Uniform Enhancement Research Articles

Comparison of Whole Heart Computed Tomography Scanners for Image Quality Lower Radiation Dosing in Coronary Computed Tomography Angiography: The CONVERGE Registry

Novel technology in coronary computed tomographic angiography allows assessment of coronary artery disease with high image quality (IQ). There are currently two wide detector "whole heart" coverage scanners available, which avoid misregistration artifacts. However, there are no data directly comparing IQ between the two scanners. The aim of the current study is to investigate if IQ is different between the most scanners of GE and Toshiba broad detector scanners. Prospective, observational, multicenter international cohort study comparing 236 consecutive patients who underwent coronary computed tomographic angiography using whole-heart scanners; 126 patients on scanner S1 ( Aquilion ONE Vision, Toshiba), and 110 patients on scanner S2 (Revolution CT, GE Healthcare). Hounsfield units were measured using regions of interest in the descending aorta at 6 points (cranial slice, level of the visualized first, second, third, and fourth spines, and the caudal slice). We also compared the coverage length (z-axis) of the full width field of view between a single rotation of the two scanners. Evaluating mean CT attenuation values Hounsfield units through the scan range, are progressively reduced across the descending aorta in the S1 group, resulting in the larger difference of contrast brightness between the cranial and caudal slices compared to the S2 group (absolute difference: S2 13.0 ± 4.4 vs S1 141.9 ± 16.4, p < 0.0001; Percent difference: 19.3 ± 2.1 vs -3.4 ± 1.2, <0.0001). The standard deviation (SD) is similar at the cranial slice between the two scanners, however, the S1 group demonstrated higher SD-differential from cranial to caudal than S2 group. Median radiation exposure was significantly lower for the S2 scanner 1.50 ± 0.75 mSv vs the S1 system 1.9 mSv (IQR 1.7-2.7 mSv) (p = 0.01). Z-axis coverage was larger for the S2 scanner 152.5 mm (244 slices × 0.625 mm/slice) than 133 mm for S1 (266 slices × 0.5 mm/slice). Although both "volume" scanners cover the whole heart z-axis with one beat, scans using the S1 scanner have a larger variability in attenuation values throughout the scan range, resulting in 20% increase in nonuniformity from cranial to caudal slice. Additionally, SD variation across the field of view, a metric of noise, is larger when using the S1 scanner vs the S2 scanner. These results indicate that the GE Revolution CT has more uniform contrast enhancement and more coverage, lower radiation and lower image noise compared to the Toshiba Aquilion ONE Vision system.

Quantitative Determination of Fatty Acid Compositions in Edible Oils Using J-Selective 13C QDEPT

We propose a J-selective quantitative distortionless enhancement by polarization transfer (J-selective QDEPT) 13C NMR method with enhanced sensitivity for accurate determination of the fatty acid compositions of edible oils. The J-selective QDEPT protocol is developed by targeted optimization of the known Q-DEPT+ experiment. Based on the one-bond C-H J-coupling constants (1JCH) which can be measured with the heteronuclear two-dimensional J-resolved 13C NMR spectrum, it is possible to optimize the polarization transfer delay Δ and the reading pulse angle ⊖, thus enabling the QDEPT experiment further enhancing 13C resonance signals which have narrow 1JCH ranges over the traditional untargeted Q-DEPT. For edible oil applications, it is demonstrated that this procedure brings a 2.2 enhancement factor against 1.3 of the traditional untargeted Q-DEPT compared to the standard inverse-gated 13C experiment, even with a shorter relaxation delay for the two QDEPT experiments. Another advantage of J-selective QDEPT is that a smaller number of quantitative scans are needed to reach a uniform enhancement for different CHn (n = 1, 2, 3) groups. These features of the J-selective QDEPT are particularly attractive for batch analysis in the food industry.

Akcesorni i ektopični lobus jetre kod istog pacijenta - prikaz slučaja

Accessory liver lobes (ALL) are defined as supranumerary liver lobes, composed of normal liver parenchyma in continuity with the liver, in contrast to ectopic liver lobes (ELL) that have no anatomical continuity with the normal liver. Case report: In this article we report on a rare radiological diagnosis of an synchronous accessory and ectopic liver lobe using ultrasonography (US) and computed tomography (CT). A 59-year-old female with no symptoms was admitted to our hospital due to preventive exam. Abdominal ultrasonography revealed a high echoic 6 cm x 5 cm soft tissue area in right anterior subhepatic space with distinct margins, a uniform echo and blood flow and was suspected to be abdominal tumor. An enhanced abdominal computed tomography (CT) showed the irregular 65 mm x 48 mm x 32 mm mass in the right hypochondrium below IV and V liver segment with clear margins, a uniform density, texture and contrast enhancement as normal liver tissue. In same patient CT also showed small 16 mm x 12 mm mass in posterior mediastinum in right retrocrural space so diagnosis of accessory and ectopic liver lobe was confirmed. An accessory liver lobe is adjacent and attached to the liver by its own mesentery, while an ectopic liver lobe is one that is completely detached from the normal liver parenchyma. Conclusion: Ultrasound can show mass in the abdomen, which is most commonly in the subhepatic area, but very rarely can initially diagnose ALL or ELL due to different echogenicity of the liver parenchyma in different acoustic windows. In the case of an atypical CT presentation, an MR examination of the abdomen is indicated but it is very rarely. Fast and accurate radiological diagnosis of ALL and ELL is important in the prevention of unnecessary invasive diagnostic procedures such as laparotomy and thoracotomy which are needed only in cases of complications.

Spontaneous intramural hematoma of the duodenum secondary to anticoagulant drug intoxication

Introduction. Duodenal hematomas are commonly traumatic, caused by blunt abdominal trauma. Nontraumatic spontaneous intramural hematomas of the duodenum are rare, and in most cases induced by anticoagulant therapy. The diagnosis is based on clinical and biochemical parameters, endoscopy, and radiological examinations. The objective of this report was to present a clinical and radiological presentation of an intramural duodenal hematoma caused by anticoagulant therapy. Case outline. A 43-year-old female was presented with epigastric pain, nausea, hematemesis, and melena. She had a positive medical history of deep venous thrombosis of the pelvis, which was diagnosed the previous month, for which she received oral anticoagulant therapy (coumarin). Physical examination revealed diffuse abdominal tenderness, while laboratory analyses showed markedly elevated international normalized ratio (INR) of prothrombin time (INR &gt; 7), which indicated the anticoagulant intoxication. Computed tomography (CT) showed luminal narrowing with uniform circumferential wall thickening of the descendent and horizontal part of duodenum, which was hyper dense in the native series and slight and uniform ring-formed enhancement in post-contrast phases, a typical CT presentation of intramural duodenal hematoma. Periduodenal and right sided pararenal hematomas were also visualized. After stopping the anticoagulant therapy and performing conservative treatment (vitamin K) with good therapeutic effect being monitored by physical examination, laboratory analyses and transabdominal ultrasonography, spontaneous resolution of the duodenal hematoma was revealed by follow-up CT examination two weeks after the onset. Conclusion. Ultrasonography and CT are useful diagnostic tools in recognition of the intramural duodenal hematoma and other locations of hemorrhage and in monitoring therapeutic effects.

Surface-Nanostructured Single Silver Nanowire: A New One-Dimensional Microscale Surface-Enhanced Raman Scattering Interface.

One-dimensional microscale surface-enhanced Raman scattering (SERS)-active interfaces have been intriguing as a newly emerging class of SERS interfaces compared to conventional macroscale SERS substrates. In this work, a stable surface-nanostructured single silver nanowire was fabricated. The nanostructures on the nanowire are formed by nanoscale silver crystal dots with diameters of 20-50 nm. The SERS signals of the crystal violet probe molecules adsorbed on the nanostructures are dramatically enhanced by both electromagnetic and chemical effects. The hot spots generated at the junctions of adjacent nanoscale dots yield highly efficient surface plasmon resonance. Simultaneously, the charge transfer on the atomic-scale silver cluster located at the nanostructured interface causes an enhancement similar to Raman resonance. The intensity distributions of the SERS peaks on the surface-nanostructured single nanowire are characterized by SERS mapping. It is found that, although the intensities of the SERS peaks are different, their SERS mapping images show uniform SERS enhancement distributions, whereas the noticeable SERS intensity distributions on the single smooth silver nanowire are mainly located on the two ends of the nanowire. A large number of nanoscale crystal dots along with the atomic-scale silver clusters are uniformly and densely distributed on the surface of the single roughened nanowire; these structural attributes induce a uniform and large surface plasmon resonance and charge transfer enhancements on the entire surface of the nanowire. This work indicates that the surface-nanostructured single silver nanowire, synthesized using a quite simple preparation method, performs as an excellent one-dimensional microscale SERS substrate with uniform and high enhancement characteristics, which shows high potential for applications as a new class of SERS-active substrates. Furthermore, the higher enhancement factor of the microscale SERS interfaces can be achieved by introducing other roughened nanowires to assemble a dimer and a trimer as micro-SERS substrates, which is consistent with the dark-field measurements.

Terahertz magnetic field enhancement in an asymmetric spiral metamaterial

We use finite element simulations in both the frequency and the time-domain to study the terahertz resonance characteristics of a metamaterial (MM) comprising a spiral connected to a straight arm. The MM acts as a RLC circuit whose resonance frequency can be precisely tuned by varying the characteristic geometrical parameters of the spiral: inner and outer radius, width and number of turns. We provide a simple analytical model that uses these geometrical parameters as input to give accurate estimates of the resonance frequency. Finite element simulations show that linearly polarized terahertz radiation efficiently couples to the MM thanks to the straight arm, inducing a current in the spiral, which in turn induces a resonant magnetic field enhancement at the center of the spiral. We observe a large (approximately 40 times) and uniform (over an area of ∼10 μm2) enhancement of the magnetic field for narrowband terahertz radiation with frequency matching the resonance frequency of the MM. When a broadband, single-cycle terahertz pulse propagates towards the MM, the peak magnetic field of the resulting band-passed waveform still maintains a six-fold enhancement compared to the peak impinging field. Using existing laser-based terahertz sources, our MM design allows to generate magnetic fields of the order of 2 T over a time scale of several picoseconds, enabling the investigation of nonlinear ultrafast spin dynamics in table-top experiments. Furthermore, our MM can be implemented to generate intense near-field narrowband, multi-cycle electromagnetic fields to study generic ultrafast resonant terahertz dynamics in condensed matter.

Dynamic Clipped Histogram Equalization Technique for Enhancing Low Contrast Images

This paper presents the dynamic clipped histogram equalization (DCLHE) for enhancing low contrast images. DCLHE chooses a clipped level at all the occupied bins and later histogram equalization is performed on the clipped histogram to get the output image. Three variants of occupied bin space are taken to enhance the low contrasted dark, gray and bright images. Experimental results show the supremacy of the work and outperform the HE variants in terms of preserving entropy, preserving all the gray levels and obtaining uniform degree enhancement.

Engraving High-Density Nanogaps in Gold Thin Films via Sequential Anodization and Reduction for Surface-Enhanced Raman Spectroscopy Applications

To realize a more rapid and accurate detection technique for diverse trace molecules, surface-enhanced Raman scattering (SERS) analysis has been extensively investigated in recent decades. However, a practical fabrication method to scalably and reproducibly produce SERS substrates with highly effective SERS-active sites and extensive optical tunability still remains an important research target. Here, we present an electrochemical pathway to generate a high-performance SERS substrate. This method provides not only ultrahigh-density hot spots as a form of nanogaps for strong and uniform SERS signal enhancement but also tunable plasmonic properties for capability of matching the plasmonic resonance wavelength with that of the Raman excitation laser. The unique Au nanopillar array decorated with ultrafine Au nanoparticles records a high SERS signal enhancement effect, which enables trace-molecule detection on the entire measured area with highly reproducible signal intensity. Also, via aptamer-functionalizat...

Tunable enhanced infrared absorption spectroscopy surfaces based on thin VO2 films

Infrared absorption spectroscopy takes advantage of the electric field enhancement to detect low amounts of materials such as monolayer biomolecules. While the plasmonic field enhancement is the popular approach, it has been demonstrated that the interference-based uniform field enhancement using a simple dielectric/metal structure exhibits higher sensitivity and larger spectral bandwidth for ultrathin materials. Here, we numerically demonstrate that the enhancement bandwidth of such interference coatings can be further increased by inserting a VO2 thin film between the dielectric and metal layers. The field enhancement spectrum blueshifts upon thermally-induced insulator-to-metal transition in the VO2 layer. The structure that maximizes the enhancement bandwidth is determined as 880-nm-thick CaF2 on 350-nm-thick VO2 on optically thick Al. The study is completed with the investigation of using a bottom metal layer as an internal heater to electrothermally induce the phase change.

Add-on plasmonic patch as a universal fluorescence enhancer

Fluorescence-based techniques are the cornerstone of modern biomedical optics, with applications ranging from bioimaging at various scales (organelle to organism) to detection and quantification of a wide variety of biological species of interest. However, the weakness of the fluorescence signal remains a persistent challenge in meeting the ever-increasing demand to image, detect, and quantify biological species with low abundance. Here, we report a simple and universal method based on a flexible and conformal elastomeric film with adsorbed plasmonic nanostructures, which we term a “plasmonic patch,” that provides large (up to 100-fold) and uniform fluorescence enhancement on a variety of surfaces through simple transfer of the plasmonic patch to the surface. We demonstrate the applications of the plasmonic patch in improving the sensitivity and limit of detection (by more than 100 times) of fluorescence-based immunoassays implemented in microtiter plates and in microarray format. The novel fluorescence enhancement approach presented here represents a disease, biomarker, and application agnostic ubiquitously applicable fundamental and enabling technology to immediately improve the sensitivity of existing analytical methodologies in an easy-to-handle and cost-effective manner, without changing the original procedures of the existing techniques.

Uniform signal enhancement in MAS NMR of half-integer quadrupolar nuclei using quadruple-frequency sweeps

We introduce two MAS schemes that allow manipulating the satellite-transition (ST) populations of half-integer quadrupolar nuclei, and which both exhibit improved robustness to the quadrupolar coupling constant (CQ). These schemes, called quadruple frequency sweep (QFS) or quadruple WURST (QWURST) are the sums of two DFS or four WURST to efficiently invert the ST populations of nuclei subject to large or small quadrupole interactions, simultaneously. These quadruple sweeps methods only require 6% more rf-power than the double sweeps ones. We demonstrate, both numerically and experimentally, that the QFS and QWURST schemes benefit from robustness to CQ and rf amplitude and offset and hence achieve uniform enhancement of the CT signal for 27Al nuclei subject to different quadrupole interactions. Although the version of QFS with repetitive accumulation can achieve higher enhancement in the S/N of the 27Al MAS spectrum, the final sensitivity gains mainly depend on the longitudinal relaxation time of different 27Al sites. We also confirm that these schemes provide an improved acceleration of the 31P-{27Al} coherence transfer in PT-J-HMQC experiments.

Correlation of CT signs with lymphatic metastasis and pathology of neuroblastoma in children.

Correlation between computed tomography (CT) signs, lymphatic metastasis and pathological features of neuroblastoma (NB) in children was investigated. A total of 374 child patients diagnosed with NB via CT scan and pathological section in Department of Pediatric of Xuzhou Children's Hospital from March 2011 to January 2017 were collected, and their clinical data were retrospectively analyzed. According to CT signs, NB calcification and invasion to surrounding tissues were evaluated, and the tumor site, tumor size, lymphatic metastasis, pathological types and clinical prognosis were analyzed. In plain CT scan, 160 cases showed clear tumor mass, and 214 cases showed blurred mass; 78 cases of tumors were uniform in density, and 296 cases were not uniform in density. Besides, there were 351 cases of calcification in mass. There were 106 cases of axial rotation of kidney, 53 cases of enlargement of renal calyce and renal pelvis, 66 cases of elevation of liver position, 71 cases of pancreas translocation, 26 cases of gastrointestinal tract translocation, 17 cases of vascular translocation and 12 cases of bladder translocation, besides 23 of the cases showed no significantly abnormal changes. Moreover, 211 cases had retroperitoneal lymphatic metastasis with soft tissue swelling in phrenic angle, abdominal aorta and renal hilum in image, and non-uniform annular enhancement or uniform enhancement in enhanced scanning. NB in right adrenal gland invaded the liver in 53 cases, invaded the kidney in 26 cases, invaded the psoas in 40 cases and blood vessels in 32 cases, and the remaining cases showed no invasion. A total of 68 cases were accompanied by pleural thickening, 34 cases by pleural effusion, 36 cases by tracheal compression, 38 cases by rib compression, and 40 cases by tumor invading into vertebral canal. Bone metastasis occurred in 182 cases; liver metastases occurred in 28 cases, and brain metastases in 35 cases. NB calcification was significantly correlated with pathological type, tumor site and lymphatic metastasis (p<0.05), but not correlated with tumor size (p>0.05); NB invasion to surrounding tissues was associated with pathological type, tumor site and clinical prognosis (p<0.05), but was not correlated with the tumor size (p>0.05). We concluded that patients with distal mediastinal mass identified by CT examination, accompanied by calcification, and invasion to surrounding tissues may suffer from NB. Tumor growth is closely correlated with tumor differentiation degree.

Color Doppler ultrasound and contrast-enhanced ultrasound in the diagnosis of lacrimal apparatus tumors.

Color Doppler ultrasound and contrast-enhanced ultrasound (CEUS) in the diagnosis of lacrimal apparatus tumors were investigated. In total, 48 patients undergoing preoperative two-dimensional and color Doppler ultrasound and CEUS examinations were included in this study. Conventional ultrasound and CEUS characteristics of 48 patients pathologically and clinically diagnosed with lacrimal apparatus tumors were retrospectively analyzed. Results of conventional ultrasound of 29 cases with pleomorphic adenoma of lacrimal gland showed moderate-hypoechogenic solid masses in lacrimal gland; CEUS displayed two enhancement modes: High, fast-developed slow-extinct and overall uniform enhancement (20/29, 68.97%) and high, fast-developed slow-extinct, centripetal, uniform or non-uniform enhancement (9/29, 31.03%); after enhancement, the mass edge was clear without changes in size. Results of conventional ultrasound of 6 cases with adenoid cystic carcinoma of lacrimal gland showed hypoechogenic solid masses with unclear edge, irregular form, non-uniform echo, and abundant blood flow signals; the CEUS displayed high, fast-developed fast-extinct and overall uniform enhancement; after enhancement, mass edge was unclear and masses were larger than that in two-dimensional ultrasound. Results of conventional ultrasound of 10 cases with lacrimal sac cyst showed non-uniform, hypoechogenic masses, or cystic solid mixed masses with clear edge but no blood flow signal; the CEUS displayed peripheral circular enhancement and no enhancement inside. Results of conventional ultrasound of 3 cases with adenocarcinoma of lacrimal sac showed hypoechogenic solid masses with unclear edge, irregular form, non-uniform echo inside, and abundant blood flow signals in lacrimal sac; CEUS displayed high, fast-developed fast-extinct and overall uniform enhancement; after enhancement, masses with irregular shapes were obviously larger than that in two-dimensional ultrasound. CEUS shows the microcirculation of tumors and surrounding tissues. Combination of two-dimensional and color Doppler ultrasound can improve the preoperative qualitative diagnosis of tumors and provide references for the selection of operation methods and determination of tumor resection scope.

Tunable nonlinear coherent perfect absorption with epsilon-near-zero plasmonic waveguides.

We propose a scheme to realize nonlinear coherent perfect absorption (CPA) at the nanoscale using epsilon-near-zero (ENZ) plasmonic waveguides. The general conditions to achieve CPA in a linear ENZ plasmonic waveguide are analyzed and presented. The proposed ENZ waveguides support an effective ENZ response at their cutoff frequency, where the CPA effect occurs under the illumination of two counterpropagating plane waves with equal amplitudes and appropriate phase distributions. In addition, the strong and uniform field enhancement inside the nanochannels of the waveguides at the ENZ resonance can efficiently boost Kerr nonlinearities, resulting in a new all-optical switching intensity-dependent CPA phenomenon that can be tunable with ultrafast speed. The proposed free-standing ENZ structures combine third-order nonlinear functionality with standing wave CPA interference effects in a nanoscale plasmonic configuration, thus leading to a novel degree of tunable light-matter interactions achieved in subwavelength regions. Our findings provide a new platform to efficiently excite nonlinear phenomena at the nanoscale and design tunable coherent perfect absorbers.

Statistical analysis of cuboctahedral silver nanocrystals Langmuir–Blodgett film SERS substrate

AbstractWith single‐molecule sensitivity, surface‐enhanced Raman scattering (SERS) has promised to be a powerful tool from chemical analysis to biosensors. However, problem with large signal fluctuations for reproducibility has impeded SERS from widespread application. The fabrication of SERS substrate with large and uniform enhancement in combination with an effective target analyte‐transfer process is crucial for applications of SERS for trace molecule detection. In this study, we performed laser‐scanning confocal mapping to characterize 3 SERS substrate samples. The substrate consists of a monolayer of cuboctahedral silver nanocrystals (AgNCs) made with Langmuir–Blodgett technique. The synthesis of the cuboctahedral AgNCs involves the use of polyvinylpyrrolidone (PVP) as a shape‐controlling agent that remains on the surface of the nanocrystals. Using PVP as an analyte, we investigate the temporal and spatial variation of PVP SERS signals from the cuboctahedral AgNC Langmuir–Blodgett film. Analyzing the enhancement probability distribution with a model allows quantitative characterization of the cuboctahedral AgNC SERS substrates. The results help to identify important SERS substrate characteristics that influence the performance of the SERS substrate.

Large-area and Free-standing 3D Superlattices Induced by Droplet Evaporation

In this article, we make our effort to scale up the synthesis of gold nanorods (GNRs) using the modified strategy. The prepared GNRs are self-assembled vertically to the substrate over an large micrometer-size area without external fields. We also demonstrate that this complex superstructure is an excellent surface-enhanced Raman scattering (SERS) substrate with uniform electric field enhancement, high intensity of hot spots and reproducible enhancement factors (EFs) in the desirable spectral range. For practical perspective, the substrate shows great promise for fluorescence and luminescence.

Effect of Ethanethiolate Spacer on Morphology and Optical Responses of Ag Nanoparticle Array-Single Layer Graphene Hybrid Systems.

Single layer graphene (SLG) and two-dimensional (2-D) plasmonic Ag nanoparticle arrays assembled by chemisorption of ethanethiol (ET) molecules (AgNPs-ET) were employed as components of two types of hybrid systems designed for surface-enhanced Raman scattering (SERS) spectral probing of SLG localized in the vicinity of plasmonic NPs. Both hybrids were characterized by optical microscopy, transmission electron microscopy (TEM), surface plasmon extinction (SPE), and SERS microRaman spectral measurements at four excitation wavelengths spanning the 445-780 nm range. SERS spectral probing of the glass/SLG/AgNPs-ET hybrid prepared by overdeposition of SLG on glass by the array of ET-modified Ag NPs has shown that the chemisorbed ET acts as an efficient molecular spacer between SLG and Ag NPs surface which, in turn, enabled to obtain SERS spectra of SLG unperturbed by doping or strain. TEM imaging and SERS spectral probing of the second hybrid prepared by overdeposition of AgNPs-ET array on glass by SLG revealed removal of the adsorbed ET molecules and annealing of Ag NPs during the SLG deposition. The characteristics of the resulting glass/AgNPs/SLG hybrid system, namely (i) broad distribution of the annealed Ag NPs sizes and shapes, (ii) SPE curve covering the overall visible spectral region, (iii) absence of the ET spectral bands in SERS spectra, and (iv) fairly uniform SERS enhancement of the G and 2D mode of SLG in the 532-780 nm range in the straight sample geometry indicate that this hybrid can provide a suitable platform for investigation of the excitation wavelength dependence of combined SERS/GERS (graphene-enhanced Raman scattering) enhancement experienced by various molecular species brought into contact with SLG in this hybrid. Finally, weak optical effects attributed to increased reflectivity of SLG in the near field of Ag NPs arrays have been observed in the excitation wavelength dependence of the SERS spectra of both types of hybrid systems.

Gold-capped silicon for ultrasensitive SERS-biosensing: Towards human biofluids analysis

Surface-enhanced Raman spectroscopy (SERS) has been widely used in a variety of biomedical, analytical, forensic and environmental investigations due to its chemical specificity, label-free nature combined with high sensitivity. Here, we report a simple method for the fabrication of reproducible and reliable, well-defined, stable SERS substrates with uniform and giant Raman enhancement suitable for routine trace chemical analysis and detection of biological compounds in complex biological fluids. We prepared porous silicone (PS) surface by a galvanostatic anodic etch of crystalline silicon wafers. The electrochemical process generates a specific layer of PS: the thickness and porosity of a given layer is controlled by the current density, the duration of the etch cycle, and the composition of the etchant solution. These substrates presented high sensitivity to p-mercaptobenzoic acid (p-MBA) at a low concentration of 10−6M and the enhancement factor of over 108 was achieved. Such high enhancement is attributed to semiconducting silicon-induced and stabilized hot spots. The uniform distribution of SERS–active ‘hot-spots’ on the Au/Si surface results in high reproducibility towards detecting p-MBA at 40 different, randomly selected positions on a single substrate (RSD=6.7%) and on twenty different SERS substrates prepared under identical conditions (RSD=8%). Designed substrates allow the ultrahigh sensitive and specific detection of human such biofluids as blood, urine and cerebrospinal fluid (CSF) in a reliable, label-free, and reproducible manner. The SERS spectra of these fluids are rich in patient-specific information and can be useful in many analytical and biomedical applications. We have shown that our developed SERS substrates allow the nanomolar detection of neopterin (bacterial infections' marker) in cerebrospinal fluid samples. In order to test the performance of our SERS method in term of low detection limit (LOD), the calibration curve i.e. plot of SERS intensity of the marker band at 695cm−1 versus the concentration of neopterin in CSF was constructed and used to calculate the neopterin concentration in clinical samples. The level of neopterin was significantly higher in CSF samples infected by Neisseria meningitidis, (54nmol/L), compared to normal (control) group, (4.3nmol/L).The high sensitivity, selectivity and stability of obtained SERS-active substrates combined with simple, low-cost, and easy method of producing offer a promising tool for SERS-based analysis in clinical trials.

Driving Chemical Reactions in Plasmonic Nanogaps with Electrohydrodynamic Flow.

Nanoparticles from colloidal solution-with controlled composition, size, and shape-serve as excellent building blocks for plasmonic devices and metasurfaces. However, understanding hierarchical driving forces affecting the geometry of oligomers and interparticle gap spacings is still needed to fabricate high-density architectures over large areas. Here, electrohydrodynamic (EHD) flow is used as a long-range driving force to enable carbodiimide cross-linking between nanospheres and produces oligomers exhibiting sub-nanometer gap spacing over mm2 areas. Anhydride linkers between nanospheres are observed via surface-enhanced Raman scattering (SERS) spectroscopy. The anhydride linkers are cleavable via nucleophilic substitution and enable placement of nucleophilic molecules in electromagnetic hotspots. Atomistic simulations elucidate that the transient attractive force provided by EHD flow is needed to provide a sufficient residence time for anhydride cross-linking to overcome slow reaction kinetics. This synergistic analysis shows assembly involves an interplay between long-range driving forces increasing nanoparticle-nanoparticle interactions and probability that ligands are in proximity to overcome activation energy barriers associated with short-range chemical reactions. Absorption spectroscopy and electromagnetic full-wave simulations show that variations in nanogap spacing have a greater influence on optical response than variations in close-packed oligomer geometry. The EHD flow-anhydride cross-linking assembly method enables close-packed oligomers with uniform gap spacings that produce uniform SERS enhancement factors. These results demonstrate the efficacy of colloidal driving forces to selectively enable chemical reactions leading to future assembly platforms for large-area nanodevices.

Laser fabrication of periodic arrays of microsquares on silicon for SERS application

Two dimensional periodic arrays of microsquares of different dimensions are fabricated by direct ns-laser writing on silicon substrate. The micro/nano structures pattern on the Si surface significantly minimizes the optical reflection by light trapping effect, but enhances the SERS signal intensity of analyte dye molecule Rhodamine B (RhB) and Methylene Blue (MB) in presence of gold nanoparticles. The dependence of surface roughness, optical reflection and SERS intensity on the laser pulse energy and line scan interval is investigated. The SEM images clearly show well-ordered features on the surface of patterned Si substrates and aggregation of micro/nanoparticles on the substrate surface. The optical reflection from the patterned surfaces reduces below 11% over a broad range of wavelengths from 300nm to 1200nm. The patterned surface can be used as a reproducible SERS substrate with a spatially uniform enhancement factor of 108. This fabrication method can be employed for preparation of multifunctional surfaces for light trapping in solar cells and for Raman signal amplification for versatile and reproducible SERS sensors.