Double profound enhancements of Cu2O nano-octahedrons connected by intertwined Ag nanovines for elevating SERS activity toward ultrasensitive pesticide detection.

Recently, hybrid plasmonic metal/semiconductor-based surface-enhanced Raman scattering (SERS) has attracted ever-increasing attention due to its combined characteristics of electromagnetic (EM) enhancement and chemical (CM) enhancement, holding great potential for trace molecular detection. Herein, we demonstrate an interesting heterostructure by linking Cu2O nano-octahedrons with intertwined Ag nanovines (NVs). The obtained Ag NVs/Cu2O heterostructures exhibit excellent SERS activity, which is about 2.7 and 7.0 times higher than that of monodispersed Ag or Au nanoparticles (NPs) modified Cu2O. The intertwined Ag NVs among adjacent Cu2O octahedrons serve as efficient electron transport channels, which can obviously promote the separation of electrons and holes, reduce the recombination of photogenerated carriers, and then improve the CM enhancement effect. Meanwhile, the accumulated electrons on plasmonic NVs can effectively optimize the collective oscillation of electrons and further improve the EM enhancement. The optimal SERS substrate possesses fascinating multifunctional SERS properties, including ultra-low detection limit (CV, 10-14 M), excellent anti-interference capability and selectivity. Finally, the established nanosensor can be effectively applied for the quantitative detection of pesticide thiram molecules in soil and biological samples, with low detection limits of 0.48 ng g-1 and 10-7 M, respectively. The proposed work demonstrates a high-performance SERS heterostructure with both improved CM enhancement and enhanced EM effect by linking adjacent Cu2O nano-octahedrons with Ag NVs, which is particularly suitable for ultrasensitive residual pesticide detection in real-world environment.

Extraordinary approach to further boost plasmonic NIR-SERS by cryogenic temperature-suppressed non-radiative recombination.

We report an effective strategy to promote the near-infrared surface-enhanced Raman scattering spectroscopy (NIR-SERS) activity by boosting the photon-induced charge transfer (PICT) efficiency at cryogenic temperature. Based on as-prepared Au/Ag nano-urchins (NUs) with abundant surface defects, the extremely low temperature (77 K) can significantly weaken the metallic lattice vibration and reduce the recombination of thermal phonons and photoexcited electrons, then accelerate the migration of energetic electrons. It enables the NIR-SERS detection limit of dye molecules to be achieved at 10-17 M, which is nearly three orders of magnitude better than that at room temperature. The present work provides a new, to the best of our knowledge, approach for ultra-trace NIR-SERS bioanalysis.

Silk fibroin fibers decorated with urchin-like Au/Ag nanoalloys: a flexible hygroscopic SERS sensor for monitoring of folic acid in human sweat.

Surface-enhanced Raman scattering (SERS) spectroscopy has become a powerful and sensitive analytical tool for the detection and assessment of chemical/biological molecules in special scenarios. Herein we propose a flexible hygroscopic SERS biocompatible sensor based on the silk fibroin fibers (SFF) decorated with urchin-like Au/Ag nanoalloys (NAs). The hybrid SFF-Au/Ag NAs with a stronger absorbance capacity (500∼1100 nm) and excellent hygroscopicity provide a remarkable higher near-infrared (NIR)-SERS activity than that of bare urchin-like Au/Ag NAs. The interesting NIR-SERS sensor enables the limit of detection (LOD) of folic acid (FA) to be achieved at nanomolar (nM, 10-9 M) level, facilitating the ultrasensitive monitoring of FA in human sweat and offering reliable real-time personal health management in the near future.

Alloyed AuPt nanoframes loaded on h-BN nanosheets as an ingenious ultrasensitive near-infrared photoelectrochemical biosensor for accurate monitoring glucose in human tears.

Photo-electro-chemical (PEC) glucose biosensor has recently attracted extensive attention due to the double advantages of both photocatalysis via photon energy utilization and electrocatalytic oxidation through extra electric field. Compared with previous shorter wavelength (violet-visible) light-induced PEC reaction, the anticipated near infrared (NIR, >~700 nm) excited PEC biosensor with multiple fascinating features should be more suitable for clinical diagnostic biology. Herein, we report an ingenious NIR-PEC biosensor by loading alloyed Au5Pt9 nanoframes on two dimensional (2D) hexagonal boron nitride (h-BN) nanosheets. The obtained h-BN/Au5Pt9 nanoframes exhibit a remarkable higher NIR-PEC activity in comparison with other as-prepared h-BN/AuPt references. The improved PEC performance is attributed to the enhanced synergetic coupling effect between Au5Pt9 nanoalloys and constitutionally stable h-BN that gives rise to a stronger absorbance capacity and pronounced localized surface plasmon resonance (LSPR) in visible-NIR region as well as high free-electron mobility of framework-like Au/Pt. Interestingly, the obtained h-BN/Au5Pt9 nanoframes excited by 808 nm NIR light provide superior PEC accuracy and sensitivity as compared to visible or other NIR light irradiation. Then, the novel 808 nm NIR-PEC biosensor was used for precise glucose monitoring in human tears with a detectable concentration of 0.03~100 µM and a low detection limit of 0.406 nM. Undoubtedly, the proposed h-BN/Au5Pt9 nanoframes as an appealing NIR-PEC glucose biosensor can possess greater potential values for practical glucose monitoring in biomedicine.

Cu2O nanocubes-grafted highly dense Au nanoparticles with modulated electronic structures for improving peroxidase catalytic performances.

Based on the intermediate states of metal ions in metal oxide nanomaterials (NMs) that acted as the primary active species, the design of high-performance nanozymes has greatly stimulated current research in diverse biomedical applications. Herein, Cu2O nanocubes-grafted highly dense Au nanoparticles (NPs) was developed as an appealing nanozyme for H2O2 colorimetric sensor and antioxidant detections. The obtained Au/Cu2O heterostructures show efficient electron-transfer from metallic NPs to Cu2O nanocubes owing to the difference of Fermi energy between two components. The modulated electronic structure of Au/Cu2O hybrids enables them to possess enhanced peroxidase catalytic activity for the oxidation of 3, 3', 5, 5'-tetramethylbenzidine (TMB) in the presence of H2O2, which is about 32% higher than that of pristine Cu2O nanocubes. Then, an excellent H2O2 colorimetric sensor was established by using Au/Cu2O heterostructures with a low limit of detection (LOD) of 0.054 µM, which is much lower than the H2O2 allowance level of US FDA regulations (ca.15 µM, 0.05 wt%). The obtained Au/Cu2O nanoproducts exhibit pronounced long-time stability with 95% peroxidase activity maintained after keeping them for 30 days, while residual 64.5% via Cu2O nanocubes. Furthermore, we assessed the anti-oxidative behavior of three natural antioxidants (tannic acid, gallic acid, tartaric acid) with the LODs as low as 0.039, 0.16 and 1.55 µM, respectively, and the antioxidant capacity in the following order: tannic acid > gallic acid > tartaric acid. Therefore, it is believed that the as-prepared Au/Cu2O nanozymes have promising potential applications in fields of biomedicine and food safety.

Graphene oxide-grafted plasmonic Au@Ag nanoalloys with improved synergistic effects for promoting hot carrier-driven photocatalysis under visible light irradiation.

Plasmonic metallic nanostructure with unique hot carrier-driven photocatalysis has recently emerged as a promising photocatalyst. Herein, we show that the plasmonic photocatalysis can be significantly promoted by supporting bimetallic Au@Ag nanoalloys (NAs) on graphene oxide (GO). The obtained Au3@Ag1/GO (molar ratio of Au to Ag∼3:1) with improved synergistic effects provides a remarkable higher visible-light (>400 nm) photocatalytic activity for a complete degradation (99.36%) of tetracycline hydrochloride (TCH) molecules within 70 min, while about 61.74% or 62.38% via monometallic Au/GO or Ag/GO. The optimum photocatalytic performance is attributed to the production of high yield hot carriers on NAs with enhanced localized surface plasmon resonance property and the pronounced photoinduced electron-transfer ability of modified GO support by overgrowth of NAs. These findings enable the optimal Au3@Ag1/GO to become an appealing high-performance photocatalyst for promoting diverse photochemical reactions.

Modified photochemical strategy to support highly-purity, dense and monodisperse Au nanospheres on graphene oxide for optimizing SERS detection.

The integration of highly-purity, dense and monodisperse plasmonic nanoparticles (NPs) on two-dimensional (2D) graphene-like support possesses great potential for optimizing surface-enhanced Raman spectroscopy (SERS). Based on ultraviolet (UV) laser-induced modified photochemical reaction, we report an ingenious and green strategy to support highly dispersed Au NPs with controllable distribution on graphene oxide (GO). Without using any stabilizing agents or other complex chemical additives, the GO with abundant oxygen-containing functional groups can be effectively excited by 375 nm laser irradiation in HAuCl4 solution, resulting in controlled reduction of Au ions and then overgrowth of highly-purity Au NPs. Highly dense and monodisperse Au NPs with uniform diameter of ~20 nm formed on GO supports can be achieved by 30 min irradiation, which can offer maximized SERS activity in comparison with GO/Au NPs obtained by other irradiation times. The optimized GO/Au NPs give rise to ultralow SERS analyses of (10-14 M) methylene blue (MB), (10-13 M) rhodamine 6G (R6G) and (10-13 M) malachite green (MG), respectively. More importantly, it can also simultaneously analyze these three aromatic dyes in a mixture condition at detection limits as low as nano-mole level (10-9-10-11 M), achieving the urgent requirement of mutually independent SERS trace detection. Therefore, the obtained GO/Au NPs with extremely high SERS activity and superior spectroscopic identification will be a prominent candidate for widespread SERS applications in real-word scenarios.

Core-shell Au@Ag nanodendrites supported on TiO2 nanowires for blue laser beam-excited SERS-based pH sensing.

The blue laser beam-excited surface-enhanced Raman scattering (SERS)-based pH sensing holds great promise for avoiding undesired thermal heating effect on some special temperature-vulnerable molecules, as compared to the vast majority studies by exciting in the red or near-infrared (NIR). Herein, we report an ingenious approach to support core-shell Au@Ag nanodendrites (NDs) on TiO2 nanowires, which can possess enhanced SERS activity under 473 nm laser excitation, owing to the improved charge-transfer effect on modified TiO2 support by inserting plasmonic Au@Ag. By using pH-indicating 4-mercaptobenzoic acid (4-MBA), the obtained TiO2/Au@Ag NDs can not only exhibit high sensitive linear-responses of pH changes ranging from pH 4.0 to 9.0 in different solutions (deionized water, NaCl, CaCl2, and MgCl2) but also provide excellent temperature stability under 4°C, 25°C and 37°C temperatures as well as good time stability after storage for 10 days. The established SERS-pH sensing by using shorter wavelength laser excitation is highly desirable for understanding physiological process in temperature-vulnerable microenvironment.

Convenient Synthesis of 3D Fluffy PtPd Nanocorals Loaded on 2D h-BN Supports as Highly Efficient and Stable Electrocatalysts for Alcohol Oxidation Reaction.

Fuel cells hold great promise for clean and sustainable energy, whereas their widespread commercialization strongly depends on the development of highly efficient and stable electrocatalysts. Herein, three-dimensional fluffy PtPd nanocorals (NCs) loaded on two-dimensional (2D) hexagonal boron nitride (h-BN) supports were successfully achieved by a simple one-step strategy based on ultraviolet (UV) laser-excited photochemical reaction. As for alcohol oxidation reaction, the h-BN/PtPd NCs with unique nanoporous surface provide more enhanced electrocatalytic performances than many previous nanocatalysts, owing to abundant active sites and plentiful charge-transfer channels formed on high electrode-electrolyte contact area. Especially, the mass activity of h-BN/PtPd NCs is about 962.8 mA mgPtPd -1 in methanol oxidation reaction in alkaline solution, which can be maintained at ∼274.9 mA mgPtPd -1 (28.6% of the initial one) even after a 5 × 104 s durability test. The present work not only offers an advanced electrocatalyst for long-term fuel cells but also provides a versatile route for construction of complex metallic nanocomposites on 2D supports, holding great potential for diverse energy-related applications.

Photochemical synthesis of ZnO@Au nanorods as an advanced reusable SERS substrate for ultrasensitive detection of light-resistant organic pollutant in wastewater.

The prospect of wielding surface-enhanced Raman spectroscopy (SERS) as a powerful technique for ultrasensitive detection of organic molecules in wastewater has received extensive attention in environmental surveillance. Based on ultraviolet (UV, 405 nm) laser irradiation of ZnO nanorods in HAuCl4 solution, ZnO@Au nanorods with controllable Au nanoparticles were successfully fabricated and established as an advanced SERS-based substrate. The reduction of Au ions was driven by the generation of electron-hole pairs via UV laser excitation of semiconductor-based nanomaterials, resulting in the moderate overgrowth of Au nanoparticles on the ZnO nanorods. The Au composition-dependent SERS analysis of crystal violet (CV) molecules revealed that the ZnO@Au nanorods with 16.21% Au contents exhibited optimized SERS activity in comparison with other nano-substrates in this paper. Furthermore, the detection limit of light-resistant methyl blue (MB) dye molecules was achieved at nanomole (nM) level of 10-9 M (0.8 µg/L), providing ultrasensitive detection of organic pollution in wastewater. Even after twenty recycles, the excellent reusability of this novel substrate with 65% original SERS intensity was achieved by subsequently eliminating the residual MB molecules via photocatalytic degradation. Therefore, the as-prepared ZnO@Au nanorods can serve as a cost-effective, clean, reusable and active SERS substrate for ultrasensitive monitoring of light-resistant organic pollutant in natural ecosystems.

Construction of pure worm-like AuAg nanochains for ultrasensitive SERS detection of pesticide residues on apple surfaces.

Ultrasensitive detection of pesticide residues on agricultural products using surface-enhanced Raman spectroscopy (SERS) is of significant interest in food security. Herein, worm-like AuAg nanochains with highly interconnected ultrafine (~6.2 nm) bimetallic particles were developed as an excellent SERS nanosensor via laser-assisted strategy. The SERS detection limit of thiram molecules on apple surfaces is about 10-7 M (0.03 ppm), which is about 200 times lower than the maximal residue limit (MRL, 7 ppm) in fruit prescribed by the U.S. Environmental Protection Agency (EPA). Importantly, the established excellent linear relationships between the SERS intensities and thiram concentrations can sensitively monitor the slight variation of pesticide residues in agriculture.

Construction of optimized Au@Ag core-shell nanorods for ultralow SERS detection of antibiotic levofloxacin molecules.

The abuse of antibiotics in animal husbandry has been regarded as a daunting public health risk, facilitating the emergence and spread of resistant pathogens to humans. Herein, bimetallic Au@Ag core-shell nanorods (NRs) with precise, controllable Ag shell-thickness (2.1~14.1 nm) were fabricated and developed for ultralow detection of levofloxacin molecules using surface enhanced Raman scattering spectroscopy (SERS). We found that the Au@Ag NRs with 7.3 nm Ag shell-thickness provided maximized SERS activity in comparison with other as-prepared nanosubstrates in this paper. The detection limit of levofloxacin molecules was achieved at a nanomole (nM) level of 0.37 ng/L (10-9 M), providing ultrasensitive assessment of antibiotics in natural ecosystems.