Surface-enhanced Raman scattering (SERS) effect was used to demonstrate ultrasensitive optical detection of nucleic acids. In this work, the SERS spectra of seven genomic DNAs from leaves of Arnica montana (L.), Fam. Compositae, Astragalus peterfii (Jáv.), Fam. Fabaceae, Kalanchoe x hybrida, Fam. Crassulaceae, strawberry (Fragaria x ananassa Duch.), Fam. Rosaceae, carnation (Dianthus caryophyllus L.), Fam. Caryophyllaceae, apple (Malus domestica Borkh.), Fam. Rosaceae and Persian violet (Exacum affine Balf.), Fam. Gentianaceae were analyzed in the wavenumber range 200-1800 cm −1 . SERS signatures, spectroscopic band assignments and structural interpretations of these plant genomic DNAs are reported. SERS spectra of nucleic acids are compared here with caution, because these signals are time-dependent. The SERS spectra corresponding to DNA from Arnica, Dianthus, Fragaria and Kalanchoe leaves show well-resolved, accurate bands, providing thus a high molecular structural information content. Based on this work, specific plant DNA-ligand interactions or DNA structural changes induced by plant stress conditions associated with their natural environment might be further investigated using SERS spectroscopy. Besides, this study will generate information that is valuable in the development of label-free DNA-based nanosensors for chemical probing in the living cell.

Raman spectra of calf thymus DNA were measured in the pH interval 6.4 to 3.45 in the presence of divalent manganese ions. pH-dependent protonation of AT and GC base pairs and conformational changes were indicated in the spectra. Protonation of adenine residues becomes obvious at pH 4.4 and continues upon lowering the pH to 3.45. Adenine protonation is connected with the disruption of AT base pairs. Protonation of GC base pairs is indicated at somewhat lower pH than that of AT base pairs, namely at pH 3.8, and continues upon lowering the pH to 3.45. At pH 3.8 unstacking of thymine residues is indicated, and spectral markers for the unstacking of adenine and cytosine were found at pH 3.45. Changes of the DNA backbone are indicated by spectral changes of conformational marker bands at 898 and 1423 cm −1 .

Ultrasensitive Raman measurements of nucleic acids are possible by exploiting the effect of surface-enhanced Raman scattering (SERS). In this work, the vibrational spectra of eight genomic DNAs from in vitro grown apple leaf tissues (Malus domestica Borkh., Fam Rosaceae, cvs. Florina, Idared, Rebra, Goldrush, Romus 3, Romus 4 and the rootstocks M9 and M26) were analyzed using surface-enhanced Raman spectroscopy, in the wavenumber range 200-1800 cm −1 . SERS signatures, spectroscopic band assignments and structural interpretations of these plant genomic DNAs are reported. Strong dependences of the SERS spectra on genomic DNA amount in the measured sample volume and on time were observed. Similarities of the SERS signals of DNAs from Rebra and Romus 3 leaves were detected. To our knowledge, this is the first SERS study on genomic DNA from leaf tissues. The present work provides a basis for future use of surface-enhanced Raman spectroscopy to analyze specific plant DNA-ligand interactions or DNA structural changes induced by plants' stress conditions associated with their natural environment. Besides, this study will generate information that is valuable in the development of low-level plant DNA-based analytical sensors.

In this paper the Raman total half bandwidths of calf-thymus DNA vibrations have been measured as a function of pH, monovalent and divalent cations' type and concentration. The dependence of different band parameters on DNA molecular subgroup structure, on pH and on Na+, Ca2+and Mg2+ions concentrations, respectively, are reported. It is shown that changes in (sub)picosecond dynamics of molecular subgroups in calf-thymus DNA can be monitored with confocal Raman microspectroscopy.The half bandwidths and the global relaxation times for the vibrations at 728 cm−1(dA), 785 cm−1(dC), 1094 cm−1(PO2−), 1377 cm−1(dA, dG, dT, dC), 1488 cm−1(dG, dA) and 1580 cm−1(dG, dA) of calf-thymus DNA are presented. The full-widths at half-height (FWHH) of the bands in calf-thymus DNA are typically in the wavenumber range from 7.4 to 31 cm−1. The bandwidths in the Raman spectra are sensitive to a dynamics active on a time scale from 0.34 to 1.44 ps.Low pH-induced melting of double helical structure in calf-thymus DNA results for some bands in shorter global relaxation times, as a consequence of the increased interaction of the base moieties with the solvent molecules.The molecular dynamics characterizing the 785, 1094, 1377 and 1580 cm−1vibrations, is faster in the case of high divalent cations DNA sample (pH 7), as compared to the respective low divalent cations DNA sample (pH 7), for both Ca2+and Mg2+ions. The vibrational energy transfer process of the guanine band at 1488 cm−1is slower for the high salt DNA sample, pH 7 as compared to the corresponding low salt DNA sample, pH 7, for both Ca2+and Mg2+. Molecular dynamics characterizing the vibration at 1488 cm−1is faster for DNA sample at high Na+ions (pH 7), as compared to the DNA sample at low Na+ions (pH 7).As far as the CaDNA and MgDNA complexes are concerned (pH 7), the global relaxation times of some base vibrations decrease for the case of magnesium ions, as compared to the case of the same concentration of calcium ions. The different ionic radius of the two types of metal cations (0.72 Å for Mg and 0.99 Å for Ca) were considered in explaining these results.Molecular relaxation processes of DNA subgroups, upon lowering the pH, in the presence of Na+, Ca2+and Mg2+ions are presented. Particularly, at low Ca2+concentration, upon lowering the pH, the molecular dynamics of DNA subgroups corresponding to vibrations at 728, 1376, 1488 and 1580 cm−1is much faster, probably due to the denaturation process of the double helical DNA.

Interaction of natural calf thymus DNA with Mn2+ions was studied by means of Raman spectroscopy. Spectra of DNA in 10 mM Na-cacodylate buffer, pH 6.2, 10 mM NaCl and in buffer containing Mn2+ions were measured at room temperature. Mn2+concentrations varied between 0 and 0.6 M. DNA backbone conformational changes and DNA denaturation were not observed in the concentration range 0 and 0.5 M, however, DNA condensation was observed at a critical concentration of 100 mM Mn2+that prevented the measurement of Raman spectra. Binding of Mn2+to the charged phosphate groups of DNA is indicated in the spectra. A high affinity of Mn2+for guanine N7 was obvious, and binding to adenine was barely suggested.

The vibrational spectra of eight genomic DNAs from leaf tissues (sword fern (Nephrolepis exaltataL.), chrysanthemum (Dendranthema grandifloraRamat.), redwood (Sequoia sempervirensD. Don. Endl.), orchids (Cymbidium × hybrida), common sundew (Drosera rotundifoliaL.), potato (Solanum tuberosumL.) and scopolia (Scopolia carniolicaJacq.)) have been analyzed using FT-Raman spectroscopy, in the wavenumber range 500–1800 cm–1.FT-Raman signatures, spectroscopic assignments and structural interpretations for these plant genomic DNAs are reported. Spectral differences among two genomic DNAs, independently extracted from chrysanthemum leaves, are to be observed between 1000–1200 cm–1. Besides, similarities in the FT-Raman spectra of genomic DNAs from potato and scopolia leaves, respectively, have been found. This might be explained by their belonging to the same family (Solanaceae). Other spectral differences among genomic plant DNAs have also been observed.These findings demonstrate that Raman spectroscopy may be exploited to distinguish different plant genomic DNAs.The present study provides a basis for future use of Raman spectroscopy to analyze specific plant DNA–ligand interactions or DNA structural changes induced by plants' stress conditions associated with their natural environment.

Abstract. In this paper the Raman total half bandwidths of calf-thymus DNA vibrations have been measured as a function of Mn 2+ ion concentration (0-600 mM), in the presence of two concentrations of Na + cations, respectively. The dependencies of the half bandwidths and of the global relaxation times on DNA molecular subgroup structure, on Mn 2+ and Na + ions concentrations, respectively, are reported. It is shown that changes in the (sub)picosecond dynamics of molecular subgroups in calf-thymus DNA can be monitored with Raman spectroscopy.In this study the Raman band parameters for the vibrations at 729 cm1376 cm −1 (dA, dG, dT, dC), 1489 cm −1 (dG, dA) and 1578 cm −1 (dG, dA) of calf thymus DNA are presented. The fullwidths at half-height (FWHH) of the bands in calf-thymus DNA are typically in the wavenumber range from 9 to 33.5 cm −1 . It can be observed that the molecular relaxation processes studied in this work, have a global relaxation time smaller than 1.179 ps and larger than 0.317 ps.Mn 2+ -induced DNA structural changes result for the vibrations at 729 cm −1 and 787 cm −1 in smaller global relaxation times, and larger half bandwidths, respectively, as compared to the starting value of 0 mM Mn 2+ . The vibrational energy transfer processes of these two subgroups (dA, dC), respectively, are slower in the case of DNA samples at 10 mM NaCl, as compared to the corresponding DNA samples at 150 mM NaCl. However, the behaviour of the global relaxation times characteristic to the bands at 729 and 787 cm −1 is similar with respect to manganese(II) ions concentration, in the case of the two values of Na + ions content, respectively.On the contrary, the molecular dynamics is slower for the base vibrations at 1376, 1489 and 1578 cm −1 , in the case of DNA samples at 150 mM NaCl, as compared to the corresponding samples at lower Na + concentration, in almost all Mn 2+ ions concentration range. The molecular relaxation processes in these three cases, respectively, are quite different for the corresponding samples with different Na + ions content, upon increasing divalent manganese ions concentration.The molecular dynamics characterizing the band near 1094 cm −1 of the DNA backbone PO 2 − symmetric stretching vibration is faster upon increasing the Mn 2+ ions concentration between 0-600 mM and seems not to be influenced by the Na + ions content, specific to our experimental conditions.

A confocal Raman microspectrometer was used to investigate the influence of Ca2+ cations on low pH-induced DNA structural changes. The effects of Ca2+ cations on the protonation mechanism of opening AT and changing the protonation of GC base pairs in DNA are discussed. Based on the observation that the midpoint of the transition of Watson-Crick GC base pairs to protonated GC base pairs lies at around pH 3 (analyzing the 681 cm(-1) line), measurements were carried out on calf thymus DNA at neutral pH and pH 3 in the presence of low and high concentrations of Ca2+ cations. Raman spectra show that low concentrations of Ca2+ cations partially protect DNA against protonation of cytosine (characteristic line at 1262 cm(-1)) and do not protect adenine (characteristic line at 1304 cm(-1)) and the N(7) of guanine (line at 1488 cm(-1)) against binding of H+. High Ca2+ concentrations can prevent protonation of cytosine and protonation of adenine (little disruption of AT pairs). Analyzing the line at 1488 cm(-1), which obtains most of its intensity from a guanine vibration, high salt was also found to protect the N(7) of guanine against protonation.