A novel electrochemical immunosensor based on nonenzymatic Ag@Au-Fe3O4 nanoelectrocatalyst for protein biomarker detection

Electrochemical biosensors for dopamine

Dopamine (DA), a key catecholamine, plays a pivotal role in the regulation of human cognition and emotions. It has profound effects on the hormonal, memory, and cardiovascular systems. Anomalies like Alzheimer's, Parkinson's, schizophrenia, and senile dementia are linked to abnormal DA levels. Consequently, the precise determination of DA levels in biological systems is critical for the accurate diagnosis and treatment of these disorders. Among all analytical techniques, electrochemical studies provide the most selective and highly sensitive methods for detecting DA in biological samples. Ascorbic acid and uric acid are two examples of small biomolecules that can obstruct the detection of DA in biological fluids. To address this issue, numerous attempts have been made to modify bare electrodes to separate the signals of these substances and enhance the electrocatalytic activity towards DA. Various surface modifiers, including coatings, conducting polymers, ionic liquids, nanomaterials, and inorganic complexes, have been employed in the modification process. Despite the reported success in DA detection using electrochemical sensors, many of these approaches are deemed too complex and costly for real-world applications. Therefore, this review aims to provide an overview of DA electrochemical biosensors that are practical for real-world applications.

Recent Trends of Bioanalytical Sensors with Smart Health Monitoring Systems: From Materials to Applications

Smart biosensors attract significant interest due to real-time monitoring of user health status, where bioanalytical electronic devices designed to detect various activities and biomarkers in the human body have potential applications in physical sign monitoring and health care. Bioelectronics can be well integrated by output signals with wireless communication modules for transferring data to portable devices used as smart biosensors in performing real-time diagnosis and analysis. In this review, the scientific keys of biosensing devices and the current trends in the field of smart biosensors, (functional materials, technological approaches, sensing mechanisms, main roles, potential applications and challenges in health monitoring) will be summarized. Recent advances in the design and manufacturing of bioanalytical sensors with smarter capabilities and enhanced reliability indicate a forthcoming expansion of these smart devices from laboratory to clinical analysis. Therefore, a general description of functional materials and technological approaches used in bioelectronics will be presented after the sections of scientific keys to bioanalytical sensors. A careful introduction to the established systems of smart monitoring and prediction analysis using bioelectronics, regarding the integration of machine-learning-based basic algorithms, will be discussed. Afterward, applications and challenges in development using these smart bioelectronics in biological, clinical, and medical diagnostics will also be analyzed. Finally, the review will conclude with outlooks of smart biosensing devices assisted by machine learning algorithms, wireless communications, or smartphone-based systems on current trends and challenges for future works in wearable health monitoring.

Aptamer-Protein Interactions: From Regulation to Biomolecular Detection

Serving as the basis of cell life, interactions between nucleic acids and proteins play essential roles in fundamental cellular processes. Aptamers are unique single-stranded oligonucleotides generated by in vitro evolution methods, possessing the ability to interact with proteins specifically. Altering the structure of aptamers will largely modulate their interactions with proteins and further affect related cellular behaviors. Recently, with the in-depth research of aptamer-protein interactions, the analytical assays based on their interactions have been widely developed and become a powerful tool for biomolecular detection. There are some insightful reviews on aptamers applied in protein detection, while few systematic discussions are from the perspective of regulating aptamer-protein interactions. Herein, we comprehensively introduce the methods for regulating aptamer-protein interactions and elaborate on the detection techniques for analyzing aptamer-protein interactions. Additionally, this review provides a broad summary of analytical assays based on the regulation of aptamer-protein interactions for detecting biomolecules. Finally, we present our perspectives regarding the opportunities and challenges of analytical assays for biological analysis, aiming to provide guidance for disease mechanism research and drug discovery.

Silver nanoparticles in electrochemical immunosensing and the emergence of silver-gold galvanic exchange detection

Nanoparticle-based electrochemical immunosensors demonstrate high sensitivity toward biomarker detection due to the large surface area of the nanoparticles and their ability to amplify the signal of the target molecule. Additionally, they have a fast response time, relatively lower cost, and can be easily miniaturized for point-of-care applications. Among noble metals, silver nanoparticles (AgNPs) have been extensively used in electrochemical sensors due to their unique properties, such as catalytic activity and excellent electrical conductivity. This Feature Article describes six approaches for incorporating AgNPs in electrochemical platforms, featuring the most recent developments in the silver-gold galvanic exchange-based detection strategy. With a few exceptions, many of these detection methods use AgNP oxidation into Ag+ ions, followed by electrodeposition of Ag+ ions onto the working electrode as zero-valent Ag metal and a final stripping step using a voltammetric technique. Combining these steps provides desirable low detection limits and good sensitivity for various biomarkers. A few other methods involved the reduction of Ag+ ions and depositing them as Ag metal onto the electrode using a reagent mixture so that the striping analysis could be performed. Typically, this reagent mixture includes Ag+ ions, a reducing agent, or an enzyme substrate. Besides, AgNPs have also been directly used to modify the surface of electrodes to facilitate kinetically favored redox-mediated electrochemical reactions. In addition to Ag detection methods, this report will also provide recent examples to illustrate how the size and shape of AgNPs impact the detection limits and sensitivity of an electrochemical assay. Finally, we discuss recent developments in lab-on-a-chip type immunosensors designed explicitly for Ag-based metalloimmunoassay detection, and we envision that this article will provide a comprehensive summary of the operational principles and new insights into such immunoassay systems.

Electrochemical immunosensor for ultrasensitive detection of human papillomaviruse type 16 L1 protein based on Ag@AuNPs-GO/SPA

Human papillomaviruse type 16 (HPV16) is a high-risk serotype. As the main protective antigen protein, L1 protein is also the target protein for diagnosis. A simple label free electrochemical immunosensor (ECIS) was fabricated for ultrasensitive detection of HPV16 L1 protein in this work. Quasi-spherical Ag@Au core-shell nanoparticles on graphene oxide (Ag@AuNPs-GO) was developed as current response amplifier and characterized by UV-Vis Spectroscopy, Transmission Electron Microscopy and energy dispersive X-ray spectroscopy. Staphylococcal protein A was decorated on the modified electrode and utilized to immobilized the Fc portion of the monoclonal antibody specific for HPV16 L1 protein. Cyclic Voltammetry, Differential Pulse Voltammetry and Electrochemical Impedance Spectroscopy were used to verify the electrochemical performance and interfacial kinetic property. The increased concentration of HPV16 L1 protein led to slow electron transport and linearly decreased differential pulse voltammetry peak current with a detection limit of 0.002 ng mL^-1 and a wide linear relationship in the range of 0.005-400 ng mL^-1at a regression coefficient (R²) of 0.9948. Furthermore, this ECIS demonstrated acceptable accuracy with good reproducibility, stability and selectivity, suggesting a promising immunological strategy for HPV typing and early screening.

Recent Advances in Electrochemical Biosensors: Applications, Challenges, and Future Scope

The electrochemical biosensors are a class of biosensors which convert biological information such as analyte concentration that is a biological recognition element (biochemical receptor) into current or voltage. Electrochemical biosensors depict propitious diagnostic technology which can detect biomarkers in body fluids such as sweat, blood, feces, or urine. Combinations of suitable immobilization techniques with effective transducers give rise to an efficient biosensor. They have been employed in the food industry, medical sciences, defense, studying plant biology, etc. While sensing complex structures and entities, a large data is obtained, and it becomes difficult to manually interpret all the data. Machine learning helps in interpreting large sensing data. In the case of biosensors, the presence of impurity affects the performance of the sensor and machine learning helps in removing signals obtained from the contaminants to obtain a high sensitivity. In this review, we discuss different types of biosensors along with their applications and the benefits of machine learning. This is followed by a discussion on the challenges, missing gaps in the knowledge, and solutions in the field of electrochemical biosensors. This review aims to serve as a valuable resource for scientists and engineers entering the interdisciplinary field of electrochemical biosensors. Furthermore, this review provides insight into the type of electrochemical biosensors, their applications, the importance of machine learning (ML) in biosensing, and challenges and future outlook.

Metallic oxide nanomaterials act as antioxidant nanozymes in higher plants: Trends, meta-analysis, and prospect

Improving plant resistance against various environmental stresses is crucial to gain higher agricultural productivity for meeting future food demands of the fast-growing global population. Nanozymes, nanomaterials (NMs) with enzyme-like activity, have shown the potential to defend environmental stresses via scavenging reactive oxygen species (ROS) and augmenting the inherent antioxidant functions of plants. However, several studies confirmed that NMs could cause oxidative damage triggered by excessive ROS. In this study, the conversion mechanism between antioxidant and oxidant activities of metallic oxidative nanozymes was systematically reviewed and evaluated using meta-analysis approach. Moreover, our work attempts to seek the optimal dose and physicochemical property of antioxidant-functionalized NMs and put forward future research directions. The meta-analysis results indicated that NMs at a low dose (below 20 ppm) exhibited antioxidant activity which could scavenge ROS and alleviate their deleterious impacts. Conversely, their oxidant activity was activated at the exposure dose above 200 ppm which might induce ROS overproduction and lead to oxidative stress. Further, root exposure tends to stimulate the oxidant activity of NMs, and the NMs modification is highly promising for improving their bioavailability. A SWOT analysis was conducted to evaluate the strengths, weaknesses, opportunities, and threats of agro-applied nanozymes. Therefore, the rational design and development of nanozymes for better antioxidant potential will be beneficial to their applications in agriculture.

A Redox Cu(II)-Graphene Oxide Modified Screen Printed Carbon Electrode as a Cost-Effective and Versatile Sensing Platform for Electrochemical Label-Free Immunosensor and Non-enzymatic Glucose Sensor

A novel copper (II) ions [Cu(II)]-graphene oxide (GO) nanocomplex-modified screen-printed carbon electrode (SPCE) is successfully developed as a versatile electrochemical platform for construction of sensors without an additionally external redox probe. A simple strategy to prepare the redox GO-modified SPCE is described. Such redox GO based on adsorbed Cu(II) is prepared by incubation of GO-modified SPCE in the Cu(II) solution. This work demonstrates the fabrications of two kinds of electrochemical sensors, i.e., a new label-free electrochemical immunosensor and non-enzymatic sensor for detections of immunoglobulin G (IgG) and glucose, respectively. Our immunosensor based on square-wave voltammetry (SWV) of the redox GO-modified electrode shows the linearity in a dynamic range of 1.0-500 pg.mL-1 with a limit of detection (LOD) of 0.20 pg.mL-1 for the detection of IgG while non-enzymatic sensor reveals two dynamic ranges of 0.10-1.00 mM (sensitivity = 36.31 μA.mM-1.cm-2) and 1.00-12.50 mM (sensitivity = 3.85 μA.mM-1.cm-2) with a LOD value of 0.12 mM. The novel redox Cu(II)-GO composite electrode is a promising candidate for clinical research and diagnosis.

Fabrication of 3D Ni/NiO/MoS2/rGO foam for enhancing sensing performance

The accurate electrochemical detection of dopamine (DA) is hard to achieve due to the serious interference of a substance with similar redox properties.

Application of magnetic nanomaterials in electroanalytical methods: A review

Magnetic nanomaterials (MNMs) have gained high attention in different fields of studies due to their ferromagnetic/superparamagnetic properties and their low toxicity and high biocompatibility. MNMs contain magnetic elements such as iron and nickel in metallic, bimetallic, metal oxide, and mixed metal oxide. In electroanalytical methods, MNMs have been applied as sorbents for sample preparation before the electrochemical detection (sorbent role), as the electrode modifier (catalytic role), and the integration of the above two roles (as both sorbent and catalytic agent). In this paper, the application of MNMs in electroanalytical methods have been classified based on the main role of the nanomaterial and discussed separately. Furthermore, catalytic activities of MNMs in electroanalytical methods such as redox electrocatalytic, nanozymes catalytic (peroxidase, catalase activity, oxidase activity, superoxide dismutase activity), catalyst gate, and nanocontainer have been discussed.

A novel sandwich-type SERS immunosensor for selective and sensitive carcinoembryonic antigen (CEA) detection

Monitoring the malignant tumors via cancer biomarkers is very significant process. Nonetheless, the practical clinical applications need selective and sensitive analytical methods/techniques. In this study, a novel sandwich type immunosensor based on surface-enhanced raman scattering (SERS) was presented including 4-mercaptobenzoic acid labeled MoS₂ nanoflowers@Au nanoparticles (MoS₂ NFs@Au NPs/ MBA) as CEASERS tag and Fe₃O₄@Au nanoparticles functionalized delaminated Ti₃C₂T_x MXene (Fe₃O₄ NPs@Au NPs/d-Ti₃C₂T_X MXene) as SERS magnetic supporting substrate for carcinoembryonic antigen (CEA) detection. Especially, the determination of single molecule by using SERS method enables early diagnosis of major diseases. In addition, this technique can be utilized for multiplex analyzes owing to narrow well-resolved peaks. The prepared CEASERS tag and SERS magnetic supporting substrate were characterized by scanning electron microscope (SEM), x-ray diffraction (XRD) method, x-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM) and fourier transform infrared spectroscopy (FTIR). A linearity of 0.0001-100.0 ng mL^-1 was observed with high sensitivity. Finally, sandwich type immunosensor demonstrated good selectivity and stability for target CEA recognition in plasma sample.

Printed Electrodes in Microfluidic Arrays for Cancer Biomarker Protein Detection

Medical diagnostics is trending towards a more personalized future approach in which multiple tests can be digitized into patient records. In cancer diagnostics, patients can be tested for individual protein and genomic biomarkers that detect cancers at very early stages and also be used to monitor cancer progression or remission during therapy. These data can then be incorporated into patient records that could be easily accessed on a cell phone by a health care professional or the patients themselves on demand. Data on protein biomarkers have a large potential to be measured in point-of-care devices, particularly diagnostic panels that could provide a continually updated, personalized record of a disease like cancer. Electrochemical immunoassays have been popular among protein detection methods due to their inherent high sensitivity and ease of coupling with screen-printed and inkjet-printed electrodes. Integrated chips featuring these kinds of electrodes can be built at low cost and designed for ease of automation. Enzyme-linked immunosorbent assay (ELISA) features are adopted in most of these ultrasensitive detection systems, with microfluidics allowing easy manipulation and good fluid dynamics to deliver reagents and detect the desired proteins. Several of these ultrasensitive systems have detected biomarker panels ranging from four to eight proteins, which in many cases when a specific cancer is suspected may be sufficient. However, a grand challenge lies in engineering microfluidic-printed electrode devices for the simultaneous detection of larger protein panels (e.g., 50-100) that could be used to test for many types of cancers, as well as other diseases for truly personalized care.

A magnetic relaxation switching and visual dual-mode sensor for selective detection of Hg2+ based on aptamers modified Au@Fe3O4 nanoparticles

The solvated mercuric ion (Hg²⁺) from industrial pollutants are highly toxic to the ecological environment and human health. Driven by urgent need for the selective and sensitive detection of Hg²⁺, a magnetic relaxation switching (MRS) based on Fe₃O₄ nanoparticles (NPs) was designed. Practically, the concentrations of Hg²⁺ in industrial pollutant is usually much higher than the detection range. Thus, gold nanoparticles (AuNPs) were synthesized on the surface of Fe₃O₄ NPs to enable the visual detection of Au@Fe₃O₄ NPs. The presence of Hg²⁺ in sample can specifically cause the aggregation of Au@Fe₃O₄-aptamers NPs through T-Hg²⁺-T base pairs, leading to the change in transverse relaxation time T₂ value of detection solution. The MRS sensor showed excellent response for Hg²⁺ ions in the range of 10 nM-100 nM and 100 nM to 5 μM. A highly sensitive and selective measurement of Hg²⁺ was obtained with a limit of detection of 2.7 nM. Noticeably, the visual detection can qualitatively analyze the Hg²⁺ beyond 5 μM by naked eye without advanced instrumentation and skilled operators.

Electrochemical biosensors: perspective on functional nanomaterials for on-site analysis

BACKGROUND

The electrochemical biosensor is one of the typical sensing devices based on transducing the biochemical events to electrical signals. In this type of sensor, an electrode is a key component that is employed as a solid support for immobilization of biomolecules and electron movement. Thanks to numerous nanomaterials that possess the large surface area, synergic effects are enabled by improving loading capacity and the mass transport of reactants for achieving high performance in terms of analytical sensitivity.

MAIN BODY

We categorized the current electrochemical biosensors into two groups, carbon-based (carbon nanotubes and graphene) and non-carbon-based nanomaterials (metallic and silica nanoparticles, nanowire, and indium tin oxide, organic materials). The carbon allotropes can be employed as an electrode and supporting scaffolds due to their large active surface area as well as an effective electron transfer rate. We also discussed the non-carbon nanomaterials that are used as alternative supporting components of the electrode for improving the electrochemical properties of biosensors.

CONCLUSION

Although several functional nanomaterials have provided the innovative solid substrate for high performances, developing on-site version of biosensor that meets enough sensitivity along with high reproducibility still remains a challenge. In particular, the matrix interference from real samples which seriously affects the biomolecular interaction still remains the most critical issues that need to be solved for practical aspect in the electrochemical biosensor.

Electrochemical immunosensor based on carboxylated single-walled carbon nanotube-chitosan functional layer for the detection of cephalexin

In this study, a sensitive and selective electrochemical immunosensor for cephalexin (CEX) determination on a glassy carbon electrode (GCE) surface was modified by a carboxylated single-walled carbon nanotubes/chitosan (SWNTs-COOH/CS) composite. The SWNTs-COOH/CS composite was used to enhance sensor performance and to enlarge the electrochemical response of CEX. The cephalosporin-ovalbumin coupling (CEX-OVA) was synthesized using the reactive ester method. The free CEX in solution could be effectively measured based on the competitive immunoreaction between CEX-antibody and CEX. Under optimal conditions, the electrochemical immunosensor offered an excellent response for CEX. The linear range was 1-800 ng/ml, with a detection limit of 45.7 ng/ml (S/N = 3). This method was applied to determine CEX in six different samples and obtained the recovery range from 80.15% to 94.04%. These results indicated that the fabricated electrochemical immunosensor and sensing method are suitable for quantification of CEX in real samples. These have great potential for wider applications in environmental and agri-food products industries.

Nanoparticles as Emerging Labels in Electrochemical Immunosensors

This review shows recent trends in the use of nanoparticles as labels for electrochemical immunosensing applications. Some general considerations on the principles of both the direct detection based on redox properties and indirect detection through electrocatalytic properties, before focusing on the applications for mainly proteins detection, are given. Emerging use as blocking tags in nanochannels-based immunosensing systems is also covered in this review. Finally, aspects related to the analytical performance of the developed devices together with prospects for future improvements and applications are discussed.

C60 Mediated Ion Pair Interaction for Label-Free Electrochemical Immunosensing with Nanoporous Anodic Alumina Nanochannels

Label-free biosensing based on the nanoporous anodic alumina (NAA) membrane emerged as a versatile biosensing platform in the recent decade. In the present work, we developed a new immunosensing strategy based on the nanochannels of NAA and the ion pair interaction mediated by electrochemistry of C₆₀. The NAA served as the matrix for the immobilization of the capture antibodies. The incubation of target antigens resulted in the formation of the immunocomplexes and thus an increase of the steric hindrance of the nanochannels. Therefore, the concentration of the redox probe transported through the nanochannels decreases, which can be detected at the working electrode modified with C₆₀. Herein, we initially found that the cathodic peak ascribed to the reduction of C₆₀ to C₆₀^- was obviously enhanced by the presence of the redox probe K₃[Fe(CN)₆] and which was contributed to the formation of a ternary ion association complex among C₆₀, tetraoctylammonium bromide, and K₃[Fe(CN)₆]. Therefore, the transportation of K₃[Fe(CN)₆] though the NAA-based bionanochannels can be detected by a C₆₀ modified electrode with an amplified signal. Choosing human epididymis protein 4 (HE4) as the model target, a linear range of 1.0 ng mL^-1 to 100 ng mL^-1 can be established between the peak current obtained from the differential pulse voltammetric response of the platform and the concentration of HE4. The detection limit was 0.2 ng mL^-1. This study not only provides a new avenue to develop the other nanochannel-based biosensing platform for a variety of other disease biomarkers but also contributes to the electrochemistry of fullerene.

Multifunctional nanozymes: enzyme-like catalytic activity combined with magnetism and surface plasmon resonance

Over decades, as alternatives to natural enzymes, highly-stable and low-cost artificial enzymes have been widely explored for various applications. In the field of artificial enzymes, functional nanomaterials with enzyme-like characteristics, termed as nanozymes, are currently attracting immense attention. Significant progress has been made in nanozyme research due to the exquisite control and impressive development of nanomaterials. Since nanozymes are endowed with unique properties from nanomaterials, an interesting investigation is multifunctionality, which opens up new potential applications for biomedical sensing and sustainable chemistry due to the combination of two or more distinct functions of high-performance nanozymes. To highlight the progress, in this review, we discuss two representative types of multifunctional nanozymes, including iron oxide nanomaterials with magnetic properties and metal nanomaterials with surface plasmon resonance. The applications are also covered to show the great promise of such multifunctional nanozymes. Future challenges and prospects are discussed at the end of this review.

Patchy gold coated Fe3O4 nanospheres with enhanced catalytic activity applied for paper-based bipolar electrode-electrochemiluminescence aptasensors

In this work, novel multifunctional patchy gold coated Fe₃O₄ hybrid nanoparticles (PG-Fe₃O₄ NPs) have been successfully synthesized in aqueous medium via a facile adsorption-reduction method. A rational formation mechanism has been proposed by monitoring the morphological evolution. The PG-Fe₃O₄ NPs retained the good magnetic property and exhibited excellent catalytical effeciency towards the electrochemical reduction of hydrogen peroxide. Chronoamperometric and amperometric experiments indicated a relatively high catalytic rate constant of 3.13 × 10⁵ M^-1 s^-1, a high sensitivity of 578.87 µA mM^-1 cm^-2 and a low Michaelis-Menten constant of 462 µM. Meanwhile, the introduction of patchy gold could help biofunctionalization via Au-S bond for different biodetection and biosensing purposes. Here, as an example, thiol-terminated aptamers were immobilized onto the patchy gold part as a signal probe to detect carcinoembryonic antigen (CEA). A related paper-based bipolar electrode-electrochemiluminescence (pBPE-ECL) aptasensor was fabricated as the low-cost, disposable and miniature platform. To improve the sensitivity, Au nanodendrites were electrodeposited at the BPE cathode as the matrix for Apt1 immobilization. This aptasensor showed a wide linear range of 0.1 pg mL^-1-15 ng mL^-1 with a low detection limit of 0.03 pg mL^-1, remaining competitive against other ones, and also demonstrating the PG-Fe₃O₄ NPs have promising potential for catalysis and bioassays.

Iron nanostructured catalysts: design and applications

This review is focused on the recent advances in the design of iron nanostructures and their catalytic applications.

A New Tactic for Label-Free Recognition of β-Trophin via Electrochemiluminescent Signalling on an AuNPs Supported Immuno-Interface

In this paper, a new strategy is reported for preparing a label-free β-trophin electrochemiluminescent (ECL) immunosensor with good specificity, reproducibility and stability. An aquagel polymer from the hydrolysis of (3-aminopropyl) trimethoxysilane acted as the linker to catch the Au nanoparticles (AuNPs) on the indium-tin oxide (ITO) substrate by a two-step method. The AuNPs play an important role in enhancing ECL and immobilizing the β-trophin antibody. This immunosensor can test for β-trophin using luminol as an ECL probe. The ECL intensity at the resultant sensor, after the direct immuno-interaction, was proportional to the concentration of β-trophin and had a low limit of quantification as 4.2 ng mL⁻¹. After deep discussions on the ECL mechanism of this immunosensor, we found that its sensitivity is greatly affected by the presence of oxygen and improved under deoxygenation. We believe that this sensor can be used for clinical cases.

A high sensitive visible light-driven photoelectrochemical aptasensor for shrimp allergen tropomyosin detection using graphitic carbon nitride-TiO2 nanocomposite

Herein, for the first time a visible-light-driven photoelectrochemical (PEC) aptasensor for shrimp tropomyosin determination was fabricated by using graphitic carbon nitride (g-C₃N₄) and titanium dioxide (TiO₂) as photoactive nanomaterials, ascorbic acid (AA) as electron donor and ruthenium (III) hexaammine (Ru(NH₃)₆³⁺) as signal enhancer. The surface of an ITO electrode was first modified with g-C₃N₄, TiO₂, and polyethyleneimine (PEI) and then the amine terminal aptamer_TROP probe was attached to PEI by the use of glutaraldehyde (GA) as cross-linker. After that, Ru(NH₃)₆³⁺ was adsorbed on aptamer to enhance the photocurrent signal. The principle of proposed PEC aptasensor is based on the formation of a selective complex between tropomyosin and immobilized aptamer_TROP probe on the surface of ITO/g-C₃N₄-TiO₂/PEI/aptamer_TROP-Ru(NH3)₆⁺³. After the incubation of tropomyosin with TROP aptamer probe, the photocurrent signal decreased due to releasing adsorbed Ru(NH₃)₆³⁺ on aptamer and preventing AA from scavenging photogenerated holes to the photoactive modified electrode. Under the optimized conditions, the fabricated PEC aptasensor was used for the determination of shrimp tropomyosin in the concentration range of 1-400ngmL^-1 with a limit of detection of 0.23ngmL^-1. The proposed PEC aptasensor exhibited high selectivity, sensitivity, and good stability.

Sequential injection system with amperometric immunosensor for sensitive determination of human immunoglobulin G

Sequential injection (SI) system incorporated with amperometric immunosensor was developed for sensitive determination of human immunoglobulin G (HIgG). A cost effective label-free immunosensor was fabricated by immobilizing anti-HIgG on a graphene oxide (GO) modified screen-printed carbon electrode (SPCE). The developed electrode was characterized by cyclic voltammetry(CV), scanning electron microscope(SEM), and energy dispersive spectroscopy(EDS) which confirmed the selective immunointeraction of HIgG to the anti-HIgG on the electrode, thus reduced the amperometric current of [Fe(CN)₆]^3-/4- redox probe. The sensing electrode was placed in a designed electrochemical flow cell of SI system, where the redox probe was propelled through and the currents before and after the immunointeraction occurred were measured amperometrically by using a simple home-made amperometer. Under the optimum condition: flow rate of 2mLmin^-1, applied potential of +350mV, [Fe(CN)₆]^3-/4- concentration of 10mM and 10min of incubation time, a linear calibration in the range of 2-100ngmL^-1 was achieved, with detection limit of 1.70ngmL^-1. The proposed system provided good repeatability and reproducibility and the application for urine sample analysis was demonstrated.

Facile synthesis of thiazole-functionalized magnetic microspheres for highly specific separation of heme proteins

Thiazole-functionalized magnetic microspheres which exhibited high selectivity to capture hemoglobin with a binding capacity of 2.02 g g⁻¹ were successfully synthesized.

Multifunctional PS@CS@Au–Fe3O4–FA nanocomposites for CT, MR and fluorescence imaging guided targeted-photothermal therapy of cancer cells

Multifunctional theranostic PS@CS@Au–Fe₃O₄–FA/ICG nanocomposites for MR, CT and fluorescence multiple-modal imaging-guided targeted photothermal therapy were fabricated, and they might be a promising theranostic nanoplatform for tumor diagnostics and treatment.