Polyvalent Biotinylated Aptamer Scaffold for Rapid and Sensitive Detection of Tau Proteins

Polyvalent Aptamers Structure-Mediated Fluorescent Aptasensor for the Early Diagnosis of Alzheimer's Disease by Coupling with HCR and CRISPR-Cas System

The early diagnosis of Alzheimer's disease (AD) plays a vital role in slowing the progression of AD and improving the quality of human life. However, it is still a challenge in the medical field. Herein, an ultrasensitive fluorescent aptasensor was designed for the detection of special phosphorylated tau181 (P-tau181) by coupling with polyvalent aptamers (PAs) structure, hybridization chain reaction (HCR), and the CRISPR-Cas system. Coupling with the signal amplification strategy, the specific recognition ability of the aptamer, and the high cleavage activity of Cas12a protein, the designed aptasensor showed a wide linear range (0.1-106 pg/mL), a low detection limit (0.069 pg/mL), high selectivity, and excellent anti-interference ability for the detection of P-tau181. Moreover, the aptasensor can efficiently analyze P-tau181 in artificial cerebro spinal fluid (aCSF) and serum, proving that it has a promising application in the early diagnosis of AD.

Recent Progress in the Application of Tau Protein Biosensors for Diagnosis of Neurodegenerative Diseases

The microtubule-associated Tau protein is found in the central nervous system (CNS) in six major isoforms. Neurodegenerative diseases have been linked to post-translational changes of Tau, most notably phosphorylation. Tau protein's molecular diversity is highly helpful in the identification of neurodegenerative illnesses. Nonetheless, one major obstacle to the early detection of brain illness is the nanoscale identification of tau proteins. The standard methods for identifying tau protein include western blotting, polymerase chain reaction (PCR), and real-time PCR. Enzyme-linked immunosorbent assay (ELISA) is another approach used. The limited sensitivity and specificity of these detections, together with the need for sophisticated equipment, are some of their drawbacks. The development of innovative and complex methods for tau protein screening is necessary to address the aforementioned issues. Biosensors are a cutting-edge instrument that may help identify various neurodegenerative biomarkers as early as feasible. This paper provides an overview of the most recent developments in the detection of neurodegenerative diseases employing biosensors built on nanotechnology and methods for imaging, electrochemical, and optical detection of the Tau protein. Furthermore, we outline the present difficulties and suggest a possible course for biosensor-based detection and intervention in the future.

Aptamer-based sensors for fluid biopsies of protein disease markers

Fluid biopsy technology, characterized by its minimally invasive nature, speed, and continuity, has become a rapidly advancing and widely applied real-time diagnostic technique. Among various biomarkers, proteins represent the most abundant class of disease indicators. The sensitive and accurate detection of protein markers in bodily fluids is significantly influenced by the control exerted by recognition ligands. Aptamers, which are structurally dynamic functional oligonucleotides, exhibit high affinity, specific recognition of targets, and notable characteristics of high editability and modularity. These features make aptamer universal "recognition-capture" components, contribute to a significant leap in their applications within the biosensor domain. In this context, we provide a comprehensive review of the extensive application of aptamer-based biosensors in fluid biopsy. We systematically compile the characteristics and construction strategies of aptamer-based biosensors tailored for fluid biopsy, including aptamer sequences, affinity (KD), fluid background, sensing technologies, sensor construction strategies, incubation time, detection performance, and influencing factors. Furthermore, a comparative analysis of their advantages and disadvantages was conducted. In conclusion, we delineate and deliberate on prospective research trajectories and challenges that lie ahead in the realm of aptamer-based biosensors for fluid biopsy.

Aptamer-based assembly systems for SARS-CoV-2 detection and therapeutics

Nucleic acid aptamers are oligonucleotide chains with molecular recognition properties. Compared with antibodies, aptamers show advantages given that they are readily produced via chemical synthesis and elicit minimal immunogenicity in biomedicine applications. Notably, aptamer-encoded nucleic acid assemblies further improve the binding affinity of aptamers with the targets due to their multivalent synergistic interactions. Specially, aptamers can be engineered with special topological arrangements in nucleic acid assemblies, which demonstrate spatial and valence matching towards antigens on viruses, thus showing potential in the detection and therapeutic applications of viruses. This review presents the recent progress on the aptamers explored for SARS-CoV-2 detection and infection treatment, wherein applications of aptamer-based assembly systems are introduced in detail. Screening methods and chemical modification strategies for aptamers are comprehensively summarized, and the types of aptamers employed against different target domains of SARS-CoV-2 are illustrated. The evolution of aptamer-based assembly systems for the detection and neutralization of SARS-CoV-2, as well as the construction principle and characteristics of aptamer-based DNA assemblies are demonstrated. The typically representative works are presented to demonstrate how to assemble aptamers rationally and elaborately for specific applications in SARS-CoV-2 diagnosis and neutralization. Finally, we provide deep insights into the current challenges and future perspectives towards aptamer-based nucleic acid assemblies for virus detection and neutralization in nanomedicine.

Polyvalent aptamer scaffold coordinating light-responsive oxidase-like nanozyme for sensitive detection of zearalenone

An efficient aptasensor was developed for the colorimetric determination of zearalenone (ZEN) based on polyvalent aptamer scaffold and light-responsive oxidase-like nanozyme. The sensitivity and efficiency of the development method were significantly improved owing to rich aptamers and signal labels (3, 4-dihydroxybenzoic acid, PCA) packed in the scaffold. The scaffold integrated functions of target recognition, surface immobilization and signal transduction. The photoresponsive nanoenzyme of TiO2-PCA was formed by PCA coordinated with Ti (IV) on the surface of TiO2. TiO2-PCA catalyzed dissolved oxygen rather than H2O2 to generate colorimetric signal by stimulating the chromogenic substrate, which made the assay greener and safer. The detection limit of colorimetric mode was 0.0087 ng/mL and the satisfactory recoveries 92.00 %-111.00 % were achieved in spiked food samples. This strategy opens new horizons for sensitive detection of small molecule hazards and promises to be a powerful tool for safeguarding food safety.

Vertical Graphene-Based Printed Electrochemical Biosensor for Simultaneous Detection of Four Alzheimer's Disease Blood Biomarkers

Early detection and timely intervention play a vital role in the effective management of Alzheimer's disease. Currently, the diagnostic accuracy for Alzheimer's disease based on a single blood biomarker is relatively low, and the combined use of multiple blood biomarkers can greatly improve diagnostic accuracy. Herein, we report a printed electrochemical biosensor based on vertical graphene (VG) modified with gold nanoparticles (VG@nanoAu) for the simultaneous detection of four Alzheimer's disease blood biomarkers. The printed electrochemical electrode array was constructed by laser etching and inkjet printing. Then gold nanoparticles were modified onto the working electrode surface via electrodeposition to further improve the sensitivity of the sensor. In addition, the entire printed electrochemical sensing system incorporates an electrochemical micro-workstation and a smartphone. The customized electrochemical micro-workstation incorporates four electro-chemical control chips, enabling the sensor to simultaneously analyze four biomarkers. Consequently, the printed electrochemical sensing system exhibits excellent analytical performance due to the large surface area, biocompatibility, and good conductivity of VG@nanoAu. The detection limit of the sensing system for Aβ40, Aβ42, T-tau, and P-tau181 was 0.072, 0.089, 0.071, and 0.051 pg/mL, respectively, which meets the detection requirements of Alzheimer's disease blood biomarkers. The printed electrochemical sensing system also exhibits good specificity and stability. This work has great value and promising prospects for early Alzheimer's disease diagnosis using blood biomarkers.

Tau Protein Biosensors in the Diagnosis of Neurodegenerative Diseases

Tau protein plays a crucial role in diagnosing neurodegenerative diseases. However, performing an assay to detect tau protein on a nanoscale is a great challenge for early diagnosis of diseases. Enzyme-linked immunosorbent assay (ELISA), western-blotting, and molecular-based methods, e.g., PCR and real-time PCR, are the most widely used methods for detecting tau protein. These methods are subject to certain limitations: the need for advanced equipment, low sensitivity, and specificity, to name a few. With the above said, it is necessary to discover advanced and novel methods for monitoring tau protein. Counted among remarkable approaches adopted by researchers, biosensors can largely eliminate the difficulties and limitations associated with conventional methods. The main objective of the present study is to review the latest biosensors developed to detect the tau protein. Furthermore, the problems and limitations of conventional diagnosis methods were discussed in detail.

Aptamer-Based Targeted Protein Degradation

The selective removal of misfolded, aggregated, or aberrantly overexpressed protein plays an essential role in maintaining protein-dominated biological processes. In parallel, the precise knockout of abnormal proteins is inseparable from the accurate identification of proteins within complex environments. Guided by these precepts, small molecules, or antibodies, are commonly used as protein recognition tools for developing targeted protein degradation (TPD) technology. Indeed, TPD has shown tremendous prospects in chronic diseases, rare diseases, cancer research, and other fields. Meanwhile, aptamers are short RNA or DNA oligonucleotides that can bind to target proteins with high specificity and strong affinity. Accordingly, aptamers are actively used in designing and constructing TPD technology. In this perspective, we provide a brief introduction to TPD technology in its current progress, and we summarize its application challenges. Recent advances in aptamer-based TPD technology are reviewed, together with corresponding challenges and outlooks.

Engineering Circular Aptamer Assemblies with Tunable Selectivity to Cell Membrane Antigens In Vitro and In Vivo

The strategy of enhancing molecular recognition by improving the binding affinity of drug molecules against targets has generated a lot of successful therapeutic applications. However, one critical consequence of such affinity improvement, generally called "on-target, off-tumor" toxicity, emerged as a major obstacle limiting their clinical usage. Herein, we provide a modular assembly strategy that affords affinity-tunable DNA nanostructures allowing for immobilizing multiple aptamers that bind to the example antigen of EpCAM with different affinities. We develop a theoretical model proving that the apparent affinity of aptamer assemblies to target cells varies with antigen density as well as aptamer valency. More importantly, we demonstrate experimentally that the theoretical model can be used to predict the least valency required for discrimination between EpCAM^high and EpCAM^low cells in vitro and in vivo. We believe that our strategy will have broad applications in an engineering nucleic acid-based delivery platform for targeted and cell therapy.

Heteromultivalent scaffolds fabricated by biomimetic co-assembly of DNA-RNA building blocks for the multi-analysis of miRNAs

Heteromultivalent scaffolds with different repeated monomers have great potential in biomedicine, but convenient construction strategies for integrating various functional modules to achieve multiple biological functions are still lacking. Here, taking advantage of the heteromultivalent effect of dendritic nucleic acids and the specific biochemical properties of microRNAs (miRNAs), we assembled novel heteromultivalent nucleic acid scaffolds by biomimetic co-assembly of DNA-RNA building blocks. In our approach, two miRNAs were used to initiate and maintain dendritic structures in an interdependent manner; so, the heteromultivalent nanostructure can only form in the presence of both miRNAs. The proposed nanostructure can be used for one-step analysis of two miRNAs in an AND logic format. Taking miR-18b-5p and miR-342-3p which are associated with Alzheimer's disease as an example, a FRET sensing system was fabricated for the simultaneous analysis of two miRNAs within one hour at picomolar concentration. Further studies show that the designed device may have the potential to distinguish between AD patients and the healthy population by analysis of two miRNAs in CSF (cerebrospinal fluid) samples, suggesting its possible applicability in clinics.

Electrochemical immunosensor based on superwettable microdroplet array for detecting multiple Alzheimer's disease biomarkers

Alzheimer's disease (AD) is a neurodegenerative disease caused by neurons damage in the brain, and it poses a serious threat to human life and health. No efficient treatment is available, but early diagnosis, discovery, and intervention are still crucial, effective strategies. In this study, an electrochemical sensing platform based on a superwettable microdroplet array was developed to detect multiple AD biomarkers containing Aβ40, Aβ42, T-tau, and P-tau181 of blood. The platform integrated a superwettable substrate based on nanoAu-modified vertical graphene (VG@Au) into a working electrode, which was mainly used for droplet sample anchoring and electrochemical signal generation. In addition, an electrochemical micro-workstation was used for signals conditioning. This superwettable electrochemical sensing platform showed high sensitivity and a low detection limit due to its excellent characteristics such as large specific surface, remarkable electrical conductivity, and good biocompatibility. The detection limit for Aβ40, Aβ42, T-tau, and P-tau181 were 0.064, 0.012, 0.039, and 0.041 pg/ml, respectively. This study provides a promising method for the early diagnosis of AD.

Portable Vertical Graphene@Au-Based Electrochemical Aptasensing Platform for Point-of-Care Testing of Tau Protein in the Blood

Alzheimer's disease (AD) is a long-term neurodegenerative disease that poses a serious threat to human life and health. It is very important to develop a portable quantitative device for AD diagnosis and personal healthcare. Herein, we develop a portable electrochemical sensing platform for the point-of-care detection of AD biomarkers in the blood. Such a portable platform integrates nanoAu-modified vertical graphene (VG@Au) into a working electrode, which can significantly improve sensitivity and reduce detection limit due to the large specific surface, excellent electrical conductivity, high stability, and good biocompatibility. The tau protein, as an important factor in the course of AD, is selected as a key AD biomarker. The results show that the linear range of this sensing platform is 0.1 pg/mL to 1 ng/mL, with a detection limit of 0.034 pg/mL (S/N = 3), indicating that this portable sensing platform meets the demand for the detection of the tau protein in the blood. This work offers great potential for AD diagnosis and personal healthcare.

Current progress in aptamer-based sensing tools for ultra-low level monitoring of Alzheimer's disease biomarkers

Alzheimer's disease (AD) as common late-life dementia is pathologically associated with the irreversible and progressive disorder, misfolding, deposition, and accumulation of the brain proteins. Especially, the formation of fibrous amyloid plaques by aggregation of amyloid-β peptides is the pathological cause of this neurologic disorder disease. Besides, tau protein isoforms destabilize the microtubule filaments through post-translational modifications and induce nerve cells' death. Amyloid-β peptides and tau proteins are considered as the critical symptom and reliable molecular biomarkers for the early diagnosis of AD. AD is characterized by impaired thinking proficiencies, cognitive decline, memory loss, and behavioral disability. Since there is no efficacious therapy for AD at present, the development of precise sensing tools for the early diagnosis of this disease is essential and crucial. Aptamer-based biosensors (aptasensors) have acquired utmost importance in the field of AD healthcare, due to excellent sensitivity and specificity, ease-of-use, cost-effectiveness, portability, and rapid assay time. Here, we highlight the recent developments and novel perspectives in the field of aptasensor design to quantitatively monitor the AD biomarkers. Finally, some results are represented to achieve a promising viewpoint for introducing the novel aptasensor test kits in the future.