Rapid and Electronic Identification and Quantification of Age-Specific Circulating Exosomes via Biologically Activated Graphene Transistors

An electro-optical platform for the ultrasensitive detection of small extracellular vesicle sub-types and their protein epitope counts

Methods for detecting proteins in small extracellular vesicles (sEVs) lack sensitivity and quantitative accuracy, missing clues about health and disease. Our study introduces the Nano-Extracellular Omics Sensing (NEXOS) platform, merging electrical (E-NEXOS) and optical detection (O-NEXOS). E-NEXOS determines the concentration of target sEV sub-types, and O-NEXOS quantifies the concentration of target protein epitopes (TEPs) on those TEVs. In this work, both technologies were compared to several sEV detection tools, showing superior detection limits for CD9+CD81+ and CD9+HER2+ sEVs. Furthermore, the additional information on TEVs and TEPs from bulk sEV samples, provided new phenotyping capabilities. We determined the average number of CD81 and HER2 proteins on CD9+ sEVs, a number which was later validated on spiked human plasma. These results highlight the compatibility of NEXOS with complex biofluids and, as importantly, hint at its many potential applications, ranging from basic research to the anticipated clinical translation of sEVs.

Nano-Brush Structure for Rapid Label-Free Differentiation of Alzheimer's Disease Stages and Direct Capture of Neuron-Derived Exosomes from Human Blood Plasma

The measurement of the neurofilament light chain (NFL) in human blood plasma/serum is a promising liquid biopsy for Alzheimer's disease (AD) diagnosis, offering advantages over conventional neuroimaging techniques recommended in clinical guidelines. Here, a controllable nano-brush structure comprising upstanding silicon nanowires coated with indium tin oxide was employed as the sensing substrate. This nano-brush structure was modified with an NFL antibody (NFLAb) via silane coupling and then further connected as the extended gate in a field-effect transistor (EGFET). Notable signal differences emerged within a 2 min timeframe, enabling the label-free differentiation in human blood plasmas among four distinct cohorts: healthy controls, subjective cognitive decline, mild cognitive impairment, and dementia due to AD. Our study indicates that achieving a surface roughness exceeding 400 nm on the modified nano-brush structure enables the effective electrical sensing in our EGFETs. These distinct electrical responses measured via the NFLAb-modified nano-brush EGFETs can be attributed to the combined effects of the captured NFLs and NFL-specific neuron-derived exosomes (NDEs) found in dementia patients, as confirmed by electron spectroscopy for chemical analysis, atomic force microscopy, and scanning electron microscopy. Finally, the potential of quantitatively detecting NDEs on the NFLAb-modified nano-brush structure was demonstrated using spiked solutions containing NFL-specific NDEs from IMR-32 neuroblast cells, wherein concentration-dependent changes were observed in the EGFETs output signal. Our findings show that the NFLAb-modified nano-brush EGFET enables rapid, label-free differentiation between healthy individuals and patients at varying stages of AD.

Extended-Gate Field-Effect Transistor Consisted of a CD9 Aptamer and MXene for Exosome Detection in Human Serum

Cancer progresses silently to the terminal stage of the impossible operable condition. There are many limitations in the treatment options of cancer, but diagnosis in an early stage can improve survival rates and low recurrence. Exosomes are the biomolecules released from cancer cells and are promising candidates for clinical diagnosis. Among them, the cluster of differentiation 9 (CD9) protein is an important exosomal biomarker that can be used for exosome determination. Therefore, here, a CD9 aptamer was first synthesized and applied to an extended-gate field-effect transistor (EGFET)-type biosensor containing a disposable sensing membrane to suggest the possibility of detecting exosomes in a clinical environment. Systematically evaluating ligands using the exponential enrichment (SELEX) technique was performed to select nucleic acid sequences that can specifically target the CD9 protein. Exosomes were detected according to the electrical signal changes on a membrane, which is an extended gate using an Au microelectrode. The fabricated biosensor showed a limit of detection (LOD) of 10.64 pM for CD9 proteins, and the detection range was determined from 10 pM to 1 μM in the buffer. In the case of the clinical test, the LOD and detection ranges of exosomes in human serum samples were 6.41 × 102 exosomes/mL and 1 × 103 to 1 × 107 exosomes/mL, respectively, showing highly reliable results with low error rates. These findings suggest that the proposed aptasensor can be a powerful tool for a simple and early diagnosis of exosomes.

Introduction of Nanomaterials to Biosensors for Exosome Detection: Case Study for Cancer Analysis

Exosomes have been gaining attention for early cancer diagnosis owing to their biological functions in cells. Several studies have reported the relevance of exosomes in various diseases, including pancreatic cancer, retroperitoneal fibrosis, obesity, neurodegenerative diseases, and atherosclerosis. Particularly, exosomes are regarded as biomarkers for cancer diagnosis and can be detected in biofluids, such as saliva, urine, peritoneal fluid, and blood. Thus, exosomes are advantageous for cancer liquid biopsies as they overcome the current limitations of cancer tissue biopsies. Several studies have reported methods for exosome isolation, and analysis for cancer diagnosis. However, further clinical trials are still required to determine accurate exosome concentration quantification methods. Recently, various biosensors have been developed to detect exosomal biomarkers, including tumor-derived exosomes, nucleic acids, and proteins. Among these, the exact quantification of tumor-derived exosomes is a serious obstacle to the clinical use of liquid biopsies. Precise detection of exosome concentration is difficult because it requires clinical sample pretreatment. To solve this problem, the use of the nanobiohybrid material-based biosensor provides improved sensitivity and selectivity. The present review will discuss recent progress in exosome biosensors consisting of nanomaterials and biomaterial hybrids for electrochemical, electrical, and optical-based biosensors.

Two-Dimensional Field-Effect Transistor Sensors: The Road toward Commercialization

The evolutionary success in information technology has been sustained by the rapid growth of sensor technology. Recently, advances in sensor technology have promoted the ambitious requirement to build intelligent systems that can be controlled by external stimuli along with independent operation, adaptivity, and low energy expenditure. Among various sensing techniques, field-effect transistors (FETs) with channels made of two-dimensional (2D) materials attract increasing attention for advantages such as label-free detection, fast response, easy operation, and capability of integration. With atomic thickness, 2D materials restrict the carrier flow within the material surface and expose it directly to the external environment, leading to efficient signal acquisition and conversion. This review summarizes the latest advances of 2D-materials-based FET (2D FET) sensors in a comprehensive manner that contains the material, operating principles, fabrication technologies, proof-of-concept applications, and prototypes. First, a brief description of the background and fundamentals is provided. The subsequent contents summarize physical, chemical, and biological 2D FET sensors and their applications. Then, we highlight the challenges of their commercialization and discuss corresponding solution techniques. The following section presents a systematic survey of recent progress in developing commercial prototypes. Lastly, we summarize the long-standing efforts and prospective future development of 2D FET-based sensing systems toward commercialization.