Electroactive poly(thionine) as imprinted polymer and reference probe simultaneously for ratiometric ion imprinted electrochemical Pb2+sensor.

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 (0.1-1000µg l-1), low detection limit (0.03µg 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).

Electrochemical activation of oxygen vacancy-rich TiO2@MXene as high-performance electrochemical sensing platform for detecting imidacloprid in fruits and vegetables.

Heterostructured TiO2@MXene rich in oxygen vacancies defects (VO-TiO2@MXene) has been developed to construct an electrochemical sensing platform for imidacloprid (IMI) determination. For the material design, TiO2 nanoparticles were firstly in situ grown on MXene and used as a scaffolding to prevent the stack of MXene nanosheets. The obtained TiO2@MXene heterostructure displays excellent layered structure and large specific surface area. After that, electrochemical activation is utilized to treat TiO2@MXene, which greatly increases the concentration of surface oxygen vacancies (VOs), thereby remarkably enhancing the conductivity and adsorption capacity of the composite. Accordingly, the prepared VO-TiO2@MXene displays excellent electrocatalytic activity toward the reduction of IMI. Under optimum conditions, cyclic voltammetry and linear sweep voltammetry techniques were utilized to investigate the electrochemical behavior of IMI at the VO-TiO2@MXene/GCE. The proposed sensor based on VO-TiO2@MXene presents an obvious reduction peak at -1.05 V(vs. Hg|Hg2Cl2) with two linear ranges from 0.07 - 10.0 µM and 10.0 - 70.0 µM with a detection limit of 23.3 nM (S/N= 3). Furthermore, the sensor provides a reliable result for detecting IMI in fruit and vegetable samples with a recovery of 97.9-103% and RSD≤ 4.3%. A sensitive electrochemical sensing platform was reported for imidacloprid (IMI) determination based on heterostructured TiO2@MXene rich in oxygen vacancy defects.

Electrochemical determination of benomyl using MWCNTs interspersed graphdiyne as enhanced electrocatalyst.

Graphdiyne (GDY) has attracted a lot of interest in electrochemical sensing application with the advantages of a large conjugation system, porous structure, and high structure defects. Herein, to further improve the sensing effect of GDY, conductive MWCNTs were chosen as the signal accelerator. To get a stable composite material, polydopamine (PDA) was employed as connecting bridge between GDY and MWCNTs-NH2, where DA was firstly polymerized onto GDY, followed by covalently linking MWCNTs-NH2 with PDA through Michael-type reaction. The formed GDY@PDA/MWCNTs-NH2 composite was then explored as an electrochemical sensor for benomyl (Ben) determination. GDY assists the adsorption and accumulation of Ben molecules to the sensing surface, while MWCNTs-NH2 can enhance the electrical conductivity and electrocatalytic activity, all of which contributing to the significantly improved performance. The proposed sensor displays an obvious oxidation peak at 0.72 V (vs. Hg|Hg2Cl2) and reveals a wide linear range from 0.007 to 10.0 µM and a low limit of detection (LOD) of 1.8 nM (S/N = 3) toward Ben detection. In addition, the sensor shows high stability, repeatability, reproducibility, and selectivity. The feasibility of this sensor was demonstrated by detecting Ben in apple and cucumber samples with a recovery of 94-106% and relative standard deviations (RSDs) less than 2.3% (n = 5). A sensitive electrochemical sensing platform was reported for benomyl (Ben) determination based on a highly stable GDY@PDA/MWCNTs-NH2 composite.

Efficient Adsorption and Electrochemical Detection of Cd2+ with a Ternary MgZnFe-Layered Double Hydroxides Engineered Porous Biochar Composite.

Their unique layered structure, large specific surface area, good stability, high negative charge density between layers, and customizable composition give layered double hydroxides (LDHs) excellent adsorption and detection performance for heavy metal ions (HMIs). However, their easy aggregation and low electrical conductivity limit the practical application of untreated LDHs. In this work, a ternary MgZnFe-LDHs engineered porous biochar (MgZnFe-LDHs/PBC) heterojunction was proposed as a sensing and adsorption material for the effective detection and removal of Cd2+ from wastewater. The growth of MgZnFe-LDHs in the PBC pores not only reduces the accumulation of MgZnFe-LDHs, but also improves the electrical conductivity of the composite. The synergistic effect between MgZnFe-LDHs and PBC enables the composite to achieve a maximum adsorption capacity of up to 293.4 mg/g for Cd2+ in wastewater. Meanwhile, the MgZnFe-LDHs/PBC-based electrochemical sensor shows excellent detection performance for Cd2+, presenting a wide linear range (0.01 ng/L-1 mg/L), low detection limit (3.0 pg/L), good selectivity, and stability. The results indicate that MgZnFe-LDHs/PBC would be a potential material for detecting and removing Cd2+ from wastewater.

An Electrochemical Sensor Based on a Porous Biochar/Cuprous Oxide (BC/Cu2O) Composite for the Determination of Hg(II).

Mercuric ion (Hg2+) in aqueous media is extremely toxic to the environment and organisms. Therefore, the ultra-trace electrochemical determination of Hg2+ in the environment is of critical importance. In this work, a new electrochemical Hg2+ sensing platform based on porous activated carbon (BC/Cu2O) modified with cuprous oxide was developed using a simple impregnation pyrolysis method. Differential pulse anodic stripping voltammetry (DPASV) was used to investigate the sensing capability of the BC/Cu2O electrode towards Hg2+. Due to the excellent conductivity and large specific surface area of BC, and the excellent catalytic activity of Cu2O nanoparticles, the prepared BC/Cu2O electrode exhibited excellent electrochemical activity. The high sensitivity of the proposed system resulted in a low detection limit of 0.3 ng·L-1 and a wide linear response in the ranges from 1.0 ng·L-1 to 1.0 mg·L-1. In addition, this sensor was found to have good accuracy, acceptable precision, and reproducibility. All of these results show that the BC/Cu2O composite is a promising material for Hg2+ electrochemical detection.

TiO2-MXene/PEDOT:PSS Composite as a Novel Electrochemical Sensing Platform for Sensitive Detection of Baicalein.

In this work, TiO2-MXene/poly (3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) composite was utilized as an electrode material for the sensitive electrochemical detection of baicalein. The in-situ growth of TiO2 nanoparticles on the surface of MXene nanosheets can effectively prevent their aggregation, thus presenting a significantly large specific surface area and abundant active sites. However, the partial oxidation of MXene after calcination could reduce its conductivity. To address this issue, herein, PEDOT:PSS films were introduced to disperse the TiO2-MXene materials. The uniform and dense films of PEDOT:PSS not only improved the conductivity and dispersion of TiO2-MXene but also enhanced its stability and electrocatalytic activity. With the advantages of a composite material, TiO2-MXene/PEDOT:PSS as an electrode material demonstrated excellent electrochemical sensing ability for baicalein determination, with a wide linear response ranging from 0.007 to 10.0 µM and a lower limit of detection of 2.33 nM. Furthermore, the prepared sensor displayed good repeatability, reproducibility, stability and selectivity, and presented satisfactory results for the determination of baicalein in human urine sample analysis.

Ultrasensitive Electrochemical Detection of cancer-Related Point Mutations Based on Surface-Initiated Three-Dimensionally Self-Assembled DNA Nanostructures from Only Two Palindromic Probes.

Sensitive and selective detection of proto-oncogenes, especially recognition of point mutation, is of great importance in cancer diagnosis. Here, a ligation-mediated technique is demonstrated for the construction of an intertwined three-dimensional DNA nanosheet (3D SDN) on an electrode surface from only two palindromic hairpin probes (HP1 and HP2), creating a powerful electrochemical biosensor (E-biosensor) for the detection of the p53 gene. First, a capturing probe (CP) is immobilized on an electrode surface via Au-S chemistry, forming an electrochemical sensing interface. In the presence of the target p53 (T), the triggering probe is covalently linked to CP by a ligase. Moreover, target hybridization/ligation/dehybridization process is repeated, amplifying the target hybridization event and increasing the content of surface-confined triggering fragments. As a result, HP1 is opened and in turn interacts with HP2, forming intertwined 3D SDN where HP1 and HP2 are alternately arranged in parallel. Common hybridization and interaction between palindromic fragments are responsible for the assembly in the horizontal and vertical directions, respectively. An electrochemical indicator, methylene blue (MB), can be inserted into 3D SDN, generating a strong electrochemical signal. Utilizing the 3D SDN-based E-biosensor, the target DNA is detected down to 3 fM with a linear response range from 10 fM to 10 nM. Single point mutations are reliably identified even in fetal bovine serum and cellular homogenate. Because of the several advantages of simple design, good universality, inexpensive instrumentation, high assay specificity, and sensitivity, the 3D SDN-based E-biosensor is expected to provide a potential platform for screening point mutation required by early clinical diagnostics and medical research.

A facile fabrication of ratiometric electrochemical sensor for sensitive detection of riboflavin based on hierarchical porous biochar derived from KOH-activated Soulangeana sepals.

Herein, a facile ratiometric electrochemical method was developed for sensitive sensing of riboflavin (RF) based on hierarchical porous biochar (HPB) modified electrode. In this sensing system, the reference paracetamol (PA) was directly added into electrolyte solution without the requirement of complex immobilization process. HPB derived from KOH-activated Soulangeana sepals displays hierarchical porous structure, high specific surface area and rich oxygen-containing functional groups, which is favorable for RF adsorption and enrichment. Besides, the excellent electronic conductivity and superior electrocatalytic activity of HPB can effectively promote the electrooxidation of RF. Moreover, the dual-signal strategy greatly improves the reproducibility and reliability of electrochemical detection. Based on the proposed ratiometric sensing platform, the sensor exhibits a wider linear range of 0.0007-10µM and a lower limit of detection of 0.2 nM. The method also presents good selectivity and has been applied to the determination of RF in milk samples with satisfactory results.

Core-shell Cu@C@ZIF-8 composite: a high-performance electrode material for electrochemical sensing of nitrite with high selectivity and sensitivity.

Herein, an efficient electrochemical sensing platform is proposed for selective and sensitive detection of nitrite on the basis of Cu@C@Zeolitic imidazolate framework-8 (Cu@C@ZIF-8) heterostructure. core-shell Cu@C@ZIF-8 composite was synthesized by pyrolysis of Cu-metal-organic framework@ZIF-8 (Cu-MOF@ZIF-8) in Ar atmosphere on account of the difference of thermal stability between Cu-MOF and ZIF-8. For the sensing system of Cu@C@ZIF-8, ZIF-8 with proper pore size allows nitrite diffuse through the shell, while big molecules cannot, which ensures high selectivity of the sensor. On the other hand, Cu@C as electrocatalyst promotes the oxidation of nitrite, thereby resulting high sensitivity of the sensor. Accordingly, the Cu@C@ZIF-8 based sensor presents excellent performance for nitrite detection, which achieves a wide linear response range of 0.1-300.0µM, and a low limit of detection of 0.033µM. In addition, the Cu@C@ZIF-8 sensor possesses excellent stability and reproducibility, and was employed to quantify nitrite in sausage samples with recoveries of 95.45%-104.80%.

Amplified electrochemical determination of niclosamide in food based on carbon nanohorn@MWCNT composite.

In this work, carbon nanohorn (CNH)-decorated multi-walled carbon nanotube (MWCNT) (CNH@MWCNT) composite was prepared and used to modify glass carbon electrode (GCE) as sensitive electrochemical sensor for niclosamide (NA) determination. Herein, the decoration of CNHs induces higher dispersibility for MWCNTs, and endows the composite with better conductivity, larger surface area, and higher catalytic activity, which leads to significantly enhanced electrochemical behavior toward NA oxidation. The parameters such as mass ratios of CNHs and MWCHTs, the amount of composite materials, the accumulation time, and the solution pH are systematically optimized. Under optimized conditions, the developed electrochemical sensor exhibits a low detection limit of 2.0 nM with a wide linear range of 7.0 nM-10.0 µM and high anti-interference ability. In addition, the sensor displays good stability, repeatability, and reproducibility. The feasibility of the assay was verified by testing NA in brown rice and rice field water samples.

ß-Cyclodextrin/CMK-8-Based Electrochemical Sensor for Sensitive Detection of Cu2.

In this work, ß-cyclodextrin (ß-CD)/mesoporous carbon (CMK-8) nanocomposite was synthesized and used as an electrochemical sensing platform for highly sensitive and selective detection of Cu2+. The morphology and structure of ß-CD/CMK-8 were characterized by scanning electron microscope (SEM) and X-ray diffraction (XRD). In addition, the dates from electrochemical impedance spectroscopy (EIS) and Cyclic voltammetry (CV) demonstrated that the ß-CD/CMK-8 possessed a fast electronic transfer rate and large effective surface area. Besides this, the ß-CD/CMK-8 composite displayed high enrichment ability toward Cu2+. As a result of these impressive features, the ß-CD/CMK-8 modified electrode provided a wide linear response ranging from 0.1 ng·L-1 to 1.0 mg·L-1 with a low detection limit of 0.3 ng·L-1. Furthermore, the repeatability, reproducibility and selectivity of ß-CD/CMK-8 towards Cu2+ were commendable. The sensor could be used to detect Cu2+ in real samples. All in all, this work proposes a simple and sensitive method for Cu2+ detection, which provides a reference for the subsequent detection of HMIs.

Highly Sensitive Electrochemical Sensor for Sunset Yellow Based on Electrochemically Activated Glassy Carbon Electrode.

Electrochemically activated glassy carbon electrode (AGCE) was fabricated and applied for sensitive and selective detection of sunset yellow (SY). The electroanalysis of SY was investigated by square wave voltammetry (SWV). Owed to the specific oxygen-contained functional groups and the outstanding conductivity of AGCE, the proposed sensor exhibits an enhanced oxidation peak current of SY when compared with non-activated glass carbon electrode (GCE). Under the optimal analytical conditions, the oxidation peak current is linear with SY concentration in the range of 0.005-1.0 µM. The low limit of detection is 0.00167 µM (S/N = 3). This method is applied for the detection of SY in the actual samples. The recovery is between 96.19 and 103.47%, indicating that AGCE is suitable for the determination of SY in beverage sample.

Electrochemical Aptasensor Based on Au Nanoparticles Decorated Porous Carbon Derived from Metal-Organic Frameworks for Ultrasensitive Detection of Chloramphenicol.

A facile and sensitive electrochemical aptamer sensor (aptasensor) based on Au nanoparticles-decorated porous carbon (AuNPs/PC) composite was developed for the efficient determination of the antibiotic drug chloramphenicol (CAP). AuNPs modified metal-organic framework (AuNPs/ZIF-8) is applied as a precursor to synthesize the porous carbon with homogeneous AuNPs distribution through a direct carbonization step under nitrogen atmosphere. The as-synthesized AuNPs/PC exhibits high surface area and improved conductivity. Moreover, the loading AuNPs could enhance the attachment of the aptamers on the surface of electrode through the Au-S bond. When added to CAP, poorly conductive aptamer-CAP complexes are formed on the sensor surface, which increases the hindrance to electron transfer resulting in a decrease in electrochemical signal. Based on this mechanism, the developed CAP aptasensor represents a wide linear detection range of 0.1 pM to 100 nM with a low detection limit of 0.03 pM (S/N = 3). In addition, the proposed aptasensor was employed for the analysis of CAP in honey samples and provided satisfactory recovery.

2D Leaf-Like Structured ZIF-L Embedded Electrochemically Reduced Graphene Oxide Composite as an Electrochemical Sensing Platform for Sensitively Detecting Benomyl.

In this work, a two-dimensional leaf-like framework-L embedded electrochemically reduced graphene oxide (ERGO@ZIF-L) was proposed as an outstanding electrode material for the sensitive electrochemical sensing of benomyl (BM). ZIF-L is surrounded by ERGO, which could effectively ensure the stability and dispersion of ZIF-L. With this unique combination, the prepared ERGO@ZIF-L displayed excellent synergistic characteristics with a large surface area, excellent conductivity, plentiful active sites, and high electrocatalytic properties, thus endowing it with high sensitivity for BM determination. The experimental parameters, such as solution pH, material volume, and accumulation time, were optimized. Under optimal conditions, the BM sensor showed a wide linear range (0.009-10.0 µM) and low-limit detection (3.0 nM). Moreover, the sensor displayed excellent stability, repeatability, and reproducibility, and good anti-interference capability. The method was successfully applied to detect BM in real-world samples.

Facile Synthesis of Nitrogen Self-Doped Porous Carbon Derived from Cicada Shell via KOH Activation for Simultaneous Detection and Removal of Cu2.

Sensitive detection and efficient removal of heavy metal ions with high toxicity and mobility are of great importance for environmental monitoring and control. Although several kinds of functional materials have been reported for this purpose, their preparation processes are complicated. Herein, nitrogen self-doped activated porous biochar (NAC) was synthesized in a facile process via an activation-carbonization strategy from cicada shell rich in chitin, and subsequently employed as an effective functional material for the simultaneous determination and removal of Cu2+ from aqueous media. With its unique porous structure and abundant oxygen-containing functional groups, along with the presence of heteroatoms, NAC exhibits high sensitivity for the electrochemical sensing of Cu2+ in concentrations ranging from 0.001 to 1000 µg·L-1, with a low detection limit of 0.3 ng·L-1. Additionally, NAC presents an excellent removal efficiency of over 78%. The maximum adsorption capacity is estimated at 110.4 mg/g. These excellent performances demonstrate that NAC could serve as an efficient platform for the detection and removal of Cu2+ in real environmental areas.

MXene-AuNP-Based Electrochemical Aptasensor for Ultra-Sensitive Detection of Chloramphenicol in Honey.

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.

Ti3C2TxMXene/nitrogen-doped reduced graphene oxide composite: a high-performance electrochemical sensing platform for adrenaline detection.

Herein, Ti3C2TxMXene/N-doped reduced graphene oxide (MXene/N-rGO) composite was employed as the electrocatalyst to construct a new electrochemical sensing platform for the determination of adrenaline (AD). The MXene/N-rGO was synthesized via a facile one-step hydrothermal method, where ethylenediamine acted as a reducing agent and N source. The doped N in rGO served as a bridge between MXene and rGO through tight hydrogen bonds. Scanning electron microscopy showed that large numbers of MXenes with accordion-like morphology were distributed on the surface of the N-rGO. The MXene/N-rGO composite displayed a synergetic catalytic effect for oxidizing AD, originating from the unique catalytic activity of N-rGO and the large surface area and satisfactory conductivity of MXene. These characteristics of composite material led to a remarkable effect on signal amplification for the detection of AD, with a wide linear range from 10.0 nM to 90.0µM and a low detection limit of 3.0 nM based on a signal to noise ratio of 3. Moreover, the MXene/N-rGO electrode displayed good stability, repeatability, and reproducibility. Additionally, the proposed sensor was successfully applied for voltammetric sensing of AD in urine with recoveries from 97.75% to 103.0%.

2D leaf-like ZIF-L decorated with multi-walled carbon nanotubes as electrochemical sensing platform for sensitively detecting thiabendazole pesticide residues in fruit samples.

Excessive use of pesticides in modern agriculture results in large amounts of pesticide residues in agricultural production, greatly threatening human health. Herein, novel two-dimensional leaf-like zeolitic imidazolate framework-L decorated with multi-walled carbon nanotubes (MWCNTs/ZIF-L) was prepared by a facile solvent way and exploited as electrode material for sensitive electrochemical sensing of thiabendazole (TBZ). Two-dimensional ZIF-L presents high surface area, large pore volume, and abundant active sites, which exhibits high enrichment ability towards TBZ molecules, while the MWCNTs interspersed on ZIF-L can prominently enhance the electron transport capability and improve the electrocatalytic activity for TBZ oxidation. Due to the intriguing synergy between the components, the MWCNTs/ZIF-L-based electrochemical sensor reveals a limit of detection (LOD) of 6.0 nmol·L-1, which is lower than that reported in most literatures. Additionally, satisfactory reproducibility and repeatability, long-term stability, and excellent selectivity are acquired. The proposed method was also applied for the detection of TBZ in apple and orange samples with acceptable recoveries.

MXene/carbon nanohorns decorated with conductive molecularly imprinted poly(hydroxymethyl-3,4-ethylenedioxythiophene) for voltammetric detection of adrenaline.

A novel molecularly imprinted sensor was developed for the voltammetric determination of adrenaline (AD). MXene/carbon nanohorn (MXene/CNH) composite with good electric conductivity and enormous accessible active sites was firstly introduced as catalytic substrate. Subsequently, molecularly imprinted polymer (MIP) film was fabricated in mixed solutions containing hydroxymethyl-3,4-ethylenedioxythiophene (functional monomer) and AD (template) through electro-polymerization process. A molecularly imprinted sensor was formed after removing the template. The morphology and elemental composition of the prepared composites were studied by scanning electron microscopy and X-ray photoelectron spectroscopy. Cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS) were used to investigate the electrochemical performance of the molecularly imprinted sensors. Under optimized conditions, the designed sensor displays a wide linear range from 1.0 nM to 60.0 µM and a low limit of detection of 0.3 nM. The developed sensor also presents good selectivity, reproducibility and long-term stability, and satisfactory feasibility in practical sample analysis. MXene/carbon nanohorns decorated with conductive molecularly imprinted poly(hydroxymethyl-3,4-ethylenedioxythiophene) was proposed for highly sensitive and selective detection of adrenaline.

Label-free electrochemical immunosensor based on Nile blue A-reduced graphene oxide nanocomposites for carcinoembryonic antigen detection.

In this article, a novel, label-free, and inherent electroactive redox immunosensor for carcinoembryonic antigen (CEA) based on gold nanoparticles (AuNPs) and Nile blue A (NB) hybridized electrochemically reduced graphene oxide (NB-ERGO) is proposed. The composite of NB-graphene oxide (NB-GO) was prepared by π-π stacking interaction. Then, chronoamperometry was adopted to simultaneously reduce HAuCl4 and nanocomposites of NB-GO for synthesizing AuNPs/NB-ERGO. The immunosensor was fabricated by capturing CEA antibody (anti-CEA) at this nanocomposite modified electrode. The immunosensor determination was based on the fact that, due to the formation of antigen-antibody immunocomplex, the decreased response currents of NB were directly proportional to the concentrations of CEA. Under optimal conditions, the linear range of the proposed immunosensor was estimated to be from 0.001 to 40 ng ml(-1) and the detection limit was estimated to be 0.00045 ng ml(-1). The proposed immunosensor was used to determine CEA in clinical serum samples with satisfactory results. The proposed method may provide promising potential application in clinical immunoassays with the properties of facile procedure, stability, high sensitivity, and selectivity.