A label-free reusable aptasensor for Alzheimer's disease

Oligomeric amyloid-β targeted contrast agent for MRI evaluation of Alzheimer's disease mouse models

Background

Oligomeric amyloid beta (oAβ) is a toxic factor that acts in the early stage of Alzheimer's disease (AD) and may initiate the pathologic cascade. Therefore, detecting oAβ has a crucial role in the early diagnosis, monitoring, and treatment of AD.

Purpose

The purpose of this study was to evaluate MRI signal changes in different mouse models and the time-dependent signal changes using our novel gadolinium (Gd)-dodecane tetraacetic acid (DOTA)- ob5 aptamer contrast agent.

Methods

We developed an MRI contrast agent by conjugating Gd-DOTA-DNA aptamer called ob5 to evaluate its ability to detect oAβ deposits in the brain using MRI. A total of 10 control mice, 9 3xTg AD mice, and 11 APP/PS/Tau AD mice were included in this study, with the age of each model being 16 or 36 weeks. A T1-weighted image was acquired at the time points before (0 min) and after injection of the contrast agent at 5, 10, 15, 20, and 25 min. The analyses were performed to compare MRI signal differences among the three groups and the time-dependent signal differences in different mouse models.

Results

Both 3xTg AD and APP/PS/Tau AD mouse models had higher signal enhancement than control mice at all scan-time points after injection of our contrast media, especially in bilateral hippocampal areas. In particular, all Tg AD mouse models aged 16 weeks showed a higher contrast enhancement than those aged 36 weeks. For 3xTg AD and APP/PS/Tau AD groups, the signal enhancement was significantly different among the five time points (0 min, 5 min, 10 min, 15 min, 20 min, and 25 min) in multiple ROI areas, typically in the bilateral hippocampus, left thalamus, and left amygdala.

Conclusion

The findings of this study suggest that the expression of the contrast agent in different AD models demonstrates its translational flexibility across different species. The signal enhancement peaked around 15-20 min after injection of the contrast agent. Therefore, our novel contrast agent targeting oAβ has the potential ability to diagnose early AD and monitor the progression of AD.

Amyloid detection in neurodegenerative diseases using MOFs

Neurodegenerative diseases (amyloid diseases such as Alzheimer's and Parkinson's), stemming from protein misfolding and aggregation, encompass a spectrum of disorders with severe systemic implications. Timely detection is pivotal in managing these diseases owing to their significant impact on organ function and high mortality rates. The diverse array of amyloid disorders, spanning localized and systemic manifestations, underscores the complexity of these conditions and highlights the need for advanced detection methods. Traditional approaches have focused on identifying biomarkers using imaging techniques (PET and MRI) or invasive procedures. However, recent efforts have focused on the use of metal-organic frameworks (MOFs), a versatile class of materials known for their unique properties, in revolutionizing amyloid disease detection. The high porosity, customizable structures, and biocompatibility of MOFs enable their integration with biomolecules, laying the groundwork for highly sensitive and specific biosensors. These sensors have been employed using electrochemical and photophysical techniques that target amyloid species under neurodegenerative conditions. The adaptability of MOFs allows for the precise detection and quantification of amyloid proteins, offering potential advancements in early diagnosis and disease management. This review article delves into how MOFs contribute to detecting amyloid diseases by categorizing their uses based on different sensing methods, such as electrochemical (EC), electrochemiluminescence (ECL), fluorescence, Förster resonance energy transfer (FRET), up-conversion luminescence resonance energy transfer (ULRET), and photoelectrochemical (PEC) sensing. The drawbacks of MOF biosensors and the challenges encountered in the field are also briefly explored from our perspective.

Peptide-antifouling interface for monitoring β-amyloid based on electrochemiluminescence resonance energy transfer

In this study, a novel antifouling electrochemiluminescence (ECL) analytical platform has been developed for the highly sensitive quantification of β-amyloid (Aβ) peptides based on the ECL resonance energy transfer (ECL-RET) mechanism. Specifically, glassy carbon electrodes (GCE) were initially coated with graphite-phase carbon nitride (g-C3N4) nanosheets, followed by the electropolymerization of polyaniline (PANI) onto the electrode surface. Subsequently, a promising peptide motif candidate (COOH-CPPPPDKDKDKDKKLVFF) was immobilized onto the PANI-modified electrode, functioning as a critical component for both antifouling and specific recognition of full-length Aβ peptides. Furthermore, this peptide motif demonstrated inhibitory effects on Aβ aggregation and dissociation. Upon immobilization of the peptide motif, Aβ aptamer-CdS QDs were bound to the electrode surface through peptide-specific interactions with Aβ, thereby facilitating the highly sensitive ECL detection of Aβ. Under the optimal conditions, the proposed biosensor exhibited an Aβ detection range from 0.1 pM to 100 nM with a detection limit of 16.1 fM. As such, this innovative platform offers a straightforward approach to antifouling, quantification, and monitoring of Aβ concentrations in the blood samples.

Metal-Organic Frameworks-Based Nanoplatforms for the Theranostic Applications of Neurological Diseases

Neurological diseases are the foremost cause of disability and the second leading cause of death worldwide. Owing to the special microenvironment of neural tissues and biological characteristics of neural cells, a considerable number of neurological disorders are currently incurable. In the past few years, the development of nanoplatforms based on metal-organic frameworks (MOFs) has broadened opportunities for offering sensitive diagnosis/monitoring and effective therapy of neurology-related diseases. In this article, the obstacles for neurotherapeutics, including delayed diagnosis and misdiagnosis, the existence of blood brain barrier (BBB), off-target treatment, irrepressible inflammatory storm/oxidative stress, and irreversible nerve cell death are summarized. Correspondingly, MOFs-based diagnostic/monitoring strategies such as neuroimaging and biosensors (electrochemistry, fluorometry, colorimetry, electrochemiluminescence, etc.) and MOFs-based therapeutic strategies including higher BBB permeability, targeting specific lesion sites, attenuation of neuroinflammation/oxidative stress as well as regeneration of nerve cells, are extensively highlighted for the management of neurological diseases. Finally, the challenges of the present research from perspective of clinical translation are discussed, hoping to facilitate interdisciplinary studies at the intersections between MOFs-based nanoplatforms and neurotheranostics.

Fluorescent Sensing Platforms for Detecting and Imaging the Biomarkers of Alzheimer's Disease

Alzheimer's disease (AD) is an irreversible neurodegenerative disease with clinical symptoms of memory loss and cognitive impairment. Currently, no effective drug or therapeutic method is available for curing this disease. The major strategy used is to identify and block AD at its initial stage. Thus, early diagnosis is very important for intervention of the disease and assessment of drug efficacy. The gold standards of clinical diagnosis include the measurement of AD biomarkers in cerebrospinal fluid and positron emission tomography imaging of the brain for amyloid-β (Aβ) deposits. However, these methods are difficult to apply to the general screening of a large aging population because of their high cost, radioactivity and inaccessibility. Comparatively, blood sample detection is less invasive and more accessible for the diagnosis of AD. Hence, a variety of assays based on fluorescence analysis, surface-enhanced Raman scattering, electrochemistry, etc., were developed for the detection of AD biomarkers in blood. These methods play significant roles in recognizing asymptomatic AD and predicting the course of the disease. In a clinical setting, the combination of blood biomarker detection with brain imaging may enhance the accuracy of early diagnosis. Fluorescence-sensing techniques can be used not only to detect the levels of biomarkers in blood but also to image biomarkers in the brain in real time due to their low toxicity, high sensitivity and good biocompatibility. In this review, we summarize the newly developed fluorescent sensing platforms and their application in detecting and imaging biomarkers of AD, such as Aβ and tau in the last five years, and discuss their prospects for clinical applications.

A liposome-based aptasensor integrated with competitive reaction enabling portable and electrochemical detection of Aβ oligomer

Aggregation of β-amyloid (Aβ) were considered as a typical pathological feature of Alzheimer's disease (AD). Extensive studies have verified that soluble Aβ oligomers (AβO) were more toxic to neurons than plaques. Herein, in this work, a glucose entrapped liposome-based portable aptasensor was fabricated for recognizing and interacting with AβO by specific aptamer on liposome (G-Lip-Apt). Then, a single strand DNA, designed to be partially complementary to AβO aptamer, was modified on amino-functionalized Fe₃O₄@SiO₂ to obtain a magnetic nanocomposite (Fe₃O₄@SiO₂/NH₂-DNA). In the presence of AβO, the specific recognition between AβO and its aptamer on G-Lip-Apt made AβO bounded with G-Lip-Apt. With subsequent introduction of Fe₃O₄@SiO₂/NH₂-DNA, the unreacted G-Lip-Apt was further linked with Fe₃O₄@SiO₂/NH₂-DNA by double stranded complementary pairing interaction. Along with the addition of TritonX-100 into the formed G-Lip-Apt/Fe₃O₄@SiO₂/NH₂-DNA complex, the encapsulated glucose was released from liposome and then measured by a personal glucose meter (PGM). Good linear correlation was acquired over concentration of 5.0-1000 nM and the limit of detection (LOD) was calculated to be 2.27 nM for AβO. The developed portable electrochemical strategy integrated magnetic separation, competitive reaction and point of care test (POCT) to achieve high sensitivity, selectivity and accuracy, therefore enabled it successfully applied to the analysis of AβO in the hippocampus and cortex of APP/PS1 transgenic AD mice.

Ethanol and NaCl-Induced Gold Nanoparticle Aggregation Toxicity toward DNA Investigated with a DNA/GCE Biosensor

Engineered nanomaterials are becoming increasingly common in commercial and consumer products and pose a serious toxicological threat. Exposure of human organisms to nanomaterials can occur by inhalation, oral intake, or dermal transport. Together with the consumption of alcohol in the physiological environment of the body containing NaCl, this has raised concerns about the potentially harmful effects of ingested nanomaterials on human health. Although gold nanoparticles (AuNPs) exhibit great potential for various biomedical applications, there is some inconsistency in the case of the unambiguous genotoxicity of AuNPs due to differences in their shape, size, solubility, and exposure time. A DNA/GCE (DNA/glassy carbon electrode) biosensor was used to study ethanol (EtOH) and NaCl-induced gold nanoparticle aggregation genotoxicity under UV light in this study. The genotoxic effect of dispersed and aggregated negatively charged gold nanoparticles AuNP1 (8 nm) and AuNP2 (30 nm) toward salmon sperm double-stranded dsDNA was monitored by cyclic and square-wave voltammetry (CV, SWV). Electrochemical impedance spectroscopy (EIS) was used for a surface study of the biosensor. The aggregation of AuNPs was monitored by UV-vis spectroscopy. AuNP1 aggregates formed by 30% v/v EtOH and 0.15 mol·L^-1 NaCl caused the greatest damage to the biosensor DNA layer.

Metal-Organic Frameworks as Sensors for Human Amyloid Diseases

Metal-organic frameworks (MOFs) are versatile compounds with emergent applications in the fabrication of biosensors for amyloid diseases. They hold great potential in biospecimen protection and unprecedented probing capabilities for optical and redox receptors. In this Review, we summarize the main methodologies employed in the fabrication of MOF-based sensors for amyloid diseases and collect all available data in the literature related to their performance (detection range, limit of detection, recovery, time of analysis, among other parameters). Nowadays, MOF sensors have evolved to a point where they can, in some cases, outperform technologies employed in the detection of several amyloid biomarkers (amyloid β peptide, α-synuclein, insulin, procalcitonin, and prolactin) present in biological fluids, such as cerebrospinal fluid and blood. A special emphasis has been given by researchers on Alzheimer's disease monitoring to the detriment of other amyloidosis that are underexploited despite their societal relevance (e.g., Parkinson's disease). There are still important obstacles to overcome in order to selectively detect the various peptide isoforms and soluble amyloid species associated with Alzheimer's disease. Furthermore, MOF contrast agents for imaging peptide soluble oligomers in living humans are also scarce (if not nonexistent), and action in this direction is unquestionably required to clarify the contentious link between the amyloidogenic species and the disease, guiding research toward the most promising therapeutic strategies.

Metal-organic frameworks: A promising option for the diagnosis and treatment of Alzheimer's disease

Beta-amyloid (Aβ) peptide is one of the main characteristic biomarkers of Alzheimer's disease (AD). Previous clinical investigations have proposed that unusual concentrations of this biomarker in cerebrospinal fluid, blood, and brain tissue are closely associated with the AD progression. Therefore, the critical point of early diagnosis, prevention, and treatment of AD is to monitor the levels of Aβ. In view of the potential of metal-organic frameworks (MOFs) for diagnosing and treating the AD, much attention has been focused in recent years. This review discusses the latest advances in the applications of MOFs for the early diagnosis of AD via fluorescence and electrochemiluminescence (ECL) detection of AD biomarkers, fluorescence detection of the main metal ions in the brain (Zn²⁺, Cu²⁺, Mn²⁺, Fe³⁺, and Al³⁺) in addition to magnetic resonance imaging (MRI) of the Aβ plaques. The current challenges and future strategies for translating the in vitro applications of MOFs into in vivo diagnosis of the AD are discussed.

Sensitive fluorescent aptasensing of tobramycin on graphene oxide coupling strand displacement amplification and hybridization chain reaction

An ultrasensitive biosensor was designed and constructed for tobramycin detection. As a target recognition component, the DNA probe consists of an aptamer region for tobramycin binding and a template for amplification. In the absence of tobramycin, the probe was locked to form a stem-loop structure. In the presence of the target, the binding of tobramycin led to a conformational change in the probe. The released 3' end was used as a primer for the strand displacement amplification (SDA) to produce a large amount of single-stranded trigger DNA, which then efficiently initiated the following hybridization chain reaction (HCR) to produce a long duplex DNA with many fluorophores. The signals were detected after the addition of graphene oxide (GO) to quench the fluorescence from excess hairpin DNA. Through sequence and reaction condition optimization, the biosensor exhibited high selectivity for tobramycin. The linearity range and limit of detection (LOD) were 0.5-30 nM and 0.06 nM, respectively. Moreover, the application of detecting tobramycin in milk and lake water samples showed that this method is reliable and could be further used in food safety control and environmental monitoring.

Engineering a thermostable biosensor based on biomimetic mineralization HRP@Fe-MOF for Alzheimer's disease

The development of disease detection by biosensors represents one of the key components of medical science. However, millions of people are still misdiagnosed each year due to the poor efficacy and thermal instability of biosensors. Using horseradish peroxidase (HRP) as a paradigm, we offer a rational design strategy to optimize the thermostability and activity of biosensors by biomimetic mineralization. To overcome the weak thermostability of the biosensor, the mineralization of Fe-MOF forms an armor on HRP that protects against high temperature. Additionally, the biomimetic mineralization HRP@Fe-MOF can double-catalyze the TMB/H₂O₂ chromogenic system for color development. The biosensor can also be recycled through simple heat treatment due to the thermally stable aptamer and biomimetic mineralization HRP@Fe-MOF. The optical biosensor based on this sensitive spectral transformation was successfully developed for the measurement of AβO with an outstanding linear range (0.0001-10 nM) and a low limit of detection (LOD) of 0.03 pM. This promising platform will open up new avenues for the detection of AβO in the early diagnosis of Alzheimer's disease (AD).

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.