Three different signal amplification strategies for the impedimetric sandwich detection of thrombin

Recent Trends in Electrochemical Sensors for Vital Biomedical Markers Using Hybrid Nanostructured Materials

This work provides a succinct insight into the recent developments in electrochemical quantification of vital biomedical markers using hybrid metallic composite nanostructures. After a brief introduction to the biomarkers, five types of crucial biomarkers, which require timely and periodical monitoring, are shortlisted, namely, cancer, cardiac, inflammatory, diabetic and renal biomarkers. This review emphasizes the usage and advantages of hybrid nanostructured materials as the recognition matrices toward the detection of vital biomarkers. Different transduction methods (fluorescence, electrophoresis, chemiluminescence, electrochemiluminescence, surface plasmon resonance, surface-enhanced Raman spectroscopy) reported for the biomarkers are discussed comprehensively to present an overview of the current research works. Recent advancements in the electrochemical (amperometric, voltammetric, and impedimetric) sensor systems constructed with metal nanoparticle-derived hybrid composite nanostructures toward the selective detection of chosen vital biomarkers are specifically analyzed. It describes the challenges involved and the strategies reported for the development of selective, sensitive, and disposable electrochemical biosensors with the details of fabrication, functionalization, and applications of hybrid metallic composite nanostructures.

A Rapid and Ultrasensitive Thrombin Biosensor Based on a Rationally Designed Trifunctional Protein

Rapid and sensitive detection of thrombin is imperative for the early diagnosis, prevention, and treatment of thrombin-related diseases. Here, an ultrasensitive and rapid thrombin biosensor is developed based on rationally designed trifunctional protein HTs, comprising three functional units, including a far-red fluorescent protein smURFP, hydrophobin HGFI, and a thrombin cleavage site (TCS). smURFP is used as a detection signal to eliminate any interference from the autofluorescence of sample matrix to increase detection sensitivity. HGFI serve as an adhesive unit to allow rapid immobilization of HTs on a multiwall plate. The TCS linking HGFI and smURFP function as a sensing element to recognize and detect thrombin. HTs immobilization is symmetrically optimized and characterized. Thrombin assay reveals the specific recognition of active thrombin in samples and the hydrolysis of the immobilized HTs, resulting in a decrease in the fluorescence intensity of the sample in a thrombin concentration-dependent manner. The limit of detection (LOD) is as low as 0.2 am in the serum. To the authors' knowledge, this is the lowest LOD ever reported for any thrombin biosensor. This study sheds light on the engineering of multifunctional proteins for biosensing.

G-Quadruplex-Forming Aptamers-Characteristics, Applications, and Perspectives

G-quadruplexes constitute a unique class of nucleic acid structures formed by G-rich oligonucleotides of DNA- or RNA-type. Depending on their chemical nature, loops length, and localization in the sequence or structure molecularity, G-quadruplexes are highly polymorphic structures showing various folding topologies. They may be formed in the human genome where they are believed to play a pivotal role in the regulation of multiple biological processes such as replication, transcription, and translation. Thus, natural G-quadruplex structures became prospective targets for disease treatment. The fast development of systematic evolution of ligands by exponential enrichment (SELEX) technologies provided a number of G-rich aptamers revealing the potential of G-quadruplex structures as a promising molecular tool targeted toward various biologically important ligands. Because of their high stability, increased cellular uptake, ease of chemical modification, minor production costs, and convenient storage, G-rich aptamers became interesting therapeutic and diagnostic alternatives to antibodies. In this review, we describe the recent advances in the development of G-quadruplex based aptamers by focusing on the therapeutic and diagnostic potential of this exceptional class of nucleic acid structures.

Target-induced structure switching of aptamers facilitates strand displacement for DNAzyme recycling amplification detection of thrombin in human serum

To monitor the thrombin concentration under the condition of abnormal blood coagulation is of clinical significance for the diagnosis of various diseases. Here, on the basis of the aptamer structure switching induced by the target molecules and the signal amplification strategy via recycling of metal-ion dependent DNAzymes, we have established a sensitive and simple fluorescent aptasensor for detecting thrombin in human serum. The thrombin target specifically binds to the aptamer sequence and causes a corresponding conformational structure switching, which leads to the formation of a toehold sequence to facilitate the strand migration displacement reaction for the generation of functional metal-ion dependent DNAzymes. These DNAzymes further cleave the fluorescently quenched hairpin substrates cyclically to yield substantially amplified fluorescence recovery for sensitively detecting thrombin in the dynamic range from 0.01 nM to 50 nM. Such an aptasensor shows a detection limit of 6.9 pM and can achieve the monitoring of thrombin in diluted human serum with high selectivity, offering a universal sensing strategy for the construction of various sensitive and simple aptasensors to detect different biomarker molecules.

Rapid detection of cocaine using aptamer-based biosensor on an evanescent wave fibre platform

The rapid detection of cocaine has received considerable attention because of the instantaneous and adverse effects of cocaine overdose on human health. Aptamer-based biosensors for cocaine detection have been well established for research and application. However, reducing the analytic duration without deteriorating the sensitivity still remains as a challenge. Here, we proposed an aptamer-based evanescent wave fibre (EWF) biosensor to rapidly detect cocaine in a wide working range. At first, the aptamers were conjugated to complementary DNA with fluorescence tag and such conjugants were then immobilized on magnetic beads. After cocaine was introduced to compete against the aptamer-DNA conjugants, the released DNA in supernatant was detected on the EWF platform. The dynamic curves of EWF signals could be interpreted by the first-order kinetics and saturation model. The semi-log calibration curve covered a working range of 10-5000 µM of cocaine, and the limit of detection was approximately 10.5 µM. The duration of the full procedure was 990 s (16.5 min), and the detection interval was 390 s (6.5 min). The specified detection of cocaine was confirmed from four typical pharmaceutic agents. The analysis was repeated for 50 cycles without significant loss of sensitivity. Therefore, the aptamer-based EWF biosensor is a feasible solution to rapidly detect cocaine.

Aptamer-modified nanomaterials: principles and applications

Aptamers are promising alternative binders that can substitute antibodies in various applications. Due to the advantages of aptamers, namely their high affinity, specificity and stability, along with the benefits originating from the chemical synthesis of aptamers, they have attracted attention in various applications including their use on nanostructured material. This necessitates the immobilization of aptamers on a solid support. Since aptamer immobilization may interfere with its binding properties, the immobilization of aptamers has to be investigated and optimized. Within this review, we give general insights into the principles and factors controlling the binding affinity of immobilized aptamers. Specific features of aptamer immobilization on nanostructured surfaces and nanoparticles are highlighted and a brief overview of applications of aptamer-modified nanostructured materials is given.