Laborious and costly detection of miRNAs has brought challenges to its practical applications, especially for home health care, rigorous military medicine, and the third world. In this work, we present a pH-responsive miRNA amplification method, which allows the detection of miRNA just using a pH test paper. The operation is easy and no other costly instrument is involved, making the method very friendly. In our strategy, a highly efficient isothermal amplification of miRNA is achieved using an improved netlike rolling circle amplification (NRCA) technique. Large amounts of H can be produced as a byproduct during the amplification to induce significant changes of pH, which can be monitored directly using a pH test paper or pH-sensitive indicators. The degree of color changes depends on the amount of miRNA, making it possible for quantitative analysis. As an example, the method is successfully applied to quantify a miRNA (miR-21) in cancer cells. The results agree well with that from the prevalent qRT-PCR analysis. It is the first time that a paper-based point-of-care testing (POCT) is developed for the detection of miRNAs, which might promote the popularization of miRNAs working as biomarkers for diagnostic purposes.

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Metal-organic frameworks (MOFs) receive more and more interest in the field of analytical chemistry for their diverse structures and multifunctionality. In this study, we have designed and fabricated nanoscale MOF-based nanoprobes for multicolor detection of DNA targets with improved sensitivity. To do so, MOF-based nanoprobes, constructed by using porous MOFs as a scaffold to load signal dyes and a DNA hairpin structure as capping shell, have been prepared. Once the target has been introduced, a competitive displacement reaction triggers the release of fluorophores from the MOFs' pores. Consequently, a significantly enhanced fluorescence signal can be observed owing to the high loading capacity of MOFs. Therefore, the stimuli-responsive nanoprobes can enable sensitive detection of DNA targets with a low detection limit of 20 fM and selective identification to discriminate single-base mismatch. Moreover, the MOFs can encapsulate different fluorophores with different DNA gatekeepers designed according to the sequence of the target DNA, resulting in more kinds of stimuli-responsive nanoprobes for multiplexed DNA analysis in the same solution. Furthermore, these smart nanoprobes reported in this paper may provide a unique MOF-based tool for detection of various targets via stimuli-responsive systems in the future to widen the applications of MOFs.

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Rapid and accurate identification of semen is critical for male infertility diagnosis and the arrangement of personalized treatment. However, the complexity and diversity of samples impose lots of restrictions in detection. To solve this problem, we propose a colorimetric sensor array in this work by coupling zirconium metal–organic frameworks (Zr-MOFs) with single-stranded-DNA-decorated gold nanoparticles (ssDNA-AuNPs) for human semen identification. Because of the coordination interactions between the Zr6 clusters and the DNA phosphate backbone, as well as π–π stacking and H-bonding, Zr-MOFs can absorb and precipitate AuNPs with the aid of single-stranded DNA. What’s more, addition of semen samples in the test solution, proteins, or other contents in the samples will affect the co-precipitation of Zr-MOFs and ssDNA-AuNPs. Subsequently, the color of the supernatant will change and a method to identify human semen can be developed. Further studies reveal that the method can completely detect different semen cases based on the differences in inclusions, demonstrating the characteristics of simplicity, feasibility, and sensitivity in the application of male infertility diagnosis.