Split-aptamer mediated regenerable temperature-sensitive electrochemical biosensor for the detection of tumour exosomes

Empowering Exosomes with Aptamers for Precision Theranostics

As information messengers for cell-to-cell communication, exosomes, typically small membrane vesicles (30-150 nm), play an imperative role in the physiological and pathological processes of living systems. Accumulating studies have demonstrated that exosomes are potential biological candidates for theranostics, including liquid biopsy-based diagnosis and drug delivery. However, their clinical applications are hindered by several issues, especially their unspecific detection and insufficient targeting ability. How to upgrade the accuracy of exosome-based theranostics is being widely explored. Aptamers, benefitting from their admirable characteristics, are used as excellent molecular recognition elements to empower exosomes for precision theranostics. With high affinity against targets and easy site-specific modification, aptamers can be incorporated with platforms for the specific detection of exosomes, thus providing opportunities for advancing disease diagnostics. Furthermore, aptamers can be tailored and functionalized on exosomes to enable targeted therapeutics. Herein, this review emphasizes the empowering of exosomes by aptamers for precision theranostics. A brief introduction of exosomes and aptamers is provided, followed by a discussion of recent progress in aptamer-based exosome detection for disease diagnosis, and the emerging applications of aptamer-functionalized exosomes for targeted therapeutics. Finally, current challenges and opportunities in this research field are presented.

Zeolitic imidazolate framework/aptamer-based fluorescence assay for the facile and high-sensitivity detection of acetamiprid

Accurate monitoring of trace pesticides in complex matrix remains a challenge in food safety supervision. Herein, we designed a facile zeolitic imidazolate framework (ZIF)-8/aptamer-based assay for the sensitive detection of acetamiprid. ZIF-8 efficiently adsorbs 6-carboxyfluorescein-labeled complementary DNA (cDNA-FAM) via electrostatic interaction, hydrogen bonding and Zn2+ coordination, which contributed to resistance to cDNA-FAM displacement by biological ligands. ZIF-8 serves as an "ion pump" that contains lots of Zn2+ who boosts cDNA-FAM adsorption and triggers the photoinduced electron transfer (PET) effect from FAM to ZIF-8, improving the sensing sensitivity. Acetamiprid could trigger the change in the adsorption state of cDNA-FAM, further tuning the PET effect and causing fluorescence conversion. The fluorescence assay showed a high sensitivity for monitoring acetamiprid with a detection limit of 0.05 ng mL-1 in the apple sample. This ZIF/DNA-based analytical platform provides a powerful tool for facile and low-cost screening of pesticide residues, with promising applications in food safety monitoring.

Inspired by game theory: Multi-signal output photoelectrochemical point-of-care immunoassay based on target-triggered organic electronic barriers

This work presents an integrated photoelectrochemical, impedance and colorimetric biosensing platform for flexible detection of cancer markers based on the targeted response by combining liposome amplification strategies and target-induced non-in situ formation of electronic barriers as the signal transduction modality on carbon-modified CdS photoanodes. Inspired by game theory, the carbon layer modified CdS hyperbranched structure with low impedance and high photocurrent response was firstly obtained by surface modification of CdS nanomaterials. Through a liposome-mediated enzymatic reaction amplification strategy, a large number of organic electron barriers were formed by a biocatalytic precipitation (BCP) reaction triggered by horseradish peroxidase released from cleaved liposomes after the introduction of the target molecule, thereby increasing the impedance characteristics of the photoanode as well as attenuating the photocurrent. The BCP reaction in the microplate was accompanied by a significant color change, which opened up a new window for point-of-care testing. Taking carcinoembryonic antigen (CEA) as a proof of concept, the multi-signal output sensing platform showed a satisfactory sensitive response to CEA with an optimal linear range of 20 pg mL^-1-100 ng mL^-1. The detection limit was as low as 8.4 pg mL^-1. Meanwhile, with the assistance of a portable smartphone and a miniature electrochemical workstation, the electrical signal obtained was synchronized with the colorimetric signal to correct the actual target concentration in the sample, further reducing the occurrence of false reports. Importantly, this protocol provides a new idea for the sensitive detection of cancer markers and the construction of a multi-signal output platform.

Recent developments in isolating methods for exosomes

Exosomes are the smallest extracellular vesicles that can be released by practically all cell types, and range in size from 30 nm to 150 nm. As the major marker of liquid biopsies, exosomes have great potential for disease diagnosis, therapy, and prognosis. However, their inherent heterogeneity, the complexity of biological fluids, and the presence of nanoscale contaminants make the isolation of exosomes a great challenge. Traditional isolation methods of exosomes are cumbersome and challenging with complex and time-consuming operations. In recent years, the emergence of microfluidic chips, nanolithography, electro-deposition, and other technologies has promoted the combination and innovation of the isolation methods. The application of these methods has brought very considerable benefits to the isolation of exosomes such as ultra-fast, portable integration, and low loss. There are significant functional improvements in isolation yield, isolation purity, and clinical applications. In this review, a series of methods for the isolation of exosomes are summarized, with emphasis on the emerging methods, and in-depth comparison and analysis of each method are provided, including their principles, merits, and demerits.

Practical tips and new trends in electrochemical biosensing of cancer-related extracellular vesicles

To tackle cancer and provide prompt diagnoses and prognoses, the constantly evolving biosensing field is continuously on the lookout for novel markers that can be non-invasively analysed. Extracellular vesicles (EVs) may represent a promising biomarker that also works as a source of biomarkers. The augmented cellular activity of cancerous cells leads to the production of higher numbers of EVs, which can give direct information on the disease due to the presence of general and cancer-specific surface-tethered molecules. Moreover, the intravesicular space is enriched with other molecules that can considerably help in the early detection of neoplasia. Even though EV-targeted research has indubitably received broad attention lately, there still is a wide lack of practical and effective quantitative procedures due to difficulties in pre-analytical and analytical phases. This review aims at providing an exhaustive outline of the recent progress in EV detection using electrochemical and photoelectrochemical biosensors, with a focus on handling approaches and trends in the selection of bioreceptors and molecular targets related to EVs that might guide researchers that are approaching such an unstandardised field.

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.