Recent advances in plasmonic Prussian blue-based SERS nanotags for biological application.

The reliability and reproducibility of surface-enhanced Raman scattering (SERS) technology is still a great challenge in bio-related analysis. Prussian blue (PB)-based SERS tags have attracted increasing interest for improving these deficiencies due to its unique Raman band (near 2156 cm-1) in the Raman-silent region, providing zero-background bio-Raman labels without interference from endogenous biomolecules. Moreover, the stable PB shell consisting of multiple layers of CN- reporters ensure a stable and strong Raman signal output, avoiding the desorption of the Raman reporter from the plasmonic region by the competitive adsorption of the analyte. More importantly, they possess outstanding multiplexing potential in biological analysis owing to the adjustable Raman shift with unique narrow spectral widths. Despite more attention having been attracted to the structure and preparation of PB-based SERS tags for their better biological applications over the past five years, there is still a great challenge for SERS suitable for applications in the actual environment. The biological applications of PB-based SERS tags are comprehensively recounted in this minireview, mainly focusing on quantification analysis, multiple-spectral analysis and cell-imaging joint phototherapy. The prospects of PB-based SERS tags in clinical diagnosis and treatment are also discussed. This review aims to draw attention to the importance of SERS tags and provide a reference for the design and application of PB-based SERS tags in future bio-applications.

Monodispersed plasmonic Prussian blue nanoparticles for zero-background SERS/MRI-guided phototherapy.

Surface-enhanced Raman scattering (SERS) and magnetic resonance imaging (MRI)-guided phototherapy are new breakthroughs in cancer therapeutics due to their complementary advantages, such as enhanced imaging spatial resolution and depth. Herein, we synthesized monodispersed Prussian blue-encapsulated gold nanoparticles (Au@PB NPs), in which the plasmonic gold core plus coordination polymer of cyanide (C[triple bond, length as m-dash]N) and iron ions coincidently become a superexcellent contrast agent for both MRI and zero-background SERS imaging. PB, as a signal source for MR and SERS, can be easily assembled onto single Au NPs, of which iron ions possess high relaxation efficiency for in vivo MRI, e.g., the longitudinal and transversal relaxation efficiency values are 0.86 mM-1 s-1 (r1) and 5.42 mM-1 s-1 (r2), respectively. Furthermore, with the help of the plasmonic enhancement of the gold core, the C[triple bond, length as m-dash]N groups exhibit a specific, strong, and stable (3S) SERS emission in the Raman-silent region (1800-2800 cm-1), allowing accurate in vivo imaging at the single or even subcellular level. More importantly, PB has remarkable absorption properties in the near infrared region, and can be used as a photosensitizer for photothermal (PT) and photodynamic (PD) therapy simultaneously. Hence, the ideal integration of a plasmonic Au core and PB shell into a single monodispersed MR-guided NP, with zero-background SERS signals, is an important candidate for both tumor navigation and in situ PT/PD treatment guided by SERS/MR dual-mode imaging.

Total Aqueous Synthesis of Au@Cu2-x S Core-Shell Nanoparticles for In Vitro and In Vivo SERS/PA Imaging-Guided Photothermal Cancer Therapy.

Both accurate tumor navigation and nanostructures with high photothermal (PT) conversion efficiency are important but remain challenging to achieve in current biomedical applications. This study reports an anion exchange-based facile and green approach for synthesizing Au@Cu2-x S core-shell nanoparticles (NPs) in an aqueous system. In addition to the PT effect of the suggested NPs, the surface-enhanced Raman scattering (SERS) is also significantly improved due to the tailored localized surface plasmon resonance coupling between the Au metal core and the Cu2-x S semiconductor shell. Using an epitaxial strategy, Au@Cu2 O NPs are first obtained by the in situ reduction of cupric hydroxide on a cresyl violet acetate-coated Au core; then, Au@Cu2-x S NPs are obtained via anion exchange between the S2- and Cu2 O shell. Both the Cu/S atomic ratio and the Cu2-x S shell thickness can be adjusted conveniently. Hence, the ideal integration of the plasmonic Au core and Cu2-x S shell into a single unit is conducive not only to highly efficient PT conversion but also to the construction of a SERS-based navigator. This new type of SERS-guided NP, with enhanced photoacoustic signals, is an important candidate for both accurate tumor navigation and nondestructive PT treatment guided in vivo by two modes of optical imaging.

Alkyne-Modulated Surface-Enhanced Raman Scattering-Palette for Optical Interference-Free and Multiplex Cellular Imaging.

The alkyne tags possess unique interference-free Raman emissions but are still hindered for further application in the field of biochemical labels due to its extremely weak spontaneous Raman scattering. With the aid of computational chemistry, herein, an alkyne-modulated surface-enhanced Raman scattering (SERS) palette is constructed based on rationally designed 4-ethynylbenzenethiol derivatives for spectroscopic signature, Au@Ag core for optical enhancement and an encapsulating polyallylamine shell for protection and conjugation. Even for the pigment rich plant cell (e.g., pollen), the alkyne-coded SERS tag can be highly discerned on two-dimension distribution impervious to strong organic interferences originating from resonance-enhanced Raman scattering or autofluorescence. In addition, the alkynyl-containing Raman reporters contribute especially narrow emission, band shift-tunable (2100-2300 cm(-1)) and tremendously enhanced Raman signals when the alkynyl group locates at para position of mercaptobenzene ring. Depending on only single Raman band, the suggested alkyne-modulated SERS-palette potentially provides a more effective solution for multiplex cellular imaging with vibrant colors, when the hyperspectral and fairly intense optical noises originating from lower wavenumber region (<1800 cm(-1)) are inevitable under complex ambient conditions.

Investigation of biosurfactant-producing indigenous microorganisms that enhance residue oil recovery in an oil reservoir after polymer flooding.

Three biosurfactant-producing indigenous microorganisms (XDS1, XDS2, XDS3) were isolated from a petroleum reservoir in the Daqing Oilfield (China) after polymer flooding. Their metabolic, biochemical, and oil-degradation characteristics, as well as their oil displacement in the core were studied. These indigenous microorganisms were identified as short rod bacillus bacteria with white color, round shape, a protruding structure, and a rough surface. Strains have peritrichous flagella, are able to produce endospores, are sporangia, and are clearly swollen and terminal. Bacterial cultures show that the oil-spreading values of the fermentation fluid containing all three strains are more than 4.5 cm (diameter) with an approximate 25 mN/m surface tension. The hydrocarbon degradation rates of each of the three strains exceeded 50%, with the highest achieving 84%. Several oil recovery agents were produced following degradation. At the same time, the heavy components of crude oil were degraded into light components, and their flow characteristics were also improved. The surface tension and viscosity of the crude oil decreased after being treated by the three strains of microorganisms. The core-flooding tests showed that the incremental oil recoveries were 4.89-6.96%. Thus, XDS123 treatment may represent a viable method for microbial-enhanced oil recovery.

Response of microbial community structure to microbial plugging in a mesothermic petroleum reservoir in China.

Microbial plugging, a microbial enhancement of oil recovery (MEOR) technique, has been applied in a candidate oil reservoir of Daqing Oil Field (China). The goal of this study is to monitor the survival of injected bacteria and reveal the response of microbial communities in field trial of microbial plugging through injection of selected microbial culture broth and nutrients. Culture-dependent enrichment and culture-independent 16S rDNA clone library methods were used. The results show that it was easy to activate targeted biopolymer-producing bacteria in a laboratory environment, and it was difficult for injected exogenous bacteria to survive. In addition, microbial communities in the oil reservoir also changed before and after the field trial. However, microbial communities, activated by fermentative medium for biopolymer-producing bacteria, appeared to show greater differences in the laboratory than in the natural reservoir. It was concluded that microbial populations monitoring was important to MEOR; results of response of microbial communities could provide a guide for the future field trials.

Expression of c-fos in the nucleus of the solitary tract following electroacupuncture at facial acupoints and gastric distension in rats.

Clinical practice has shown that acupuncture at facial acupoints has curative effects on some visceral diseases (especially gastrointestinal diseases). However, the physiological basis has not been clarified yet. In the present study, expression of c-fos in the nucleus of the solitary tract (NTS) of rats following gastric distension and electroacupuncture (EA) at Yangbai (GB14) and Sibai (ST2) as well as Jiache (ST6) acupoints was observed by using immunohistochemistry technique. After EA at the three facial acupoints, c-fos immunoreactive (c-fos-IR) neurons were mainly distributed in the medial (mNTS) and intermediate subnucleus of the NTS, and a few were scatteredly distributed in the dorsalmedial and commissural subnucleus of the NTS. Furthermore, there is difference in the number of c-fos-IR neurons in the mNTS following EA at the three facial acupoints. The number in the EA at ST2 and GB14 group is the highest and the lowest, respectively. Gastric distension induces obviously the expression of c-fos, which is mainly confined in the mNTS. The results suggest that the noxious visceral and somatic afferent information from the stomach and face may converge in the mNTS, which may be involved in the effect of EA at facial acupoints on the gastrointestinal pain.

Effects of electroacupuncture on gastric myoelectric activity and substance P in the dorsal vagal complex of rats.

Acupuncture has been widely applied to treat gastrointestinal diseases in the clinic. However, its precise mechanism remains unknown. In the present study, effects of electroacupuncture (EA) at Zusanli acupoints (ST36) on gastric myoelectric activity and substance P (SP) in the dorsal vagal complex (DVC) were observed. EA at ST36 significantly increased the frequency of slow waves and the frequency of the spike potentials superimposed on the slow waves, which persisted for 90 min after cessation of EA and was completely abolished after bilateral vagotomy. Meanwhile, the mean optical density of SP immunoreactive fibers in the DVC increased following EA. The results suggested that EA at ST36 promoted the gastric myoelectric activity, which was regulated by the vagus, and SP in the DVC may be involved in the excitatory effects. Furthermore, EA had a relative long-term post-effect. We presumed that DVC may be a supraspinal center in the effect of EA on gastric function.