Chitosan stabilized gold nanoparticle based electrochemical ractopamine immunoassay

A SERS/electrochemical dual-signal readout immunosensor using highly-ordered Au/Ag bimetallic cavity array as the substrate for simultaneous detection of three β-adrenergic agonists

A surface-enhanced Raman scattering (SERS)/electrochemical dual-signal readout immunosensor was developed for simultaneous detection of β-adrenergic agonists salbutamol (SAL), ractopamine (RAC) and phenylethanolamine A (PA). The highly-ordered gold/silver bimetallic cavity array (BMCA) was prepared by electrodepositing Au/Ag nanoparticles to the interstice of highly ordered close-packed polystyrene templates. After electrochemical and SERS characterization, the BMCA was used as the substrate for constructing SERS/electrochemical dual-signal readout immunosensor. 3,3',5,5'-tetramethylbenzidine (TMB), methylene blue (MB) and Nile blue (NB) were selected as the dual-signal reporters, and hybridization chain reaction (HCR) was used as the signal amplifier. The immunoprobe was prepared by absorption of the antibody (Ab) and constructing HCR system embedded with electro/SERS reporter on Au nanoparticles (NPs). After competitive immuno-reaction between coating antigen and analyte for limited Ab on immunoprobe, the SERS/electrochemical dual-signals on BMCA were measured for quantitatively detecting SAL, RAC and PA simultaneously. SAL, RAC and PA were detected in concentration range of 1 pg mL^-1 to 100 ng mL^-1 with LOD of 0.8, 0.4, and 1.3 pg mL^-1, respectively. The applicability of the proposed immunosensor in spiked pork liver samples was verified by the recovery of 95.0%-108.5% with RSD of 6.9%-10.7%. It was proven that the immunosensor was able to detect multiple β-adrenergic agonists with high sensitivity, specificity, accuracy and precision. The immunosensor can be used as a platform for the determination of other small molecular compounds in biological, food and environmental analytical fields.

Current Advances in Immunoassays for the Detection of β2-Agonists

β2-agonists are a group of synthetic phenylethanolamine compounds which are traditionally used for treating bronchospasm. These compounds can also increase skeletal muscle mass and decrease body fat. The illegal use of β2-agonists in food-producing animals results in residue of β2-agonists in edible tissues and causes adverse health effects in humans. Thus, the detection of β2-agonists at trace level in complex sample matrices is of great importance for monitoring the abuse of β2-agonists. Many methods have been developed to detect β2-agonists. Among them, a variety of antigen–antibody interaction-based techniques have been established to detect β2-agonists in various samples, including animal feed, urine, serum, milk, tissues and hair. In this review, we summarized current achievement in the extraction of β2-agonists from testing samples and detection of β2-agonists using immunological techniques. Future perspectives were briefly discussed.

A flexible paper based electrochemical portable biosensor towards recognition of ractopamine as animal feed additive: Low cost diagnostic tool towards food analysis using aptasensor technology

Due to the costly and time-consuming traditional techniques, providing a low-cost, portability and flexibility diagnostic tool with the ability to monitor and detect various animal feed additive is highly demanded. Over the years, paper-based biosensors have emerged as point of care (POC) diagnostic, easy-to-use and miniaturized tools. However, they have been suffered from low sensitivity. Aptamer as appropriate bioreceptor can overcome the most common disadvantage of paper based sensor by increasing selectivity and sensitivity. In this study, a novel paper-based electrochemical aptasensor was successfully developed to detection of ractopamine (RAC). RAC concentration was evaluated using a designed three-electrode paper based biodevice system. Under the optimal experimental conditions, the engineered aptasensor provided good sensitivity and selectivity for the detection of RAC. Using proposed flexible sensor RAC was determined in the range of 0.001 µM to 100 mM which the lower limit of quantitation (LLOQ) was obtained as 0.01 µM. Finally, aptasensor was used to the monitoring of RAC in untreated human plasma specimens which LLOQ and linear range were 0.01 µM and 0.01 µM to 10 mM, respectively. We hope that the exploitation of aptamer in electrochemical paper based sensor will be able to broaden our understanding for developing the application of low-cost and portable biodevices for the sensitive and selective paper-based sensor to identify other chemical and biological compounds.

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.

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.

Solution-Plasma-Assisted Bimetallic Oxide Alloy Nanoparticles of Pt and Pd Embedded within Two-Dimensional Ti3C2T x Nanosheets as Highly Active Electrocatalysts for Overall Water Splitting

Exploiting high-efficiency and low-cost bifunctional electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) has been actively encouraged because of their potential applications in the field of clean energy. In this paper, we reported a novel electrocatalyst based on an exfoliated two-dimensional (2D) MXene (Ti₃C₂T _x) loaded with bimetallic oxide alloy nanoparticles (NPs) of Pt and Pd (represented by PtO _aPdO _bNPs@Ti₃C₂T _x), which was synthesized via solution plasma (SP) modification. The prepared materials were then utilized as highly efficient bifunctional electrocatalysts toward the HER and OER in alkaline solution. At a high plasma input power (200 W), bimetallic oxide alloy nanoparticles of Pt and Pd or nanoclusters with different metallic valence states were deposited onto the Ti₃C₂T _x nanosheets. Because of the synergism of the noble-metal NPs and the Ti₃C₂T _x nanosheets, the electrocatalytic results revealed that the as-prepared PtO _aPdO _bNPs@Ti₃C₂T _x nanosheets under the plasma input power of 200 W for 3 min only required a low overpotential to attain 10 mA cm^-2 for the HER (-26.5 mV) in 0.5 M H₂SO₄ solution and OER (1.54 V) in 0.1 M KOH solution. Moreover, water electrolysis using this catalyst achieved a water splitting current density of 10 mA cm^-2 at a low cell voltage of 1.53 V in 1.0 M KOH solution. These results suggested that the hybridization of the extremely low usage of PtO _a/PdO _b NPs (1.07 μg cm^-2) and Ti₃C₂T _x nanosheets by SP will expand the applications of other clean energy reactions to achieve sustainable energy.

Bifunctional aptasensor based on novel two-dimensional nanocomposite of MoS2 quantum dots and g-C3N4 nanosheets decorated with chitosan-stabilized Au nanoparticles for selectively detecting prostate specific antigen

A novel nanostructured biosensing platform was designed based on two-dimensional (2D) nanocomposite of graphitic carbon nitride (g-C₃N₄) nanosheets and MoS₂ quantum dots (MoS₂ QDs), followed by decoration with chitosan-stabilized Au nanoparticles (CS-AuNPs) (denoted as MoS₂QDs@g-C₃N₄@CS-AuNPs), of which CS-AuNPs were prepared by plasma enhanced-chemical vapor deposition. Owning to the good surface plasmon performance of the CS-AuNPs and excellent electrochemical activity of MoS₂QDs@g-C₃N₄ nanosheets, the as-obtained 2D MoS₂QDs@g-C₃N₄@CS-AuNPs nanocomposite was simultaneously explored to construct both surface plasmon resonance spectroscopy (SPR) sensor and electrochemical aptasensor. The MoS₂QDs@g-C₃N₄@CS-AuNPs-based aptasensor shows strong bio-binding affinity toward the prostate specific antigen (PSA) targeted aptamer strands as compared to the individual component, including MoS₂ QDs, g-C₃N₄, and CS-AuNPs. When detecting PSA, the low limit of detection (LOD) of 0.71 pg mL^-1 deduced by electrochemical aptasensor is three orders of magnitude lower than that deduced by SPR sensor (0.77 ng mL^-1). As expected, both SPR sensor and electrochemical aptasensor demonstrate good selectivity, highly stability, acceptable reproducibility, and well consistent applicability in human serum. The satisfactory results suggest potential application of the MoS₂QDs@g-C₃N₄@CS-AuNPs in bifunctional biosensing fields and clinical monitoring of cancer markers.

Reproducible Molecularly Imprinted Piezoelectric Sensor for Accurate and Sensitive Detection of Ractopamine in Swine and Feed Products

This paper describes the development of a reproducible molecularly imprinted piezoelectric sensor for the accurate and sensitive detection of ractopamine (RAC) in swine and feed products. The synthesized molecularly imprinted polymer (MIP) was directly immobilized on the surface of a quartz crystal microbalance (QCM) Au chip as the recognition element. The experimental parameters in the fabrication, measurement and regeneration process were evaluated in detail to produce an MIP-based piezoelectric sensor with high sensing capability. The developed piezoelectric sensor was verified to perform favorably in the RAC analysis of swine and feed products, with acceptable accuracy (recovery: 75.9⁻93.3%), precision [relative standard deviation (n = 3): 2.3⁻6.4%], and sensitivity [limit of detection: 0.46 ng g-1 (swine) and 0.38 ng g-1 (feed)]. This portable MIP-based chip for the piezoelectric sensing of RAC could be reused for at least 30 cycles and easily stored for a long time. These results demonstrated that the developed MIP-based piezoelectric sensor presents an accurate, sensitive and cost-effective method for the quantitative detection of RAC in complex samples. This research offers a promising strategy for the development of novel effective devices used for use in food safety analysis.