Ultra-sensitive and rapid detection of Salmonella enterica and Staphylococcus aureus to single-cell level by aptamer-functionalized carbon nanotube field-effect transistor biosensors.

Foodborne diseases caused by Salmonella enterica (S. enterica) and Staphylococcus aureus (S. aureus) significantly impact public health, underscoring the imperative for highly sensitive, rapid, and accurate detection technologies to ensure food safety and prevent human diseases. Nanomaterials hold great promise in the development of high-sensitivity transistor biosensors. In this work, field-effect transistor (FET) comprising high-purity carbon nanotubes (CNTs) were fabricated and modified with corresponding nucleic acid aptamers for the high-affinity and selective capture of S. enterica and S. aureus. The aptamer-functionalized CNT-FET biosensor demonstrated ultra-sensitive and rapid detection of these foodborne pathogens. Experimental results indicated that the biosensor could detect S. enterica at a limit of detection (LOD) as low as 1 CFU in PBS buffer, and S. aureus at an LOD of 1.2 CFUs, achieving single-cell level detection accuracy with exceptional specificity. The biosensor exhibited a rapid response time, completing single detections within 200 s. Even in the presence of interference from six complex food matrices, the biosensor maintained its ultra-sensitive (3.1 CFUs) and rapid response (within 200 s) characteristics for both pathogens. The developed aptamer-functionalized CNT-FET biosensor demonstrates a capability for low-cost, ultra-sensitive, label-free, and rapid detection of low-abundance S. enterica and S. aureus in both buffer solutions and complex environments. This innovation holds significant potential for applying this detection technology to on-site rapid testing scenarios, offering a promising solution to the pressing need for efficient and reliable pathogen monitoring in various settings.

A micro-carbon nanotube transistor for ultra-sensitive, label-free, and rapid detection of Staphylococcal enterotoxin C in food.

Staphylococcal enterotoxin C (SEC) is an enterotoxin produced by Staphylococcus aureus, which can cause intestinal diseases. Therefore, it is of great significance to develop a sensitive detection method for SEC to ensure food safety and prevent foodborne diseases in humans. A field-effect transistor (FET) based on high-purity carbon nanotubes (CNTs) was used as a transducer, and a nucleic acid aptamer with high affinity was used for recognition to capture the target. The results indicated that the biosensor achieved an ultra-low theoretical detection limit of 1.25 fg/mL in PBS, and its good specificity was verified by detecting target analogs. Three typical food homogenates were used as the solution to be measured to verify that the biosensor had a swift response time (within 5 min after sample addition). An additional study with a more significant basa fish sample response also showed excellent sensitivity (theoretical detection limit of 8.15 fg/mL) and a stable detection ratio. In summary, this CNT-FET biosensor enabled the label-free, ultra-sensitive, and fast detection of SEC in complex samples. The FET biosensors could be further used as a universal biosensor platform for the ultrasensitive detection of multiple biological toxic pollutants, thus considerably stopping the spread of harmful substances.

Control strategy of stable walking for a hexapod wheel-legged robot.

This paper provides a legged stable walking control strategy based on multi-sensor information feedback about BIT-NAZA-II, a large load parallel hexapod wheel-legged robot developing for the problem of vertical contact impact and horizontal sliding of heavy leg robot in complex terrain environments. The BIT-NAZA-II robot has six legs and six wheels, and the wheels are installed on the foot-end. The wheels of each foot-end for the legs of the robot are locked when walking with legs. In order to realize the smooth transition between swing phase and stance phase, the leg motion is divided into different stages for control by state machine switching controller based on event (SMSCE). In the Z-direction, in order to avoid the shaking of the body caused by the contact impact at the moment of contact between the foot-end and the ground during the walking of the robot, an active compliance controller (ACC) based on impedance control (IC) is applied to solve the problem of contact impact. Moreover, in the X-direction, the swing leg retraction (SLR) based on Bezier curve (BC) is introduced to generate the foot-end trajectory of the robot, which solves the slip problem of the heavy leg robot and improves the horizontal stability. Finally, the control strategy of stable walking is respectively verified by the simulations and experiments. The results show that the ACC based on IC can effectively reduce the contact impact between the foot-end and the ground in the Z-direction and improve the stability of body. Besides, the anti-sliding ability is realized after introducing SLR based on BC in the X-direction, and we also verify that stable walking control strategy is effective, which provides a reference value for the stable walking of heavy leg robot in complex terrain.