In this study, a SERS LFM that achieves ultra- sensitive and high throughput diagnosis of the nucleic acids of RTI pathogens was described. Core shell SERS nanotags encoded with two RDs were chosen as signal labels and combined on a microarray immobil- ized on a NC membrane for rapid quantification of the nucleic acids from eleven RTIs on a single strip. The volume of sample required, reagent consump- tion, material cost, duration of assay preparation and detection, in addition to operation of the test have been reduced because the multiplex assays have been integrated onto one SERS LFM. The LOD for influenza A, parainfluenza 1, parainfluenza 3, respiratory syncytial virus, coxiella burnetii, legionella pneumophila, influenza B, parainfluenza 2, adenovirus, chlamydophila pneumoniae, and mycoplasma pneumoniae were 0.031 pM, 0.030 pM, 0.038 pM, 0.038 pM, 0.040 pM, 0.039 pM, 0.035 pM, 0.032 pM, 0.040 pM, 0.039 pM, and 0.041 pM, respectively. The LOQ for influenza A, parainfluenza 1, parainfluenza 3, respiratory syncytial virus, coxiella burnetii, legionella pneumophila, influenza B, para- influenza 2, adenovirus, chlamydophila pneumoniae, and mycoplasma pneumoniae were 0.157 pM, 0.149 pM, 0.261 pM, 0.219 pM, 0.326 pM, 0.256 pM, 0.195 pM, 0.167 pM, 0.272 pM, 0.353 pM, and 0.351 pM, respectively. The LDR of these eleven RTI pathogen nucleic acids were 1 pM-50 nM, which cover 5 orders of magnitude. The test benefitted from signal amplification of the encoded SERS nanotags and the 2×3 microarray embedded on the NC membrane, and the high SVR of the NC membrane. It is foreseeable
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In conclusion, a set of new extreme red shifted SERS nanotags have been designed and synthesized to demonstrate unprecedented performance using 1280-nm excitation, a set of chalcogenopyrylium dye reporter molecules, and HGNs. These nanotags show a LOD in the picomolar range. The dye molecules are unique NIR reporters as they have multiple chalcogen attachment groups which allow them to bind strongly to the gold surface of the HGN and thus produce intense SERS signals. Dyes 1-14 with the more widely used gold nanoparticles or HGNs with conventional Raman reporters such as BPE were unable to match the combined performance of the chalcogenopyrylium dyes and HGNs indicating the unexpected and superior performance of SERS nanotags based on the combination of these dyes and the tunable HGNs. This significant result now makes SERS nanotags available for future use in a wide range of optical applications with 1280-nm excitation including deep tissue analysis and will provide a basis for future studies into harnessing their unique spectral properties.
Specifically in this work, the SERS capabilities of HGNs functionalised with 17 different chalcogenopyrylium dyes (chalcogen nanotags) were investigated using a hand-held 1064 nm Raman spectrometer. It should be noted that an inorganic salt, specifically potassium chloride (KCl) was used to aggregate the nanotags as it increases the SERS signal by screening the Coloumbic repulsion energy between the nanoparticles allowing the reporter molecules to adhere more closely to the nanoparticle surface. We have previously shown that reproducible and stable nanotags (HGNs functionalised with a Raman reporter) can be prepared when 30 mM KCl is used as the aggregating agent.(28, 31) It was found at a concentration greater than 30 mM the HGNs precipitated out of solution and below this, weaker SERS signals were observed. Moreover, we demonstrated that by using this optimal concentration of KCl the LSPR of the HGNs did not shift but the enhancement in SERS signal was undeniable. Extinction spectroscopy, dynamic light scattering and zeta potential analysis were used previously to investigate the stability of the nanotags and it was found that for both the commercial reporter BPE (1,2-bis(4-pyridyl)ethylene) and chalcogenopyrylium dye 14, that upon adding the Raman reporter and aggregating with KCl, the LSPR of the HGNs did not shift nor was there broadening of the peak however slight dampening in the absorption maxima was observed. Further, a size increase and a decrease in zeta potential values indicated a change to the colloidal solution but ultimately it was concluded that the nanotags were stable and not over-aggregating.(28, 31) In addition, it is important to note that the plasmon resonance frequencies, hence LSPR of the HGNs (which is 710 nm, figure S1, ESI) does not need to match the excitation frequency of the laser for effective SERS to be achieved.(31-34) Therefore, by exploiting our previous knowledge SERS nanotags which are optimal for use in the SWIR region have been developed. Moreover, in this work the SERS response from chalcogen nanotags were compared to commercial reporters BPE and AZPY (4,4-azopyridine) also adsorbed onto the surface of HGNs and aggregated with 30 mM KCl. BPE and AZPY were chosen as they are non-resonant commercial reporters which have previously been exploited and shown to provide excellent SERS responses with HGNs and other SERS substrates at this laser wavelength.(31, 35-37)
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detecting such DNA anomalies in multiplex in clinic is extremely useful. To this end, as a proof-of-concept, we coupled SERS with end-point PCR for a simple 3-plex assay to simultaneously amplify DNA sequences that resulted in BRAF V600E (c.1799T>A), c-Kit L576P (c.1727T>C) and NRAS Q61K (c.181C>A) mutations (Figure 1A). Each forward primer had a 15 nt unique barcode sequence followed by an internal carbon spacer upstream of the mutation-specific sequence. This effectively created a 5’ overhang after PCR as DNA polymerases cannot extend beyond the carbon spacer on the reverse strand. The reverse primers contained a 5’-biotin molecule which later allowed for convenient enrichment by streptavidin coated magnetic beads (SMB). If a mutation was present, the resulting PCR amplicon would have a biotin handle on one end and a 5’ overhang barcode on the other. SERS-nanotags were gold nanoparticles (AuNPs) modified with Raman reporters and DNA probes that were complementary to barcodes sequences on the amplicons thus resulting in a SERS/DNA/biotin molecule. After enrichment with SMB to remove excess SERS nanotags, the identity of the remaining SERS nanotags was ascertained with a Raman spectrometer, which in turn, reflected the presence of a particular mutation. Raman reporters used in this study were 4-Mercaptobenzoic acid (MBA) for BRAF V600E at Raman shift of 1076 cm -1 ,
In this work we have presented an improved method for HGN synthesis which both improves the stability and shifts the SPR to longer wavelengths making them advantageous for use in many biomedical applications where nanostructures with a SPR in the NIR region are desirable. In addition to this we have systematically compared the stability of three different materials commonly used as stabilising agents and tested their tolerance to different salt and pH environments. The results indicated that in regards to HGNs, PEG is the most suitable stabilising agent increasing stability to high salt concentrations and pH extremes with an inherent stability over one month in up to 5 M NaCl and in both acidic and alkaline environments. Additionally, HGNs stabilised with PEG provide greater long term stability to the nanoparticles with no reduction in stability over at least three months. We have also achieved SERS of stabilised HGNs at both 785 nm and 1064 nm excitation using a newly synthesised class of Raman reporter molecules. Overall, PEG-stabilised HGNs synthesised within this work possess a combination of increased stability across a range of environments, long term stability and SERS signals in the NIR region making them excellent SERS substrates for potential use in many biomedical applications.
In conclusion, the combination of 100 nm AuNPs encapsulated with chalcogenopyrylium dyes have shown limits of detection in the picomolar range, which is extremely low as Raman scattering is intrinsically weak at this excitation wavelength. In addition, these unique nanotags have proven to be better than commercially available ones and the fact that they are compatible with a range of NIR laser excitations, demonstrates their flexibility which could be essential for future advancements in biomedical and optical applications specific to the IR range.
Surface enhanced Raman Scattering (SERS) tags are in situ probes that can provide sensitive and selective probes for optical analysis in biological materials. Engineering tags for use in the near infrared (NIR) region is of particular interest since there is an uncongested spectral window for optical analysis due to the low background absorption and scattering from many molecules. An improved synthesis has resulted in the formation of hollow gold nanoshells (HGNs) with a localised surface plasmon resonance (LSPR) between 800 and 900 nm which provide effective SERS when excited at 1064 nm. Seven Raman reporters containing aromatic amine or thiol attachment groups were investigated. All were effective but 1, 2 -bis(4- pyridyl)ethylene (BPE) and 4,4-azopyridine (AZPY) provided the largest enhancement. At approximately monolayer coverage, these two reporters appear to pack with the main axis of the molecule perpendicular or nearly perpendicular to the surface giving strong SERS and thus providing effective 1064 nm gold SERS nanotags.
nanoprobes were designed for the detection of separate DNA sequences. The probes consist of a DNA hairpin with a Raman probe at one end and a thiol group at the other to attach to the metal surface. Without the target DNA, the MS probe is in a hairpin loop so that the Raman reporter is close to the metal surface resulting in a high SERS signal. Hybridisation of a complementary sequence separates the probe from the metal surface thus decreasing signal. Since SERS decreases when the target hybridises to the probe, this is a negative “on to off” assay which has disadvantages as discussed previously. However, the assay has been successfully applied for the detection of multiple DNA sequences without a need for target labelling or wash steps. This work has recently been further developed into a SERS-based molecular sentinel-on-chip (MSC) assay (Figure 6). 99 This MSC assay involved the functionalisation of a nanowave chip with MS
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Currently, the commonly used laboratory methods such as atomic fluorescence spectroscopy (AFS), atomic absorption spectroscopy (AAS), inductively coupled plasma-atomic emission spectrometry or mass spectro- metry (ICP-AES or ICP-MS) allow the detection of low arsenic concentration, but they are expensive, bulky, and usually involved in sophisticated and time-consuming preparations of the samples, making them infeasible for field assays. Moreover, these techniques cannot distin- guish different arsenic species, such as arsenite (As(III)) and arsenate (As(V)), without sample pretreatments. In this case, the SERS technique, which can be used in conjunction with commercially available portable Raman systems, has emerged as a potentially promising solution in field assays due to its ability to provide ultrasensitive, reliable, non-invasive, nondestructive, fast, simple, and cost-effective measurements. It has been demonstrated that SERS technique is able to identify, detect, and screen single and multiple contaminants simultaneously in a small volume of sample [25,27]. More significantly, it is incomparable in speciation analysis including distin- guishing among the arsenic species with no need for any complex sample preparation because it can provide a nice “fingerprint” of materials of interest . The first SERS spectrum of arsenate at high concentrations (> 100 mg·l -1 ) was reported by Greaves and Griffith  using silver sols. Recently, Mulvihill et al.  fabricated Langmuir-Blodgett (LB) monolayers of polyhedral Ag nanocrystals for arsenate SERS detection in groundwater samples with low concentrations (< 10 μ g·l -1
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SEPs made of metallic spherical cores are efficient enough for imaging, but larger amounts are required to yield good signals. To increase the SERS efficiency of SEPs, similar constructs were produced by using aggregates instead of individual nanoparti- cles. These structures are also usually encapsulated in silica, PEG or mixed BSA–glu- taraldehyde for stability and protection of the SERS codes (Henry et al. 2016). This approach creates a collection of hot spots within the SEPs, leading to a considerable intensity increase. However, the limited control over aggregate geometric features (size, configuration and gap separation) that can usually be imposed in most of the nanofabrication methods determines significant intensity variability from SEP to SEP. Moreover, the final cluster sizes are relatively large. This factor is very important, as there is an intrinsic size limitation of around 300 nm after which the hydrodynamic stability of the particles is lost (Barbé et al. 2004; Feliu et al. 2017). On the contrary, when homogeneous assemblies such as dimers (Fig. 2c), trimers or even assemblies with higher coordination numbers can be prepared in high yields (Pazos-Perez et al. 2012; Romo-Herrera et al. 2011; Vilar-Vidal et al. 2016), the size limitations pose no longer a problem while extraordinary field enhancements for SERS are indeed gener- ated. However, their current synthetic protocols are tedious and require multiple puri- fication steps.
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Inspired by the clinical potential of Pd-porphyrinoids and to address the above chal- lenges, we have taken the approach of using the unique photophysical properties of nanomaterials to achieve in vivo monitoring of these fluorescently inac- tive photosensitizers by exploiting their sur- face-enhanced Raman scattering (SERS), as illustrated in Figure 1A. We have previously reported on the use of self-assembling porphyrin-lipids (pyrolipid) on the surface of gold nanoparticles to develop stable, bright SERS agents for in vivo molecular imaging. These nanoparticles can be synthesized in a facile procedure, since pyrolipid acts as both the SERS reporting agent, photosensitizer, and the nanoparticle-stabilizing compound. Herein, we demonstrate the development of Pd-pyrolipid theranostic nanoparticles (PdPL-NPs) that, when excited by red light (638 nm), simultane- ously are both photodynamically active and emit a bright SERS signal. This represents a possible new approach for in vivo reporting of fluorescently inactive photosensitizers, in which the PDT and real-time SERS reporting function of the nanoconstruct utilize the same excitation wavelength from a single photo- sensitizer construct. More broadly, for photosensitiz- ers, while fluorescence and PDT rely on two compet- ing mechanisms, nano-enabled SERS reporting pho- tosensitizers use two complementary orthogonal
To investigate the use of the structured gold surface for electrochemical SERS, we recorded spectra for ad- sorbed pyridine as a function of the electrode potential, Fig. 3. The gold surfaces are stable under these condi- tions and give excellent SER spectra consistent with the published spectra for pyridine at silver electrode sur- faces [1,2,19] and the published work for pyridine on gold [4,25]. The two bands at 1010 and 1037 cm 1 have been assigned to symmetric ring breathing modes and occur at frequencies close to those for pyridine in aque- ous solution. The band at 1026 cm 1 has been assigned to pyridine chemisorbed at the metal surface through the nitrogen lone pair. Between 0.2 and 0.6 V, as the potential is taken more negative the overall intensity of the band at 1010 cm 1 decreases whilst that at 1037 cm 1 remains approximately constant, neither
presence of NaCl, there are AgCl molecules and AgNP/ AgCl aggregations, in which spherical AgNPs were linked by means of strongly hydrophobic AgCl molecules to form the hemline and groove of grating that was called as quasi-nanograting [19,20]. The Raman scattering photons of ST molecules on the grating take place due to diffrac- tion and resonance that caused the signal to be enhanced greatly. When NaCl increased, the five strong SERS peaks at 347, 614, 1,376, 1,535, and 1,644 cm −1 enhanced due to more AgNP/AgCl aggregations forming. This also demon- strated that there are AgNPs and AgCl molecules in the system. According to the references of [12,21], the peak at 347 cm −1 was ascribed to the C-C stretch vibration, the peak at 614 cm −1 was ascribed to the benzene in-plane, the peak at 1,376 cm −1 was ascribed to the C-N in-plane, the peak at 1,535 cm −1 was ascribed to the benzene ring stretch, and the peak 1,644 cm −1 was ascribed to the C = N stretch. Under the selected conditions for the
The performance of this sensor will be affected by PCF’s structure, substrates of SERS and so on. To improve it’s performance, this paper proposed a novel solid core PCF, and gave the simulation result by finite element method. The result indicated that this kind of solid core PCF has large mode area, so can improve SERS PCF sensor performance remarkably.
The ability to reliably predict the magnitude of SERS enhancement factors by using DFT modeling is crucial to the fundamental understanding of the chemi- sorption phenomena involving analytes adsorbed on SERS-active surfaces of gold, silver, and copper. The molecular modeling of adsorbed analytes by DFT not only allows the prediction of Raman shift of bulk and adsorbed analytes for different vibrational modes, it also allows the calculation of the energy gap be- tween the HOMO of the analytes and the LUMO of the metal and the Mulliken charges on the various atoms of the analyte molecules . Both these parame- ters elucidate the chemisorption phenomena and contribute to predicting the strengths of the chemical enhancement effect. In the case of aniline, explanation for the strong interactions between the NH 2 group and the gold substrate is
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The investigation into the SERS properties of various enediol ligands attached to trititanate nanotubes has shown interesting results. These nanotubes have a scroll structure with a diameter of 8 nm and lengths of in excess of 100 nm. We see a dependence on the SERS effect related to the proximity of the functional group to the benzene ring for this system. This study offers further insights into catechol coatings of nanomaterials and SERS by the chemical method. We expect this composite material to have applications in bioimaging [20, 21] and in bio and chemical [22, 23]
Oligonucleotide sequences used for probes and targets were purchased from ADT Technologies. Distilled water was used for all chemical reactions. A Varian Cary 300Bio UV-Visible Spectrophotometer with Temperature Controller attached was used for all extinction measurements, with Cary software used for data analysis. For SERS measurements, the instrument used was an inVia Raman Microscope by Renishaw, fitted with a 514 nm Flexible Laser Solutions Modu-Laser and a Leica DMLM microscope platform. All Raman data interpretation was carried out using GRAMS AI software. The dynamic light scattering instrument used was a Zetasizer Nano series by Malvern.
and were subsequently rinsed with ethanol and dried in nitrogen [8,42]. All the Raman spectra were measured with a confocal Raman spectroscopic system (model inVia, Renishaw Hong Kong Ltd., Kowloon Bay, Hong Kong, China). The spectrograph uses 1,200 g mm −1 gratings, a 785-nm laser and a scan type of SynchroScan. The incident laser power was set to be 0.147 mW for all SERS substrates. All the SERS spectra were collected using × 50, NA = 0.5, long working distance objective and the laser spot size is about 2 μm. SERS spectra were recorded with an accumulation time of 10 s. After the SAM of benzene thiol was formed on the substrate surface, a single scan was performed. To get an accurate approximation of the enhancement factors, we measured the neat Raman spectrum of benzene thiol. For the measurement of the neat Raman spectrum of benzene thiol, the power of the 785-nm laser was 1.031 mW, the accumulation time was 10 s, the spot size was 20 μm, and the depth of focus was 18 μm.
Five additional substrates were prepared under selected optimum conditions (e.g. at potential scan rate 100 mV/s after 30 cycles) to evaluate the homogeneity and repeatability of the Ag film fabrication process. A total of ten measurements were made on each sample, at different locations, to calculate the mean and standard deviation of the two most intense Raman peaks of R6G (612 and 1650 cm −1 ). The standard deviation deteriorated with a decreasing concentration. The RSD values less than 34 % (at higher concentrations less than 20%) (Table 3) demonstrate the excellent SERS activity and reproducibility and in turn also the good repeatability of the fabrication process as well the ability for the electrodeposition technique to control surface morphology.
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To evaluate the effectiveness of magnetic-induced aggregation, we investigated the SERS signal of the M AgNSs after being attracted by a magnet. The 4-FBT-treated M AgNSs were re-dispersed in water, and a drop of the solution (0.5 mg/ml) was placed on a glass slide. Then, we placed a magnet underneath the glass slide, as shown in Fig 1b. After 10 min, the M AgNSs were completely accumulated around the magnet. In contrast, when a drop of the AgNS solution was placed on a glass slide in the same manner, the magnet did not collect the AgNSs because they have no magnetic property. As shown in Fig 4a, the SERS intensity of the aggregated M AgNSs is 12 times stronger than that of the non-aggregated AgNSs, showing the strong enhancement of the SERS signal by magnetic-induced aggregation. Different concentrations of 4-FBT solutions were treated with M AgNSs to investigate the limit of detection (LOD) by this method. As shown in Fig 4b, the intensity of the SERS signal decreased as the concentration of 4-FBT decreased. And finally, the SERS signal of 4-FBT could be obtained at a concentration as low as 1 nM, which corresponds to 0.16 ppb.