Negative aptamer selection—often called negative selection or counter-selection—is a deliberate filtering step in SELEX(Systematic Evolution of Ligands by EXponential enrichment) designed to remove sequences that bind to the wrong things. Instead of enriching binders to your intended target, negative selection enriches your final pool for what you actually want in real-world use: high specificity, low background, and minimal cross-reactivity. In modern aptamer discovery, negative selection is not “optional polish.” It is one of the most effective ways to prevent selection artifacts—like aptamers that bind to beads, linkers, tags, surfaces, common matrix components, or closely related off-target molecules—from dominating your pool. 1) What “Negative Aptamer Selection” Means (and Why It Exists) During SELEX, you start with a huge randomized DNA/RNA library and iteratively enrich sequences that bind. The catch is that many sequences bind strongly to unintended components in the experimental system: immobilization substrates (e.g., beads, membranes) affinity tags or capture molecules (e.g., streptavidin–biotin systems) blockers, serum proteins, plastic, or assay buffers structurally similar molecules (analogs) that you must not bind Negative selection introduces a decoy binding step: you expose the library to an unwanted target (or “negative target”), then discard the sequences that bind it and keep…
Aptamers are short, single-stranded nucleic acids—typically ~20–100 nucleotides—that fold into defined 3D shapes and bind targets (proteins, small molecules, ions, cells) with high affinity and specificity. They are often described as “chemical antibodies,” but they behave differently: their binding comes from nucleic-acid folding + surface complementarity, and their performance is tightly linked to sequence chemistry, structure, and degradation pathways. When your core question is “DNA aptamers or RNA aptamers?”, the best answer is not a slogan. It’s a decision based on (1) structural needs, (2) stability environment, (3) manufacturability, (4) modification strategy, and (5) application constraints. 1) The Fundamental Difference: Structural Vocabulary vs Environmental Toughness RNA aptamers: richer folding vocabulary RNA has a 2′-OH group on the ribose, which expands hydrogen-bonding possibilities and supports a larger “structural vocabulary” (hairpins, internal loops, bulges, pseudoknots, complex tertiary contacts). In practice, this often means more diverse and intricate 3D conformations, which can translate into excellent binding performance for some targets. Takeaway: Choose RNA when the target demands highly nuanced shape recognition (e.g., challenging protein surfaces or structured RNA targets). DNA aptamers: generally more chemically stable and simpler DNA lacks the 2′-OH group and is typically more resistant to base-catalyzed…
“CATALOG APTAMERS & REAGENTS” usually refers to ready-to-order, pre-characterized aptamer affinity binders and the supporting assay reagents that make those binders usable in real experiments (e.g., labeling, immobilization, buffers, and controls). Aptamers themselves are short, single-stranded DNA or RNA (or related chemistries) selected from very large libraries to bind a specific target with high affinity and specificity—often described as antibody-like binding, but built from nucleic acids and produced by chemical synthesis. 1) What Are Aptamers (and Why They Matter as Reagents)? Aptamers are single-stranded nucleic acids that fold into 3D structures capable of recognizing targets such as proteins, small molecules, ions, or even cells. They are typically discovered through SELEX (Systematic Evolution of Ligands by EXponential enrichment), an iterative selection process that enriches sequences that bind the desired target. What makes aptamers especially “catalog-friendly” is that once a sequence is known, it can be reliably reproduced by chemical synthesis, and easily chemically modified (for example, adding a fluorophore or biotin) to fit common assay formats. 2) “Catalog Aptamers” vs Custom Aptamer Discovery Catalog Aptamers (ready-to-order) Catalog aptamers are fixed, known sequences that have been previously selected and are sold as standard products. Their main value…
