Direct preparation of well-dispersed graphene/gold nanorod composites and their application in electrochemical sensors for determination of ractopamine

Advancements in Mercury-Free Electrochemical Sensors for Iron Detection: A Decade of Progress in Electrode Materials and Modifications

Efforts to quantify iron ion concentrations across fields such as environmental, chemical, health, and food sciences have intensified over the past decade, which drives advancements in analytical methods, particularly electrochemical sensors known for their simplicity, portability, and reliability. The development of electrochemical methods using non-mercury electrodes is increasing as alternatives to environmentally unsafe mercury-based electrodes. However, detecting iron species such as Fe(II) and Fe(III) remains challenging due to their distinct chemical properties, continuous oxidation-state interconversion, presence of interfering species, and complex behavior in diverse environments and matrixes. Selective trace detection demands careful optimization of electrochemical methods, including proper electrode materials selection, electrode surface modifications, operating conditions, and sample pretreatments. This review critically evaluates advancements over the past decade in mercury-free electrode materials and surface modification strategies for iron detection. Strategies include incorporating a variety of nanomaterials, composites, conducting polymers, membranes, and iron-selective ligands to improve sensitivity, selectivity, and performance. Despite advancements, achieving ultra-low detection limits in real-world samples with minimal interference remains challenging and emphasizes the need for enhanced sample pretreatment. This review identifies challenges, knowledge gaps, and future directions and paves the way for advanced iron electrochemical sensors for environmental monitoring, health diagnostics, and analytical precision.

Recent advances in surface modified gold nanorods and their improved sensing performance

Gold nanorods (AuNRs) have received tremendous attention recently in the fields of sensing and detection applications due to their unique characteristic of surface plasmon resonance. Surface modification of the AuNRs is a necessary path to effectively utilize their properties for these applications. In this Article, we have focused both on demonstrating the recent advances in methods for surface functionalization of AuNRs as well as their use for improved sensing performance using various techniques. The main surface modification methods discussed include ligand exchange with the assistance of a thiol-group, the layer by layer assembly method, and depositing inorganic materials with the desired surface and morphology. Covered techniques that can then be applied for using these functionalized AuNRs include colourimetric sensing, refractive index sensing and surface enhance Raman scattering sensing. Finally, the outlook on the future development of surface modified AuNRs for improved sensing performance is considered.

Biochar-supported Cu nanocluster as an electrochemical ultrasensitive interface for ractopamine sensing

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Carbon confined Cu nanoclusters (CuNCs@CNFs) were fabricated for the enhanced sensing performance of ractopamine (RAC).

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The CuNCs@CNFs expressed ultrasensitivity and high selectivity in the electrochemical detection of RAC.

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A wide linear range and low LOD of RAC was obtained using CuNCs@CNFs based RAC sensor.

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The established RAC sensor was successfully used in sensitive detection of RAC in meat samples.

Electrochemical sensors actually involve an electrocatalytic process involving an efficient and selective energy conversion that is related to the morphology and size of the interface of the modified materials. Ultrasmall nanoclusters or single atoms generate a greater catalytic ability than normal nanomaterials. In this study biochar-supported Cu nanoclusters (CuNCs@CNFs) were fabricated via a carbon confinement synthesis method toward ultrasensitive electrochemical sensing of ractopamine (RAC). RAC is a β-adrenergic receptor agonist that is illegally used as a feed additive to significantly improve muscle accretion, resulting in RAC accumulation in meat-based food products. The unique structure of CuNCs@CNFs and the interconnectivity between the CuNCs and the CNFs enable the nanocomposite to significantly enhance conductivity and electrocatalytic activity. Using the CuNCs@CNFs-based sensor, RAC was determined with a high sensitivity of 1641 μA μM⁻¹ cm⁻². The feasibility of detecting RAC in spiked meat samples was also carried out with satisfactory recoveries ranging from 91.39 % to 94.58 %.

Nanoarchitectonics of graphene based sensors for food safety monitoring

Since the desire for the real-time food quality monitoring, plenty of research effort has been made to develop novel tools and to offer extremely efficient detection of food contaminants. Unique electrical, mechanical, and thermal properties make graphene an important material in the field of sensor research. The material can be manufactured into flakes, sheets, films and with its oxidized derivatives could be almost used for a limitless set of application. Herein, current graphene-based sensors for food quality monitoring, novel designs, sensing mechanisms and elements of sensor systems and potential challenges will be outlined and discussed.

Titanium nanoparticle anchored functionalized MWCNTs for electrochemical detection of ractopamine in porcine samples with ultrahigh sensitivity

We develop a disposable electrochemical sensor using a titanium nanoparticles (Ti NPs)-anchored functionalized multi-walled carbon nanotube (Ti@f-MWCNTs) composite as electrochemical sensing interface for the detection of ractopamine (RAC). The sensor demonstrated superior electrochemical sensing ability with a broad linear response range (0.01-185 μM) and ultralow detection limit (0.0038 µM). In addition, the stability, repeatability, reproducibility, and anti-interference ability of the Ti@f-MWCNTs sensor were satisfactory. The practicability of the sensor was effectively employed for the determination of RAC in porcine samples including pork, pig urine, and pig serum with substantial recoveries in the range of 92%-99% and a relative standard deviation of less than 5%.

Advances of Drugs Electroanalysis Based on Direct Electrochemical Redox on Electrodes: A Review

The strong development of mankind is inseparable from the proper use of drugs, and the electroanalytical research of drugs occupies an important position in the field of analytical chemistry. This review mainly elaborates the research progress of drugs electroanalysis based on direct electrochemical redox on various electrodes for the recent decade from 2011 to 2021. At first, we summarize some frequently used electrochemical data processing and electrochemical mechanism research derivation methods in the literature. Then, according to the drug therapeutic and application/usage purposes, the research progress of drugs electrochemical analysis is classified and discussed, where we focus on drugs electrochemical reaction mechanism. At the same time, the comparisons of electrochemical sensing performance of the drugs on various electrodes from recent studies are listed, so that readers can more intuitively compare and understand the electroanalytical sensing performance of each modified electrode for each of the drug. Finally, this review discusses the shortcomings and prospects of the drugs electroanalysis based on direct electrochemical redox research.

Rapid Detection of Ractopamine and Salbutamol in Swine Urine by Immunochromatography Based on Selenium Nanoparticles

Purpose

The purpose of this study was to establish a lateral flow immunoassay using selenium nanoparticles (Se-NPs) as a probe to detect ractopamine (RAC) and salbutamol (SAL) in swine urine.

Methods

SDS and PEG were used as templates to prepare Se-NPs; anti-RAC monoclonal antibodies or anti-SAL monoclonal antibodies were labelled with Se-NPs; and rapid detection kits were prepared. The sensitivity, specificity, and stability were measured, and actual samples were analysed.

Results

The Se-NPs were spherical with a diameter of 40.63 ± 5.91 nm, and were conjugated successfully with an anti-RAC antibody to give a total diameter of 82.33 ± 17.91 nm. The detection limit of a RAC kit in swine urine was 1 ng/mL, and that of a SAL kit was 3 ng/mL. Both procedures could be completed within 5 minutes. No cross-reaction occurred with clenbuterol, bambuterol and phenylethanolamine A. Samples were tested consistently across different batches of kits for swine urine. The results of the kits were identical to those of actual clinical samples analysed by ELISA, and the coincidence rate was 100%.

Conclusion

The assay kit does not require any special device for reading the results, and the readout is a simple colour change that can be evaluated with the naked eye. It is easy to operate, sensitive, specific, and stable This kit is suitable for the rapid and real-time detection of RAC and SAL residues in swine urine samples.

Clinical Trial Registration

Swine urines samples were used under approval from the Experimental Animal Ethics committee of the Joint National Laboratory for Antibody Drug Engineering, Henan University.

d-Penicillamine functionalized dendritic fibrous nanosilica (DFNS-DPA): synthesise and its application as an innovative advanced nanomaterial towards sensitive quantification of ractopamine

During the twentieth century, ractopamine (RAC) as one of the important and frequently used feed additives and doping agents has attracted considerable attention in the animal breeding industry and sports competitions.

Two-dimensional binary nanosheets (Bi2Te3@g-C3N4): Application toward the electrochemical detection of food toxic chemical

Bismuth telluride is considered as an efficient and super-active electrocatalyst in the sector of electrochemical application. Herein, we prepared binary nanosheets (Bi₂Te₃) through simple solvothermal and hydrothermal method. Furthermore, to enhance the electrocatalytic activity, graphitic carbon nitrides nanosheets (g-C₃N₄) were used to prepare the composition of Bi₂Te₃/g-C₃N₄ binary nanosheets (BNs) with help of hydrothermal energy. Moreover, Bi₂Te₃/g-C₃N₄ hybrid was characterized by various techniques (XRD, XPS, SEM, TEM, EDS and EIS analysis). The electrochemical performance of Bi₂Te₃/g-C₃N₄ BNs modified GCEs were analyzed by electrochemical technique (DPV, EIS and CV methods). As modified the Bi₂Te₃/g-C₃N₄ BNs modified electrode exhibits excellent electrochemical activity towards food toxic ractopamine (RAC) with high-sensitive and nano-molar detection limit (LOD). Besides, the practical ability was analyzed to detect the RAC in meat samples using Bi₂Te₃/g-C₃N₄ BNs modified GCE.

One-Step Solution-Immersion Process of Hydrophobic Octyl Graphene Oxide-Modified Nickel Foam for Highly Efficient Oil-Water Separation

Hydrophobic foam was prepared by immersing nickel foam in a dispersion of octyl group-grafted graphene oxide (GO) and used to clean up oil-water mixtures. Octyl graphene oxide (C₈-GO) was synthesized using GO and triethoxyoctylsilane by a solvothermal method. The resulting coverage of the foam was characterized, and the surface morphology of the foam was also investigated. The static water contact angle (SWCA) was measured to evaluate the change in wettability of the developed foam. The pristine smooth microstructure of the nickel foam became rough after being covered with the C₈-GO nanosheets. The SWCA of C₈-GO nickel foam (C₈-GO NF) surface was approximately 147°. The C₈-GO NF can float on the surface of the water in contrast to the easy-sinking unmodified foam, demonstrating good hydrophobicity. Furthermore, the C₈-GO NF showed outstanding performance in organic compound adsorption and excellent efficiency in oil-water separation. The reusability and durability of the obtained foam are evaluated to highlight its usability in more complicated scenarios. The use of C₈-GO NF was proved to be a promising strategy for oil-water separation under harsh circumstance.

AgNPs/QDs@GQDs nanocomposites developed as an ultrasensitive impedimetric aptasensor for ractopamine detection

Developing easy-to-use and miniaturized sensors for in-field monitoring of targets which is related to human health is necessary. Ractopamine (RAC) is a feed additive with serious side effects that is forbidden in many countries. This study reports the fabrication of an impedimetric aptasensor for ultrasensitive and selective detection of the RAC in human biological fluids. Accordingly, an efficient nanocomposites was synthesized by a beneficial combination of graphene quantum dots (GQDs), quantum dots (QDs) and silver nanoparticles (AgNPs) for modifying a glassy carbon electrode (GCE). This nanocomposite is promising to present a synergistic effect in the increase of the active surface area of the modified electrode to more load the biocapture of the target. Next, the RAC-binding aptamer (Apt) was attached to the AgNPs/QDs@GQDs/GCE surface and a sensitive layer for the RAC detection was embedded. A RAC-Apt complex was formed upon adding the RAC and the changes of the electrochemical behavior were studied by some electrochemical techniques such as electrochemical impedance spectroscopy (EIS). Under optimal conditions, the charge transfer resistance (R_ct) value was increased linearly with increasing of the RAC concentrations in the range of 1 fM to 901.4 nM. Limit of detection (LOD) was calculated to be 330 aM which is superior by other reported electrochemical methods in the RAC sensing. The applicability of the aptasensor was tested in human urine and blood serum as the real samples and satisfactory results of specificity were achieved. It seems that the proposed strategy not only provides a new ultrasensitive strategy for RAC detection but also expands the application of the sensing interface to develop other aptasensors by changing the Apt sequence.

Sonochemical synthesis of perovskite-type barium titanate nanoparticles decorated on reduced graphene oxide nanosheets as an effective electrode material for the rapid determination of ractopamine in meat samples

A simple and facile ultrasound based sonochemical method to incorporate Perovskite-type barium titanate (BaTiO₃) nanoparticles inside the layered and reduced graphene oxide sheets (rGOs) is reported. BaTiO₃@rGOs nanocomposite was characterized by FESEM, HRTEM, EDX, mapping, XRD, XPS and EIS. The results show that the decoration and also incorporation of BaTiO₃ nanoparticles in the multi-layered and ultrasound reduced graphene oxide matrix. Non-enzymatic and differential pulse voltammetric sensor of ractopamine (food toxic) based on the BaTiO₃@rGOs nanocomposite modified screen printed carbon electrode is developed. Compared with the original BaTiO₃/SPCE and rGOs/SPCE, the BaTiO₃@rGOs/SPCE displays excellent current response towards ractopamine and gives linearity in the range of 0.01-527.19 µM ractopamine in neutral phosphate buffer (pH 7.0). The BaTiO₃@rGOs nanocomposite modified sensor also exhibits valuable ability of anti-interference to electroactive analytes. Furthermore, the as-prepared BaTiO₃ NPs@rGOs/SPCE has been applied to the determination of ractopamine in pork and chicken samples.

Photoelectrochemical determination of ractopamine based on inner filter effect between gold nanoparticles and graphitic carbon nitride-copper(II) polyphthalocyanine coupled with 3D DNA stabilizer

Copper(II) polyphthalocyanine (CuPPc) was combined with graphitic carbon nitride (g-C₃N₄) to form a heterojunction with enhanced photoelectrochemical (PEC) signal. A sensitive PEC method was developed for determination of ractopamine based on a PEC inner filter effect between gold nanoparticles (AuNPs) and the g-C₃N₄/CuPPc. A gold electrode was modified with g-C₃N₄/CuPPc and the DNA was linked to the AuNPs. Initially, the PEC signal is weak due to the inner filter effect between the AuNPs and g-C₃N₄/CuPPc. In the presence of ractopamine, it interacts with the aptamer and the complementary chain (C chain) is released. This triggers the entropy-driven cyclic amplification and results in the release of the substrate B chain (SB chain) from three-dimensional DNA stabilizer. The probe is released from the electrode due to the interaction of probe DNA and the SB chain. As a result, the PEC signal increases linearly in the 0.1 pmol·L^-1 to 1000 pmol·L^-1 ractopamine concentration range. The detection limit is 0.03 pM, and the relative standard deviation is 3.4% (at a 10 pmol·L^-1 level; for n = 11). The method has been successfully applied to the determination of ractopamine in pork samples. Graphical abstract Schematic presentation of detection method based on PEC inner filter effect between AuNPs and the g-C₃N₄/CuPPc being fabricated for ractopamine. 3D DNA was used as stabilizer to decrease the PEC blank signal.

Cross-linked chitosan/thiolated graphene quantum dots as a biocompatible polysaccharide towards aptamer immobilization

Chitosan has a number of commercial and possible biomedical uses. Chitosan as a polysaccharide is a bioactive polymer with a variety of applications due to its functional properties such as antibacterial activity, non-toxicity, ease of modification, and biodegradability. In this work, cross-linked chitosan/thiolated graphene quantum dot as a biocompatible polysaccharide was modified by gold nanoparticle and used for immobilization of ractopamine (RAC) aptamer. A highly specific DNA-aptamer (5'-SH-AAAAAGTGCGGGC-3'), selected to RAC was immobilized onto thiolated graphene quantum dots (GQDs)-chitosan (CS) nanocomposite modified by gold nanostructures (Au NSs) and used for quantification of RAC. Different shapes of gold nanostructures with various sizes from zero-dimensional nanoparticles to spherical structures were prepared by one-step template-assistant green electrodeposition method. Fully electrochemical methodology was used to prepare a new transducer on a glassy carbon surface which provided a high surface area to immobilize a high amount of the aptamer. Therefore, a label free electrochemical (EC) apta-assay for ultrasensitive detection of RAC was developed. A special immobilization media consisting of Au NSs/GQDs-CS/Cysteamine (CysA) was utilized to improve conductivity and performance of the biosensor. The RAC aptamer was attached on the Au NSs of the composite membrane via AuS bond. The fabrication process of the EC aptamer based assay was characterized by some electrochemical techniques. The peak currents obtained by differential pulse voltammetry decreased linearly with the increasing of RAC concentrations and the apta-assay responds approximately over a wide dynamic range of RAC concentration from 0.0044 fM to 19.55 μM. The low limit of quantification was 0.0044 fM.

Enhancement of surface plasmon resonance signals using a MIP/GNPs/rGO nano-hybrid film for the rapid detection of ractopamine

A novel surface plasmon resonance (SPR) sensor that uses molecular imprinted polymers (MIPs) coated with gold nanoparticles (GNPs) and reduced graphene oxide (rGO) as a sensing nano-hybrid film was developed for detection of ractopamine. The MIPs were synthesized by precipitation polymerization and characterized by scanning electron microscopy and Scatchard analysis. The GNPs/rGO composite was synthesized by a single-step reduction of graphene oxide and HAuCl4 solution. The MIP/GNPs/rGO nano-hybrid film was immobilized onto a bare sensor chip and exhibited remarkable sensitivity and stability by the “grafting to” method with the assistance of ionic liquid (IL) as a binder. The prepared sensor showed class-specific selectivity for ractopamine (RAC) and its analogs under optimized conditions. The novel SPR sensor had a wide linear range over an RAC concentration from 20 to 1000 ng/mL with a detection limit of 5 ng/mL (S/N=3). The results demonstrated that the MIP/GNPs/rGO nano-hybrid film was suitable as the recognition element of the SPR sensorfor rapid screening and detection of beta-agonists such as RAC.

Electrochemical detection of ractopamine based on a molecularly imprinted poly-o-phenylenediamine/gold nanoparticle–ionic liquid–graphene film modified glass carbon electrode

An electrochemical sensor for sensitive detection of ractopamine (RAC) was fabricated by using molecularly imprinted polymer (MIP) incorporation with graphene (GR), ionic liquid (IL) and gold nanoparticle (AuNPs) nanocomposites.

Label free electrochemical aptasensor for ultrasensitive detection of ractopamine

A label free electrochemical (EC) aptasensor for ultrasensitive detection of ractopamine (RAC) was developed. A special immobilization media consisting of gold nanoparticles/poly dimethyl diallyl ammonium chloride-graphene composite (AuNPs/PDDA-GN) was utilized to improve conductivity and performance of the biosensor. The RAC aptamer was attached on AuNPs of the composite membrane via Au-S bond. The fabrication process of the EC aptasensor was characterized by electrochemical impedance spectroscopy and cyclic voltammetry. The peak currents obtained by differential pulse voltammetry decreased linearly with the increasing of RAC concentrations and the sensor responds approximately logarithmically over a wide dynamic range of RAC concentration from 1.0 × 10(-12)mol/L to 1.0 × 10(-8)mol/L. The linear correlation coefficient of the developed aptasensor was 0.998, the limit of detection was 5.0 × 10(-13)mol/L. The proposed EC aptasensor displayed good stability, reproducibility and robust operation in animal urine. Particularly, the generality of the fabrication approach of electrochemical aptasensor is highlighted with a further example for illegal drugs detection via the aptamer identification.

An ultrasensitive electrochemical DNA biosensor based on graphene/Au nanorod/polythionine for human papillomavirus DNA detection

An ultrasensitive electrochemical DNA biosensor for human papillomavirus (HPV) detection was developed by electrochemical impedance spectroscopy and differential pulse voltammetry. A capture probe was immobilized on a glassy carbon electrode modified with graphene/Au nanorod/polythionine (G/Au NR/PT). Two auxiliary probes were designed and used to long-range self-assemble DNA nanostructure. The target DNA can connect DNA structure to the capture probe on the electrode surface. [Ru(phen)3](2+) was selected as a redox indicator for amplifying electrochemical signal significantly. Enhanced sensitivity was obtained through combining the excellent electric conductivity of G/Au NR/PT architecture and the long-range self-assembly DNA nanostructure with the multi-signal amplification. The DNA biosensor displayed excellent performance for HPV DNA detection over the range from 1.0×10(-13) to 1.0×10(-10) mol/L with a detection limit of 4.03×10(-14) mol/L. Furthermore, the proposed method can also be used for the detection of HPV DNA in human serum samples and provides a potential application of DNA detection in clinic research.

One-pot in situ photochemical synthesis of graphene oxide/gold nanorod nanocomposites for surface-enhanced Raman spectroscopy

One-pot process is demonstrated that produces gold nanorods/graphene oxide nanocomposites that can be used as highly sensitive surface-enhanced Raman spectroscopy substrates.

Amplified electrochemical genotyping of single-nucleotide polymorphisms using a graphene–gold nanoparticles modified glassy carbon platform

A triple signal amplification strategy for the single nucleotide polymorphisms (SNPs) genotyping is reported using the graphene–gold nanoparticles (GR–AuNPs) as a sensitive platform and monobase-modified silver and gold nanoparticles (M-NPs).