“Completion of SELEX” refers to the point in the Systematic Evolution of Ligands by EXponential enrichment (SELEX)workflow where iterative selection rounds have produced an enriched nucleic-acid pool (DNA or RNA) that contains high-affinity, high-specificity binding sequences (aptamers) for a defined target, and further rounds provide diminishing improvements. In practical terms, completion is less a single universal round number and more a decision point supported by enrichment evidence, performance metrics, and downstream readiness. 1) SELEX in One Picture (Why “Completion” Exists at All) SELEX is an iterative evolutionary loop performed in vitro: Start with a diverse library (randomized nucleic-acid sequences). Bind the library to a target (protein, small molecule, cell surface, complex mixture, etc.). Partition: separate binders from non-binders (the critical “selection” step). Elute and amplify the binders (PCR for DNA; RT-PCR for RNA). Repeat with increasing stringency (less target, harsher washes, counter-selection, etc.). “Completion” matters because every additional round costs time, introduces amplification bias, and can over-enrich “fast amplifiers” rather than “best binders.” Modern practice treats completion as an optimization endpoint, not a ritual number of rounds. 2) What “Completion of SELEX” Typically Means (Conceptual Definition) A common knowledge-centered definition is: The pool has converged toward one…
What “SELEX Aptamer Selection” Means SELEX stands for Systematic Evolution of Ligands by Exponential Enrichment. In plain terms, SELEX aptamer selectionis an iterative laboratory workflow that starts with a huge pool of random DNA or RNA sequences and repeatedly enriches the fraction that binds a chosen target with high affinity and specificity. The “winners” are called aptamers—single-stranded nucleic acids that fold into 3D shapes capable of target recognition, often compared to “chemical antibodies,” but made by selection and synthesis rather than immune systems. Core Concept: Darwinian Evolution in a Test Tube SELEX is essentially variation + selection + amplification: Variation: Begin with a randomized oligonucleotide library (often ~10^13–10^16 unique sequences). Selection: Expose the library to the target; keep sequences that bind. Amplification: PCR (or RT-PCR for RNA workflows) amplifies binders to create the next-round pool. Increasing stringency: Each round tightens conditions (less target, harsher washes, more competitors), enriching the best binders over multiple cycles. Most conventional SELEX workflows run multiple rounds (often roughly 6–15) before candidates are sequenced and characterized. The Classic SELEX Workflow (Step-by-Step, With the “Why”) 1) Library design (the “starting universe”) A typical library contains: A random region (e.g., N30–N60) that can…
“Diagnostics and Therapeutics” is the paired engine of modern healthcare: diagnostics generate actionable evidence about what is happening in the body, and therapeutics use that evidence to choose (and adjust) interventions that improve outcomes. As medicine becomes more data-rich—through molecular testing, advanced imaging, and continuous monitoring—the relationship between diagnostics and therapeutics is shifting from a linear “test-then-treat” workflow to a dynamic feedback loop that refines decisions over time. 1) What “Diagnostics” Means (Beyond Simply Naming a Disease) In clinical practice, diagnostics refers to the tools and methods used to detect, characterize, and track disease-related signals. Importantly, diagnostics is not a single test—it’s a system of evidence that supports decisions across the entire care pathway: Screening diagnostics: detect risk or early disease signals before symptoms are obvious. Diagnostic confirmation: distinguish between conditions with similar presentations. Prognostic diagnostics: estimate likely disease course and severity. Predictive diagnostics: forecast whether a patient is likely to benefit from a specific therapy (a key concept in precision medicine). Monitoring diagnostics: measure response, relapse, or adverse effects over time, enabling treatment adjustment. Major diagnostic categories used today Clinical laboratory diagnostics (blood, urine, tissue, etc.) and medical imaging are foundational, but the fastest-growing…
Aptamers are short, single-stranded nucleic acid molecules (DNA or RNA) that fold into specific 3D shapes and bind targets with high affinity and selectivity—often compared to how antibodies recognize antigens, but built from nucleic acids rather than proteins. Unlike a “generic DNA strand,” an aptamer’s function comes from structure: loops, stems, bulges, pseudoknots, and other motifs that create a binding surface matching a target’s geometry and chemistry. Targets can include proteins, peptides, small molecules, ions, and even whole cells (depending on the selection strategy). Why Aptamers Matter (and How They Differ From Antibodies) Aptamers are often described as “chemical antibodies,” but the differences are exactly why they’re valuable. Key advantages frequently highlighted Low immunogenicity (reduced risk of provoking immune responses) High stability and the ability to refold after denaturation in many cases Easy chemical synthesis (batch consistency, scalable manufacturing) Straightforward modification (labels, linkers, immobilization handles) Trade-offs you should know Nuclease sensitivity (especially RNA aptamers) can be a limitation in biological fluids unless stabilized. Selection bias can occur during discovery (e.g., PCR bias), meaning “best in the tube” isn’t always “best in reality.” Very high affinity does not automatically guarantee best real-world specificity; selection conditions matter. …
