Infrared Microscopy Research Articles

Infrared Spectroscopy and Imaging at Nanometer Scale

Infrared (IR) vibrational spectroscopy is one of the oldest and the most widely used analytical tool for the characterization of chemical species in samples. Spatially resolved IR spectroscopy, the IR spectro‐microscopy, may offer information on the spatial arrangement of chemical species on sample surfaces as well as the chemical identity of the species. However, conventional far‐field IR microscopy offers spatial resolution of 5 μm, which is not nearly enough for fully characterizing the sample structures in many cases. In this article, we review the recently developed spectro‐microscopy methods that can overcome the diffraction limit of light and offer chemical maps of samples at nanometric scales. We mainly focus on IR near‐field microscopy, IR photothermal microscopy, IR photo‐induced force microscopy, and finally the IR‐Visible photothermal lensing microscopy. The key principles of each technique, practical merits, and limitations are described.

Soil burial-induced chemical and thermal changes in starch/poly (lactic acid) composites

Soil burial degradation was confirmed to be an efficient waste disposal method for the biodegradable materials with short service life, such as starch/poly (lactic acid) (PLA) composite. The biodegradation behavior about chemical and thermal properties of starch/PLA composite was analyzed by using X-ray photoelectron spectroscopy (XPS), infrared microscopy (IRM), differential scanning calorimetry (DSC), and thermal gravimetric analysis (TGA). XPS and IRM results indicated that the biodegradation of PLA occurred at the ester groups in PLA chains. XPS demonstrated the cleavage of CO linkages between glucose rings in starch. DSC and TGA results showed that the starch/PLA composite degraded faster than the pure PLA. During the soil burial degradation, the glass transition temperature of starch/PLA composite exhibited an obviously decrease while it had a slight variation for PLA. The thermal stability of starch/PLA composite shifted towards to that of PLA when they were subjected to soil burial for the same time. It is established that the starch can accelerate the degradation of PLA-based materials, which will enlarge the markets of biodegradable PLA materials used for short service life products.

Differentiation of mixed soil-borne fungi in the genus level using infrared spectroscopy and multivariate analysis

Early detection of soil-borne pathogens, which have a negative effect on almost all agricultural crops, is crucial for effective targeting with the most suitable antifungal agents and thus preventing and/or reducing their severity. They are responsible for severe diseases in various plants, leading in many cases to substantial economic losses. In this study, infrared (IR) spectroscopic method, which is known as sensitive, accurate and rapid, was used to discriminate between different fungi in a mixture was evaluated. Mixed and pure samples of Colletotrichum, Verticillium, Rhizoctonia, and Fusarium genera were measured using IR microscopy. Our spectral results showed that the best differentiation between pure and mixed fungi was obtained in the 675–1800 cm−1 wavenumber region. Principal components analysis (PCA), followed by linear discriminant analysis (LDA) as a linear classifier, was performed on the spectra of the measured classes. Our results showed that it is possible to differentiate between mixed-calculated categories of phytopathogens with high success rates (~100%) when the mixing percentage range is narrow (40–60) in the genus level; when the mixing percentage range is wide (10–90), the success rate exceeded 85%. Also, in the measured mixed categories of phytopathogens it is possible to differentiate between the different categories with ~100% success rate.

PDMS-Based Microfluidic Device for Infrared-Transmission Spectro-Electrochemistry

Abstract Polydimethylsiloxane (PDMS) is a well-known material used in making microfluidic devices through soft lithography. PDMS strongly absorbs infrared (IR) light in the mid infrared region, which can be alleviated by using thin-film PDMS devices. However, IR detection with PDMS devices usually requires an IR-transparent backbone material. Here, we report a microfluidic system using a 160 µm PDMS thin-film device (50-µm path length) without a supporting backbone for IR spectroelectrochemistry (IR-SEC). The PDMS device is assembled with four layers: microchannel-supporting window, microchannel thin film, electrode-embedded thin film, and electrode-supporting window. In this work, mapping of ferrocyanide oxidation was investigated under an IR microscope. An electrochemical reaction, occurring between the working and counter electrodes, was observed clearly. Moreover, the electron-transfer process of ferrocyanide oxidation was investigated from the IR absorbance spectrum. This mapping study demonstrates that the relationship between the electrochemical reactants and products partly agree well with the Nernst equation. Accordingly, PDMS thin-film devices have the capability for studying electrochemical reactions by using IR-SEC measurements with low sample consumption.

Detection of animal by-products in bone ashes by near infrared spectroscopy coupled with microscopy

Bovine spongiform encephalopathy is a mortal bovine disease. Epidemiologic studies have linked the disease to animal feed contaminated with infected protein. In Argentina, the feeding of bovines with components of animal origin is banned, except for fishmeal and bone ash. Nowadays, optical microscopy is used to analyze animal feed and its components. In this method, technical analytical expertise is very important. This is why the development of a methodology that produces results which can be rapidly and automatically compared is urgently needed. The specific infrared microscopy method presented in this work delivers qualitative results in terms of the presence or absence of animal particles by applying specific decision rules. The object of this work was to assess the methodology of near infrared microscopy for the qualitative determination of the presence of particles of animal origin in matrices of bone ash. The spectra were collected by an image microscope coupled to a Fourier transform infrared spectrometer operating in the reflection mode. Four mappings were done per sample, obtaining 1000 spectra per mapping. They were selected from an area on the slide of 50 particles in the axis X and 20 particles in the axis Y. Spectra were automatically collected at these points. In order to find the fragments of animal origin in the samples, a specific software program was developed. The program analyzed the spectra and evaluated the presence of bone fragments. From the validation results, it could be inferred that 4000 spectra should be observed in order to achieve a detection limit of 0.05 g bone fragments 100 g−1 bone ash. Selectivity, intermediate precision and repeatability were also analyzed with satisfactory results. Therefore, the validated method can be easily applied in routine analysis of bone ashes.

A smart thermoregulatory nanocomposite membrane with improved thermal properties: simultaneous use of graphene family and micro-encapsulated phase change material

This study is an attempt to improve the thermal properties of polyacrylamide (PAAm) membrane using graphene oxide (GO) and reduced graphene oxide (rGO) as a static modifier and phase change material micro-capsules (mPCMs) as a dynamic modifier at the same time. Fourier transform infra-red spectroscopy, X-ray diffraction and transmission electron microscopy were applied to prove GO and rGO synthesis. Dynamic heat transfer simulation apparatus and the transient heat transfer model were used to study the transient temperature behavior of the samples. Scanning electron microscopy and differential scanning calorimetry were also used to study the morphological properties and thermal behavior of hydrogels containing mPCMs. The addition of GO and rGO to the PAAm matrix increased thermal conductivity 2 and 2.5 times more than pure PAAm. Moreover, studying the transient temperature rates and mathematical simulations for PAAm containing GO and rGO revealed that rGO had better performance than GO in improving thermal properties. These hybrid nanocomposites increased the thermal conductivity of the fabrics thanks to the presence of rGO nanosheets and heat absorption capacity by mPCMs. It was also found that the presence of rGO improved the heat absorption performance of mPCMs to some extent. This long-awaited improvement in the thermal properties of the hydrogel membrane can be potentially harnessed to enhance user comfort in protective clothing.

Adsorption of CO2 and Methane on Covalent Organic Polymer

Development of covalent organic polymer (COP) is a potential new class of adsorbent for CO2 separation from natural gas mainly due to their good hydrothermal stability, chemical tuning flexibility and low cost. CO2 and methane adsorption on COP-1 was studied under atmospheric condition (101.3 kPa, 298 K). COP-1 was synthesized via catalyst-free polycondensation of cyanuric chloride and piperazine. The properties of COP-1 were characterized using several analytical methods such as Fourier Transform Infra-Red (FTIR), N2 adsorption and desorption measurement and Field Transmission Electron Microscopy in coupled of Energy Dispersive X-ray Spectroscopy (FESEM-EDS). Reversible CO2 adsorption isotherm on COP-1 reflects low heat of adsorption which is beneficial to energy minimization in adsorbent regeneration process. Furthermore, moderate specific surface area COP-1 (88.5 m2/g) shows about nine times CO2 uptake higher than methane. The highly selective adsorption performance provides a promising insight in application of COP adsorbent for CO2 removal in natural gas field.

Synthesis of ZnO Nanoparticles by Using an Atmospheric-Pressure Plasma Jet

In this study, zinc oxide nanoparticles were synthesized by using an at-mospheric-pressure plasma jet in NaOH-HNO3 electrolytic system. Atmos-pheric-Pressure Plasma Jet was successfully used as the cathode and Znsheet was used as the anode. The characterization of zinc oxide was obtained by X-ray powder diffraction (XRD), Fourier transformation infra-red (FTIR) and transmission electron microscope (TEM). The results show that the morphology of zincoxide nanocrystals obtained by this technology is mainly dependent on the electrolytic media, current density and reaction temperature. The average grain size of ZnO nanoparticles is around 50.4 nm. These results encourage preparing these nanostructures for using in a great interest applications in solar cells, UV light emitting diodes, gassensors, etc. This technique is low cost, scalable and general and should allow a wide range of nanoparticle materials to be synthesized in the gas or liquid phase.

Hydrogenolysis of sorbitol over Ni supported on Ca- and Ca(Sr)-hydroxyapatites

Ca-hydroxyapatite (HAP) was synthesized with different morphologies, in needle (N), sphere (S) and rod (R) shapes. A partially Sr-substituted sample (Ca(Sr)-hydroxyapatite) with the stoichiometric composition of Sr0.6Ca9.4(PO4)6(OH)2, and possessing a rod shaped morphology was also hydrothermally synthesized (SrHAP-R). The samples were characterized by X-ray diffraction, Fourier-Transform infra-red spectroscopy (FT-IR), scanning and transmission electron microscopy (SEM and TEM), X-ray photoelectron spectroscopy (XPS) and surface area measurement. Nickel (6 wt%) was loaded on the samples by an impregnation method. Rod-shaped hydroxyapatite (HAP-R) was more crystalline than the others. FT-IR results showed characteristic bands for (PO4)3− and OH vibrations. XPS results indicated Ni to be in the 2+ state, and O 1s satellite features revealed a phosphoric oxide environment in all the samples. The catalytic activities of the Ni-containing samples were tested in the hydrogenolysis of sorbitol into ethylene and propylene glycols in an aqueous medium in a stirred high pressure reactor at different process conditions. The most active catalyst was Ni/SrHAP-R. The catalyst was reusable many times with only a minor activity loss.

Formulation of novel chitosan guargum based hydrogels for sustained drug release of paracetamol

The report presents the formulation of hydrogel based on biopolymers chitosan and guar gum after cross-linking for sustained release of a commonly used orally prescribed analgesic Paracetamol. The oral ingestion of Paracetamol is associated with complications of the gastric tract and liver metabolism that can be effectually avoided by using transdermal drug delivery systems. The formulated transdermal patch was characterized for physicochemical properties including swelling, bonding pattern (using FTIR Fourier Transform Infra-Red and Scanning Electron Microscopy SEM) and antimicrobial activity. Biocompatibility and cytotoxicity was examined in vitro using cell culture in HeLa cell lines. After characterizing the novel formulated hydrogel were employed for the preparation of drug encapsulated in alginate beads as a transdermal patch. After formulation of the transdermal patch, the drug release was studied using an avian skin model. The results followed zero order kinetics and Non-Fickian law for diffusion. Paracetamol due to its small molecular mass (151.163g/mol) released in a sustained manner. The released drug successfully retained its biological effects including anti-inflammatory and anti-protease activity, indicating no interaction between the drug and the formulated hydrogel. It was shown that the formulated hydrogels could be safely used as a dermal patch for the sustained drug release of Paracetamol.

Biosynthesis and characterization of silver nanoparticles from fungal species and its antibacterial and anticancer effect

Silver nanoparticles have gained considerable importance in recent years due to their diverse medicinal activities. In the present study, we have explored filamentous fungi Penicillium italicum for the extracellular biosynthesis of silver nanoparticles (AgNPs) and evaluated its antibacterial and anticancer effects. The nanoparticles were characterized by using UV–Visible and Fourier transform infra-red (FTIR) spectroscopy and transmission electron microscopy (TEM) analysis. UV–Visible spectra showed specific absorption peak at 422.67 nm which confirmed the presence of nanoparticles. FTIR spectroscopy analysis revealed the presence of alcohols, phenols, alkenes, and amines that play major roles in stabilizing the synthesized AgNPs. Transmission electron microscopy (TEM) analysis showed spherical shape of AgNPs with size ranges from 14.5 nm to 23.3 nm. Antibacterial studies against Staphylococcus aureus, Salmonella enterica, Bacillus cereus, and Escherichia coli through disc diffusion method revealed 20 mm (for 40 μg/ml) of inhibition of zone especially for S. enterica and exhibited excellent synergistic effect when combined with moxifloxacin and streptomycin. Further, in anticancer studies, these nanoparticles demonstrated good anticancer effect against HEp-2 cancer cell line with IC50 value at 30 μg/ml through MTT assay.

A study of the relationship between the migration of image silver and perceived yellowing of silver gelatine photographs

Silver gelatine photographs were the most dominant photographic process of the twentieth century from the 1880s until the 1960s. They are prone to yellowing, mirroring and fading which is largely attributed to the effects of pollutants, relative humidity and residual processing chemicals. Experts in the conservation of photographs claim they can determine the causes of deterioration with the naked eye: the effects of humidity result in a more yellowed appearance, whilst the presence of residual chemicals results in a redder appearance. This work aims to investigate if the same deterioration processes can be diagnosed in photographic prints with a spectrophotometer by addressing two questions: (1) In new and artificially aged silver gelatine photographs is it possible to distinguish between discolouration caused by silver migration and that caused by the presence of residual sulfur? (2) What are the complexities of applying these findings to historic photographs? A set of test photographs, some well processed and some insufficiently washed was developed and artificially aged. These were compared to a small collection of historical photographs of different ages, paper types and image colours. Samples were assessed using visual observation, residual silver and hypo spot tests, colour measurements including L*a*b* and reflectance spectra, Fourier transform infra-red (FTIR) spectroscopy and transmission electron microscopy (TEM). After artificial ageing the well processed test photographs were more yellowed, TEM indicated that this was due to colloidal silver formation. The insufficiently washed test photographs were more red but also darker, TEM showed these samples to have more homogeneous silver filaments, thought to be due to silver sulfide formation. The results for the historical photographs were similar but more subtle. A larger sample set is needed to investigate this more extensively. Further investigation on historical samples, with colour measurements and residual silver and fixer spot tests will take place.

Extreme blue-shifted photoluminescence from quantum confinement of core–shell ZnO

We employed a rudimentary technique of solution chemistry to synthesize ZnO nanostructures of various sizes. The crystal structure and bond alignment were studied through X-ray diffraction technique. Raman and Fourier Transformed Infra-Red Spectroscopy and Transmission Electron Microscopy were employed to reveal the morphology and the formation of core–shell nanostructures. We observed that ZnO4 tetrahedral distortion and nano-confinement impart c-axial evolution of structure. The quantum confinement of the core resulted in extreme blue-shifted photoluminescence. The experimental value of energy band gap was validated by a quantum mechanical approach with effective mass approximation. We also observed ~900% increase in current under illumination as compared to dark current. The wide band photoluminescence and enhanced photocurrent are suitable for the application in white-light emitting diodes, photo-detectors and solar cells.

Thermal Profiles Within the Channel of Planar Gunn Diodes Using Micro-Particle Sensors

This letter describes the use of a novel micro-particle sensor ( ${\sim }3{\mu }\text{m}$ diameter) and infra-red microscopy to measure the temperature profile within the active channel (typically 3- ${\mu }\text{m}$ length and 120- ${\mu }\text{m}$ width) of planar Gunn diodes. The method has enabled detailed temperature measurements showing an asymmetrical temperature profile along the active width of these devices. The asymmetrical temperature profile suggests a similar behavior in the channel current density, which may contribute to the lower than expected RF output power.

Impact of Material Shade and Distance from Light Curing Unit Tip on the Depth of Polymerization of Composites.

This study aimed to evaluate the effect of the composite shade and distance from the light-curing unit (LCU) tip on the irradiance reaching the bottom of composite disks and on the depth of polymerization. Composites of three shades (opaque - OXDC, bleach - BXL, and A2) were inserted into molds with 3-mm of thickness positioned over a spectrometer and photo-activated with the LCU (Bluephase) tip placed at 0 or 1 cm from the composite surface. The mean irradiance reaching the bottom of composite was recorded during the entire photo-activation (30 s). Specimens (2 x 2 x 4 mm) were polymerized and used to map the degree of conversion achieved in different depths from irradiated surface. Specimens were sectioned into slices that were positioned over the platform of the infra-red microscope connected to the spectrometer to map the conversion. The conversion was measured in eight different depths every 500-µm. Increasing the distance of LCU tip reduced the irradiance only for A2. Interposing OXDC disks resulted in lowest values of irradiance and A2 the highest one. A tendency to decrease the conversion was observed towards the bottom of specimens for all experimental conditions, and the slope was more accentuated for OXDC. Differences among shades and distances from LCU tip were evident only beyond 1.5-2.0 mm of depth. In conclusion, both composite shade and distance from LCU tip might affect the light-transmission and depth of polymerization, while the effect of last was more pronounced.

Dative post synthetic methods on SBUs of MWCNT@MOFs hybrid composite and its effect on CO2 uptake properties

Two hybrid materials composed of metal-organic framework (MIL-100(Cr) and Cu3(BTC)2) and carboxyl-modified multi-wall carbon nanotubes (MWCNTs) were synthesized successfully in situ and characterized by nitrogen adsorption-desorption isotherms, X-Ray Diffraction (XRD), Fourier Transform Infrared (FT–IR) and Scanning Electron Microscopy (SEM). The gas adsorption properties of both of these hybrid materials were compared to the pristine MIL-100(Cr) and Cu3(BTC)2 materials. Carbon dioxide adsorption capacity is increased about 64% and 76% (from 5.8 to 9.52mmolg−1 and from 4.53 to 8mmolg−1) respectively at 298K and 18bar. The increment in the CO2 adsorption capacity of composite is attributed to the increase of micropore volume of MIL-100(Cr) and Cu3(BTC)2 by MWCNT incorporation. Then frameworks of CNT@Cu3(BTC)2-En and CNT@MIL-100(Cr)-En (En=ethylenediamine) were functionalized with the primary amine via post modification. It was found that CNT@Cu3(BTC)2-En (4.7mmolg−1) shows a higher adsorption capacity for acidic gas as compared to CNT@MIL-100(Cr)-En (3.7mmolg−1) at 298K and 1bar.

Using Infrared Spectroscopy and Multivariate Analysis to Detect Antibiotics' Resistant Escherichia coli Bacteria.

Bacterial pathogens are one of the primary causes of human morbidity worldwide. Historically, antibiotics have been highly effective against most bacterial pathogens; however, the increasing resistance of bacteria to a broad spectrum of commonly used antibiotics has become a global health-care problem. Early and rapid determination of bacterial susceptibility to antibiotics has become essential in many clinical settings and, sometimes, can save lives. Currently classical procedures require at least 48 h for determining bacterial susceptibility, which can constitute a life-threatening delay for effective treatment. Infrared (IR) microscopy is a rapid and inexpensive technique, which has been used successfully for the detection and identification of various biological samples; nonetheless, its true potential in routine clinical diagnosis has not yet been established. In this study, we evaluated the potential of this technique for rapid identification of bacterial susceptibility to specific antibiotics based on the IR spectra of the bacteria. IR spectroscopy was conducted on bacterial colonies, obtained after 24 h culture from patients' samples. An IR microscope was utilized, and a computational classification method was developed to analyze the IR spectra by novel pattern-recognition and statistical tools, to determine E. coli susceptibility within a few minutes to different antibiotics, gentamicin, ceftazidime, nitrofurantoin, nalidixic acid, ofloxacin. Our results show that it was possible to classify the tested bacteria into sensitive and resistant types, with success rates as high as 85% for a number of examined antibiotics. These promising results open the potential of this technique for faster determination of bacterial susceptibility to certain antibiotics.

Preparation and properties of microcrystalline cellulose/hydroxypropyl starch composite films

In this paper, microcrystalline cellulose (MCC)/hydroxypropyl starch (HPS) composite films are prepared by the solution casting method, and the effect of different amounts of microcrystalline cellulose on the properties of the films is investigated. The structure of MCC/HPS composite materials is characterized by Fourier transform infra-red and scanning election microscopy, and thermal stability, mechanical properties, hygroscopicity, and water vapor permeability of the composite films are also tested. According to the test results, with increasing MCC amounts, glass transition temperature, thermal stability, and tensile strength of MCC/HPS composite films are improved, while the hygroscopicity and water vapor permeability of MCC/HPS composite materials are decreased. When the content of MCC reaches 6 wt%, the maximum increase of the glass transition temperature is about 9.63 °C, and the tensile strength of MCC/HPS composite films are increased by 300% compared with that of HPS films. Moreover, the addition of MCC helps to expand the application of hydroxypropyl starch in the packaging field.

Effect of Potassium Permanganate Treatment on the Macromolecular, Morphological, Thermal and crystallographic structures of Plantain (Musa paradisiaca) Fiber

Natural fiber extracted from Plantain ( Musa paradisiaca ) fibers were treated with potassium permanganate (KMnO 4 )—acetone solution at various concentrations for different soaking time. In order to identify the effect of this chemical modification on the macromolecular, morphological, crystallographic structures and thermal properties of the fibers, X-Ray Diffraction (XRD), Fourier Transform Infra-red (FTIR), Thermogravimetric analysis (TGA) and Scanning Electron Microscope (SEM) was used. Wide angle X-Ray Diffraction analysis shows a significant change in the macromolecular and the crystallographic parameters of the fiber, Fourier Transform Infra-red (FTIR) spectral confirm the partial removal of wax, hemicellulose, and lignin content. Thermogravimetric analysis (TGA) shows that thermal stability of the fibers increases after treatment, while Scanning Electron Microscope (SEM) micrographs indicate enhance surface roughness of treated fibers. Treated Fibres with 0.05% KMnO 4 -acetone solution for 3min (05K3) was found to have the highest degree of crystallinity, bulk density, enhance surface roughness, good thermal stability and crystallite size.

Characterizations of Newly Fabricated Composite Materials Based on Organoclay Incorporated Polymeric Matrix

This article reports the synthesis of engineered materials i.e. composite materials based on matrix (polymeric polyacrylic acid) and reinforcement (organic clay) through 6-hour and 12-hour ultrasonication at different intervals. All the precursors and desired composite materials were characterized by Fourier transform infra-red (FT-IR) and scanning electron microscopy (SEM) techniques. The disappearance of Si-O characteristic peak after ultrasonication justifies the fabrication and incorporation of organoclay in the polymeric structure of polyacrylic acid as revealed by FT-IR analysis. The SEM images interpreted the surface morphology, porosity, distribution and compatibility of matrix and reinforcement in it, which has been achieved successfully in this study for exfoliation form.