Surface‐enhanced Raman spectroscopy of biomolecules. Part I.—water‐soluble proteins, dipeptides and amino acids

Abstract

Surface-enhanced Raman (SER) spectra of water-soluble proteins (lysozyme and bovine serum albumin), dipeptides and amino acids were analysed. Chemisorption is a necessary condition for the appearance of SER spectra on silver electrodes and hydrosols for these compounds. The Raman cross-section enhancement per molecule may reach a factor of 10s-106, depending closely on the frequency of the vibration band considered. The mechanism of enhancement has a short-range character and is attributed to the rc-electron complexes of the aromatic amino acids sidechains and u-complexes of the molecular group containing unsbared electron pairs with the metal. The effect of induced optical activity in the visible region for aromatic amino acids adsorbed by silver hydrosols has been elucidated. (iii) What are the lowest concentrations for the detection of SER soectra of biomolecules in different INTRODUCTIONIt has recently been d e m~n s t r a t e d '~~ that very large (in some instances up to lo9) enhancements of the Raman cross-section for molecules in the close vicinity of a metal surface result from the superposition of two main mechanisms, described as electromagnetic and molecular (or 'chemical'). Enhancement of the local electromagnetic field near 'rough' metal surface induces the electromagnetic mechanism, whereas the 'molecular' mechanism is connected with the appearance of new excited states for the molecule-metal complexes in the process of chemisorption.Surface-enhanced Raman (SER) and surfaceenhanced resonance Raman (SERR) spectroscopy are based on these mechanisms and have been widely used in investigations of biological molecule^.^-^ Three important questions relating to the applicability of SERS and SERRS to sophisticated problems in molecular biology, bioorganic and physical chemistry are the following :(i) What are the molecular mechanisms of interaction of the biomolecules with the metal surface under the experimental conditions typical of SERS appearance and is it possible to make measurements preserving the native conformation of the molecule? (ii) What is the real dependence of the Raman crosssection enhancement on the distance between the metal and the molecule? Is the mechanism of enhancement short-range or long-range and will it be possible to detect all normal vibrations of macromolecules or only vibrations of groups which directly contact the surface? experimental systems (electrodes, hydrosols, surfaces with the regular roughnesses)? Is it possible to detect high-quality SER spectra of subpicogram amounts of different classes of biomolecules for successful competition with the traditional techniques in biotechnology and genetic engineering? This paper deals with applications of SERS to the study of water-soluble proteins adsorbed on silver electrodes. A comparison of the spectra of some amino acids and model compounds was made and a new effect, induced by adsorption optical activity in the visible region, was revealed. In subsequent papers in this series the possibility of the selective application of ...

Single Molecule Vibrational Fine-structure of Tyrosine Adsorbed on Ag Nano-Crystals

“…3. Although the broad and unresolved features that characterize spectra measured with long integration times are a sum of strongly fluctuating contributions, the overall intensity profile, with peaks at around 1164, 1355, and 1580 cm -1 , and a spectral gap around 1420 cm -1 , is in excellent agreement with previously published SERS data on Tyr in aqueous Agcolloid solutions [11,13,[15][16][17]. We are thus confident that the spectral fluctuations illustrated in Fig.…”

“…It is thus a suitable molecule for testing the generality of singlemolecule SERS. Secondly, Tyr is an example of a range of biomolecules which have very broad SERS spectra [4,5,11]. It has previously been difficult to determine to what extent this is due to homogeneous or inhomogeneous broadening effects.…”

“…The great majority of previous SERS studies on biomolecules, including amino acids, have utilized Agparticles in aqueous solution [4,11,[13][14][15][16][17]. Although reports by Kneipp et al show that SERS-SMS is possible in solution [1,18], this methodology has the disadvantage that the temporal spectral evolution of single molecules cannot be followed.…”

Surface‐enhanced Raman scattering of 3‐phenylpropionic acid (hydrocinnamic acid)

“…This compound has an additional interest because it is related to phenylalanine, an amino acid which has hardly been studied by SERS. 29,30 EXPERIMENTAL Colloidal silver solutions were prepared in deionized and triply distilled water according to the method described by Creighton et al, 31 which basically consists of reducing an aqueous solution of 10 3 M AgNO 3 with an excess of NaBH 4 . In this way, one volume of 10 3 M AgNO 3 is added to three volumes of 2 ð 10 3 M NaBH 4 , that has been previously cooled to 0-5°C, dropwise and with vigorous stirring.…”

Activation of Nanoparticles by Biosorption for E. coli Detection in Milk and Apple Juice

“…The automated mapping device of the Raman could be of great help since it can scan every spot of the sample. Moreover, the [38] 457 Band observed in the SERS spectra of proteins, peptides, and amino acids [39,42] 582 Carbohydrates [35,43] 620 Band observed in the SERS spectra of proteins, peptides, and amino acids; δ (COO − ) [23,44] 672 Adenine from flavin [51] 772 and 906 Nucleic acids (cytidine, uracil) [40,41,46,47] 945 C-N stretch [51] 990 Phenylalanine (in proteins) [36] 1,029…”