A novel aptasensor strategy for protein detection based on G-quadruplex and exonuclease III-aided recycling amplification

Recent advances in the selection of cancer-specific aptamers for the development of biosensors

An early diagnosis has the potential to greatly decrease cancer mortality. For that purpose, specific cancer biomarkers have been molecularly targeted by aptamer sequences to enable an accurate and rapid detection. Aptamer-based biosensors for cancer diagnostics are a promising alternative to those using antibodies, due to their high affinity and specificity to the target molecules and advantageous production. Synthetic nucleic acid aptamers are generated by in vitro Systematic Evolution of Ligands by Exponential enrichment (SELEX) methodologies that have been improved over the years to enhance the efficacy and to shorten the selection process. Aptamers have been successfully applied in electrochemical, optical, photoelectrochemical and piezoelectrical-based detection strategies. These aptasensors comprise a sensitive, accurate and inexpensive option for cancer detection being used as point-of-care devices. This review highlights the recent advances in cancer biomarkers, achievements and optimizations made in aptamer selection, as well as the different aptasensors developed for the detection of several cancer biomarkers.

A protein triggering exponential amplification reaction enables label- and wash-free one-pot protein assay with high sensitivity

Methods capable of sensitive and facile quantification of low-abundant proteins play critical roles in disease diagnosis and treatment. Herein, on a rationally designed aptamer-based hairpin structure-switching template, we developed a protein triggering exponential amplification reaction (PTEXPAR) method. The platelet-derived growth factor BB (PDGF-BB) is used as model analyte in the current proof-of-concept experiments. This method can detect PDGF-BB specifically with a detection limit as low as 4.9 fM. Additionally, the proposed PTEXPAR strategy allows label- and wash-free one-pot quantification of protein within ~35 min. Moreover, it is potentially universal because hairpin template can be easily designed for other proteins by changing the corresponding aptamer sequence.

Aptamers used for biosensors and targeted therapy

Aptamers are single-stranded nucleic acid sequences that can bind to target molecules with high selectivity and affinity. Most aptamers are screened in vitro by a combinatorial biology technique called systematic evolution of ligands by exponential enrichment (SELEX). Since aptamers were discovered in the 1990s, they have attracted considerable attention and have been widely used in many fields owing to their unique advantages. In this review, we present an overview of the advancements made in aptamers used for biosensors and targeted therapy. For the former, we will discuss multiple aptamer-based biosensors with different principles detected by various signaling methods. For the latter, we will focus on aptamer-based targeted therapy using aptamers as both biotechnological tools for targeted drug delivery and as targeted therapeutic agents. Finally, challenges and new perspectives associated with these two regions were further discussed. We hope that this review will help researchers interested in aptamer-related biosensing and targeted therapy research.

Highly Specific Recognition of Guanosine Using Engineered Base-Excised Aptamers

Purines and their derivatives are highly important molecules in biology for nucleic acid synthesis, energy storage, and signaling. Although many DNA aptamers have been obtained for binding adenine derivatives such as adenosine, adenosine monophosphate, and adenosine triphosphate, success for the specific binding of guanosine has been limited. Instead of performing new aptamer selections, we report herein a base-excision strategy to engineer existing aptamers to bind guanosine. Both a Na⁺ -binding aptamer and the classical adenosine aptamer have been manipulated as base-excising scaffolds. A total of seven guanosine aptamers were designed, of which the G16-deleted Na⁺ aptamer showed the highest bindng specificity and affinity for guanosine with an apparent dissociation constant of 0.78 mm. Single monophosphate difference in the target molecule was also recognizable. The generality of both the aptamer scaffold and excised site were systematically studied. Overall, this work provides a few guanosine binding aptamers by using a non-SELEX method. It also provides deeper insights into the engineering of aptamers for molecular recognition.