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H. Schulz
biochemical processes and a more detailed knowledge concerning plant diseases
at the molecular level. generally, all polarisable molecules occurring in plant
tissues generate Raman spectra. Contrary to infrared spectroscopy, it is possible
to analyse fresh plants without performing any sample pre-treatments, because
of the low polarizability index of water producing negligible Raman signal intensity.
Surface-enhanced Raman scattering (SERS), first observed in 1974, relies on
electronic and chemical interactions between the excitation laser light, the analyte
molecule and the SERS substrate (gold or silver nanoparticles). using this technique, the detection sensitivity can be enhanced up to 6–10 orders of magnitude
over conventional Raman spectroscopy [1]. Recent development of reproducible
SERS substrates provides new challenges to detect individual plant components
even when they occur in lower concentration [2–4]. usually the production of
the metal nanoparticles is performed by reduction of the metal salts with a suitable reducing agent. however, it has been found that certain plants such as alfalfa
( Medicago sativa), carrots ( Daucus carota) green tea ( Camellia sinensis) and red
cabbage ( Brassica oleracea var. capitata f. rubra) are able to reduce spontaneously
metal colloids [4–6]. In the absence of the metal colloids, Raman spectra could not
be obtained for most of the plant material for excitations at 514, 633 and 785 nm
due to the strong fluorescence of individual plant substances. generally, the presence of the gold colloids enabled strong SERS spectra, whereas the spectra of silver
colloids were weaker and exhibited more noise than those registered for gold. the
Raman spectrum of carrot was an exception, showing strong carotenoid signals,
which were not visible in presence of gold colloids. most peaks of the SERS spectra were attributed to adenine dinucleotide (NAd) and other adenine-containing
materials, but also some contributions from flavins, chlorophyll and lipids were
assigned.
In order to describe the individual gene functions, protein regulation and the
production of small molecular weight metabolites, the variation within the biological systems has been studied at the genomic, proteomic and metabolomic
levels. the metabolome is defined as the total sum of small molecular weight
substances (metabolites) present in an organism which participate in metabolic
reactions required for growth, maintenance and normal functions [7]. At present,
it is estimated that the number of metabolites detected in the plant kingdom may
reach a number up to 200,000. For targeted and non-targeted analysis and quantification as well as metabolic fingerprinting, techniques such as Raman and infrared
spectroscopy are valuable analytical tools beside NmR and mS. they provide
the opportunity for unbiased high-throughput measurements of the whole system
[8] and are comparatively inexpensive. In contrast to the other techniques used
for metabolome studies, more or less no sample preparation is necessary which
also guarantees that all plant substances are analysed without any discrimination
related to less solubility.
H. Schulz
biochemical processes and a more detailed knowledge concerning plant diseases
at the molecular level. generally, all polarisable molecules occurring in plant
tissues generate Raman spectra. Contrary to infrared spectroscopy, it is possible
to analyse fresh plants without performing any sample pre-treatments, because
of the low polarizability index of water producing negligible Raman signal intensity.
Surface-enhanced Raman scattering (SERS), first observed in 1974, relies on
electronic and chemical interactions between the excitation laser light, the analyte
molecule and the SERS substrate (gold or silver nanoparticles). using this technique, the detection sensitivity can be enhanced up to 6–10 orders of magnitude
over conventional Raman spectroscopy [1]. Recent development of reproducible
SERS substrates provides new challenges to detect individual plant components
even when they occur in lower concentration [2–4]. usually the production of
the metal nanoparticles is performed by reduction of the metal salts with a suitable reducing agent. however, it has been found that certain plants such as alfalfa
( Medicago sativa), carrots ( Daucus carota) green tea ( Camellia sinensis) and red
cabbage ( Brassica oleracea var. capitata f. rubra) are able to reduce spontaneously
metal colloids [4–6]. In the absence of the metal colloids, Raman spectra could not
be obtained for most of the plant material for excitations at 514, 633 and 785 nm
due to the strong fluorescence of individual plant substances. generally, the presence of the gold colloids enabled strong SERS spectra, whereas the spectra of silver
colloids were weaker and exhibited more noise than those registered for gold. the
Raman spectrum of carrot was an exception, showing strong carotenoid signals,
which were not visible in presence of gold colloids. most peaks of the SERS spectra were attributed to adenine dinucleotide (NAd) and other adenine-containing
materials, but also some contributions from flavins, chlorophyll and lipids were
assigned.
In order to describe the individual gene functions, protein regulation and the
production of small molecular weight metabolites, the variation within the biological systems has been studied at the genomic, proteomic and metabolomic
levels. the metabolome is defined as the total sum of small molecular weight
substances (metabolites) present in an organism which participate in metabolic
reactions required for growth, maintenance and normal functions [7]. At present,
it is estimated that the number of metabolites detected in the plant kingdom may
reach a number up to 200,000. For targeted and non-targeted analysis and quantification as well as metabolic fingerprinting, techniques such as Raman and infrared
spectroscopy are valuable analytical tools beside NmR and mS. they provide
the opportunity for unbiased high-throughput measurements of the whole system
[8] and are comparatively inexpensive. In contrast to the other techniques used
for metabolome studies, more or less no sample preparation is necessary which
also guarantees that all plant substances are analysed without any discrimination
related to less solubility.