Aptamers are oligonucleotide sequences (DNA or RNA) consisting of 20-110 nucleotides. Aptamers have high molecular recognition capabilities for different types of targets such as nucleic acids, proteins, cells, and some small molecules, can distinguish subtle differences, and have high affinity and specificity, and are easy to chemically modify. Aptamers are usually oligonucleotide fragments obtained from nucleic acid molecule libraries using in vitro screening technology, namely systematic evolution of ligands by exponential enrichment (SELEX). The structure and function of aptamers are similar to antibodies, but they are smaller in size, have shorter production time, lower cost, and are easier to synthesize. Based on the characteristics of aptamers that can specifically bind to a variety of target molecules, they are widely used in food safety, environmental monitoring, biomedical research and other fields. Aptamers can be used in drug development to design drugs that target specific molecules; many aptamers are used to make biosensors that can diagnose some specific infectious diseases; aptamers can be used as carriers to deliver genes to specific cells or tissues, and have certain application prospects in gene therapy. Since nucleic acid aptamers can be prepared and screened in vitro, the possibility of contamination is small, and nucleic acid aptamers are not immunogenic, so they will not cause rejection reactions when used as therapeutic drugs.

Nucleic Acid Aptamer Screening Based on SELEX Technology:

Nucleic acid aptamer screening is mainly based on SELEX technology. The basic principle of SELEX aptamer library screening is to synthesize a single-stranded oligonucleotide library in vitro, and then put the target molecule into an oligonucleotide library containing approximately 10^15 different sequences for incubation. The oligonucleotides that are not bound to the target molecule are washed away with deionized water to separate them, and then eluted with a high concentration of salt solution to obtain oligonucleotides that can bind to the target molecule, and PCR is used to amplify the oligonucleotides that can bind to the target molecule before the next round of screening. Repeat the above steps for multiple rounds of screening, and each round of screening includes the steps of binding to the target molecule, separating the unbound sequence, and amplifying the bound sequence. The number of aptamers that can bind to the target molecule gradually increases with the increase of screening rounds, and the specificity also increases with the repeated screening process, and finally the oligonucleotide sequence that binds to the target molecule with high specificity is screened out. When screening RNA aptamers through RNA aptamer library synthesis service, RNA must be reverse transcribed into DNA first, and then the subsequent SELEX aptamer library screening is carried out. The advantage of DNA aptamer library synthesis service lies in the stability of DNA aptamers themselves, while the RNA aptamers prepared by RNA aptamer library synthesis service have stronger affinity and specificity with the target molecule.

Fig. 1 Schematic diagram of nucleic acid aptamer screening based on SELEX technology

When screening nucleic acid aptamers, insufficient repetitions may result in low specificity and affinity of the aptamer. Therefore, with the continuous development of technology, the traditional SELEX aptamer library screening technology has been continuously improved and a series of related technologies have been derived. IP-SELEX is a SELEX technology coupled with immunoprecipitation; Cell-SELEX operates at the cellular level and is suitable for screening aptamers that recognize cell surface molecules; Apta-Seq combines high-throughput sequencing technology to screen large-scale libraries simultaneously, which can greatly improve the efficiency of screening. In addition, there are AFM-SELEX of atomic force microscopy and CE-SELEX of capillary electrophoresis, which greatly improve the success rate of SELEX technology. The screening of nucleic acid aptamers is mainly to discover the specific nucleic acid sequence of aptamers that bind to the target molecule with high affinity. The nucleic acid aptamers obtained through screening can provide new ideas for the development of drugs in disease treatment, improve the accuracy and sensitivity of disease diagnosis, and promote the further development of gene therapy technology.

Antigen Types for Nucleic Acid Aptamer Screening:

Antigens that can be used for nucleic acid aptamer screening mainly include peptides, proteins, viruses, bacteria, cells, tissues, and small molecules. Peptides and proteins have complex structures and functions, and nucleic acid aptamers can bind to proteins with high affinity and specificity; viruses and bacteria, as common pathogens, have complex structures and antigenic epitopes; nucleic acid aptamers can bind to them and are used for the detection and diagnosis of viruses and bacteria; the composition of cells and tissues is relatively complex and there are interactions. Cell-SELEX technology can directly screen nucleic acid aptamers that bind to specific cells or tissues for cell recognition and disease diagnosis; small molecules such as drugs and metabolites usually have low molecular weight and simpler structure; therefore, designing nucleic acid aptamers that bind to small molecules requires higher accuracy and specificity.

Table 1. Comparison of different antigen types for nucleic acid aptamer screening

TekBiotech is committed to providing customers with high-affinity and high-specificity nucleic acid aptamer screening technology services, and providing strong support for customers' subsequent downstream R&D work such as aptamer function verification, in vivo function verification and development of drugs targeting specific molecules, including affinity verification, competitive ELISA verification, in vitro targeted cell functional verification, in vivo targeted inhibition function verification of aptamers and signal pathway blocking function verification, etc. TekBiotech has many years of project experience and insights in nucleic acid aptamer screening (SELEX technology). After years of development, TekBiotech has established a complete nucleic acid aptamer screening system, which can provide customers with high-quality nucleic acid aptamer screening services for targets such as proteins, peptides, amino acids, and small molecule compounds, including RNA aptamer library synthesis services and DNA aptamer library synthesis services. The nucleic acid aptamer library established by TekBiotech can reach a capacity of 10^10-10^11, which is sufficient to screen small molecule nucleic acid aptamers for various targets and meet the downstream experimental needs of customers. Through 6-10 rounds of pressure screening, we can obtain nucleic acid aptamers with high affinity and high specificity. Based on the SELEX technology platform, the affinity of nucleic acid aptamers screened by TechBio can reach nM-pM level. TekBiotech can also provide a variety of supporting downstream verification experiments, including but not limited to nucleic acid aptamer affinity verification, competitive ELISA verification, flow blocking verification, etc. Customers only need to provide screening targets and project requirements, and TechBio scientists will provide reasonable customized solutions based on customer project requirements to solve customers' scientific research problems.