Dendritic DNA-porphyrin as mimetic enzyme for amplified fluorescent detection of DNA

An ultrasensitive and specific electrochemical biosensor for DNA detection based on T7 exonuclease-assisted regulatory strand displacement amplification

An electrochemical biosensor for determination of DNA is developed based on T7 exonuclease-assisted regulatory strand displacement dual recycling signal amplification strategy. First, the hairpin probe recognized and bound the target DNA to form a double strand nucleotide structure, and then the T7 exonuclease was introduced. After be digested by T7 exonuclease, the target DNA was released and entered the next cycle of T7 exonuclease-assisted recycle amplification, while accompanied by a large number of mimic targets (output DNAs) into another cycle. Second, the mimic target reacted with double-chain substrated DNA (CP) by a regulated toehold exchange mechanism, yielding the product complex of detection probes with the help of assisted DNA (S). Finally, after many cycles, a large number of detection probes were produced for binding numerous streptavidin-alkaline phosphatases. The electrochemical biosensor showed very high sensitivity and selectivity with a dynamic response ranged from 0.1 fM to 10 pM with a detection limit of 31.6 aM. Furthermore, this proposed biosensor was successfully applied to the detection of target DNA in 20% diluted serum. The developed strategy has been demonstrated to have the potential for application in molecular diagnostics.

Multifunctional DNA dendrimer nanostructures for biomedical applications

DNA nanomaterials have attracted ever-increasing attention over the past decades due to their incomparable programmability and multifunctionality. In particular, DNA dendrimer nanostructures, as a major research focus, have been applied in the fields of biosensing, therapeutics, and protein engineering, benefiting from their highly branched configuration. With the aid of specific recognition probes and inherent signal amplification, DNA dendrimers can achieve ultrasensitive detection of nucleic acids, proteins, cells, and other substances, such as lipopolysaccharides (LPS), adenosine triphosphate (ATP), and exosomes. By virtue of their void-containing structures and biocompatibility, DNA dendrimers can deliver drugs or functional nucleic acids into target cells in chemotherapy, immunotherapy, and gene therapy. Furthermore, DNA dendrimers are being applied in protein engineering for efficient directed evolution of proteins. This review summarizes the main research progress of DNA dendrimers, concerning their assembly methods and biomedical applications as well as the emerging challenges and perspectives for future research.

Porphyrins as Colorimetric and Photometric Biosensors in Modern Bioanalytical Systems

Advances in porphyrin chemistry have provided novel materials and exciting technologies for bioanalysis such as colorimetric sensor array (CSA), photo-electrochemical (PEC) biosensing, and nanocomposites as peroxidase mimetics for glucose detection. This review highlights selected recent advances in the construction of supramolecular assemblies based on the porphyrin macrocycle that provide recognition of various biologically important entities through the unique porphyrin properties associated with colorimetry, spectrophotometry, and photo-electrochemistry.

A nanocomposite prepared from bifunctionalized ionic liquid, chitosan, graphene oxide and magnetic nanoparticles for aptamer-based assay of tetracycline by chemiluminescence

A nanocomposite was prepared from a bifunctionalized ionic liquid, chitosan on magnetic nanoparticle-modified graphene oxide (IL/Chit@MGO). It was used in a chemiluminescencc (CL) assay for tetracycline. The materials were characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray powder diffraction, nitrogen adsorption-desorption isotherm, vibrating sample magnetometry and zeta potentials. Subsequently, a tetracycline-binding aptamer (TC-Apt) acting as a recognition element, and G-quadruplex DNAzyme (G-DNAzyme) acting as a signal amplification component were modified on IL/Chit@MGO. So, the bifunctional G-DNAzyme/TC-Apt/IL/Chit@MGO was prepared. The IL/Chit@MGO is found to possess excellent loading capability for TC-Apt. This is attributed to the large specific surface and abundant charge on the surface of IL/Chit@MGO. The composite was used to construct a CL assay for tetracycline. Tetracycline binds to TC-Apt and causes the release of the G-DNAzyme. The latter catalyzes the CL of luminol-H₂O₂ CL system at pH 7.4. Under optimized conditions, the blue CL at the emission wavelength of 425 nm increases linearly in the 0.16 pM to 2.0 nM concentration range, and the detection limit is 21 fM (at 3σ). The assay is selective, reproducible and stable. The assay was applied to tetracycline detection in practical samples. The apparent recoveries are 98.0% to 101.3% for the milk sample and 97.0% to 102.2% for the water sample. Graphical abstractG-quadruplex DNAzyme (G-DNAzyme) and tetracycline aptamer (TC-Apt) bifunctionalized ionic liquid/chitosan@magnetic graphene oxide (IL/Chit@MGO) was prepared. The nanocomposite was used to construct a chemiluminescence (CL) assay for tetracycline.

Chronocoulometric aptamer based assay for staphylococcal enterotoxin B by target-triggered assembly of nanostructured dendritic nucleic acids on a gold electrode

A rapid and ultrasensitive method is described for the detection of staphylococcal enterotoxin B (SEB). It is based on the formation of a dendritic DNA superstructure by integrating (a) target-induced triggering of DNA release with (b) signal amplification by a hybridization chain reaction. Partially complementary pairing of aptamer and trigger DNA forms a duplex structure. The capture DNA is then placed on the surface of a gold electrode through gold-thiol chemistry. In the presence of SEB, the aptamer-target conjugate is compelled to form. This causes the release of trigger DNA owing to a strong competition with SEB. The trigger DNA is subsequently hybridized with the partial complementary sequences of the capture DNA to trigger HCR with three auxiliary DNA sequances (referred to as H1, H2, H3). Finally, the dendritic DNA superstructure is bound to hexaammineruthenium(III) cation by electrostatic adsorption and assembled onto the modified gold electrode. This produces an amplified electrochemical signal that is measured by chronocoulometry. Under optimal conditions, the charge difference increases linearly with the logarithm of the SEB concentrations in the range from 5 pg·mL^-1 to 100 ng·mL^-1 with a detection limit as low as 3 pg·mL^-1 (at S/N = 3). Graphical abstract An electrochemical switching strategy is presented for the sensitive detection of Staphylococcus enterotoxin B based on target-triggered assembly of dendritic nucleic acid nanostructures.

Label-free detection of fibrinogen based on the fibrinogen-enhanced peroxidase activity of a fibrinogen-hemin composite

A simple, label-free colorimetric method for the determination of fibrinogen (Fib) in plasma is presented. In this work, it was observed that Fib interacted with hemin to form a hemin-Fib composite. Because Fib prevented hemin from the formation of m-oxo-dimers, the hemin-Fib composite possesses excellent peroxidase-like activity. Importantly, the peroxidase-like activity of Fib-hemin increased with the increase in the Fib. This allows us to utilize the H₂O₂-ABTS colorimetric system for the quantitative analysis of Fib. This optimized method provided a linear determination range of 2.0-100 pM with a correlation of 0.9975. The limit of detection for Fib was experimentally determined to be 0.7 pM based on a signal-to-noise ratio (S/N) of 3. This novel approach provides a rapid, sensitive, cost efficient and robust bioassay for detection of Fib in pathology and clinical applications.