Aptamers have been increasingly applied in biomedical field as a class of biorecognition elements that possess many advantages such as high specificity and binding affinity, easy synthesis, easy modification, small size, non-toxicity and good stability. Many diseases like cancer exhibit cellular aberrations at morphological and molecular levels. Medical diagnosis based on molecular features can be highly specific and extremely sensitive when proper recognition molecule and an efficient signal transduction system are employed. However, bioanalysis of human diseases at the molecular level is an extremely challenging field because effective probes to identify and recognize biomarkers of diseases are not readily available. Traditional bio-recognition molecule, antibody has been exploited to develop excellent diagnosis assays in many formats, but antibodies are insufficient to match the requirements of fast and portable biosensors for point-of-care applications, which are at high demand in pathogenic bacteria detection as well as other diseases like cancer. Aptamers are short single-stranded oligonucleotides, which can be selected from random combinatorial library by SELEX in vitro. This relatively new biorecognition agent has superior intrinsic characteristics for biosensor development. In this review, we first present major aptamer selection technologies and the main formats of biosensors, which were frequently employed in aptasensor development. Then, the current state of aptamers as applied to medical diagnosis was discussed for specifically cancer and pathogen diagnosis. Finally, an overview of aptamer-nanomaterials conjugates was presented in many applications such as diagnosis, bioimaging, and theranostics.

Discovery of alternative sources of antimicrobial agents are essential in the ongoing battle against microbial pathogens. Legislative and scientific challenges considerably hinder the discovery and use of new antimicrobial drugs, and new approaches are in urgent demand. On the other hand, rapid, specific and sensitive detection of airborne pathogens is becoming increasingly critical for public health. In this respect affinity oligonucleotides, aptamers, provide unique opportunities for the development of nanotechnological solutions for such medical applications. In recent years, aptamers specifically recognizing microbial cells and viruses showed great potential in a range of analytical and therapeutic applications. This article describes the significant advances in the development of aptamers targeting specific pathogens. Therapeutic application of aptamers as neutralizing agents demonstrates great potential as a future source of antimicrobial agent.

One significant constraint in the advancement of biosensors is the signal-to-noise ratio, which is adversely affected by the presence of interfering factors such as blood in the sample matrix. In the present investigation, a specific aptamer binding was chosen for its affinity, while exhibiting no binding affinity towards non-target bacterial cells. This selective binding property was leveraged to facilitate the production of magnetic microparticles decorated with aptamers. A novel assay was developed to effectively isolate S. pneumoniae from PBS or directly from blood samples using an aptamer with an affinity constant of 72.8 nM. The capture experiments demonstrated efficiencies up to 87% and 66% are achievable for isolating spiked S. pneumoniae in 1 mL PBS and blood samples, respectively. Graphical abstract