Silicon Diffraction Gratings Research Articles

Accurate Prediction of Antimicrobial Susceptibility for Point-of-Care Testing of Urine in Less than 90 Minutes via iPRISM Cassettes.

The extensive and improper use of antibiotics has led to a dramatic increase in the frequency of antibiotic resistance among human pathogens, complicating infectious disease treatments. In this work, a method for rapid antimicrobial susceptibility testing (AST) is presented using microstructured silicon diffraction gratings integrated into prototype devices, which enhance bacteria-surface interactions and promote bacterial colonization. The silicon microstructures act also as optical sensors for monitoring bacterial growth upon exposure to antibiotics in a real-time and label-free manner via intensity-based phase-shift reflectometric interference spectroscopic measurements (iPRISM). Rapid AST using clinical isolates of Escherichia coli (E. coli) from urine is established and the assay is applied directly on unprocessed urine samples from urinary tract infection patients. When coupled with a machine learning algorithm trained on clinical samples, the iPRISM AST is able to predict the resistanceor susceptibility of a new clinical sample with an Area Under the Receiver Operating Characteristic curve (AUC) of ∼ 0.85 in 1 h, and AUC > 0.9 in 90 min, when compared to state-of-the-art automated AST methods used in the clinic while being an order of magnitude faster.

Кремниевые решетки с блеском для мягкого рентгеновского и экстремального ультрафиолетового излучения: влияние формы профиля штриха и случайной шероховатости на дифракционную эффективность

The effect of the groove profile shape and random roughness of the reflecting facet of five silicon diffraction gratings (1°-4° blaze angle, period 0.4, 1.4, 2, and 4 μm, various coatings) operating in the soft X-ray and extreme ultraviolet radiation ranges on the outflow of the diffraction efficiency from working orders is studied. Diffraction gratings were fabricated by wet etching of Si(111) vicinal wafers and characterized by atomic force microscopy to determine the shape of the groove profile and roughness. The diffraction efficiency of gratings operating in classical and conical diffraction mounts was calculated based on realistic groove profiles by computer simulation using the PCGrateTM code and taking into account the scattering intensity using Nevot-Croce or Debye-Waller corrections or using the Monte Carlo method (rigorously). The effect of the groove profile shape and roughness on the diffraction efficiency of the fabricated Si gratings is shown.

Shining light in blind alleys: deciphering bacterial attachment in silicon microstructures.

With new advances in infectious disease, antifouling surfaces, and environmental microbiology research comes the need to understand and control the accumulation and attachment of bacterial cells on a surface. Thus, we employ intrinsic phase-shift reflectometric interference spectroscopic measurements of silicon diffraction gratings to non-destructively observe the interactions between bacterial cells and abiotic, microstructured surfaces in a label-free and real-time manner. We conclude that the combination of specific material characteristics (i.e., substrate surface charge and topology) and characteristics of the bacterial cells (i.e., motility, cell charge, biofilm formation, and physiology) drive bacteria to adhere to a particular surface, often leading to a biofilm formation. Such knowledge can be exploited to predict antibiotic efficacy and biofilm formation, and enhance surface-based biosensor development, as well as the design of anti-biofouling strategies.

Designing Bacterial Chemotactic Receptors Guided by Photonic Femtoliter Well Arrays for Quantifiable, Label-Free Measurement of Bacterial Chemotaxis

Whole cell bioreporters, such as bacterial cells, can be used for environmental and clinical sensing of specific analytes. However, the current methods implemented to observe such bioreporters in the form of chemotactic responses heavily rely on microscope analysis, fluorescent labels, and hard-to-scale microfluidic devices. Herein, we demonstrate that chemotaxis can be detected within minutes using intrinsic optical measurements of silicon femtoliter well arrays (FMAs). This is done via phase-shift reflectometric interference spectroscopic measurements (PRISM) of the wells, which act as silicon diffraction gratings, enabling label-free, real-time quantification of the number of trapped bacteria cells in the optical readout. By generating unsteady chemical gradients over the wells, we first demonstrate that chemotaxis toward attractants and away from repellents can be easily differentiated based on the signal response of PRISM. The lowest concentration of chemorepellent to elicit an observed bacterial response was 50 mM, whereas the lowest concentration of chemoattractant to elicit a response was 10 mM. Second, we employed PRISM, in combination with a computational approach, to rapidly scan for and identify a novel synthetic histamine chemoreceptor strain. Consequently, we show that by using a combined computational design approach, together with a quantitative, real-time, and label-free detection method, it is possible to manufacture and characterize novel synthetic chemoreceptors in Escherichia coli (E. coli).

Laser-written nanoporous silicon diffraction gratings for biosensors

Surface-relief diffraction gratings and planar diffraction gratings directly written on nanoporous silicon layers using 514nm continuous-wave lasers at very low power (less than 20mW) were demonstrated. Diffraction-based biosensing application to detect arachidonic acid was experimentally demonstrated at incident light wavelength of 632.8nm. A comparison in sensing applications was made between the two types of gratings to show the distinct advantage of the planar grating with selective functionalization. Laser-written planar gratings enable directly immobilizing biomolecules in the laser oxidized area of nanoporous silicon, resulting in a new patterned functionalization technique for biosensing applications. The functionalization technique can not only simplify the functionalization procedure in biosensing but also it has potential to increase the sensitivity of sensors by accurately defining grating patterns using the laser direct writing technique.

Multilayer porous silicon diffraction gratings operating in the infrared

Transmission diffraction gratings operating at 1,565 nm based on multilayer porous silicon films are modeled, fabricated, and tested. Features down to 2 μm have been patterned into submicron-thick mesoporous films using standard photolithographic and dry etching techniques. After patterning of the top porous film, a second anodization can be performed, allowing an under-layer of highly uniform porosity and thickness to be achieved. High transmission greater than 40% is measured, and modeling results suggest that a change in diffraction efficiency of 1 dB for a 1% change in normalized refractive index can be achieved. Preliminary measurement of solvent vapor shows a large signal change from the grating sensor in agreement with models.

Porous silicon structures for low-cost diffraction-based biosensing

We present a strategy for label-free biosensing using porous silicon diffraction gratings. The gratings are fabricated using a cost-effective, high-throughput stamping technique. Unlike traditional diffraction-based biosensors that rely on microcontact printing or lithography to create gratings for the localization of analytes on the top surface of the grating, in our structure analytes are free to infiltrate the porous network and increase the effective refractive index of the grating. The large surface area of porous silicon available for molecular binding offers the potential for enhanced diffraction response compared to nonporous gratings with limited surface area. Small molecule detection of 3-aminopropyltriethoxysilane is demonstrated.

External cavity diode lasers with E-beam written silicon diffraction gratings

Performance of external cavity diode lasers with silicon gratings produced by E-beam writing and subsequent reactive ion etching is described. Optical amplifiers used in the experiments were based on single quantum well heterostructures grown by molecular beam epitaxy. The lasers were set up in the Littrow configuration and have been designed to allow for wavelength tuning in the range centred at 960 nm.

Submicrometer period silicon diffraction gratings by porous etching

AbstractWe have developed a new technique to manufacture diffraction gratings on porous silicon and on silicon interface. Using holography facilitate to adjust the periodic length of gratings in the submicron range. The holographically exposured and developed photoresist applied on the silicon surface provides the mask for the ion implantation. The sinusoidal grating between the substrate and the porous silicon layer is achieved after the anodic etch process. The PS layer can be removed by alkali etching. Sinusoidal one‐ and two‐dimensional diffraction gratings have been produced with 375 nm periodic length. Their AFM images are shown. The diffraction efficiencies were measured. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Spectral characteristics of plane multilayer amplitude diffraction gratings for the soft x-ray range

Several spectral characteristics of plane multilayer amplitude molybdenum—silicon diffraction gratings (1000 and 2000 lines mm-1), fabricated by electron-beam lithography, were determined with a broadband laser-plasma source of soft x-rays. The gratings, with the multilayer structure period 11.5 nm, were investigated at near-normal incidence and at an angle of incidence of 36o in a quasi-stigmatic spectrograph system with moderate dispersion. The spectral profile of resonant reflection by the gratings was determined in the first and second interference orders of the multilayer structure for different angles of incidence. The line spectrum of multiply charged F(V) and F(VI) ions was recorded in the 16.0–18.5 nm range by means of these multilayer gratings and the resolving power of the gratings was estimated.