Sandwich capture ultrasensitive sensor based on biohybrid interface for the detection of Cronobacter sakazakii

A simple, rapid and ultrasensitive visual sensing method for the detection of Cronobacter sakazakii (C. sakazakii) based on a biohybrid interface was established. During the entire sensing process, quadruple-cascade amplification showed its superior sensing performance. First, the prepared immunomagnetic beads (IMB) were used to isolate and enrich specific targets from the food matrix. After adding the fusion aptamer, the aptamer sequence specifically recognized the target and formed the immune sandwich structure of antibody-target-fusion aptamer. In addition, the fusion aptamer also included the template sequence of exponential amplification reaction (EXPAR), which contained the antisense sequence of the G-rich sequence. Therefore, a large number of G-rich sequences can be generated after EXPAR can be triggered in the presence of Bst. DNA polymerase, nicking endonuclease, cDNA, and dNTP. They were self-assembled into G-quadruplex structures and then combined with hemin to form G4/hemin DNAzyme, resulting in visible coloration and measuring absorbance at 450 nm for quantitative detection. The assay showed a limit of detection (LOD) of 2 CFU/mL in pure culture and 12 CFU/g in milk powder in optimal conditions. This method provides a promising strategy for rapid and point-of-care testing (POCT) since it does not require DNA extraction, medium culturing, and expensive instrumentation. KEY POINTS: •Single-cell level detection of C. sakazakii with ultrasensitive and rapidness •The fusion aptamer integrated recognition and amplification •Sensing analysis of C. sakazakii based on cascade amplification of biohybrid interface.

An ultrasensitive aptamer-antibody sandwich cortisol sensor for the noninvasive monitoring of stress state

Cortisol is a major glucocorticoid that can affect physiological activities in the human body. Besides, it is also a biomarker that can reflect the stress state of the body. Therefore, in order to monitor stress states in a sensitive and non-invasive manner, an ultra-sensitive aptamer-antibody sandwich sensor modified with multi-walled carbon nanotubes, ordered mesoporous carbon CMK-3, and silver nanoparticles (MWCNTs/CMK-3/AgNPs) was proposed for non-invasive detection of cortisol in human saliva. The MWCNTs/CMK-3/AgNPs nanocomposite was fixed on the surface of the glassy carbon electrodes (GCEs) as the material for the first round of signal amplification, and secondary signal amplification was realized by conjugating cortisol antibodies with gold nanoparticles (AuNPs). Finally, the aptamer-antibody sandwich pattern was used to specifically recognize and bind cortisol. The concentration response range for this aptamer-antibody sandwich sensor is 0.1 pg/mL-10 ng/mL, and the limit of detection (LOD) is 0.09 pg/mL. So far, the LOD of this sensor has been relatively low, showing its good sensitivity, selectivity, stability, and reproducibility. Furthermore, it has been successfully applied to detect cortisol in saliva samples to compare the stress states of postgraduates and undergraduates.