Highly sensitive electrochemical detection of paraoxon ethyl in water and fruit samples based on defect-engineered graphene nanoribbons modified electrode

Prussian Blue Nanosphere/Fe-Metal Organic Frameworks/Ce Nanocomposite as a Colorimetric Sensing Platform for Direct Detection in Organophosphorus Pesticides in Fetal Bovine Serum

Acute pesticide poisoning has resulted in several symptoms that threaten life safety. Thus, developing a rapid detection method would facilitate the identification of toxicants as soon as possible. This study presented an affordable and straightforward detection platform based on a core-shell structure nanocomposite of Prussian blue/Fe-metal-organic frameworks/Ce nanocomposite material, which exhibited peroxidase-like activity and multiple capture sites [marked as phosphate buffer (PB)/Fe-MOF/Ce NPs]. Fe3+ and Fe2+ are located at the core of PB nanoparticles (PB NPs), metal-porphyrin as a metal-organic framework (MOF) shell, and Ce NPs grown on the shell. A practical, economical, accurate, and colorimetric strategy was synthesized to detect organophosphorus pesticides directly in fetal bovine serum. The solution-based PB/Fe-MOF/Ce NP colorimetric sensor demonstrated an ultrasensitive detection performance and excellent reproducibility. The absorbance variation of dichlorvos, methamidophos, and dimethoate follows the linear equation of y = 0.093x + 0.024, y = 0.083x + 0.017, and y = 0.114x + 0.117 under a low content, and the limit of detection (LOD) of the colorimetric sensor was determined using 3s/slope, which was as low as 5.6, 4.8, and 6.5 μg/L, respectively, with the recovery rates ranging from 83.4% to 98.6% and an RSD less than 6%. This study provides an excellent method for effectively detecting acute poisoning samples and offers profound insights for further improving the treatment efficiency of pesticide poisoning, and it has excellent prospects in clinical point-of-care testing.

Recent advances in glucose monitoring utilizing oxidase electrochemical biosensors integrating carbon-based nanomaterials and smart enzyme design

Glucose oxidase (GOx), as a molecular recognition element of glucose biosensors, has high sensitivity and selectivity advantages. As a type of biosensor, the glucose oxidase electrode exhibits advantages such as ease of operation, high sensitivity, and strong specificity, promising broad application prospects in biomedical science, the food industry, and other fields. In recent years, with the advancement of nanotechnology, research efforts to enhance the performance of GOx biosensors have primarily focused on improving the conductive properties and specific surface area of nanomaterials, while neglecting the potential to modify the structure of the core component, GOx itself, to improve biosensor performance. Rapid modification of the GOx surface through chemical modification techniques yields a new modified enzyme (mGOx). Meanwhile, composite techniques involving carbon nanomaterials can be employed to further enhance sensor performance. This article reviews the construction methods and optimization strategies of glucose oxidase electrodes in recent years, along with research progress in their application in electrochemical sensing for glucose detection, and provides an outlook for future developments.

Rationally Designed Cerium-Assembled Carbon Dot Phosphatase-Like Nanozyme Hydrogel in Tandem with 5,7-Dimethoxycoumarin for Sensitive, Selective, Wide-Range, Complementary Dual-Mode Biosensing of Paraoxon

The development of a sensitive, selective, and wide-range biosensor for paraoxon detection is critically demanded due to its high toxicity and environmental prevalence. While complementary multimode biosensing platforms offer enhanced performance like high sensitivity and a wide detection range by synergizing multiple detection strategies, their implementation remains challenging because of compromised reaction compatibility. To address this, an integrated complementary colorimetric/fluorescence dual-mode biosensing platform based on a rationally designed cerium-assembled carbon dot phosphatase-like nanozyme hydrogel (Ce-CDBM) in tandem with 5,7-dimethoxycoumarin (5,7-DMC) is presented for sensitive, selective, and wide-range detection of paraoxon. The Ce-CDBM nanoarchitecture, synthesized via cerium coordination with a carbon dot derived from 2-methylimidazole and 1,2,3,4-butanetetracarboxylic acid, exhibits dual functionalities: high phosphatase-like activity and amplified fluorescence quenching capability. Ce-CDBM enables specific hydrolysis of paraoxon to generate yellow 4-nitrophenol (4-NP), achieving colorimetric paraoxon detection with a limit of detection (LOD) of 1.2 μM. Simultaneously, the formation of a highly stable nonfluorescent ternary complex (5,7-DMC/4-NP/Ce-CDBM) facilitates the highly efficient static photoinduced electron transfer, significantly amplifying fluorescence quenching for ultrasensitive paraoxon detection with a LOD of 15.4 nM. This colorimetric/fluorescence dual-mode biosensing platform overcomes the intrinsic limitations of single-signal approaches by operating under identical hydrolysis conditions while expanding the dynamic range by 3 orders of magnitude. Furthermore, a smartphone-assisted portable platform was developed for on-site visual quantification of paraoxon in cauliflower and Chinese cabbage matrices, demonstrating recoveries of 99-114% with relative standard deviations below 5%. This work establishes a paradigm for designing compatible multimode biosensors through rational nanozyme engineering and synergistic signal amplification strategies.

Preconcentration-enhanced electrochemical detection of paraoxon in food and environmental samples using reduced graphene oxide-modified disposable sensors

Organophosphates, such as paraoxon, are widely used as insecticides in agriculture, making their detection in environmental and food samples crucial due to their high toxicity. This study presents the development of an electrochemical sensor for the detection of paraoxon, using a screen-printed carbon electrode (SPCE) modified with electrochemically reduced graphene oxide (rGO). The modification enhanced the sensor's electrical conductivity and electrochemical performance. A novel preconcentration approach, involving potential pulses at -1.0 and 0.0 V, was employed to improve the adsorption of paraoxon on the electrode surface. Detection was performed by square wave voltammetry, and under optimized conditions, the rGO-SPCE sensor exhibited a linear range from 1.0 to 30 μmol L-1, with detection and quantification limits of 0.26 and 0.86 μmol L-1, respectively. The sensor demonstrated excellent repeatability (RSD = 4.22%), reproducibility (RSD = 7.14%), and selectivity (RSD < 9.22%). The method was successfully applied to tap water, grape and apple juices, and canned corn water samples, achieving recoveries of approximately 98% at the lowest concentration (1.0 μmol L-1) with minimal matrix effects. This approach offers a simple, low-cost, and rapid method for paraoxon detection in water and food samples.

Vanadium-Based Metal-Organic Frameworks with Peroxidase-like Activity as a Colorimetric Sensing Platform for Direct Detection of Organophosphorus Pesticides

Colorimetry based on the bioenzyme inhibition strategy holds promising application prospects in the field of organophosphorus pesticide (OPs) detection. However, overcoming the challenges of the high cost and low stability of bioenzymes remains crucial. In this study, we successfully synthesized a peroxidase vanadium-based metal-organic framework (MOF) nanozyme named MIL-88B(V) and employed its mediated bioenzyme-free colorimetric strategy for direct OPs detection. The experimental results demonstrated that MIL-88B(V) exhibited a remarkable affinity and a remarkable catalytic rate. When the OPs target is added, it can be anchored on the MOF surface through a V-O-P bond, effectively inhibiting the MOF's activity. Subsequently, leveraging the advantages of smartphones such as convenience, speed, and sensitivity, we developed a paper sensor integrated into a smartphone for efficient OPs detection. The as-designed nanozyme-based colorimetric assay and paper sensor presented herein offer notable advantages, including affordability, speed, stability, wide adaptability, low cost, and accuracy in detecting OPs, thus providing a versatile and promising analytical approach for real sample analysis and allowing new applications of V-based MOF nanozymes.

Recombinant Organophosphorus acid anhydrolase (OPAA) enzyme-carbon quantum dot (CQDs)-immobilized thin film biosensors for the specific detection of Ethyl Paraoxon and Methyl Parathion in water resources

Organophosphates pesticide (OP) toxicity through water resources is a large concern globally among all the emerging pollutants. Detection of OPs is a challenge which needs to be addressed considering the hazardous effects on the health of human beings. In the current research thin film biosensors of recombinant, Organophosphorus acid anhydrolase (OPAA) enzyme along with carbon quantum dots (CQDs) immobilized in thin films were developed. OPAA-CQDs thin film biosensors were used for the specific detection of two OPs Ethyl Paraoxon (EP) and Methyl Parathion (MP) in river water and household water supply. Recombinant OPAA enzyme was expressed in E. Coli, purified and immobilized on the CQD containing chitosan thin films. The CQDs used for this purpose were developed by a one-pot hydrothermal method from phthalic acid and Tri ethylene diamine. The properties of CQDs, OPAA and thin films were characterized using techniques like XPS, TEM, XRD, enzyme activity and CLSM measurements. Biosensing studies of EP and MP were performed by taking fluorescence measurements using a fiber optic spectrometer. The analytical parameters of biosensing were compared against an estimation carried out using the HPLC method. The biosensing performance indicates that the OPAA-CQDs thin film-based biosensors were able to detect both EP and MP in a range of 0-100 μM having a detection limit of 0.18 ppm/0.69 ppm for EP/MP, respectively with a response time of 5 min. The accuracy of estimation of EP/MP when spiked in water resources lie in the range of ∼100-102% which clearly indicates the OPAA-CQD based thin film biosensors can function as a point-of-use method for the detection of OP pesticides in complex water resources.

Electrochemical Sensors based on Gold-Silver Core-Shell Nanoparticles Combined with a Graphene/PEDOT:PSS Composite Modified Glassy Carbon Electrode for Paraoxon-ethyl Detection

Herein, a nonenzymatic detection of paraoxon-ethyl was developed by modifying a glassy carbon electrode (GCE) with gold-silver core-shell (Au-Ag) nanoparticles combined with the composite of graphene with poly(3,4-ethylenedioxythiophene)/poly(styrenesulfonate) (PEDOT:PSS). These core-shell nanoparticles (Au-Ag) were synthesized using a seed-growth method and characterized using UV-vis spectroscopy and high-resolution transmission electron microscopy (HR-TEM) techniques. Meanwhile, the structural properties, surface morphology and topography, and electrochemical characterization of the composite of Au-Ag core-shell/graphene/PEDOT:PSS were analyzed using infrared spectroscopy, field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and electrochemical impedance spectroscopy (EIS) techniques. Moreover, the proposed sensor for paraoxon-ethyl detection based on Au-Ag core-shell/graphene/PEDOT:PSS modified GCE demonstrates good electrochemical and electroanalytical performance when investigated with cyclic voltammetry (CV), differential pulse voltammetry (DPV), and chronoamperometry techniques. It was found that the synergistic effect between Au-Ag core-shell nanoparticles and the composite of graphene/PEDOT:PSS provides a higher conductivity and enhanced electrocatalytic activity for paraoxon-ethyl detection at an optimum pH of 7. At pH 7, the proposed sensor for paraoxon-ethyl detection shows a linear range of concentrations from 0.2 to 100 μM with a limit of detection of 10 nM and high sensitivity of 3.24 μA μM-1 cm-2. In addition, the proposed sensor for paraoxon-ethyl confirmed good reproducibility, with the possibility of being further developed as a disposable electrode. This sensor also displayed good selectivity in the presence of several interfering species such as diazinon, carbaryl, ascorbic acid, glucose, nitrite, sodium bicarbonate, and magnesium sulfate. For practical applications, this proposed sensor was employed for the determination of paraoxon-ethyl in real samples (fruits and vegetables) and showed no significant difference from the standard spectrophotometric technique. In conclusion, this proposed sensor might have a potential to be developed as a platform of electrochemical sensors for pesticide detection.

Liquid crystal-based sensor for real-time detection of paraoxon pesticides based on acetylcholinesterase enzyme inhibition

A liquid crystal-based assay (LC) was developed to monitor paraoxon by incorporating a Cu²⁺ -coated substrate and the inhibitory effect of paraoxon with acetylcholinesterase (AChE). We observed that thiocholine (TCh), a hydrolysate of AChE and acetylthiocholine (ATCh), interfered with the alignment of 5CB films through a reaction between Cu²⁺ ions and the thiol moiety of TCh. The catalytic activity of AChE was inhibited in the presence of paraoxon due to the irreversible interaction between TCh and paraoxon; consequently, no TCh molecule was available to interact with Cu²⁺ on the surface. This resulted in a homeotropic alignment of the liquid crystal. The proposed sensor platform sensitively quantified paraoxon with a detection limit of 2.20 ± 0.11 (n = 3) nM within a range of 6 to 500 nM. The specificity and reliability of the assay were verified by measuring paraoxon in the presence of various suspected interfering substances and spiked samples. As a result, the sensor based on LC can potentially be used as a screening tool for accurate evaluation of paraoxon and other organophosphorus compounds.

Design and fabrication of new anticancer sensor for monitoring of daunorubicin using 1-methyl-3-octylimidazolinium chloride and tin oxide/nitrogen-doped graphene quantum dot nanocomposite electrochemical sensor

In this study, a novel tin oxide/nitrogen-doped graphene quantum dot nanocomposite (SnO₂-NDGQD) and 1-methyl-3-octylimidazolinium chloride (1M3OICl) ionic liquid amplified carbon paste electrode (CPE) was fabricated as an efficient and fast-response sensor to determine daunorubicin, an anticancer drug. The electrochemical characteristics of daunorubicin at the surface of the 1M3OICl/SnO₂-NDGQD/CPE was explored via various voltammetric methods. The high-resolution transmission electron microscope (HR-TEM) images were recorded to examine the morphological structure of the as-synthesized nanocomposites. The 1M3OICl/SnO₂-NDGQD/CPE offered a wide linear concentration of 0.001-280.0 μM with a low detection limit of 0.40 nM at the optimized experimental conditions using square wave voltammetric (SWV) method. In a nutshell, the developed electrode illustrated outstanding selectivity in the presence of interfering agents and long-term stability. The1M3OICl/SnO₂-NDGQD/CPE was used as new and powerful analytical tool for determination of daunorubicin in real samples with recovery range 98.75%-104.8%.