{"id":347,"date":"2026-04-05T15:31:46","date_gmt":"2026-04-05T07:31:46","guid":{"rendered":"http:\/\/47.85.58.59\/?p=347"},"modified":"2026-04-05T15:31:46","modified_gmt":"2026-04-05T07:31:46","slug":"alpha-lifetech-aptamer-selex-protocol","status":"publish","type":"post","link":"https:\/\/blog.alphalifetech.com\/index.php\/2026\/04\/05\/alpha-lifetech-aptamer-selex-protocol\/","title":{"rendered":"Alpha Lifetech-Aptamer Selex Protocol"},"content":{"rendered":"

SELEX (Systematic Evolution of Ligands by EXponential enrichment)<\/a>\u00a0protocol used for aptamer selection. The process involves several steps, including library preparation, target binding, washing, elution, amplification, and multiple rounds of selection to isolate high-affinity aptamers.<\/p>\n

Materials<\/h2>\n

Target molecule: Protein, small molecule, cell, etc.<\/p>\n

Aptamer<\/a>\u00a0library: Single-stranded DNA (ssDNA) or RNA, typically containing 10^12\u201310^15 random sequences flanked by constant primer binding regions for amplification.<\/p>\n

Binding buffer: For aptamer-target interaction (e.g., PBS, TBS, or another suitable buffer for the target).<\/p>\n

Washing buffer: For removing non-specifically bound sequences (binding buffer with added salts or detergents as needed).<\/p>\n

Elution buffer: To release bound aptamers (typically with heat, pH shift, or high salt).<\/p>\n

PCR or RT-PCR reagents: For amplifying selected aptamers (for DNA aptamers: dNTPs, polymerase, primers; for RNA aptamers: reverse transcriptase, RNA polymerase, nucleotides, etc.).<\/p>\n

Magnetic beads or other target immobilization materials (optional): For easier separation of bound\/unbound sequences.<\/p>\n

Agarose gel and gel extraction kit (optional): For verifying and purifying PCR products.<\/p>\n

Protocol Steps<\/h2>\n

Preparation of the\u00a0Aptamer<\/a>\u00a0Library<\/h3>\n

Oligonucleotide Library: Synthesize or obtain a single-stranded DNA (ssDNA) or RNA library containing 40\u201380 nucleotides, with random sequences in the middle (20\u201340 nucleotides) flanked by fixed primer binding sites for amplification.<\/p>\n

Initial Concentration: Dilute the library to a concentration of approximately 1\u201310 \u03bcM in binding buffer, ensuring enough diversity to explore possible aptamers.<\/p>\n

Target Immobilization (Optional)<\/h3>\n

If using a solid support (e.g., magnetic beads), immobilize the target molecule onto the surface.<\/p>\n

For proteins: Covalently link or adsorb the protein to beads or plates.<\/p>\n

For small molecules: Link the molecule to a larger carrier molecule or use direct immobilization.<\/p>\n

Binding of\u00a0Aptamer<\/a>s to Target<\/h3>\n

Incubation: Mix the aptamer library with the target molecule in binding buffer. Incubate the mixture for a suitable amount of time, typically 30 minutes to 2 hours, depending on the target\u2019s properties and binding kinetics.<\/p>\n

Temperature: Perform binding at room temperature or at a temperature suited for the target (some aptamers may require specific conditions, such as 37\u00b0C).<\/p>\n

Volume: Use an appropriate ratio of aptamer library and target, with the library in excess to allow for competitive binding among sequences.<\/p>\n

Washing Unbound Sequences<\/h3>\n

After the incubation period, remove unbound and weakly bound sequences by washing with washing buffer (binding buffer supplemented with salts or detergents).<\/p>\n

Washing method:<\/p>\n

For bead-based selection: Apply a magnetic field to retain beads and wash several times with buffer to remove unbound sequences.<\/p>\n

For non-bead-based selection: Centrifugation or filtration can be used to separate bound and unbound sequences.<\/p>\n

Perform several washes (typically 3\u20135) to ensure only high-affinity aptamers remain bound.<\/p>\n

Elution of Bound\u00a0Aptamer<\/a>s<\/h3>\n

Elute the bound aptamers from the target by changing conditions to disrupt the aptamer-target interaction.<\/p>\n

Elution methods:<\/p>\n

Heat elution: Heating the sample to 70\u201395\u00b0C to denature aptamers and release them.<\/p>\n

Salt elution: Using high-salt buffer to disrupt ionic interactions.<\/p>\n

pH shift elution: Using acidic or basic buffers to change binding affinity.<\/p>\n

Collect the eluted aptamers for amplification.<\/p>\n

Amplification by PCR or RT-PCR<\/h3>\n

For DNA aptamers: Amplify the eluted aptamers directly using PCR.<\/p>\n

For RNA aptamers:<\/p>\n

First, reverse transcribe the eluted RNA aptamers into complementary DNA (cDNA) using reverse transcriptase.<\/p>\n

Amplify the cDNA by PCR.<\/p>\n

Use T7 RNA polymerase to transcribe the PCR products back into RNA for the next round of selection.<\/p>\n

PCR Conditions:<\/p>\n

Set up a PCR reaction with primers complementary to the flanking sequences of the aptamer library.<\/p>\n

Typical PCR program:<\/p>\n

Initial denaturation: 94\u00b0C for 2 minutes.<\/p>\n

Denaturation: 94\u00b0C for 30 seconds.<\/p>\n

Annealing: 55\u201365\u00b0C for 30 seconds (depending on primer design).<\/p>\n

Extension: 72\u00b0C for 30 seconds.<\/p>\n

Repeat for 20\u201325 cycles.<\/p>\n

Final extension: 72\u00b0C for 5 minutes.<\/p>\n

Gel Verification: Run a portion of the PCR product on an agarose gel to verify amplification and purity.<\/p>\n

Preparation for Next Round of SELEX<\/h3>\n

ssDNA Generation (for DNA aptamers):<\/p>\n

Convert the double-stranded PCR product to ssDNA. You can use several methods:<\/p>\n

Strand separation: Using a biotin-labeled primer and streptavidin-coated magnetic beads to separate strands.<\/p>\n

Asymmetric PCR: Amplify ssDNA directly by using unequal primer concentrations.<\/p>\n

For RNA aptamers: Transcribe the amplified DNA back into RNA using T7 RNA polymerase, and purify the RNA.<\/p>\n

Repeat SELEX Rounds<\/h3>\n

Use the newly amplified or transcribed aptamers for subsequent rounds of selection.<\/p>\n

Increase the stringency of the selection process with each round by:<\/p>\n

Decreasing the concentration of the target molecule.<\/p>\n

Increasing the number of washing steps to remove weaker binders.<\/p>\n

Decreasing the incubation time.<\/p>\n

Perform 8\u201315 rounds of selection to enrich for high-affinity aptamers.<\/p>\n

Sequence and Analyze\u00a0Aptamer<\/a>s<\/h3>\n

After the final round of selection, clone and sequence individual aptamer candidates to identify the most promising aptamer sequences.<\/p>\n

Cloning: Insert PCR products into a plasmid vector and transform into bacteria for colony selection.<\/p>\n

Sequencing: Perform Sanger sequencing or use next-generation sequencing (NGS) to identify aptamer sequences.<\/p>\n

Binding Assays: Perform binding assays to determine the affinity (Kd) of the selected aptamers for the target.<\/p>\n

Key Considerations<\/h2>\n

Target Selection: Ensure that the target is in its native or functional form to allow for proper binding during SELEX.<\/p>\n

Library Diversity: The initial library should be highly diverse to ensure that potential high-affinity aptamers are present.<\/p>\n

Stringency Control: Gradually increasing the stringency of washing and binding conditions can help eliminate low-affinity aptamers.<\/p>\n

Negative SELEX: Consider performing negative selection rounds to eliminate aptamers that bind to non-specific targets.<\/p>\n

Following this protocol,\u00a0aptamers<\/a>\u00a0with high affinity and specificity for a particular target can be successfully selected for various applications, including diagnostics, therapeutics, and research<\/p>\n","protected":false},"excerpt":{"rendered":"

SELEX (Systematic Evolution of Ligands by EXponential enrichment)\u00a0protocol used for aptamer selection. The process involves several steps, including library preparation, target binding, washing, elution, amplification, and multiple rounds of selection to isolate high-affinity aptamers. Materials Target molecule: Protein, small molecule, cell, etc. Aptamer\u00a0library: Single-stranded DNA (ssDNA) or RNA, typically containing 10^12\u201310^15 random sequences flanked by … <\/p>\n","protected":false},"author":1,"featured_media":44,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"slim_seo":{"title":"Alpha Lifetech-Aptamer Selex Protocol - Alpha Lifetech","description":"SELEX (Systematic Evolution of Ligands by EXponential enrichment) \u00a0protocol used for aptamer selection. The process involves several steps, including library pr"},"footnotes":""},"categories":[7],"tags":[],"class_list":["post-347","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-targeting-ligands"],"_links":{"self":[{"href":"https:\/\/blog.alphalifetech.com\/index.php\/wp-json\/wp\/v2\/posts\/347","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/blog.alphalifetech.com\/index.php\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blog.alphalifetech.com\/index.php\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blog.alphalifetech.com\/index.php\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/blog.alphalifetech.com\/index.php\/wp-json\/wp\/v2\/comments?post=347"}],"version-history":[{"count":1,"href":"https:\/\/blog.alphalifetech.com\/index.php\/wp-json\/wp\/v2\/posts\/347\/revisions"}],"predecessor-version":[{"id":348,"href":"https:\/\/blog.alphalifetech.com\/index.php\/wp-json\/wp\/v2\/posts\/347\/revisions\/348"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/blog.alphalifetech.com\/index.php\/wp-json\/wp\/v2\/media\/44"}],"wp:attachment":[{"href":"https:\/\/blog.alphalifetech.com\/index.php\/wp-json\/wp\/v2\/media?parent=347"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blog.alphalifetech.com\/index.php\/wp-json\/wp\/v2\/categories?post=347"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blog.alphalifetech.com\/index.php\/wp-json\/wp\/v2\/tags?post=347"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}