pH-responsive DNA hydrogels with ratiometric fluorescence for accurate detection of miRNA-21.

DNA hydrogels are powerful candidates for stable and sensitive detection of disease-related nucleic acids. However, the ability to accurately detect is the cornerstone of disease diagnosis. To improve the accuracy of DNA hydrogels for detecting targets, we herein reported the design of pH-responsive DNA hydrogels with ratiometric fluorescence. The DNA hydrogels were prepared from the pH-sensitive ZnO-NH2 and CO-Y-DNA probe assembled by the three complementary strands. With the use of miRNA-21 as the model analyte, the DNA hydrogels were applied to fluorescence ratio detection. Under acidic conditions, the ZnO-NH2 was decomposed, thereby releasing the CO-Y-DNA probe. Target miRNA-21 hybridized to the CO-Y-DNA probe, causing the change of fluorescence ratio between TAMRA and Cy5 that both modified in the CO-Y-DNA probe. The developed DNA hydrogels exhibited high accuracy and sensitivity with a low detection limit to 83 pM. In addition, the DNA hydrogels showed long-term stability against DNase I and GSH.

Double G-quadruplexes in a copper nanoparticle based fluorescent probe for determination of HIV genes.

A DNA-templated copper nanoparticle (CuNP) probe has been developed for the determination of the human immunodeficiency virus oligonucleotide (HIV-DNA). The function of the probe relies on affinity binding-induced DNA hybridization associated with the use of double G-quadruplexes. Double-stranded DNA (dsDNA) with poly(AT-TA) bases was used as a template for synthesis of dsDNA-CuNPs. These have weak fluorescence. In the next step, two G-rich sequences that are linked to both sides of the ds-DNA are locked by HIV complementary DNA (cDNA). If HIV-DNA is introduced, it will hybridize with cDNA, thereby transforming the two G-rich sequences into G-quadruplexes. This enhances the fluorescence of the adjacent dsDNA-CuNPs. Fluorescence increases linearly in the 1 to 200 and 250-1000 nM HIV-DNA concentration range, and the detection limit is 13 pM. This enzyme-free fluorometric assay is time-saving, easily operated, and therefore has large potential in biosensing because it may be extended to various other DNA targets. Graphic abstract Double-strand DNA-templated copper nanoparticles (DNA-CuNPs) have weak fluorescence. When Human Immunodeficiency Virus oligonucleotide (HIV-DNA) is added, it completely hybridized with HIV complementary DNA (cDNA). As a result, the two exposed G-rich sequences are transformed into G-quadruplexes, and an apparent increase in the fluorescence intensity can be observed. (AA: ascorbic acid).

An interference-free and label-free sandwich-type magnetic silicon microsphere -rGO-based probe for fluorescence detection of microRNA.

An interference-free and label-free sensing platform was developed for the highly sensitive detection of microRNA-21 (miRNA-21) in vitro by magnetic silicon microsphere (MNP)-reduced graphene oxide (rGO)-based sandwich probe. In this method, DNA capture probes (P1) were connected with MNPs at the 5' end and hybridized with completely complementary target miRNA. Subsequently, rGO was retained and induced the fluorescence quenching in the supernatant. Through the magnetic separation, the supernatant environment was simplified and the interference to analytical signal was eliminated. When DNA capture probe-modified magnetic silicon microspheres (MNP-P1) were adsorbed through rGO in the absence of a target and formed a sandwich structure, the formed nanostructure was easily removed from the solution by a magnetic field and the fluorescence intensity was maximally recovered. This proposed strategy, which both overcame the expensive and cumbersome fluorescent labeling, and eliminated interference to analytical signal for guaranteeing high signal-to-background ratio, exhibited high sensitivity with a detection limit as low as 0.098nM and special selectivity toward miRNA-21. The method was potentially applicable for not only detection of miRNA-21 but also various biomarker analyses just by changing capture probes.

A resonance light scattering sensor based on bioinspired molecularly imprinted polymers for selective detection of papain at trace levels.

A novel resonance light scattering sensor based on the molecularly imprinted polymers (MIPs) technique was developed for specific recognition of the trace quantities of papain (Pap). In this sensor, as the specific recognition element, an excellent biocompatibility of protein-imprinted polymer without fluorescent materials was easily prepared, which based on the effective synthesis of mussel-inspired bionic polydopamine (PDA) on the surface of SiO2 nanoparticles (SiO2@PDA NPs). This recognition element could capture the target protein selectively, which led to the enhancement of resonance light scattering intensity with the increasing of the target protein concentration. The sensor was applied to determine Pap in the linear concentration range of 2.0-20.0 nM with a correlation coefficient r = 0.9966, and a low detection limit of 0.63 nM. The relative standard deviation for 14 nM of Pap was 1.02% (n = 7). In addition, the specificity study confirmed the resultant Pap-imprinted SiO2@PDA NPs had a high-selectivity to Pap, and the practical analytical performance was further examined by evaluating the detection of Pap in the dietary supplement with satisfactory results, with good recoveries of 97.5-105.3%.