Immobilization-free and label-free electrochemical DNA biosensing based on target-stimulated release of redox reporter and its catalytic redox recycling

Herein, we demonstrate a simple, homogenous and label-free electrochemical biosensing system for sensitive nucleic acid detection based on target-responsive porous materials and nuclease-triggered target recycling amplification. The Fe(CN)63- reporter was firstly sealed into the pores of Fe3O4 nanoparticles by probe DNA. Target DNA recognition triggered the controllable release of Fe(CN)63- for the redox reaction with the electron mediator of methylene blue enriched in the dodecanethiol assembled electrode and thereby generating electrochemical signal. The exonuclease III (Exo III)-assisted target recycling and the catalytic redox recycling between Fe(CN)63- and methylene blue contributed for the enhanced signal response toward target recognition. The low detection limit toward target was obtained as 478 fM and 1.6 pM, respectively, by square wave voltammetry and cyclic voltammetry methods. It also possessed a well-discrimination ability toward mismatched strands and high tolerance to complex sample matrix. The coupling of bio-gated porous nanoparticles, nuclease-assisted target amplification and catalytic redox recycling afforded the sensing system with well-controllable signal responses, sensitive and selective DNA detection, and good stability, reusability and reproducibility. It thus opens a new avenue toward the development of simple but sensitive electrochemical biosensing platform.

Swelling of Serum-Stable DNA Nanoparticles upon Target-Induced Conformational Rearrangement of Sensing Probes for the Signal-On Detection of Cancer-Related Genes

Nuclease-resistant assay probes are of significant importance for biochemical analysis and disease diagnosis. In this contribution, a reconfigurable lipidic moiety-attached DNA nanoparticle (LDN) is constructed from a cholesterol-conjugated multifunctional hairpin-type DNA probe (Chol-DP) by hydrophobicity-mediated self-assembly. The LDN holds high serum stability and displays a low false-positive signal even in a complex biological milieu. The hydrophobic cholesterol moiety enables the hydrophobicity-mediated assembly, while hydrophilic DNA sequence serves as a recognition element and a polymerization template. The initiator-activated strand displacement amplification (SDA) reaction can convert the hairpin-shaped probe into rigid double-stranded DNA (dsDNA), causing the conformational rearrangement-based LDN swelling that can be used to reliably and fluorescently signal the cancer-related p53 gene. The size increase and structural reconfiguration are confirmed by dynamic light scattering (DLS) analysis and confocal microscopy imaging, respectively. Target p53 is specifically detected down to 10 pM. The whole assay process involved only several simple mixing steps. Recovery test and blind test further confirm the feasibility of the use of the LDN for the detection of target DNA in a complex biological milieu, indicating a promising nanotool for biomedical applications.

Donor-Acceptor Compensated ZnO Semiconductor for Photoelectrochemical Biosensors

Hindering the recombination of a photogenerated carrier is a crucial method to enhance the photoelectrochemical performance of ZnO due to its high exciton binding energy. Herein, the intramolecular donor-acceptor compensated semiconductor ZnO (I-D/A ZnO), introducing C dopants and oxygen vacancies, was prepared with the assistance of ascorbic acid (AA). According to the DFT calculations, the asymmetry DOS could lead to the longer carrier lifetime and the smaller electron transfer resistance. Then, the photoelectrochemical biosensor toward glucose was regarded as a model to discuss the application of ZnO in biosensors. As a result, the biosensor based on I-D/A ZnO showed good performance with high sensitivity, low limit of detection, and fine anti-interference, meaning that I-D/A ZnO is a promising semiconductor for photoelectrochemical biosensors.

Label-Free and Ultrasensitive Biomolecule Detection Based on Aggregation Induced Emission Fluorogen via Target-Triggered Hemin/G-Quadruplex-Catalyzed Oxidation Reaction

Fluorescence biosensing strategy has drawn substantial attention due to their advantages of simplicity, convenience, sensitivity, and selectivity, but unsatisfactory structure stability, low fluorescence quantum yield, high cost of labeling, and strict reaction conditions associated with current fluorescence methods severely prohibit their potential application. To address these challenges, we herein propose an ultrasensitive label-free fluorescence biosensor by integrating hemin/G-quadruplex-catalyzed oxidation reaction with aggregation induced emission (AIE) fluorogen-based system. l-Cysteine/TPE-M, which is carefully and elaborately designed and developed, obviously contributes to strong fluorescence emission. In the presence of G-rich DNA along with K⁺ and hemin, efficient destruction of l-cysteine occurs due to hemin/G-quadruplex-catalyzed oxidation reactions. As a result, highly sensitive fluorescence detection of G-rich DNA is readily realized, with a detection limit down to 33 pM. As a validation for the further development of the proposed strategy, we also successfully construct ultrasensitive platforms for microRNA by incorporating the l-cysteine/TPE-M system with target-triggered cyclic amplification reaction. Thus, this proposed strategy is anticipated to find use in basic biochemical research and clinical diagnosis.

Highly effective molecule converting strategy based on enzyme-free dual recycling amplification for ultrasensitive electrochemical detection of ATP

An enzyme-free and highly effective molecule converting strategy was described for the sensitive electrochemical detection of ATP based on target-driven catalytic hairpin assembly and Mg²⁺-dependent DNAzymes.

Sensitive and selective detection of the p53 gene based on a triple-helix magnetic probe coupled to a fluorescent liposome hybridization assembly via rolling circle amplification

Developing a sensitive and selective sensing platform for the p53 gene and its mutation analysis is essential and may aid in early cancer screening and assessment of prognosis.