Smartphone-assisted colorimetric biosensor for on-site detection of Cr3+ ion analysis.

A simple and low-cost biosensor has been established for the detection of Cr3+ ion by using the image processing function of the smartphone. In the presence of Cr3+ ion, its dependent DNAzyme can specifically cleave the substrate strand, resulting in the release of ligation probe, which will trigger hyperbranched rolling circle amplification (HRCA) to produce hydrogen ions, causing the color change of the solution containing cresol red. A free APP named "Pixel Picker" has been further used to measure the RGB values. It can be well found that the R/G values correlate with Cr3+ ion concentrations with a linear detection range of 0.5 µM-500 µM and a lowest detection limit of 0.12 µM. In addition, the proposed biosensor has been successfully applied to determine Cr3+ ions in various milks. In a word, the constructed smartphone-assisted colorimetric biosensor has the advantages of simplicity, low cost, high specificity and anti-interference ability.

Application of Chemoselective Ligation in Biosensing.

With the advantages of mild reaction condition as well as high stereoselectivity and efficiency, chemoselective ligations including oxime chemistry, hydrazone chemistry, cycloaddition reaction, C-C multiple bond addition reaction, nucleophilic rings opening reaction, and alkynes-based reaction, have been applied in the field of biosensing. In this review, the roles of these chemoselective ligations for the construction of biosensors have been summarized. The ligations can serve for reactant preparation, interface modification, signal probe synthesis, molecular recognition, signal amplification, and output. Meanwhile, their recent applications for detection of various targets including small molecules, metal ions, protein, and nucleic acid so on, have been reviewed. Moreover, the development trend of these ligations in biosensing has also been prospected in this review.

DNAzyme-based colorimetric assay and its application for lipopolysaccharide analysis assisted by oxime chemistry.

Herein, for the first time, we propose that the cleavage activity of DNAzyme is accompanied by the release of hydroxyl ions, which can be used for colorimetric assay. Subsequently, we further construct a colorimetric strategy for lipopolysaccharide (LPS) analysis by using this property. Detailly, DNAzyme is split into two fragments separately modified with aldehyde group and hydroxylamine group, which can be linked together through oxime chemistry and the presence of LPS can prevent the formation of oxime bond. The formed whole DNAzyme can mediate the release of hydroxyl ions serving for colorimetric signal output. Taking LPS as model targets, DNAzyme-based colorimetric assay has been successfully constructed. This work not only provides a colorimetric strategy to analyze DNAzyme activity, but also gives a new insight to enrich the versatility of DNAzymes and to enhance their multifunctionality.

Chemoselective ligation assisted DNA walker for analysis of double targets.

Chemoselective ligation assisted DNA walker with input and output of double signals, has been constructed through simultaneous assistance of oxime chemistry and alkyne-azide cycloaddition. The constructed DNA walker has been further developed as a biosensor with lipopolysaccharide (LPS) and 5-hydroxymethyl-2-furaldehyde (HMF) as targets. The biosensor owns one-to-one mapping functionality and can sensitively distinguish all cases of two targets through the unique output signal feature. Moreover, the biosensor can simultaneously analyze LPS and HMF. This work provides a new insight for analysis of double targets based on chemoselective ligation assisted DNA walker.

Hydrazone chemistry mediated toehold strand displacement cascade and its application for 5-hydroxymethylfurfural analysis.

Hydrazone chemistry has been firstly explored as capturing mode for interface supported toehold strand displacement cascade (TSDC). The method has been further established for analysis of 5-hydroxymethylfurfural (HMF) based on hydrazone chemistry-mediated TSDC. HMF containing aldehyde group can be covalently captured by hydrazine group around magnetic bead through the formation of hydrazone bond, so as to inhibit the immobilization of hybrid duplex and the occurrence of TSDC. Thereby, HMF will cause the change of the fluorescence of modified magnetic bead. With simplicity, specificity, and sensitivity, the method has been successfully applied to analyze HMF in food samples. This paper gives a new insight to explore capturing mode for interface supported TSDC and the established method can be extended for analysis of saccharic derivatives.

Fabrication of pH-Adjusted Boronic Acid-Aptamer Conjugate for Electrochemical Analysis of Conjugated N-Glycolylneuraminic Acid.

In this work, the boronic acid-aptamer conjugate (BAAC) is elaborately designed and explored as a recognition unit. The admirable properties of the pH-dependent boronic acid ester are integrated with the specific capturing capability of the modified aptamer; thus, BAAC can efficiently and selectively bind with the target by adjusting the pH values. An electrochemical biosensor based on pH-adjusted BAAC has been further developed for the analysis of CNeu5Gc, an important biomarker of different kinds of cancer. The boronic acid moiety in BAAC can react with CNeu5Gc to form a BAAC-CNeu5Gc complex under acidic conditions, followed by the release of CNeu5Gc from the complex and subsequent capture by the aptamer moiety with the adjustment of the pH value to alkalinity. With simplicity, high specificity, and efficiency, the biosensor exhibits a wide linear range from 2.816 to 3603.960 ng/mL with a low detection limit of 1.224 ng/mL and can be applied to analyze CNeu5Gc in animal food samples. Besides, this work can also provide a kind of modified aptamer, i.e., the chemical capturing group-modified aptamer, to give a new viewpoint for the exploration of other functionalized aptamers.