Lai Shanshan,Guo Jiahong,Li Xin,Yu Xiaoxiao,Lai Guosong
Fluorescence biosensors hold significant importance for testing antibiotic residues which seriously endanger public health. However, how to adopt appropriate strategies to address the false result disadvantage involved in traditional single-channel biosensors is still a great challenge. Meanwhile, too much attention focused on designing signal amplification strategies of biosensors unavoidably decreases their detection efficiency. Herein, we combined the designed dual DNA recycling amplification strategy with CRISPR/Cas12a-mediated dual-channel signal output mode to successfully develop a novel ratiometric fluorescence biosensor for testing kanamycin (Kana) residues in complex sample matrices. The first recycling was formed from an exonuclease-assisted aptamer recognition reaction, which also triggered another cascade DNA recycling to amplify the release of the Cas12a activator. With the non-discrimination cleavage of Cas12a to cause reverse fluorescence changes of copper nanoclusters and an AMAC-labeled signal DNA, the ratiometric signal transduction strategy was constructed. Under optimal conditions, this biosensor could be applied for ultrasensitive testing of Kana antibiotics in a five-order of magnitude wide linear range with a low detection limit of 17.2 fg mL −1 . Benefiting from the self-correction function of the ratiometric signal transduction mode, it showed promising practicality in lake water and milk samples with the relative error less than 4.9% to the standard ELISA results. Besides CRISPR/Cas12a-based fluorescence output efficiency improvement, this biosensor also excluded the complicated manipulations and expensive instruments required in traditional methods. Therefore, it provides a good choice for expanding the application of fluorescence biosensing technology for practical analysis application. Graphical
An aptamer based assay is described for the colorimetric detection of adenosine. The presence of adenosine triggers the deformation of hairpin DNA oligonucleotide (HP1) containing adenosine aptamer and then hybridizes another unlabeled hairpin DNA oligonucleotide (HP2). This leads to the formation of a double strand with a blunt 3′ terminal. After exonuclease III (Exo III)-assisted degradation, the guanine-rich strand (GRS) is released from HP2. Hence, the adenosine-HP1 complex is released to the solution where it can hybridize another HP2 and initiate many cycles of the digestion reaction with the assistance of Exo III. This leads to the generation of a large number of GRS strands after multiple cycles. The GRS stabilize the red AuNPs against aggregation in the presence of potassium ions. If, however, GRS forms a G-quadruplex, it loses its ability to protect gold nanoparticles (AuNPs) from salt-induced AuNP aggregation. Therefore, the color of the solution changes from red to blue which can be visually observed. This colorimetric assay has a 0.13 nM detection limit and a wide linear range that extends from 5 nM to 1 μM.
Schematic presentation of a colorimetric aptamer biosensor for adenosine detection based on DNA cycling amplification and salt-induced aggregation of gold nanoparticles.
Naked eye-based detection has received increasing research interest due to the simplicity nature of this type of assay. However, improving the sensitivity of the naked eye detection method for the monitoring of trace amount of target molecules remains a major challenge. Herein, we describe a biobarcode and an enzyme-assisted DNA recycling hybrid amplification strategy for naked eye detection of sub-picomolar carcinoembryonic antigen (CEA), a cancer biomarker. The presence of CEA and the corresponding antibodies results in the formation of immunocomplexes and the capture of the biobarcodes in a microplate. The massive barcode DNAs released from the biobarcodes hybridize with the G-quadruplex inactive hairpin DNA probes and form catalytic nicking sites for N.BstNBI endonuclease , which cleaves the barcode DNA/hairpin partial dsDNA, releases the G-quadruplex active sequences and recycles the barcode DNA. Due to the barcode DNA recycling process, numerous G-quadruplex active sequences are generated and associate with hemin to form peroxidase mimicking enzymes, which convert colorless ABTS 2− to green color intensified ABTS − to achieve naked eye detection of CEA down to 0.025 ng mL −1 (0.14 pM). The naked eye detection strategy reported herein can be applied also to complicated serum sample matrix , making this approach hold great promise for point-of-care diagnostic applications.
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