A FRET-based detection of N-acetylneuraminic acid using CdSe/ZnS quantum dot and exonuclease III-assisted recycling amplification strategy

A FRET based ultrasensitive fluorescent aptasensor for 6'-sialyllactose detection

As a kind of human milk oligosaccharide, 6'-sialyllactose (6'-SL) plays an important role in promoting infant brain development and improving infant immunity. The content of 6'-SL in infant formula milk powder is thus one of the important nutritional indexes. Since the lacking of efficient and rapid detection methods for 6'-SL, it is of great significance to develop specific recognition elements and establish fast and sensitive detection methods for 6'-SL. Herein, using 6'-SL specific aptamer as the recognition element, catalytic hairpin assembly as the signal amplification technology and quantum dots as the signal label, a fluorescence biosensor based on fluorescence resonance energy transfer (FRET) was constructed for ultra-sensitive detection of 6'-SL. The detection limit of this FRET-based fluorescent biosensor is 0.3 nM, and it has some outstanding characteristics such as high signal-to-noise ratio, low time-consuming, simplicity and high efficiency in the actual sample detection. Therefore, it has broad application prospect in 6'-SL detection.

Exonuclease-based aptasensors: Promising for food safety and diagnostic aims

As of today's requirement, developing cost-effective smart sensing tools with ultrahigh sensitivity for food safety insurance is of special importance. For this purpose, aptamer-based biosensors (aptasensors) powered by the superiorities of the recycling signal amplification strategies have been expanded especially. Target recycling supported by enzymes is an appealing approach for implementing signal amplification. As the supreme biocatalyst enzymes, exonucleases can inaugurate signal improvement by involving a single target in a process would result in appreciable repeating cycles of the cleavage of the phosphodiester bonds between the building blocks of the nucleic acid strands, and also, their terminals. Although there are diverse substances for catalyzing amplification strategies, including nanoparticles, carbon-based nanocomposites, and quantum dots (QDs), exonucleases are of superiority over them by simplifying the amplification process with no need for the complicated pre-treatment processes. The outstanding selectivity and great sensitivity of the aptasensors tuned by amplification potency of exonucleases nominate them as the promising sensing tools for label-free, ease-of-use, cost-effective, and real-time diagnosis of diverse targets. Here, we summarize the achievements and perspectives in the scientific branch of aptasensor design for the qualitative monitoring of diverse targets by cooperation of exonucleases with the conspicuous potential for the signal amplification. Finally, some results are expressed to provide a comprehensive viewpoint for developing novel nuclease-based aptasensors in the future.

Metal selenide nanomaterials for biomedical applications

Metal selenide nanomaterials have received enormous attention as they possess diverse compositions, microstructures, and properties. The combination of selenium with various metallic elements gives the metal selenide nanomaterials distinctive optoelectronic and magnetic properties, such as strong near-infrared absorption, excellent imaging properties, good stability, and long in vivo circulation. This makes metal selenide nanomaterials advantageous and promising for biomedical applications. This paper summarizes the research progress in the last five years in the controlled synthesis of metal selenide nanomaterials in different dimensions and with different compositions and structures. Then we discuss how surface modification and functionalization strategies are well-suited for biomedical fields, including tumor therapy, biosensing, and antibacterial biological applications. The future trends and issues of metal selenide nanomaterials in the biomedical field are also discussed.

Electrochemical Evaluation of Tumor Development via Cellular Interface Supported CRISPR/Cas Trans-Cleavage

Evaluating tumor development is of great importance for clinic treatment and therapy. It has been known that the amounts of sialic acids on tumor cell membrane surface are closely associated with the degree of cancerization of the cell. So, in this work, cellular interface supported CRISPR/Cas trans-cleavage has been explored for electrochemical simultaneous detection of two types of sialic acids, i.e., N-glycolylneuraminic acid (Neu5Gc) and N-acetylneuraminic acid (Neu5Ac). Specifically, PbS quantum dot-labeled DNA modified by Neu5Gc antibody is prepared to specifically recognize Neu5Gc on the cell surface, followed by the binding of Neu5Ac through our fabricated CdS quantum dot-labeled DNA modified by Sambucus nigra agglutinin. Subsequently, the activated Cas12a indiscriminately cleaves DNA, resulting in the release of PbS and CdS quantum dots, both of which can be simultaneously detected by anodic stripping voltammetry. Consequently, Neu5Gc and Neu5Ac on cell surface can be quantitatively analyzed with the lowest detection limits of 1.12 cells/mL and 1.25 cells/mL, respectively. Therefore, a ratiometric electrochemical method can be constructed for kinetic study of the expression and hydrolysis of Neu5Gc and Neu5Ac on cell surface, which can be further used as a tool to identify bladder cancer cells at different development stages. Our method to evaluate tumor development is simple and easy to be operated, so it can be potentially applied for the detection of tumor occurrence and development in the future.

Construction of a fluorescence biosensor for ochratoxin A based on magnetic beads and exonuclease III-assisted DNA cycling signal amplification

Specific and sensitive detection of hazardous mycotoxins in agricultural crops is one of the most important goals of food safety. A fluorescence biosensor for sensitive detection of ochratoxin A (OTA) was constructed via magnetic beads and the exonuclease III (Exo III)-assisted trigger DNA circle amplification approach. Exo III-assisted trigger DNA circle amplification can be utilized as an effective strategy for the sensitive detection of OTA. The employment of streptavidin labeled magnetic beads offers a manner for the accumulation and separation of the hairpin signal probe sDNA-FAM in solution. After target specific recognition, the aptamers combined with OTA were released and the remaining block DNA (bDNA) probes captured the signal probes on magnetic bead modified fluorophores. Subsequently, the enzyme digestion reaction leads to the fluorophore free solution. Exo III-assisted DNA circle amplification contributed to the high sensitivity of the presented OTA fluorescence aptasensor. The experimental results demonstrate that the aptasensor is sensitive with the limit of detection as low as 0.28 ng mL^-1 for OTA, which was lower than that of the proposed aptasensors reported by the other literature on fluorescence methods. Additionally, the developed aptasensor with the diverse aptamer sequence shows promising potential applications in food monitoring.

Self-assembled nanoplatforms with ZIF-8 as a framework for FRET-based glutathione sensing in biological samples

A nanoprobe was constructed by embedding QDs and a rhodamine B derivative (RBD) into ZIF-8. Then, the ultraviolet absorption of RBD that reacted with glutathione can overlap with the emission spectrum of the QDs, causing FRET-based glutathione sensing.