Recently, many studies have shown the potential use of circulating exosomes as novel biomarkers for monitoring and predicting a number of complex diseases, including cancer. However, reliable and cost-effective detection of exosomes in routine clinical settings, still remain a difficult task, mainly due to the lack of adequately easy and fast assay platforms. Therefore, we demonstrate here the development of a visible and simple method for the detection of exosomes by integrating single-walled carbon nanotubes that being excellent water solubility (s-SWCNTs) and aptamer. Aptamers, specific to exosomes transmembrane protein CD63, are absorbed onto the surface of s-SWCNTs and improve the minic peroxidase activity of s-SWCNTs, which can efficiently catalyze HO-mediated oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) and lead to a change from colorless to blue in solution. However, after adding exosomes, the aptamers are bound with CD63, leaving from the surface of s-SWCNTs through conformational changes, which results the color of solution from deep to moderate, and this can be observed by the naked eye and monitored by UV-vis spectrometry. Under optimal conditions, the linear range of exosomes is estimated to be 1.84×10 to 2.21×10 particles/μL with a detection of limit (LOD) of 5.2×10 particles/μL. Consequently, a visible and simple approach detecting exosomes is successfully constructed. Moreover, this proposed colorimetric aptasensor can be universally applicable for the detection of other targets by simple change the aptamer.

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Recently, sensitive and selective detection of exosomal microRNAs (miRNAs) has been garnering significant attention, because it is related to many complex diseases, including cancer. Herein, we report a ratiometric fluorescent bioprobe based on DNA-labeled carbon dots (DNA-CDs) and 5,7-dinitro-2-sulfo-acridone (DSA) coupling with the target-catalyzing signal amplification for the detection of exosomal miRNA-21. There was high fluorescence resonance energy transfer (FRET) efficiency between carbon dots (CDs) and DSA when the bioprobe was assembled. However, in the presence of the target, with disassembling of the fluorescent bioprobe, the fluorescence intensities of CDs and DSA were changed simultaneously. Because of the ratio of dual fluorescence intensities, this ratiometric fluorescent bioprobe was able to cancel out environmental fluctuations by calculating emission intensity ratio at two different wavelengths, being robust and stable enough for detection of exosomal miRNA-21. In addition, we displayed that a single miRNA-21 can catalyze the disassembly of multiple CDs with DSA theoretically, yielding significant change in the fluorescence ratio for the detection of miRNA-21. With this signal amplification strategy, the limit of detection was as low as 3.0 fM. Furthermore, because of the introduction of lock nucleic acid to mediate the strand displacement reaction, the selectivity of this strategy was improved remarkably, even against single base mismatch sequence. More importantly, our strategy could monitor the dynamic change of exosomal miRNA-21, which maybe becomes a potential tool to distinguish cancer exosomes and nontumorigenic exosomes. In a short, this ratiometric fluorescence bioprobe possessed high stability, sensitivity and selectivity coupling with ease of operation and cost efficiency, leading to great potential for wide application.

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The simultaneous detection of various mycotoxins is indispensable for food safety since the agricultural products are often contaminated by multiple mycotoxins. Herein, we report a signal-enhancement fluorescent aptasensor based on DNA-scaffolded silver nanoculsters (DNA/AgNCs) for simultaneous detection of Ochratoxin A (OTA) and Aflatoxin B1 (AFB1). The OTA aptamer (Ap1) and the AFB1 aptamer (Ap2) immobilized on magnetic beads surface hybridize with signal probe1 (Sp1) and signal probe2 (Sp2), respectively. In the presence of these two mycotoxins, the single-strand Sps are released after Aps binding with mycotoxins due to the higher stability of mycotoxin-Ap. Through the magnetic separation, the Sps in the supernatant liquid are acted as the corresponding scaffolds to synthesize AgNCs with different photoluminescence emission bands. Intriguingly, we find that the fluorescence intensity is obviously increased after adding Zn(Ⅱ)-ion into the system, leading to a linear range from 0.001 ng/mL to 0.05 ng/mL both for OTA and AFB1 with the detection limit of 0.2 pg/mL for OTA and 0.3 pg/mL for AFB1. The proposed fluorescent aptasensor shows excellent performance towards the analytical application in real samples, providing a new model for the simultaneous detection for other mycotoxins by simple change of the aptamer.

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Based on a highly efficient 2'-O-methyl modified G-quadruplex-hemin DNAzyme and duplex-specific nuclease (DSN) assisted target recycling, a novel label-free electrochemical biosensor for microRNA-21 (miR-21) detection is developed here. By employing the strategy, this DNA biosensor can detect as low as 8 aM miR-21 and exhibits high discrimination ability even against a single-base mismatch.