Versatile aptasensor for electrochemical quantification of cell surface glycan and naked-eye tracking glycolytic inhibition in living cells

Multilayered Fe3O4@(ZIF-8)3 combined with a computer-vision-enhanced immunosensor for chloramphenicol enrichment and detection

The misuse and overuse of chloramphenicol poses severe threats to food safety and human health. In this work, we developed a magnetic solid-phase extraction (MSPE) pretreatment material coated with a multilayered metal-organic framework (MOF), Fe3O4 @ (ZIF-8)3, for the separation and enrichment of chloramphenicol from fish. Furthermore, we designed an artificial-intelligence-enhanced single microsphere immunosensor. The inherent ultra-high porosity of the MOF and the multilayer assembly strategy allowed for efficient chloramphenicol enrichment (4.51 mg/g within 20 min). Notably, Fe3O4 @ (ZIF-8)3 exhibits a 39.20% increase in adsorption capacity compared to Fe3O4 @ZIF-8. Leveraging the remarkable decoding abilities of artificial intelligence, we achieved the highly sensitive detection of chloramphenicol using a straightforward procedure without the need for specialized equipment, obtaining a notably low detection limit of 46.42 pM. Furthermore, the assay was successfully employed to detect chloramphenicol in fish samples with high accuracy. The developed immunosensor offers a robust point-of-care testing tool for safeguarding food safety and public health.

Harnessing aptamers for the biosensing of cell surface glycans - A review

Cell surface glycans (CSGs) are essential for cell recognition, adhesion, and invasion, and they also serve as disease biomarkers. Traditional CSG recognition using lectins has limitations such as limited specificity, low stability, high cytotoxicity, and multivalent binding. Aptamers, known for their specific binding capacity to target molecules, are increasingly being employed in the biosensing of CSGs. Aptamers offer the advantage of high flexibility, small size, straightforward modification, and monovalent recognition, enabling their integration into the profiling of CSGs on living cells. In this review, we summarize representative examples of aptamer-based CSG biosensing and identify two strategies for harnessing aptamers in CSG detection: direct recognition based on aptamer-CSG binding and indirect recognition through protein localization. These strategies enable the generation of diverse signals including fluorescence, electrochemical, photoacoustic, and electrochemiluminescence signals for CSG detection. The advantages, challenges, and future perspectives of using aptamers for CSG biosensing are also discussed.

Joint concanavalin A-aptamer enabled dual recognition for anti-interference visual detection of Salmonella typhimurium in complex food matrices

Given that food poisoning and infectious diseases caused by Salmonella typhimurium (S. typhimurium) draw intensive public health concerns, developing rapid, accurate, and cost-effective approaches to detect the pathogen is of crucial importance. Herein, we proposed a concanavalin A (Con A)-aptamer joint strategy to realize dual recognition for the strongly specific, visual, and highly sensitive determination of S. typhimurium. Compared with currently used single identification strategies, Con A and aptamer could recognize different sites of S. typhimurium to enhance the utilization rate of these sites for better sensing. The developed assay offered specific detection of S. typhimurium against other bacteria in a remarkably wide concentration range of 7.0 × 10¹ ∼ 7.0 × 10⁹ CFU/mL, along with a detection limit as low as 23 CFU/mL. Real sample analyses of milk and pork demonstrated the excellent reliability and practicability of our assay, providing great potential for food safety analysis.

A Novel Fluorescent Sensor Based on Aptamer and qPCR for Determination of Glyphosate in Tap Water

Glyphosate (GLYP) is a broad-spectrum, nonselective, organic phosphine postemergence herbicide registered for many food and nonfood fields. Herein, we developed a biosensor (Mbs@dsDNA) based on carboxylated modified magnetic beads incubated with NH2-polyA and then hybridized with polyT-glyphosate aptamer and complementary DNA. Afterwards, a quantitative detection method based on qPCR was established. When the glyphosate aptamer on Mbs@dsDNA specifically recognizes glyphosate, complementary DNA is released and then enters the qPCR signal amplification process. The linear range of the method was 0.6 μmol/L−30 mmol/L and the detection limit was set at 0.6 μmol/L. The recoveries in tap water ranged from 103.4 to 104.9% and the relative standard deviations (RSDs) were <1%. The aptamer proposed in this study has good potential for recognizing glyphosate. The detection method combined with qPCR might have good application prospects in detecting and supervising other pesticide residues.

Nanotechnology‐based electrochemical biosensors for monitoring breast cancer biomarkers

Breast cancer is categorized as the most widespread cancer type among women globally. On-time diagnosis can decrease the mortality rate by making the right decision in the therapy procedure. These features lead to a reduction in medication time and socioeconomic burden. The current review article provides a comprehensive assessment for breast cancer diagnosis using nanomaterials and related technologies. Growing use of the nano/biotechnology domain in terms of electrochemical nanobiosensor designing was discussed in detail. In this regard, recent advances in nanomaterial applied for amplified biosensing methodologies were assessed for breast cancer diagnosis by focusing on the advantages and disadvantages of these approaches. We also monitored designing methods, advantages, and the necessity of suitable (nano) materials from a statistical standpoint. The main objective of this review is to classify the applicable biosensors based on breast cancer biomarkers. With numerous nano-sized platforms published for breast cancer diagnosis, this review tried to collect the most suitable methodologies for detecting biomarkers and certain breast cancer cell types.

Aptamers as Theragnostic Tools in Prostate Cancer

Despite of the capacity that several drugs have for specific inhibition of the androgen receptor (AR), in most cases, PCa progresses to an androgen-independent stage. In this context, the development of new targeted therapies for prostate cancer (PCa) has remained as a challenge. To overcome this issue, new tools, based on nucleic acids technology, have been developed. Aptamers are small oligonucleotides with a three-dimensional structure capable of interacting with practically any desired target, even large targets such as mammalian cells or viruses. Recently, aptamers have been studied for treatment and detection of many diseases including cancer. In PCa, numerous works have reported their use in the development of new approaches in diagnostics and treatment strategies. Aptamers have been joined with drugs or other specific molecules such as silencing RNAs (aptamer–siRNA chimeras) to specifically reduce the expression of oncogenes in PCa cells. Even though these studies have shown good results in the early stages, more research is still needed to demonstrate the clinical value of aptamers in PCa. The aim of this review was to compile the existing scientific literature regarding the use of aptamers in PCa in both diagnosis and treatment studies. Since Prostate-Specific Membrane Antigen (PSMA) aptamers are the most studied type of aptamers in this field, special emphasis was given to these aptamers.

Recent Development of Nanomaterials-Based Cytosensors for the Detection of Circulating Tumor Cells

The accurate analysis of circulating tumor cells (CTCs) holds great promise in early diagnosis and prognosis of cancers. However, the extremely low abundance of CTCs in peripheral blood samples limits the practical utility of the traditional methods for CTCs detection. Thus, novel and powerful strategies have been proposed for sensitive detection of CTCs. In particular, nanomaterials with exceptional physical and chemical properties have been used to fabricate cytosensors for amplifying the signal and enhancing the sensitivity. In this review, we summarize the recent development of nanomaterials-based optical and electrochemical analytical techniques for CTCs detection, including fluorescence, colorimetry, surface-enhanced Raman scattering, chemiluminescence, electrochemistry, electrochemiluminescence, photoelectrochemistry and so on.

Electrochemical aptasensor based on gold modified thiol graphene as sensing platform and gold-palladium modified zirconium metal-organic frameworks nanozyme as signal enhancer for ultrasensitive detection of mercury ions

Gold modified thiol graphene (Au@HS-rGO) was prepared and applied as sensing platform for constructing the electrochemical aptasensor. While gold-palladium modified zirconium metal-organic frameworks (AuPd@UiO-67) nanozyme was employed as signal enhancer for detecting mercury ions (Hg²⁺) sensitively. Herein, gold nanoparticles (Au NPs) were modified on HS-rGO to form the thin Au@HS-rGO layer. Then the substrate strand (Apt1) was modified on the platform through Au-S bond. The signal strand (Apt2) was further decorated on the platform in the presence of Hg²⁺. Herein, the Apt2 was labeled with AuPd@UiO-67 nanozyme, which exhibited catalase-like properties to catalyze H₂O₂, thereby generating the electrical signal. With the concentration of Hg²⁺ increased, the amount of modified Apt2-AuPd@UiO-67 increased, leading to the rise of current response. Since the current responses were linear with concentration of Hg²⁺, the detection of Hg²⁺ can be achieved. Under the optimum conditions, the prepared electrochemical aptasensor exhibited wide linear range from 1.0 nmol/L to 1.0 mmol/L, along with a low detection limit of 0.16 nmol/L. Moreover, the electrochemical aptasensor showed excellent selectivity, reproducibility and stability, together with superior performance in actual water sample analysis. Therefore, this proposed electrochemical aptasensor may have promising applications and provide references for environmental monitoring and management.

Targeted SPION siderophore conjugate loaded with doxorubicin as a theranostic agent for imaging and treatment of colon carcinoma

Recently, the siderophores have opened new horizons in nanomedicine. The current study aimed to design a theranostic platform based on superparamagnetic iron oxide nanoparticles-pyoverdine (SPION/PVD) conjugates bound to MUC1 aptamer (MUC1_Apt) and loaded with doxorubicin (DOX) as an anti-cancer agent. The SPION/PVD complex was covalently conjugated to MUC1_Apt and loaded with DOX to prepare a targeted drug delivery system (SPION/PVD/MUC1_Apt/DOX). The investigation of cellular cytotoxicity and uptake of formulations by MTT and flow cytometry in both MUC1 positive (C26) and MUC1 negative (CHO) cell lines revealed that MUC1_Apt could improve both cellular uptake and toxicity in the C26 cell line. The evaluation of tumor-targeting activity by in vivo bio-distribution showed that the targeted formulation could enhance tumor inhibitory growth effect and survival rate in C26 tumor-bearing mice. Furthermore, the potential of synthesized SPION/PVD/MUC1_Apt/DOX complex as diagnostic agents was investigated by magnetic resonance imaging (MRI) which improved the contrast of tumor site in MRI. Our findings confirm that aptamer-targeted PVD chelated the SPION as a diagnostic agent and loaded with DOX as a chemotherapeutic drug, would be beneficial as a novel theranostic platform.

Recent Advances in Aptamer Sensors

Recently, aptamers have attracted attention in the biosensing field as signal recognition elements because of their high binding affinity toward specific targets such as proteins, cells, small molecules, and even metal ions, antibodies for which are difficult to obtain. Aptamers are single oligonucleotides generated by in vitro selection mechanisms via the systematic evolution of ligand exponential enrichment (SELEX) process. In addition to their high binding affinity, aptamers can be easily functionalized and engineered, providing several signaling modes such as colorimetric, fluorometric, and electrochemical, in what are known as aptasensors. In this review, recent advances in aptasensors as powerful biosensor probes that could be used in different fields, including environmental monitoring, clinical diagnosis, and drug monitoring, are described. Advances in aptamer-based colorimetric, fluorometric, and electrochemical aptasensing with their advantages and disadvantages are summarized and critically discussed. Additionally, future prospects are pointed out to facilitate the development of aptasensor technology for different targets.

Application of magnetic nanomaterials in electroanalytical methods: A review

Magnetic nanomaterials (MNMs) have gained high attention in different fields of studies due to their ferromagnetic/superparamagnetic properties and their low toxicity and high biocompatibility. MNMs contain magnetic elements such as iron and nickel in metallic, bimetallic, metal oxide, and mixed metal oxide. In electroanalytical methods, MNMs have been applied as sorbents for sample preparation before the electrochemical detection (sorbent role), as the electrode modifier (catalytic role), and the integration of the above two roles (as both sorbent and catalytic agent). In this paper, the application of MNMs in electroanalytical methods have been classified based on the main role of the nanomaterial and discussed separately. Furthermore, catalytic activities of MNMs in electroanalytical methods such as redox electrocatalytic, nanozymes catalytic (peroxidase, catalase activity, oxidase activity, superoxide dismutase activity), catalyst gate, and nanocontainer have been discussed.

Aptamer based recognition of cancer cells: Recent progress and challenges in bioanalysis

Rapid and accurate monitoring of cancer cells with high sensitivity is essential for a successful cancer treatment. As high-affinity nucleic acid ligands, aptamers can improve the properties of detection methods by conjugating with intracellular or extracellular cancer biomarkers. Despite the advances in the early detection and treatment of cancer cells, lacking effective early detection tools is one of the causes of a high mortality rate. Aptasensors, which are based on the specificity of aptamer-target recognition, with transduction for analytical purposes have received particular attention due to their high sensitivity and selectivity, simple instrumentation, as well as low production cost. In this review, some selective and sensitive methods were summarized based on advanced nanomaterials towards aptasensing of cancer cells, such as blood, breast, cervical, colon, gastric, liver, and lung cancer cells. This review summarizes advances from 2010 to June 2020 in the development of aptasensors for cancer cell detection. Various aptasensing strategies are assessed according to their potential for reaching relevant limits of sensitivity, specificity, and degrees of multiplexing. Furthermore, we address the remaining challenges and opportunities to integrate aptasensing platforms into point-of-care solutions. Finally, the advantages and limitations of aptamer-based aptasensing strategies were reviewed.

Cascaded multiple recycling amplifications for aptamer-based ultrasensitive fluorescence detection of protein biomarkers

Highly sensitive detection of molecular biomarkers plays a significant role in diagnosing various types of diseases at the early stage. We demonstrated in this paper an ultrasensitive aptamer-based fluorescence method for detecting mucin 1 (MUC1) in human serum via a cascaded multiple recycling signal amplification strategy. The MUC1 target molecules present in the samples cause structure switching of the hairpin aptamer probes, which initiates three cascaded recycling cycles for the cleavage of the fluorescently quenched signal probes to recover significant fluorescence for highly sensitive detection of MUC1. The developed method has a linear range from 100 fM to 1 nM for MUC1 detection. Besides, owing to the substantial signal amplification by the integrated and cascaded recycling cycles, a low detection limit of 35 fM is achieved with high selectivity. Moreover, the monitoring of trace MUC1 in human serum can also be realized with such a method, indicating its great potential for highly sensitive detection of different disease biomarkers.

Translating in vitro diagnostics from centralized laboratories to point-of-care locations using commercially-available handheld meters

There is a growing demand for high-performance point-of-care (POC) diagnostic technologies where in vitro diagnostics (IVD) is fundamental for prevention, identification, and treatment of many diseases. Over the past decade, a shift of IVDs from the centralized laboratories to POC settings is emerging. In this review, we summarize recent progress in translating IVDs from centralized labs to POC settings using commercially available handheld meters. After introducing typical workflows for IVDs and highlight innovative technologies in this area, we discuss advantages of using commercially available handheld meters for translating IVDs from centralized labs to POC settings. We then provide comprehensive coverage of different signal transduction strategies to repurpose the commercially-available handheld meters, including personal glucose meter, pH meter, thermometer and pressure meter, for detecting a wide range of targets by integrating biochemical assays with the meters for POC testing. Finally, we identify remaining challenges and offer future outlook in this area.

Analysis of glycan expression on cell surfaces by using a glassy carbon electrode modified with MnO2 nanosheets and DNA-generated electrochemical current

Electrochemical assay for analysis of cell surface glycan expression is reported. Mannose on human breast cancer cells (type MCF-7) is selected as the glycan model. Gold nanoparticles are modified with binding aptamer for MCF-7 cells and act as electrochemical probe. The analysis of cell surface glycan expression follows a traditional sandwich protocol. Concanavalin A that can specifically recognize mannose is immobilized onto MnO₂ nanosheets modified electrode for the capture of MCF-7 cells. Then, the modified gold nanoparticles are immobilized onto the electrode via the binding between MCF-7 cell and aptamer on the gold nanoparticles. The aptamer on the gold nanoparticles reacts with molybdate. More specifically, the reaction of the phosphate backbone of aptamer with molybdate results in the formation of a redox-active molybdophosphate precipitate and generates an electrochemical current. The current intensity at 0.20 V (vs. Ag/AgCl) is recorded to test the linear range of the assay. The assay shows an obvious response to MCF-7 cells with a wide linear range from 1.0 × 10³ to 1.0 × 10⁶ cells mL^-1 and a limit of detection down to 300 cells mL^-1. The assay can be used to selectively monitor the change of mannose expression on cell surfaces upon the treatment with the N-glycan inhibitor. Graphical abstractSchematic of an electrochemical assay for analysis of cell surface glycan expression of MCF-7 cancer cells.

Acetylcholinesterase-catalyzed silver deposition for ultrasensitive electrochemical biosensing of organophosphorus pesticides

This work reports, for the first time, acetylcholinesterase-catalyzed silver deposition for sensitive electrochemical detection of organophosphorus pesticides.

Aptamer-based electrochemical cytosensors for tumor cell detection in cancer diagnosis: A review

Circulating tumor cells, a type of viable cancer cell circulating from primary or metastatic tumors in the blood stream, can lead to the parallel development of primary tumors and metastatic lesions. Highly selective and sensitive detection of tumor cells has become a hot research topic and can provide a basis for early diagnosis of cancers and anticancer drug evaluation to develop the best treatment plan. Aptamers are single-stranded oligonucleotides that can bind to target tumor cells in unique three-dimensional structures with high specificity and affinity. Aptamer-based methods or signal amplification methods using aptamers show great potential in improving the selectivity and sensitivity of electrochemical (EC) cytosensors for tumor cell detection. This review covers the remarkable developments in aptamer-based EC cytosensors for the identification of cell type, cell counting and detection of crucial proteins on the cell surface. Various EC techniques have been developed for cancer cell detection, including common voltammetry or impedance, electrochemiluminescence and photoelectrochemistry in a direct approach (aptamer-target cell), sandwich approach (capture probe-target cell-signaling probe) or other approach. The current challenges and promising opportunities in the establishment of EC aptamer cytosensors for tumor cell detection are also discussed.

Bioengineered silver nanoparticles capped with bovine serum albumin and its anticancer and apoptotic activity against breast, bone and intestinal colon cancer cell lines

The aim of the current study was to biosynthesize the silver nanoparticles (AgNPs) from the bacterial strain of Bacillus cereus (ATCC 14579) extracellularly. When bacterial extract was challenged with 1 mM silver nitrate (AgNO3) the color of the extract changed into brown confirms the formation of nanoparticles. These nanoparticles were capped with bovine serum albumin (BSA). UV- visible spectroscopy showed the absorption peak at 420 nm indicates the formation of AgNPs. Fourier Infra -red (FTIR) attenuated total reflection (ATR) spectroscopy showed amide and amine group associated with AgNPs that stabilizes the nanoparticles. Energy dispersive x-ray spectroscopy (EDX) showed a strong peak of silver confirms the presence of silver. Thermo gravimetric analysis (TGA) analysis was used to determine the protein degradation showed less protein degradation at higher temperature confirms the stability of nanoparticles. Transmission electron microscopy (TEM) showed the AgNPs are well dispersed and spherical, and 5.37 nm to 17.19 whereas albumin coated nanoparticles are size ranges from 11.26 nm to 23.85 nm. The anticancer effect of capped AgNPs (cAgNPs) showed the IC50 value against breast cancer MCF-7 at 80 μg/mL, intestinal colon cancer HCT- 116 60 μg/mL, and bone cancer osteosarcoma MG-63 cell line80 μg/mL while against normal fibroblast cells 3T3 cells showed the IC50 value at 140 μg/mL. Lactate dehydrogenase assay (LDH) showed higher toxicity on MCF-7, HCT-116, and MG-63 cells. The apoptotic study clearly showed the blebbing of membrane, chromatin condensation due to the production of reactive oxygen species (ROS) by ethidium bromide and acridine orange dual staining method. The DNA analysis showed the complete fragmentation of the DNA of treated cells when compared with control cells.

Bifunctional cleavable probes for in situ multiplexed glycan detection and imaging using mass spectrometry

In situ analysis of glycans is of great significance since they mediate a range of biological activities. Aberrant changes of glycosylation are closely related to cancer onset and progression. In this work, bifunctional laser cleavable mass probes (LCMPs) were developed for in situ glycan detection from both cells and tissues using laser desorption ionization mass spectrometry (LDI-MS). Specific recognition of glycans was achieved by lectins, and inherent signal amplification was achieved by the conversion of the detection of glycans to that of mass tags which overcame the low ionization efficiency and complicated mass spectra of glycans. Multiplexed glycan profiling was easy to implement due to the simple and generic synthetic route to LCMPs and serial alternative mass tags, which offers high sensitivity, low interference and in situ detection of glycans. Moreover, as an excellent inherent matrix, LCMPs facilitated direct glycan detection from the cell surface and tissue imaging using LDI-MS. Intrinsic and fine glycan distribution in human cancer and paracancerous tissues was strictly demonstrated by MS imaging to explore the correlation between glycosylation and various cancers. This approach presented a versatile LDI-MS based platform for fast and in situ multiplexed glycan engineering, thus providing a new perspective in glycobiology and clinical diagnosis.

Aptasensors as a new sensing technology developed for the detection of MUC1 mucin: A review

Mucin 1 protein (MUC1) is a membrane-associated glycoprotein overexpressed in the majority of human malignancies and considered as a predominant protein biomarker in cancers. Owing to the crucial role of MUC1 in cancer dissemination and metastasis, detection and quantification of this biomarker is of great importance in clinical diagnostics. Today, there exist a wide variety of strategies for the determination of various types of disease biomarkers, especially MUC1. In this regard, aptamers, as artificial single-stranded DNA or RNA oligonucleotides with catalytic and receptor properties, have drawn lots of attention for the development of biosensing platforms. So far, various sensitivity-enhancement techniques in combination with a broad range of smart nanomaterials have integrated into the design of novel aptamer-based biosensors (aptasensors) to improve detection limit and sensitivity of analyte determination. This review article provides a brief classification and description of the research progresses of aptamer-based biosensors and nanobiosensors for the detection and quantitative determination of MUC1 based on optical and electrochemical platforms.

Study of the Stability of Functionalized Gold Nanoparticles for the Colorimetric Detection of Dipeptidyl Peptidase IV

In this report, we investigated three stabilization strategies of gold nanoparticles and their practical application for the visual detection of dipeptidyl peptidase IV (DPP-IV). Citrate-capped gold nanoparticles (Au NPs) are generally unstable in high-ionic-strength samples. Au NPs are easily tagged with various proteins and biomolecules rich in amino acids, leading to important biomedical applications including targeted drug delivery, cellular imaging, and biosensing. The investigated assays were based on different modes of stabilization, such as the incorporation of polyethylene glycol (PEG) groups, stabilizer peptide, and bifunctionalization. Although all approaches provided highly stable Au NP platforms demonstrated by zeta potential measurements and resistance to aggregation in a high-ionic-strength saline solution, we found that the Au NPs modified with a separate stabilizer ligand provided the highest stability and was the only platform that demonstrated sensitivity to the addition of DPP-IV, whilst PEGylated and peptide-stabilized Au NPs showed no significant response.

RNA-Cleaving DNAzymes: Old Catalysts with New Tricks for Intracellular and In Vivo Applications

DNAzymes are catalytically active DNA molecules that are normally isolated through in vitro selection methods, among which RNA-cleaving DNAzymes that catalyze the cleavage of a single RNA linkage embedded within a DNA strand are the most studied group of this DNA enzyme family. Recent advances in DNA nanotechnology and engineering have generated many RNA-cleaving DNAzymes with unique recognition and catalytic properties. Over the past decade, numerous RNA-cleaving, DNAzymes-based functional probes have been introduced into many research areas, such as in vitro diagnostics, intracellular imaging, and in vivo therapeutics. This review focus on the fundamental insight into RNA-Cleaving DNAzymes and technical tricks for their intracellular and in vivo applications, highlighting the recent progress in the clinical trial of RNA-Cleaving DNAzymes with selected examples. The challenges and opportunities for the future translation of RNA-cleaving DNAzymes for biomedicine are also discussed.

Silicon nanodot-based aptasensor for fluorescence turn-on detection of mucin 1 and targeted cancer cell imaging

We report herein a new dual-color fluorescent aptasensor for detection of tumor marker mucin 1 (MUC1) and targeted imaging of MCF-7 cancer cells based on the specific interaction between MUC1 and its aptamer S2.2. The aptasensor was prepared by covalent attachment of the cyanine (Cy5)-tagged aptamer S2.2 to fluorescent silicon nanodot (SiND). The fluorescence of S2.2-Cy5 could be quenched by the SiND carrier in the absence of MUC1, and its fluorescence was restored in the presence of MUC1 due to structure switching of S2.2. This aptasensor exhibits specificity for MUC1-possitive MCF-7 cells rather than MUC1-negative MCF-10A cells and Vero cells. The SiND plays multiple roles in this fluorescence assay, making the method easier compared with other approaches. The limit of detection and precision of this method for MUC1 was 1.52 nM and 3.6% (10 nM, n = 7), respectively. The linear range was 3.33-250 nM, and the recoveries in spiked human serum were in the range of 87-108%. This is a simple, selective, sensitive and reliable method, which can well achieve not only quantitative analysis of tumor marker but also dual-color visualization of single cancer cells.

Applications of Cancer Cell-Specific Aptamers in Targeted Delivery of Anticancer Therapeutic Agents

Aptamers are single-stranded oligonucleotides that specifically bind and interact with their corresponding targets, including proteins and cells, through unique three-dimensional structures. Numerous aptamers have been developed to target cancer biomarkers with high specificity and affinity, and some are employed as versatile guiding ligands for cancer-specific drug delivery and anti-cancer therapeutics. In this review, we list the aptamers that target tumor surface biomarkers and summarize the representative applications of aptamers as agonists and antagonists that activate anti-cancer and inactivate pro-cancer biomarkers, respectively. In addition, we describe applications of aptamer-drug or aptamer-oligonucleotide conjugates that can deliver therapeutic agents, including small interfering RNAs, micro RNAs, short hairpin RNAs, and chemotherapeutic molecules, to cancer cells. Moreover, we provide examples of aptamer- conjugated nano-vehicles, in which cancer-targeting oligonucleotide aptamers are conjugated with nano-vehicles such as liposomes, micelles, polymeric nanoparticles, and quantum dots. Conjugation of aptamers with anti-cancer drugs and nano-vehicles will facilitate innovative applications of aptamer-based cancer therapeutics.

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.