Characterization of the specific interaction between the DNA aptamer sgc8c and protein tyrosine kinase-7 receptors at the surface of T-cells by biosensing AFM

Modulated Cell Internalization Behavior of Icosahedral DNA Framework with Programmable Surface Modification

Surface modification could enhance the cell internalization efficiency of nanovehicles for targeted gene or drug delivery. However, the influence of surface modification parameters, including recognition manners, valences, and patterns, is often clouded, especially for the endocytosis of DNA nanostructures in customized shapes. Focusing on an icosahedral DNA framework, we systematically programmed three distinct types of ligands with diverse valence and spatial distribution on their outer surface to study the internalization efficiency, endocytic pathways, and postinternalization fate. The comparison in different aspects of parameters deepens our understanding of the intricate relationship between surface modification and cell entry behavior, offering insights crucial for designing and optimizing DNA framework nanostructures for potent cell-targeted purposes.

A thiolated oxidized guar gum and sodium alginate dual-network microspheres with enhanced gastric acid resistance and mucoadhesion for delivery of probiotics

Probiotics offer numerous beneficial functions for human bodies, while the low survival rate under gastric acid and short retention time in the intestine are the major obstacles to their utilization. To address these issues, we designed a novel dual-network hydrogel microsphere that combines gastric acid resistance with enhanced mucoadhesion, aiming for the targeted delivery of probiotics. Thiolated oxidized guar gum (SOGG) was disulfide-linked to form the first network, and sodium alginate (SA) was cross-linked with Ca2+ to form the second network. Under the protection of the interpenetrating dual network microspheres, a much higher viability of Lactobacillus rhamnosus (LGG) (8.73 log CFU/mL) was achieved in simulated gastric fluid, compared to the zero-survival rate of free LGG. Mucoadhesion tests showed that the adhesion rate of SOGG/SA microspheres to the intestinal mucosa was 1.75 times higher than that of thiol-free microspheres. In vivo studies revealed that LGG-loaded microspheres significantly enhanced intestinal barrier function, remodeled the gut microbiome, and alleviated DSS-induced colitis in mice. Overall, SOGG/SA microspheres provide an effective strategy to the challenges of probiotic reduction in the stomach and rapid expulsion from the intestines, enhancing their health benefits.

Targeted delivery of AZD5363 to T-cell acute lymphocytic leukemia by mSiO2-Au nanovehicles

T-cell acute lymphocytic leukemia (T-ALL) is the most common cancer in children, with a low survival rate because of drug resistance and a high recurrence rate. Targeted delivery of chemotherapy drugs can reduce their side effects and improve their efficacy. The abnormality of phosphatidylinositol-3-kinase/protein kinase B/ mammalian target of rapamycin (PI3K/Akt/mTOR) pathway plays a key role in T-ALL occurrence. AZD5363 is a selective Akt inhibitor with promising therapeutic potential for tumors encoded by the PI3K/Akt/mTOR pathway. However, the toxicity and side effects have limited its application in treating T-ALL. This study aimed to design a delivery system for targeting AZD5363 to T-ALL by sgc8c aptamer designed as mesoporous silica (mSiO2) decorated with Au nanoparticles. The cell-specific targeting and cytotoxicity of mSiO2-Au-AZD5363-Apt were investigated. The mSiO2-Au nanovehicles were found feasible for AZD5363 delivery, with high loading efficiency and pH-responsive release in the acidic lysosome. More importantly, mSiO2-Au-AZD5363-Apt nanovehicles could specifically recognize and enter T-ALL cells in vitro and in vivo, effectively inhibiting the proliferation of CCRF-CEM cells. In conclusion, mSiO2-Au-AZD5363-Apt provided an effective therapeutic method for the targeted treatment of T-ALL.

A flexible wearable device coupled with injectable Fe3O4 nanoparticles for capturing circulating tumor cells and triggering their deaths

Elimination of circulating tumor cells (CTCs) in the blood can be an effective therapeutic approach to disrupt metastasis. Here, a strategy is proposed to implement flexible wearable electronics and injectable nanomaterials to disrupt the hematogenous transport of CTCs. A flexible device containing an origami magnetic membrane is used to attract Fe₃O₄@Au nanoparticles (NPs) that are surface modified with specific aptamers and intravenously injected into blood vessels, forming an invisible hand and fishing line/bait configuration to specifically capture CTCs through bonding with aptamers. Thereafter, thinned flexible AlGaAs LEDs in the device offer an average fluence of 15.75 mW mm^-2 at a skin penetration depth of 1.5 mm, causing a rapid rise of temperature to 48 °C in the NPs and triggering CTC death in 10 min. The flexible device has been demonstrated for intravascular isolation and enrichment of CTCs with a capture efficiency of 72.31% after 10 cycles in a simulated blood circulation system based on a prosthetic upper limb. The fusion of nanomaterials and flexible electronics reveals an emerging field that utilizes wearable and flexible stimulators to activate biological effects offered by nanomaterials, leading to improved therapeutical effects and postoperative outcomes of diseases.

Investigation on protein dimerization and evaluation of medicine effects by single molecule force spectroscopy

Monitoring the dimerization state of the mesenchymal-epithelial transition factor (Met) was essential for in-depth understanding of the tumor signal transduction network. At present, the dimerization activation pathway of Met protein was mainly studied at the macro level, while the research at the single molecule level was far from comprehensive. Herein, the dimerization activation of Met protein's extracellular domain induced by ligand hepatocyte growth factor (HGF) was dynamically studied by single-molecule force spectroscopy. Met protein was immobilized on a biomimetic lipid membrane for ensuring its physiological environment, and then the Met dimers were recognized by bivalent probe which was formed by two Met-binding aptamers. Then the dimeric state of Met protein could be distinguished from monomeric state of Met protein through some parameters, (such as unimodal ratio, bimodal ratio and separation work). The unimodal indicates the occurrence of single molecule binding event, and the bimodal represents the occurrence of double binding event (also represents the presence of Met dimer). Before HGF treatment, most of the Met protein on the lipid membrane was still in the form of monomer, so the unimodal ratio in the force curve was larger (78.8 ± 5.2%), and the bimodal ratio was smaller (17.0 ± 4.1%). After HGF treatment, the unimodal ratio decreased to 54.0 ± 7.4%, and the bimodal ratio increased to 43.2 ± 7.3%. It was due to the formation of dimers after the binding of Met protein on the fluidity lipid membrane with HGF. In addition, the average separation work increased to about 2 times after HGF treatment. Given that studies of Met protein dimerization inhibitors have contributed to the development of more potent and safe inhibitors to significantly inhibit tumor metastasis, the effects of different medicines (including anticoagulant medicines, different antibiotics and anti-cancer medicines) on the dimerization activation of Met protein were then explored by the platform described above. The results showed that anticoagulant medicines heparin and its analogs can significantly inhibit HGF-mediated Met protein activation, while different antibiotics and anticancer medicines had no significant effect on the dimerization of Met protein. This work provided a platform for studying protein dimerization as well as for screening Met protein dimerization inhibitors at the single-molecule level.

Construction of Probiotic Double-Layered Multinucleated Microcapsules Based on Sulfhydryl-Modified Carboxymethyl Cellulose Sodium for Increased Intestinal Adhesion of Probiotics and Therapy for Intestinal Inflammation Induced by Escherichia coli O157:H7

The decreased number of viable bacteria and the ability of Bifidobacterium to adhere to and colonize the gut in the gastrointestinal environment greatly limit their efficacy. To solve this problem, thiolated carboxymethyl cellulose sodium (CMC) probiotic double-layered multinucleated microcapsules with Bifidobacterium adolescentis FS2-3 in the inner layer and Bacillus subtilis SN15-2 embedded in the outer layers were designed. First, the viable counts and release rates of microcapsules were examined by in vitro simulated digestion assays, and it was found that microcapsules were better protected from gastrointestinal digestion than the controls. Compared with free Bifidobacterium strains, double-layered multinucleated microcapsules have higher viable bacterial survival rates and storage stability. Second, through in vitro rheology, tensile tests, isotherm titration calorimetry, and adhesion tests, it was observed that thiolated CMC could enhance the strong interaction of Bifidobacterium with intestinal mucus and significantly promote the proliferation and growth of probiotics. Finally, double-layered multinucleated microcapsules containing B. adolescentis FS2-3 and B. subtilis SN15-2 modified with sulfhydryl-modified CMC were studied in the intestine. Alleviation of Escherichia coli O157:H7 induced intestinal inflammation. The results showed that microencapsulation could significantly increase the colon content of Bifidobacterium, relieve intestinal inflammation symptoms in mice with bacterial enteritis, and repair the intestinal microbiota disorder caused by inflammation. The probiotic double-layered multinucleated microcapsules prepared in this study can improve the survival rate of probiotics and promote proliferation, adhesion, and colonization of probiotics.

Ligand Dilution Analysis Facilitates Aptamer Binding Characterization at the Single-Molecule Level

Cell-specific aptamers offer a powerful tool to study membrane receptors at the single-molecule level. Most target receptors of aptamers are highly expressed on the cell surface, but difficult to analyze in situ because of dense distribution and fast velocity. Therefore, we herein propose a random sampling-based analysis strategy termed ligand dilution analysis (LDA) for easily implemented aptamer-based receptor study. Receptor density on the cell surface can be calculated based on a regression model. By using a synergistic ligand dilution design, colocalization and differentiation of aptamer and monoclonal antibody (mAb) binding on a single receptor can be realized. Once this is accomplished, precise binding site and detailed aptamer-receptor binding mode can be further determined using molecular docking and molecular dynamics simulation. The ligand dilution strategy also sets the stage for an aptamer-based dynamics analysis of two- and three-dimensional motion and fluctuation of highly expressed receptors on the live cell membrane.

A fluorescent probe for protein tyrosine kinase 7 detection in serum and cell imaging

Tyrosine protein kinase 7 (PTK7) is overexpressed in breast cancer, which is considered as a cancer marker for breast cancer diagnosis. Therefore, a simple fluorescent probe for PTK7 detection and cell imaging was developed. In the developed probe, Fe₃O₄ magnetic nanoparticles were used as the fluorescent separator, and the fluorescence of carbon dots were used as the detection signal. The probe was worked by control the configurations of the aptamer of PTK7, the aptamer would be open chains by recognition of PTK7, which bond with carbon dots and show fluorescent signal. Based on the remarkably high affinity and selectivity of aptamer for PTK7, the excellent fluorescence property of carbon dots and the outstanding magnetism of Fe₃O₄ magnetic nanoparticles, the developed probe showed satisfied results for PTK7 detection in serum and MCF-7 cell imaging. The probe detected PTK7 in the range of 0.2-200 ng mL^-1 with a detection limit of 0.0347 ng mL^-1, and successfully imaged the cancer cell expressed PTK7. The results indicate that the nano-fluorescent probe has great potential for clinical applications.

Nanotechnology-based diagnostics and therapeutics in acute lymphoblastic leukemia: a systematic review of preclinical studies

Background: Leukemia is a malignant disease that threatens human health and life. Nano-delivery systems improve drug solubility, bioavailability, and blood circulation time, and release drugs selectively at desired sites using targeting or sensing strategies. As drug carriers, they could improve therapeutic outcomes while reducing systemic toxicity. They have also shown promise in improving leukemia detection and diagnosis. The study aimed to assess the potential of nanotechnology-based diagnostics and therapeutics in preclinical human acute lymphoblastic leukemia (h-ALL). Methods: We performed a systematic search through April 2022. Articles written in English reporting the toxicity, efficacy, and safety of nanotechnology-based drugs (in the aspect of treatment) and specificity, limit of detection (LOD), or sensitivity (in the aspect of the detection field) in preclinical h-ALL were included. The study was performed according to PRISMA instructions. The methodological quality was assessed using the QualSyst tool. Results: A total of 63 original articles evaluating nanotechnology-based therapeutics and 35 original studies evaluating nanotechnology-based diagnostics were included in this review. As therapeutics in ALL, nanomaterials offer controlled release, targeting or sensing ligands, targeted gene therapy, photodynamic therapy and photothermic therapy, and reversal of multidrug-resistant ALL. A narrative synthesis of studies revealed that nanoparticles improve the ratio of efficacy to the toxicity of anti-leukemic drugs. They have also been developed as a vehicle for biomolecules (such as antibodies) that can help detect and monitor leukemic biomarkers. Therefore, nanomaterials can help with early diagnostics and personalized treatment of ALL. Conclusion: This review discussed nanotechnology-based preclinical strategies to achieve ALL diagnosis and therapy advancement. This involves modern drug delivery apparatuses and detection devices for prompt and targeted disease diagnostics. Nonetheless, we are yet in the experimental phase and investigational stage in the field of nanomedicine, with many features remained to be discovered as well as numerous problems to be solved.

Advances in aptamer-based drug delivery vehicles for cancer therapy

Overall, aptamers are special classes of nucleic acid-based macromolecules that are beginning to investigate because of their capability of avidity binding to a specific target for clinical use. Taking advantage of target-specific medicine led to more effective therapeutic and limitation of side effects of drugs. Herein, we discuss several aptamers and their binding capability and capacity for selecting tumor biomarkers and usage of them as targeting ligands for the functionalization of nanomaterials. We review recent applications based on aptamers and several nanoparticles to rise efficacy and develop carrier systems such as graphene oxide, folic acid, gold, mesopores silica, and various polymers and copolymer, polyethylene glycol, cyclodextrin, chitosan. The nanocarriers have been characterized by particle size, zeta potential, aptamer conjugation, and drug encapsulation efficiency. Hydrodynamic diameter and Zeta potential can used in order to monitor aptamers' crosslinking, in-vitro drug release, intracellular delivery of nanocarriers, and cellular cytotoxicity assay. Also, they are studied for cellular uptake and internalization to types of cancer cell lines such as colorectal, breast, prostate, leukemia and etc. The results are investigated in in-vivo cytotoxicity assay and cell viability assay. Targeted cancer therapy seems a good and promising strategy to overcome the systemic toxicity of chemotherapy.

Advances in aptamer-based nuclear imaging

Aptamers are short oligonucleotides that bind to specific target molecules. They have been extensively explored in biomedical applications, including biosensing, medical imaging, and disease treatment. Their adjustable affinity for specific biomarkers stimulates more translational efforts, such as nuclear imaging of tumors in preclinical and clinical settings. In this review, we present recent advances of aptamer-based nuclear imaging and compare aptamer tracers with other biogenic probes in forms of peptides, nanobodies, monoclonal antibodies, and antibody fragments. Fundamental properties of aptamer-based radiotracers are highlighted and potential directions to improve aptamer's imaging performance are discussed. Despite many translational obstacles to overcome, we envision aptamers to be a versatile tool for cancer nuclear imaging in the near future.

In Vivo Evaluation of Sgc8-c Aptamer as a Molecular Imaging Probe for Colon Cancer in a Mouse Xenograft Model

Recent biotechnological applications in the field of clinical oncology led to the identification of new biomarkers as molecular targets of cancer, and to broad developments in the field of personalized medicine. Aptamers are oligonucleotides (ssDNA or RNA) that are selected to specifically recognize a molecular target with high affinity and specificity. Based on this, new horizons for their use as molecular imaging probes are being explored. The objective of this work was to evaluate the Sgc8-c aptamer conjugated with Alexa Fluor 647 fluorophore as an imaging probe in a colon tumor xenograft mouse model, with potential application in molecular imaging. In this study, the LS174T cell line was used to induce colorectal adenocarcinoma in nude mice. After confirmation of PTK7 overexpression by immunohistochemistry, in vivo studies were performed. Pharmacokinetic, in vivo and ex vivo biodistribution imaging, and a competition assay were evaluated by fluorescence imaging. In vivo visualization of the probe in the tumors was assessed two hours after aptamer probe administration, exhibiting excellent tumor-to-background ratios in biodistribution studies and high specificity in the competition test. Our results demonstrated the functionality of Scg8-c as an imaging probe for colon cancer, with potential clinical applications.

Aptamer-Targeted Photodynamic Platforms for Tumor Therapy

Achieving controlled and accurate delivery of photosensitizers (PSs) into tumor sites is a major challenge in conventional photodynamic therapy (PDT). Aptamer is a short oligonucleotide sequence (DNA or RNA) with a folded three-dimensional structure, which can selectively bind to specific small molecules, proteins, or the whole cells. Aptamers could act as ligands and be modified onto PSs or nanocarriers, enabling specific recognition and binding to tumor cells or their membrane proteins. The resultant aptamer-modified PSs or PSs-containing nanocarriers generate amounts of reactive oxygen species with light irradiation and obtain superior photodynamic therapeutic efficiency in tumors. Herein, we overview the recent progress in the designs and applications of aptamer-targeted photodynamic platforms for tumor therapy. First, we focus on the progress on the rational selection of aptamers and summarize the applications of aptamers which have been applied for targeted tumor diagnosis and therapy. Then, aptamer-targeted photodynamic therapies including various aptamer-PSs, aptamer-nanocarriers containing PSs, and aptamer-nano-photosensitizers are highlighted. The aptamer-targeted synergistically therapeutic platforms including PDT, photothermal therapy, and chemotherapy, as well as the imaging-guided theranostics, are also discussed. Finally, we offer an insight into the development trends and future perspectives of aptamer-targeted photodynamic platforms for tumor therapy.

Multivalent Sgc8c-aptamer decorated polymer scaffolds for leukemia targeting

T-cell acute lymphoblastic leukemia causes a disproportional amount of immature white blood cells in the patients' bone marrow. The significant undesired side effects associated with traditional chemotherapy treatment prompted us to study a more effective treatment strategy. We decorated polyisocyanopeptide scaffolds with the selective leukemia cell binding aptamer sgc8c and found that the polymers inhibit proliferation by G0/G1-phase arrest, serving as an opportunity for future therapeutic strategies.

Organization of Protein Tyrosine Kinase-7 on Cell Membranes Characterized by Aptamer Probe-Based STORM Imaging

Protein tyrosine kinase-7 (PTK7), as an important membrane receptor, regulates various cellular activities, including cell polarity, movement, migration, and invasion. Although lots of research studies focused on revealing its functions from the aspect of the expression of the gene and protein are present, the relationship between the spatial distribution at the single-molecule level and the function remains unclear. Through combining aptamer probe labeling and super-resolution imaging technology, after verifying the specificity and superiority of the aptamer probe, a more significant clustering distribution of PTK7 is found on the MCF10A cell basal membrane than on the apical membrane, which is thought to be related to their specific functions on different membranes. By exploring the relationship between the assembly of PTK7 and lipid rafts, actin cytoskeleton, and carbohydrate chains on the membrane, the unique distribution of PTK7 on disparate membranes is revealed to be probably because of the varied dominant position of these three factors. These findings present the detailed spatial information of PTK7 and the related potential organization mechanism on the cell membrane, which will facilitate a better understanding of the relationship between the molecular assembly and its function, as well as the overall structure of the cell membrane.

Recent advances in understanding oligonucleotide aptamers and their applications as therapeutic agents

The innovative discovery of aptamers was based on target-specific treatment in clinical diagnostics and therapeutics. Aptamers are synthetic, single-stranded oligonucleotides, simply described as chemical antibodies, which can bind to diverse targets with high specificity and affinity. Aptamers are synthesized by the SELEX technique, and possess distinctive properties as small size (10-50 kDa), higher stability, easy manufacture and less immunogenicity. These oligonucleotides are easily degraded by nucleases, so require some important modifications like capping and incorporation of modified nucleotides. RNA aptamers can be modified chemically on 2' positions using -NH3, -F, -deoxy, or -OMe groups to enhance their nuclease resistance. Aptamers have been employed for multiple purposes, as direct drugs or aptamer-drug conjugates targeted against different diseased cells. Different aptamer-conjugated nanovehicles (e.g., micelles, liposomes, silica nano-shells) have been designed to transport diverse anticancer-drugs like doxorubicin and cisplatin in bulk to minimize systemic cytotoxicity. Some drug-loaded nanovehicles (up to 97% loading capacity) and conjugated with specific aptamer resulted in more than 60% tumor inhibition as compared to unconjugated drug-loaded nanovehicles which showed only 31% cancer inhibition. In addition, aptamers have been widely used in basic research, food safety, environmental monitoring, clinical diagnostics and therapeutics. Different FDA-approved RNA and DNA aptamers are now available in the market, used for the treatment of diverse diseases, especially cancer. These aptamers include Macugen, Pegaptanib, etc. Despite a good progress in aptamer use, the present-day chemotherapeutics and drug targeting systems still face great challenges. Here in this review article, we are discussing nucleic acid aptamers, preparation, role in the transportation of different nanoparticle vehicles and their applications as therapeutic agents.

Current Perspectives on Aptamers as Diagnostic Tools and Therapeutic Agents

Aptamers are synthetic single-stranded DNA or RNA sequences selected from combinatorial oligonucleotide libraries through the well-known in vitro selection and iteration process, SELEX. The last three decades have witnessed a sudden boom in aptamer research, owing to their unique characteristics, like high specificity and binding affinity, low immunogenicity and toxicity, and ease in synthesis with negligible batch-to-batch variation. Aptamers can specifically bind to the targets ranging from small molecules to complex structures, making them suitable for a myriad of diagnostic and therapeutic applications. In analytical scenarios, aptamers are used as molecular probes instead of antibodies. They have the potential in the detection of biomarkers, microorganisms, viral agents, environmental pollutants, or pathogens. For therapeutic purposes, aptamers can be further engineered with chemical stabilization and modification techniques, thus expanding their serum half-life and shelf life. A vast number of antagonistic aptamers or aptamer-based conjugates have been discovered so far through the in vitro selection procedure. However, the aptamers face several challenges for its successful clinical translation, and only particular aptamers have reached the marketplace so far. Aptamer research is still in a growing stage, and a deeper understanding of nucleic acid chemistry, target interaction, tissue distribution, and pharmacokinetics is required. In this review, we discussed aptamers in the current diagnostics and theranostics applications, while addressing the challenges associated with them. The report also sheds light on the implementation of aptamer conjugates for diagnostic purposes and, finally, the therapeutic aptamers under clinical investigation, challenges therein, and their future directions.

Control of Ligand-Binding Specificity Using Photocleavable Linkers in AFM Force Spectroscopy

In recent decades, atomic force microscopy (AFM), in particular the force spectroscopy mode, has become a method of choice to study biomolecular interactions at the single-molecule level. However, grafting procedures as well as determining binding specificity remain challenging. We report here an innovative approach based on a photocleavable group that enables in situ release of the ligands bound to the AFM tip and thus allows direct assessment of the binding specificity. Applicable to a wide variety of molecules, the strategy presented here provides new opportunities to study specific interactions and deliver single molecules with high spatiotemporal resolution in a wide range of applications, including AFM-based cell biology.

Nucleic Acid Aptamer: A Novel Potential Diagnostic and Therapeutic Tool for Leukemia

Leukemia immunotherapy has been dominant via using synthetic antibodies to target cluster of differentiation (CD) molecules, nevertheless inevitable cytotoxicity and immunogenicity would limit its development. Recently, increasing reports have focused on nucleic acid aptamers, a class of high-affinity nucleic acid ligands. Aptamers purportedly serve as “chemical antibodies”, have negligible cytotoxicity and low immunogenicity, and would be widely applied for the therapy and diagnosis of various diseases, especially leukemia. In the preclinical applications, nucleic acid aptamers have displayed the augmented specificity and selectivity via recognizing targets on leukemia cells based on unique three-dimensional conformations. As small molecules with nucleic acid characteristics, aptamers need to be chemically modified to resist nuclease degradation, renal clearance and improve binding affinities. Moreover, aptamers can be linked with neoteric detection techniques to enhance sensitivity and selectivity of diagnosis and therapy. In this review, we summarized aptamers’ preparation, chemical modification and conjugation, and discussed the application of aptamers in diagnosis and treatment of leukemia through highly specifically recognizing target molecules. Significantly, the application prospect of aptamers in fusion genes would be introduced.

DNA Aptamers in the Detection of Leukemia Cells by the Thickness Shear Mode Acoustics Method

By using the thickness shear mode acoustics method (TSM) and single-molecule force spectroscopy (SMFS) we studied the interactions between DNA aptamers (sgc8c) specific to the protein tyrosine kinase 7 (PTK7), which is localized in the membranes of leukemia lymphoblastics (MOLT-4), and lymphocyte (Jurkat) cell lines, as well with PTK7-negative U266 myeloid leukemia cells. The TSM method allowed the development of a highly sensitive, label-free biosensor for the detection leukemia cells with a limit of detection of (195±20) cells/mL. SMFS approved the high selectivity of the sgc8c aptamers to the PTK7 receptors at the cell surface and allowed determining the binding probability of the aptamers to the PTK7 receptors at different cell lines.

Investigations on the interface of nucleic acid aptamers and binding targets

Nucleic acid aptamers are single-stranded DNA or RNA of 20-100 nucleotides in length that have attracted substantial scientific interest due to their ability to specifically bind to target molecules via the formation of three-dimensional structures. Compared to traditional protein antibodies, aptamers have several advantages, such as their small size, high binding affinity, specificity, flexible structure, being chemical synthesizable and modifiable, good biocompatibility, high stability and low immunogenicity, which all contribute to their widely applications in the biomedical field. To date, much progress has been made in the study and applications of aptamers, however, detailed information on how aptamers bind to their targets is still scarce. Over the past few decades, many methods have been introduced to investigate the aptamer-target binding process, such as measuring the main kinetic or thermodynamic parameters, detecting the structural changes of the binding complexes, etc. Apart from traditional physicochemical methods, various types of molecular docking programs have been applied to simulate the aptamer-target interactions, while these simulations also have limitations. To facilitate the further research on the interactions, herein, we provide a brief review to illustrate the recent advances in the study of aptamer-target interactions. We summarize the binding targets of aptamers, such as small molecules, macromolecules, and even cells. Their binding constants (KD) are also summarized. Methods to probe the aptamer-target binding process, such as surface plasmon resonance (SPR), circular dichroism spectroscopy (CD), isothermal titration calorimetry (ITC), footprinting assay, truncation and mutation assay, nuclear magnetic resonance spectroscopy (NMR), X-ray crystallography and molecular docking simulation are indicated. The binding forces mediating the aptamer-target interactions, such as hydrogen bonding, electrostatic interaction, the hydrophobic effect, π-π stacking and van der Waals forces are summarized. The challenges and future perspectives are also discussed.

The structure and function of cell membranes studied by atomic force microscopy

The cell membrane, involved in almost all communications of cells and surrounding matrix, is one of the most complicated components of cells. Lack of suitable methods for the detection of cell membranes in vivo has sparked debates on the biochemical composition and structure of cell membranes over half a century. The development of single molecule techniques, such as AFM, SMFS, and TREC, provides a versatile platform for imaging and manipulating cell membranes in biological relevant environments. Here, we discuss the latest developments in AFM and the progress made in cell membrane research. In particular, we highlight novel structure models and dynamic processes, including the mechanical properties of the cell membranes.