Homogeneously ultrasensitive electrochemical detection of adenosine triphosphate based on multiple signal amplification strategy

A convenient fluorescent/electrochemical dual-mode biosensor for accurate detection of Pb2+ based on DNAzyme cycle

The presence of heavy metals in the ecological environment is a serious threat to human health. Therefore, it is very important to establish a simple and sensitive method for the detection of heavy metals. Currently, most of the methods are single-channel sensing, and these methods are prone to false-positive signals, which reduces the accuracy. In this work, Pb²⁺-DNAzyme was immobilized on magnetic beads (MBs) using a linkage of biotin and streptavidin and successfully applied to the construction of a fluorescent/electrochemical dual-mode (DM) biosensor. The supernatant after magnetic separation formed a double strand on the electrode, which was combined with methylene blue (MB) for electrochemical detection (EC). At the same time, FAM-d was added to the precipitate, and after magnetic separation, the supernatant was subjected to fluorescent detection (FL). Under optimal conditions, the signal response of the constructed dual-mode biosensor showed a good linear relationship with the concentration of Pb²⁺. The DNAzyme-based dual-mode biosensor achieved sensitive and selective detection of Pb²⁺ with good accuracy and reliability, opening a new way for the development of biosensing strategies for the detection of Pb²⁺. More importantly, the sensor has high sensitivity and accuracy for the detection of Pb²⁺ in actual sample analysis.

Electrochemical DNA Biosensors Based on Labeling with Nanoparticles

This work reviews the field of DNA biosensors based on electrochemical determination of nanoparticle labels. These labeling platforms contain the attachment of metal nanoparticles (NPs) or quantum dots (QDs) on the target DNA or on a biorecognition reporting probe. Following the development of DNA bioassay, the nanotags are oxidized to ions, which are determined by voltammetric methods, such as pulse voltammetry (PV) and stripping voltammetry (SV). The synergistic effects of NPs amplification (as each nanoprobe releases a large number of detectable ions) and the inherent sensitivity of voltammetric techniques (e.g., thanks to the preconcentration step of SV) leads to the construction of ultrasensitive, low cost, miniaturized, and integrated biodevices. This review focuses on accomplishments in DNA sensing using voltammetric determination of nanotags (such as gold and silver NPs, and Cd- and Pb-based QDs), includes published works on integrated three electrode biodevices and paper-based biosystems, and discusses strategies for multiplex DNA assays and signal enhancement procedures. Besides, this review mentions the electroactive NP synthesis procedures and their conjugation protocols with biomolecules that enable their function as labels in DNA electrochemical biosensors.

Target-protecting dumbbell molecular probe against exonucleases digestion for sensitive detection of ATP and streptavidin

In this work, a versatile dumbbell molecular (DM) probe was designed and employed in the sensitively homogeneous bioassay. In the presence of target molecule, the DM probe was protected from the digestion of exonucleases. Subsequently, the protected DM probe specifically bound to the intercalation dye and resulted in obvious fluorescence signal which was used to determine the target molecule in return. This design allows specific and versatile detection of diverse targets with easy operation and no sophisticated fluorescence labeling. Integrating the idea of target-protecting DM probe with adenosine triphosphate (ATP) involved ligation reaction, the DM probe with 5'-end phosphorylation was successfully constructed for ATP detection, and the limitation of detection was found to be 4.8 pM. Thanks to its excellent selectivity and sensitivity, this sensing strategy was used to detect ATP spiked in human serum as well as cellular ATP. Moreover, the proposed strategy was also applied in the visual detection of ATP in droplet-based microfluidic platform with satisfactory results. Similarly, combining the principle of target-protecting DM probe with streptavidin (SA)-biotin interaction, the DM probe with 3'-end biotinylation was developed for selective and sensitive SA determination, which demonstrated the robustness and versatility of this design.

Multi-level logic gate operation based on amplified aptasensor performance

Conventional electronic circuits can perform multi-level logic operations; however, this capability is rarely realized by biological logic gates. In addition, the question of how to close the gap between biomolecular computation and silicon-based electrical circuitry is still a key issue in the bioelectronics field. Here we explore a novel split aptamer-based multi-level logic gate built from INHIBIT and AND gates that performs a net XOR analysis, with electrochemical signal as output. Based on the aptamer-target interaction and a novel concept of electrochemical rectification, a relayed charge transfer occurs upon target binding between aptamer-linked redox probes and solution-phase probes, which amplifies the sensor signal and facilitates a straightforward and reliable diagnosis. This work reveals a new route for the design of bioelectronic logic circuits that can realize multi-level logic operation, which has the potential to simplify an otherwise complex diagnosis to a "yes" or "no" decision.

Dual recognition unit strategy improves the specificity of the adenosine triphosphate (ATP) aptamer biosensor for cerebral ATP assay

Adenosine triphosphate (ATP) aptamer has been widely used as a recognition unit for biosensor development; however, its relatively poor specificity toward ATP against adenosine-5'-diphosphate (ADP) and adenosine-5'-monophosphate (AMP) essentially limits the application of the biosensors in real systems, especially in the complex cerebral system. In this study, for the first time, we demonstrate a dual recognition unit strategy (DRUS) to construct a highly selective and sensitive ATP biosensor by combining the recognition ability of aptamer toward A nucleobase and of polyimidazolium toward phosphate. The biosensors are constructed by first confining the polyimidazolium onto a gold surface by surface-initiated atom transfer radical polymerization (SI-ATRP), and then the aptamer onto electrode surface by electrostatic self-assembly to form dual-recognition-unit-functionalized electrodes. The constructed biosensor based on DRUS not only shows an ultrahigh sensitivity toward ATP with a detection limit down to the subattomole level but also an ultrahigh selectivity toward ATP without interference from ADP and AMP. The constructed biosensor is used for selective and sensitive sensing of the extracellular ATP in the cerebral system by combining in vivo microdialysis and can be used as a promising neurotechnology to probing cerebral ATP concentration.

Electrochemical current rectification-a novel signal amplification strategy for highly sensitive and selective aptamer-based biosensor

Electrochemical aptamer-based (E-AB) sensors represent an emerging class of recently developed sensors. However, numerous of these sensors are limited by a low surface density of electrode-bound redox-oligonucleotides which are used as probe. Here we propose to use the concept of electrochemical current rectification (ECR) for the enhancement of the redox signal of E-AB sensors. Commonly, the probe-DNA performs a change in conformation during target binding and enables a nonrecurring charge transfer between redox-tag and electrode. In our system, the redox-tag of the probe-DNA is continuously replenished by solution-phase redox molecules. A unidirectional electron transfer from electrode via surface-linked redox-tag to the solution-phase redox molecules arises that efficiently amplifies the current response. Using this robust and straight-forward strategy, the developed sensor showed a substantial signal amplification and consequently improved sensitivity with a calculated detection limit of 114nM for ATP, which was improved by one order of magnitude compared with the amplification-free detection and superior to other previous detection results using enzymes or nanomaterials-based signal amplification. To the best of our knowledge, this is the first demonstration of an aptamer-based electrochemical biosensor involving electrochemical rectification, which can be presumably transferred to other biomedical sensor systems.