Aptamer-based molecular recognition for biosensor development

Breast cancer detection based on cancer antigen 15-3; emphasis on optical and electrochemical methods: A review

Cancer antigen 15-3 (CA 15-3) is a crucial marker used in the diagnosis and monitoring of breast cancer (BC). The demand for early and precise cancer detection has grown, making the creation of biosensors that are highly sensitive and specific essential. This review paper provides a thorough examination of the progress made in optical and electrochemical biosensors for detecting the cancer biomarker CA 15-3. We focus on explaining their fundamental principles, sensitivity, specificity, and potential for point-of-care applications. The performance attributes of these biosensors are assessed by considering their limits of detection, reaction times, and operational stability, while also making comparisons to conventional methods of CA 15-3 detection. In addition, we explore the incorporation of nanomaterials and innovative transducer components to improve the performance of biosensors. This paper conducts a thorough examination of recent studies to identify the existing obstacles. It also suggests potential areas for future research in this fast progressing field.The paper provides insights into their advancement and utilization to enhance patient outcomes. Both categories of biosensors provide significant promise for the detection of CA 15-3 and offer distinct advantages compared to conventional analytical approaches.

A miniprotein receptor electrochemical biosensor chip based on quantum dots

Recently protein binders have emerged as a promising substitute for antibodies due to their high specificity and low cost. Herein, we demonstrate an electrochemical biosensor chip through the electronic labelling strategy using lead sulfide (PbS) colloidal quantum dots (CQDs) and the unnatural SARS-CoV-2 spike miniprotein receptor LCB. The unnatural receptor can be utilized as a molecular probe for the construction of CQD-based electrochemical biosensor chips, through which the specific binding of LCB and the spike protein is transduced to sensor electrical signals. The biosensor exhibits a good linear response in the concentration range of 10 pg mL-1 to 1 μg mL-1 (13.94 fM to 1.394 nM) with the limit of detection (LOD) being 3.31 pg mL-1 (4.607 fM for the three-electrode system) and 9.58 fg mL-1 (0.013 fM for the HEMT device). Due to the high sensitivity of the electrochemical biosensor, it was also used to study the binding kinetics between the unnatural receptor LCB and spike protein, which has achieved comparable results as those obtained with commercial equipment. To the best of our knowledge, this is the first example of using a computationally designed miniprotein receptor based on electrochemical methods, and it is the first kinetic assay performed with an electrochemical assay alone. The miniprotein receptor electrochemical biosensor based on QDs is desirable for fabricating high-throughput, large-area, wafer-scale biochips.

Recent advances in microbial fuel cell-based self-powered biosensors: a comprehensive exploration of sensing strategies in both anode and cathode modes

With the rapid development of society, it is of paramount importance to expeditiously assess environmental pollution and provide early warning of toxicity risks. Microbial fuel cell-based self-powered biosensors (MFC-SPBs) have emerged as a pivotal technology, obviating the necessity for external power sources and aligning with the prevailing trends toward miniaturization and simplification in biosensor development. In this case, vigorous advancements in MFC-SPBs have been acquired in past years, irrespective of whether the target identification event transpires at the anode or cathode. The present article undertakes a comprehensive review of developed MFC-SPBs, categorizing them into substrate effect and microbial activity effect based on the nature of the target identification event. Furthermore, various enhancement strategies to improve the analytical performance like accuracy and sensitivity are also outlined, along with a discussion of future research trends and application prospects of MFC-SPBs for their better developments.

Responsive Janus droplets as modular sensory layers for the optical detection of bacteria

The field of biosensor development is fueled by innovations in new functional transduction materials and technologies. Material innovations promise to extend current sensor hardware limitations, reduce analysis costs, and ensure broad application of sensor methods. Optical sensors are particularly attractive because they enable sensitive and noninvasive analyte detection in near real-time. Optical transducers convert physical, chemical, or biological events into detectable changes in fluorescence, refractive index, or spectroscopic shifts. Thus, in addition to sophisticated biochemical selector designs, smart transducers can improve signal transmission and amplification, thereby greatly facilitating the practical applicability of biosensors, which, to date, is often hampered by complications such as difficult replication of reproducible selector-analyte interactions within a uniform and consistent sensing area. In this context, stimuli-responsive and optically active Janus emulsions, which are dispersions of kinetically stabilized biphasic fluid droplets, have emerged as a novel triggerable material platform that provides as a versatile and cost-effective alternative for the generation of reproducible, highly sensitive, and modular optical sensing layers. The intrinsic and unprecedented chemical-morphological-optical coupling inside Janus droplets has facilitated optical signal transduction and amplification in various chemo- and biosensor paradigms, which include examples for the rapid and cost-effective detection of major foodborne pathogens. These initial demonstrations resulted in detection limits that rival the capabilities of current commercial platforms. This trend article aims to present a conceptual summary of these initial efforts and to provide a concise and comprehensive overview of the pivotal kinetic and thermodynamic principles that govern the ability of Janus droplets to sensitively and selectively respond to and interact with bacteria.

A highly sensitive competitive aptasensor for AFB1 detection based on an exonuclease-assisted target recycling amplification strategy

Aflatoxin B₁ (AFB₁) is a typical mycotoxin found in agricultural products, and poses a huge threat to both humans and animals. Accurate and rapid measurement of AFB₁ is essential for environmental analysis and food safety. Based on molecular docking simulation design and exonuclease-assisted target recycling amplification, we designed a competitive fluorescence aptasensor to detect AFB₁ rapidly and sensitively. According to the molecular docking simulations, a complementary strand (cDNA) was designed by searching for potential binding sites of the aptamer, which had the lowest binding energy. Magnetic beads modified with biotin-Apt were used as the capture probe, while FAM-labeled cDNA acted as the reporter probe. By using EXO I for target recycling amplification, this aptasensor was highly sensitive and selective for AFB₁. The detection limit of the suggested aptasensor under optimal conditions was 0.36 ng mL^-1 (S/N = 3) in the range of 1-1000 ng mL^-1 (R² = 0.991). The developed aptasensor was successfully used to analyze AFB₁ in oil samples.

Overview on the Design of Magnetically Assisted Electrochemical Biosensors

Electrochemical biosensors generally require the immobilization of recognition elements or capture probes on the electrode surface. This may limit their practical applications due to the complex operation procedure and low repeatability and stability. Magnetically assisted biosensors show remarkable advantages in separation and pre-concentration of targets from complex biological samples. More importantly, magnetically assisted sensing systems show high throughput since the magnetic materials can be produced and preserved on a large scale. In this work, we summarized the design of electrochemical biosensors involving magnetic materials as the platforms for recognition reaction and target conversion. The recognition reactions usually include antigen-antibody, DNA hybridization, and aptamer-target interactions. By conjugating an electroactive probe to biomolecules attached to magnetic materials, the complexes can be accumulated near to an electrode surface with the aid of external magnet field, producing an easily measurable redox current. The redox current can be further enhanced by enzymes, nanomaterials, DNA assemblies, and thermal-cycle or isothermal amplification. In magnetically assisted assays, the magnetic substrates are removed by a magnet after the target conversion, and the signal can be monitored through stimuli-response release of signal reporters, enzymatic production of electroactive species, or target-induced generation of messenger DNA.

Preferential interactions of surface-bound engineered single stranded DNA with highly aromatic natural organic matter: Mechanistic insights and implications for optimizing practical aquatic applications

Engineered short-chain single stranded DNA (ssDNA) are emerging materials with various environmental applications, such as aptasensor, selective adsorbent, and hydrological tracer. However, the lack of fundamental understanding on the interactions of such materials with natural organic matter (NOM) hinders the improvement of their application performance in terms of sensitivity, selectivity, and stability. In this study, we investigated the interactions of ssDNA (four strands with systematically varied length and sequence) with two humic acids (Suwannee River humic acid (SRHA) and Aldrich humic acid (AHA)) and two humic-like NOM present in local aquatic matrices (ROM in river water and WOM in wastewater). Detailed, molecular level interaction mechanisms were obtained by probing the colloidal stability of the ssDNA-coated gold nanoparticles, coupled with product characterization using a suite of microscopic and spectroscopic techniques. Our study revealed that π-π interactions and divalent cation bridging were the major mechanisms for ssDNA-NOM interactions. ssDNA preferentially interacted with NOM with high aromaticity (AHA > SRHA/WOM/ROM). With divalent cations present (especially Ca²⁺), even a small amount of AHA could completely shield ssDNA, whereas the extent of shielding by SRHA/WOM/ROM depended on the relative content of ssDNA and NOM and whether bridges formed. The extent of shielding of ssDNA by NOM provides a potential answer to the reported conflicting effects of natural water matrices on the performance of DNA-based sensors. Taken together, our findings provide insights into the transformations of engineered ssDNA under environmentally relevant conditions as well as implications for their performance optimization in practical aquatic applications (e.g., from DNA design to pretreatment strategy).

Rapid and label-free detection of aflatoxin B1 using a rationally truncated aptamer and via circular dichroism measurement

We describe a simple aptamer assay for the rapid analysis of aflatoxin B1 (AFB1), a potently carcinogenic fungal metabolite. The original anti-AFB1 aptamer was rationally truncated, obtaining a short aptamer that displayed better performance. Different concentrations of AFB1 were detected by measuring the circular dichroism spectra of this short aptamer. The detection limit reached 0.6 nM, which was lower than that of the original aptamer (80 nM).

Preparation of Surface Plasmon Resonance Aptasensor for Human Activated Protein C Sensing

Nucleic acid aptamers are an emerging class of artificial ligands and have recently gained attention in several areas. Here we report the design of a surface plasmon resonance (SPR) aptasensor for highly sensitive and selective sensing of human activated protein C (APC). First, DNA aptamer (DNA-Apt) specific for APC is complexed with N-methacryloyl-L-cysteine (MAC) monomer. Then, 2-hydroxyethyl methacrylate (HEMA) and cyanamide are mixed with the DNA-Apt/MAC complex. The SPR aptasensor is characterized by atomic force microscopy, ellipsometry, and contact angle measurements. Selectivity of SPR aptasensor is carried out in the presence of myoglobin (Myb), hemoglobin (Hb), and bovine serum albumin (BSA). Limit of detection (LOD) and limit of quantification (LOQ) values are 1.5 ng mL^-1 and 5.2 ng mL^-1, respectively. DNA-Apt SPR aptasensor performance for APC detection is also examined in artificial plasma.

A signal-on fluorescent aptasensor by sensitized Tb3+ luminescence for detection of melamine in milk

A fluorescent aptasensor based on sensitized terbium(III) luminescence was constructed to detect melamine in milk. Tb³⁺ as the fluorescence probe can be sensitized by a guanine-rich single-stranded DNA sequence, so the complementary sequence of the polythymidine aptamer (cDNA) was modified with six consecutive guanine bases (G6). In the absence of melamine, melamine aptamer combined with cDNA to form a double helix structure, and G6 hybridized with the extended cytosine bases in the aptamer, resulting in low fluorescence intensity of Tb³⁺. In the presence of melamine, cDNA was released due to the specific recognition of melamine to the aptamer, resulting in stronger sensitized fluorescence intensity of Tb³⁺. Under the optimum conditions, the linear concentration of melamine in the milk ranged from 1.0 μg/mL to 10.0 μg/mL. This aptasensor can be used for the accurate and rapid detection of melamine in milk with a detection limit of 0.02 μg/mL, and has the advantages of high sensitivity, high efficiency, simple operation and low cost.

Physical and Chemical Sensors on the Basis of Laser-Induced Graphene: Mechanisms, Applications, and Perspectives

Laser-induced graphene (LIG) is produced rapidly by directly irradiating carbonaceous precursors, and it naturally exhibits as a three-dimensional porous structure. Due to advantages such as simple preparation, time-saving, environmental friendliness, low cost, and expanding categories of raw materials, LIG and its derivatives have achieved broad applications in sensors. This has been witnessed in various fields such as wearable devices, disease diagnosis, intelligent robots, and pollution detection. However, despite LIG sensors having demonstrated an excellent capability to monitor physical and chemical parameters, the systematic review of synthesis, sensing mechanisms, and applications of them combined with comparison against other preparation approaches of graphene is still lacking. Here, graphene-based sensors for physical, biological, and chemical detection are reviewed first, followed by the introduction of general preparation methods for the laser-induced method to yield graphene. The preparation and advantages of LIG, sensing mechanisms, and the properties of different types of emerging LIG-based sensors are comprehensively reviewed. Finally, possible solutions to the problems and challenges of preparing LIG and LIG-based sensors are proposed. This review may serve as a detailed reference to guide the development of LIG-based sensors that possess properties for future smart sensors in health care, environmental protection, and industrial production.

FluCell-SELEX Aptamers as Specific Binding Molecules for Diagnostics of the Health Relevant Gut Bacterium Akkermansia muciniphila

Based on their unique properties, oligonucleotide aptamers have been named a gift of biological chemistry to life science. We report the development of DNA aptamers as the first high-affinity binding molecules available for fast and rapid labeling of the human gut bacterium Akkermansia muciniphila with a certain impact on Alzheimer´s disease. Fast and reliable analyses of the composition of microbiomes is an emerging field in microbiology. We describe the molecular evolution and biochemical characterization of a specific aptamer library by a FluCell-SELEX and the characterization of specific molecules from the library by bioinformatics. The aptamer AKK13.1 exerted universal applicability in different analysis techniques in modern microbiology, including fluorimetry, confocal laser scanning microscopy and flow cytometry. It was also functional as a specific binding entity hybridized to anchor primers chemically coupled via acrydite-modification to the surface of a polyacrylamide-hydrogel, which can be prototypically used for the construction of affinity surfaces in sensor chips. Together, the performance and methodological flexibility of the aptamers presented here may open new routes not only to develop novel Akkermansia-specific assays for clinical microbiology and the analyses of human stool samples but may also be an excellent starting point for the construction of novel electronic biosensors.

Label free structure-switching fluorescence polarization detection of chloramphenicol with truncated aptamer

In this study, the original chloramphenicol aptamer containing 80 bases was truncated to 30 bases with high affinity by the SYBR Green I assay. It was found that the ionic strength and type affect the recognition of aptamers, especially magnesium ion played a vital role in the binding process. Furthermore, the binding performance of aptamer, including binding mode, key binding sites and conformational changes were further investigated by circular dichroism spectroscopy, UV-vis absorption spectrum and molecular docking. Based on these research data, we inferred that chloramphenicol bound to the minor groove region in the aptamer double helix. Finally, the optimized aptamer LLR10 was used to develop a novel label free fluorescence polarization assay to detect chloramphenicol within SYBR Green I as the source of fluorescence polarization signal. Under optimal conditions, the designed method showed a linear detection range of 0.1-10 nM with a detection limit of 0.06 nM. Additionally, the aptasensor exhibited a high accuracy to the detection of chloramphenicol in milk samples with a recovery rate from 93.7% to 98.4%. Therefore, the developed label free fluorescence polarization aptasensor provides a new idea for the rapid, reliable and sensitive detection of chloramphenicol, which can be applied to food safety control.

Biosensors for the detection of organophosphate exposure by a new diethyl thiophosphate-specific aptamer

OBJECTIVE

An aptamer specifically binding to diethyl thiophosphate (DETP) was constructed and incorporated in an optical sensor and electrochemical techniques to enable the specific measurement of DETP as a metabolite and a biomarker of organophosphate exposure.

RESULTS

A DETP-bound aptamer was selected from the library using capillary electrophoresis-systematic evolution of ligands by exponential enrichment (CE-SELEX). A colorimetric method revealed that the aptamer had the highest affinity for DETP, with a mean K_d value (± SD) of 0.103 ± 0.014 µM. The docking results and changes in resistance showed that the selectivity of the aptamer for DETP was higher than that for the similar structures of dithiophosphate (DEDTP) and diethyl phosphate (DEP). The altered amplitude of cyclic voltammetry showed a linear range of DETP detection covering 0.0001-10 µg/ml with a limit of detection of 0.007 µg/ml. The recovery value of a real sample of pH 7 was 97.2%.

CONCLUSIONS

The current method showed great promise in using the DETP-specific aptamer to detect the exposure history to organophosphates by measuring their metabolites, although degradation of organophosphate parent compounds might occur.

Selection of DNA Aptamers for Root Exudate l-Serine Using Multiple Selection Strategies

Agricultural biosensing can aid decisions about crop health and maintenance, because crops release root exudates that can inform about their status. l-Serine has been found to be indicative of nitrogen uptake in wheat and canola. The development of a biosensor for l-serine could allow farmers to monitor crop nutrient demands more precisely. The development of robust l-serine-binding DNA aptamers is described. Because small molecules can be challenging targets for Systematic Evolution of Ligands by EXponential enrichment (SELEX), three separate DNA libraries were used for SELEX experiments. A l-homocysteine aptamer was randomized to create a starting library for a l-serine selection (randomized SELEX). The final selection rounds of the l-homocysteine selection were also used as a starting library for l-serine (redirected SELEX). Finally, an original DNA library was used (original SELEX). All three SELEX experiments produced l-serine-binding aptamers with micromolar affinity, with Red.1 aptamer having a K_d of 7.9 ± 3.6 μM. Truncation improved the binding affinity to 5.2 ± 2.7 μM, and from this sequence, a Spiegelmer with improved nuclease resistance was created with a K_d of 2.0 ± 0.8 μM. This l-serine-binding Spiegelmer has the affinity and stability to be incorporated into aptamer-based biosensors for agricultural applications.

Amplified Fluorescent Aptasensor for Ochratoxin A Assay Based on Graphene Oxide and RecJf Exonuclease

In this study, we developed an aptamer-based fluorescent sensing platform for the detection of ochratoxin A (OTA) based on RecJ_f exonuclease-assisted signal amplification and interaction between graphene oxide (GO) and the OTA aptamer (OTA-apt). After optimizing the experimental conditions, the present aptamer-based sensing system can exhibit excellent fluorescent response in the OTA assay, with a limit of detection of 0.07 ng/mL. In addition to signal amplification, this strategy is also highly specific for other interfering toxins. Furthermore, this aptasensor can be reliably used for assessing red wine samples spiked with different OTA concentrations (2.4, 6 and 20 ng/mL). The proposed assay plays an important role in the field of food safety and can be transformed for detecting other toxins by replacing the sequence that recognizes the aptamer.

Mapping the binding region of aptamer targeting small molecule: Dabigatran etexilate, an anti-coagulant

Aptamers are single-stranded DNA or RNA, which have attracted considerable scientific interest due to their characteristic of specific and selective binding to target molecules. They are evolved from the in vitro process known as systematic evolution of ligands by exponential enrichment (SELEX). This paper reports a simple experimental approach to elucidate the binding region of small targets binding aptamers. A previously isolated 60-mer aptamer for the anti-coagulant dabigatran etexilate (DBG) was used for this investigation. Complimentary sequences labelled with a fluorophore and a quencher were used for testing the binding region by change in the fluorescence signal. The full-length aptamer was truncated to multiple shorter copies including a 38 nucleotides sequence that showed 47 fold high affinity compared to the original aptamer. Circular dichroism spectroscopy (CD) measurements indicate that the 38-mer is remarkably more sensitive than the parent aptamer. The truncated 38-mer sequence was used to construct a turn-on fluorescence sensor with the detection limit of 1 nM. The performance of the sensor was examined in blood serum samples and showed excellent recovery percentages exceeding 98%. The reported screening protocol could be applied to the growing small targets aptasensors that require efficient binding aptamer sequences coupled with optimum signal transduction methods.

DNA aptamers targeting Leishmania infantum H3 protein as potential diagnostic tools

Leishmaniasis is a disease caused by a parasite of the genus Leishmania that affects millions of people worldwide. These parasites are characterized by the presence of a DNA-containing granule, the kinetoplastid, located in the single mitochondrion at the base of the cell's flagellum. Interestingly, these flagellates do not condense chromatin during mitosis, possibly due to the specific molecular features of their histones. Although histones are extremely conserved proteins, kinetoplastid core histone sequences diverge significantly from those of higher eukaryotes. This divergence makes kinetoplastid core histones potential diagnostic and/or therapeutic targets. Aptamers are short single-stranded nucleic acids that are able to recognize target molecules with high affinity and specificity. Their binding capacity is a consequence of the particular three-dimensional structure acquired depending on their sequence. These molecules are currently used for detection, diagnosis and therapeutic purpose. Starting from a previously obtained ssDNA aptamer population against rLiH3 protein we have isolated two individual aptamers, AptLiH3#4 and AptLiH3#10. Next, we have performed ELONA, Western blot and slot blot assays to establish aptamer specificity and affinity for LiH3 histone. In addition, ELONA assays using peptides corresponding to overlapped sequences of LiH3 were made to map the aptamers:LiH3 interaction. Finally, different assays using aptamers were performed in order to evaluate the possibility of using these aptamers as sensing molecule to recognize the endogenous protein LiH3. Our results indicate that both aptamers have high affinity and specificity for the target and are able to detect the endogenous LiH3 histone protein in promastigotes lysates. In silico analysis reveals that these two aptamers have different potential secondary structure among them, however, both of them are able to recognize the same peptide sequences present in the protein. In conclusion, our findings indicate that these aptamers could be used for LiH3 histone detection and, in consequence, as potential biosensing molecules in a diagnostic tool for leishmaniasis.

Analytical techniques for the detection of glycated haemoglobin underlining the sensors

The increase in concentrations of blood glucose results arise in the proportion of glycated haemoglobin. Therefore, the percentage of glycated haemoglobin in the blood could function as a biomarker for the average glucose level over the past three months and can be used to detect diabetes. The study of glycated haemoglobin tends to be complex as there are about three hundred distinct assay techniques available for evaluating glycated haemoglobin which contributes to some differences in the recorded values from the similar samples. This review outlines distinct analytical methods that have evolved in the recent past for precise recognition of the glycated - proteins.

Cytokine and Cancer Biomarkers Detection: The Dawn of Electrochemical Paper-Based Biosensor

Although the established ELISA-based sensing platforms have many benefits, the importance of cytokine and cancer biomarkers detection for point-of-care diagnostics has propelled the search for more specific, sensitive, simple, accessible, yet economical sensor. Paper-based biosensor holds promise for future in-situ applications and can provide rapid analysis and data without the need to conduct in a laboratory. Electrochemical detection plays a vital role in interpreting results obtained from qualitative assessment to quantitative determination. In this review, various factors affecting the design of an electrochemical paper-based biosensor are highlighted and discussed in depth. Different detection methods, along with the latest development in utilizing them in cytokine and cancer biomarkers detection, are reviewed. Lastly, the fabrication of portable electrochemical paper-based biosensor is ideal in deliberating positive societal implications in developing countries with limited resources and accessibility to healthcare services.

Aptameric biosensor for the sensitive detection of major shrimp allergen, tropomyosin

The development of a sensitive and rapid detection approach for allergens in various food matrices is essential to assist patients in managing their allergies. The most common methods used for allergen detection are based on immunoassays, PCR and mass spectrometry. However, all of them are very complex and time-consuming. Herein, an aptamer biosensor for the detection of the major shrimp allergen tropomyosin (TM) was developed. Graphene oxide (GO) was used as a platform for screening of the minimal-length aptamer sequence required for high-affinity target binding. A fluorescein dye labeled GO quenches the truncated aptamer by π-stacking interactions. After the addition of TM, the fluorescence was restored due to the competitive binding of the aptamer to GO. One of the truncated aptamers was found to bind to TM with four-fold higher affinity (30 nM) compared to the full-length aptamer (124 nM), with a limit of detection (LOD) of 2 nM. The aptamer-based sensor demonstrates the sensitive, selective, and specific detection of TM in 30 min. The performance of the sensor was confirmed using TM spiked chicken soup, resulting in a high percentage recovery (~97 ± 10%). The association of GO and labelled aptamer sensor platform has shown the rapid detection of TM in food, which is compared to other methods very sensitive, specific and performs in high throughput application.

Detection of target collagen peptides with single amino acid mutation using two fluorescent peptide probes

Collagen with a single amino acid substitution is the main cause of a plethora of heritable disorders such as Osteogenesis Imperfecta and Ehlers-Danlos syndrome. Though significant advances have been achieved in the development of protein assays, it remains very challenging to distinguish a protein with a single amino acid mutation from the wild-type protein. A novel fluorescent self-quenching assay has been constructed to detect target collagen peptides with a single amino acid mutation using two probe peptides. The hybridization of the probe peptide and the natural target collagen peptide results in a complete heterotrimer and strong fluorescence, whereas the mixture of the probe peptide and the mutation collagen sequences leads to a partial homotrimer and pronounced fluorescence self-quenching. The extent of fluorescence quenching is dependent on the identity of the residue replacing Gly following the order of Ala < Ser < Arg, while the Gly-Ala mutation causes the mildest fluorescence loss. The probe peptide-based fluorescence self-quenching assay facilitates specific detection of the target collagen sequence with a single Gly mutation at the nM level. The simultaneous utilization of both probe peptides enables efficient discrimination between different mutation peptides. To our knowledge, our work may be the first report of a robust analytical assay that can identify collagen fragments with single amino acid mutation, which will greatly contribute to deciphering the molecular mechanism of Osteogenesis Imperfecta as well as developing novel diagnostic strategies.

Gluten Detection Methods and Their Critical Role in Assuring Safe Diets for Celiac Patients

Celiac disease, wheat sensitivity, and allergy represent three different reactions, which may occur in genetically predisposed individuals on the ingestion of wheat and derived products with various manifestations. Improvements in the disease diagnostics and understanding of disease etiology unveiled that these disorders are widespread around the globe affecting about 7% of the population. The only known treatment so far is a life-long gluten-free diet, which is almost impossible to follow because of the contamination of allegedly "gluten-free" products. Accidental contamination of inherently gluten-free products could take place at any level from field to shelf because of the ubiquity of these proteins/grains. Gluten contamination of allegedly "gluten-free" products is a constant threat to celiac patients and a major health concern. Several detection procedures have been proposed to determine the level of contamination in products for celiac patients. The present article aims to review the advantages and disadvantages of different gluten detection methods, with emphasis on the recent technology that allows identification of the immunogenic-gluten peptides without the use of antibodies. The possibility to detect gluten contamination by different approaches with similar or better detection efficiency in different raw and processed foods will guarantee the safety of the foods for celiac patients.

Nanotetrahedron-assisted electrochemical aptasensor with cooperatively-folding aptamer chimera for sensitive and selective detection of lysozyme in red wines

Although aptamers show great potential in the field of analytical chemistry, their intrinsic shortcomings of relatively weak affinity and selectivity in complex working environment limit their applicability to real analysis, because the flexibility of aptamers makes the specific aptatopes (i.e., binding sites for targets) in the conformational structure unstable and deficient. Herein, an anti-lysozyme aptamer and lysozyme were chosen as models. An aptamer chimera which could cooperatively fold to provide stable aptatopes for lysozyme was designed for improvement of the anti-lysozyme aptamers' recognition ability, and an electrochemical aptasensor was then developed based on the aptamer chimera, with assistance of a rigid DNA nanotetrahedron as a spacer to orientate the aptamer chimera on the electrodes. The nanotetrahedron-aptamer chimera-based aptasensor presented highly sensitive and selective detection towards lysozyme in red wines, furnishing a 42-fold lower LOD (17.9 pmol L^-1) and better selectivity than that of the aptasensor with the original aptamer. Moreover, the developed aptasensor was characterized by good recovery (91.3-109.0%), good accuracy, repeatability and stability, indicating the excellent practical applicability of the cooperatively-folding aptamer chimera in real world. This proof-of-concept study can be referred for any other aptamers, analytes, and samples.

Label-Free Fluorescent Aptasensor for Small Targets via Displacement of Groove Bound Curcumin Molecules

Signal transduction based on fluorescence is one of the most common optical aptasensors for small molecules. Sensors with a number of unique features including high sensitivity, low cost, and simple operation can be constructed easily. However, the label-free fluorescent approach is limited to synthetic dyes that bind strongly to the aptamer sequence and result in a diminished sensor operation with high detection limits. In this study, we report the use of curcumin as a fluorescent probe to signal aptamer/small target binding events. A substantial enhancement in curcumin's fluorescent emission was observed when bound into the grooves of vitamin D₃ (VTD3) binding aptamer, as an example. However, the introduction of the target molecule causes the aptamer to undergo a conformational change that favors complexing the target molecule over binding the curcumin dye. The sensor was able to detect VTD3 down to 1 fM concentration in buffer solutions and extracted blood samples, operate at a wide dynamic range, and discriminate against potential biological interfering molecules including VTD2. The operation of the curcumin based fluorescent sensor is at least six orders of magnitude more sensitive than a VTD3 sensor constructed with the synthetic dye SYBR Green I. The generality of the reported label-free approach was applied with a previously isolated 75-mer bisphenol-A (BPA) aptamer, confirming that the reported sensing strategy is not confined on a particular aptamer sequence. Our work not only reports a novel sensor format for the detection of small molecules, but also serves fluorescent sensor's most pressing need being novel fluorophores for multiplex targets detection.

A competitive thrombin-linked aptamer assay for small molecule: aflatoxin B1

We described a competitive thrombin-linked aptamer assay for small molecule, using aflatoxin B₁ (AFB₁) as a model, taking advantage of aptamer affinity binding and enzymatic activity of thrombin. We designed a dual functional DNA probe that contained the aptamer sequence for thrombin and the aptamer sequence for AFB₁. Thrombin was labeled on the DNA probe by affinity binding between thrombin and anti-thrombin aptamer. This thrombin-labeled DNA probe was attached on AFB₁-bovine serum albumin conjugate (BSA-AFB₁) coated on a microplate through the affinity interaction between AFB₁ and anti-AFB₁ aptamer. The thrombin attached on the microplate catalyzed the cleavage of peptide substrate into detectable product, generating signal for detection. In the presence of AFB₁, free AFB₁ competed with BSA-AFB₁ in the binding to the limited amount of DNA probe, leading to signal decrease. Detection of AFB₁ was achieved by measuring the signal change. Under optimized conditions, AFB₁ was successfully detected in the range from 0.5 nM to 1 μM when fluorogenic peptide substrate of thrombin and fluorescence analysis were applied. The use of chromogenic peptide substrate in the assay allowed the detection of AFB₁ ranging from 0.5 to 125 nM by simple absorbance analysis. The thrombin-linked aptamer assay showed good selectivity towards AFB₁, and enabled the detection of AFB₁ spiked in diluted beer and corn flour. This TLAA strategy extends the analytical application of thrombin and aptamers in detection of small molecules. Graphical abstract.

Systematic truncating of aptamers to create high-performance graphene oxide (GO)-based aptasensors for the multiplex detection of mycotoxins

Graphene oxide (GO)-based aptasensors are currently one of the most popular sensing platforms for the simple and rapid detection of various targets. Unfortunately, the GO-based aptasensors with long aptamer strands typically show unsatisfactory performance resulting from insignificant structural transformations upon target binding. We report herein the utilization of an aptamer-truncating strategy to combat such a challenge. Taking a pre-selected anti-aflatoxin B1 (AFB1) aptamer (P-AFB1-50) as a trial system, we sequentially remove the extraneous nucleotides within the aptamer by means of circular dichroism (CD) spectroscopy and binding affinity analysis. Particularly, the ratio of the quenching constants between the GO sheets and the truncated aptamers (labelled with fluorophores) in the absence and presence of the target was determined for each of the truncated aptamers to evaluate the optimal sequence. As a result, the truncated aptamer comprising 40 nucleotides was confirmed to show the highest FL output and the best detection limit upon conjugation with GO sheets. More importantly, we demonstrated that this truncating strategy is versatile, i.e., it can be easily extended to other aptamer systems (anti-ochratoxin A (OTA) aptamer, P-OTA-61, as an example) for extraneous nucleotide identification. Impressively, the two optimal truncated aptamers can work together on GO sheets to achieve a simultaneous detection of two different mycotoxins (i.e., AFB1 and OTA) in one single test. Essentially, this research opens a new avenue for the design and testing of aptamer-/GO-based-sensing platforms for rapid, low-cost and multiplex quantification of analytical targets of interest.

Fluorometric determination of lipopolysaccharides via changes of the graphene oxide-enhanced fluorescence polarization caused by truncated aptamers

A broad-spectrum ssDNA aptamer containing 80 nucleotides (LA80) and capable of binding to four different sources of lipopolysaccharides (LPSs) was truncated. Two strategies are used to produce truncated aptamers of different length. The results show that LA27, a 27-nt aptamer, retained broad-spectrum capability and has a higher affinity (K_d = 46.2 ± 9.5 nM). A graphene oxide based fluorescence polarization assay (excitation/emission wavelengths: 485/520 nm) was worked out using FAM-labeled LA27. It can detect LPSs from Salmonella entericaserotype typhimurium, Pseudomonas aeruginosa 10 and Escherichia coli 055:B5 with enhanced performance (4.8 to 29-fold improvements) compared to LA80. The assay can be performed within 30 min, and the detection limits are 38.7, 88.0 and 154 ng·mL^-1, respectively. Graphical abstract Schematic presentation of the assay: A shorter aptamer, with higher affinity than its original aptamer, was obtained by truncated strategies. This core aptamer lead to release easily and enhance the sensivity of the GO-based fluorescence polarization assay.

Functional-DNA-Driven Dynamic Nanoconstructs for Biomolecule Capture and Drug Delivery

The discovery of sequence-specific hybridization has allowed the development of DNA nanotechnology, which is divided into two categories: 1) structural DNA nanotechnology, which utilizes DNA as a biopolymer; and 2) dynamic DNA nanotechnology, which focuses on the catalytic reactions or displacement of DNA structures. Recently, numerous attempts have been made to combine DNA nanotechnologies with functional DNAs such as aptamers, DNAzymes, amplified DNA, polymer-conjugated DNA, and DNA loaded on functional nanoparticles for various applications; thus, the new interdisciplinary research field of "functional DNA nanotechnology" is initiated. In particular, a fine-tuned nanostructure composed of functional DNAs has shown immense potential as a programmable nanomachine by controlling DNA dynamics triggered by specific environments. Moreover, the programmability and predictability of functional DNA have enabled the use of DNA nanostructures as nanomedicines for various biomedical applications, such as cargo delivery and molecular drugs via stimuli-mediated dynamic structural changes of functional DNAs. Here, the concepts and recent case studies of functional DNA nanotechnology and nanostructures in nanomedicine are reviewed, and future prospects of functional DNA for nanomedicine are indicated.

Label-Free Detection of Tear Biomarkers Using Hydrogel-Coated Gold Nanoshells in a Localized Surface Plasmon Resonance-Based Biosensor

The dependence of the localized surface plasmon resonance (LSPR) of noble-metal nanomaterials on refractive index makes LSPR a useful, label-free signal transduction strategy for biosensing. In particular, by decorating gold nanomaterials with molecular recognition agents, analytes of interest can be trapped near the surface, resulting in an increased refractive index surrounding the nanomaterial, and, consequently, a red shift in the LSPR wavelength. Ionic poly( N-isopropylacrylamide- co-methacrylic acid) (PNM) hydrogels were used as protein receptors because PNM nanogels exhibit a large increase in refractive index upon protein binding. Specifically, PNM hydrogels were synthesized on the surface of silica gold nanoshells (AuNSs). This composite material (AuNS@PNM) was used to detect changes in the concentration of two protein biomarkers of chronic dry eye: lysozyme and lactoferrin. Both of these proteins have high isoelectric points, resulting in electrostatic attraction between the negatively charged PNM hydrogels and positively charged proteins. Upon binding lysozyme or lactoferrin, AuNS@PNM exhibits large, concentration-dependent red shifts in LSPR wavelength, which enabled the detection of clinically relevant concentration changes of both biomarkers in human tears. The LSPR-based biosensor described herein has potential utility as an affordable screening tool for chronic dry eye and associated conditions.

Development of aptamer fluorescent switch assay for aflatoxin B1 by using fluorescein-labeled aptamer and black hole quencher 1-labeled complementary DNA

Aflatoxin B1 (AFB1) is one of the most toxic mycotoxins and draws great concern in health and food safety. A DNA aptamer against AFB1 having a stem-loop structure shows high binding affinity to AFB1 and promise in assay development for AFB1 detection. Based on the structure-switching property of the aptamer, we report an aptamer fluorescence assay for AFB1 detection. Aptamer with fluorescein (FAM) label at 5' end was used as affinity ligand, while its short complementary DNA (cDNA) with BHQ1 (black hole quencher 1) label at 3' end was used as a quencher. In the absence of AFB1, FAM-labeled aptamer hybridized with BHQ1-labeled cDNA, forming a duplex of cDNA and aptamer, resulting in fluorescence quenching of FAM. When AFB1 bound with aptamer, the BHQ1-labeled cDNA was displaced from aptamer, causing fluorescence restoration of FAM. We tested a series of FAM-labeled aptamers and BHQ1-labeled cDNAs with different lengths. The lengths of the aptamer stem and the cDNA, Mg²⁺ in binding buffer, and temperature had significant influence on the performance of the assay. Under optimized conditions, we achieved sensitive detection of AFB1 by using a 29-mer FAM-labeled aptamer and a 14-mer BHQ1-labeled cDNA, and the detection limit of AFB1 reached 0.2 nM. The maximum fluorescence recovery rate of FAM-labeled aptamer caused by AFB1 was about 69-fold. This method enabled the detection of AFB1 in complex sample matrix, e.g., diluted wine samples and maize flour samples. This aptamer-based fluorescent assay for AFB1 determination shows potential for broad applications. Graphical abstract ᅟ.

Current Conjugation Methods for Immunosensors

Recent advances in the development of immunosensors using polymeric nanomaterials and nanoparticles have enabled a wide range of new functions and applications in diagnostic and prognostic research. One fundamental challenge that all immunosensors must overcome is to provide the specificity of target molecular recognition by immobilizing antibodies, antibody fragments, and/or other peptides or oligonucleotide molecules that are capable of antigen recognition on a compact device surface. This review presents progress in the application of immobilization strategies including the classical adsorption process, affinity attachment, random cross-linking and specific covalent linking. The choice of immobilization methods and its impact on biosensor performance in terms of capture molecule loading, orientation, stability and capture efficiency are also discussed in this review.

Real-time and label-free detection of bisphenol A by an ssDNA aptamer sensor combined with dual polarization interferometry

DPI is an efficient and reliable platform for detection of organic pollutants and toxicants.

Detection of human neutrophil elastase by aptamer affinity capillary electrophoresis coupled with laser-induced fluorescence using specified site fluorescently labeled aptamer

As a multifunctional serine protease, human neutrophil elastase (HNE) plays critical roles in a variety of physiopathological processes, such as acute lung injury, emphysema, atherosclerosis, and arthritis. The quantification of HNE is important in many applications. In this paper, we report an aptamer affinity capillary electrophoresis coupled with laser-induced fluorescence (CE-LIF) assay for detection of HNE using a tetramethylrhodamine (TMR)-labeled DNA aptamer probe. The affinity complex of HNE and DNA aptamer probe was well separated from the unbound aptamer probe in CE separation based on the difference of electrophoretic mobility. Broad complex peaks appeared due to possible multiple binding. The 45-mer aptamer having TMR labeling on the 40th T base was used as affinity probe, as larger complex peaks were obtained. We investigated the effects of various metal cations (Na⁺, K⁺, and Mg²⁺) in sample buffer on the binding of HNE and the aptamer in CE-LIF analysis. The presence of Na⁺, K⁺, or Mg²⁺ in sample buffer caused a decrease of complex peaks, and Mg²⁺ showed a larger effect. Under optimized conditions, this aptamer CE-LIF assay enabled the detection of HNE at 0.5 nM. This assay showed good specificity and allowed for detection of HNE spiked in diluted human serum sample. Graphical abstract The complex of HNE and DNA aptamer probe was isolated from the unbound aptamer probe in CE separation due to difference of electrophoretic mobility, allowing a CE-LIF assay for HNE.

Unraveling Prion Protein Interactions with Aptamers and Other PrP-Binding Nucleic Acids

Transmissible spongiform encephalopathies (TSEs) are a group of neurodegenerative disorders that affect humans and other mammals. The etiologic agents common to these diseases are misfolded conformations of the prion protein (PrP). The molecular mechanisms that trigger the structural conversion of the normal cellular PrP (PrP^C) into the pathogenic conformer (PrP^Sc) are still poorly understood. It is proposed that a molecular cofactor would act as a catalyst, lowering the activation energy of the conversion process, therefore favoring the transition of PrP^C to PrP^Sc. Several in vitro studies have described physical interactions between PrP and different classes of molecules, which might play a role in either PrP physiology or pathology. Among these molecules, nucleic acids (NAs) are highlighted as potential PrP molecular partners. In this context, the SELEX (Systematic Evolution of Ligands by Exponential Enrichment) methodology has proven extremely valuable to investigate PrP–NA interactions, due to its ability to select small nucleic acids, also termed aptamers, that bind PrP with high affinity and specificity. Aptamers are single-stranded DNA or RNA oligonucleotides that can be folded into a wide range of structures (from harpins to G-quadruplexes). They are selected from a nucleic acid pool containing a large number (10¹⁴–10¹⁶) of random sequences of the same size (~20–100 bases). Aptamers stand out because of their potential ability to bind with different affinities to distinct conformations of the same protein target. Therefore, the identification of high-affinity and selective PrP ligands may aid the development of new therapies and diagnostic tools for TSEs. This review will focus on the selection of aptamers targeted against either full-length or truncated forms of PrP, discussing the implications that result from interactions of PrP with NAs, and their potential advances in the studies of prions. We will also provide a critical evaluation, assuming the advantages and drawbacks of the SELEX (Systematic Evolution of Ligands by Exponential Enrichment) technique in the general field of amyloidogenic proteins.

Highly Sensitive Detection of Bisphenol A by NanoAptamer Assay with Truncated Aptamer

For the sensitive quantification of bisphenol A (BPA), we have developed NanoAptamer assay, which employs aptamer and complementary signaling DNA, a set of quantum dots (QD), and magnetic beads (MBs). Signaling DNA-QD₆₅₅ was tethered to MB-QD₅₆₅ via the aptamer. The affinity of the aptamer to BPA resulted in the release of the signaling DNA-QD₆₅₅ from the complex and hence the corresponding decrease in the QD₆₅₅ fluorescence measurement signal. Three new aptamers (23, 58, and 24-mer) were designed via truncation of the reference aptamer (73-mer). The sensitivity and selectivity of each aptamer for BPA detection via NanoAptamer assay were investigated. One of the truncated aptamers (24-mer) has shown a significantly better performance (limit of detection, LOD, 0.17 pg/mL) than the reference 73-mer aptamer (LOD, 570 pg/mL). It has also shown the best selectivity for BPA detection over BPA analogues (i.e., bisphenol B, bisphenol C, and diethylstilbestrol). It corresponded to a normalized fluorescence change of 33.7% at the environmentally relevant concentration of 1 ng/mL (1 ppb) BPA; however, the analogues remained unchanged (2.3-3.9%).

Direct fluorescence anisotropy assay for cocaine using tetramethylrhodamine-labeled aptamer

Development of simple, sensitive, and rapid method for cocaine detection is important in medicine and drug abuse monitoring. Taking advantage of fluorescence anisotropy and aptamer, this study reports a direct fluorescence anisotropy (FA) assay for cocaine by employing an aptamer probe with tetramethylrhodamine (TMR) labeled on a specific position. The binding of cocaine and the aptamer causes a structure change of the TMR-labeled aptamer, leading to changes of the interaction between labeled TMR and adjacent G bases in aptamer sequence, so FA of TMR varies with increasing of cocaine. After screening different labeling positions of the aptamer, including thymine (T) bases and terminals of the aptamer, we obtained a favorable aptamer probe with TMR labeled on the 25th base T in the sequence, which exhibited sensitive and significant FA-decreasing responses upon cocaine. Under optimized assay conditions, this TMR-labeled aptamer allowed for direct FA detection of cocaine as low as 5 μM. The maximum FA change reached about 0.086. This FA method also enabled the detection of cocaine spiked in diluted serum and urine samples, showing potential for applications. Graphical Abstract The binding of cocaine to the TMR-labeled aptamer causes conformation change and alteration of the intramolecular interaction between TMR and bases of aptamer, leading to variance of fluorescence anisotropy (FA) of TMR, so direct FA analyis of cocaine is achieved.

A novel method for detection of H9N2 influenza viruses by an aptamer-real time-PCR

H9N2 Influenza subtype has emerged in Tunisia causing epidemics in poultry and resulting in major economic losses. New mutations in their hemagglutinin and neuraminidase proteins were acquired, suggesting their potential to directly infect humans. Effective surveillance tools should be implemented to help prevent potential spillover of the virus across species. We have developed a highly sensitive real time immuno-polymerase chain reaction (RT-I-PCR) method for detecting H9N2 virus. The assay applies aptamers as ligands to capture and detect the virus. First, a panel of specific ssDNA aptamers was selected via a one step high stringency protocol. Next, the panel of selected aptamers was characterized for their affinities and their specificity to H9N2 virus. The aptamer showing the highest binding affinity to the virus was used as ligand to develop a highly sensitive sandwich Aptamer I-PCR. A 3-log increase in analytical sensitivity was achieved as compared to a routinely used ELISA antigen test, highlighting the potential of this approach to detect very low levels of virus particles. The test was validated using clinical samples and constitutes a rapid and a label-free platform, opening a new venue for the development of aptamer -based viability sensing for a variety of microorganisms of economic importance in Tunisia and surrounding regions.

An aptamer assay using rolling circle amplification coupled with thrombin catalysis for protein detection

We describe a sensitive aptamer-based sandwich assay for protein detection on microplate by using rolling circle amplification (RCA) coupled with thrombin catalysis. This assay takes advantage of RCA generating long DNA oligonucleotides with repeat thrombin-binding aptamer sequence, specific aptamer affinity binding to achieve multiple thrombin labeling, and enzyme activity of thrombin for signal generation. Protein target is specifically captured by antibody-coated microplate. Then, an oligonucleotide containing an aptamer for protein and a primer sequence is added to form a typical sandwich structure. Following a template encoded with complementary sequence of aptamer for thrombin, RCA reaction extends the primer sequence into a long oligonucleotide. Many thrombin molecules bind with the RCA product. Thrombin catalyzes the conversion of its chromogenic or fluorogenic peptide substrates into detectable products for final quantification of protein targets. We applied this strategy to the detection of a model protein target, platelet-derived growth factor-BB (PDGF-BB). Due to double signal amplifications from RCA and thrombin catalysis, this assay enabled the detection of PDGF-BB as low as 3.1 pM when a fluorogenic peptide substrate was used. This assay provides a new way for signal generation in RCA-involved assay through direct thrombin labeling, circumventing time-consuming preparation of enzyme-conjugate and affinity probes. This method has promise for a variety of analytical applications.

Integrated microfluidic system for rapid detection of influenza H1N1 virus using a sandwich-based aptamer assay

The rapid spread of influenza-associated H1N1 viruses has caused serious concern in recent years. Therefore, there is an urgent need for the development of automatic, point-of-care devices for rapid diagnosis of the influenza virus. Conventional approaches suffer from several critical issues; notably, they are time-consuming, labor-intensive, and are characterized by relatively low sensitivity. In this work, we present a new approach for fluorescence-based detection of the influenza A H1N1 virus using a sandwich-based aptamer assay that is automatically performed on an integrated microfluidic system. The entire detection process was shortened to 30min using this chip-based system which is much faster than the conventional viral culture method. The limit of detection was significantly improved to 0.032 hemagglutination unit due to the high affinity and high specificity of the H1N1-specific aptamers. The results showed that the two-aptamer microfluidic system had about 10(3) times higher sensitivity than the conventional serological diagnosis. It was demonstrated that the developed microfluidic system may play as a powerful tool in the detection of the H1N1 virus.

A review on electronic bio-sensing approaches based on non-antibody recognition elements

In this review, recent advances in the development of electronic detection methodologies based on non-antibody recognition elements such as functional liposomes, aptamers and synthetic peptides are discussed. Particularly, we highlight the progress of field effect transistor (FET) sensing platforms where possible as the number of publications on FET-based platforms has increased rapidly. Biosensors involving antibody-antigen interactions have been widely applied in diagnostics and healthcare in virtue of their superior selectivity and sensitivity, which can be attributed to their high binding affinity and extraordinary specificity, respectively. However, antibodies typically suffer from fragile and complicated functional structures, large molecular size and sophisticated preparation approaches (resource-intensive and time-consuming), resulting in limitations such as short shelf-life, insufficient stability and poor reproducibility. Recently, bio-sensing approaches based on synthetic elements have been intensively explored. In contrast to existing reports, this review provides a comprehensive overview of recent advances in the development of biosensors utilizing synthetic recognition elements and a detailed comparison of their assay performances. Therefore, this review would serve as a good summary of the efforts for the development of electronic bio-sensing approaches involving synthetic recognition elements.

Synthetic genetic polymers: advances and applications

Advances and applications of synthetic genetic polymers (xeno-nucleic acids) are reviewed in this article. The types of synthetic genetic polymers are summarized. The basic properties of them are elaborated and their technical applications are presented. Challenges and prospects of synthetic genetic polymers are discussed.

DNA Aptamers in the Diagnosis and Treatment of Human Diseases

Aptamers have a promising role in the field of life science and have been extensively researched for application as analytical tools, therapeutic agents and as vehicles for targeted drug delivery. Compared with RNA aptamers, DNA aptamers have inherent advantages in stability and facility of generation and synthesis. To better understand the specific potential of DNA aptamers, an overview of the progress in the generation and application of DNA aptamers in human disease diagnosis and therapy are presented in this review. Special attention is given to researches that are relatively close to practical application. DNA aptamers are expected to have great potential in the diagnosis and treatment of human diseases.

Screening and Identification of ssDNA Aptamer for Human GP73

As one tumor marker of HCC, Golgi Protein 73 (GP73) is given more promise in the early diagnosis of HCC, and aptamers have been developed to compete with antibodies as biorecognition probes in different detection system. In this study, we utilized GP73 to screen specific ssDNA aptamers by SELEX technique. First, GP73 proteins were expressed and purified by prokaryotic expression system and Nickle ion affinity chromatography, respectively. At the same time, the immunogenicity of purified GP73 was confirmed by Western blotting. The enriched ssDNA library with high binding capacity for GP73 was obtained after ten rounds of SELEX. Then, thirty ssDNA aptamers were sequenced, in which two ssDNA aptamers with identical DNA sequence were confirmed, based on the alignment results, and designated as A10-2. Furthermore, the specific antibody could block the binding of A10-2 to GP73, and the specific binding of A10-2 to GP73 was also supported by the observation that several tumor cell lines exhibited variable expression level of GP73. Significantly, the identified aptamer A10-2 could distinguish normal and cancerous liver tissues. So, our results indicate that the aptamer A10-2 might be developed into one molecular probe to detect HCC from normal liver specimens.