Core Principle Nitrocellulose membrane filter binding exploits a simple but powerful property: nitrocellulose avidly binds proteins and protein-nucleic acid complexes, but does not efficiently bind free, single-stranded DNA or RNA. By passing a mixture of the target protein and a random oligonucleotide library through the membrane, sequences that bind to the protein are retained (as a complex), while unbound sequences are washed away. Typical Workflow of a Service Provider A professional service will manage this complex, iterative process for you: 1. Project Design & Library Synthesis Consultation: Defining your target (purified protein is essential), desired aptamer properties (affinity, specificity, buffer conditions), and format (DNA or RNA). Library Design: A synthetic library of up to 10^15 random sequences (e.g., 40-60 nt random core, flanked by constant primer regions) is prepared. 2. The SELEX Cycles (Iterative Screening) Incubation: The target protein is incubated with the nucleic acid library under optimized conditions (buffer, temperature, time). Positive Selection (Binding & Capture): The mixture is passed through a nitrocellulose membrane. Protein-aptamer complexes stick to the membrane. Washing: Mild washing removes weakly bound or non-specific sequences. Elution: Bound sequences are recovered by denaturing the protein (e.g., using heat, phenol-chloroform, or high-concentration urea). Amplification: For DNA SELEX: The eluted DNA is directly amplified by PCR. For…
