Gold nanoparticles-doped MXene heterostructure for ultrasensitive electrochemical detection of fumonisin B1 and ampicillin.

Early transition metal carbides (MXene) hybridized by precious metals open a door for innovative electrochemical biosensing device design. Herein, we present a facile one-pot synthesis of gold nanoparticles (AuNPs)-doped two-dimensional (2D) titanium carbide MXene nanoflakes (Ti3C2Tx/Au). Ti3C2Tx MXene exhibits high electrical conductivity and yields synergistic signal amplification in conjunction with AuNPs leading to excellent electrochemical performance. Thus Ti3C2Tx/Au hybrid nanostructure can be used as an electrode platform for the electrochemical analysis of various targets. We used screen-printed electrodes modified with the Ti3C2Tx/Au electrode and functionalized with different biorecognition elements to detect and quantify an antibiotic, ampicillin (AMP), and a mycotoxin, fumonisin B1 (FB1). The ultralow limits of detection of 2.284 pM and 1.617 pg.mL-1, which we achieved respectively for AMP and FB1 are far lower than their corresponding maximum residue limits of 2.8 nM in milk and 2 to 4 mg kg-1 in corn products for human consumption set by the United States Food and Drug Administration. Additionally, the linear range of detection and quantification of AMP and FB1 were, respectively, 10 pM to 500 nM and 10 pg mL-1 to 1 µg mL-1. The unique structure and excellent electrochemical performance of Ti3C2Tx/Au nanocomposite suggest that it is highly suitable for anchoring biorecognition entities such as antibodies and oligonucleotides for monitoring various deleterious contaminants in agri-food products.

Nanozymatic degradation and simultaneous colorimetric detection of tetracycline.

Tetracycline (TC) is a broad-spectrum antibiotic that can enter and accumulate in the human body via the food chain. Even in small concentrations, TC can cause several malignant health effects. We developed a system to simultaneously degrade the presence of TC in food matrices using titanium carbide MXene (FL-Ti3C2Tx). The FL-Ti3C2Tx exhibited biocatalytic property that activates hydrogen peroxide (H2O2) molecules in 3, 3', 5, 5'-tetramethylbenzidine (TMB environment. During the FL-Ti3C2Tx reaction, the catalytic products released turn the color of the H2O2/TMB system bluish-green. However, when TC is present, the bluish-green color does not appear. Via quadrupole time-of-flight mass spectrometry, we found that the TC is degraded by FL-Ti3C2Tx / H2O2 in preference to H2O2/TMB redox reaction, which intervenes in the color change. Hence, we developed a colorimetric assay to detect TC with a LOD of 615.38 nM and proposed two TC degradation pathways that facilitate the highly sensitive colorimetric bioassay.

Oxygen-terminated few-layered Ti3C2Tx MXene nanosheets as peroxidase-mimic nanozyme for colorimetric detection of kanamycin.

Nanomaterials-based bioinspired enzyme mimics are gaining increased attention as alternatives to biocatalysts. Herein, we report synthesizing oxygen-terminated few-layered titanium-based MXene nanosheets (OFL-Ti-MN). OFL-Ti-MN possesses horseradish peroxidase (HRP) activity in catalyzing the oxidation of colorless 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of hydrogen peroxide (H2O2), which turns the solution color bluish-green. The solution color fades quickly when kanamycin (KAN) is added to this system. This reaction indicates that KAN can prevent color change in the OFL-Ti-MN/TMB-H2O2 system. Based on this strategy, we developed an OFL-Ti-MN-based colorimetric sensor to detect and quantify KAN. The sensor exhibited a dynamic range from 15.28 nM to 46.14 µM and a calculated limit of detection (LOD) of 15.28 nM. From the insight gained from the peroxidase-mimic property of OFL-Ti-MN, we proposed a mechanism for the inhibition effect of KAN on peroxidase and peroxidase-mimic enzymes. The proposed mechanism can potentially help elucidate the reasons for the antibacterial function of KAN and its side effects in humans.