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…
What is Whole-cell SELEX? Whole-cell SELEX (Systematic Evolution of Ligands by EXponential enrichment) is a technique used to discover aptamers (single-stranded DNA or RNA molecules) that bind specifically to a target living cell. Unlike traditional SELEX that uses a purified protein target, whole-cell SELEX presents the target in its native, complex cellular environment. This allows for the selection of aptamers against: Native cell-surface proteins in their proper folding and post-translational modifications. Complex targets like transmembrane receptors in their natural lipid environment. Unknown surface biomarkers without prior knowledge of the cell's molecular makeup. Specific cell states (e.g., activated, cancerous, infected) based on differences in surface expression. The Core Process: How Whole-cell SELEX Works A professional service will manage this complex, iterative pipeline: Library & Design: Starting with a vast, random synthetic oligonucleotide library (10^14 - 10^15 unique sequences). Positive Selection: Incubating the library with the target cells (e.g., cancer cells, stem cells, bacteria). Aptamers that bind to any surface structure are retained. Counter-Selection (Critical Step): The bound pool is then exposed to non-target or control cells (e.g., healthy cells, a different cell line). Sequences that bind to these are discarded. This step is crucial for generating specificity. Elution & Amplification: Aptamers specifically bound to the target cells are recovered, amplified by PCR…
Aptamer Capture-SELEX Service refers to a specialized, outsourced process where a company or academic core facility performs the entire Capture-SELEX procedure to develop DNA or RNA aptamers for a client's specific target molecule. This is a crucial service for researchers and companies who need high-affinity, specific aptamers but lack the specialized equipment, expertise, or time to run the SELEX process in-house. Let's break down what this service entails. 1. What is Capture-SELEX? First, understand the standard SELEX (Systematic Evolution of Ligands by EXponential enrichment). It's an iterative process to select aptamers from a vast random oligonucleotide library (10^14 - 10^15 different sequences). Capture-SELEX is a specific variant designed primarily for small molecules or targets that are difficult to immobilize directly on a solid support without affecting their structure/function. The Key Difference: Instead of immobilizing the target itself, a short, complementary "capture strand" is immobilized on beads or a surface. The initial ssDNA library is designed with a region complementary to this capture strand. The target is free in solution. How it Works: The library is bound to the surface via the capture strand. The target molecule is introduced in solution. Only library sequences that fold into a structure capable of binding the target will undergo a conformational change. This binding event often weakens or…
