A simple and label-free electrochemical aptasensor was developed for ultra-sensitive determination of chloramphenicol (CAP) based on a 2D transition of metal carbides (MXene) loaded with gold nanoparticles (AuNPs). The embedded AuNPs not only inhibit the aggregation of MXene sheets, but also improve the quantity of active sites and electronic conductivity. The aptamers (Apts) were able to immobilize on the MXene–AuNP modified electrode surface through Au–S interaction. Upon specifically binding with CAP with high affinity, the CAP–Apt complexes produced low conductivity on the aptasensor surface, leading to a decreased electrochemical signal. The resulting current change was quantitatively correlated with CAP concentration. Under optimized experimental conditions, the constructed aptasensor exhibited a good linear relationship within a wide range of 0.0001–10 nM and with a low detection limit of 0.03 pM for CAP. Moreover, the developed aptasensor has been applied to the determination of CAP concentration in honey samples with satisfactory results.

In view of the serious side effects of chlortetracycline (CTC) on the human body, it is particularly important to develop rapid, sensitive, and selective technologies for the detection of CTC in food. In this work, a molecularly imprinted electrochemical sensor with [Fe(CN)₆]^3−/4− as signal probe was proposed for the highly sensitive and selective detection of CTC. For this purpose, TiO₂, which acts as an interlayer scaffold, was uniformly grown on the surface of Ti₃C₂T_x sheets through a simple two-step calcination process using Ti₃C₂T_x as the precursor to effectively avoid the stacking of Ti₃C₂T_x layers due to hydrogen bonding and van der Waals forces. This endowed TiO₂@Ti₃C₂T_x with large specific surface, abundant functional sites, and rapid mass transfer. Then, polypyrrole molecularly imprinted polymers (MIPs) with outstanding electrical conductivity were modified on the surface of TiO₂@Ti₃C₂T_x via simple electro-polymerization, where the pyrrole was employed as a polymeric monomer and the CTC provided a source of template molecules. This will not only provide specific recognition sites for CTC, but also facilitate electron transport on the electrode surface. The synergistic effects between TiO₂@Ti₃C₂T_x and polypyrrole MIPs afforded the TiO₂@Ti₃C₂T_x/MIP-based electrochemical sensor excellent detection properties toward CTC, including ultra-low limits of detection (LOD) (0.027 nM), a wide linear range (0.06–1000 nM), and outstanding stability, reproducibility, selectivity, and feasibility in real samples. The results indicate that this strategy is feasible and will broaden the horizon for highly sensitive and selective detection of CTC.

In this work, an electrochemical sensor based on ion-imprinted polymer/Au nanoparticles/porous biochar (IIP/AuNPs/PBC) composite was proposed for the highly selective and sensitive detection of Pb²⁺. In this work, poly (thionine) (pTHI) served simultaneously as imprinted polymer and reference probe. It could not only realize the specific detection of Pb²⁺, but also provide an internal reference signal to eliminate the influence of human and environmental factors on the detection signal and further improve the stability of the sensor. In addition, the AuNPs/PBC composite with large specific surface area, excellent electron transport and electrocatalytic performance could effectively enhance the detection signal as a carrier material. At the same time, the AuNPs on the PBC surface would promote the formation of uniform and stable IIP through Au–S bonds. The synergistic effect between IIP, AuNPs/PBC and ratiometric signal mode gave the Pb²⁺ sensor excellent performance, including a wide linear range (0.1–1000 μg l⁻¹), low detection limit (0.03 μg l⁻¹, S/N = 3), excellent selectivity and stability. All these results indicate that the proposed sensor could provide a meaningful reference for highly selective detection of heavy metal ions (HMIs).