Nanoporous Gold-Modified Screen-Printed Electrodes for the Simultaneous Determination of Pb2+ and Cu2+ in Water.

In this study, nanoporous gold (NPG) was deposited on a screen-printed carbon electrode (SPCE) by the dynamic hydrogen bubble template (DHBT) method to prepare an electrochemical sensor for the simultaneous determination of Pb2+ and Cu2+ by square wave anodic stripping voltammetry (SWASV). The electrodeposition potential and electrodeposition time for NPG/SPCE preparation were investigated thoroughly. Scanning electron microscopy (SEM) and energy-dispersive X-ray diffraction (EDX) analysis confirmed successful fabrication of the NPG-modified electrode. Electrochemical characterization exhibits its superior electron transfer ability compared with bare and nanogold-modified electrodes. After a comprehensive optimization, Pb2+ and Cu2+ were simultaneously determined with linear range of 1-100 µg/L for Pb2+ and 10-100 µg/L for Cu2+, respectively. The limits of detection were determined to be 0.4 µg/L and 5.4 µg/L for Pb2+ and Cu2+, respectively. This method offers a broad linear detection range, a low detection limit, and good reliability for heavy metal determination in drinking water. These results suggest that NPG/SPCE holds great promise in environmental and food applications.

Cellulose acetate-coated capacitive sensor for determining carbon-cycle enzymes activity and as a microbial Indicator for soil health.

This study demonstrates cellulose acetate (CA)-coated screen-printed carbon electrodes (SPCEs) for soil microbial activity detection. A capacitive sensor design utilizes a coated CA layer for effective insulation in electrolytes, eliminating the need for additional signal protection. Optimization involved comparing spin and dip coating methods, with a one-layer 10-second dip coating identified as the best balance between quality and yield. These CA/SPCEs exhibited remarkable stability over a month, suggesting their potential for long-term use in monitoring agricultural soils. Analysis of CA/SPCE profile and thickness provided insights into surface characteristics and the impact of the CA coating on electrode roughness. ATR-FTIR analysis, along with capacitive sensing, demonstrated superior sensitivity and precision for monitoring CA film degradation compared to mechanical gauges. Chemical degradation studies suggest CA's potential immunity in near-neutral environments, while enzymatic degradation investigations revealed dominance by enzymes, particularly in the initial stages. The CA/SPCE sensor responds to both enzymatic and chemical degradation, potentially serving as an indicator of total soil microbial activity. Soil experiments explored CA/SPCE with Cap-S for microbial activity sensing. Significant differences in the long-term degradation rate were observed in mycorrhizal fungi-enriched soil compared to controls, highlighting microbial influences. This study underscores the adaptability and versatility of this technology, particularly for assessing C-cycle microbial activity in agricultural fields.

One-pot electrochemical detection of foodborne pathogen based on in situ nucleic acid amplification and wash-free assay.

A signal amplification electrochemical biosensor chip was developed to integrate loop-mediated isothermal amplification (LAMP) based on in situ nucleic acid amplification and methyl blue (MB) serving as the hybridization redox indicator for sensitive and selective foodborne pathogen detection without a washing step. The electrochemical biosensor chip was designed by a screen-printed carbon electrode modified with gold nanoparticles (Au NPs) and covered with polydimethylsiloxane membrane to form a microcell. The primers of the target were immobilized on the Au NPs by covalent attachment for in situ amplification. The electroactive MB was used as the electrochemical signal reporter and embedded into the double-stranded DNA (dsDNA) amplicons generated by LAMP. Differential pulse voltammetry was introduced to survey the dsDNA hybridization with MB, which differentiates the specifically electrode-unbound and -bound labels without a washing step. Pyrene as the back-filling agent can further improve response signaling by reducing non-specific adsorption. This method is operationally simple, specific, and effective. The biosensor showed a detection linear range of 102-107 CFU mL-1 with the limit of detection of 17.7 CFU mL-1 within 40 min. This method showed promise for on-site testing of foodborne pathogens and could be integrated into an all-in-one device.

Fabrication of Strontium Molybdate with Functionalized Carbon Nanotubes for Electrochemical Determination of Antipyretic Drug-Acetaminophen.

In recent years, there has been a significant interest in the advancement of electrochemical sensing platforms to detect antipyretic drugs with high sensitivity and selectivity. The electrochemical determination of acetaminophen (PCT) was studied with strontium molybdate with a functionalized carbon nanotube (SrMoO4@f-CNF) nanocomposite. The SrMoO4@f-CNF nanocomposite was produced by a facial hydrothermal followed by sonochemical treatment, resulting in a significant enhancement in the PCT determination. The sonochemical process was applied to incorporate SrMoO4 nanoparticles over f-CNF, enabling a network-like structure. Moreover, the produced SrMoO4@f-CNF composite structural, morphological, and spectroscopic properties were confirmed with XRD, TEM, and XPS characterizations. The synergistic effect between SrMoO4 and f-CNF contributes to the lowering of the charge transfer resistance (Rct=85 Ω·cm2), a redox potential of Epc=0.15 V and Epa=0.30 V (vs. Ag/AgCl), and a significant limit of detection (1.2 nM) with a wide response range of 0.01-28.48 µM towards the PCT determination. The proposed SrMoO4@f-CNF sensor was studied with differential pulse voltammetry (DPV) and cyclic voltammetry (CV) techniques and demonstrated remarkable electrochemical properties with a good recovery range in real-sample analysis.

Contributing to the management of viral infections through simple immunosensing of the arachidonic acid serum level.

A trendsetting direct competitive-based biosensing tool has been developed and implemented for the determination of the polyunsaturated fatty acid arachidonic acid (ARA), a highly significant biological regulator with decisive roles in viral infections. The designed methodology involves a competitive reaction between the target endogenous ARA and a biotin-ARA competitor for the recognition sites of anti-ARA antibodies covalently attached to the surface of carboxylic acid-coated magnetic microbeads (HOOC-MµBs), followed by the enzymatic label of the biotin-ARA residues with streptavidin-horseradish peroxidase (Strep-HRP) conjugate. The resulting bioconjugates were magnetically trapped onto the sensing surface of disposable screen-printed carbon transducers (SPCEs) to monitor the extent of the biorecognition reaction through amperometry. The operational functioning of the exhaustively optimized and characterized immunosensing bioplatform was highly convenient for the quantitative determination of ARA in serum samples from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2-) and respiratory syncytial virus (RSV)-infected individuals in a rapid, affordable, trustful, and sensitive manner.

4-Ethylphenyl Sulfate Detection by an Electrochemical Sensor Based on a MoS2 Nanosheet-Modified Molecularly Imprinted Biopolymer.

One of the gut-derived uremic toxins 4-ethylphenyl sulfate (4-EPS) exhibits significantly elevated plasma levels in chronic kidney diseases and autism, and its early quantification in bodily fluids is important. Therefore, the development of rapid and sensitive technologies for 4-EPS detection is of significant importance for clinical diagnosis. In the current work, the synthesis of a molecularly imprinted biopolymer (MIBP) carrying 4-EPS specific cavities only using the biopolymer polydopamine (PDA) and molybdenum disulfide (MoS2) nanosheets has been reported. The fabricated electrode was prepared using screen-printed carbon electrodes on a polyvinyl chloride substrate. The synthesized material was characterized using several techniques, and electrochemical studies were performed using cyclic voltammetry (CV) and differential pulse voltammetry (DPV) techniques. The DPV technique for the electrochemical sensing of 4-EPS using the fabricated sensor (PDA@MoS2-MIBP) determined a sensitivity of 0.012 µA/ng mL/cm2 and a limit of detection of 30 ng/mL in a broad linear range of 1-2200 ng/mL. Also, the interferent study was performed to evaluate the selectivity of the fabricated sensor along with the control and stability study. Moreover, the performance of the sensor was evaluated in the spiked urine sample, and a comparison was made with the data obtained by ultraperformance liquid chromatography-tandem mass spectroscopy.

Thiol-based chemically modified carbon screen-printed electrode for simultaneous quantification of trace level Pb(II) and Cd(II).

Present work reports, the development of a novel electrochemical sensor based on a diazonium-coupling reaction and covalent attachment of the -NH2 group of cysteamine (Cyst) on screen-printed carbon electrode (SPCE), for simultaneous determination of Pb(II) and Cd(II). Initially, the in-situ generated 4-carboxyphenyl (4-CP) diazonium salt was electro-grafted to generate 4-CP/SPCE, followed by covalent bonding of terminal carboxylic group of 4-CP with -NH2 group of Cyst to give Cyst/4-CP/SPCE. The modified electrode showed an enhanced selectivity and sensitivity toward the quantification of Pb(II) and Cd(II) using square wave anodic stripping voltammetry (SWASV) without mutual interference. Under optimal experimental conditions, the newly designed sensor showed a wide linear range of 0.01 µM to 0.7 µM. The limit of detection (LOD) obtained was 0.882 nM (0.09 ppb) and 0.65 nM (0.134 ppb) for Cd(II) and Pb(II), respectively. The modified SPCE exhibited good stability, selectivity, and reproducibility. Furthermore, the sensor was successfully applied for the determination of Pb(II) and Cd(II) ions in water samples which illustrated excellent recoveries in different spiked samples and the results were in line with the standard ICP-AES analysis.

Cytochrome c electrochemical detection utilizing molecularly imprinted poly(3, 4-ethylenedioxythiophene) on a disposable screen printed carbon electrode.

Cytochrome c (cyt c) has been found to play a function in apoptosis in cell-free models. This work presents the creation of molecularly imprinted conducting poly(3, 4-ethylenedioxythiopene) (MIPEDOT) on the surface of a screen printed carbon electrode (SPCE) for cyt c. Cyt c was imprinted by electropolymerization due to the presence of an EDOT monomer hydrophobic functional group on SPCE, using CV to obtain highly selective materials with excellent molecular recognition ability. MIPEDOT was characterized by CV, EIS, and DPV using ferricyanide/ferrocyanide as a redox probe. Further, the characterization of the sensor was accomplished using SEM for surface morphological confirmation. Using CV, the peak current measured at the potential of +1 to -1 V (vs. Ag/AgCl) is linear in the cyt c concentration range from 1 to 1200 pM, showing a remarkably low detection limit of 0.5 pM (sensitivity:0.080 µA pM). Moreover, the applicability of the approach was successfully confirmed with the detection of cyt c in biological samples (human plasma). Similarly, our research has proven a low-cost, simple, and efficient sensing platform for cyt c detection, rendering it a viable tool for the future improvement of reliable and exact non-encroaching cell death detection.

Nitrocellulose/acrylic resin coated screen-printed carbon electrode to construct a capacitive immunosensor for anti-BSA.

The capacitive immunosensor, known for its label-free simplicity, has great potential for point-of-care diagnostics. However, the interaction between insulation and recognition layers on the sensing electrode greatly affects its performance. This study introduces a pioneering dual-layer strategy, implementing a novel combination of acrylic resin (AR) and nitrocellulose (NC) coatings on screen-printed carbon electrodes (SPCEs). This innovative approach not only enhances the dielectric properties of the capacitive sensor but also streamlines the immobilization of recognizing elements. Particularly noteworthy is the superior reliability and insulation offered by the AR coating, surpassing the limitations of traditional self-assembled monolayer (SAM) modifications. This dual-layer methodology establishes a robust foundation for constructing capacitive sensors optimized specifically for liquid medium-based biosensing applications. The NC coating in this study represents a breakthrough in effectively immobilizing BSA, unraveling the capacitive response intricately linked to the quantity of adsorbed recognizing elements. The results underscore the prowess of the proposed immunosensor, showcasing a meticulously defined linear calibration curve for anti-BSA (ranging from 0 to 25 µg/ml). Additionally, specific interactions with anti-HAS and anti-TNF-α further validate the versatility and efficacy of the developed immunosensor. This work presents a streamlined and highly efficient protocol for developing label-free immunosensors for antibody determination and introduces a paradigm shift by utilizing readily available electrodes and sensing systems. The findings are poised to catalyze a significant acceleration in the advancement of biosensor technology, opening new avenues for innovative applications in point-of-care diagnostics.

Electrospun EU/HPMC nanofibers decorated by ZIF-8 nanoparticle as the advanced electrochemical biosensor modifier for sensitive and selective detection of c-MET cancer biomarker in human plasma sample.

This research presents a selective and sensitive electrochemical biosensor for the detection of the mesenchymal-epithelial transition factor (c-MET). The biosensing is based on a modification of the SPCE (screen-printed carbon electrode) with the electrospun nanofiber containing eudragit (EU), hydroxypropyl methylcellulose (HPMC), and Zeolite imidazolate frameworks (ZIF-8) nanoparticles. EU/HPMC/ZIF-8 nanofibers have presented a high capability of electron transfer, and more active surface area than bare SPCE due to synergistic effects between EU, HPMC, and ZIF-8. On the other hand, EU/HPMC nanofibers provided high porosity, flexible structures, high specific surface area, and good mechanical strength. The presence of ZIF-8 nanoparticles improved the immobilization of anti-c-MET on the modified SPCE and also resulted in increasing the conductivity. By c-MET incubation on the modified SPCE, c-MET was connected to anti-c-MET, and consequently the electrochemical signal of [Fe(CN)6]3-/4- as the anion redox probe was reduced. In order to investigate the structural and morphological characteristics and elemental composition of electrospun nanofibers, various characterization methods including FE-SEM, XRD, FTIR, and EDS were used. Under optimum conditions with a working potential range -0.3-0.6 V (vs. Ag/AgCl), linear range (LR), correlation coefficient (R2), sensitivity, and limit of detection (LOD) were acquired at 100 fg/mL-100 ng/mL, 0.9985, 53.28 µA/cm2.dec, and 1.28 fg/mL, respectively. Moreover, the mentioned biosensor was investigated in a human plasma sample to determine c-MET and showed ideal results including reproducibility, stability, and good selectivity against other proteins.

Portable wireless electrochemical sensing of breviscapine using core-shell ZIFs-derived Co nanoparticles embedded in N-doped carbon nanotube polyhedra-modified electrode.

A core-shell ZIF-67@ZIF-8-derived Co nanoparticles embedded in N-doped carbon nanotube polyhedra (Co/C-NCNP) hybrid nanostructure was prepared by a pyrolysis method. The synthesized Co/C-NCNP was modified on the screen-printed carbon electrode and used for the portable wireless sensitive determination of breviscapine (BVC) by differential pulse voltammetry. The Co/C-NCNP had a large surface area and excellent catalytic activity with increasing Co sites to combine with BVC for selective determination, which led to the improvement of the sensitivity of the electrochemical sensor. Under optimized conditions, the constructed sensor had linear ranges from 0.15 to 20.0 µmol/L and 20.0 to 100.0 µmol/L with the limit of detection of 0.014 µmol/L (3S0/S). The sensor was successfully applied to BVC tablet sample analysis with satisfactory results. This work provided the potential applications of zeolitic imidazolate framework-derived nanomaterials in the fabrication of electrochemical sensors for the sensitive detection of drug samples.

The High Stability and Selectivity of Electrochemical Sensor Using Low-Cost Diamond Nanoparticles for the Detection of Anti-Cancer Drug Flutamide in Environmental Samples.

In this study, a novel electrochemical sensor was created by fabricating a screen-printed carbon electrode with diamond nanoparticles (DNPs/SPCE). The successful development of the sensor enabled the specific detection of the anti-cancer drug flutamide (FLT). The DNPs/SPCE demonstrated excellent conductivity, remarkable electrocatalytic activity, and swift electron transfer, all of which contribute to the advantageous monitoring of FLT. These qualities are critical for monitoring FLT levels in environmental samples. Various structural and morphological characterization techniques were employed to validate the formation of the DNPs. Remarkably, the electrochemical sensor demonstrated a wide linear response range (0.025 to 606.65 µM). Additionally, it showed a low limit of detection (0.023 µM) and high sensitivity (0.403 µA µM-1 cm-2). Furthermore, the practicability of DNPs/SPCE can be successfully employed in FLT monitoring in water bodies (pond water and river water samples) with satisfactory recoveries.

A Portable Electrochemical Dopamine Detector Using a Fish Scale-Derived Graphitized Carbon-Modified Screen-Printed Carbon Electrode.

In this paper, a highly conductive alkali-activated graphitized carbon (a-GC) was prepared using tilapia fish scales as precursors through enzymolysis, activation and pyrolytic carbonization methods. The prepared a-GC was modified on the surface of a screen-printed carbon electrode to construct a flexible portable electrochemical sensing platform, which was applied to the differential pulse voltametric detection of dopamine (DA) using a U-disk electrochemical workstation combined with a smart phone and Bluetooth. The prepared a-GC possesses good electrical conductivity, a large specific surface area and abundant active sites, which are beneficial for the electrooxidation of DA molecules and result in excellent sensitivity and high selectivity for DA analysis. Under the optimal conditions, the oxidation peak current of DA increased gradually, with its concentrations in the range from 1.0 µmol/L to 1000.0 µmol/L, with the detection limit as low as 0.25 µmol/L (3S/N). The proposed sensor was further applied to the determination of DA in human sweat samples, with satisfactory results, which provided an opportunity for developing noninvasive early diagnosis and nursing equipment.

Electrochemical determination of riboflavin in pharmaceuticals using unmodified screen printed carbon electrodes.

In this study, we have devised an efficient and rapid approach to detect riboflavin (also known as Vitamin B2 or VB2) utilizing an unaltered screen-printed carbon electrode (SPCE). The unmodified screen-printed electrodes are created within the laboratory, where carbon ink is applied to a ceramic substrate. All experiments pertaining to the investigation of electrochemical behavior and the fine-tuning of crucial experimental parameters were conducted through cyclic voltammetry (CV). For quantitative assessments, square wave voltammetry (SWV) was employed. The findings indicate that unaltered SPCEs exhibit robust current signals during the riboflavin redox reaction. Riboflavin displays a distinct oxidation peak at - 0.136 V (vs. Ag/AgCl, 3.0 M KCl) in a Britton-Robinson buffer solution (BRBS) at pH 2, which was employed for quantification. The electrode demonstrates a broad linear range from 0.05 to 10 µM, boasting a detection limit of 0.03 µM. Repeatability stands at 1.45%, while reproducibility is 6.61%. Testing the influence of common interfering compounds yielded negligible results. The sensor effectively determines riboflavin content in pharmaceutical formulations without any prior treatment. This method presents an economical, modifier-free sensor with exceptional sensitivity and cost-effectiveness, making it suitable for rapid riboflavin quantification.

Modified exfoliated graphene functionalized with carboxylic acid-group and thionine on a screen-printed carbon electrode as a platform for an electrochemical enzyme immunosensor.

An enzyme immunoassay was developed based on the coulometric measurement of immunoglobulin M (IgM) against Hantaan viruses (HTNV) by using virus-like particles (VLPs) as recognition molecules. The surface functionalization of screen-printed carbon electrodes (SPCEs) was achieved through paste-exfoliated graphene that was modified with a COOH group and a thionine mediator through supramolecular-covalent scaffolds, on SPCEs by using the binder contained in the ink. After the covalent immobilization of the antibody, the sensor was used for the sandwich enzyme immunoassay of IgM against HTNV. By using HTNV VLPs as the second recognization molecules, the resulting sensor efficiently monitored the reaction of IgM against HTNV and anti-IgM antibody with high specificity. By attaching HTNV nucleocapsid protein antibody conjugate with horseradish peroxidase (HRP) onto VLPs, the signal response of the assay was derived from the coulometric measurement of H2O2 reduction mediated by thionine on the electrode surface after the application of a potential (- 0.2 V vs. Ag/AgCl). The ratio of charges measured before or after H2O2 addition was used to quantify IgM because these charges could be used as background charges or total charges, respectively. The ratio exhibited good agreement with IgM concentration within a range 0.1 to 1000 pg mL-1, and a detection limit of 0.06 pg mL-1 was obtained. The assay demonstrated high sensitivity and specificity toward HTNV-specific IgM in serum.

Screen-Printed Carbon Electrode Modified with Carbon Nanotubes and Copper Film as a Simple Tool for Determination of Trace Concentrations of Lead Ions.

A copper film-modified, carboxyl-functionalized, and multi-walled carbon nanotube (MWCNT-COOH)-modified screen-printed carbon electrode (CuF/MWCNTs/SPCE) was used for lead determination using anodic stripping voltammetry. The main parameters were investigated and optimized during the development of the research procedure. The most optimal electrolyte concentrations were determined to be 0.4 M HCl and 6.3 × 10-5 M Cu(II). The optimal parameters for voltammetric stripping measurements are as follows: an accumulation potential of -0.7 V; an accumulation time of 120 s; and a pulse amplitude and pulse time of 120 mV and 2 ms, respectively. The effect of surface active substances and humic substances as potential interferents present in aqueous environmental samples was investigated. The validation of the procedure was carried out using certified reference materials, like waste water SPS-WW1 and environmental matrix TM-25.5. In addition, the developed procedure was applied to investigate lead recovery from natural environmental water, such as rivers and lakes.

A toluidine blue/porous organic polymer/2D MoSe2 nanocomposite as an electrochemical signaling platform for a sensitive label-free aflatoxin B1 bioassay in some crops.

A label-free electrochemical immunosensor using a toluidine blue (TB)/porous organic polymer (POP)/two-dimensional molybdenum diselenide (2D MoSe2) nanocomposite is developed for highly sensitive detection of aflatoxin B1 (AFB1) in selected crops. A POP/2D MoSe2 composite material is employed to modify the surface of a screen-printed carbon electrode (SPCE). Subsequently, TB is adsorbed on the modified SPCE surface, and the resulting TB/POP/2D MoSe2 composite is then used to construct a biosensor. The new POP/2D MoSe2 nanocomposite offers a high surface-to-volume area and is a good electroactive and biocompatible adsorbent for loading TB probe and capture antibodies. Adsorbed TB onto the POP/2D MoSe2 nanocomposite is utilized as a redox probe for the signal amplification unit. This TB/POP/2D MoSe2 nanocomposite provides good electron transfer properties of TB redox probe, good electrical conductivity, good biocompatibility, and likable adsorption ability, thus obtaining a sufficient immobilization quantity of antibodies for the sensor construction. After immobilization of the anti-AFB1 antibody and blocking with BSA on the composite surface, the immunosensor is obtained for the detection of AFB1. Under optimum conditions, the sensor shows a linear logarithmic range of 2.5-40 ng mL-1 with a limit of detection (LOD) of 0.40 ng mL-1. The developed sensor provides several advantages in terms of simplicity, low cost, short analysis time, high selectivity, stability, and reproducibility. Additionally, the proposed immunosensor is successfully validated by the detection of AFB1 in rice, corn, and peanut samples. Utilizing the TB/POP/2D MoSe2 nanocomposite, this label-free electrochemical immunosensor demonstrates outstanding sensitivity and selectivity in detecting AFB1, making it a valuable tool for ensuring the safety of agricultural products and enhancing food security.

Application of Ag nanoparticles decorated on graphene nanosheets for electrochemical sensing of CEA as an important cancer biomarker.

In this research, a novel biosensing platform is described based on graphene nano-sheets decorated with Ag nano-particles (GNSs@Ag NPs). The designed electrochemical aptasensor was employed to determine carcinoembryonic antigen (CEA), an important cancer biomarker. Inherently, aptasensing interfaces provide high sensitivity for CEA tumor marker because of the high specific surface area and excellent conductivity of the prepared GNSs@Ag NPs composite. The established assay demonstrated a wide linear range from 0.001 pg/mL to 10 pg/mL with a correlation coefficient of 0.9958 and low detection limit (DL) of 0.5 fg/mL based on S/N = 3 protocol. The derived biosensor illustrated acceptable selectivity towards common interfering species including HER2, VEGF, IgG, MUC1 and CFP10. In addition, the aptsensor showed good reproducibility and fast response time. The applicability of the suggested strategy in human serum samples was also examined and compared to the commercial enzyme-linked immunosorbent assay (ELISA). Based on the experimental data, it was found that the discussed sensing platform can be exerted in the monitoring of CEA in different cancers for early diagnosis.

Electrochemical Sensing Platform Based on Carbon Dots for the Simultaneous Determination of Theophylline and Caffeine in Tea.

A simple and selective method for the determination of caffeine (CAF) and theophylline (THEO) has been developed for a glassy carbon electrode (GCE) modified with a composite including carbon dots (CDs) and chitosan (CS). To our knowledge, there are no previous studies that analyze a CDs-modified GCE for the presence of CAF and THEO. The electrochemical behavior of a GCE modified with a CDs-CS composite was studied in acidic medium by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). Considering the sensor analytical parameters, the same linear concentrations range was found for CAF and THEO ranging from 1 × 10-5 to 5 × 10-3 mol L-1 with the same detection limit (LOD) of 1 × 10-6 mol L-1. The reproducibility and repeatability data were satisfactory in terms of RSD%. Moreover, the storage stability was evaluated, evidencing good results whatever the experimental conditions used. The developed sensor was applied for the simultaneous determination of CAF and THEO in tea and drug, and results were compared with those obtained with HPLC-ESI-MS in SIR mode as an independent method optimized on purpose. The electrochemical sensor presents the undoubled advantages in terms of cheapness, portability, and ease of use, since it does not require skilled personnel.

A Highly Sensitive Electrochemical Sensor for Capsaicinoids and Its Application in the Identification of Illegal Cooking Oil.

Capsaicinoids, mostly from chili peppers, are widely used in daily life. Capsaicinoids are considered to be markers for the identification of illegal cooking oil (ICO), which is a serious threat to public health. The identification of capsaicinoids can help reveal food-related fraud, thereby safeguarding consumers' health. Here, a novel and ultrasensitive method was established with a signal amplification strategy for the detection of capsaicinoids. AuNPs@Fe3O4 nanocomposites were functionalized with 4-aminothiophenol (4-atp). After diazotization, 4-atp on AuNPs@Fe3O4 reacted with capsaicinoids and formed capsaicinoids-azo-atp-AuNPs@Fe3O4. Ultimately, capsaicinoids-azo-atp-AuNPs@Fe3O4 was dropped onto the surface of a screen-printed carbon electrode (SPCE) and detected via the differential pulse voltammetry (DPV) method. AuNPs@Fe3O4 nanocomposites increased the specific surface area of the electrode. Moreover, the diazotization-coupling reaction enriched the analytes on the electrode surface. Liquid-liquid extraction was used for sample pretreatment. Under a pH value of 9.0 and concentration of 0.20 mol/L for the supporting electrolyte, the linearity of capsaicinoids in ICO is from 0.10 to 10.00 ng/mL, and the limit of detection (S/N = 3) is 0.05 ng/mL. This method is ultra-sensitive, reliable, and cost-effective for the detection of capsaicinoids. Herein, this method provides a promising tool for the identification of ICO.