On the basis of different types of experiments, the authors develop implicitly the model of surface-enhanced Raman scattering (SERS) of adsorbates on metal surfaces. The long-range enhancement by resonances of the macroscopic laser and Stokes field is separated quantitatively from the metal electron-mediated resonance Raman effect. The latter mechanism proceeds by increased electron-photon coupling at an atomically rough surface and by temporary charge transfer to orbitals of the adsorbates. This model can account for the chemical specificity and vibrational selectivity of SERS and (partly) for the SERS specificity of the various metals.

https://iopscience.iop.org/article/10.1088/0953-8984/4/5/001/pdf

Surface-enhanced Raman scattering

Silver chromate-graphene oxide (Ag2CrO4-GO) composites are prepared by a facile precipitation method. The resulting Ag2CrO4-GO composites exhibit excellent photocatalytic activity and stability towards the degradation of the dyes and phenol in aqueous solution under visible-light irradiation. The optimal composite with 1.0 wt% GO content shows the highest photocatalytic activity for methylene blue (MB) degradation, which is 3.5 times that of pure Ag2CrO4 particles. The enhanced photocatalytic activity is mainly attributed to the formation of Ag2CrO4-GO Z-scheme heterojunction that can not only facilitate the separation and transfer of the photogenerated charge carriers, but also preserve a strong oxidation and reduction ability. The high photocatalytic stability is due to the successful inhibition of the photocorrosion of Ag2CrO4 by transferring the photogenerated electrons of Ag2CrO4 to GO. The present work provides a new understanding into design and fabrication of the GO/silver compound composite photocatalysts.

Enhanced photocatalytic activity and stability of Z-scheme Ag2CrO4-GO composite photocatalysts for organic pollutant degradation

Ag-coated Au colloidal particles have been prepared by reduction of Ag+ in the presence of preformed Au colloids. The composition of the Au100-xAgx particles was varied from x = 0 to 80. SERS spectra of pyridine, p-nitroso-N,N‘-dimethylaniline (p-NDMA), and trans-1,2-bis(4-pyridyl)ethylene (BPE) have been obtained with these colloids. At monolayer Ag coverages (x < 10), the optical spectra of Ag-coated Au particles are indistinguishable from uncoated Au particles. However, the SERS behavior of aggregated colloids with 647.1 nm excitation is extremely dependent upon the Ag:Au ratio. Very small amounts of Ag (x ≤ 5) lead to an increase in SERS intensity, but further increases lead to complete loss of signal. For p-NDMA and pyridine, these data can be explained by Ag inhibition of adsorbate-induced aggregation. The initial increase in SERS intensity results from production of smaller aggregates that exhibit a surface plasmon band in better alignment with the excitation wavelength; higher ratios of Ag elimina...

Ag-Clad Au Nanoparticles: Novel Aggregation, Optical, and Surface-Enhanced Raman Scattering Properties

To provide rapid and accurate detection of DNA markers in a straightforward, inexpensive, and multiplex format, an alternative surface-enhanced Raman scattering based probe was designed and fabricated to covalently attach both DNA probing sequence and nonfluorescent Raman tags to the surface of gold nanoparticles (DNA-AuP-RTag). The intensity of Raman signal of the probes could be controlled through the surface coverage of the nonfluorescent Raman tags (RTags). Detection sensitivity of these probes could be optimized by fine-tuning the amount of DNA molecules and RTags on the probes. Long-term stability of the DNA-AuP-RTag probes was found to be good (over 3 months). Excellent multiplexing capability of the DNA-AuP-RTag scheme was demonstrated by simultaneous identification of up to eight probes in a mixture. Detection of hybridization of single-stranded DNA to its complementary targets was successfully accomplished with a long-term goal to use nonfluorescent RTags in a Raman-based DNA microarray platform.

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Surface-Enhanced Raman Scattering Based Nonfluorescent Probe for Multiplex DNA Detection

Dynamic electrochemical methods, which have long held an important place among the techniques of the coordination chemist, have generally remained unexploited by those seeking to understand the complex and often elusive chemistry of metal centres in proteins. For a number of reasons, electron transfer between electrodes and proteins' has been regarded as being too slow and irreversible to provide useful information. This article seeks to counter such a view and outlines the advances that have been made towards achieving and interpreting voltammetric responses from metal-containing active sites. The main theme, exploitation, is developed through discussion of several investigations that demonstrate the advantages that are now on offer from electrodes that “talk” to metalloproteins. Far from being restricted to measurements of stable equilibria, voltammetry can address reactive states; species which are thermodynamically inaccessible by normal chemical titration or which display interesting yet complicating dynamic properties such as structural change or catalytic activity. In such cases, the coupled processes are visualised and may be investigated quantitatively and under controlled conditions. The resolution of chemical activity which is thus afforded extends even to multi-site enzyme complexes.

Probing metalloproteins by voltammetry

Surface enhanced raman scattering and photodimerization of pyridyl-substituted ethylenes at a silver electrode surface

Single-crystal Raman spectra of paraelectric (NH4)2SO4

The Raman spectra of crystalline Na2CrO4 and Na2CrO4·4H2O

Stammreich and co-workers1 first noted that the absorption bands in the infrared spectra- of triclinic potassium dichromate appear in pairs, and they postulated that this effect might be due to different non-equivalent arrangements of dichromate ions in the crystal lattice. Vinh and co-workers2 have obtained the Raman spectrum of triclinic potassium dichromate and have recently suggested that this doubling effect points to the presence of an inversion center in the crystal lattice3. We have also studied the Raman spectrum of potassium dichromate. Our spectra appear to be better resolved than those previously reported, thereby enabling a more complete assignment. Our work also benefits from a recent and highly refined x-ray structure study4, and we have been able to verify the space group assignment of that study.

Robert L. Carter

Papers

Surface enhanced raman scattering and photodimerization of pyridyl-substituted ethylenes at a silver electrode surface

Single-crystal Raman spectra of paraelectric (NH4)2SO4

The Raman spectra of crystalline Na2CrO4 and Na2CrO4·4H2O

Vibrational, Spectrum of Triclinic Potassium Dichromate

Raman spectra of the double-anion salts M3ZnCl4NO3 (M+ = K+, Rb+, NH4).