Core Concept & Purpose The goal is to subtract sequences that bind to: The immobilization matrix/surface (e.g., streptavidin beads, nitrocellulose filters, chip surface). Closely related molecules or structural analogs (e.g., to ensure an aptamer for drug A doesn't bind metabolite B). Components of the selection buffer or the cellular milieu where the aptamer will be used (e.g., serum proteins for therapeutic aptamers). By pre-incubating the DNA library with these "negative targets" before exposure to the desired target, non-specific binders are captured and discarded. Only the unbound, "cleaned" library proceeds to the positive selection round. Key Features of a Professional Negative SELEX Service Strategic Design: Experts design the optimal order, frequency, and stringency of negative vs. positive selection rounds. Relevant Negative Targets: The service advises on and sources the most critical counter-targets (e.g., using the exact resin from positive selection for matrix subtraction, or sourcing specific protein analogs). Dedicated Rounds: Entire selection rounds may be dedicated to negative selection against a key interferent. Pre-SELEX Depletion: Often, the initial naive library is pre-depleted against the matrix to remove common surface binders from the start. Typical Integration into a Service Workflow Within a broader SELEX project (e.g., Protein-SELEX), a Negative SELEX step is woven in as follows: Pre-Clearance (Round 0): The initial DNA library is…
