An ssDNA aptamer selected by Cell-SELEX for the targeted imaging of poorly differentiated gastric cancer tissue

Current developments of SELEX technologies and prospects in the aptamer selection with clinical applications

Aptamers are single-stranded oligonucleotide sequences capable of binding to specific ligands with high affinity. In this manner, they are like antibodies but have advantages such as lower manufacturing costs, lower immunogenicity, fewer batch-to-batch differences, a longer shelf life, high tolerance to different molecular milieus, and a greater number of potential targets. Due to their special features, they have been used in drug delivery, biosensor technology, therapy, and diagnostics. The methodology that allowed its production was the "Systematic Evolution of Ligands by Exponential enrichment" (SELEX). Unfortunately, the traditional protocol is time-consuming and laborious. Therefore, numerous variants with considerable optimization steps have been developed, nonetheless, there are still challenges to achieving real applications in the clinical field. Among them, are control of in vivo activities, fast renal filtration, degradation by nucleases and toxicity testing. This review focuses on current technologies based on SELEX, the critical factors for successful aptamer selection, and its upcoming biomedical and biotechnological applications.

Aptamer-based technology for gastric cancer theranostics

Gastric cancer is one of the most common causes of cancer death worldwide. This cancer exhibits high molecular and phenotype heterogeneity. The overall survival rate for gastric cancer is very low because it is always diagnosed in the advanced stages. Therefore, early detection and treatment are of great significance. Currently, biomedical studies have tapped the potential clinical applicability of aptamer-based technology for gastric cancer diagnosis and targeted therapy. Herein, we summarize the enrichment and evolution of relevant aptamers, followed by documentation of the recent developments in aptamer-based techniques for early diagnosis and precision therapy for gastric cancers.

Screening and Identification of DNA Nanostructure Aptamer Using the SELEX Method for ‎Detection of Epsilon Toxin

Background

Epsilon toxin (ETX), produced by Clostridium perfringens, is one of the most potent toxins known, with a lethal potency approaching that of botulinum neurotoxins. Epsilon toxin is responsible for enteritis. Therefore, the development of rapid and simple methods to detect ETX is imperative. Aptamers are single-stranded oligonucleotides that can bind tightly to specific target molecules with an affinity comparable to that of monoclonal antibodies (mAbs). DNA aptamers can serve as tools for the molecular identification of organisms, such as pathogen subspecies.

Objectives

This study aimed to isolate high-affinity single-stranded DNA (ssDNA) aptamers against ETX.

Methods

This study identified aptamers using the Systematic Evolution of Ligands by Exponential Enrichment (SELEX) method, enzyme-linked apta-sorbent assay (ELASA), and surface plasmon resonance (SPR) to determine the affinity and specificity of the newly obtained aptamers targeting ETX.

Results

Several aptamers obtained through the SELEX process were studied. Among them, 2 aptamers, ETX clone 3 (ETX3; dissociation constant (Kd = 8.4 ± 2.4E-9M) and ETX11 (Kd = 6.3 ± 1.3E-9M) had favorable specificity for ETX. The limits of detection were 0.21 and 0.08 μg/mL for ETX3 and ETX11, respectively.‎.

Conclusions

The discovered aptamers can be used in various aptamer-based rapid diagnostic tests for the detection of ETX.

Aptamer nucleotide analog drug conjugates in the targeting therapy of cancers

Aptamers are short single-strand oligonucleotides that can form secondary and tertiary structures, fitting targets with high affinity and specificity. They are so-called "chemical antibodies" and can target specific biomarkers in both diagnostic and therapeutic applications. Systematic evolution of ligands by exponential enrichment (SELEX) is usually used for the enrichment and selection of aptamers, and the targets could be metal ions, small molecules, nucleotides, proteins, cells, or even tissues or organs. Due to the high specificity and distinctive binding affinity of aptamers, aptamer-drug conjugates (ApDCs) have demonstrated their potential role in drug delivery for cancer-targeting therapies. Compared with antibodies which are produced by a cell-based bioreactor, aptamers are chemically synthesized molecules that can be easily conjugated to drugs and modified; however, the conventional ApDCs conjugate the aptamer with an active drug using a linker which may add more concerns to the stability of the ApDC, the drug-releasing efficiency, and the drug-loading capacity. The function of aptamer in conventional ApDC is just as a targeting moiety which could not fully perform the advantages of aptamers. To address these drawbacks, scientists have started using active nucleotide analogs as the cargoes of ApDCs, such as clofarabine, ara-guanosine, gemcitabine, and floxuridine, to replace all or part of the natural nucleotides in aptamer sequences. In turn, these new types of ApDCs, aptamer nucleotide analog drug conjugates, show the strength for targeting efficacy but avoid the complex drug linker designation and improve the synthetic efficiency. More importantly, these classic nucleotide analog drugs have been used for many years, and aptamer nucleotide analog drug conjugates would not increase any unknown druggability risk but improve the target tumor accumulation. In this review, we mainly summarized aptamer-conjugated nucleotide analog drugs in cancer-targeting therapies.

Identification of the target protein of the metastatic colorectal cancer-specific aptamer W3 as a biomarker by aptamer-based target cells sorting and functional characterization

Metastasis is a leading cause of cancer-related deaths. Hence, the discovery of more reliable metastasis-related biomarkers is crucial to improve the survival rate of cancer patients. W3 is an aptamer previously produced by the subtractive cell-SELEX using metastatic colorectal cancer cells as target cells and non-metastatic cells as negative cells. In this study, we aimed to evaluate whether the target molecule of W3 can potentially act as a metastatic biomarker. First, we obtained two cell subpopulations with different expression levels of the target molecule by W3-based cell sorting. Subsequently, we demonstrated that W3^high cells have a higher metastatic potential than W3^low cells both in vitro and in vivo. Further, immunohistochemical analysis revealed that W3 target expression is positively associated with metastasis and poor prognosis of CRC patients. Using mass spectrometry (MS) combined with pull-down, we identified that Ephrin type-A receptor 2 (EphA2) is the target of W3. EphA2's potential as a metastatic predictor was demonstrated by capturing W3-positive circulating tumor cells from CRC patients using a W3 probe. Based on these results, we put forward a stratagem for cell-SELEX-based biomarker discovery: selecting an aptamer through subtractive cell-SELEX towards the phenotype of interest; evaluating the functional phenotype of the target molecule by aptamer-based target cell sorting and analysis of clinical samples; and identifying the aptamer's target molecule using MS and aptamer-based target enrichment. This stratagem not only shortens the time for the clinical application of aptamers but also enables a more targeted and efficient discovery of biomarkers.

Cell-specific aptamers as potential drugs in therapeutic applications: A review of current progress

Cell-specific aptamers are a promising emerging player in the field of disease therapy. This paper reviews the multidimensional research progress made in terms of their classification, modification, and application. Based on the target location of cell-specific aptamers, it is defined and classified cell-specific aptamers into three groups including aptamers for cell surface markers, aptamers for intracellular components, and aptamers for extracellular components. Moreover, the modification methods of aptamers to achieve improved stability and affinity are concluded. In addition, recent advances in the application of cell-specific aptamers are discussed, mainly focusing on the increasing research attraction of cell state improving helpers and cell recruitment mediators in the improvement of cellular microenvironments to achieve successful disease therapy. This review also highlights 11 types of clinical aptamer drugs. Finally, the challenges and future directions of potential clinical applications are presented. In summary, we believe that cell-specific aptamers are promising drugs in disease therapy.

An electrochemical PAH-modified aptasensor for the label-free and highly-sensitive detection of saxitoxin

Saxitoxin (STX), is one of the most dangerous and widespread paralytic shellfish toxins, causing a severe threat to the ecosystem and human health. So, it is important and highly essential to develop novel techniques for STX detection in a convenient, desirable, and low-cost manner. Herein, this study developed an electrolyte-insulator-semiconductor (EIS) sensor covered with a layer-by-layer prepared, positively-charged weak polyelectrolyte layer of poly (allylamine hydrochloride) (PAH) for the label-free detection of STX. The specific aptamer (Apt) sensitive to STX was electrostatically adsorbed onto the PAH layer. This leads to a preferentially flat orientation of the Apt within the Debye length, thus yielding a reduced charge-screening influence and a higher sensor signal. Each step of sensor surface modification, i.e. PAH adsorption, immobilization of Apt, and attachment of STX, was monitored by capacitance-voltage (C-V) and constant-capacitance (ConCap) measurements. Furthermore, atomic force microscopy (AFM) was employed to characterize the surface morphology and roughness of the PAH layer. Fluorescence microscopy was used to confirm the effective immobilization of Apt onto the PAH-modified EIS sensor. The results showed that the detection range of this aptasensor for STX detection was 0.5-100 nM and the detection limit was as low as 0.05 nM. Furthermore, this aptasensor showed good selectivity and 9 days' stability. The mussel tissue extraction test suggested that this aptasensor can be used to detect STX in real samples. This aptasensor provides a convenient approach for moderate, rapid, and label-free detection of marine biological toxins.

Aptamer Targets Triple-Negative Breast Cancer through Specific Binding to Surface CD49c

Simple Summary

Targeted therapy directed against many biomarkers has not shown significant improvement in outcome in TNBC, and therefore it is urgent to discover more biomarker candidates. Here, we found a DNA aptamer that bound to TNBC cells and identified CD49c as a specific surface marker for TNBC cells using the aptamer-facilitated biomarker discovery technology. The findings suggest that this DNA aptamer can be a drug delivery vehicle and CD49c is a potential target of targeted therapy for TNBC.

Abstract

Although targeted cancer therapy can induce higher therapeutic efficacy and cause fewer side effects in patients, the lack of targetable biomarkers on triple-negative breast cancer (TNBC) cells limits the development of targeted therapies by antibody technology. Therefore, we investigated an alternative approach to target TNBC by using the PDGC21T aptamer, which selectively binds to poorly differentiated carcinoma cells and tumor tissues, although the cellular target is still unknown. We found that synthetic aptamer probes specifically bound cultured TNBC cells in vitro and selectively targeted TNBC xenografts in vivo. Subsequently, to identify the target molecule on TNBC cells, we performed aptamer-mediated immunoprecipitation in lysed cell membranes followed by liquid chromatography tandem mass spectrometry (LC-MS/MS). Sequencing analysis revealed a highly conserved peptide sequence consistent with the cell surface protein CD49c (integrin α3). For target validation, we stained cultured TNBC and non-TNBC cells with an aptamer probe or a CD49c antibody and found similar cell staining patterns. Finally, competition cell-binding assays using both aptamer and anti-CD49c antibody revealed that CD49c is the biomarker targeted by the PDGC21T aptamer on TNBC cells. Our findings provide a molecular foundation for the development of targeted TNBC therapy using the PDGC21T aptamer as a targeting ligand.

Aptamer-armed nanostructures improve the chemotherapy outcome of triple-negative breast cancer

Triple-negative breast cancer is an aggressive subtype of breast cancer that is primarily treated using systemic chemotherapy due to the lack of a specific cell surface marker for drug delivery. Cancer cell-specific aptamer-mediated drug delivery is a promising targeted chemotherapy for marker-unknown cancers. Using a poorly differentiated carcinoma cell-specific DNA aptamer (PDGC21T), we formed a self-assembling circinate DNA nanoparticle (Apt^21TNP) that binds triple-negative breast cancer cells. Using our previously designed pH-sensitive dendrimer-conjugated doxorubicin (DDOX) as the payload, we found that each nanoparticle loaded 30 doxorubicin molecules to form an Apt^21TNP-DDOX nanomedicine that is stable in human plasma. Upon cell binding, Apt^21TNP-DDOX is internalized by triple-negative breast cancer cells through the macropinocytosis pathway. Once inside cells, the low pH microenvironment in lysosomes induces doxorubicin drug payload release from Apt^21TNP-DDOX. Our in vitro studies demonstrate that Apt^21TNP-DDOX can preferentially bind triple-negative breast cancer cells to induce cell death. Further, we show that Apt^21TNP-DDOX can accumulate in subcutaneous MDA-MB-231 tumors in mice following systemic administration to reduce tumor burden, minimize side effects, and improve animal survival. Together, our results demonstrate that Apt^21TNP-mediated doxorubicin delivery is a potent, targeted chemotherapy for triple-negative breast cancer that may alleviate side effects in patients.

Targeted immunotherapy of triple-negative breast cancer by aptamer-engineered NK cells

Triple-negative breast cancer (TNBC) is an aggressive subtype of breast cancer comprised of cells that lack expression of targetable biomarkers. Nucleic acid aptamers are a group of molecular ligands that can specifically bind to their targets with high affinity. The ssDNA aptamer PDGC21-T recognizes poorly differentiated cancer cells and tumor tissues through an unidentified cell surface target(s). Because TNBC tumor cells are poorly differentiated, the aptamer PDGC21-T is a promising therapeutic candidate to target TNBC tumor cells. In vitro study revealed that synthetic aptamer probes selectively targeted TNBC cell lines. To assess aptamer immunotherapeutic targeting capability, we generated aptamer-engineered NK cells (ApEn-NK) using aptamer probes as a targeting ligand and NK cells as a therapeutic agent. Cell clustering formation assays revealed that ApEn-NK bound both suspended and adherent TNBC cells with high affinity. In a functional study, ApEn-NK treatment triggered apoptosis and death of cultured TNBC cells. Finally, systemic administration of ApEn-NK in mice harboring TNBC xenografts resulted in significant inhibition of lung metastasis relative to parental NK cell treatments. Unlike chemotherapy, ApEn-NK treatment did not affect body weight in treated mice. We demonstrate a novel approach for targeted TNBC immunotherapy.

Cell-SELEX-based selection of ssDNA aptamers for specifically targeting BRAF V600E-mutated melanoma

Malignant melanoma is regarded as the most aggressive form of skin cancer, and is responsible for most death caused by skin cancer. BRAF mutations occur in approximately 40-50% of melanomas, with V600E being the most common mutation. Testing for BRAF mutations and targeted therapy have markedly improved long-term survival for patients with BRAF-mutated melanoma. Here, we report two aptamers, CH1 and CH5 generated by Cell-SELEX, against BRAF V600E-mutated human melanoma cells A375. The two aptamers exhibited high affinity to target cells with low dissociation constants (K_d) in the nanomolar range. Furthermore, the binding of two aptamers to target cells was independent of incubation temperature, and their molecular targets were demonstrated to be membrane proteins on the cell surface. We also demonstrated that aptamer CH1 was able to bind to metastatic colorectal cancer cells harboring BRAF V600E mutation, indicating a relationship between aptamer CH1 and BRAF V600E-related metastatic cancer. Owing to the structure stability and high selectivity to BRAF V600E-mutated targeting cells, aptamer CH1 holds great potential as a molecular probe for the detection of BRAF V600E-mutated metastatic melanoma.

Applications of Aptamer-Bound Nanomaterials in Cancer Therapy

Cancer is still a major disease that threatens human life. Although traditional cancer treatment methods are widely used, they still have many disadvantages. Aptamers, owing to their small size, low toxicity, good specificity, and excellent biocompatibility, have been widely applied in biomedical areas. Therefore, the combination of nanomaterials with aptamers offers a new method for cancer treatment. First, we briefly introduce the situation of cancer treatment and aptamers. Then, we discuss the application of aptamers in breast cancer treatment, lung cancer treatment, and other cancer treatment methods. Finally, perspectives on challenges and future applications of aptamers in cancer therapy are discussed.

An Electrochemical Ti3C2Tx Aptasensor for Sensitive and Label-Free Detection of Marine Biological Toxins

Saxitoxin (STX) belongs to the family of marine biological toxins, which are major contaminants in seafood. The reference methods for STX detection are mouse bioassay and chromatographic analysis, which are time-consuming, high costs, and requirement of sophisticated operation. Therefore, the development of alternative methods for STX analysis is urgent. Electrochemical analysis is a fast, low-cost, and sensitive method for biomolecules analysis. Thus, in this study, an electrolyte-insulator-semiconductor (EIS) sensor based on aptamer-modified two-dimensional layered Ti3C2Tx nanosheets was developed for STX detection. The high surface area and rich functional groups of MXene benefited the modification of aptamer, which had specific interactions with STX. Capacitance-voltage (C-V) and constant-capacitance (ConCap) measurement results indicated that the aptasensor was able to detect STX with high sensitivity and good specificity. The detection range was 1.0 nM to 200 nM and detection limit was as low as 0.03 nM. Moreover, the aptasensor was found to have a good selectivity and two-week stability. The mussel tissue extraction test suggested the potential application of this biosensor in detecting STX in real samples. This method provides a convenient approach for low-cost, rapid, and label-free detection of marine biological toxins.

Aptamers isolated against mosquito-borne pathogens

Mosquito-borne diseases are a major threat to public health. The shortcomings of diagnostic tools, especially those that are antibody-based, have been blamed in part for the rising annual morbidity and mortality caused by these diseases. Antibodies harbor a number of disadvantages that can be clearly addressed by aptamers as the more promising molecular recognition elements. Aptamers are defined as single-stranded DNA or RNA oligonucleotides generated by SELEX that exhibit high binding affinity and specificity against a wide variety of target molecules based on their unique structural conformations. A number of aptamers were developed against mosquito-borne pathogens such as Dengue virus, Zika virus, Chikungunya virus, Plasmodium parasite, Francisella tularensis, Japanese encephalitis virus, Venezuelan equine encephalitis virus, Rift Valley fever virus and Yellow fever virus. Intrigued by these achievements, we carry out a comprehensive overview of the aptamers developed against these mosquito-borne infectious agents. Characteristics of the aptamers and their roles in diagnostic, therapeutic as well as other applications are emphasized.

Selection and identification of an ssDNA aptamer to NB4 cell

This study was to find the aptamers with high affinity and specificity binding to acute promyelocytic leukemia (APL) NB4 cell line.

These aptamers targeted NB4 cells were selected from a random single‐stranded DNA (ssDNA) library of systematic evolution of ligands by exponential enrichment (CELL‐SELEX). The binding rate of FITC‐ssDNA library and NB4 cells was monitored using flow cytometry and fluorescence microscope. After cloned and sequenced, the structure, specificity, and affinity of these candidate aptamers were further analyzed.

After a total of 19 rounds of selection, the ssDNA library was enriched and the BR (19.9%) of the 16th round was 12 times of the first round (1.6%). Three enriched aptamers were obtained from 21 positive clones of the 16th round, and the predicted secondary structures of these aptamers were mainly stem‐loop. The aptamer CX9 had the highest affinity, and the equilibrium dissociation constant (Kd) was 16.2 nM. The fluorescence intensity of CX9 binding to NB4 cells was stronger than HL60 and K562 cells under fluorescence microscopy.

The study indicates that aptamer CX9 exhibits high affinity and specificity with NB4 cells and lay a foundation for the rapid diagnostic method to detect APL with fluorescence‐labeled aptamer.

In silico molecular docking in DNA aptamer development

Aptamers are single-stranded DNA or RNA oligonucleotides generated by SELEX that exhibit binding affinity and specificity against a wide variety of target molecules. Compared to RNA aptamers, DNA aptamers are much more stable and therefore are widely adopted in a number of applications especially in diagnostics. The tediousness and rigor associated with certain steps of the SELEX intensify the efforts to adopt in silico molecular docking approaches together with in vitro SELEX procedures in developing DNA aptamers. Inspired by these endeavors, we carry out an overview of the in silico molecular docking approaches in DNA aptamer generation, by detailing the stepwise procedures as well as shedding some light on the various softwares used. The in silico maturation strategy and the limitations of the in silico approaches are also underscored.

A novel method for sensitive detection of Escherichia coli O157:H7 based on an aptamer and hybridization chain reaction

This work developed a novel assay for the detection of Escherichia coli O157:H7 (E. coli O157:H7), which is based on the specific recognition of an aptamer (H0) for E. coli O157:H7, the signal amplification of a hybridization chain reaction (HCR) and the adsorption and quenching effect of graphene oxide (GO). The feasibility of this work was verified through control experiments. The concentration of GO, the HCR time, the concentration of H0, and the concentration of H1/H2 were optimized. A series of E. coli O157:H7 dilutions were detected under the optimal conditions, and the detection range was 2.6 × 10² to 2.6 × 10⁸ CFU mL^-1. The linear equation is y = 591.1x- 943.9, R² = 0.995, and LOD is 5 × 10¹ CFU mL^-1. Milk samples were used for the spike recovery experiment, and the recovery rate was 92.6-103.6%. This method shortens the detection time greatly and provides a new strategy for food safety monitoring.

Chemical Modification of Aptamers for Increased Binding Affinity in Diagnostic Applications: Current Status and Future Prospects

Aptamers are short single stranded DNA or RNA oligonucleotides that can recognize analytes with extraordinary target selectivity and affinity. Despite their promising properties and diagnostic potential, the number of commercial applications remains scarce. In order to endow them with novel recognition motifs and enhanced properties, chemical modification of aptamers has been pursued. This review focuses on chemical modifications, aimed at increasing the binding affinity for the aptamer's target either in a non-covalent or covalent fashion, hereby improving their application potential in a diagnostic context. An overview of current methodologies will be given, thereby distinguishing between pre- and post-SELEX (Systematic Evolution of Ligands by Exponential Enrichment) modifications.

Rolling Circle Amplification-Based Polyvalent Molecular Beacon Probe-Assisted Signal Amplification Strategies for Sensitive Detection of B16 Cells

We developed a simple and sensitive signal amplification method for the detection of B16 cells based on the combination of rolling circle amplification (RCA) and molecular beacons (MBs). A long-chain structure of DNA synthesized by RCA was used to turn on aptamer-based MBs. Because of the multiple complementary repeat units, the RCA scaffold hybridized tens or hundreds of MBs to form polyvalent aptamer probes. The unfold ability and the fluorescence intensity of MBs were both improved by RCA, as compared to short single chains. The cell experiment results demonstrated that RCA-based polyvalent MBs were significantly more effective than monovalent MBs in targeting B16 cells and signal sensitivity because of their multivalent effects. The establishment of this strategy would provide a powerful platform for early clinical diagnostics of cancer cells.

GMBP1-conjugated manganese oxide nanoplates for in vivo monitoring of gastric cancer MDR using magnetic resonance imaging

Multidrug resistance (MDR) is a huge challenge for gastric cancer chemotherapy. Therefore, MDR accurate monitoring is of great significance for the treatment of gastric cancer. GMBP1, an extracellular internalization peptide, can target MDR gastric cancer cells through specific binding to GRP78, which is an MDR-related protein that is overexpressed in gastric cancer cells. Herein, we constructed GMBP1 conjugated Mn₃O₄ nanoplates (Mn₃O₄@PEG-GMBP1 NPs) for in vivo monitoring of MDR gastric cancer through magnetic resonance imaging (MRI). The generated Mn₃O₄@PEG-GMBP1 NPs had a size of about 11 nm and exhibited a good colloidal stability in PBS and in 10% FBS medium. Serial in vivo MRI studies in mice demonstrated that the magnetic resonance signal intensity, at the tumor site, reached a peak at 3 h after tail vein injection of Mn₃O₄@PEG-GMBP1 NPs. The specific targeting ability of MDR gastric cancer cells (SGC7901/ADR) by Mn₃O₄@PEG-GMBP1 NPs was authenticated in vitro, in vivo and by immunofluorescence analysis experiments. The systematic safety evaluation indicated that the toxicity of Mn₃O₄@PEG-GMBP1 NPs in mice was negligible. Therefore, the GMBP1 conjugated Mn₃O₄ nanoplates can be clinically used for accurate imaging and monitoring of MDR gastric cancer.

Advances of aptamers screened by Cell-SELEX in selection procedure, cancer diagnostics and therapeutics

Aptamers are a class of short artificial single-stranded oligo(deoxy) nucleotides that can bind to different targets, which generated by Systematic Evolution of Ligands by Exponential Enrichment (SELEX). Due to excellent selectivity and high affinity to targets, aptamers hold considerable potential as molecular probe in diverse applications ranging from ensuring food safety, monitoring environment, disease diagnosis to therapy. This review highlights recent development and challenges about aptamers screened by Cell-SELEX, and its application about cancer diagnostics and therapeutics. Advances about some operation methods such as seperation method and culture method in aptamers selection procedure were summarized in this paper. Some common challenges and technological difficulties such as nonspecific binding and biostability were discussed. Up to now, the recent endeavors about cancer diagnostic and therapeutic applications of aptamers are summarized and expatiated. Most of aptamers screened by Cell-SELEX took tumor cells as target cells, and such aptamers have been assembled to various aptasensor for cancer diagnosis. Aptamers conjugated various drugs or nanomaterials are functioned for cancer target therapy to improve drugs delivery efficiency and reduce side effects. Furthermore, the duplexed aptamer is discussed to be applied for cancer cells detection and some conflicts of theories about duplexed aptamer designs are analyzed.

Nanomaterial-based aptamer sensors for arsenic detection

Arsenic (As) is a highly toxic contaminant in the environment and a serious carcinogen for the human being. The toxicity of arsenic significantly threatens environmental and human health. The effective removing technology for arsenic remains challenging, and one of the reasons is due to the lack of powerful detection method in the complex environmental matrix. There is thus an urgent need to develop novel analytical methods for arsenic, preferably with the potential for the field-testing. To combat arsenic pollution and maintain a healthy environment and eco-system, many analytical methods have been developed for arsenic detection in various samples. Among these strategies, biosensors hold great promise for rapid detection of arsenic, in particular, nanomaterials-based aptamer sensors have attracted significant attention due to their simplicity, high sensitivity and rapidness. In this paper, we reviewed the recent development and applications of aptamer sensors (aptasensors) based-on nanomaterial for arsenic detection, in particular with emphasis on the works using optical and electrochemical technologies. We also discussed the recent novel technology in aptasensors development for arsenic detection, including nucleic acid amplification for signal enhancement and device integration for the portability of arsenic sensors. We are hoping this review could inspire further researches in developing novel nanotechnologies based aptasensors for possible on-site detection of arsenic.

Competitive electrochemical aptasensor based on a cDNA-ferrocene/MXene probe for detection of breast cancer marker Mucin1

A competitive electrochemical aptasensor based on a cDNA-ferrocene/MXene probe is used to detect the breast cancer marker Mucin1 (MUC1). MXene (Ti₃C₂) nanosheets with excellent electrical conductivity and large specific surface area are selected as carriers for aptamer probes. The ferrocene-labeled complementary DNA (cDNA-Fc) is first bound on the surface of MXene to form a cDNA-Fc/MXene probe. Then, the MUC1 aptamer is fixed to the electrode by Au-S bonds. The sensing electrode is named Apt/Au/GCE. After the probe is complementary to the aptamer, a cDNA-Fc/MXene/Apt/Au/GCE aptasensor is fabricated. When the aptasensor is used for detection of MUC1, a competitive process happens between the cDNA-ferrocene/MXene probe and MUC1, which makes cDNA-Fc/MXene probe detach from the sensing electrode, resulting in a decrease in electrical signal. The difference in the corresponding peak current before and after the competition can be used to indicate the quantitative change in bound MUC1. The proposed competitive electrochemical aptasensor gives a wide linear range of 1.0 pM-10 μM and a low detection limit of 0.33 pM (S/N = 3), which is promising for clinical diagnosis.