Dual-mode photoelectrochemical/electrochemical sensor based on Z-scheme AgBr/AgI-Ag-CNTs and aptamer structure switch for the determination of kanamycin

A fluorescent aptasensor for enzyme-free and sensitive detection of kanamycin based on entropy-driven strand displacement reaction

BACKGROUND

Kanamycin is an antibiotic that can easily cause adverse side effects if used improperly. Due to the extremely low concentrations of kanamycin in food, quantitative detection of kanamycin becomes a challenge. As one of the DNA self-assembly strategies, entropy-driven strand displacement reaction (EDSDR) does not require enzymes or hairpins to participate in the reaction, which greatly reduces the instability of detection results. Therefore, it is a very beneficial attempt to construct a highly sensitive and specific fluorescence detection method based on EDSDR that can detect kanamycin easily and quickly while ensuring that the results are effective and stable.

RESULTS

We created an enzyme-free fluorescent aptamer sensor with high specificity and sensitivity for detecting kanamycin in milk by taking advantage of EDSDR and the high specific binding between the target and its aptamer. The specific binding can result in the release of the promoter chain, which then sets off the pre-planned EDSDR cycle. Fluorescent label modification on DNA combined with the fluorescence quenching-recovery mechanism gives the sensor impressive fluorescence response capabilities. The research results showed that within the concentration range of 0.1 nM-50 nM, there was a good relationship between the fluorescence intensity of the solution and the concentration of kanamycin. Specificity experiments and actual sample detection experiments confirmed that the biosensor could achieve highly sensitive and specific detection of trace amounts of kanamycin in food, with a detection limit of 0.053 nM (S/N = 3).

SIGNIFICANCE

To our knowledge, this is the first strategy to combine EDSDR with fluorescence to detect kanamycin in food. Accurate results can be obtained in as little as 90 min with no enzymes or hairpins involved in the reaction. Furthermore, our enzyme-free biosensing method is straightforward, highly sensitive, and extremely specific. It has many possible applications, including monitoring antibiotic residues and food safety.

NIR-driven photoelectrochemical-fluorescent dual-mode biosensor based on bipedal DNA walker for ultrasensitive detection of microRNA

Optical biosensors have become powerful tools for bioanalysis, but most of them are limited by optic damage, autofluorescence, as well as poor penetration ability of ultraviolet (UV) and visible (Vis) light. Herein, a near-infrared light (NIR)-driven photoelectrochemical (PEC)-fluorescence (FL) dual-mode biosensor has been proposed for ultrasensitive detection of microRNA (miRNA) based on bipedal DNA walker with cascade amplification. Fueled by toehold-mediated strand displacement (TMSD), the bipedal DNA walker triggered by target miRNA-21 is formed through catalytic hairpin assembly (CHA), which can efficiently move along DNA tracks on CdS nanoparticles (CdS NPs)-modified fluorine doped tin oxide (FTO) electrode, resulting in the introduction of upconversion nanoparticles (UCNPs) on electrode surface. Under 980 nm laser irradiation, the UCNPs serve as the energy donor to emit UV/Vis light and excite CdS NPs to generate photocurrent for PEC detection, while the upconversion luminescence (UCL) at 803 nm is monitored for FL detection. This PEC-FL dual-mode biosensor has achieved the ultrasensitive and accurate analysis of miRNA-21 in human serum and different gynecological cancer cells. Overall, the proposed dual-mode biosensor can not only couple the inherent features of each single-mode biosensor but also provide mutual authentication of testing results, which opens up a new avenue for early diagnosis of miRNA-related diseases in clinic.

The composite of bismuth oxyiodide-bismuth/nitrogen-doped carbon for photoreduction and electrochemical/photoelectrochemical dual-model sensing of Cr(VI)

A porous bismuth oxyiodide-metal bismuth/nitrogen-doped carbon (BiOI-Bi/N-C) composite composed of BiOI nanosheets, N-C sheets, and metallic Bi nanoparticles was prepared. BiOI-Bi/N-C exhibited remarkable cathodic photoelectrochemical activity and rapid adsorption capacity for Cr(VI) ions. Interestingly, the photocatalytic process of BiOI-Bi/N-C toward Cr(VI) was pH dependent. Under acidic medium, the synthesized material displayed efficient photocatalysis and achieved 95.0% photoreduction efficacy for Cr(VI) ions to Cr³⁺ within 30 min under visible light irradiation. Under neutral medium, Cr(VI) state showed a different photocatalytic process, and Cr(OH)₃ as a product covered on BiOI-Bi/N-C, which decreased the electrochemical (EC) and photoelectrochemical (PEC) performance of BiOI-Bi/N-C. Based on the findings, BiOI-Bi/N-C was utilized as EC/PEC dual-model sensing interface for the detection of Cr(VI) ions. The presented dual-model sensing method displayed an ultralow limit of detection down to 6.8 pM for EC and 3.2 pM for PEC. It demonstrated the practical application potential for the assay of Cr(VI) in real samples.

Electrochemical determination of benomyl using MWCNTs interspersed graphdiyne as enhanced electrocatalyst

Graphdiyne (GDY) has attracted a lot of interest in electrochemical sensing application with the advantages of a large conjugation system, porous structure, and high structure defects. Herein, to further improve the sensing effect of GDY, conductive MWCNTs were chosen as the signal accelerator. To get a stable composite material, polydopamine (PDA) was employed as connecting bridge between GDY and MWCNTs-NH₂, where DA was firstly polymerized onto GDY, followed by covalently linking MWCNTs-NH₂ with PDA through Michael-type reaction. The formed GDY@PDA/MWCNTs-NH₂ composite was then explored as an electrochemical sensor for benomyl (Ben) determination. GDY assists the adsorption and accumulation of Ben molecules to the sensing surface, while MWCNTs-NH₂ can enhance the electrical conductivity and electrocatalytic activity, all of which contributing to the significantly improved performance. The proposed sensor displays an obvious oxidation peak at 0.72 V (vs. Hg|Hg₂Cl₂) and reveals a wide linear range from 0.007 to 10.0 µM and a low limit of detection (LOD) of 1.8 nM (S/N = 3) toward Ben detection. In addition, the sensor shows high stability, repeatability, reproducibility, and selectivity. The feasibility of this sensor was demonstrated by detecting Ben in apple and cucumber samples with a recovery of 94-106% and relative standard deviations (RSDs) less than 2.3% (n = 5). A sensitive electrochemical sensing platform was reported for benomyl (Ben) determination based on a highly stable GDY@PDA/MWCNTs-NH₂ composite.