Core Principle: Real-Time Interaction Analysis An SPR biosensor (e.g., Biacore, Nicoya Lifesciences) detects changes in the refractive index on a thin gold sensor surface. Target Immobilization: The pathogen target (e.g., a purified viral protein) is covalently coupled to the sensor chip surface in a controlled manner. Library Injection: The random-sequence DNA/RNA library is flowed over the chip in a continuous buffer stream. Real-Time Monitoring: The SPR signal (measured in Resonance Units, RU) increases as library members bind to the immobilized target. Precise Fraction Collection: Instead of manual washing and elution, the instrument's microfluidic system can collect the specifically bound sequences by switching to an elution buffer (e.g., high salt, low pH, or denaturing conditions) at a precisely defined moment, often based on the real-time binding curve. Amplification: The collected fraction is PCR-amplified to generate the pool for the next round. Typical SPR-SELEX Service Workflow 1. Chip Preparation & Target Immobilization: The service provider will select an appropriate sensor chip (e.g., CMS carboxymethyl dextran) and optimal chemistry (amine coupling, streptavidin-biotin) to immobilize the client's purified target, ensuring a stable, active, and oriented surface. 2. Selection Rounds with Kinetic Control: Library Contact: The naïve or enriched pool is injected over the target surface and a reference surface (for subtraction of…
Capillary Electrophoresis SELEX (CE-SELEX) Aptamer Screening Service is a highly efficient, solution-phase selection technology that uses capillary electrophoresis to separate target-bound aptamer sequences from unbound ones based on their charge-to-size ratio shift, rather than on physical immobilization. It is renowned for its ability to generate high-affinity aptamers with fewer selection rounds and with exceptional stringency. Core Principle: Separation by Mobility Shift In a capillary filled with buffer, an electric field is applied. All molecules migrate based on their net charge and size (their electrophoretic mobility). The target molecule (e.g., a protein) has a specific mobility. A single-stranded DNA or RNA library has a different, faster mobility (due to its high negative charge/size ratio). When an aptamer binds to the target, it forms a complex. This complex has a distinctly different mobility (usually slower) than the free library. CE instrumentation with on-column UV or fluorescence detection can precisely collect only the shifted peak containing the target-aptamer complexes, physically discarding >99.9% of unbound sequences in a single round. Typical CE-SELEX Service Workflow 1. Project Design & Characterization: Consultation: Defining the purified, soluble target (ideal for proteins, peptides, small molecules). Mobility Calibration: The service provider first runs the target and the naïve library separately to establish their baseline migration times. 2. The Selection…
Core Concept: SELEX SELEX (Systematic Evolution of Ligands by Exponential Enrichment) is an iterative process to select high-affinity, specific nucleic acid aptamers (ssDNA or RNA) against a target molecule. The magnetic bead-based method revolutionizes this by using beads as a solid, easily separable support, drastically improving speed and efficiency. How Magnetic Bead-Based SELEX Works (The Process) A professional service provider will execute this cyclic process, usually over 8-15 rounds: Key Advantages of the Magnetic Bead Method (Why it's the service of choice) Rapid Separation: Magnetic stands enable quick washing and buffer exchange, shortening each selection round from hours to minutes. Reduced Non-Specific Binding: Efficient washing minimizes background, leading to cleaner selection. Automation-Friendly: Perfectly suited for robotic liquid handlers, enabling high-throughput, reproducible selections. Flexibility with Targets: Immobilized Targets: Proteins, small molecules, cells, or viruses can be directly conjugated to the beads. Counter-Selection: Beads coated with non-target molecules (e.g., a related protein, cell type) can be used to subtract non-specific binders, dramatically enhancing specificity. What a Full-Service Provider Typically Offers 1. Project Design & Consultation Target characterization and strategy (native vs. tagged protein, cell surface marker). Selection of library type (DNA, RNA, modified nucleotides like 2'-F for stability). Design of counter-selection steps. 2. The SELEX Selection Process Library Synthesis: Starting with…
