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 Aβ₄₀, Aβ₄₂, 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.     

Ultrasensitive Detection of SARS-CoV‑2 by Flexible Metal Oxide Field-Effect Transistors

The pandemic of coronavirus disease 2019 (COVID-19) reflects the great significance of rapid and accurate detection of pathogens by new sensing technologies. Antibody based biosensors with high sensitivity comparable to golden standard polymerase chain reaction (PCR) and miniaturized device features allow the detection of pathogens in portable and flexible formats. Herein, flexible metal oxide electrolyte-gated field-effect transistors (EGFETs) are reported to serve as the biosensors for rapid and ultrasensitive severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) detection. The semiconducting layer of the EGFETs associates with hybrid material of PEI doped metal oxides that not only improves the transistor performance, but also regulates microstructure forming higher surface-to-volume ratio, which brings more antibodies immobilization, resulting in higher sensitive, and faster response for detecting SARS-CoV-2. Comprehensive studies of materials and interfacing engineering of the EGFETs not only build the strong foundation for the EGFET sensors to show excellent sensitivity with a limit of detection from 0.14 fg ml⁻¹ for SARS-CoV-2 S1 proteins, and 0.09 copies µl⁻¹ for SARS-CoV-2 viruses, but also offer good mechanical properties to enable thin, soft flexible sensing platforms. This work provides a new strategy from materials to devices as innovative schemes for virus/pathogens detection.     

FluorMango,an RNA-Based Fluorogenic Biosensor for the Direct and Specific Detection of Fluoride

Nucleic acids are not only essential actors of cell life but also extremely appealing molecular objects in the development of synthetic molecules for biotechnological application, such as biosensors to report on the presence and concentration of a target ligand by emission of a measurable signal. In this work, FluorMango, a fluorogenic ribonucleic acid (RNA)-based biosensor specific for fluoride is introduced. The molecule consists of two RNA aptamer modules, a fluoride-specific sensor derived from the crcB riboswitch which changes its structure upon interaction with the target ion, and the light-up RNA Mango-III that emits fluorescence when complexed with a fluorogen. The two modules are connected by an optimized communication module identified by ultrahigh-throughput screening, which results in extremely high fluorescence of FluorMango in the presence of fluoride, and background fluorescence in its absence. The value and efficiency of this biosensor by direct monitoring of defluorinase activity in living bacterial cells is illustrated, and the use of this new tool in future screening campaigns aiming at discovering new defluorinase activities is discussed.     

Flexible Nanoarchitectonics for Biosensing and Physiological Monitoring Applications

Flexible and implantable electronics hold tremendous promises for advanced healthcare applications, especially for physiological neural recording and modulations. Key requirements in neural interfaces include miniature dimensions for spatial physiological mapping and low impedance for recognizing small biopotential signals. Herein, a bottom-up mesoporous formation technique and a top-down microlithography process are integrated to create flexible and low-impedance mesoporous gold (Au) electrodes for biosensing and bioimplant applications. The mesoporous architectures developed on a thin and soft polymeric substrate provide excellent mechanical flexibility and stable electrical characteristics capable of sustaining multiple bending cycles. The large surface areas formed within the mesoporous network allow for high current density transfer in standard electrolytes, highly suitable for biological sensing applications as demonstrated in glucose sensors with an excellent detection limit of 1.95 µm and high sensitivity of 6.1 mA cm⁻² µM⁻¹, which is approximately six times higher than that of benchmarking flat/non-porous films. The low impedance of less than 1 kΩ at 1 kHz in the as-synthesized mesoporous electrodes, along with their mechanical flexibility and durability, offer peripheral nerve recording functionalities that are successfully demonstrated in vivo. These features highlight the new possibilities of our novel flexible nanoarchitectonics for neuronal recording and modulation applications.     

Stimuli-Responsive and Reversible Nanoassemblies of G-Triplexes

G-triplex (G3) structures formed with three consecutive G-tracts have recently been identified as a new emerging guanine-rich DNA fold. There could likely be a wide range of biological functions for G3s as occurring for G-quadruplex (G4) structures formed with four consecutive G-tracts. However, in comparison to the many reports on G4 nanoassemblies that organize monomers together in a controllable manner, G3-favored nanoassemblies have yet to be explored. In this work, we found that a natural alkaloid of sanguinarine can serve as a dynamic ligand glue to reversibly switch the dimeric nanoassemblies of the thrombin binding aptamer G3 (TBA-G3). The glue planarity was considered to be a crucial factor for realizing this switching. More importantly, external stimuli including pH, sulfite, O₂ and H₂O₂ can be employed as common regulators to easily modulate the glue's adhesivity for constructing and destructing the G3 nanoassemblies as a result of the ligand converting between isoforms. However, this assembly behavior does not occur with the counterpart TBA-G4. Our work demonstrates that higher-order G3 nanoassemblies can be reversibly operated by manipulating ligand adhesivity. This provides an alternative understanding of the unique behavior of guanine-rich sequences and focuses attention on the G3 fold since the nanoassembly event investigated herein might occur in living cells.     

Enzymatic Beacons for Specific Sensing of Dilute Nucleic Acid**

Enzymatic beacons, or E-beacons, are 1 : 1 bioconjugates of the nanoluciferase enzyme linked covalently at its C-terminus to hairpin forming ssDNA equipped with a dark quencher. We prepared E-beacons biocatalytically using HhC, the promiscuous Hedgehog C-terminal protein-cholesterol ligase. HhC attached nanoluciferase site-specifically to mono-sterylated hairpin oligonucleotides, called steramers. Three E-beacon dark quenchers were evaluated: Iowa Black, Onyx-A, and dabcyl. Each quencher enabled sensitive, sequence-specific nucleic acid detection through enhanced E-beacon bioluminescence upon target hybridization. We assembled prototype dabcyl-quenched E-beacons specific for SARS-CoV-2. Targeting the E484 codon of the virus Spike protein, E-beacons (80×10⁻¹² M) reported wild-type SARS-CoV-2 nucleic acid at ≥1×10⁻⁹ M by increased bioluminescence of 8-fold. E-beacon prepared for the SARS-CoV-2 E484K variant functioned with similar sensitivity. Both E-beacons could discriminate their target from the E484Q mutation of the SARS-CoV-2 Kappa variant. Along with mismatch specificity, E-beacons are two to three orders of magnitude more sensitive than synthetic molecular beacons.     

基于多酸复合物的电化学生物传感器在食品分析中的研究进展

多金属氧酸盐（POMs）具有结构和组成多样性的优点，在电化学生物传感器领域被认为是一类颇具前景的功能性阴离子电极修饰材料。通过将POMs与碳基材料、贵金属和金属有机框架等纳米材料复合形成多酸复合物，可以克服其导电能力差和比表面积小的缺陷，将进一步拓展POMs在电化学生物传感器领域的应用范围。该文综述了近年来基于POMs基复合物电化学生物传感器的构建方法，以及POMs基复合物在食品分析领域中的研究进展，并探讨了POMs基复合物未来的挑战和发展前景。将POMs基复合物制备与电化学生物传感器构建这两项技术不断融合将逐渐提升相关传感器的检测性能。     

Accurately Detecting Trace-Level Infectious Agents by an Electro-Enhanced Graphene Transistor

For epidemic prevention and control, molecular diagnostic techniques such as field-effect transistor (FET) biosensors is developed for rapid screening of infectious agents, including Mycobacterium tuberculosis, SARS-CoV-2, rhinovirus, and others. They obtain results within a few minutes but exhibit diminished sensitivity (<75%) in unprocessed biological samples due to insufficient recognition of low-abundance analytes. Here, an electro-enhanced strategy is developed for the precise detection of trace-level infectious agents by liquid-gate graphene field-effect transistors (LG-GFETs). The applied gate bias preconcentrates analytes electrostatically at the sensing interface, contributing to a 10-fold signal enhancement and a limit of detection down to 5 × 10⁻¹⁶ g mL⁻¹ MPT64 protein in serum. Of 402 participants, sensitivity in tuberculosis, COVID-19 and human rhinovirus assays reached 97.3% (181 of 186), and specificity is 98.6% (213 of 216) with a response time of <60 s. This study solves a long-standing dilemma that response speed and result accuracy of molecular diagnostics undergo trade-offs in unprocessed biological samples, holding unique promise in high-quality and population-wide screening of infectious diseases.     

Biocatalytic Metal-Organic Frameworks: Promising Materials for Biosensing

The highly efficient and specific catalysis of enzymes allows them to recognize a myriad of substrates, which enables biosensing. However, the fragility of natural enzymes severely restricts their practical applications. Metal-organic frameworks (MOFs) with porous networks and attractive functions have been intelligently employed as supports to encase enzymes and protect them against harsh environments. More importantly, customizable construction and composition affords the intrinsic enzyme-like activity of some MOFs (known as nanozymes), which provides an alternative route for the construction of robust enzyme mimics. This review will introduce the concept of these biocatalytic MOFs, with special emphasis on how biocatalytic processes that operate in these materials can reverse the plight of native enzyme-based biosensing. In addition, the present challenges and future outlooks in this research field are briefly discussed.     

Boosting Sensitivity and Reliability in Field-Effect Transistor-Based Biosensors with Nanoporous MoS2 Encapsulated by Non-Planar Al2O3 (Adv. Funct. Mater. 42/2023)

Field-effect transistors-based biosensors (bio-FETs) have been considered an important technology for label-free and ultrasensitive point-of-care diagnostics. However, practical applications using bio-FETs are limited due to the trade-off between sensing reliability and sensitivity. This study suggests a reliable and sensitive bio-FETs based on nanoporous molybdenum disulfide (MoS₂) channels encapsulated by a non-planar high-k aluminum oxide (Al₂O₃) dielectric layer. Nanoporous MoS₂ thin film is fabricated with an abundant edge area and periodically ordered nanopores via block copolymer lithography. The ultra-thin Al₂O₃ dielectric layer deposited along the nanoporous structure of the MoS₂ realizes effective electrostatic control of charged biomolecules over the MoS₂ channel. In addition, it plays important roles in not only enhancing the electrical performance of the nanoporous MoS₂ bio-FETs, that is, mobility, hysteresis, and subthreshold swing, but also achieving effective biomolecular immobilization on the device surface. The nanoporous MoS₂ channel structure surrounded by non-planar Al₂O₃ detects a prostate cancer biomarker with an ultra-low limit of detection of 1 fg mL⁻¹. Moreover, the excellent selectivity, high sensitivity, and clinical reliability of the nanoporous MoS₂ bio-FETs are also confirmed. The proposed device platform provides new insights and technical advances in the field of FETs based sensors for future point-of-care devices.