Ternary heterostructures of 1D/2D/2D CuCo2S4/CuS/Ti3C2 MXene: Boosted amperometric sensing for chlorpyrifos

Ti3C2 MXene/MoS2@AuNPs ternary nanocomposite for highly sensitive electrochemical detection of phoxim residues in fruits

Phoxim, extensively utilized in agriculture as an organothiophosphate insecticide, has the potential to cause neurotoxicity and pose human health hazards. In this study, an electrochemical enzyme biosensor based on Ti3C2 MXene/MoS2@AuNPs/AChE was constructed for the sensitive detection of phoxim. The two-dimensional multilayer structure of Ti3C2 MXene provides a robust framework for MoS2, leading to an expansion of the specific surface area and effectively preventing re-stacking of Ti3C2 MXene. Additionally, the synergistic effect of self-reduced grown AuNPs with MoS2 further improves the electrical conductivity of the composites, while the robust framework provides a favorable microenvironment for immobilization of enzyme molecules. Ti3C2 MXene/MoS2@AuNPs electrochemical enzyme sensor showed a significant response to phoxim in the range of 1 × 10-13 M to 1 × 10-7 M with a detection limit of 5.29 × 10-15 M. Moreover, the sensor demonstrated excellent repeatability, reproducibility, and stability, thereby showing its promising potential for real sample detection.

Highly sensitive turn-on electrochemical sensing of organophosphorus pesticides by integration of homogeneous reaction and heterogeneous catalytic signal amplification

Enzyme-inhibited electrochemical sensor is a promising strategy for detecting organophosphorus pesticides (OPs). However, the poor stability of enzymes and the high oxidation potential of thiocholine signal probe limit their potential applications. To address this issue, an indirect strategy was proposed for highly sensitive and reliable detection of chlorpyrifos by integrating homogeneous reaction and heterogeneous catalysis. In the homogeneous reaction, Hg2+ with low oxidation potential was employed as signal probe for chlorpyrifos detection since its electroactivity can be inhibited by thiocholine, which was the hydrolysate of acetylthiocholine catalyzed by acetylcholinesterase. Additionally, Co,N-doped hollow porous carbon nanocage@carbon nanotubes (Co,N-HPNC@CNT) derived from ZIF-8@ZIF-67 was utilized as high-performance electrode material to amplify the stripping voltammetry signal of Hg2+. Thanks to their synergistic effect, the sensor exhibited outstanding sensing performance, excellent stability and good anti-interference ability. This strategy paves the way for the development of high-performance OP sensors and their application in food safety.

MOF-derived Co2CuS4 nanoparticles with gold-decorated reduced graphene oxide for electrochemical determination of chloramphenicol in real samples

Despite the beneficial effects of antibiotics such as chloramphenicol (CAP), they exert some destructive impacts on human health. We designed an electrochemical sensor based on reduced graphene oxide (rGO)/Au/Co2CuS4 nanohybrid for determination of CAP in food and biological samples. The Co2CuS4 was synthesized from binuclear metal-organic framework (CoCu-BDC) through a two-step process. Nanohybrid was characterized by X-ray photoelectron spectroscopy and transmission electron microscopy. The rGO/Au/Co2CuS4 provides more active sites and good electrical conductivity to reduce charge transfer resistance and improve the electrocatalytic activity for determination of CAP. The prepared sensor has a wide linear range from 7 to 141 nM with a limit of detection of 2.5 nM and a limit of quantification of 21.92 nM. It also provided high selectivity and repeatability with a relative standard deviation of 2.6%. Stability studies showed that the electrode has acceptable performance with efficiency of 95% after 33 days.

Rapid and label-free electrochemical aptasensor based on a palladium nanoparticles/titanium carbide/polyethyleneimine functionalized nitrogen-doped carbon nanotubes composite for amplified detection of streptomycin

A novel electrochemical aptasensor for the determination of streptomycin (STR) was constructed in this work. We prepared a palladium nanoparticles/titanium carbide/polyethyleneimine-functionalized nitrogen-doped carbon nanotube (Pd@Ti3C2-PEI-NCNTs) composite via hydrothermal-assisted formic acid reduction and employed it as a substrate material for anchoring a NH2-functionalized aptamer (Apt) to the surface of an electrode through the Pd-N bond. The Pd@Ti3C2-PEI-NCNTs composite increased the electrochemically active surface area and conductivity of the electrode, achieving substantial signal amplification (1.87 times). The constructed aptasensor demonstrated accurate STR detection via specific recognition between the Apt and STR, with a detection range and limit of 0.01-700 and 0.003 nmol/L, respectively. The aptasensor also exhibited excellent selectivity, stability, reproducibility, practicability and shorter assay times (60 min). Furthermore, molecular docking and molecular dynamic also elucidated the binding mechanism between the aptamer and STR molecules. Overall, this method is expected to be a helpful tool for detecting STR in food.

Defective porphyrin-based metal-organic framework nanosheets derived from V2CTx MXene as a robust bioplatform for impedimetric aptasensing 17β-estradiol

An electrochemical aptasensor was prepared for the efficient, sensitive, and selective detection of 17β-estradiol. The sensor was based on a defective two-dimensional porphyrin-based metal-organic framework derived from V₂CT_x MXene. The resulting metal-organic framework nanosheets benefited from the advantages of V₂CT_x MXene nanosheets and porphyrin-based metal-organic framework, two-dimensional porphyrin-based metal-organic framework nanosheets demonstrated amplified electrochemical response and enhanced aptamer-immobilization ability compared with V₂CT_x MXene nanosheets. The sensor's detection limit was ultralow at 0.81 fg mL^-1 (2.97 fM), and the 17β-estradiol concentration range was wide, thereby outperforming most reported aptasensors. The high selectivity, superior stability and reproducibility, and excellent regeneration performance of the constructed aptasensor indicated its remarkable potential application for 17β-estradiol determination in diverse real samples. This aptasensing strategy can be used to analyze other targets by replacing the corresponding aptamer.

In-situ growth of SnO2 nanoparticles on Nb2CTx nanosheets as highly sensitive electrochemical sensing platform for organophosphorus pesticide detection

In this study, the SnO₂/Nb₂CT_x MXene nanocomposite containing 0D/2D interfaces was prepared by situ growth strategy of one-step hydrothermal method. A SnO₂/Nb₂CT_x MXene based acetylcholinesterase (AChE) biosensor was constructed for pesticide detection. Highly conductive Nb₂CT_x MXene, acting as substrate material, restrained the agglomeration of nanoparticles (NPs) and accelerated electron migration due to the confinement effect and well-known accordion-like layered structure. In addition, SnO₂ anchored on both sides of the Nb₂CT_x MXene nanosheets effectively provided a large surface area, abundant surface groups and active sites, which preserved numbers of electrons at the interface of the heterojunction. The SnO₂/Nb₂CT_x MXene hybrids with outstanding conductivity, good biocompatibility and structural stability were beneficial for AChE immobilization. Under the optimized conditions, as-fabricated electrochemical biosensor demonstrated superior performance with linear detection range of 5.1 × 10^-14 - 5.1 × 10^-7 M for chlorpyrifos, along with the limit of detection (LOD) down to 5.1 × 10^-14 M (calculated for 10% inhibition). Furthermore, it is highly expected that this biosensor can be applied for the detection of other organophosphorus pesticides in the environment, providing an effective nanoplatform in biosensing field.

Integration of Metallic Nanomaterials and Recognition Elements for the Specifically Monitoring of Pesticides in Electrochemical Sensing

Although all countries have been controlling the excessive use of pesticides, incidents of pesticide residues still existed. Electrochemical biosensors are extensively applied detection techniques to monitor pesticides with the help of different types of biorecognition components mainly including, antibodies, aptamers, enzymes (i.e., acetylcholinesterase, organophosphorus hydrolase, etc.), and synthetic molecularly imprinted polymers. Besides, the electrode materials mainly affected the sensitivity of electrochemical biosensors. Metallic nanomaterials with various structures and excellent electrical conductivity were desirable choice to construct electrochemical platforms to achieve the detection with high sensitivity and good specificity toward the target. This work reviewed the developed metallic materials including monometallic nanoparticles, bimetallic nanomaterials, metal atoms, metal oxides, metal molybdates, metal-organic frameworks, MXene, etc. Integration of recognition elements endowed the electrode materials with higher specificity toward the target pesticide. Besides, future challenges of metallic nanomaterials-based electrochemical biosensors for the detection of pesticides are also discussed and described.

A High-Performance Hybrid Biofuel Cell with a Honeycomb-Like Ti3 C2 Tx /MWCNT/AuNP Bioanode and a ZnCo2 @NCNT Cathode for Self-Powered Biosensing

This work focusses on developing a hybrid enzyme biofuel cell-based self-powered biosensor with appreciable stability and durability using murine leukemia fusion gene fragments (tDNA) as a model analyte. The cell consists of a Ti₃ C₂ T_x /multiwalled carbon nanotube/gold nanoparticle/glucose oxidase bioanode and a Zn/Co-modified carbon nanotube cathode. The bioanode uniquely exhibits strong electron transfer ability and a high surface area for the loading of 1.14 × 10^-9  mol cm^-2 glucose oxidase to catalyze glucose oxidation. Meanwhile, the abiotic cathode with a high oxygen reduction reaction activity negates the use of conventional bioenzymes as catalysts, which aids in extending the stability and durability of the sensing system. The biosensor offers a 0.1 fm-1 nm linear range and a detection limit of 0.022 fm tDNA. Additionally, the biosensor demonstrates a reproducibility of ≈4.85% and retains ≈87.42% of the initial maximal power density after a 4-week storage at 4 °C, verifying a significantly improved long-term stability.