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Here we report the SERS spectroscopy study of the herring sperm DNA adsorbed on the silvered porous silicon. Porous silicon has been fabricated by an electrochemical anodic etching of a highly doped n-type silicon wafer. It has been shown that the following silver immersion deposition on porous silicon lead to the formation of a layer of silver nano- and microparticles assembled in a quasi-ordered array. Reflectance spectroscopy has revealed that the silver layer demonstrates the surface plasmon resonance band expanded to near-IR range. Preliminary SERS measurements with rhodamine 6G have showed that the silvered porous silicon is characterized by a very good reproducibility of the SERS signal and one-year shelf life. It has been found that the silvered porous silicon is SERS-active in relation to the herring sperm DNA under the excitation at 473, 633 and 785 nm. Collection of the SERS spectra of the DNA molecules in the random points of the silvered porous silicon has resulted in their weak reproducibility typical for the solid SERS substrates. However, the SERS mapping has helped to find the classical DNA spectra. In addition, the herring sperm DNA at an extremely low concentration of 1 mg mL−1 has been detected with the SERS substrate based on the silvered porous silicon.
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Detection of DNA molecules by SERS
spectroscopy with silvered porous
silicon as an active substrate
Kseniya Girel*
, Ekaterina Yantcevich
, Grigory Arzumanyan
, Nelya Doroshkevich
and Hanna Bandarenka**
Belarusian State University of Informatics and Radioelectronics, P. Brovka str. 6, 220013 Minsk, Belarus
Joint Institute for Nuclear Research, 6 Joliot-Curie Str., 141980 Dubna, Russia
Dubna State University, 19 Universitetskaya Str., 141982 Dubna, Russia
Received 19 June 2016, revised 13 September 2016, accepted 6 October 2016
Published online 1 November 2016
Keywords DNA, porous silicon, silver, surface enhanced Raman scattering
Corresponding author: e-mail, Phone: þ375 17 293 88 43, Fax: þ375 17 293 88 54
e-mail, Phone: þ375 17 292 23 60
Here we report the SERS spectroscopy study of the herring
sperm DNA adsorbed on the silvered porous silicon.
Porous silicon has been fabricated by an electrochemical
anodic etching of a highly doped n-type silicon wafer. It
has been shown that the following silver immersion
deposition on porous silicon lead to the formation of a
layer of silver nano- and microparticles assembled in a
quasi-ordered array. Reectance spectroscopy has revealed
that the silver layer demonstrates the surface plasmon
resonance band expanded to near-IR range. Preliminary
SERS measurements with rhodamine 6G have showed that
the silvered porous silicon is characterized by a very good
reproducibility of the SERS signal and one-year shelf life.
It has been found that the silvered porous silicon is SERS-
active in relation to the herring sperm DNA under the
excitation at 473, 633 and 785 nm. Collection of the SERS
spectra of the DNA molecules in the random points of the
silvered porous silicon has resulted in their weak
reproducibility typical for the solid SERS substrates.
However, the SERS mapping has helped to nd the
classical DNA spectra. In addition, the herring sperm DNA
at an extremely low concentration of 1 mg mL
has been
detected with the SERS substrate based on the silvered
porous silicon.
ß2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
1 Introduction Detection of DNA molecules today
is widely used in many areas of human life such as medical
diagnostics, gene therapy, forensic science, etc. [1, 2]. For
many years, the polymerase chain reaction and uorescent
spectroscopy have been the most popular methods used in
practice to study DNA [3]. Such methods are proven and
reliable but often require expensive chemicals and take
a long time to get results. Surface enhanced Raman
scattering (SERS) spectroscopy is an alternative attractive
way to study DNA with its remarkable ability of single
molecule detection [4]. The study of the DNA components
by the SERS spectroscopy was rst reported in 1980 [5].
The authors showed the SERS spectra of the 10
adenine, adenosine, and adenosine-50-monophosphate at
the electrochemically roughened silver electrode. Later
the detection limit of the DNA components was improved
to 10
M with SERS-active silver colloids [6]. Further
progress in an engineering of the SERS substrates has
driven a tremendous interest to study DNA by the SERS
spectroscopy [79]. However, the practical application of
this method is still in its infancy comparing to the
traditional techniques of the DNA detection. It is mostly
caused by severe dependence of the spectral quality and
reproducibility on variations of the DNA conformation
and/or packing density on the SERS substrates. For
example, it was shown that the SERS spectrum of l-DNA
in the silver colloid is slightly shifted with respect to the
conventional Raman spectrum [7]. The other paper
reported on a weak reproducibility of signal-to-noise
ratios in the SERS spectra of the DNA molecules adsorbed
on the solid SERS substrate made of gold nanoshells [8].
In addition, small amount of organic compound can
Phys. Status Solidi A, 15 (2016) / DOI 10.1002/pssa.201600432
applications and materials science
ß2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
degrade under the laser excitation [10]. It is especially
typical for blue (near-UV) irradiation favorable for an
activation of the silver-based SERS substrates. In
assessing the potential of SERS spectroscopy for the
DNA study, it is, therefore, important to adjust to the
measurements with the selected SERS substrates, i.e., to
nd correlation between the measuring regimes, the
substrate type, and the resulting spectra.
It has been previously shown that the SERS substrates
based on a silvered porous silicon (PS) give rise to a strong
enhancement of the signal from a rhodamine 6G [11] and a
cationic Cu(II)-tetrakis(4-N-methylpyridyl) porphyrin
resulting in an extremely high sensitivity [12]. In this
article, we investigate the effect of such substrates on the
spectra of the herring sperm DNA to choose optimal
conditions of the SERS measurements resulting in a reliable
DNA study.
2 Experimental
2.1 Sample preparation Monocrystalline n
Si wafers were used as initial substrates. Prior to PS
formation Si wafer was cleaned in a solution of NH
O mixed in a volume ratio of 1:1:4 according
to the procedure described elsewhere [13]. The native
was removed from the Si wafer in diluted HF (4.5%).
The front face of the Si wafer was then rendered porous
to a depth of 5 mm by an electrochemical anodic etching
in a mixture of HF, H
O, and C
OH at a current density
of 100 mA cm
. The sample was rinsed with deionized
water and spun dry.
The Si wafer with porous front face was cut into a
number of 5 7 mm samples. Each sample was immersed in
a water-ethanol solution of 3 mM AgNO
for 70 min
resulting in a deposition of silver nanoparticles on PS. The
silvered PS samples were rinsed with deionized water and
then air-dried.
An adsorption of analyte molecules was realized by a
drop deposition of R6G water solution or herring sperm
DNA in 0.01 M NaCl water solution on the silvered PS.
The shelf life of the SERS substrates was assessed by
the SERS measurements after 1, 6, and 12 months of their
keeping in a zipped plastic bag. Prior to the analyte
deposition, the substrate was refreshed in diluted HCl
for 30 s.
2.2 Measurements Electrochemical process was
carried out with the potentiostat/galvanostat AUTOLAB
PGSTAT302n. A scanning electron microscope (SEM)
Hitachi S-4800 was used to study the morphology of the
silvered PS. Reectance spectra of the samples were
recorded in the range from 200 to 1100 nm with MC 122
Proscan spectrometer. The Raman and SERS spectra were
measured with a 3D scanning confocal microscope
Confotec NR500. Laser wavelengths of 473, 633, and
785 nm were used to excite the samples. Laser powers
were 1.45, 0.68, and 0.86 mW, respectively. During SERS
measurements, the power of the blue laser was reduced by
two orders of magnitude while the power of the red laser
was reduced by one order of magnitude. Laser spot
diameters were about 300 nm (for the wavelength of
473 nm), 400 nm (for the wavelength of 633 nm), and
500 nm (for the wavelength of 785 nm).
3 Characterization of the SERS substrates The
regimes and solutions for the silvered PS were chosen
based on the results reported elsewhere [12]. Such
conditions were shown to provide the greatest intensity
of the SERS signal. In this work, the morphology of the
most active sample was accurately studied. The quantita-
tive analysis of Fig. 1 revealed that the silver deposit is
composed of the particles of two size ranges. The sizes of
the particles in the rstgrouparevariedfrom10to150nm
while the second group has larger particles of 150700 nm
in diameter. The content of the small particles is about
83%. Namely such nanoparticles are favorable for the
SERS effect. The distance between many nanoparticles is
no longer than 10 nm promising so-called hot spots
where a huge SERS intensity takes place.
The optimal excitation wavelength must match the
surface plasmon resonance (SPR) band of the SERS
substrate. Here the SPR of the silvered PS was found from
its reectance spectrum. Figure 2 shows that the
absorbance band related to the SPR is atypically wide
for the silver nanoparticles and reaches near-IR region.
This effect is observed due to different plasmon oscillation
modes in the small silver particles of a non-uniform size
The SERS activity of the silvered PS was veried by the
detection of 10
M R6G. The spot-to-spot and sample-to-
sample deviation of the SERS signal varied from 5 to 7%. In
addition, the SERS substrates demonstrated an extremely
long shelf life up to 1 year.
Figure 1 SEM top views of the PS samples after the immersion
into 3 mM AgNO
solution for 70 min.
2 K. Girel et al.: Detection of DNA molecules by SERS spectroscopy
ß2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
4 SERS study of DNA The Raman and SERS
measurements of the herring sperm DNA were carried
out under different laser wavelengths ranging from blue to
near-IR regions (Fig. 3).
The peaks observed in the Raman spectra around
730 cm
(adenine), 787 cm
(thymine, cytosine),
1104 cm
(v(CO), deoxyribose-phosphate),
1242 cm
(cytosine, adenine), 1381 cm
guanine, adenine), 1490 cm
(guanine, adenine), and
1581 cm
(guanine, adenine) are the characteristic
Raman bands of the herring sperm DNA molecules [10].
SERS spectra were collected in 10 random points of the
silvered PS. Remarkably, the silvered PS demonstrates
SERS activity for all lasers proving the suggestion
proposed in the previous section. However, the SERS
spectra of DNA recorded in different points of the
silvered PS samples show weak reproducibility which is
in a good accordance with the data reported elsewhere [8].
Despite some bands of the DNA bases can be recognized,
their intensity and position are not stable enough. The
variation of the DNA SERS spectra mainly appear due to
changes in molecules conformation after their deposition
anddryingonthesilveredPS as well as an increase of
randomness under laser irradiation. The intensity and the
band position also depend on wavelength and power of
the laser and accumulation time. For example, long UV
radiation can destroy the DNA molecular group and
bonds. Thus power of 473 nm laser was reduced about
two orders of magnitude. Pronounced dominance of the
adenine band is caused by its greater Raman cross section
compared with that of guanine, cytosine, and thymine [8].
An increased background hiding the DNA bands from
1300 to 1600 cm
in the spectra collected under blue
excitation can be explained by the decomposition of
the DNA bases in the presence of noble metal and severe
irradiation [7].
The following SERS mapping of the substrates
allowed to nd identiable the SERS spectra of the
herring sperm DNA collected under each laser excitation
(Fig. 4).
The silver nanoparticles of the same sizes were
organized in the monolayer in some places on PS
(see Fig. 1). We suppose this provided the DNA molecule
alignment and a stable surface enhancement along the
molecule resulting in the possibility to see the classical
Figure 2 Reectance spectrum of the PS samples after the
immersion into 3 mM AgNO
solution for 70 min.
Figure 3 Raman (a) and SERS (b) spectra of the 10
M herring
sperm DNA collected under the 473 (panel 1), 633 (panel 2), and
785 (panel 3) nm excitation wavelengths.
Phys. Status Solidi A (2016) 3 ß2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
DNA spectrum. As shown in Fig. 2, the SPR maximum is
about 500520 nm and the SERS activity is expected to be
stronger at the excitation of 473 nm than 633 and 785 nm.
However, comparing SERS intensities in Fig. 4 shows that
the situation is opposite proving the assumption on the
destruction of the DNA molecules under excitation with
wavelength close to the UV.
Finally, the SERS mapping was used to detect the
herring sperm DNA at an extremely low concentration of
M. In Fig. 5, comparison of two SERS spectra of the
DNA molecules at different concentrations is presented.
The SERS spectra were recorded under the 473 nm
excitation wavelength as both red and near-IR lasers
showed no results for the lowest concentration. In contrast
to the regime applied in case of Fig. 4, accumulation time
was increased from 1 to 5 s. In spite of the shift of
some bands and new bands arising it can be argued that the
DNA molecules at the 0.01 mg mL
concentration can be
5 Conclusions The results on the DNA study by the
SERS spectroscopy with the silvered PS presented here
were partially similar to those with solid SERS substrates
that gave surface enhancement from DNA but weak
reproducibility of the spectra. This was typical for the
measurements in random points on the SERS substrate.
However, from the results of this article it is likely that
the classical spectra of the DNA molecules can be found
by the SERS substrate mapping. Moreover, the prospects
for the DNA detection by the SERS spectroscopy with
lasers of 473, 633, and 785 nm wavelengths are very
encouraging. The most promising result is in the
detection of the DNA molecules at very low concentra-
tion (10
M) with the silvered PS. According to our
knowledge, detection of such a small amount of DNA has
not been reported elsewhere. It shows an advantage of the
developed silvered PS compared to other solid SERS-
active substrates. Although in a competitive eld, the
SERS substrate based on PS is a very unusual material
in the DNA study by SERS spectroscopy.
Acknowledgements The authors would like to thank
very much Dr. Andrei Panarin and Dr. Sergei Terekhov for the
fruitful discussions on the SERS spectroscopy of the DNA
molecules as well as Dr. Vitaly Bondarenko for the useful
consultation on formation and properties of porous silicon.
This work has been supported in parts by the Belarusian State
Research Program Photonics, opto- and micro-electronics
(task no. 1.4.01), the Belarusian Republican Foundation for
Fundamental Research (grant no. T16-099), and JINR (theme
no. 04-4-1111).
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Figure 4 SERS spectra of the 10
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Figure 5 The SERS spectra of the 10
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spectra were collected under the 473 nm excitation wavelength.
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Phys. Status Solidi A (2016) 5 ß2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
... For example, plasma synthesis or thermolysis at which the metallic NPs are formed during the high-temperature decomposition of solids containing metallic ions, molecular anions, or organometallic complexes [9]. The undoubted advantage of the liquid substrates is the ability to objectively study the structure of long molecules such as DNA because the metallic NPs cover these molecules, preventing their deformation and allowing the registration of stable spectra [10], while the solid substrates cause changes in the conformation of molecules resulting in a lack or a shift of characteristic bands [11,12]. The liquid substrates demonstrate a high enhancement factor due to the many hot spots via NPs aggregation. ...
... The SERS-active substrates based on porous silicon make it possible to perform analyses of the wide range of analytes including the tetrapyrrolic molecules [74,84], proteins [94] and peptides [79,113], DNA [12,73], microRNA [62], gases [37,41,43,45], physiological fluids [97], thiols [95,114], and so forth. The femtomolar detection limit has been demonstrated for organic dye R6G [37,89,115], while the enhancement factor for some substrates can rise to an enormous value from 10 8 [106,108,116,117] to 10 11 [41]. ...
... Recently, silvered mesoporous silicon based on n + -type silicon wafers were reported as effective SERS-active substrates which can be applied to the detection of DNA [12], phospholipids [115], and peptides, as well as for the reliable study of their secondary structure [113]. ...
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... Reproducibility is one of the important factors to judge the quality of SERS substrate. The reproducibility of the SERS signal of DNA molecules on AgNPs coated pSi shows a shelf life of one year, demonstrated by Girel's group.302 ...
... Ultra-low detection of small organic molecules by SERSspectroscopy has been easily achieved using AgNPs/PS or GNPs/PS substrates [106,[124][125][126]135,155,156]. Identification and analysis of organic objects such as tetrapyrrolic molecules [157], peptides [138,139], proteins [108,114,149], enzymes [158], nucleic acids [106,159], antibiotics [58,147], DNA [160], microRNA [161], serum blood [114,162,163], physiological fluids [164], bacteria [165], cells [166], antioxidant [95] and aflatoxins [108] has been already reported. It should be noticed that single-molecule detection is not always required for the analysis of multicomponent substances. ...
Surface-enhanced Raman scattering (SERS) spectroscopy is one of the most prospective methods combining state-of-the-art nanomaterials and optical techniques for highly sensitive express-analysis and detection of organic and bioorganic objects in liquids and gases. Special programs have been recently started all over the world to bring the SERS-spectroscopy closer to wide implementation in medical diagnostics, forensics, security, monitoring sanitary conditions, etc. Despite outstanding features of SERS-spectroscopy, its effective practical use has been particularly slowed down by moderate reproducibility, non-versatility, and restrictions imposed by commercially available SERS-active substrates to measurement and storage regimes. The present review reports SERS-active substrates constituted by noble metals' nanoparticles (NPs) and porous silicon (PS), which potentially can be a tool to overcome the above-mentioned limitations. The PS template acts as a highly ordered host nanomaterial for the formation of a variety of metallic nanostructures, which morphological and optical properties can be easily tuned for the best performance to meet the customer requirements via managing PS synthesis regimes. An indubitable advantage of PS is the compatibility of its fabrication process with basic microelectronics operations and micro-electromechanical systems (MEMS) that make it possible to integrate SERS-active areas in a silicon chip. In contrast to the previously published reviews in the field, this one covers the most recent results on formation, characterization, and application of PS-based substrates demonstrating prominent SERS-activity that have been achieved for the last decade including modifications with graphene or Bragg structures, detection of molecules at amount down to attomolar concentration, bacteria recognition, etc.
... Adenine adsorption on silver and gold nanoparticles and electrodes exhibits desirable surface-enhanced Raman scattering (SERS) signal strength, which is suitable for the detection of diseases, DNA hybridization and many biomedical and agricultural applications [1]. Therefore, it has become one of the most frequently studied biomolecules along with the rapid increase in SERS research in recent years [2][3][4]. ...
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... In contrast to c-Si, the por-Si material provides more electrons for reduction and centers for nucleation of the silver atoms due to an extremely developed nanostructured surface. In this work, we used the silvered por-Si substrates that have been well-studied before [53,57]. The SERS-active layer of these substrates presents non-continuous film composed of quasi-spherical silver particles of polycrystalline nature, which dominating sizes are in the range of 10-150 nm, however, some of them have diameters of 150-700 nm (see Figure S2). ...
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We registered surface enhanced Raman scattering (SERS) spectra of the human lactoferrin molecules adsorbed on a silvered porous silicon (por-Si) from 10−6–10−18 M solutions. It was found that the por-Si template causes a negative surface potential of silver particles and their chemical resistivity to oxidation. These properties provided to attract positively charged lactoferrin molecules and prevent their interaction with metallic particles upon 473 nm laser excitation. The SERS spectra of lactoferrin adsorbed from 10−6 M solution were rather weak but a decrease of the concentration to 10−10 M led to an enormous growth of the SERS signal. This effect took place as oligomers of lactoferrin were broken down to monomeric units while its concentration was reduced. Oligomers are too large for a uniform overlap with electromagnetic field from silver particles. They cannot provide an intensive SERS signal from the top part of the molecules in contrast to monomers that can be completely covered by the electromagnetic field. The SERS spectra of lactoferrin at the 10−14 and 10−16 M concentrations were less intensive and started to change due to increasing contribution from the laser burned molecules. To prevent overheating the analyte molecules on the silvered por-Si were protected with graphene, which allowed the detection of lactoferrin adsorbed from the 10−18 M solution.
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Analyzing biomolecules is essential for disease diagnostics, food safety inspection, environmental monitoring and pharmaceutical development. Surface-enhanced Raman spectroscopy (SERS) is a powerful tool for detecting biomolecules due to its high sensitivity, rapidness and specificity in identifying molecular structures. This review focuses on the SERS analysis of biomolecules originated from humans, animals, plants and microorganisms, combined with nanomaterials as SERS substrates and nanotags. Recent advances in SERS detection of target molecules were summarized with different detection strategies including label-free and label-mediated types. This comprehensive and critical summary of SERS analysis of biomolecules might help researchers from different scientific backgrounds spark new ideas and proposals.
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Silvered porous silicon was utilized as an active substrate for a detection of small amounts of meldonium by surface enhanced Raman scattering (SERS) spectroscopy. We were able to detect the meldonium in its water solutions at the concentrations of 10−2–10−6M. Immersion of the silvered porous silicon in the meldonium solutions at the 10−4M concentration and lower led to the dimers’ formation. At the concentrations larger than 10−3M, a greater contribution to the enhancement of the Raman intensity was caused by a chemical mechanism while the smaller amounts were detected mostly due to an electromagnetic mechanism.
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Plasmonic nanostructures demonstrating an activity in the surface-enhanced Raman scattering (SERS) spectroscopy have been fabricated by an immersion deposition of silver nanoparticles from silver salt solution on mesoporous silicon (meso-PS). The SERS signal intensity has been found to follow the periodical repacking of the silver nanoparticles, which grow according to the Volmer-Weber mechanism. The ratio of silver salt concentration and immersion time substantially manages the SERS intensity. It has been established that optimal conditions of nanostructured silver layers formation for a maximal Raman enhancement can be chosen taking into account a special parameter called effective time: a product of the silver salt concentration on the immersion deposition time. The detection limit for porphyrin molecules CuTMPyP4 adsorbed on the silvered PS has been evaluated as 10(-11) M.
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The surface enhanced Raman spectra of the nucleic acid bases guanine, adenine, thymine and cytosine adsorbed on small particles of colloidal silver have been recorded in the spectral range of 100 to 1700 cm−1. Prominent SERS bands for these bases are the ring-breathing modes at 653 cm−1 in guanine, 728 cm−1 in adenine, 789 cm−1 in thymine and 797 cm−1 in cytosine. This new spectroscopic method provides a powerful technique for in situ investigations of adsorbed nucleic acid components of a rather dilute aqueous solution (10−6 M).
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Nickel nanowires have been formed by stationary electrochemical deposition of nickel into mesoporous silicon templates from the modified Watts bath. Monitoring of the porous silicon potential during the electrochemical deposition has given the determination of the emergence of Ni on the outer surface of porous layer. Maximum filling factor of porous silicon with Ni has been achieved to 67%. The pore dimensions have been found to define the length and diameter of the Ni nanowires that have equaled to 10 μm and 100–120 nm, respectively. The polycrystalline nature of the nickel nanowires, as well as the expansion of nickel lattice constant in comparison with bulk material has been established by analyzing the X-ray diffraction spectra. The synthesized samples have possessed ferromagnetic properties, which have been confirmed by temperature measurements of the magnetization. Smaller values of the specific magnetization of the Ni/PS samples and the atomic magnetic moment of Ni atoms at the low temperature with respect to those of bulk material have been suggested to be mostly caused by formation of nickel silicide at the beginning of the Ni electrochemical deposition.
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We have optimized the procedure for preparation of nanostructured silver films on the surface of mesoporous silicon (PSi) to use them as active substrates in surface-enhanced Raman scattering (SERS) spectroscopy. The greatest enhancement of the SERS signal was observed for samples obtained when the silver was deposited on PSi from an aqueous AgNO3 solution with concentration 1⋅10–2 M over a 10–15 minute period. The detection limit for rhodamine 6G on SERS-active substrates prepared by the optimized procedure was 1⋅10–10 M. The enhancement factor for the SERS signal on these surfaces was estimated as ≈2⋅108. We have shown that SERS-active substrates based on mesoporous silicon are promising for detection and study of complex organic compounds, in particular tetrapyrrole molecules.
The ability to detect multiple disease-related targets from a single biological sample in a quick and reliable manner is of high importance in diagnosing and monitoring disease. The technique known as surface enhanced Raman scattering (SERS) has been developed for the simultaneous detection of multiple targets present in biological samples. Advances in the SERS method have allowed for the sensitive and specific detection of biologically relevant targets, such as DNA and proteins, which could be useful for the detection and control of disease. This review focuses on the strengths of SERS for the detection of target molecules from complex mixtures and the clinical relevance of recent work combining SERS with multiplexed detection of biological targets.
Single-molecule Raman spectroscopy of a cyanine dye in aqueous silver colloidal solution with the use of surface-enhanced Raman scattering at near-infrared excitation (NIR-SERS) is reported. A characteristic Poisson distribution of SERS signals due to the Brownian motion of single dye molecule-loaded silver particles reflects the probability of finding 0, 1, or 2 1,1 ' -diethyl-2,2 ' cyanine (PIC) molecules in the probed volume during an actual measurement and is evidence that single-molecule detection by SERS has been achieved. Spectra measured in 1 s collection time with 100 mW nonresonant 830 nm excitation provide a clear ''fingerprint'' of a single PIC molecule by showing its typical Raman lines between 700 and 1700 cm -1. Single-molecule Raman signals are also detected for the first time at the anti-Stokes side of the excitation laser. Effective Raman cross sections for PIC of 10 -16 cm2 per molecule can be inferred from the ratio between ''pumped'' anti-Stokes and Stokes signals.
In the presence of cyclic organic compounds, the photo-reduced reaction of silver ions could occur under the inducement of the laser irradiation, forming silver colloids of aggregated silver atoms. In this study, the formation of the colloids induced by laser irradiation was proved by means of Raman scattering, UV-Vis spectrum and Scanning Electron Microscope (SEM). The Raman signals of nucleic acid bases were slightly enlarged because of the surface-enhanced Raman scattering activity brought by the aggregation of silver atoms. Furthermore, the experiment results show that Raman spectra with a high signal-to-noise ratio and good repeatability could be obtained by this method and the Raman spectra of nucleic acid bases obtained were similar to those obtained in Lee-Meisel silver colloid and on silver membrane surface. Although there were some new peaks and shifts in our Raman study, the classical characteristic peaks could also be found and used to identify different species. Owing to its simple operation, surface-enhanced Raman scattering (SERS) of colloids prepared by photo-reduced silver nitrate shows great application value in the in situ detection of small molecules.
The Raman spectra of herring sperm DNA in native fibres and after heat treatments to 40, 91, and 200°C were presented. The Raman spectral bands indicated that the damage of the heating on the DNA conformation is limited below the melting point. The damage of the DNA molecular structure increased with a rise in temperature above the melting point. The damage was first observed in adenine and deoxyribose. The Raman spectra of DNA in aqueous solution and after ultraviolet radiation were reported. The experimental results proved that the ultraviolet radiation had a serious influence on the DNA molecular conformation and damaged the hydrogen bonds and groups among the purine and pyrimidine bases. The denaturation was irreversible.
A controllable silver nanoparticle aggregate system has been synthesized by adding different amounts of ethanol to cetyltrimethylammonium bromide (CTAB) capped silver nanoparticles (Ag-nps), which could be used as highly efficient surface-enhanced Raman scattering (SERS) active substrates. This ethanol-induced aggregation can be attributed to preferential dissolution of CTAB into ethanol, which leads a partial removal of the protective CTAB layer on Ag-nps. The optical and morphological properties of these aggregates under various volumes of ethanol were explored via UV−vis spectroscopy and atomic force microscopy. Two common probe molecules, Rhodamine 6G (R6G) and 4-aminothiophenol (4-ATP) were used for testing the SERS activity on these substrates at very low concentrations. It was found that the SERS enhancement ability is dependent on the ethanol volume used. The SERS enhancement factors of 4-ATP were estimated to be as large as 8.1 × 108 for b2 vibration modes and 6.8 × 106 for a1 vibration modes. Good stability of the substrates was demonstrated by measuring the Raman activity with time. The optimized SERS-active substrate with the largest enhancement ability shown in this study could be used to detect double-strand DNA. The great advantage for this SERS-based DNA detection is that a dye label is not needed. It showed the potential of this Ag-nps aggregate system as a convenient and powerful SERS-active substrate for DNA detection.
The free radical chain oxidation of organic compounds has historically been referred to by organic and physical chemists as autoxidation. The peroxide products of the reaction can serve as initiators of the process under certain conditions, and under those circumstances, the rate of oxygen consumption increases over time as peroxide products are formed. Tyrosyl radicals in myoglobin and hemoglobin also initiate peroxidation reactions that play a potentially significant role in rhabdomyolysis, subarachnoid hemorrhage, malaria, and sickle cell disease. The pentadienyl carbon radicals derived from linoleate and the other fatty acid esters have the odd electron spin distributed principally on the two terminal carbons and one central carbon of the five-carbon framework. Cholesterol, a monounsaturated sterol lipid, is an order of magnitude more reactive than oleate, a monounsaturated fatty acid.