Colorimetric and SERS dual-mode detection of GSH in human serum based on AuNPs@Cu-porphyrin MOF nanozyme.

BACKGROUND: Rapid and accurate detection of glutathione content in human blood plays an important role in real-time tracking of related diseases. Currently, surface-enhanced Raman scattering/spectroscopy (SERS) combined with nanozyme material has been proven to have excellent properties in the detection applications compared to many other methods because of it combines the advantages of trace detection capability of SERS and efficient catalytic activity of nanozymes. However, there are still existing problems in real sample detection, and to achieve quantitative detection is still challenging. RESULTS: In this study, gold nanoparticles (AuNPs) were synthesized in situ on the surface of two-dimensional Cu-porphyrin metal-organic framework (MOF) nanosheets to produce the AuNPs@Cu-porphyrin MOF nanozyme, which exhibited both oxidase-like activity and SERS detection ability. On one hand, the intrinsic oxidase-like activity of the nanozyme could be inhibited due to the chelation of glutathione (GSH) and Cu, which thus led to the visual color change of the solution. On the other hand, the abundant Raman "hot spots" at the nanogap generated by Au NPs and the internal standard (IS) signal provided by Cu-meso-tetra (4-carboxyphenyl) porphine (Cu-TCPP) MOF improved the sensitivity and quantitative accuracy of detection. SIGNIFICANCE AND NOVELTY: A dual-mode signal output sensor based on the nanozyme was thus established, which could be used in the trace detection of GSH. Such a dual-mode sensor possesses excellent detection performance, with the advantage of both wide detection range from 1 to 300 µM in the colorimetric detection mode and high sensitivity with LOD of 5 nM in the SERS detection mode, and can be applied to GSH detection in actual serum samples with reliable results.

Determining the inherent selectivity for carbon radical hydroxylation versus halogenation with high-spin oxoiron(iv)-halide complexes: a concerted rebound step.

A synthetic iron model can process both halogenation and hydroxylation with vague selectivity, which is different from halogenase even though these structures are used for the simulation of halogenase. The key factor of the synthetic oxo-iron model mediated hydroxylation or the halogenation is still under debate. Herein density functional theory calculation is used to investigate the hydroxylation versus halogenation of propylene by the complex [FeIV(O)(TQA)(X)]+ (X = F, Cl, Br). Our results suggest that a concerted rebound mechanism (between the -X and the hydroxyl ligands after the hydrogen abstraction) leads to the formation of two different kinds of products.

The molecular structure, spectroscopic features and electronic properties of tioxolone under the external electric field.

It is very helpful to understand the properties of molecules by studying a series of physical and chemical changes in molecules under an external electric field (EEF). Tioxolone is an important bioactive compound for its wide applications in the medical field. In this work, density function theory calculations combined with EEF were used to investigate the structure, spectra and electronic properties of tioxolone. The calculated results indicate that the bond lengths, bond angles, total energy, dipole moment, charge and aromaticity of tioxolone change under EEF. As EEF increases, the energy gap of tioxolone gradually reduces and makes it easier to participate in chemical reactions. Under the effect of EEF, the infrared and UV-Vis spectra show vibrational stark effect, which causes a redshift or blueshift of the frequency. These results help to understand the effect of EEF on structures and electronic properties for tioxolone, which will further provide effective guidance for the various application of tioxolone.

Galvanic-Cell-Reaction-Driven Deposition of Large-Area Au Nanourchin Arrays for Surface-Enhanced Raman Scattering.

Here we report a low-cost synthetic approach for the direct fabrication of large-area Au nanourchin arrays on indium tin oxide (ITO) via a facile galvanic-cell-reaction-driven deposition in an aqueous solution of chloroauric acid and poly(vinyl pyrrolidone) (PVP). The homogeneous Au nanourchins are composed of abundant sharp nanotips, which can served as nanoantennas and increase the local electromagnetic field enhancement dramatically. Finite element theoretical calculations confirm the strong electromagnetic field can be created around the sharp nanotips and located in the nanogaps between adjacent tips of the Au nanourchins. In addition, the interparticle nanogaps between the neighboring Au nanourchins may create additional hotspots, which can induce the higher electromagnetic field intensity. By using rhodamine 6G as a test molecule, the large-area Au nanourchin arrays on ITO exhibit active, uniform, and reproducible surface-enhanced Raman scattering (SERS) effect. To trial their practical application, the Au nanourchin arrays are utilized as SERS substrates to detect 3,3’,4,4’-tetrachlorobiphenyl (PCB-77) one congener of polychlorinated biphenyls (PCBs) as a notorious class of persistent organic pollutants. The characteristic Raman peaks can be still identified when the concentration of PCB-77 is down to 5 × 10−6 M.

Highly Sensitive and Selective Surface-Enhanced Raman Spectroscopy Label-free Detection of 3,3',4,4'-Tetrachlorobiphenyl Using DNA Aptamer-Modified Ag-Nanorod Arrays.

An improved label-free approach for highly sensitive and selective detection of 3,3',4,4'-tetrachlorobiphenyl (PCB-77), a type of polychlorinated biphenyl, via surface-enhanced Raman spectroscopy (SERS) using DNA aptamer-modified Ag-nanorod arrays as the effective substrate is reported. The devised system consists of Ag-nanorod (Ag-NR) arrays with the PCB-77 binding aptamers anchored covalently to the Ag surfaces through a thiol linker. The aptamers are made of single-stranded DNA (ssDNA) oligomers, with one end standing on the Ag surface, and upon conjugation with PCB-77, the ssDNA molecules can change their conformation to hairpin loops, so that the Raman intensity of guanines at the other end of the DNA strand increases accordingly. As such, the intensity ratio I(656 cm(-1))/I(733 cm(-1)) increases concomitantly with the increase of the concentration of PCB-77, making the quantitative evaluation of trace amounts of PCB-77 attainable. Moreover, it is found that the DNA aptamer-based Ag-NR arrays can be more responsive with a lower and optimal density of the DNA molecules modified on the substrate surface, and the best sensitivity for detection of PCB-77 can be achieved with the lower detection limit approaching 3.3 × 10(-8) M. This work therefore demonstrates that the design of aptamer-modified Ag-NRs can be used as a practically promising SERS substrate for label-free trace detection of persistent organic pollutants (POPs) in the environment.

ß-Cyclodextrin coated SiO2@Au@Ag core-shell nanoparticles for SERS detection of PCBs.

A new type of surface-enhanced Raman scattering (SERS) substrate consisting of ß-cyclodextrin (ß-CD) coated SiO2@Au@Ag nanoparticles (SiO2@Au@Ag@CD NPs) has been achieved. Our protocol was a simplified approach as the fabrication and modification of the silver shell were realized in a single-step reaction by taking advantage of ß-CD as both the reducing and stabilizing agents. The as-synthesized SiO2@Au@Ag@CD NPs were uniform in size and demonstrated high SERS activity and reproducibility. The substrates consisting of the SiO2@Au@Ag@CD NPs were employed for SERS detection of polychlorinated biphenyls (PCBs) including PCB-3, PCB-29 and PCB-77. The SERS detection sensitivity was significantly improved due to enrichment of more PCB molecules captured by ß-CD on the substrate surface, as confirmed by the appearance of the new Raman bands which are attributed to the complexes between ß-CD and PCBs according to the theoretical simulation. Therefore, this work presents a novel approach to the fabrication of effective SERS substrates that can be employed for rapid determination of trace amounts of PCBs in the environment with high detection sensitivity and recognition selectivity.

Flexible membranes of Ag-nanosheet-grafted polyamide-nanofibers as effective 3D SERS substrates.

We report on a synthetic approach to produce self-supported flexible surface-enhanced Raman scattering (SERS) active membranes consisting of polyamide (PA) nanofibers grafted with vertical Ag-nanosheets, via a combinatorial process of electrospinning PA-nanofiber membranes, assembling Au-nanoparticles on the PA-nanofibers as seeds for subsequent growth of Ag-nanosheets, and electrodepositing Ag-nanosheets on the electrospun PA-nanofibers. As a high density of Ag-nanosheets are vertically grown around each PA-nanofiber in the three-dimensional (3D) networked PA-nanofiber membranes, homogeneous nano-scaled gaps between the neighboring Ag-nanosheets are formed, leading to a high density of 3D SERS "hot spots" within the Ag-nanosheet-grafted PA-nanofiber membranes. The Ag-nanosheet-grafted PA-nanofiber membranes demonstrate high SERS activity with excellent Raman signal reproducibility for rhodamine 6G over the whole membrane. For a SERS-based trial analysis of polychlorinated biphenyls (PCBs, a kind of global environmental hazard), the 3D SERS substrate membranes are modified with mono-6-ß-cychlodextrin to effectively capture PCB molecules. As a result, not only a low concentration down to 10(-6) M is reached, but also two congeners of PCBs in their mixed solution are identified, showing promising potential in SERS-based rapid detection of trace organic pollutants such as PCBs in the environment.

Ag-nanoparticle-decorated Au-fractal patterns on bowl-like-dimple arrays on Al foil as an effective SERS substrate for the rapid detection of PCBs.

Large-area Au-aggregate-assembled fractal patterns with tailored sizes and densities are achieved by sputtering Au nanoparticles on hexagonally patterned bowl-shaped-dimples on Al foil and subsequent annealing. After decorating with much smaller Ag nanoparticles, the resultant substrates exhibit an active and reproducible SERS effect.

Large-scale homogeneously distributed Ag-NPs with sub-10 nm gaps assembled on a two-layered honeycomb-like TiO2 film as sensitive and reproducible SERS substrates.

We present a surface-enhanced Raman scattering (SERS) substrate featured by large-scale homogeneously distributed Ag nanoparticles (Ag-NPs) with sub-10 nm gaps assembled on a two-layered honeycomb-like TiO(2) film. The two-layered honeycomb-like TiO(2) film was achieved by a two-step anodization of pure Ti foil, with its upper layer consisting of hexagonally arranged shallow nano-bowls of 160 nm in diameter, and the lower layer consisting of arrays of about fifty vertically aligned sub-20 nm diameter nanopores. The shallow nano-bowls in the upper layer divide the whole TiO(2) film into regularly arranged arrays of uniform hexagonal nano-cells, leading to a similar distribution pattern for the ion-sputtered Ag-NPs in each nano-cell. The lower layer with sub-20 nm diameter nanopores prevents the aggregation of the sputtered Ag-NPs, so that the Ag-NPs can get much closer with gaps in the sub-10 nm range. Therefore, large-scale high-density and quasi-ordered sub-10 nm gaps between the adjacent Ag-NPs were achieved, which ensures homogeneously distributed 'hot spots' over a large area for the SERS effect. Moreover, the honeycomb-like structure can also facilitate the capture of target analyte molecules. As expected, the SERS substrate exhibits an excellent SERS effect with high sensitivity and reproducibility. As an example, the SERS substrate was utilized to detect polychlorinated biphenyls (PCBs, a kind of persistent organic pollutants as global environmental hazard) such as 3,3',4,4'-pentachlorobiphenyl (PCB-77) with concentrations down to 10(-9) M. Therefore the large-scale Ag-NPs with sub-10 nm gaps assembled on the two-layered honeycomb-like TiO (2) film have potentials in SERS-based rapid trace detection of PCBs.