Enhanced Detection Specificity and Sensitivity of Alzheimer’s Disease Using Amyloid-β-Targeted Quantum Dots

Optical nanomaterial-based detection of biomarkers in liquid biopsy

Liquid biopsy, which is a minimally invasive procedure as an alternative to tissue biopsy, has been introduced as a new diagnostic/prognostic measure. By screening disease-related markers from the blood or other biofluids, it promises early diagnosis, timely prognostication, and effective treatment of the diseases. However, there will be a long way until its realization due to its conceptual and practical challenges. The biomarkers detected by liquid biopsy, such as circulating tumor cell (CTC) and circulating tumor DNA (ctDNA), are extraordinarily rare and often obscured by an abundance of normal cellular components, necessitating ultra-sensitive and accurate detection methods for the advancement of liquid biopsy techniques. Optical biosensors based on nanomaterials open an important opportunity in liquid biopsy because of their enhanced sensing performance with simple and practical properties. In this review article, we summarized recent innovations in optical nanomaterials to demonstrate the sensitive detection of protein, peptide, ctDNA, miRNA, exosome, and CTCs. Each study prepares the optical nanomaterials with a tailored design to enhance the sensing performance and to meet the requirements of each biomarker. The unique optical characteristics of metallic nanoparticles (NPs), quantum dots, upconversion NPs, silica NPs, polymeric NPs, and carbon nanomaterials are exploited for sensitive detection mechanisms. These recent advances in liquid biopsy using optical nanomaterials give us an opportunity to overcome challenging issues and provide a resource for understanding the unknown characteristics of the biomarkers as well as the mechanism of the disease.

Intranasal Drug Delivery by Nanotechnology: Advances in and Challenges for Alzheimer's Disease Management

Alzheimer's disease, a progressive neurodegenerative condition, is characterized by a gradual decline in cognitive functions. Current treatment approaches primarily involve the administration of medications through oral, parenteral, and transdermal routes, aiming to improve cognitive function and alleviate symptoms. However, these treatments face limitations, such as low bioavailability and inadequate permeation. Alternative invasive methods, while explored, often entail discomfort and require specialized assistance. Therefore, the development of a non-invasive and efficient delivery system is crucial. Intranasal delivery has emerged as a potential solution, although it is constrained by the unique conditions of the nasal cavity. An innovative approach involves the use of nano-carriers based on nanotechnology for intranasal delivery. This strategy has the potential to overcome current limitations by providing enhanced bioavailability, improved permeation, effective traversal of the blood-brain barrier, extended retention within the body, and precise targeting of the brain. The comprehensive review focuses on the advancements in designing various types of nano-carriers, including polymeric nanoparticles, metal nanoparticles, lipid nanoparticles, liposomes, nanoemulsions, Quantum dots, and dendrimers. These nano-carriers are specifically tailored for the intranasal delivery of therapeutic agents aimed at combatting Alzheimer's disease. In summary, the development and utilization of intranasal delivery systems based on nanotechnology show significant potential in surmounting the constraints of current Alzheimer's disease treatment strategies. Nevertheless, it is essential to acknowledge regulatory as well as toxicity concerns associated with this route; meticulous consideration is required when engineering a carrier. This comprehensive review underscores the potential to revolutionize Alzheimer's disease management and highlights the importance of addressing regulatory considerations for safe and effective implementations. Embracing this strategy could lead to substantial advancements in the field of Alzheimer's disease treatment.

Functional Nanomaterials for the Diagnosis of Alzheimer's Disease: Recent Progress and Future Perspectives

Alzheimer's disease (AD) is one of the main causes of dementia worldwide, whereby neuronal death or malfunction leads to cognitive impairment in the elderly population. AD is highly prevalent, with increased projections over the next few decades. Yet current diagnostic methods for AD occur only after the presentation of clinical symptoms. Evidence in the literature points to potential mechanisms of AD induction beginning before clinical symptoms start to present, such as the formation of amyloid beta (Aβ) extracellular plaques and neurofibrillary tangles (NFTs). Biomarkers of AD, including Aβ 40, Aβ 42, and tau protein, amongst others, show promise for early AD diagnosis. Additional progress is made in the application of biosensing modalities to measure and detect significant changes in these AD biomarkers within patient samples, such as cerebral spinal fluid (CSF) and blood, serum, or plasma. Herein, a comprehensive review of the emerging nano-biomaterial approaches to develop biosensors for AD biomarkers' detection is provided. Advances, challenges, and potential of electrochemical, optical, and colorimetric biosensors, focusing on nanoparticle-based (metallic, magnetic, quantum dots) and nanostructure-based biomaterials are discussed. Finally, the criteria for incorporating these emerging nano-biomaterials in clinical settings are presented and assessed, as they hold great potential for enhancing early-onset AD diagnostics.

A BODIPY-based ICT probe for ratiometric and chromo-fluorogenic detection of hazardous oxalyl chloride

Herein, a novel long wavelength monostyryl BODIPY derivative (BDZ-1) has been synthesized by rational design and used to detect oxalyl chloride, a highly reactive and harmful chemical to humans and other living organisms, with high sensitivity and selectivity. The purple solution of BDZ-1 changed to pink color immediately upon the addition of oxalyl chloride and the weak red fluorescence changed to strong orange fluorescence simultaneously. In addition, the practicability of BDZ-1 was further explored by using a smartphone application, allowing the sensitive and selective on-site detection of oxalyl chloride.

Potential of fluorescent nanoprobe in diagnosis and treatment of Alzheimer's disease

Alzheimer's disease (AD) is well known for its insidious nature, slow progression and high incidence as a neurodegenerative disease. In the past, diagnosis of AD mainly depended on analysis of a patient's cognitive ability and behavior. Without a unified standard for analysis methods, this is prone to produce incorrect diagnoses. Currently, definitive diagnosis mainly relies on histopathological examination. Because of the advantages of precision, noninvasiveness, low toxicity and high spatiotemporal resolution, fluorescent nanoprobes are suitable for the early diagnosis of AD. This review summarizes the research progress of different kinds of fluorescent nanoprobes for AD diagnosis and therapy in recent years and provides an outlook on the development prospects of fluorescent nanoprobes.

Plasmonic Nanoparticles as Optical Sensing Probes for the Detection of Alzheimer's Disease

Alzheimer's disease (AD), considered a common type of dementia, is mainly characterized by a progressive loss of memory and cognitive functions. Although its cause is multifactorial, it has been associated with the accumulation of toxic aggregates of the amyloid-β peptide (Aβ) and neurofibrillary tangles (NFTs) of tau protein. At present, the development of highly sensitive, high cost-effective, and non-invasive diagnostic tools for AD remains a challenge. In the last decades, nanomaterials have emerged as an interesting and useful tool in nanomedicine for diagnostics and therapy. In particular, plasmonic nanoparticles are well-known to display unique optical properties derived from their localized surface plasmon resonance (LSPR), allowing their use as transducers in various sensing configurations and enhancing detection sensitivity. Herein, this review focuses on current advances in in vitro sensing techniques such as Surface-enhanced Raman scattering (SERS), Surface-enhanced fluorescence (SEF), colorimetric, and LSPR using plasmonic nanoparticles for improving the sensitivity in the detection of main biomarkers related to AD in body fluids. Additionally, we refer to the use of plasmonic nanoparticles for in vivo imaging studies in 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 review on advances of treatment modalities for Alzheimer's disease

Alzheimer's disease (AD) is a multifactorial neurodegenerative disease which is mainly characterized by progressive impairment in cognition, emotion, language and memory in older population. Considering the impact of AD, formulations of pharmaceutical drugs and cholinesterase inhibitors have been widely propagated, receiving endorsement by FDA as a form of AD treatment. However, these medications were gradually discovered to be ineffective in removing the root of AD pathogenesis but merely targeting the symptoms so as to improve a patient's cognitive outcome. Hence, a search for better disease-modifying alternatives is put into motion. Having a clear understanding of the neuroprotective mechanisms and diverse properties undertaken by specific genes, antibodies and nanoparticles is central towards designing novel therapeutic agents. In this review, we provide a brief introduction on the background of Alzheimer's disease, the biology of blood-brain barrier, along with the potentials and drawbacks associated with current therapeutic treatment avenues pertaining to gene therapy, immunotherapy and nanotherapy for better diagnosis and management of Alzheimer's disease.

Nitrogen-Doped Carbonized Polymer Dots: A Potent Scavenger and Detector Targeting Alzheimer's β-Amyloid Plaques

The fibrillization and deposition of β-amyloid protein (Aβ) are recognized to be the pathological hallmarks of Alzheimer's disease (AD), which signify the need for the effective detection and inhibition of Aβ accumulation. Development of multifunctional agents that can inhibit Aβ aggregation, rapidly disaggregate fibrils, and image aggregates is one of the effective strategies to treat and diagnose AD. Herein, the multifunctionality of nitrogen-doped carbonized polymer dots (CPDs) targeting Aβ aggregation is reported. CPDs inhibit the fibrillization of Aβ monomers and rapidly disintegrate Aβ fibrils by electrostatic interactions, hydrogen-bonding and hydrophobic interactions with Aβ in a time scale of seconds to minutes. Moreover, the interactions make CPDs label Aβ fibrils and emit enhanced red fluorescence by the binding, so CPDs can be used for in vivo imaging of the amyloids in transgenic Caenorhabditis elegans CL2006 as an AD model. Importantly, CPDs are demonstrated to scavenge the in vivo amyloid plaques and to promote the lifespan extension of CL2006 strain by alleviating the Aβ-triggered toxicity. Taken together, the multifunctional CPDs show an exciting prospect for further investigations in Aβ-targeted AD treatment and diagnosis, and this study provides new insight into the development of carbon materials in AD theranostics.

Nanomaterial synthesis, an enabler of amyloidosis inhibition against human diseases

Amyloid diseases are global epidemics with no cure currently available. In the past decade, the use of engineered nanomaterials as inhibitors or probes against the pathogenic aggregation of amyloid peptides and proteins has emerged as a new frontier in nanomedicine. In this Minireview, we summarize for the first time the pivotal role of chemical synthesis in enabling the development of this multidisciplinary field.

Quantum Dots as Promising Theranostic Tools Against Amyloidosis: A Review

Amyloids are highly ordered beta sheet rich stable protein aggregates, which have been found to play a significant role in the onset of several degenerative diseases such as Alzheimer's disease, Huntington's disease, Parkinson's disease, Type II diabetes mellitus and so on. Aggregation of proteins leading to amyloid fibril formation via intermediate(s), is thought to be a nucleated condensation polymerization process associated with many pathological conditions. There has been extensive research to identify inhibitors of these disease oriented aggregation processes. In recent times, quantum dots, with their unique physico-chemical properties have grabbed the attention of scientific community due to its applications in medical sciences. Quantum dots are nano-particles usually made of semiconductor materials which emit fluorescence upon radiation. The wavelength of fluorescence emission varies with changes in size of quantum dots. Several studies have reported significant inhibitory effects of these quantum dots towards amyloidogenesis, thereby presenting themselves as promising candidates against amyloidosis. Further, studies have also revealed amyloid detection capacity of quantum dots with sensitivity and specificity better than conventional probes. In the current review, we will discuss the various effects of quantum dots on protein aggregation pathways, their mechanism of actions and their potentials as effective therapeutics against amyloidosis.

The Extent of Human Apolipoprotein A-I Lipidation Strongly Affects the β-Amyloid Efflux Across the Blood-Brain Barrier in vitro

Much evidence suggests a protective role of high-density lipoprotein (HDL) and its major apolipoprotein apoA-I, in Alzheimer's disease (AD). The biogenesis of nascent HDL derived from a first lipidation of apoA-I, which is synthesized by the liver and intestine but not in the brain, in a process mediated by ABCA1. The maturation of nascent HDL in mature spherical HDL is due to a subsequent lipidation step, LCAT-mediated cholesterol esterification, and the change of apoA-I conformation. Therefore, different subclasses of apoA-I-HDL simultaneously exist in the blood circulation. Here, we investigated if and how the lipidation state affects the ability of apoA-I-HDL to target and modulate the cerebral β-amyloid (Aβ) content from the periphery, that is thus far unclear. In particular, different subclasses of HDL, each with different apoA-I lipidation state, were purified from human plasma and their ability to cross the blood-brain barrier (BBB), to interact with Aβ aggregates, and to affect Aβ efflux across the BBB was assessed in vitro using a transwell system. The results showed that discoidal HDL displayed a superior capability to promote Aβ efflux in vitro (9 × 10-5 cm/min), when compared to apoA-I in other lipidation states. In particular, no effect on Aβ efflux was detected when apoA-I was in mature spherical HDL, suggesting that apoA-I conformation, and lipidation could play a role in Aβ clearance from the brain. Finally, when apoA-I folded its structure in discoidal HDL, rather than in spherical ones, it was able to cross the BBB in vitro and strongly destabilize the conformation of Aβ fibrils by decreasing the order of the fibril structure (-24%) and the β-sheet content (-14%). These data suggest that the extent of apoA-I lipidation, and consequently its conformation, may represent crucial features that could exert their protective role in AD pathogenesis.

Quantum dots-based sandwich immunoassay for sensitive detection of Alzheimer's disease-related Aβ1-42

Amyloid-beta peptide 1-42 (Aβ_1-42) is known as a component of amyloid plaques in association with Alzheimer's disease. Herein, we developed a reliable and remarkably sensitive sandwich immunoassay to detect the Aβ_1-42 using quantum dots (QDs) as fluorescent label. In the presence of Aβ_1-42, the biotinylated Anti-beta Amyloid 1-16 (N-Ab) recognized the target and formed C-Ab-Aβ_1-42-N-Ab sandwich immunocomplexes. Then Streptavidin-QDs conjugated to biotinylated N-Ab and the concentration of Aβ_1-42 was determined by detecting the fluorescence intensity in the supernatant. This method is faster and more efficient than the previous approach we reported. It also has reasonable sensitivity and selectivity. Under the optimized conditions, the linear range is 5.0 to 100 pM (0.023-0.45 ng/mL) and the detection limit is 1.7 pM (7.6 pg/ mL). In addition, this method has been successfully applied to detect the Aβ_1-42 in human cerebrospinal fluid sample.

Generation of Clickable Pittsburgh Compound B for the Detection and Capture of β-Amyloid in Alzheimer's Disease Brain

The benzothiazole-aniline derivative Pittsburgh Compound B (PiB) is the prototypical amyloid affinity probe developed for the in vivo positron emission tomography (PET) detection of amyloid beta (Aβ) deposits in Alzheimer's disease (AD). Specific high-affinity binding sites for PiB have been found to vary among AD cases with comparable Aβ load, and they are virtually absent on human-sequence Aβ deposits in animal models, none of which develop the full phenotype of AD. PiB thus could be an informative probe for studying the pathobiology of Aβ, but little is known about the localization of PiB binding at the molecular or structural level. By functionalizing the 6-hydroxy position of PiB with a PEG₃ spacer and a terminal alkyne (propargyl) moiety, we have developed a clickable PiB compound that was derivatized with commercially available azide-labeled fluorophores or affinity-tags using copper-catalyzed azide-alkyne cycloaddition reactions, commonly referred to as "click" chemistry. We have determined that both the clickable PiB derivative and its fluorescently labeled conjugate have low nanomolar binding affinities for synthetic Aβ aggregates. Furthermore, the fluorescent-PiB conjugate can effectively bind Aβ aggregates in human AD brain homogenates and tissue sections. By covalently coupling PiB to magnetic beads, Aβ aggregates were also affinity-captured from AD brain extracts. Thus, the clickable PiB derivative described herein can be used to generate a wide variety of covalent conjugates, with applications including the fluorescence detection of Aβ, the ultrastructural localization of PiB binding, and the affinity capture and structural characterization of Aβ and other cofactors from AD brains.

Self-assembling peptide and protein amyloids: from structure to tailored function in nanotechnology

Self-assembled peptide and protein amyloid nanostructures have traditionally been considered only as pathological aggregates implicated in human neurodegenerative diseases. In more recent times, these nanostructures have found interesting applications as advanced materials in biomedicine, tissue engineering, renewable energy, environmental science, nanotechnology and material science, to name only a few fields. In all these applications, the final function depends on: (i) the specific mechanisms of protein aggregation, (ii) the hierarchical structure of the protein and peptide amyloids from the atomistic to mesoscopic length scales and (iii) the physical properties of the amyloids in the context of their surrounding environment (biological or artificial). In this review, we will discuss recent progress made in the field of functional and artificial amyloids and highlight connections between protein/peptide folding, unfolding and aggregation mechanisms, with the resulting amyloid structure and functionality. We also highlight current advances in the design and synthesis of amyloid-based biological and functional materials and identify new potential fields in which amyloid-based structures promise new breakthroughs.