A highly sensitive and specific electrochemical sensing method for robust detection of Escherichia coli lac Z gene sequence

Proximity hybridization induced molecular machine for signal-on electrochemical detection of α-synuclein oligomers

α-synuclein oligomer is a marker of Parkinson's disease. The traditional enzyme-linked immunosorbent assay for α-synuclein oligomer detection is not conducive to large-scale application due to its time-consuming, high cost and poor stability. Recently, DNA-based biosensors have been increasingly used in the detection of disease markers due to their high sensitivity, simplicity and low cost. In this study, based on the DNAzyme-driven DNA bipedal walking method, we developed a signal-on electrochemical sensor for the detection of α-syn oligomers. Bipedal DNA walkers have a larger walking area and faster walking kinetics, providing higher amplification efficiency compared to conventional DNA walkers. The DNA walker is driven via an Mg2+-dependent DNAzyme, and the binding-induced DNA walker will continuously clamp the MB, resulting in the proliferation of Fc confined near the GE surface. The linear range and limit of detection were 1 fg/mL to 10 pg/mL and 0.57 fg/mL, respectively. The proposed signal-on electrochemical sensing strategy is more selective. It will play a significant role in the sensitive and precise electrochemical analysis of other proteins.

DNA aptamer-based non-faradaic impedance biosensor for detecting E. coli

Developing a real-time, portable, and inexpensive sensor for pathogenic bacteria is crucial since the conventional detection approaches such as enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR) assays are high cost, time-consuming, and require an expert operator. Here we present a portable, inexpensive, and convenient impedance-based biosensor using Interdigitated Electrode (IDE) arrays to detect Escherichia coli (E. coli) as a model to demonstrate the feasibility of an impedance-based biosensor. We manipulated the affinity of the IDE array towards E. coli (E. coli BL21 series) by functionalizing the IDEs' surface with an E. coli outer membrane protein (OMP) Ag1 Aptamer. To determine the dominant factors affecting the sensitivity and the performance of the biosensor in detecting E. coli, we investigated the roles of the substrate material used in the fabrication of the IDE, the concentration of the aptamer, and the composition of the carboxy aliphatic thiol mixture used in the pre-treatment of the IDE surface. In the sensing experiments we used an E. coli concentration range of 25-1000 cfu mL-1 and confirmed the binding of the OMP Ag1 Aptamer to the outer membrane protein of the E. coli by Field Emission Scanning Electron Microscopy (FESEM), Optical Microscopy, and Atomic Force Microscopy (AFM). By tuning the surface chemistry, the IDEs' substrate material, and the concentration of the OMP Ag1 Aptamer, our sensor could detect E. coli with the analytical sensitivity of approximately 1.8 Ohm/cfu and limit of detection of 9 cfu mL-1. We found that the molecular composition of the self-assembled monolayer (SAM) formed on the top of the IDEs before the attachment of the OMP Ag1 Aptamer significantly impacted the sensitivity of the sensor. Notably, with straightforward changes to the molecular recognition elements, this platform device can be used to detect a wide range of other microorganisms and chemicals relevant for environmental monitoring and public health.

Two kanamycin electrochemical aptamer-based sensors using different signal transduction mechanisms: A comparison of electrochemical behavior and sensing performance

Two typical kanamycin-A (KAN-A) electrochemical aptamer-based sensors employing different signal transduction mechanisms were deliberately designed and constructed with a similar structure. One sensor (sensor-1) was based on the classical probe conformation changing mode (PCCM) with a methylene blue (MB) label used as an electrochemical tag; the other sensor (sensor-2) used the target-induced signal probe shifting (TISPS) method with a free MB label in the assay solution. The difference in signal transduction mechanisms resulted in big differences in basic electrochemical behavior and comprehensive sensing performance. The results show that both sensor types exhibit different electrochemical behavior in square wave voltammetry, cyclic voltammetry, and in sensitivity, with detection limits of 3.0 nM for sensor-1 and 60.0 pM for sensor-2 in buffer. When validated for practical and quantitative detection of tap water and milk samples, both sensing methods performed well with detection limits of <260 nM and measurement times of <40 min. In addition, accuracy was good with mean recoveries of 72.3-92.6% and precision was acceptable with a relative standard deviation (RSD) of ≤14.2%. The basis for the similarities and differences in performance is also presented.

Voltammetric determination of the Escherichia coli DNA using a screen-printed carbon electrode modified with polyaniline and gold nanoparticles

The authors describe an electrochemical assay for fast detection of Escherichia coli (E. coli). It is based on a dual signal amplification strategy and the use of a screen-printed carbon electrode (SPCE) whose surface was modified with a polyaniline (PANI) film and gold nanoparticles (AuNPs) via cyclic voltammetry (CV). In the next step, avidin was covalently immobilized on the PANI/AuNP composite on the SPCE surface. Subsequently, the biotinylated DNA capture probe was immobilized onto the PANI/AuNP/avidin-modified SPCE by biotin-avidin interaction. Then, DNA of E.coli, digoxigenin-labeled DNA detector probe and anti-digoxigenin-labeled horseradish peroxidase (HRP) were placed on the electrode. 3,3',5,5'-Tetramethylbenzidine (TMB) and H₂O₂ solution were added and the CV electrochemical signal was generated at a potential of -0.1 V (vs. Ag/AgCl) and a scan rate 50 mV.s^-1. The assay can detect 4 × 10⁶ to 4 CFU of E. coli without DNA amplification. The biosensor is highly specific over other pathogens including Klebsiella pneumoniae, Proteus mirabilis, Enterococcus faecalis, Staphylococcus haemolyticus and Pseudomonas aeruginosa. It can be concluded that this genosensor has an excellent potential for rapid and accurate diagnosis of E.coli inflicted infections. Graphical Abstract Schematic of an electrochemical E. coli genosensor based on sandwich assay on a polyaniline/gold nanoparticle-modified screen printed carbon electrode (SPCE). The biosensor can detect 4 × 10⁶ to 4 CFU of E. coli without DNA amplification.

A target-induced logically reversible logic gate for intelligent and rapid detection of pathogenic bacterial genes

A target-induced Feynman gate acts as an intelligent biosensor to distinguish all information of the targets from the output signal patterns.

Molecular beacon mediated circular strand displacement strategy for constructing a ratiometric electrochemical deoxyribonucleic acid sensor

A novel ratiometric electrochemical sensor for sensitive and selective determination of deoxyribonucleic acid (DNA) had been developed based on signal-on and signal-off strategy. The target DNA hybridized with the loop portion of ferrocene (Fc) labeled hairpin probe immobilized on the gold electrode (GE), the Fc away from the surface of GE and the methylene blue (MB) was attached to an electrode surface by hybridization between hairpin probe and MB labeled primer. Such conformational changes resulted in the oxidation peak current of Fc decreased and that of MB increased, and the changes of dual signals are linear with the concentration of DNA. Furthermore, with the help of strand-displacement polymerization, polymerase catalyzed the extension of the primer and the sequential displacement of the target DNA, which led to the release of target and another polymerization cycle. Thus the circular strand displacement produced the multiplication of the MB confined near the GE surface and Fc got away from the GE surface. Therefore, the recognition of target DNA resulted in both the "signal-off" of Fc and the "signal-on" of MB for dual-signal electrochemical ratiometric readout. The dual signal strategy offered a dramatic enhancement of the stripping response. The dynamic range of the target DNA detection was from 10(-13) to 10(-8) mol L(-1) with a detection limit down to 28 fM level. Compared with the single signaling electrochemical sensor, the dual-signaling electrochemical sensing strategy developed in this paper was more selective. It would have important applications in the sensitive and selective electrochemical determination of other small molecules and proteins.