What is SELEX and What are Aptamers? Aptamers: Often called "chemical antibodies," they are short, single-stranded DNA or RNA oligonucleotides that fold into specific 3D shapes to bind with high affinity and specificity to a target molecule (e.g., a viral protein, whole bacterium, or parasite surface marker). SELEX (Systematic Evolution of Ligands by EXponential enrichment): This is the iterative combinatorial chemistry process used to discover aptamers from a vast random library (10^14-10^15 unique sequences). It involves repeated cycles of: 1) Binding the library to the target, 2) Separating bound from unbound sequences, 3) Amplifying the bound sequences, and 4) Starting a new, enriched cycle. Core Components of a Pathogen SELEX Service A professional service will typically manage the entire pipeline: 1. Project Design & Target Preparation: Consultation: Defining the precise target (e.g., whole inactivated SARS-CoV-2, Salmonella outer membrane protein, Plasmodium lysate). Counter-SELEX: A critical step for pathogen specificity. The process is run against related non-targets (e.g., host cells, non-pathogenic bacterial strains) to filter out cross-reactive aptamers, ensuring the final aptamers distinguish between pathogen and non-pathogen. 2. The SELEX Execution: Performing multiple (usually 8-15) rounds of the selection process under optimized conditions (buffer, temperature, washing stringency). 3. Next-Generation Sequencing (NGS) & Bioinformatics: After the final rounds, the enriched pool is sequenced using NGS. Bioinformatic analysis identifies sequence…
What is a Bacterial Aptamer Screening Service? It is a specialized contract research service where a provider uses Systematic Evolution of Ligands by Exponential Enrichment (SELEX) to discover and develop single-stranded DNA or RNA aptamers that bind with high affinity and specificity to a bacterial target. The target can be: Whole bacterial cells (e.g., E. coli O157:H7, Salmonella typhimurium). Specific bacterial components (e.g., surface proteins like pili, flagella, capsular polysaccharides, secreted toxins). Key virulence factors (e.g., endotoxins like LPS). The resulting aptamers are powerful recognition elements for diagnostics, therapeutics, and research. Core Steps in the Service Pipeline A typical full-service offering includes: 1. Project Design & Target Preparation: Consultation: Defining the goal (e.g., detection of a specific strain, therapeutic neutralization). Target Choice: Deciding between whole cells (for broad detection) or purified components (for precise targeting). Counter-SELEX: Using related non-target cells (e.g., non-pathogenic strain) to eliminate cross-reactive aptamers and ensure specificity. 2. Library Synthesis & SELEX Process: Library Design: Using a random-sequence oligonucleotide library (typically ~10^14 different molecules). Selection Rounds (8-15 cycles): Iteratively incubating the library with the target, washing away unbound sequences, eluting the bound ones, and amplifying them via PCR (for DNA) or RT-PCR (for RNA). Monitoring: Using quantitative PCR or flow cytometry to track enrichment progress. 3. Next-Generation Sequencing (NGS) & Bioinformatics:…
What is a Metal Ion-Targeted Aptamer Screening Service? It is a contract research service where a specialized laboratory uses an in vitro selection process (most commonly SELEX - Systematic Evolution of Ligands by EXponential Enrichment) to identify single-stranded DNA or RNA oligonucleotides (aptamers) that bind with high affinity and specificity to a specific metal ion (e.g., Pb²⁺, Hg²⁺, UO₂²⁺, As³⁺, Cd²⁺). Unlike aptamers for proteins, metal ion aptamers often rely on the ion's unique coordination chemistry to induce a specific fold or structural switch in the oligonucleotide. Core Service Workflow (The Screening Process) A typical service provider would follow these steps: Design & Library Synthesis: Creation of a vast random-sequence oligonucleotide library (10¹⁴ - 10¹⁵ different sequences). Target Preparation: The target (e.g., Pb²⁺) is often presented in a specific buffer system that controls charge, pH, and the presence of competing ions to drive selection for the desired specificity. Selection Rounds (SELEX Cycle): Binding: Incubate the library with the target metal ion. Partition: Separate metal-bound sequences from unbound ones. This is the most critical and challenging step for small ions. Techniques include: Immobilization: Cheating the ion to a solid support (beads). Capture-SELEX: Using a complementary strand or an auxiliary molecule. Size-based separation: If binding induces a conformational change (e.g., dimerization). Amplification: PCR (for…
1. What Are Aptamers? Aptamers are short, single-stranded DNA or RNA oligonucleotides (typically 20-80 bases) that fold into specific 3D structures, allowing them to bind to target molecules (like hormones) with high affinity and specificity, similar to antibodies. They are often called "chemical antibodies." 2. Why Target Hormones with Aptamers? Hormones are critical signaling molecules (e.g., insulin, cortisol, thyroid hormones, estradiol, adrenaline). Aptamers against them offer unique advantages: High Specificity: Can distinguish between structurally similar hormones (e.g., T3 vs. T4). Synthetic & Reproducible: Produced chemically with minimal batch-to-batch variation. Stability: More thermally stable than antibodies. Modifiability: Can be easily labeled with fluorescent dyes, quenchers, or nanoparticles for detection. Low Immunogenicity: Ideal for in vivo diagnostic or therapeutic applications. 3. Core Components of the Screening Service A full-service provider would typically offer the following pipeline: a. Design & Library Construction: Use of a vast random oligonucleotide library (10^14 - 10^15 unique sequences). Customization of library design based on hormone properties (small molecule vs. peptide/protein). b. SELEX Process (The Core Screening): This is an iterative, in vitro selection process. Incubation: The library is exposed to the target hormone (immobilized or in solution). Partitioning: Unbound sequences are washed away; bound sequences (aptamer candidates) are retained. Elution & Amplification: Bound sequences are eluted and amplified by PCR…
What is an Aptamer? First, a quick definition: Aptamers are short, single-stranded DNA or RNA oligonucleotides that bind to a specific target molecule (like proteins, toxins, cells) with high affinity and specificity. They are often called "chemical antibodies" but offer advantages like easier synthesis, higher stability, and lower cost. What is Toxin-Targeted Aptamer Screening? This service involves the in vitro selection and development of custom aptamers designed to bind specifically to a toxic substance. The core technology is called SELEX (Systematic Evolution of Ligands by EXponential enrichment). The process screens vast random libraries (10^14 - 10^15 different sequences) against the toxin to isolate the few sequences that bind tightly and specifically. Key Steps in the Service Pipeline Project Consultation & Target Definition: Clarify the toxin (e.g., mycotoxins like Aflatoxin B1, marine toxins like Saxitoxin, bacterial toxins like Botulinum, environmental toxins like heavy metals). Define the desired application (Detection/Biosensing, Neutralization, Capture/Purification). Specify the sample matrix (food extract, blood serum, environmental water). Library Design & SELEX Strategy: Design of a naive single-stranded DNA or RNA library. Choosing the appropriate SELEX variant: Negative Selection/Counter-SELEX: To exclude sequences that bind to similar non-toxin molecules or the assay matrix (crucial for specificity). Capture-SELEX: For small toxins that can't be immobilized. Cell-SELEX: If the…
Antibody: A large, Y-shaped protein produced naturally by the immune system (B cells) in response to a foreign substance (antigen). It is a biological molecule. Aptamer: A short, single-stranded piece of DNA or RNA (or modified nucleotides) that is artificially engineered in a lab to bind to a specific target. It is a chemical molecule. Key Differences at a Glance Feature Antibody Aptamer Chemical Nature Protein (IgG, etc.) Nucleic Acid (DNA or RNA) Origin Biological (from animals) Chemical (SELEX process in vitro) Size Large (~150 kDa) Small (~10-30 kDa) Production Requires animal immunization or cell culture. Batch-to-batch variability possible. Synthetic, produced by chemical synthesis. Highly reproducible. Targets Primarily immunogenic targets (proteins, pathogens). Limited to targets that elicit an immune response. Extremely broad: ions, small molecules, proteins, cells, viruses, tissues. Can target toxins or non-immunogenic substances. Stability Sensitive to temperature (often requires refrigeration), pH, and proteases. Can denature. Thermally stable, can be renatured after denaturation. Resistant to harsh conditions (pH, organic solvents). Modification Difficult to modify chemically without affecting function. Site-specific conjugation is complex. Easy to chemically modify with reporters, drugs, or linkers at precise locations. Immunogenicity Can itself trigger an immune response (especially non-human antibodies). Generally low immunogenicity, but can be designed to be non-immunogenic. Cost…
1. Therapeutics & Medicine This is one of the most promising areas. Drugs: The first FDA-approved aptamer drug is Pegaptanib (Macugen) for treating age-related macular degeneration. It binds to VEGF, a protein that promotes abnormal blood vessel growth. Targeted Drug Delivery: Aptamers can be attached to drug nanoparticles or toxins, acting as a "homing device" to deliver the payload specifically to cancer cells or diseased tissues, minimizing side effects. Antidotes: "Antidote" or control oligonucleotides can be designed to bind and deactivate an aptamer's function, allowing for precise control of therapeutic activity—something very difficult with antibodies. Antiviral & Antibacterial Agents: They can bind to and neutralize viruses (like HIV, influenza, SARS-CoV-2) or specific bacterial proteins. 2. Diagnostics & Biosensing Aptamers are powerful tools for detecting molecules. Aptamer-based Assays: Used in ELISA-like formats (sometimes called ELASA) to detect biomarkers for diseases (cancer, infections) in blood or other samples. Point-of-Care Tests: Integrated into portable biosensors (aptasensors) for rapid, on-site detection of pathogens, toxins, or hormones. They can use optical, electrochemical, or mass-sensitive methods. Medical Imaging: Labeled with fluorescent dyes or radioisotopes, aptamers can help visualize tumors or diseased tissues during surgery or in scans. 3. Research & Biotechnology Protein Function Studies: Used to inhibit specific proteins in cells or in vitro to study their biological function, similar to using…
Aptamers are single-stranded DNA or RNA oligonucleotides (typically 20-80 bases) that fold into specific 3D structures capable of binding target molecules with high affinity and specificity, earning them the nickname "chemical antibodies." Their unique properties make them promising agents for targeted liver cancer therapy. Why Aptamers Are Suitable for Liver Cancer Targeting Molecular Recognition Capabilities Can be selected against specific liver cancer biomarkers (ASGPR, GPC3, EGFR, etc.) High binding affinity (nM to pM range) Specific discrimination between cancerous and normal hepatocytes Advantages Over Antibodies Smaller size (5-25 kDa) for better tissue penetration Chemical synthesis without batch variation Lower immunogenicity Easier modification and conjugation Higher thermal stability Key Targeting Strategies for Liver Cancer 1. Targeted Drug Delivery Aptamer-drug conjugates: Direct conjugation of chemotherapeutic agents (doxorubicin, sorafenib derivatives) Nano-carrier guidance: Aptamers decorating nanoparticles, liposomes, or micelles containing drugs Targeted prodrug activation: Aptamer-mediated delivery of enzyme prodrug systems 2. Targeted Gene Therapy Delivery of siRNA/miRNA to regulate oncogene expression CRISPR/Cas9 delivery for gene editing Examples: Anti-GPC3 aptamers delivering VEGF siRNA to inhibit angiogenesis 3. Multifunctional Theranostic Applications Combined imaging (fluorescence, PET, MRI) and therapy Aptamer-conjugated agents for image-guided surgery or ablation 4. Immomodulation Targeting immune checkpoint molecules (PD-1/PD-L1) Redirecting immune cells to tumor sites Clinically Relevant Targets…
Why Aptamers are Promising for Liver Cancer Imaging Compared to traditional antibodies, aptamers offer key advantages for in vivo applications: Small Size (5-15 kDa): Enables better tissue penetration and faster blood clearance, leading to higher tumor-to-background ratios. Low Immunogenicity: Reduced risk of allergic reactions or neutralization upon repeated administration. Ease of Chemical Synthesis & Modification: Can be stably produced, and easily conjugated with dyes, radionuclides, or nanoparticles. Rapid Tissue Penetration & Clearance: Ideal for imaging shortly after injection. Engineerable Flexibility: Can be designed as multivalent or bispecific constructs. Key Steps in Developing Aptamers for Liver Cancer Imaging Target Selection: Identifying a molecule highly expressed on liver cancer cells but low on normal hepatocytes is critical. Prime targets include: Glypican-3 (GPC3): A heparan sulfate proteoglycan overexpressed in 70-80% of hepatocellular carcinomas (HCC). Alpha-fetoprotein (AFP): A classic serum biomarker, with membrane-bound forms also present on HCC cells. Epithelial Cell Adhesion Molecule (EpCAM): Expressed on cancer stem cells in HCC and cholangiocarcinoma. Asialoglycoprotein Receptor (ASGPR): Highly expressed on normal hepatocytes but often dysregulated in HCC; useful for "background" subtraction or targeting specific isoforms. Receptor Tyrosine Kinases: Like c-Met or VEGFR2. Aptamer Generation: Typically done via SELEX (Systematic Evolution of Ligands by EXponential enrichment). For liver cancer, Cell-SELEX using live HCC cells vs. normal hepatocytes is preferred, as it identifies aptamers…
Aptamers are emerging as powerful molecular tools for the in vitro detection of liver cancer, offering a promising alternative to traditional antibodies. Here’s a comprehensive breakdown: What are Aptamers? Aptamers are short, single-stranded DNA or RNA oligonucleotides (or peptides) that bind to specific target molecules (proteins, cells, small molecules) with high affinity and specificity. They are selected in vitro through a process called SELEX (Systematic Evolution of Ligands by Exponential Enrichment). Why Aptamers for Liver Cancer Diagnosis? Compared to conventional antibodies, aptamers offer key advantages for diagnostics: High Specificity & Affinity: Can distinguish between healthy and cancerous biomarkers. Small Size: Better tissue penetration and access to epitopes. In Vitro Synthesis: Chemically produced, resulting in low batch-to-batch variation. Stability: Thermally stable and easily modifiable. Non-Immunogenic: Suitable for repeated use in assays. Key Targets for Liver Cancer Detection Aptamers are developed to detect liver cancer (primarily Hepatocellular Carcinoma, HCC) by targeting: Circulating Protein Biomarkers: Alpha-fetoprotein (AFP): The most widely used serum biomarker for HCC, but with limited sensitivity/specificity. AFP-specific aptamers are used in electrochemical, fluorescent, and colorimetric sensors to improve detection limits. Glypican-3 (GPC3): A cell-surface proteoglycan overexpressed in >70% of HCCs. GPC3 aptamers are central to many sensitive detection platforms. Vascular Endothelial Growth Factor (VEGF): Associated with angiogenesis and metastasis. Platelet-Derived Growth Factor (PDGF): Involved in…
