Anti-CD44 antibodies grafted immunoaffinity Fe3O4@MnO2 nanozymes with highly oxidase-like catalytic activity for specific detection of triple-negative breast cancer MDA-MB-231 cells

Cell-enzyme-linked immunosorbent assay (CELISA) is extensively applied for cancer diagnosis and screening because of its simple operation, high sensitivity, and intuitive color change. However, the unstable horseradish peroxidase (HRP), hydrogen peroxide (H₂O₂) and non-specificity have led to a high false negative rate, which limits its application. In this study, we have developed an innovative immunoaffinity nanozyme aided CELISA based on anti-CD44 monoclonal antibodies (mAbs) bioconjugated manganese dioxide-modified magnetite nanoparticles (Fe₃O₄@MnO₂ NPs) for the specific detection of triple-negative breast cancer MDA-MB-231 cells. The ^CD44FM nanozymes were fabricated to replace unstable HRP and H₂O₂ to counteract possible negative effects in conventional CELISA. Results suggested that ^CD44FM nanozymes displayed remarkable oxidase-like activities over an extensive pH and temperature range. The bioconjugation of CD44 mAbs enabled ^CD44FM nanozymes to enter MDA-MB-231 cells selectively via over-expressed CD44 antigens on the membrane surface of these cells, and then catalyzed oxidation of the chromogenic substrate TMB, further achieving specific detection of these cells. Additionally, this study exhibited high sensitivity and low detection limit for MDA-MB-231 cells with a quantitation range of just 186 cells. To sum up, this report developed a simple, specific and sensitive assay platform based on ^CD44FM nanozymes, which could provide a promising strategy for targeted diagnosis and screening of breast cancer.

Radiomics, aptamers and nanobodies: New insights in cancer diagnostics and imaging

At present, cancer is a major health issue and the second leading cause of mortality worldwide. Researchers have been working hard on investigating not only improved therapeutics but also on early detection methods, both critical to increasing treatment efficacy and developing methods for disease prevention. Diagnosis of cancers at an early stage can promote timely medical intervention and effective treatment and will result in inhibiting tumor growth and development. Several advances have been made in the diagnostics and imagining technologies for early tumor detection and deciding an effective therapy these include radiomics, nanobodies, and aptamers. Here in this review, we summarize the main applications of radiomics, aptamers, and the use of nanobody-based probes for molecular imaging applications in diagnosis, treatment planning, and evaluations in the field of oncology to develop quantitative and personalized medicine. The preclinical data reported to date are quite promising, and it is predicted that nanobody-based molecular imaging agents will play an important role in the diagnosis and management of different cancer types in near future.

Application and development of aptamer in cancer: from clinical diagnosis to cancer therapy

Traditional anticancer therapies can cause serious side effects in clinical treatment due to their nonspecific of tumor cells. Aptamers, also termed as 'chemical antibodies', are short DNA or RNA oligonucleotides selected from the synthetic large random single-strand oligonucleotide library by systematic evolution of ligands by exponential enrichment (SELEX) to bind to lots of different targets, such as proteins or nucleic acid structures. Aptamers have good affinities and high specificity with target molecules, thus may be able to act as drugs themselves to directly inhibit the proliferation of tumor cells, or own great potentialities in the targeted drug delivery systems which can be used in tumor diagnosis and target specific tumor cells, thereby minimizing the toxicity to normal cells. Here we review the unique properties of aptamer represents a great opportunity when applied to the rapidly developing fields of biotechnology and discuss the recent developments in the use of aptamers as powerful tools for analytic, diagnostic and therapeutic applications for cancer.

Potential use of aptamers for diagnosis and treatment of pancreatic cancer

Pancreatic cancer (PC) is highly malignant with a low 5-year survival rate. PC currently does not have good early diagnostic markers and responses poorly to chemotherapeutic drugs. The search for better biomarkers and developing more effective chemotherapy are important ways to improve the healthcare of PC patients. Aptamers are single-stranded nucleic acids with high binding affinity and specificity to target molecules. Many aptamers against different forms of cancer including PC have been selected for both diagnostic and therapeutic use. Aptamers can work as ligands to distinguish tumour cells from normal cells. Using cells as selection targets, the obtained aptamers have been used to discover new cancer biomarkers after identification of the binding target. Aptamers have been shown to have antagonists effect on cancer cell proliferation, apoptosis, and metastasis. In addition, aptamers have been used as carriers to deliver therapeutic agents to selectively kill PC cells. This review summarises the potential use of aptamers in the diagnosis and treatment of PC.

pH-Sensitive micelles with mitochondria-targeted and aggregation-induced emission characterization: synthesis, cytotoxicity and biological applications

Subcellular organelle-specific reagents for simultaneous tumor targeting, imaging, and treatment are of enormous interest in cancer therapy. Herein, we present a mitochondria targeting micelle (PEG-AIE-TPP) by conjugating a triphenylphosphonium (TPP) with a fluorogen which can undergo aggregation-induced emission (AIE). At first, the in vitro and in vivo properties of the PEG-AIE-TPP micelle were characterized in detail. It was found that the micelle was reasonably stable at physiological pH and highly sensitive to mildly acidic pH stimuli. Importantly, this micelle could selectively localize and accumulate in the mitochondria, thus generating an aggregation-induced emission (AIE) effect as confirmed by the green fluorescence. Additionally, the micelle exhibited selective cytotoxicity to cancer cells and negligible toxicity to normal cells in vitro. The in vivo imaging and ex vivo imaging results showed that the accumulation tendency of the micelle at the tumor region was obvious. We also further proved the biocompatible, tumor targeting ability and antitumor activity of the PEG-AIE-TPP micelle in MCF-7 tumor-bearing mice. Accordingly, this mitochondria-targeted therapeutic micelle with good stability, biocompatibility, and tumor-targeting and antitumor activity provides a potentially unique tumor-targeted system for cancer therapy.

The potential of aptamers for cancer research

Aptamers are promising alternatives to antibodies and can be used as high affinity agents for the cancer detection and the targeted drug transportation. In this manuscript, we highlight the advantages of aptamers, such as high affinities, specificity and excellent chemical stabilities, which are likely to benefit for the diagnosis of cancer in its early stages and then achieve molecular-level treatment. Also, we discuss the challenges and problems in the current application of aptamers.

Current Advances in Aptamers for Cancer Diagnosis and Therapy

Nucleic acid aptamers are single-stranded oligonucleotides that interact with target molecules with high affinity and specificity in unique three-dimensional structures. Aptamers are generally isolated by a simple selection process called systematic evolution of ligands by exponential enrichment (SELEX) and then can be chemically synthesized and modified. Because of their high affinity and specificity, aptamers are promising agents for biomarker discovery, as well as cancer diagnosis and therapy. In this review, we present recent progress and challenges in aptamer and SELEX technology and highlight some representative applications of aptamers in cancer therapy.

Highly sensitive visual detection of mutant DNA based on polymeric nanoparticles-participating amplification

Taking advantage of the nanoparticles' large surface area and structural repeating characteristics, polymeric nanoparticles-participating polymerization-based amplification system was designed to enhance the sensitivity of detection.

Aptamers Selected by Cell-SELEX for Molecular Imaging

Conventional diagnostics for cancer rely primarily on anatomical techniques. However, these techniques cannot monitor the changes at the molecular level in normal cells, which possibly signal the onset of cancer at its very earliest stages. For accurate prediction of the carcinogenesis at the molecular level, targeting ligands have been used in combination with imaging probes to monitor this biological process. Among these targeting ligands, aptamers have high binding affinity to various targets ranging from small molecules to whole organisms, and, hence, exceptional recognition ability. Many recent studies have been reported on aptamer-based molecular imaging, clearly indicating its clinical and diagnostic utility. In this review, we will discuss some key results of these studies.

Aptamers as drug delivery vehicles

The benefits of directed and selective therapy for systemic treatment are reasons for increased interest in exploiting aptamers for cell-specific drug delivery. Nucleic acid based pharmaceuticals represent an interesting and novel tool to counter human diseases. Combining inhibitory potential and cargo transfer upon internalization, nanocarriers as well as various therapeutics including siRNAs, chemotherapeutics, photosensitizers, or proteins can be imported via these synthetic nucleic acids. However, widespread clinical application is still hampered by obstacles that must be overcome. In this review, we give an overview of applications and recent advances in aptamer-mediated drug delivery. We also introduce prominent selection methods as well as useful approaches in choice of drug and conjugation method. We discuss the challenges that need to be considered and present strategies that have been applied to achieve intracellular delivery of effectors transported by readily internalized aptamers.

Nucleic acid aptamers for living cell analysis

Cells as the building blocks of life determine the basic functions and properties of a living organism. Understanding the structure and components of a cell aids in the elucidation of its biological functions. Moreover, knowledge of the similarities and differences between diseased and healthy cells is essential to understanding pathological mechanisms, identifying diagnostic markers, and designing therapeutic molecules. However, monitoring the structures and activities of a living cell remains a challenging task in bioanalytical and life science research. To meet the requirements of this task, aptamers, as "chemical antibodies," have become increasingly powerful tools for cellular analysis. This article reviews recent advances in the development of nucleic acid aptamers in the areas of cell membrane analysis, cell detection and isolation, real-time monitoring of cell secretion, and intracellular delivery and analysis with living cell models. Limitations of aptamers and possible solutions are also discussed.

Dual-aptamer modification generates a unique interface for highly sensitive and specific electrochemical detection of tumor cells

Because circulating tumor cells (CTCs) have been proven to be an important clue of the tumor metastasis, their detection thus plays a pivotal role in the diagnosis and prognosis of cancer. Herein, we fabricate an electrochemical sensor by directly conjugating two cell-specific aptamers, TLS1c and TLS11a, which specifically recognize MEAR cancer cells, to the surface of a glassy carbon electrode (GCE) via the formation of amide bonds. The two aptamers are simultaneously conjugated to the GCE surface via precisely controlled linkers: TLS1c through a flexible linker (a single-stranded DNA T15; ss-TLS1c) and TLS11a through a rigid linker (a double-stranded DNA T15/A15; ds-TLS11a). It is found that such ss-TLS1c/ds-TLS11a dual-modified GCEs show greatly improved sensitivity in comparison with those modified with a single type of aptamer alone or ds-TLS1c/ds-TLS11a with both rigid linkers, suggesting that our optimized, rationally designed electrode-aptamer biosensing interface may enable better recognition and thus more sensitive detection of tumor cells. Through the utilization of this dual-aptamer-modified GCE, as few as a single MEAR cell in 10(9) whole blood cells can be successfully detected with a linear range of 1-14 MEAR cells. Our work demonstrates a rather simple yet well-designed and ultrasensitive tumor cell detection method based on the cell-specific aptamer-modified GCE, showing a promising potential for further CTC-related clinical applications.

Dual responsive enzyme mimicking activity of AgX (X=Cl, Br, I) nanoparticles and its application for cancer cell detection

Chitosan (CS) modified silver halide (AgX, X=Cl, Br, I) (CS-AgX) nanoparticles (NPs) were found to possess dual responsive enzyme mimetic activities. In the presence of H2O2, they were able to oxidize various colorimertic dyes, namely, peroxidase-like activity. Upon photoactivation, CS-AgX NPs could also oxidize the typical substrates in the absence of H2O2. Taking CS-AgI as an example, it was found that the photostimulated enzyme mimetics of CS-AgI NPs showed several unprecedented advantages over natural peroxidase or other existing alternatives based on nanomaterials, such as excellent enzyme-like activity over a broad pH range (3.0-7.0), the independence of hydrogen peroxide on activity, the easily regulated activity by light irradiation, and the good reutilization without significant loss of catalytic activity. The mechanism of the dual responsive enzyme-like activity of CS-AgI was investigated. On the basis of these findings, the photoactivated CS-AgI was designed to develop a facile, cheap, rapid, and highly sensitive colorimetric assay to detect cancer cells. The detection limit of the method for MDA-MB-231 was estimated to be as low as 100 cells, which was much lower than that reported by the method using peroxidase mimetics based on nanomaterials. We believe that CS-AgX NPs with dual responsive enzyme-mimicking activity, especially the excellent photostimulated enzyme-like activity, may find widely potential applications in biosensors.

Mediator-free triple-enzyme cascade electrocatalytic aptasensor with exonuclease-assisted target recycling and hybridization chain reaction amplification

The amplified sensitive detection of protein is essential to biomedical research as well as clinical diagnosis. Here, we developed an ultrasensitive mediator-free triple-enzyme cascade electrocatalytic aptasensor for thrombin detection on the basis of exonuclease-assisted target recycling and hybridization chain reaction (HCR) amplification strategy. The double strands constructed by the hybridization of thrombin binding aptamer (S1) with its complementary strand (S2) were firstly assembled on the electrode. Upon addition of target to the system, the S1 recognized thrombin and left off electrode to make space for assembly of hybrid-primer probe (H0). Then, the H0 triggered the HCR to form the multi-functional hemin/G-quadruplex DNAzyme nanowires. In the mediator-free triple-enzyme cascade electrocatalytic amplification system, the hemin/G-quadruplex DNAzyme nanowires here simultaneously played three roles: the redox probe, NADH oxidase and HRP-mimicking DNAzyme, respectively, which effectively avoided the fussy redox probe and enzyme labeling process, serving a useful alternative or supplement to conventional assays that typically suffer from complexity and poor sensitivity. Additionally, in order to improve the assembly amount of hemin/G-quadruplex DNAzyme nanowire, the exonuclease-assisted target recycling amplification was used for the continuous removal of S1. As a result, the proposed method can detect thrombin specifically with a detection limit as low as 20 fM.

Incorporating graphene oxide and gold nanoclusters: a synergistic catalyst with surprisingly high peroxidase-like activity over a broad pH range and its application for cancer cell detection

A synergistic graphene oxide-gold nanocluster (GO-AuNC) hybrid has been constructed as an enzyme mimic that is able to show high catalytic activity over a broad pH range, especially at neutral pH. Importantly, the target-functionalized hybrid has been applied as a robust nanoprobe for selective, quantitative, and fast colorimetric detection of cancer cells.

Integrated tyramide and polymerization-assisted signal amplification for a highly-sensitive immunoassay

A novel strategy for ultrasensitive detection of model protein based on the integration of tyramide signal amplification (TSA) and polymerization-assisted signal amplification was proposed. The surface-initiated atom transfer radical polymerization (SI-ATRP) of glycidyl methacrylate (GMA) was triggered by the initiator-coupled protein immobilized on the electrode surface through sandwiched immunoreactions. Growth of long chain polymeric materials provided numerous epoxy groups for subsequent coupling of horseradish peroxidase (HRP), which in turn significantly increased the loading of quantum dots (QDs) labeled tyramide in the presence of hydrogen peroxide. As a result, electrochemiluminescence (ECL) and square-wave voltammetric (SWV) measurements showed 9.4- and 10.5-fold increase in detection signal in comparison with the unamplified method, respectively. To demonstrate the feasibility of this approach, human immunoglobulin G antigen (IgG) as a model target protein was employed and the detection limits were 0.73 and 0.09 pg mL(-1) for ECL and SWV, respectively. The results showed that sensitivity of the presented immunoassay significantly increased by one-order of magnitude and offered great application promises in providing a sensitive, specific, and potent method for biological detection.

Electrochemical Techniques as Powerful Readout Methods for Aptamer-based Biosensors

Aptamers are single-stranded nucleic acids that can be selected in vitro with special folding structures to bind to many different small-molecule, protein, and cellular targets. Over the past two decades, aptamers have become novel promising recognition elements for the fabrication of biosensors. These ‘aptasensors’ have several advantages over antibodies in that they are relatively easy to synthesise or modify in vitro, and can be appended with linkers and reporters for adaptation to various sensing strategies. In this chapter, we introduce the various electrochemical techniques that can be used as powerful readout methods for aptasensors, providing a brief introduction to aptamers and related electrochemical techniques, and then a detailed description of various branches within the field, including labelled strategies, unlabelled strategies, and enzyme-amplified strategies. For each type of approach, several basic and improved design principles will be addressed. It is hoped that, through this discussion, readers will get a sense of how several variables (aptamers, targets and redox reporters) are successfully combined with electrochemical techniques in order to produce a series of sensing platforms with high selectivity and sensitivity.

Aptamer-functionalized nanoparticles for medical applications: challenges and opportunities

With advances in aptamer selection technologies and nanomedicine, aptamer-functionalized nanoparticles are being explored as promising platforms for targeted therapeutic and diagnostic applications. In this Perspective, we outline recent progress in this field, as exemplified by Bamrungsap et al. in this issue of ACS Nano. Furthermore, we highlight the challenges and opportunities in translating current proof-of-concept designs into in vivo applications, with emphasis on the intrinsic properties of aptamers and their interplay with nanoparticles. With continuous efforts, we expect aptamer-functionalized nanoparticles to advance from preclinical into clinical development for further evaluation.

Cation exchange in aptamer-conjugated CdSe nanoclusters: a novel fluorescence signal amplification for cancer cell detection

Fluorescence signal amplification by cation exchange in aptamer-conjugated CdSe nanoclusters, a biological self-assembly of CdSe quantum dots, was developed as a novel method for cancer cell detection.

Recent developments in protein and cell-targeted aptamer selection and applications

Because of their easily modified chemical structures and wide range of targets, aptamers are ideal candidates for various applications, such as biomarker discovery, target diagnosis, molecular imaging, and drug delivery. Aptamers are oligonucleotide sequences that can bind to their targets specifically via unique three dimensional (3-D) structures. Usually, aptamers are obtained from repeated rounds of in vitro or in vivo selection termed SELEX (Systematic Evolution of Ligands by EXponential enrichment), which can generate aptamers with high affinity and specificity for many kinds of targets, such as biomedically important proteins and even cancer cells. In this review, some basic principles and recent developments in the design of SELEX process are discussed, hopefully to provide some guidelines towards performing more efficient aptamer isolation procedures. Moreover, the biomedical and bioanalytical applications of aptamers are further reviewed, based on some smart biochemical modifications of these oligonucleotide structures.