Infrared Absorption Microscopy Research Articles

Improving photocatalytic performance: Creation and assessment of nanostructured SnO2 thin films, pure and with nickel doping, using spray pyrolysis

This study investigates conductive, transparent films of undoped and Ni-doped SnO2 deposited through water solvent spray pyrolysis, aiming to combat environmental water pollution. Examining these films using X-ray diffraction (XRD), Fourier transform infrared absorption microscopy (FTIR), UV–Vis spectrophotometer, and Hall effect, the research focuses on photocatalytic degradation kinetics using rhodamine B (RhB) as a model pollutant from the textile industry.XRD results confirm tetragonal structures of SnO2 and Ni: SnO2 films with crystallite sizes ranging from 21.83 to 19.52 nm. The sprayed films exhibit resistivity variations (7.1 × 10−3 to 4.5 × 10−3) Ω.cm and figure of merit variations [(1.49 × 10−4 to 25.03 × 10−4); (2.69 × 10−4 to 9.1 × 10−4)] (Ω/sq)−1. Optical properties include ∼73% light transmission, ∼20% reflection, and ∼7% absorptance, with porosity (8.65–11.44)%, refractive index (2.88–1.57), extinction coefficient (0.0043–0.0013), dielectric constants (8.31–2.48 and 0.025–0.0041), optical density [(3.9 × 10+10–7.86 × 10+09) S−1], skin depth [(2.06 × 10−3–6.7 × 10−3) cm−1], and optical band gap with Urbach energy [(3.8–3.6) eV and (0.67–0.43) eV] obtained at 550 nm.The photocatalytic process, crucial for water pollution treatment, exhibits pH sensitivity (12.3–1.7) over varied times (0–90 min) and is influenced by the SnO2 thin film elaboration method. Notably, 0.5 M-concentration SnO2 films show the most efficient photocatalytic degradation rates. This research highlights the potential of SnO2 in environmentally friendly water pollution treatment, emphasizing its practical application in addressing crucial environmental challenges.

Deep image restoration for infrared photothermal heterodyne imaging.

Infrared photothermal heterodyne imaging (IR-PHI) is an all-optical table top approach that enables super-resolution mid-infrared microscopy and spectroscopy. The underlying principle behind IR-PHI is the detection of photothermal changes to specimens induced by their absorption of infrared radiation. Because detection of resulting refractive indexand scattering cross section changes is done using a visible (probe) laser, IR-PHI exhibits a spatial resolution of ∼300nm. This is significantly below the mid-infrared diffraction limit and is unlike conventional infrared absorption microscopy where spatial resolution is of order ∼5μm. Despite having achieved mid-infrared super-resolution, IR-PHI's spatial resolution is ultimately limited by the visible probe laser's diffraction limit. This hinders immediate application to studying samples residing in spatially congested environments. To circumvent this, we demonstrate further enhancements to IR-PHI's spatial resolution using a deep learning network that addresses the Abbe diffraction limit as well as background artifacts, introduced by experimental raster scanning. What results is a twofold improvement in feature resolution from 300 to ∼150 nm.

Vibrational imaging for label-free cancer diagnosis and classification

The first key step in the detection and classification of most cancers is the microscopic assessment of thin tissue slices, the so-called “histopathology”. This procedure is still nowadays, similarly to 150 years ago, performed by staining the tissue with two or more dyes able to bind to specific biological structures, followed by visual inspection by the histopathologist under the bright-field optical microscope. This approach involves long manual procedures which can be accompanied by human errors, subjectivity, and lack of reproducibility. Vibrational microscopies are capable of directly providing chemical and biomolecular information on tissues, identifying them through their fingerprint vibrational spectra without the need of staining and, thus, constitute powerful tools for label-free and objective tumour identification. The two most established techniques, spontaneous Raman microscopy and infrared absorption microscopy, suffer, respectively, from long acquisition times and low spatial resolution. These limitations can be overcome by novel and more technically demanding approaches such coherent Raman scattering and photothermal infrared microscopy. Here we present an extended overview of the major advances in the field of vibrational imaging for cancer diagnosis. We start from a detailed description of the different technologies and then present examples of their applications to tissue imaging for cancer assessment. We critically compare the presented approaches, discussing the steps required to bring these powerful technologies from bench to bedside.

Binding of tyrosine kinase inhibitor to epidermal growth factor receptor: surface-enhanced infrared absorption microscopy reveals subtle protein secondary structure variations.

Surface-Enhanced Infrared Absorption (SEIRA) has been proposed as a valuable tool for protein binding studies, but its performances have been often proven on model proteins undergoing severe secondary structure rearrangements, while ligand binding only marginally involves the protein backbone in the vast majority of the biologically relevant cases. In this study we demonstrate the potential of SEIRA microscopy for highlighting the very subtle secondary structure modifications associated with the binding of Lapatinib, a tyrosine kinase inhibitor (TKI), to epidermal growth factor receptor (EGFR), a well-known driver of tumorigenesis in pathological settings such as lung, breast and brain cancers. By boosting the performances of Mid-IR plasmonic devices based on nanoantennas cross-geometry, accustoming the protein purification protocols, carefully tuning the protein anchoring methodology and optimizing the data analysis, we were able to detect EGFR secondary structure modification associated with few amino acids. A nano-patterned platform with this kind of sensitivity bridges biophysical and structural characterization methods, thus opening new possibilities in studying of proteins of biomedical interest, particularly for drug-screening purposes.

Infrared photothermal heterodyne imaging: Contrast mechanism and detection limits

Infrared photothermal heterodyne imaging (IR-PHI) is an ultrasensitive technique for achieving super-resolution, infrared imaging throughout the mid-infrared “fingerprint” spectral region (2.5–10μm). An achieved spatial resolution of ∼300nm is up to 30-fold smaller than the infrared diffraction limit. In this study, we establish IR-PHI’s signal contrast mechanism and benchmark the technique’s capabilities using the characteristic infrared vibrational transitions of individual polystyrene (PS) and poly(methyl methacrylate) (PMMA) beads. The analysis of acquired results reveals that IR-PHI contrast originates from a competing, photothermally induced specimen size and refractive index changes to backscattering cross sections. For PS and PMMA, thermo-optic refractive index contributions dominate and are responsible for medium-free IR-PHI signal contrast. Our analysis simultaneously establishes IR-PHI’s current, medium-free peak absorption cross-sectional limit-of-detection to be σabs=3×10−18m2. This improved understanding of IR-PHI signal contrast provides a framework for future developments in super-resolution infrared absorption microscopy and spectroscopy.

Detection of antibiotic resistant Escherichia Coli bacteria using infrared microscopy and advanced multivariate analysis.

Bacterial resistance to antibiotics is becoming a global health-care problem. Bacteria are involved in many diseases, and antibiotics have been the most effective treatment for them. It is essential to treat an infection with an antibiotic to which the infecting bacteria is sensitive; otherwise, the treatment is not effective and may lead to life-threatening progression of disease. Classical microbiology methods that are used for determination of bacterial susceptibility to antibiotics are time consuming, accounting for problematic delays in the administration of appropriate drugs. Infrared-absorption microscopy is a sensitive and rapid method, enabling the acquisition of biochemical information from cells at the molecular level. The combination of Fourier transform infrared (FTIR) microscopy with new statistical classification methods for spectral analysis has become a powerful technique, with the ability to detect structural molecular changes associated with resistivity of bacteria to antibiotics. It was possible to differentiate between isolates of Escherichia (E.) coli that were sensitive or resistant to different antibiotics with good accuracy. The objective computational classifier, based on infrared absorption spectra, is highly sensitive to the subtle infrared spectral changes that correlate with molecular changes associated with resistivity. These changes enable differentiating between the resistant and sensitive E. coli isolates within a few minutes, following the initial culture. This study provides proof-of-concept evidence for the translational potential of this spectroscopic technique in the clinical management of bacterial infections, by characterizing and classifying antibiotic resistance in a much shorter time than possible with current standard laboratory methods.

The influence of annealing temperature on the synthesis of silicon quantum dots embedded in hydrogenated amorphous Si-rich silicon carbide matrix

Hydrogenated amorphous silicon carbide thin films (a-SiC:H) were prepared by plasma-enhanced chemical vapor deposition (PECVD) and thermal annealed at temperatures of 900, 1050, and 1200°C, respectively. The influence of annealing temperature on the silicon quantum dot (QD) synthesis was investigated by Raman scattering spectroscopy, X-ray diffraction spectroscopy, and high-resolution transmission electron microscopy. The influence of annealing temperature on the chemical bonding configurations was revealed by Fourier transform infrared absorption microscopy. The element ratios of the as-deposited sample were deduced by X-ray photoelectron spectroscopy. Results reveal that the samples are in silicon-rich nature. Silicon in the as-deposited sample and the 900°C annealed sample are amorphous. When the annealing temperature is increased to 1050°C, crystal silicon QDs have come into being. The calculated number density is about 2.15±0.03×1012cm−2 and more than 80±3% of the silicon QDs fall within a narrow size range of 2–3nm. When the annealing temperature is increased to 1200°C, the average size of crystal silicon QDs is tuned from 2.6 to 3.2nm, while the crystallinity is enhanced from 56.7±2.5 to 67.1±1.5%. We attribute the influence of annealing temperature on the synthesis of silicon QDs to be dependent on the evolution of chemical bonding configurations and the agglomeration of silicon atoms from the host matrix.

Development of Pump-Probe Nanoscopy Architecture

Although modern optical microscopy allows the achievement of sub-diffraction resolution, most of the current techniques rely on a fluorescence contrast mechanism. Moreover, deep tissue imaging remains a challenging task especially for thick and highly scattering biological objects. The infrared absorption/saturation microscopy method is designed to overcome these issues [1, 2], having InfraRed Nanoscopy (IRN) as an instrumental perspective. The main idea behind IRN is an absorption/saturation effect similar to conventional pump-probe in which the first pump beam modifies the carrier density inside the sample, followed by intensity changes in the transmitted probe beam. By introducing an additional doughnut shaped pump beam one can transiently saturate the induced transition in the periphery of the focal spot, and collect the signal generated from the central sub-diffraction area. This is useful mainly for infrared absorption microscopy. The IR range operates in the transparency window of biological tissues and by selecting specific wavelengths one can observe selected vibrational modes. Therefore, such a technique could be applied for the imaging of non-fluorescent species, which is important for various biological applications.In this work we outline the architecture of a saturated transient absorption microscope, directed towards the development of a microscopy platform comprising a pump-probe setup and STED nanoscope [3]. Pump and probe wavelengths can be tuned from the visible (400-500 nm) to the near IR (800-1000 nm) spectral ranges, according to the sample properties. This permits accessing explicit spatial and dynamical information about the sample for applications in cellular biophysics and nanochemistry. We also indicate the possibility of implementing 3D super-resolution capability.Supporting grants: LANIR, FP7/20012-2015, 280804 and PRIN, MIUR 2010JFYFY2_002.1. C. Silien, et al., Opt. Express 20(28), 29694-29704 (2012).2. W. Pu et al., Nat. Photonics 6, 449-453 (2013).3. S. Galiani, et al., Opt. Express 20(7), 7362-7374 (2012).

A framework for far-field infrared absorption microscopy beyond the diffraction limit

A framework is proposed for infrared (IR) absorption microscopy in the far-field with a spatial resolution below the diffraction limit. The sub-diffraction resolution is achieved by pumping a transient contrast in the population of a selected vibrational mode with IR pulses that exhibit alternating central minima and maxima, and by probing the corresponding absorbance at the same wavelength with adequately delayed Gaussian pulses. Simulations have been carried out on the basis of empirical parameters emulating patterned thin films of octadecyltrichlorosilane and a resolution of 250 nm was found when probing the CH₂ stretches at 3.5 μm with pump energies less than ten times the vibrational saturation threshold.

High-pressure synthesis and characterization of diamond from a sulfur–carbon system

Diamond crystallization in the sulfur–graphite system has been studied at P=7 GPa and T=1750–1850°C in experiments with a duration up to 7 h. It has been found that diamond nucleation and crystallization occur both at the interface between the graphite and sulfur melt and directly within the carbon–saturated sulfur melt. Diamond crystals with maximum size up to 500 μm were synthesized. The crystals had cube–octahedral morphology with minor faces of trapezohedron. Goniometric measurements revealed that crystallographic indexes of the trapezohedron faces are {411} and {944}. Spectroscopic characterization of sulfur–synthesized diamonds by means of infrared absorption microscopy and cathodoluminescence has been made for the first time. It was found that crystals contain nitrogen impurity in the form of A aggregates with concentration up to approximately 700 at. ppm. An absorption band with a maximum at 1050 cm −1, whose origin is not clear, was observed in the IR spectra. The cathodoluminescence spectra of these diamonds were found to comprise of the well-known H3 and 575-nm systems as well as a broad emission band.

Synthesis of diamond with the highest nitrogen concentration

Nitrogen concentrations in diamond grown from non-metallic solvent–catalysts such as Na 2 CO 3 and Na 2 SO 4 have been measured using infrared absorption microscopy. It was found that 1200 to 1900 atomic ppm of nitrogen atoms are incorporated in the crystals when a sample container made of boron nitride was used, although a few hundred ppm of nitrogen were present when an NaCl container was used instead of BN. Such high concentrations of nitrogen have not been found in synthetic diamonds when conventional metallic solvent–catalysts are used. The result of this study is consistent with the inference that natural diamond, in which high concentrations of nitrogen are usually present, grew from molten rocks, i.e., non-metallic catalysts.

On long-range lattice perfection in natural type 1a diamond

Abstract Several methods have been applied to examine the lattice perfection in a natural diamond that was uncommonly low in density of dislocations and other sources of long-range strains, but which belonged to the commonest optical type 1a. Infrared absorption microscopy and cathodoluminescence topography demonstrated an exceptionally uniform distribution of nitrogen impurity content, with a concentration of about 0.1%. Defect-imaging examinations by birefringence, X-ray single-crystal and double-crystal topography (which were facilitated by optically polished surfaces on the specimen) were applied to select the most strain-free volume, which was then probed by synchrotron radiation double-crystal diffractometry. A 220-reflection, symmetrical Laue case rocking curve only about 0.25 arc second wider than that calculated for perfect diamond was recorded. Analysis was expressed in terms of apparent value of ε = F″g/F″0, the ratio of imaginary parts of the structure factor for orders g and 0. The observed profile for g = 220 and wavelength 0.154 nm was well fitted by apparent ε = 0.69 (theoretical ε = 0.96). Minor asymmetry in the flanks of the experimental profile was explained by the presence of a small component of incoherent scattering in the diffracted beam.

Orientation-dependent nitrogen incorporation on vicinals on synthetic diamond cube growth surfaces

New phenomena significant in relation to optical properties of diamond and to inhomogeneity of impurity distribution in synthetic diamond are reported. Evidence has been collected from (a) optical transmission at 430 nm, (b) Schlieren photography, (c) birefringence, (d) infrared absorption microscopy, (e) differential abrasion resistance patterns, (f) cathodoluminescence topography with analysis of polarisation of emission, and (g) X-ray topography with synchrotron and conventional sources; and is detailed and correlated for one specimen, supplemented by data from a second, similar specimen. The bulk of the specimens comprised material belonging to one cube growth sector, designated (001). They did not contain the seed, which had been polished away. The specimens were slab-shaped, bounded by a pair of polished surfaces parallel to (001), nearer and further from the seed, respectively. The principal feature of interest on both surfaces parallel to (001) was a “Maltese Cross” type of cathodoluminescence feature, radiating from a growth centre that had dominated growth in the direction [001] throughout the thickness of the slab (1 mm), entirely covering the (001) growth surface up to its maximum width of 3 mm exposed on the specimen surface remoter from the seed. The arms of the Maltese Cross brightest in visible emission (peak wavelength ≈ 525 nm) expanded radially in the cube diagonal directions ±[110] and ±[1 1 0]. Their cathodoluminescence emitted in the direction normal to the (001) surface was partially polarised with E-vector parallel to the radial direction in each arm. Less bright emission from arms pointing in the cube directions ±[100] and ±[010] was unpolarised in this [001] view. Application of techniques (a), (b) and (d) showed that the former, diagonal arms were at least 25% to 30% richer than the latter arms in nitrogen impurity present in singly-substituted atomic state, measured at a distance of 600 μm from the cross centre. Differences in impurity incorporation and optical properties are attributed to differences in surface structure on vicinal slopes of a low-elevation growth pyramid. Regarding polarisation of cathodoluminescence emitted in the [001] direction, the diamond structure fourfold screw symmetry normal to (001) provides the foundation for a growth step model that can account for unpolarised emission from the cross arms pointing towards ±[100] and ±[010], and the 90° rotation of partial polarisation direction between arms pointing towards ±[110] and those pointing towards ±[1 1 0].