What is Subtractive SELEX? It is a specialized version of SELEX used to generate aptamers (single-stranded DNA or RNA oligonucleotides) that bind with high affinity and specificity to a target of interest (e.g., a protein, cell, small molecule) while actively excluding binding to closely related non-targets (e.g., a non-pathogenic vs. pathogenic strain, a healthy vs. cancerous cell, or a target in a complex mixture). The "subtractive" step removes sequences that bind to unwanted counter-targets, ensuring the final aptamer pool is highly specific. Core Workflow of a Subtractive SELEX Service A typical service follows these key stages: 1. Project Design & Library Synthesis Client Consultation: Defining the target of interest (e.g., recombinant protein, whole cell) and the critical counter-target(s) for subtraction (e.g., isotype control protein, non-target cell line). Library Design: A service provider synthesizes a vast random-sequence oligonucleotide library (typically 10^14 - 10^15 unique sequences) flanked by constant primer regions. 2. The Subtractive SELEX Cycle (Repeated 8-15 Rounds) This is the iterative heart of the service: * a. Negative Selection (Subtraction): The oligonucleotide pool is incubated with the counter-target (or complex background, like serum). Sequences that bind to this unwanted material are discarded. * b. Positive Selection: The unbound sequences from (a) are then incubated with the target of interest. The bound sequences are recovered. * c. Washing: Non-specific or weakly bound sequences are washed away.…
