Antibody coated conductive polymer for the electrochemical immunosensing of Human Cardiac Troponin I in blood plasma

Critical Suitability Evaluation of Caco-2 Cells for Gut-on-a-Chip

Currently, culturing Caco-2 cells in a Gut-on-a-chip (GOC) is well-accepted for developing intestinal disease models and drug screening. However, Caco-2 cells were found to overexpress surface proteins (e.g., P-gp) compared with the normal intestinal epithelial cells in vivo. To critically evaluate the challenge and suitability of Caco-2 cells, a GOC integrated with a carcinoembryonic antigen (CEA) biosensor was developed. This three-electrode system electrochemical sensor detects CEA by antigen-antibody specific binding, and it exhibits high selectivity, excellent stability, and good reproducibility. Under dynamic culturing in the GOC, Caco-2 cells exhibited an intestinal villus-like structure and maintained tissue barrier integrity. Meanwhile, CEA was discovered to be secreted from 0 to 0.22 ng/mL during the 10-day culturing of Caco-2 cells. Especially, CEA secretion increased significantly with the differentiation of Caco-2 cells after 6 days of culturing. The sustained high-level CEA secretion may induce cells to avoid apoptotic stimuli, which faithfully reflects the efficacy of a new drug and the mechanism of intestinal disease. Different kinds of cell types (e.g., intestinal primary cells, stem cell-induced differentiation) in the GOC should be attempted for drug screening in the future.

Structure Remodeling Strategy for Open-Cage NiFe@Fe-bis-PBA with Enhanced Peroxidase-like Activity To Monitor Tumor Markers

The inherent metal elements and structures of Prussian blue analogue (PBA) nanozymes have restricted their enzyme-mimicking activity. Therefore, the rational regulation of PBA nanozymes to improve their catalytic activity is highly desirable for biosensing applications. Herein, we propose a structure remodeling strategy to construct an open-cage Fe PBA-anchored NiFePBA (NiFe@Fe bis-PBA) nanozyme with significantly enhanced enzyme-mimicking activity. The formation process and mechanism for this bis-PBA nanozyme were studied in detail. Specifically, a cubic NiFePBA precursor was first synthesized and modified with polyvinylpyrrolidone (PVP). With the aid of hydrochloric acid, the added potassium ferricyanide was reduced by PVP and re-coordinated on the surface of NiFePBA to form the NiFe@Fe bis-PBA nanozyme with a special open-cage core-shell structure. The resultant NiFe@Fe bis-PBA nanozyme was further exploited to immobilize secondary antibodies, serving as a novel signal probe for developing highly sensitive electrochemical immunosensors for monitoring tumor markers. The constructed electrochemical immunosensor possesses a very wide linear range of 0.005-100 ng/mL and a low detection limit of 0.89 pg/mL for alpha-fetoprotein with high specificity and acceptable reproducibility and stability. This work offers a general and promising strategy for remodeling PBA nanozymes with a very favorable structure and metal element distribution, which enhances their enzyme-mimicking properties for applications in different fields.

Wearable and implantable biosensors: mechanisms and applications in closed-loop therapeutic systems

This review article examines the current state of wearable and implantable biosensors, offering an overview of their biosensing mechanisms and applications. We also delve into integrating these biosensors with therapeutic systems, discussing their operational principles and incorporation into closed-loop devices. Biosensing strategies are broadly categorized into chemical sensing for biomarker detection, physical sensing for monitoring physiological conditions such as pressure and temperature, and electrophysiological sensing for capturing bioelectrical activities. The discussion extends to recent developments in drug delivery and electrical stimulation devices to highlight their significant role in closed-loop therapy. By integrating with therapeutic devices, biosensors enable the modulation of treatment regimens based on real-time physiological data. This capability enhances the patient-specificity of medical interventions, an essential aspect of personalized healthcare. Recent innovations in integrating biosensors and therapeutic devices have led to the introduction of closed-loop wearable and implantable systems capable of achieving previously unattainable therapeutic outcomes. These technologies represent a significant leap towards dynamic, adaptive therapies that respond in real-time to patients' physiological states, offering a level of accuracy and effectiveness that is particularly beneficial for managing chronic conditions. This review also addresses the challenges associated with biosensor technologies. We also explore the prospects of these technologies to address their potential to transform disease management with more targeted and personalized treatment solutions.

Paper electrochemical immunosensor for the rapid screening of Galectin-3 patients with heart failure

A paper electrochemical immunosensor for the combined binding and quantification of the heart failure (HF) biomarker Galectin-3 has been developed. The simple design of the new sensor is comprised of paper material that is decorated with gold nanostructures, to maximize its electroactive surface area, and functionalized with target-specific recognition molecules to selectively bind the protein from aqueous solutions. The binding of the protein caused the blockage of the electron flow to the sensor electroactive surface, thus causing its oxidation potential to shift and the corresponding current to reduce quantitatively with the increase in the protein concentration within the working range of 0.5ng/mL-8ng/mL (LOQ-0.5 ng/mL). This novel sensor was able to quantify Galectin-3 concentration in saliva samples from HF patients and healthy controls within 20 min with good reproducibility (RSD = 3.64%), without the need for complex sample processing steps. The electrochemical measurements of the patient samples were cross validated by ELISA where the percent agreement between the two methods was found to be 92.7% (RSD = 7.20%). Therefore, the new paper immunosensor sensor has a strong potential for rapid and cost-effective screening of the Galectin 3 biomarker at points of care, thus supporting the timely diagnosis of heart failure.

Covalent organic framework-based immunosensor to detect plasma Latexin reveals novel biomarker for coronary artery diseases

It is a great challenge to develop an efficient and rapid method to detect of biomarkers of cardiovascular disease. In this research, a differential pulse voltammetry (DPV)-based ultrasensitive immunosensor for the detection of plasma Latexin (LXN) has been established. With the aim to increase the surface area of the bare glassy carbon electrode (GCE), multi-walled carbon nanotube-graphene oxide has been developed. Covalent organic frameworks (COFs) are dropped with gold nanoparticles (AuNPs), secondary antibody and thionine (Thi-Ab2-Au-COFs) act as the signal probe with high electronic conductivity. Under the ideal conditions, the immunosensor displayed a broad linear response range from 0.01 ng mL-1 to 100 ng mL-1, with a detection limit of 50 pg mL-1 (S/N = 3). The immunosensor also demonstrates outstanding sensitivity, repeatability, and stability. Finally, we utilized the designed immunosensor to detect plasma LXN in coronary artery disease (CAD) patients, and the data showed that plasma LXN was significantly increased in CAD patients with a good performance of ROCAUC (AUC 0.871, 95 % CI 0.725-1.0, p = 0.002), indicating plasma LXN is a potential biomarker of cardiovascular disease. This immunosensor is a promising strategy for screening CAD patients in clinical practice.

Conductive Polymers and Their Nanocomposites: Application Features in Biosensors and Biofuel Cells

Conductive polymers and their composites are excellent materials for coupling biological materials and electrodes in bioelectrochemical systems. It is assumed that their relevance and introduction to the field of bioelectrochemical devices will only grow due to their tunable conductivity, easy modification, and biocompatibility. This review analyzes the main trends and trends in the development of the methodology for the application of conductive polymers and their use in biosensors and biofuel elements, as well as describes their future prospects. Approaches to the synthesis of such materials and the peculiarities of obtaining their nanocomposites are presented. Special emphasis is placed on the features of the interfaces of such materials with biological objects.

Sulfonated Starch-Graft-Polyaniline@Graphene Electrically Conductive Nanocomposite: Application for Tyrosinase Immobilization

The interaction of tyrosinase with sulfonated starch-graft-polyaniline@graphene (SSt-g-PANI@G) nanocomposite was investigated by electrochemical methods. The activity of the immobilized tyrosinase (Tyase) was proved by the electrochemical detection of three substrates (L-dopa, caffeic acid, and catechol). The SSt-g-PANI@G nanocomposite was characterized by Fourier-transform infrared spectra (FT-IR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy-dispersive X-ray analysis (EDX), and thermogravimetric analysis (TGA). To immobilize tyrosinase on the surface of the nanocomposite, a simple drop-casting technique was used. The presence of sulfuric acid and hydroxyl groups in SSt, amine groups in PANI, and high surface-to-volume ratio and electrical conductivity of graphene in the prepared nanocomposite led to good enzyme immobilization on the electrode surface. The modified electrode showed a suitable catalytic effect on the electrochemical redox agent, compared with the bare electrode. The peak current responses for three substrates were studied with a calibration curve derived using cyclic voltammetry (CV) and differential pulse voltammetry (DPV). In addition, the fabricated SSt-g-PANI@G/Tyase/GCE showed a more suitable response to catechol, L-dopa, and caffeic acid substrates, respectively.

A paper-based optical sensor for the screening of viruses through the cysteine residues of their surface proteins: A proof of concept on the detection of coronavirus infection

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) is a serious threat to human health. Current methods such as reverse transcription polymerase chain reaction (qRT-PCR) are complex, expensive, and time-consuming. Rapid, and simple screening methods for the detection of SARS-CoV-2 are critically required to fight the current pandemic. In this work we present a proof of concept for, a simple optical sensing method for the screening of SARS-CoV-2 through its spike protein subunit S1. The method utilizes a target-specific extractor chip to bind the protein from the biological specimens. The disulfide bonds of the protein are then reduced into a biothiol with sulfhydryl (SH) groups that react with a blue-colored benzothiazole azo dye-Hg complex (BAN-Hg) and causes the spontaneous change of its blue color to pink which is observable by the naked eye. A linear relationship between the intensity of the pink color and the logarithm of reduced S1 protein concentration was found within the working range 130 ng.mL⁻¹-1.3 pg mL⁻¹. The lowest limit of detection (LOD) of the assay was 130 fg mL⁻¹. A paper based optical sensor was fabricated by loading the BAN-Hg sensor onto filter paper and used to screen the S1 protein in spiked saliva and patients’ nasopharyngeal swabs. The results obtained by the paper sensor corroborated with those obtained by qRT-PCR. The new paper-based sensing method can be extended to the screening of many viruses (e.g. the human immunodeficiency virus, the human polyomavirus, the human papilloma virus, the adeno associated viruses, the enteroviruses) through the cysteine residues of their capsid proteins. The new method has strong potential for screening viruses at pathology labs and in remote areas that lacks advanced scientific infrastructure. Further clinical studies are warranted to validate the new sensing method.

Multilayered Mesoporous Composite Nanostructures for Highly Sensitive Label-Free Quantification of Cardiac Troponin-I

Cardiac troponin-I (cTnI) is a well-known biomarker for the diagnosis and control of acute myocardial infarction in clinical practice. To improve the accuracy and reliability of cTnI electrochemical immunosensors, we propose a multilayer nanostructure consisting of Fe₃O₄-COOH labeled anti-cTnI monoclonal antibody (Fe₃O₄-COOH-Ab₁) and anti-cTnI polyclonal antibody (Ab₂) conjugated on Au-Ag nanoparticles (NPs) decorated on a metal–organic framework (Au-Ag@ZIF-67-Ab₂). In this design, Fe₃O₄-COOH was used for separation of cTnI in specimens and signal amplification, hierarchical porous ZIF-67 extremely enhanced the specific surface area, and Au-Ag NPs synergically promoted the conductivity and sensitivity. They were additionally employed as an immobilization platform to enhance antibody loading. Electron microscopy images indicated that Ag-Au NPs with an average diameter of 1.9 ± 0.5 nm were uniformly decorated on plate-like ZIF-67 particles (with average size of 690 nm) without any agglomeration. Several electrochemical assays were implemented to precisely evaluate the immunosensor performance. The square wave voltammetry technique exhibited the best performance with a sensitivity of 0.98 mA mL cm⁻² ng⁻¹ and a detection limit of 0.047 pg mL⁻¹ in the linear range of 0.04 to 8 ng mL⁻¹.