Novel ratiometric electrochemical aptasensor based on broad-spectrum aptamer recognition for simultaneous detection of penicillin antibiotics in milk.

To effectively monitor multi-residues of penicillin antibiotics (PENs) in milk, we developed a novel ratiometric electrochemical aptasensor enabling simultaneous detection of PENs. The aptasensor employed a broad-spectrum aptamer as a recognition element, niobium carbide functionalized with methylene blue (Nb2C-MB) as a reference signal generator, and a ferrocene-labeled aptamer (Fc-Apt) as an output signal. Electrodes were modified with Fe-N-C doped carbon nanotubes (Fe-N-C-CNTs) to amplify detection signals further. During detection, Fc-Apt binding to PENs decreased Fc current intensity (IFc) and increased MB current intensity (IMB). The simultaneous detection of PENs was achieved using IMB/IFc as a quantitative signal. Under optimal conditions, a good linear relationship between IMB/IFc and antibiotic concentration was observed, indicating the aptasensor had a robustness. The limits of detection of aptasensor for four penicillin antibiotics and their mixed targets were 0.093-0.191 nM. This work provides a new approach to multi-residue detection of the same class of antibiotics.

Screening of broad-spectrum aptamer and development of electrochemical aptasensor for simultaneous detection of penicillin antibiotics in milk.

Penicillin antibiotics (PENs) play an important role in killing pathogenic bacteria. However, the residues of various penicillin antibiotics in milk gradually accumulate in the human body with the increase of milk intake, which causes direct harm to the human body. Aptamers can be used as recognition element of sensors. It is great significance to use broad-spectrum aptamers for simultaneous detection of PENs. In this study, we reported the screening and identification of DNA aptamers for PENs. The aptamers were screened by graphene oxide-systematic evolution of ligands by exponential enrichment (GO-SELEX). The broad-spectrum aptamers with high affinity and specificity were successfully obtained after 13 rounds of screening. The affinity and specificity of candidate aptamers were analyzed by a GO fluorescence competition method. Further sequence analysis revealed that a truncated 47 nt aptamer (P-11-1) had a higher affinity than the original 79 nt aptamer. The truncated aptamer P-11-1 was used as a recognition element, and an electrochemical aptasensor was prepared using gold nanoparticles (AuNPs) combined with ferroferric oxide-multi walled carbon nanotube (Fe3O4-MWCNTs) complex. The results showed that the developed aptasensor achieved the simultaneous detection of PENs in milk samples across a concentration range of 2 nM-10,000 nM, achieving a limit of detection of 0.667 nM. This methodology provided a simple and sensitive new thinking for antibiotic multi-residue detection.

Strain modulation on the spin transport properties of PTB junctions with MoC2 electrodes.

Based on MoC2 nanoribbons and poly-(terphenylene-butadiynylene) (PTB) molecules, we designed MoC2-PTB molecular spintronic devices and investigated their spin-dependent electron transport properties by using spin-polarized density functional theory and the non-equilibrium Green's function method. As a typical MXene material, it is found that the magnetic contribution of MoC2 nanoribbons mainly comes from the delocalized 3d electron of edge Mo atoms. Owing to the obvious spin-splitting near the Fermi level of the MoC2 nanoribbon electrode, the spin states can be effectively injected into the central scattering region under an external bias voltage. In addition, we also studied the effects of z-axis strain on the spin transport properties of the PTB molecular device, where the strain was controlled within the range of -9% to 9%. Under a compressed strain, spin current increases obviously, and the spin-filtering efficiency (SFE) decreases slightly. Nevertheless, under a tensile strain, we found that the SFE increases but spin current decreases. Moreover, z-axis strain can induce a negative differential resistance (NDR) effect at a high bias point. This work would expand the potential applications of new two-dimensional (2D) materials in the field of molecular spintronic devices.

In Situ Study of Structure-Activity Relationship between Structure and Tribological Properties of Bulk Layered Materials by Four-Ball Friction Tester.

Encouragingly, a lot of research studies have demonstrated that two-dimensional (2D) nanosheets applied as an additive in oils show preferable friction-reducing and wear resistance performance. However, the current issue was that an elusive way could be adopted to probe the structure-activity relationship between the structure and tribological properties of bulk layered materials due to the structural evolution during friction testing. In this study, we studied the structure-activity relationship between the structure and tribological properties of bulk layered materials (graphite, h-BN, WS2, and MoS2) by an in situ four-ball friction tester. The morphological and structural changes of the layered materials after in situ four-ball-milling were detected by a series of characterizations. This study revealed the friction-induced nanostructural evolution behaviors of bulk layered materials by a four-ball mode.