP. The MnO 2 nanosheets exhibit intrinsic biomimetic oxidase activity, which can catalyze the oxidation of the colorless 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonate) diammonium salt (ABTS) into green oxidized ABTS (oxABTS). Upon the introduction of ACP, l-ascorbic acid-2-phosphate can be dephosphorylated to ascorbic acid, which arouses the disintegration of MnO 2 nanosheets into Mn 2+ ions. This disintegration weakens the enzyme mimicking activity of the MnO 2 nanosheets, leading to the impediment of the oxidation of ABTS. Conversely, in the absence of ACP, the ABTS is rapidly oxidized by MnO 2 , leading to a significant colorimetric signal change. The absorbance difference at 420 nm displayed a linear relationship with the concentration of ACP ranging from 0.075 to 0.45 mU·mL -1 , generating a detection limit of 0.046 mU·mL -1 . In the inhibition assays, this sensing platform provided simple detection for parathion-methyl (PM), a representative inhibitor of ACP. The facile evaluation of the inhibitory effect of PM, including its IC50 toward ACP, was also realized.