Amino-Functionalized Ti₃C₂ MXene Quantum Dots as Photoluminescent Sensors for Diagnosing Histidine in Human Serum

As an emerging zero-dimensional nanomaterial, MXene quantum dots (MQDs) have aroused the interest of researchers because of their unique physical and chemical characteristics. Here, a straightforward hydrothermal strategy was used to successfully produce the amino-functionalized Ti₃C₂ MQDs. The functionalized Ti₃C₂ MQDs exhibited bright blue fluorescence (FL), which was derived from its size effect and surface defects. In addition, Ni²⁺ can bind to the amino groups on the surface of Ti₃C₂ MQDs. The absorption of the excitation light by the light-absorbing substance causes nickel ions to effectively quench the photoluminescence of Ti₃C₂ MQDs, which can be explained by the internal filter effect (IFE). At the same time, the strong affinity of histidine (His) for Ni²⁺, which is absorbed by His to form a stable complex, causes Ni²⁺ to dissociate from the Ti₃C₂ MQD surface and restore the FL. Thus, a fluorescent sensor for detecting the His content in serum was developed. Overall, this work provides a method for the detection of His and shows that the Ti₃C₂ MQDs have great potential in biomedical and biosensing applications.