DNA aptamers selection and characterization for development of impedimetric aptasensor for Bacillus cereus at different growing stages

The physiology(membrane integrity,intracellular esterase and redox activity)of individual pathogenic bacteria is various in different growing phase,which has a profound significance for food safety testing and control.In this work,the aptamers against B.cereus in different growing phase was firstly selected based on whole bacterium-SELEX screening approach.Out of 32 candidate aptamers screened,aptamer B15 and B16 showed relatively high binding affinity with an apparent dissociation constant(Kd value)of 16.134.98 nM and 20.675.23 nM,respectively.A label-free impedance based aptasensor was further fabricated based on the screened aptamer,immobilized onto the GCE/Au surface.With the addition of B.cereus,the electron transfer process was prevented and exhibited a significant decrease in the electron-transfer resistance.Under optimal conditions,the fabricated aptasensor can achieve high sensitive detection of B.cereus as low as 10 cfu/mL.A satisfactory recovery of 90.5%–105.3%was achieved for the B.cereus detection in spiked milk samples,exhibiting its prospect in the sensitive detection of B.cereus in daily life.

Multifunctional Ce-MOF@PdNPs with colorimetric fluorescent electrochemical activity for ultrasensitive and accurate detection of diethylstilbestrol

The development of biosensors is gaining tremendous attention in various fields due to their extraordinary advantages, however, their sensitivity and accuracy are still challenging. Herein, we proposed a novel multifunctional nanocomposite Ce-MOF@PdNPs (MOF = metal-organic framework, PdNPs = Pd nanoparticles)-mediated triple-readout aptasensor for accurate and reliable detection of diethylstilbestrol (DES), in which Ce-MOF@PdNPs exhibited excellent peroxidase (POD)-like activity, fluormetric, and electro conductive properties. In addition, enzymes-assisted target recycling amplification was utilized to improve the sensitivity, that is the specific binding of aptamer and DES triggered an Exo III enzyme-assisted recycling reaction. The generated F-DNA was captured by the H3 strand linked to Ce-MOF@PdNPs immobilized on the electrode, exposing cleavage sites and activating the Nt.BbvCI enzyme-assisted recycling reaction, leading to the dissociation of Ce-MOF@PdNPs and a significant reduced electrochemical signal. The collected Ce-MOF@PdNPs solution also induced a proportional change in the color and fluorescence, achieving a colorimetric and fluormetric detection functionality. The detection limit under colorimetric mode was 0.16 and 0.76 ng/mL under fluorescence mode, and 0.87 pg/mL under electrochemical mode. This triple-readout aptasensor exhibits high sensitivity, selectivity and accuracy, providing a new idea for designing novel biosensing platforms for veterinary drug residue detection.