A simple aptasensor for Aβ40 oligomers based on tunable mismatched base pairs of dsDNA and graphene oxide

Multifunctional porphyrin-substituted phenylalanine-phenylalanine nanoparticles for diagnostic and therapeutic applications in Alzheimer's disease

β-Amyloid (Aβ) peptides are believed as the diagnostic biomarkers and therapeutic targets of Alzheimer's disease (AD). Their complexes with copper ions can catalyze the generation of reactive oxygen species (ROS) to further promote neuronal death. Herein, we suggested that porphyrin-substituted phenylalanine-phenylalanine nanoparticles (TPP-FF NPs) could inhibit the aggregation of Aβ monomers, disassemble the fibrillar Aβ aggregates under light illumination, and depressing the Cu2+-induced generation of ROS. Meanwhile, the TPP-FF NPs could be used as the nanocarriers and quenchers of fluorescently-labeled probes for the detection of Aβ oligomer (AβO). Inhibition of Aβ assembly and dissolution of Aβ aggregates were monitored by Thioflavin T (ThT)-based fluorescent assay and characterized by atomic force microscopy. The Aβ/Cu2+-induced generation of ROS was limited by TPP-FF NPs. The fluorescein-labeled probe aptamers attached on the surface of TPP-FF NPs emitted low fluorescence. The interaction between AβO and aptamers induced the release of the probes from the surface of TPP-FF NPs, driving the fluorophore far away from the quenchers and turning on the fluorescence. The signal-on strategy can be used for the detection of AβO with a low detection limit. This work should be evaluable for the development of multifunctional candidates for the diagnosis and treatment of AD.

The Role of Reactive Oxygen Species in Alzheimer's Disease: From Mechanism to Biomaterials Therapy

Alzheimer's disease (AD) is a chronic, insidious, and progressive neurodegenerative disease that remains a clinical challenge for society. The fully approved drug lecanemab exhibits the prospect of therapy against the pathological processes, while debatable adverse events conflict with the drug concentration required for the anticipated therapeutic effects. Reactive oxygen species (ROS) are involved in the pathological progression of AD, as has been demonstrated in much research regarding oxidative stress (OS). The contradiction between anticipated dosage and adverse event may be resolved through targeted transport by biomaterials and get therapeutic effects through pathological progression via regulation of ROS. Besides, biomaterials fix delivery issues by promoting the penetration of drugs across the blood-brain barrier (BBB), protecting the drug from peripheral degradation, and elevating bioavailability. The goal is to comprehensively understand the mechanisms of ROS in the progression of AD disease and the potential of ROS-related biomaterials in the treatment of AD. This review focuses on OS and its connection with AD and novel biomaterials in recent years against AD via OS to inspire novel biomaterial development. Revisiting these biomaterials and mechanisms associated with OS in AD via thorough investigations presents a considerable potential and bright future for improving effective interventions for AD.

Recent advances of biocompatible optical nanobiosensors in liquid biopsy: towards early non-invasive diagnosis

Liquid biopsy is a non-invasive diagnostic method that can reduce the risk of complications and offers exceptional benefits in the dynamic monitoring and acquisition of heterogeneous cell population information. Optical nanomaterials with excellent light absorption, luminescence, and photoelectrochemical properties have accelerated the development of liquid biopsy technologies. Owing to the unique size effect of optical nanomaterials, their improved optical properties enable them to exhibit good sensitivity and specificity for mitigating signal interference from various molecules in body fluids. Nanomaterials with biocompatible and optical sensing properties play a crucial role in advancing the maturity and diversification of liquid biopsy technologies. This article offers a comprehensive review of recent advanced liquid biopsy technologies that utilize novel biocompatible optical nanomaterials, including fluorescence, colorimetric, photoelectrochemical, and Raman broad-spectrum-based biosensors. We focused on liquid biopsy for the most significant early biomarkers in clinical medicine, and specifically reviewed reports on the effectiveness of optical nanosensing technology in the detection of real patient samples, which may provide basic evidence for the transition of optical nanosensing technology from engineering design to clinical practice. Furthermore, we introduced the integration of optical nanosensing-based liquid biopsy with modern devices, such as smartphones, to demonstrate the potential of the technology in portable clinical diagnosis.

Gold Nanoparticle-Decorated Catalytic Micromotor-Based Aptassay for Rapid Electrochemical Label-Free Amyloid-β42 Oligomer Determination in Clinical Samples from Alzheimer's Patients

Micromotor (MM) technology offers a valuable and smart on-the-move biosensing microscale approach in clinical settings where sample availability is scarce in the case of Alzheimer's disease (AD). Soluble amyloid-β protein oligomers (AβO) (mainly AβO42) that circulate in biological fluids have been recognized as a molecular biomarker and therapeutic target of AD due to their high toxicity, and they are correlated much more strongly with AD compared to the insoluble Aβ monomers. A graphene oxide (GO)-gold nanoparticles (AuNPs)/nickel (Ni)/platinum nanoparticles (PtNPs) micromotors (MMGO-AuNPs)-based electrochemical label-free aptassay is proposed for sensitive, accurate, and rapid determination of AβO42 in complex clinical samples such as brain tissue, cerebrospinal fluid (CSF), and plasma from AD patients. An approach that implies the in situ formation of AuNPs on the GO external layer of tubular MM in only one step during MM electrosynthesis was performed (MMGO-AuNPs). The AβO42 specific thiolated-aptamer (AptAβO42) was immobilized in the MMGO-AuNPs via Au-S interaction, allowing for the selective recognition of the AβO42 (MMGO-AuNPs-AptAβO42-AβO42). AuNPs were smartly used not only to covalently bind a specific thiolated-aptamer for the design of a label-free electrochemical aptassay but also to improve the final MM propulsion performance due to their catalytic activity (approximately 2.0× speed). This on-the-move bioplatform provided a fast (5 min), selective, precise (RSD < 8%), and accurate quantification of AβO42 (recoveries 94-102%) with excellent sensitivity (LOD = 0.10 pg mL-1) and wide linear range (0.5-500 pg mL-1) in ultralow volumes of the clinical sample of AD patients (5 μL), without any dilution. Remarkably, our MM-based bioplatform demonstrated the competitiveness for the determination of AβO42 in the target samples against the dot blot analysis, which requires more than 14 h to provide qualitative results only. It is also important to highlight its applicability to the potential analysis of liquid biopsies as plasma and CSF samples, improving the reliability of the diagnosis given the heterogeneity and temporal complexity of neurodegenerative diseases. The excellent results obtained demonstrate the analytical potency of our approach as a future tool for clinical/POCT (Point-of-care testing) routine scenarios.

Advances in targeted tracking and detection of soluble amyloid-β aggregates as a biomarker of Alzheimer's disease

Misfolding and aggregation of amyloid-β (Aβ) peptides are key hallmarks of Alzheimer's disease (AD). With accumulating evidence suggesting that different Aβ species have varied neurotoxicity and implications in AD development, the discovery of affinity ligands and analytical approaches to selective distinguish, detect, and monitor Aβ becomes an active research area. Remarkable advances have been achieved, which not only promote our understanding of the biophysical chemistry of the protein aggregation during neurodegeneration, but also provide promising tools for early detection of the disease. In view of this, we summarize the recent progress in selective and sensitive approaches for tracking and detection of Aβ species. Specific attentions are given to soluble Aβ oligomers, due to their crucial roles in AD development and occurrence at early stages. The design principle, performance of targeting units, and their cooperative effects with signal reporters for Aβ analysis are discussed. The applications of the novel targeting probes and sensing systems for dynamic monitoring oligomerization, measuring Aβ in biosamples and in vivo imaging in brain are summarized. Finally, the perspective and challenges are discussed regarding the future development of Aβ-targeting analytical tools to explore the unknown field to contribute to the early diagnosis and treatment of AD.

Magneto-assisted enzymatic DNA walkers for simultaneous electrochemical detection of amyloid-beta oligomers and Tau

DNA walkers have been widely explored and applied as biosensor elements to detect disease-related biomarkers. Traditional interface-anchored DNA walkers typically have a fixed swing arm range and an orientation of the preset track, which might complicate the design of a sensor system and limit its application in more scenes. We propose a simple electrochemical aptasensor to accurately detect Alzheimer's disease (AD) based on a nicking enzyme-powered DNA walker. In this method, bifunctional magnetic nanoparticles are used to identify and capture Aβ oligomers (AβO) and Tau and release the DNA walker. As the DNA walker moves freely on the surface of the electrode, the nicking enzymes circularly cleave and release the two signal substrate chains, significantly amplifying the signal. It has been demonstrated that the constructed sensor can sensitively detect AβO and Tau, and the combined analysis of dual markers improves the accuracy of AD diagnosis. Furthermore, this method can distinguish normal individuals from AD patients in real cerebrospinal fluid samples. The excellent performance of this biosensor makes it promising for clinical applications in diagnosing AD patients and prognosis assessment.

Graphene- and MXene-based materials for neuroscience: diagnostic and therapeutic applications

MXenes and graphene are two-dimensional materials that have gained increasing attention in neuroscience, particularly in sensing, theranostics, and biomedical engineering. Various composites of graphene and MXenes with fascinating thermal, optical, magnetic, mechanical, and electrical properties have been introduced to develop advanced nanosystems for diagnostic and therapeutic applications, as exemplified in the case of biosensors for neurotransmitter detection. These biosensors display high sensitivity, selectivity, and stability, making them promising tools for neuroscience research. MXenes have been employed to create high-resolution neural interfaces for neuroelectronic devices, develop neuro-receptor-mediated synapse devices, and stimulate the electrophysiological maturation of neural circuits. On the other hand, graphene/derivatives exhibit therapeutic applicability in neuroscience, as exemplified in the case of graphene oxide for targeted delivery of therapeutic agents to the brain. While MXenes and graphene have potential benefits in neuroscience, there are also challenges/limitations associated with their use, such as toxicity, environmental impacts, and limited understanding of their properties. In addition, large-scale production and commercialization as well as optimization of reaction/synthesis conditions and clinical translation studies are very important aspects. Thus, it is important to consider the use of these materials in neuroscience research and conduct further research to obtain an in-depth understanding of their properties and potential applications. By addressing issues related to biocompatibility, long-term stability, targeted delivery, electrical interfaces, scalability, and cost-effectiveness, MXenes and graphene have the potential to greatly advance the field of neuroscience and pave the way for innovative diagnostic and therapeutic approaches for neurological disorders. Herein, recent advances in therapeutic and diagnostic applications of graphene- and MXene-based materials in neuroscience are discussed, focusing on important challenges and future prospects.

A label-free dually-amplified aptamer sensor for the specific detection of amyloid-beta peptide oligomers in cerebrospinal fluids

Amyloid-beta peptide oligomer (Aβo) is widely acknowledged to be associated with Alzheimer's disease (AD). The immediate and accurate detection of Aβo may provide the index for tracking the progress of the state of the disease, as well as some useful information for investigating the pathology of AD. In this work, based on a triple helix DNA which triggers a series of circular amplified reactions in the presence of Aβo, we designed a simple and label-free colorimetric biosensor with dually-amplified signal for the specific detection of Aβo. The sensor displays some advantages including high specificity, high sensitivity, low detection limit down to 0.23 pM, and wide detection range with three orders of magnitude from 0.3472 to 694.44 pM. Furthermore, the proposed sensor was successfully applied for detecting Aβo in artificial and real cerebrospinal fluids with satisfactory results, suggesting the potential application of the proposed sensor for state-monitoring and pathological studies of AD.

A High-Quality CdSe/CdS/ZnS Quantum-Dot-Based FRET Aptasensor for the Simultaneous Detection of Two Different Alzheimer's Disease Core Biomarkers

The simultaneous detection of two different biomarkers for the point-of-care diagnosis of major diseases, such as Alzheimer’s disease (AD), is greatly challenging. Due to the outstanding photoluminescence (PL) properties of quantum dots (QDs), a high-quality CdSe/CdS/ZnS QD-based fluorescence resonance energy transfer (FRET) aptasensor for simultaneously monitoring the amyloid-β oligomers (AβO) and tau protein was proposed. By engineering the interior inorganic structure and inorganic−organic interface, water-soluble dual-color CdSe/CdS/ZnS QDs with a near-unity PL quantum yield (>90%) and mono-exponential PL decay dynamics were generated. The π−π stacking and hydrogen bond interaction between the aptamer-functionalized dual-color QDs and gold nanorods@polydopamine (Au NRs@PDA) nanoparticles resulted in significant fluorescence quenching of the QDs through FRET. Upon the incorporation of the AβO and tau protein, the fluorescence recovery of the QDs-DNA/Au NRs@PDA assembly was attained, providing the possibility of simultaneously assaying the two types of AD core biomarkers. The lower detection limits of 50 pM for AβO and 20 pM for the tau protein could be ascribed to the distinguishable and robust fluorescence of QDs and broad spectral absorption of Au NRs@PDA. The sensing strategy serves as a viable platform for the simultaneously monitoring of the core biomarkers for AD and other major diseases.

Fluorescent aptasensor based on conformational switch-induced hybridization for facile detection of β-amyloid oligomers

Aβ oligomers (AβO) are a dominant biomarker for early Alzheimer's disease diagnosis. A fluorescent aptasensor coupled with conformational switch-induced hybridization was established to detect AβO. The fluorescent aptasensor is based on the interaction of fluorophore-labeled AβO-specific aptamer (FAM-Apt) against its partly complementary DNA sequence on the surface of magnetic beads (cDNA-MBs). Once the FAM-Apt binds to AβO, the conformational switch of FAM-Apt increases the tendency to be captured by cDNA-MBs. This causes a descending fluorescence of supernatant, which can be utilized to determine the levels of AβO. Thus, the base-pair matching above 12 between FAM-Apt and cDNA-MBs with increasing hybridizing free energies reached the ascending fluorescent signal equilibrium. The optimized aptasensor showed linearity from 1.7 ng mL^-1 to 85.1 (R = 0.9977) with good recoveries (79.27-109.17%) in plasma. Furthermore, the established aptasensor possesses rational selectivity in the presence of monomeric Aβ, fibrotic Aβ, and interferences. Therefore, the developed aptasensor is capable of quantifying AβO in human plasma and possesses the potential to apply in clinical cases.

Aptamer-conjugated graphene oxide-based surface assisted laser desorption ionization mass spectrometry for selective extraction and detection of Aβ1–42 in an Alzheimer’s disease SH-SY5 cell model

The generation and accumulation of amyloid-beta peptide (Aβ_1–42) in amyloid plaques are key characteristics of Alzheimer’s disease (AD); thus, specific detection of Aβ_1–42 is essential for the diagnosis and treatment of AD. Herein, an aptamer-conjugated graphene oxide (Apt-GO) sensor was synthesized by π-π and hydrophobic interactions using thiol poly (ethylene glycol) amine (SH-PEG-NH₂) as a spacer unit. Then, it was applied to selective capture of Aβ_1–42, and the resulting complex was directly analyzed by surface-assisted laser desorption ionization mass spectrometry (SALDI-MS). The results revealed that the Apt-GO could enhance the detection specificity and reduce non-specific adsorption. This method was validated to be sensitive in detecting Aβ_1–42 at a low level in human serum (ca. 0.1 μM) within a linear range from 0.1 to 10 μM. The immobilizing amount of aptamer on the GO was calculated to be 36.1 nmol/mg (RSD = 11.5%). In conclusion, this Apt-GO-based SALDI-MS method was sensitive and efficient in selective extraction and detection of Aβ_1–42, which proved to be a good option for early AD diagnosis.

Electrocatalysis of Copper Sulfide Nanoparticle-Engineered Covalent Organic Frameworks for Ratiometric Electrochemical Detection of Amyloid-β Oligomer

Amyloid-β oligomer (AβO) is widely regarded as a reliable biomarker for the early diagnosis of Alzheimer's disease (AD). In this study, a signal on-off ratiometric electrochemical immunosensor has been developed for ultrasensitive detection of AβO. To achieve the dual-signal ratiometric strategy, ultrasmall copper sulfide nanoparticle-engineered covalent organic framework hybrid nanocomposites (CuS@COFs) were utilized as excellent electrocatalysts toward hydroquinone (HQ) oxidation to produce detectable signals. Meanwhile, electroactive thionine (Thi) and Aβ antibody-modified gold nanoparticles (Thi-AuNPs-Ab bioconjugates) were designed as another electrochemical indicator. Based on these two signals, an ultrasensitive sandwich-like electrochemical immunosensor was established for AβO detection. The introduction of AβO resulted in a remarkable decline in the electrochemical signal of HQ but an increase in the signal of Thi. Under optimum conditions, the ratios between the double signals (I_Thi/I_HQ) showed a proportional linear relationship with the AβO concentration (1 pM-1 μM) with a low detection limit of 0.4 pM (S/N = 3), and the biosensor was able to determine the content of AβO in real cerebrospinal fluid samples with satisfactory results. The ratiometric strategy proposed in our study offers a sensitive and efficient approach for early diagnosis of AD, and this work will promote the further applications of engineered COFs in electrochemical sensors.

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.

Facile and foldable point-of-care biochip for nucleic acid based-colorimetric detection of murine norovirus in fecal samples using G-quadruplex and graphene oxide coated microbeads

Norovirus is one of the most common causes of gastroenteritis, a disease characterized by diarrhea, vomiting, and stomach pain. A rapid on-site identification of the virus from fecal samples of patients is a prerequisite for accurate medical management. Here, we demonstrate a rapid nucleic acid-based detection platform as an on-site biosensing tool that can concentrate viruses from fecal samples. Moreover, it can perform RNA extraction and identification, and signal amplification using G-quadruplex and hemin containing DNA probes (G-DNA probes) and graphene oxide (GO)-coated microbeads. Briefly, murine noroviruses are lysed without chemicals on the surface of the GO microbeads. Subsequently, the target RNA is hybridized with G-DNA probes, and the resultant RNA/G-DNA probe complex is separated from unbound G-DNA probes using GO beads and is mixed with the detection buffer (ABTS/H₂O₂). Presence of murine noroviruses causes a colorimetric change of the buffer from colorless to green. Thus, we integrated all processes required to detect murine noroviruses in stool samples in a simple foldable microfluidic chip. Moreover, it can detect 10¹ pfu of the virus in 30 min in a fecal sample.

Ultrasensitive Detection of Amyloid β Oligomers Based on the "DD-A" FRET Binary Probes and Quadrivalent Cruciform DNA Nanostructure-Mediated Cascaded Amplifier

The reported donor donor-acceptor ("DD-A") fluorescence resonance energy transfer (FRET) was typically achieved through random collisions and interactions of DNA molecules in the bulk solution, which has inevitable defects, including weak biological stability, slow reaction kinetics, and low hybridization efficiency. In order to overcome these deficiencies, this work developed a quadrivalent cruciform DNA nanostructure (qCDN)-mediated cascaded catalyzed hairpin assembly (CHA) amplifier for the fluorescence detection of amyloid β oligomer species (AβOs). First, four H1 and four H2 hairpins were assembled on one qCDN to obtain qCDNH1 and qCDNH2, respectively. In the presence of AβOs, strand C was released from the P1-C hybrid hairpin and then alternately opened qCDNH1 and qCDNH2 to trigger the qCDN-mediated CHA. As a result, double donors in H1 and one acceptor in H2 were mutually closed, and the porous DNA nanonet with a high loading of "DD-A" FRET binary probes was formed. The FRET efficiency was approximately 78%, and the initial reaction rate was 25-fold faster than the conventional CHA. The detection limit of AβOs was as low as 0.69 pM. The combination of the "DD-A" FRET binary probes and qCDN-mediated cascaded amplifier exhibited great promise for detecting biomarkers with trace levels.

Clinically oriented Alzheimer's biosensors: expanding the horizons towards point-of-care diagnostics and beyond

The development of minimally invasive and easy-to-use sensor devices is of current interest for ultrasensitive detection and signal recognition of Alzheimer's disease (AD) biomarkers. Over the years, tremendous effort has been made on diagnostic platforms specifically targeting neurological markers for AD in order to replace the conventional, laborious, and invasive sampling-based approaches. However, the sophistication of analytical outcomes, marker inaccessibility, and material validity strongly limit the current strategies towards effectively predicting AD. Recently, with the promising progress in biosensor technology, the realization of a clinically applicable sensing platform has become a potential option to enable early diagnosis of AD and other neurodegenerative diseases. In this review, various types of biosensors, which include electrochemical, fluorescent, plasmonic, photoelectrochemical, and field-effect transistor (FET)-based sensor configurations, with better clinical applicability and analytical performance towards AD are highlighted. Moreover, the feasibility of these sensors to achieve point-of-care (POC) diagnosis is also discussed. Furthermore, by grafting nanoscale materials into biosensor architecture, the remarkable enhancement in durability, functionality, and analytical outcome of sensor devices is presented. Finally, future perspectives on further translational and commercialization pathways of clinically driven biosensor devices for AD are discussed and summarized.

Recent Developments in Aptasensors for Diagnostic Applications

Aptamers are exciting smart molecular probes for specific recognition of disease biomarkers. A number of strategies have been developed to convert target-aptamer binding into physically detectable signals. Since the aptamer sequence was first discovered, a large variety of aptamer-based biosensors have been developed, with considerable attention paid to their potential applications in clinical diagnostics. So far, a variety of techniques in combination with a wide range of functional nanomaterials have been used for the design of aptasensors to further improve the sensitivity and detection limit of target determination. In this paper, the advantages of aptamers over traditional antibodies as the molecular recognition components in biosensors for high-throughput screening target molecules are highlighted. Aptamer-target pairing configurations are predominantly single- or dual-site binding; the design of recognition modes of each aptamer-target pairing configuration is described. Furthermore, signal transduction strategies including optical, electrical, mechanical, and mass-sensitive modes are clearly explained together with examples. Finally, we summarize the recent progress in the development of aptamer-based biosensors for clinical diagnosis, including detection of cancer and disease biomarkers and in vivo molecular imaging. We then conclude with a discussion on the advanced development and challenges of aptasensors.

Antibody-Free Determinations of Low-Mass, Soluble Oligomers of Aβ42 and Aβ40 by Planar Bilayer Lipid Membrane-Based Electrochemical Biosensor

Alzheimer's disease (AD) is the most common neurodegenerative disease among the elderly. Abnormal aggregates of both β-amyloid peptide (Aβ) subtypes, Aβ₄₂ and Aβ₄₀, are the typical neuropathology hallmarks of AD. However, because of the lack of specific recognition elements such as an antibody and aptamer, it is difficult to differentiate and determine the oligomers of Aβ₄₂ and Aβ₄₀ in clinic. In this paper, we developed a planar bilayer lipid membrane (BLM)-based electrochemical biosensor. According to the dynamic differences on oligomer-induced BLM damage, both low-mass, soluble oligomers of Aβ₄₂ and Aβ₄₀ (L-Aβ₄₂O and L-Aβ₄₀O) were measured in turn by electrochemical impedance spectroscopy. The BLM was supported by a porous 11-mercaptoundecanoic acid layer on a gold electrode, which amplified the impedance signal corresponding to the membrane damage and improved the detection sensitivity. The weakly charged surface of the BLM ensured the low non-specific adsorption of coexisting proteins in cerebrospinal fluid (CSF). Using the electrochemical biosensor, L-Aβ₄₂O was determined within 20 min, with a linear range from 5 to 500 pM and a detection limit of 3 pM. Meanwhile, L-Aβ₄₀O was determined within 60 min, with a linear range from 60 pM to 6.0 nM and a detection limit of 26 pM. The recoveries in oligomer-spiked artificial CSF and human CSF samples confirmed the accuracy and applicability of this proposed method in clinic. This work provides an antibody-free, highly selective, and sensitive method for simultaneous detections of L-Aβ₄₂O and L-Aβ₄₀O in real CSF samples, which is significant for the early diagnosis and prognosis of AD.

Advances in fluorescent probes for detection and imaging of amyloid-β peptides in Alzheimer's disease

Amyloid plaques generated from the accumulation of amyloid-β peptides (Aβ) fibrils in the brain is one of the main hallmarks of Alzheimer's disease (AD), a most common neurodegenerative disorder. Aβ aggregation can produce neurotoxic oligomers and fibrils, which has been widely accepted as the causative factor in AD pathogenesis. Accordingly, both soluble oligomers and insoluble fibrils have been considered as diagnostic biomarkers for AD. Among the existing analytical methods, fluorometry using fluorescent probes has exhibited promising potential in quantitative detection and imaging of both soluble and insoluble Aβ species, providing a valuable approach for the diagnosis and drug development of AD. In this review, the most recent advances in the fluorescent probes for soluble or insoluble Aβ aggregates are discussed in terms of design strategy, probing mechanism, and potential applications. In the end, future research directions of fluorescent probes for Aβ species are also proposed.

A general configurational strategy to quencher-free aptasensors

The aptasensor, developed from the aptamer, has aroused wide concern in recent years owing to its high sensitivity and specificity. However, the quenching unit involved in the most of the aptasensors is indispensable to the fabrication of an aptasensor, which would undoubtedly increase the complexity of the device. In this study, a facile strategy was developed for construction of the quencher-free aptasensors, in which the quenching units can be omitted, and only an aptamer strand and a fluorophore are necessary. Distinguishable from the configuration of the traditional ones, the aptasensors developed in this work rationally employed the intrinsic quenching abilities of the analytes to directly regulate the fluorescence of the fluorophore. Furthermore, the aptamer strand as a discriminatory unit efficiently captured the corresponding analytes to around the fluorophores. As a result, the fluorescence of the aptasensor can be significantly sensitive to the analytes. The generality of the current design is evidenced by the successful fabrication of seven quencher-free aptasensors for Cu²⁺, Ag⁺, Hg²⁺, ATP and dopamine through 6-FAM labeling aptamers of Cu²⁺, Ag⁺, Hg²⁺, ATP, dopamine, 5-TAMRA and ROX labeling aptamers of Cu²⁺. Present strategy endows an aptasensor with a simple structure, high selectivity and fine sensitivity. The configuration of the quencher-free aptasensors fabricated in this work can be readily utilized for more aptasensors.

Potential of Microfluidics and Lab-on-Chip Platforms to Improve Understanding of "prion-like" Protein Assembly and Behavior

Human aging is accompanied by a relevant increase in age-associated chronic pathologies, including neurodegenerative and metabolic diseases. The appearance and evolution of numerous neurodegenerative diseases is paralleled by the appearance of intracellular and extracellular accumulation of misfolded proteins in affected brains. In addition, recent evidence suggests that most of these amyloid proteins can behave and propagate among neural cells similarly to infective prions. In order to improve understanding of the seeding and spreading processes of these "prion-like" amyloids, microfluidics and 3D lab-on-chip approaches have been developed as highly valuable tools. These techniques allow us to monitor changes in cellular and molecular processes responsible for amyloid seeding and cell spreading and their parallel effects in neural physiology. Their compatibility with new optical and biochemical techniques and their relative availability have increased interest in them and in their use in numerous laboratories. In addition, recent advances in stem cell research in combination with microfluidic platforms have opened new humanized in vitro models for myriad neurodegenerative diseases affecting different cellular targets of the vascular, muscular, and nervous systems, and glial cells. These new platforms help reduce the use of animal experimentation. They are more reproducible and represent a potential alternative to classical approaches to understanding neurodegeneration. In this review, we summarize recent progress in neurobiological research in "prion-like" protein using microfluidic and 3D lab-on-chip approaches. These approaches are driven by various fields, including chemistry, biochemistry, and cell biology, and they serve to facilitate the development of more precise human brain models for basic mechanistic studies of cell-to-cell interactions and drug discovery.

A facile biosensor for Aβ40O based on fluorescence quenching of prussian blue nanoparticles

Amyloid β peptide oligomeFrs (AβOs) have been proved to be crucial biomarkers of Alzheimer's disease (AD). To explore an applicable method for the determination of AβOs is significant for the early AD diagnosis. Prussian blue nanoparticles (PBNPs), as one excellent nanomaterials, have the advantages of good stability, favorable biocompatibility, low cost, easy preparation and controllable shape. PBNPs was found to be of the fluorescence quenching ability to fluorophores, and the adsorption of DNA onto PBNPs surface occurred via the binding of phosphate skeleton in DNA to Fe²⁺/Fe³⁺ in PBNPs. On basis of this, carboxyl fluorescein (FAM) modified Aβ₄₀O-targeting aptamer (FAM-Apt_Aβ) was adsorbed onto PBNPs. And FAM-Apt_Aβ@PBNPs-based fluorescent aptasensor for the determination of Aβ₄₀O was developed. Upon incubating FAM-Apt_Aβ@PBNPs with Aβ₄₀O, the fluorescence intensity of the FAM-Apt_Aβ@PBNPs obviously increased comparing to the initial fluorescence intensity of the FAM-Apt_Aβ@PBNPs. The changes in the fluorescence intensity of the FAM-Apt_Aβ@PBNPs were linear with the Aβ₄₀O concentrations ranging from 1.00 nM to 100 nM. Moreover, AD patients and healthy persons can be distinguished using this method to determine Aβ₄₀O concentrations in human cerebrospinal fluid samples from AD patients and healthy persons. It demonstrates that this PBNPs-based aptasensor is not only simple and cost-effective, but also sensitive, selective and more applicable. This fluorescent sensing strategy is promising for the development of aptasensor in clinical fields.