Photoelectrochemical determination of the activity of M.SssI methyltransferase, and a method for inhibitor screening

HpaII-assisted and linear amplification-enhanced isothermal exponential amplification fluorescent strategy for rapid and sensitive detection of DNA methyltransferase activity

The detection of methyltransferase (MTase) activity is of great significance in methylation-related disease diagnosis and drug screening. Herein, a HpaII-assisted and linear amplification-enhanced exponential amplification strategy is proposed for sensitive and label-free detection of M.SssI MTase activity. The P1 probe contains self-complementary sequence 5'-CTAGCCGGCTAG-3' at 3'-terminal. After denaturation and annealing, P1 probes hybridize with itself to generate P1 duplexes. M.SssI MTase induces methylation of cytosine at 5'-CG-3' in P1 duplexes, and thus, HpaII fails to cleave at 5'-CCGG-3' due to methylation sensitivity, leaving P1 duplex intact. Then, these intact P1 duplexes are extended along 3'-terminal through Vent (exo^-) DNA polymerase to generate dsDNA, which is recognized and nicked at the recognition sites by Nt.BstNBI, releasing two copies of primer X. Primer X hybridizes with X' at the amplification template T1 (X'-Y'-X') and then serves as primers to trigger the exponential amplification reaction (EXPAR). The point of inflection (POI) values of real-time fluorescence curves is linearly correlated with the logarithm of M.SssI MTase concentration in the range of 0.125 [Formula: see text] 8 U mL^-1 with a low detection limit of 0.034 U mL^-1. In the absence of M.SssI, P1 duplexes are cut by HpaII and separated into ssDNA under the executed temperature of EXPAR and thus unable to trigger the amplification. The strategy provides good selectivity against other types of MTases and protein and is able to detect M.SssI activity in human serum. Furthermore, the analytical method has the generality and can be extended to the analysis of other types of DNA MTases.

A SnO2/Bi2S3-based photoelectrochemical aptasensor for sensitive detection of tobramycin in milk

Abuse of tobramycin (TOB) causes a series of diseases. Therefore, the development of rapid and sensitive method for analyzing TOB in food products is necessary. In this work, aptamer modified SnO₂/Bi₂S₃-based photoelectrochemical (PEC) sensor was developed for the determination of TOB in milk. Under optimal condition, a wide linear response for TOB from 5 to 50 nmol/L with a limit of detection of 4.28 nmol/L is reached. The possible detection mechanism is that TOB molecules are specifically captured by aptamer, increasing electron transfer resistance and declining the photocurrent. Thanks to the favorably matched energy level of SnO₂, and Bi₂S₃, the PEC aptasensor exhibits high sensitivity, and with the aid of oxalate, the sensitivity of the sensor is further improved. Importantly, the stability of the PEC aptasensor is also satisfactory due to the calcination of SnO₂/Bi₂S₃ at 450 °C.

Photoelectrochemical immunosensor for methylated RNA detection based on WS2 and poly(U) polymerase-triggered signal amplification

A novel photoelectrochemical immunosensor has been constructed for the determination of methylated RNA. MoS₂ nanosheets with large specific area were employed as photoactive material, gold nanoparticles were used as signal amplification unit and immobilization matrix of 4-mercaptophenylboronic acid, anti-m⁶A antibody was adopted as methylated RNA recognition reagent, and poly(U) polymerase-mediated RNA chain extension and Ru(NH₃)₆³⁺ were used as assisted signal amplification unit. With the sensitization effect of Ru(NH₃)₆³⁺, the photoactivity of WS₂ nanosheets was improved greatly, which also improved the sensitivity. Using visible-light excitation and ascorbic acid as electron donor, the sensitive determination of methylated RNA was achieved by monitoring the photocurrent change with different concentrations of methylated RNA. This photoelectrochemical immunosensor has a wide linear relationship with methylated RNA concentration from 0.05 to 35 nM under optimal experimental conditions. The low detection limit of 14.5 pM was realized based on 3σ criterion. In addition to the good selectivity, this sensor also presents high reproducibility with a relative standard deviation of 1.4% for the photocurrent of seven electrodes. The applicability of the developed method was also investigated by detecting the level of methylated RNA in corn seedling leaves with and without sulfadiazine treatment. Graphical abstract A novel photoelectrochemical immunosensor was developed for methylated RNA detection using the photoactive material of MoS2 and poly(U) polymerase-mediated RNA chain extension.

A flexible carbon nanotube-modified poly(styrene-butadiene)-based dopamine sensor

In this work, a multi-walled carbon nanotube-modified flexible poly(styrene-butadiene) fiber membrane material was prepared for the sensitive and selective electrochemical detection of dopamine (DA) in human serum and DA injection. The flexible fiber membrane prepared by electrospinning technology is expected to realize its application in wearable devices. The obtained conductive film-based electrochemical sensor can effectively minimize interference caused by ascorbic acid and uric acid. Under the optimized experimental conditions of differential pulse voltammetry, DA gives a linear response in the range of 1-650 μM (R² = 0.996). The detection limit of DA (signal-to noise ratio = 3) was determined to be 0.062 μM.

Label-free and near-zero-background-noise photoelectrochemical assay of methyltransferase activity based on a Bi2S3/Ti3C2 Schottky junction

Based on Bi₂S₃/Ti₃C₂ nanosheets, a label-free photoelectrochemical sensing platform with near-zero background noise was developed for M.SssI methyltransferase activity assay.

Colorimetric determination of the activity of methyltransferase based on nicking enzyme amplification and the use of gold nanoparticles conjugated to graphene oxide

A method is described for the colorimetric determination of the activity of CpG methyltransferase (M.SssI). It is based on (a) the crosslinking effect between dsDNA-modified gold nanoparticles (AuNPs) and graphene oxide (GO), and (b) an amplification reaction with the aid of a nicking enzyme. To avoid the aggregation of AuNPs (which would produce false signals), a hairpin DNA was connected to the AuNPs. Thus, the red color of the solution (measured at 530 nm) increases linearly with the activity of M.SssI from 0.2 to 60 U·mL^-1, and the limit of detection is 67 U·mL^-1. This is superior to some reported strategies. The method was successfully applied to analyze spiked serum samples. Conceivably, it represents a powerful tool for use in drug development and diagnosis. Graphical abstracts A method based on the conjugated cross-linking effect between dsDNA modified Au NPs and GO coupled with an amplification reaction of nicking enzyme has been developed for colorimetric detection of the activity of CpG methyltransferase (M.SssI).

A photoelectrochemical sandwich immunoassay for protein S100β, a biomarker for Alzheimer's disease, using an ITO electrode modified with a reduced graphene oxide-gold conjugate and CdS-labeled secondary antibody

A sandwich-type photoelectrochemical immunoassay is described for the protein S100ß which is an Alzheimer's disease biomarker found in the astrocytes of the brain. Antibody against S100ß (anti-S100ß) was labeled with CdS quantum dots and then acted as a secondary antibody. The labeled antibody was characterized by FTIR, ultraviolet-visible and fluorescence spectroscopy. An indium-tin oxide (ITO) electrode was modified with a nanocomposite prepared from reduced graphene oxide and gold nanoparticles. Then, a sol-gel film containing isocyanate functional groups (-N=C=O) was cast on the surface of the electrode. The NCO group reacts with amino groups of the labeled antibody to covalently bind them to the surface. The S100β was bound by the primary immobilized antibody on the rGO-Au/ITO electrode and then sandwiched with the labeled secondary antibody. Cyclic voltammetry and electrochemical impedance spectroscopy were applied to confirm the stepwise changes in the electrochemical properties of the electrode surface. The photoelectrochemical immunoassay, typically operated at a potential of +0.2 V (vs. Ag|AgCl_sat) gives a signal that is related to the logarithm of the S100β concentration in the range from 0.25 to 10 ng·mL^-1 with a lower detection limit of 0.15 pg·mL^-1. The method was successfully applied to the determination of S100β in human serum samples. Graphical abstract Schematic presentation of an immunosensor which is based on an indium tin oxide modified with reduced graphene oxide decorated with gold nanocomposite and antibody. The immunosensor was applied for the determination of S100β biomarker by using in the labeled antibody.