From biogenesis to aptasensors: advancements in analysis for tumor-derived extracellular vesicles research.

Extracellular vesicles (EVs) are enclosed by a nanoscale phospholipid bilayer membrane and typically range in size from 30 to 200 nm. They contain a high concentration of specific proteins, nucleic acids, and lipids, reflecting but not identical to the composition of the parent cell. The inherent characteristics and variety of EVs give them extensive and unique advantages in the field of cancer identification and treatment. Recently, EVs have been recognized as potential tumor markers for the detection of cancer. Aptamers, which are molecules of single-stranded DNA or RNA, demonstrate remarkable specificity and affinity for their targets by adopting distinct tertiary structures. Aptamers offer various advantages over their protein counterparts, such as reduced immunogenicity, the ability for convenient large-scale synthesis, and straightforward chemical modification. In this review, we summarized EVs biogenesis, sample collection, isolation, storage and characterization, and finally provided a comprehensive survey of analysis techniques for EVs detection that are based on aptamers.

Cell-SELEX and application research of a DNA aptamer against esophageal squamous cell carcinoma (ESCC) cell line TE-1.

Esophageal cancer is a common cancer with high morbidity and mortality that severely threatens the safety and quality of human life. The strong metastatic nature of esophageal cancer enables it to metastasize more quickly and covertly, making it difficult for current diagnostic and treatment methods to achieve efficient early screening, as well as timely and effective treatment. As a promising solution, nucleic acid aptamers, a kind of special single-stranded DNA or RNA oligonucleotide selected by the Systematic Evolution of Ligands by Exponential Enrichment (SELEX) technology, can specifically bind with different molecular targets. In this paper, random DNA single-stranded oligonucleotides were used as the initial library. Using TE-1 cells and HEEC cells as targets, specific binding sequences were selected by 15 rounds of the cell-SELEX method, and the aptamer sequence that binds to TE-1 cells with the most specificity was obtained and named Te4. The Te4 aptamer was further validated for binding specificity, binding affinity, type of target, in vitro cytotoxicity when conjugated with DOX(Te4-DOX), and in vivo distribution. Results of in vitro validation showed that Te4 has outstanding binding specificity with a Kd value of 51.16 ± 5.52 nM, and the target type of Te4 was preliminarily identified as a membrane protein. Furthermore, the cytotoxicity experiment showed that Te4-DOX has specific cytotoxicity towards cultured TE-1 cells. Finally, the results of the in vivo distribution experiment showed that the Te4 aptamer is able to specifically target tumor regions in nude mice, showing great potential to be applied in future diagnosis and targeted therapy of esophageal cancer.

Selection of a High-Affinity DNA Aptamer for the Recognition of Cadmium Ions.

Cadmium ions as toxic metallic pollutants have been dramatically risen due to industrial production, which causes serious environmental damages and potential health risks. Thus, developing sensitive and specific probes to recognize cadmium ions is vital for human and environmental safety. In this work, the aptamer as a capture probe was selected for the identification of cadmium ions. The modified SELEX method based on immobilizing ssDNA libraries on streptavidin magnetic beads was used to the high-affinity aptamer selection for binding cadmium ions. After 9 rounds of selection, 4 ssDNA sequences with the highest enrichment were obtained, and the Cd-1 aptamer exhibited the highest affinity to cadmium ions. The dissociation constant Kd value of the Cd-1 aptamer was 81.39 µM for cadmium ions. Later, we also investigated the binding specificity of Cd-1 aptamer toward other heavy metal ions. Given the availability of immobilizing ssDNA library on matrix, we believe the strategy also applies to discover other ions in a reproducible manner.

A Novel Strategy for Liquid Exfoliation of Ultrathin Black Phosphorus Nanosheets.

As an emerging two-dimensional layered material, black phosphorus nanosheets show unparalleled optical and electronic properties. Although black phosphorus nanosheets have attracted much attention in the photoelectric field, their applications in biomedical field were still limited due to their poor biocompatibility of current synthesis strategies. Herein, we propose a novel synthetic strategy for black phosphorus nanosheets that rely on Tween 20-assisted liquid exfoliation and post-processing in deoxygenated water. Microscopic and spectroscopic analysis suggested that the produced black phosphorus nanosheets dispersions exhibited good stability and higher yield compared with other currently prepared methods. Because of their ultrahigh exfoliation efficiency, the black phosphorus flakes present few-layer and even monolayer, which are thinner than the most dispersions of black phosphorus. Thus, this method enables mass-production of high-quality few-layer black phosphorus with high biocompatibility, and has the potential to be directly used in the biological field.

Application of magnetic nanoparticles in nucleic acid detection.

Nucleic acid is the main material for storing, copying, and transmitting genetic information. Gene sequencing is of great significance in DNA damage research, gene therapy, mutation analysis, bacterial infection, drug development, and clinical diagnosis. Gene detection has a wide range of applications, such as environmental, biomedical, pharmaceutical, agriculture and forensic medicine to name a few. Compared with Sanger sequencing, high-throughput sequencing technology has the advantages of larger output, high resolution, and low cost which greatly promotes the application of sequencing technology in life science research. Magnetic nanoparticles, as an important part of nanomaterials, have been widely used in various applications because of their good dispersion, high surface area, low cost, easy separation in buffer systems and signal detection. Based on the above, the application of magnetic nanoparticles in nucleic acid detection was reviewed.

Recent advances in biosensor for detection of lung cancer biomarkers.

Lung cancer is primary cancer threatening human life worldwide with the highest mortality rate. The early detection of lung cancer plays a critical role in the early diagnosis and subsequent treatment. However, the conventional methodologies limit the applications due to the low sensitivity, being expensive, and invasive procedure. Tumor markers as biochemical parameters can reflect cancer occurrence and progression, which show sensitivity, convenience, and low cost in developing biosensors, and act as good candidates for fabricating biosensors of detecting lung cancer. This review describes various biosensors (2013-2019) for detection of lung cancer biomarkers. Firstly, the various reported tumor markers of lung cancer are briefly described. Then, the advancements of designing biosensors for sensitive, stable, and selective identification of lung cancer biomarkers are systematically provided, with a specific focus on the main clinical biomarkers such as neuron-specific enolase (NSE), cytokeratin 19 fragment (CYFRA 21-1). Finally, the recent challenges and further opportunities for developing effective biosensors for early diagnosis of lung cancer are discussed.

Advanced Diagnostic Strategies for Clostridium difficile Infection (CDI).

Clostridium difficile infection (CDI) is a leading cause of nosocomial intestinal diseases and produces considerable morbidity and mortality among inpatients globally. The increasing incidence of CDI, especially of its severe cases, creates a growing financial burden internationally. The pathogen responsible for CDI, C. difficile, is an anaerobic, spore-bearing Gram-positive bacillus that colonizes gastrointestinal tract in humans and animals. The bacterium can transfer from one host to another via the oral-fecal route and is consequently a public health concern in the community as well as hospitals. CDI also has implications for the personal hygiene of patients and medical workers. Classical risk factors for CDI include old age, long inpatient stay, and use of antibacterial agents. Clinical manifestations and a positive laboratory assay are both needed for an accurate diagnosis of CDI. Laboratory testing for C. difficile should distinguish between toxigenic and non-toxigenic strains, as well as asymptomatic colonization and the clinical manifestations of infection. Most stand-alone assays do not attain the desired sensitivity and specificity, and thus multistep algorithms and automated assays have emerged in recent years. Hospitals have adopted various assays, combining their conjunct advantages to enable rapid results, accurate diagnosis, and decreased expenditure. This strategy ultimately prevents misdiagnosis and over-diagnosis simultaneously. In this review, we describe common strategies for diagnosis of CDI and compare commercially available multistep and automatic assays.

Aptasensors for pesticide detection.

Pesticide contamination has become one of the most serious problems of public health in the world, due to their wide application in agriculture industry to guarantee the crop yield and quality. The detection of pesticide residues plays an important role in food safety management and environment protection. However, the conventional detection methodologies cannot realize highly sensitive, selective and on-site detection, which limits their applications. Aptamers are short single-stranded oligonucleotides (RNA or DNA) selected by SELEX method, which can selectively bind to their targets with high affinity. Compared with the commonly used antibodies or enzymes in designing biosensors, aptamers exhibit better stability, low molecular weight, easy modification and low cost, and were regarded as excellent candidates for developing aptasensors for pesticide detection. In this review, application of aptamers for pesticide detection was reviewed. Firstly, aptamers specifically bind to various pesticides were first summarized. Secondly, the progresses and highlights of developing aptasensors for highly-sensitive and selective detection of pesticide residues were systematically provided. Finally, the present challenges and future perspectives for developing novel highly-effective aptasensor for the detection of pesticide residues were discussed.

Molecular Imprinting Polymers Electrochemical Sensor Based on AuNPs/PTh Modified GCE for Highly Sensitive Detection of Carcinomaembryonic Antigen.

A novel molecular imprinted polymer (MIP) electrochemical sensor was successfully fabricated for sensitive detection of carcinomaembryonic antigen (CEA). We used CEA as template, dopamine (DA) as imprinted monomers. Through controlling electropolymerization, a "PDA-CEA"complex was achieved. After elution, the specific cavities adsorbed the target molecules. In addition, polythionine (PTh) and AuNPs were applied as the electrode modifying materials to enhance electron transfer rate and improve detection signal. Using differential pulse voltammetry (DPV) detection, the peak current decreased with the increase in concentration of CEA, and the linear response range of the MIP sensor was from 0.001 ng/mL to 1000 ng/mL with the detection limit as low as 0.2589 pg/mL. The MIP sensor had a low sample consumption, good stability, and high sensitivity, and could become a new promising method for the detection of CEA. Furthermore, this MIP sensor was demonstrated in testing CEA in human serum sample with satisfactory results.

Immunosensors Based on Nanomaterials for Detection of Tumor Markers.

Nanomaterials have been widely used to immobilize biomolecules, amplify the signals and concentrate the analytes for detection with good properties including large surface area, good adsorption capacity and high surface activity. In recent years, nanomaterials such as carbon nanomaterials, noble metal nanomaterials, polymers, are widely applied to research and develop immunosensors with high sensitivity and selectivity, which monitor the antigen-antibody reaction for the detection of tumor markers. This review provides an introduction of immunosensors and focuses on the design of electrochemical (EC) immunosensors, electrochemical luminscence (ECL) immunosensors and photoelectrochemical (PEC) immunosensors based on nanomaterials in nearly three years.