A highly sensitive label-free electrochemical immunosensor based on poly(indole-5-carboxylicacid) with ultra-high redox stability

Portable photoelectrochemical immunoassay with micro-electro-mechanical-system for alpha-fetoprotein in hepatocellular carcinoma

Early detection of cancer has a profound impact on patient survival and treatment outcomes considering high treatment success rates and reduced treatment complexity. Here, we developed a portable photoelectrochemical (PEC) immune platform for sensitive testing of alpha-fetoprotein (AFP) based on Pt nanocluster (Pt NCs) loaded defective-state g-C3N4 photon-electron transducers. The broad forbidden band structure of g-C3N4 was optimized by the nitrogen doping strategy and additional homogeneous porous structure was introduced to further enhance the photon utilization. In addition, the in-situ growth of Pt NCs provided efficient electron transfer catalytic sites for sacrificial agents, which were used to further improve the sensitivity of the sensor. Efficient photoelectric conversion under a hand-held flashlight was determined by the geometry of the transducer and the energy band design, and the portable design of the PEC sensor was realized. The developed sensing platform exhibited a wide linear response range (0.1-50 ng mL-1) and low limit of detection (0.043 ng mL-1) for AFP under optimum conditions. This work provides a new idea for designing portable PEC biosensing platforms to meet the current mainstream POC testing needs.

NLISA versus enzyme-linked immunosorbent assay: Nanozyme-linked immunosorbent array based on platinum sub-nanocluster nanozyme for α-fetoprotein detection

Rapid and accurate identification of tumor metabolic markers is important for early tumor diagnosis and individualized treatment. Here, a stable monodisperse sub-nanometer platinum (Pt) material was developed as a highly efficient nanozyme with a specific activity of peroxidase as high as 20.86 U mg-1 through the growth of in situ domain-limited Pt quantum dots via the polymer polyvinylpyrrolidone. Further, the synthesis of large quantities of Pt-loaded SiO2 (Pt-SiO2 ) was determined by silylation reaction and used for naked eye colorimetric testing of human alpha-fetoprotein (AFP). In particular, the immunization incubation process occurred in preprepared microplates. A nanozyme-based immunomodel was constructed in the presence of the target AFP, and a chromogenic reaction occurred with exogenous hydrogen peroxide and the chromogenic substrate tetramethylbenzidine. On optimization of experimental conditions, the dynamic working response range for AFP was found to be 0.05-20 ng mL-1 , with a limit of detection of 38.7 pg mL-1 . This work provides a new strategy to design efficient nanozyme-based enzyme-linked immunochromatographic platforms to meet the practical use of replacing natural enzymes.

Formation of a Conducting Polymer by Different Electrochemical Techniques and Their Effect on Obtaining an Immunosensor for Immunoglobulin G

In this work, a conducting polymer (CP) was obtained through three electrochemical procedures to study its effect on the development of an electrochemical immunosensor for the detection of immunoglobulin G (IgG-Ag) by square wave voltammetry (SWV). The glassy carbon electrode modified with poly indol-6-carboxylic acid (6-PICA) applied the cyclic voltammetry technique presented a more homogeneous size distribution of nanowires with greater adherence allowing the direct immobilization of the antibodies (IgG-Ab) to detect the biomarker IgG-Ag. Additionally, 6-PICA presents the most stable and reproducible electrochemical response used as an analytical signal for developing a label-free electrochemical immunosensor. The different steps in obtaining the electrochemical immunosensor were characterized by FESEM, FTIR, cyclic voltammetry, electrochemical impedance spectroscopy, and SWV. Optimal conditions to improve performance, stability, and reproducibility in the immunosensing platform were achieved. The prepared immunosensor has a linear detection range of 2.0-16.0 ng·mL^-1 with a low detection limit of 0.8 ng·mL^-1. The immunosensing platform performance depends on the orientation of the IgG-Ab, favoring the formation of the immuno-complex with an affinity constant (Ka) of 4.32 × 10⁹ M^-1, which has great potential to be used as point of care testing (POCT) device for the rapid detection of biomarkers.

Nano-Scaled Materials and Polymer Integration in Biosensing Tools

The evolution of biosensors and diagnostic devices has been thriving in its ability to provide reliable tools with simplified operation steps. These evolutions have paved the way for further advances in sensing materials, strategies, and device structures. Polymeric composite materials can be formed into nanostructures and networks of different types, including hydrogels, vesicles, dendrimers, molecularly imprinted polymers (MIP), etc. Due to their biocompatibility, flexibility, and low prices, they are promising tools for future lab-on-chip devices as both manufacturing materials and immobilization surfaces. Polymers can also allow the construction of scaffold materials and 3D structures that further elevate the sensing capabilities of traditional 2D biosensors. This review discusses the latest developments in nano-scaled materials and synthesis techniques for polymer structures and their integration into sensing applications by highlighting their various structural advantages in producing highly sensitive tools that rival bench-top instruments. The developments in material design open a new door for decentralized medicine and public protection that allows effective onsite and point-of-care diagnostics.

An Immunosensor Using Electroactive COF as Signal Probe for Electrochemical Detection of Carcinoembryonic Antigen

Two kinds of two-dimensional (2D) covalent-organic frameworks (COF) were used to construct a sandwich-type electrochemical immunosensor for a proof-of-concept study. Vinyl-functionalized COFTab-Dva could be linked with Ab1 by the thiol-ene "click" reaction. Electroactive COFTFPB-Thi was modified with gold nanoparticles (AuNPs) to ensure the successful connection with Ab2 through Au-S bond. Meanwhile, electroactive COFTFPB-Thi was used to as signal probe to realize both the detection of carcinoembryonic antigen (CEA) and the amplification of detection signal. In detection process of the sandwich-type electrochemical immunosensor, glassy carbon electrode (GCE) was modified with 2D COFTab-Dva first then connected with Ab1 by the thiol-ene "click" reaction, next quantitative CEA was captured, followed by specificially capturing signal probe of Ab2/AuNPs/COFTFPB-Thi where AuNPs acted as nanocarriers of Ab2 and COFTFPB-Thi served as the signal producers. As the amount of CEA was increased, the amount of signal probe captured to the electrode was also increased, and the peak signal intensity of the redox reaction of COFTFPB-Thi was enhanced accordingly. Thus, the quantitative detection of CEA could be realized according to the peak signal intensity of electroactive COFTFPB-Thi. The electrochemical immunosensor owned wide detection range of 0.11 ng/mL-80 ng/mL, low detection limit of 0.034 ng/mL and good practicability. This study opens up a new revelation for quantitative detection of CEA using electroactive COF as enhanced signal probe.

Boosting the Electrochemical Performance of PI-5-CA/C-SWCNT Nanohybrid for Sensitive Detection of E. coli O157:H7 From the Real Sample

Redox activity is an important indicator for evaluating electrochemical biosensors. In this work, we have successfully polymerized indole-5-carboxylic acid into poly-5-carboxyindole nanomaterials (PI-5-CA), using its superior redox activity, and introduced carboxylated single-walled carbon nanotubes (C-SWCNTs) to synthesize a composite material. Finally, a synthesized composite material was used for the modification of the glass carbon electrode to fabricate the PI-5-CA/C-SWCNTs/GCE-based immunosensor and was successfully applied for the sensitive detection of E. coli O157:H7. The fabricated immunosensor exhibited an outstanding electrocatalytic activity toward the detection of E. coli O157:H7 with a remarkably lowest limit of detection (2.5 CFU/ml, LOD = 3 SD/k, n = 3) and has a wide linear range from 2.98×101 to 2.98×107 CFU/ml. Inspired from the excellent results, the fabricated electrode was applied for the detection of bacteria from real samples (water samples) with a good recovery rate (98.13–107.69%) as well as an excellent stability and specificity. Owing to its simple preparation, excellent performance, and detection time within 30 min, our proposed immunosensor will open a new horizon in different fields for the sensitive detection of bacteria from real samples.

A novel electrochemical immunosensor based on Fe3O4@graphene nanocomposite modified glassy carbon electrode for rapid detection of Salmonella in milk

Foods contaminated by foodborne pathogens have always been a great threat to human life. Herein, we constructed an electrochemical immunosensor for Salmonella detection by using a Fe₃O₄@graphene modified electrode. Because of the excellent electrical conductivity and mechanical stability of graphene and the large specific surface area of Fe₃O₄, the Fe₃O₄@graphene nanocomposite exhibits an excellent electrical signal, which greatly increased the sensitivity of the immunosensor. Gold nanoparticles were deposited on Fe₃O₄@graphene nanocomposite by electrochemical technology for the immobilization of the antibody. Cyclic voltammetry was selected to electrochemically characterize the construction process of immunosensors. The microstructure and morphology of related nanocomposites were analyzed by scanning electron microscopy. Under optimized experimental conditions, a good linear relationship was achieved in the Salmonella concentration range of 2.4 × 10² to 2.4 × 10⁷ cfu/mL, and the limit of detection of the immunosensor was 2.4 × 10² cfu/mL. Additionally, the constructed immunosensor exhibited acceptable selectivity, reproducibility, and stability and provides a new reference for detecting pathogenic bacteria in milk.

Electrochemical immunosensor development based on core-shell high-crystalline graphitic carbon nitride@carbon dots and Cd0.5Zn0.5S/d-Ti3C2Tx MXene composite for heart-type fatty acid-binding protein detection

Acute myocardial infarction (AMI) is a significant health problem owing to its high mortality rate. Heart-type fatty acid-binding protein (h-FABP) is an important biomarker in the diagnosis of AMI. In this work, an electrochemical h-FABP immunosensor was developed based on Cd_0.5Zn_0.5S/d-Ti₃C₂T_x MXene (MXene: Transition metal carbide or nitride) composite as signal amplificator and core-shell high-crystalline graphitic carbon nitride@carbon dots (hc-g-C₃N₄@CDs) as electrochemical sensor platform. Firstly, a facile calcination technique was applied to the preparation of hc-g-C₃N₄@CDs and immobilization of primary antibody was performed on hc-g-C₃N₄@CDs surface. Then, the conjugation of the second antibody to Cd_0.5Zn_0.5S/d-Ti₃C₂T_x MXene was carried out by strong π-π and electrostatic interactions. The prepared electrochemical h-FABP immunosensor was characterized by transmission electron microscopy (TEM), scanning electron microscopy (SEM), x-ray diffraction (XRD) method, Fourier-transform infrared spectroscopy (FTIR), x-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV), and electrochemical impedance spectroscopy (EIS). The prepared electrochemical h-FABP immunosensor indicated a good sensitivity with detection limit (LOD) of 3.30 fg mL^-1 in the potential range +0.1 to +0.5 V. Lastly, low-cost, satisfactory stable, and environmentally friendly immunosensor was presented for the diagnosis of acute myocardial infarction.

Poly(indole-5-carboxylic acid)/reduced graphene oxide/gold nanoparticles/phage-based electrochemical biosensor for highly specific detection of Yersinia pseudotuberculosis

Yersinia pseudotuberculosis is an enteric bacterium causing yersiniosis in humans. The existing Yersinia pseudotuberculosis detection methods are time-consuming, requiring a sample pretreatment step, and are unable to discriminate live/dead cells. The current work reports a phage-based electrochemical biosensor for rapid and specific detection of Yersinia pseudotuberculosis. The conductive poly(indole-5-carboxylic acid), reduced graphene oxide, and gold nanoparticles are applied for surface modification of the electrode. They possess ultra-high redox stability and retain 97.7% of current response after performing 50 consecutive cycles of cyclic voltammetry.The specific bacteriophages vB_YepM_ZN18 we isolated from hospital sewage water were immobilized on modified electrodes by Au-NH₂ bond between gold nanoparticles and phages. The biosensor fabricated with nanomaterials and phages were utilized to detect Yersinia pseudotuberculosis successfully with detection range of 5.30 × 10² to 1.05 × 10⁷ CFU mL^-1, detection limit of 3 CFU mL^-1, and assay time of 35 min. Moreover, the biosensor can specifically detect live Yersinia pseudotuberculosis without responding to phage-non-host bacteria and dead Yersinia pseudotuberculosis cells. These results suggest that the proposed biosensor is a promising tool for the rapid and selective detection of Yersinia pseudotuberculosis in food, water, and clinical samples.

New immunoprobe: Dual-labeling ZIF-8 embellished with multifunctional bovine serum albumin lamella for electrochemical immunoassay of tumor marker

A new immunoprobe, which can initiate the sedimentation of Ag nanoparticles (NPs) on an electrode surface, was developed for the electrochemical detection of carbohydrate antigen 72-4 (CA 72-4). To design the immunoprobe, zeolitic imidazolate frameworks (ZIFs) were employed as the carrier to enrich thionine molecules, then bovine serum albumin (BSA) was modified on the electrode surface. Advantageously, BSA, served as an anchor to further attach the labeling antibodies (Ab₂) and alkaline phosphatase (ALP) to also be modified on the surface through covalent bonding. To construct the immunosensor, multiwalled carbon nanotube-graphene oxide composites were employed to provide active sites, and the electrodeposited Au NPs were used to immobilize coating antibodies. In the presence of CA 72-4, a sandwich immunosensor was established, and a cascade reaction was initiated to deposit Ag NPs under the catalysis, which can further improve the conductivity of electrode interface. Under the optimal conditions, the immunosensor displayed excellent performance with a wide linear range from 1 μU mL^-1 to 10 U mL^-1 and an ultralow detection limit of 0.438 μU mL^-1 (S/N = 3).

Recent Advances of Conducting Polymers and Their Composites for Electrochemical Biosensing Applications

Conducting polymers (CPs) have been at the center of research owing to their metal-like electrochemical properties and polymer-like dispersion nature. CPs and their composites serve as ideal functional materials for diversified biomedical applications like drug delivery, tissue engineering, and diagnostics. There have also been numerous biosensing platforms based on polyaniline (PANI), polypyrrole (PPY), polythiophene (PTP), and their composites. Based on their unique properties and extensive use in biosensing matrices, updated information on novel CPs and their role is appealing. This review focuses on the properties and performance of biosensing matrices based on CPs reported in the last three years. The salient features of CPs like PANI, PPY, PTP, and their composites with nanoparticles, carbon materials, etc. are outlined along with respective examples. A description of mediator conjugated biosensor designs and enzymeless CPs based glucose sensing has also been included. The future research trends with required improvements to improve the analytical performance of CP-biosensing devices have also been addressed.

Advances in immunosensor technology

In recent years, advances in immunosensor device fabrication have significantly expanded the use of this technology in a broad range of applications including clinical diagnosis, food analysis, quality control, environmental studies and industrial monitoring. The most important aspect in fabrication is to obtain a design that provides a low detection limit. The utilization of nanomaterials as a label, catalyst and biosensing transducer is, perhaps, the most popular approach in ultrasensitive devices. This chapter reviews recent advances in immunosensor fabrication and summarizes the most recent studies. Strategies employed to significantly improve sensitivity and specificity of immunosensor technology and the advantages and limitations thereof are explored.

Triple-nanostructuring-based noninvasive electro-immune sensing of CagA toxin for Helicobacter pylori detection

BACKGROUND

Helicobacter pylori (H pylori) is gram-negative, spiral, and microaerophilic bacteria which can survive in ~2%-10% oxygen level. It was reported to populate in human gastric mucosa and leads to gastric cancer without any age or gender difference.

MATERIALS AND METHODS

In this study, we are targeting label-free electrochemical immunosensor development for rapid H pylori detection after covalently immobilizing the antibody (CagA) over the nanomaterials modified Au electrode. Titanium oxide nanoparticles (TiO₂ NPs), carboxylated multi-walled carbon nanotubes (c-MWCNT), and conducting polymer polyindole carboxylic acid (Pin5COOH) composites (TiO₂ NPs/c-MWCNT/Pin5COOH) were synthesized and further utilized in immunosensor development as an electrochemical interface onto Au electrode. The stepwise modifications of CagAantibody/TiO₂ NPs/c-MWNCT/Pin5COOH/Au electrode were electrochemically studied.

RESULTS

Possessing the unique features of advanced materials, the proposed immunosensor reported low sensing limit of 0.1 ng/mL in dynamic linear range of 0.1-8.0 ng/mL with higher stability and reproducibility. Furthermore, developed sensor-based determination of H pylori in five human stool specimens has shown good results with suitable accuracy.

CONCLUSIONS

This work lays strong foundation toward developing nanotechnology-enabled electrochemical sensor for ultrasensitive and early detection of H pylori in noninvasively collected clinical samples.

Improving the reproducibility, accuracy, and stability of an electrochemical biosensor platform for point-of-care use

Electrochemical biosensors possess numerous desirable qualities for target detection, such as portability and ease of use, and are often considered for point-of-care (POC) development. Label-free affinity electrochemical biosensors constructed with semiconductor manufacturing technology (SMT)-produced electrodes and a streptavidin biomediator currently display the highest reproducibility, accuracy, and stability in modern biosensors. However, such biosensors still do not meet POC guidelines regarding these three characteristics. The purpose of this research was to resolve the limitations in reproducibility and accuracy caused by problems with production of the biosensors, with the aim of developing a platform capable of producing devices that exceed POC standards. SMT production settings were optimized and bioreceptor immobilization was improved through the use of a unique linker, producing a biosensor with exceptional reproducibility, impressive accuracy, and high stability. Importantly, the three characteristics of the sensors produced using the proposed platform all meet POC standards set by the Clinical and Laboratory Standards Institute (CLSI). This suggests possible approval of the biosensors for POC development. Furthermore, the detection range of the platform was demonstrated by constructing biosensors capable of detecting common POC targets, including circulating tumor cells (CTCs), DNA/RNA, and curcumin, and the devices were optimized for POC use. Overall, the platform developed in this study shows high potential for production of POC biosensors.