Attenuated total reflection Fourier-transform infrared (ATR-FTIR) imaging of tissues and live cells

Effects of endodontic root canal irrigants on tooth dentin revealed by infrared spectroscopy: a systematic literature review

BACKGROUND

Root canal irrigation endodontic solutions have effects on the chemistry of dentin. Infrared spectroscopy is a non-destructive chemical characterization method where the strength of absorption often correlates with mineral or organic composition.

OBJECTIVES

To survey effects of commonly used irrigation solutions on the composition of root dentin as detected by widely-available Fourier transform infrared spectroscopy (FTIR) methods.

METHODS

Electronic databases were searched for articles published between 1983 to 2023. After risk of bias assessments (OHAT), studies were grouped according to effects per irrigation solution. Inclusion criteria comprised in vitro studies that used extracted human or bovine teeth, treated by irrigation solutions characterized using FTIR spectroscopy and presenting spectral data. Publications that did not share FTIR spectra were excluded.

RESULTS

A wide range of concentrations, durations, and methodologies have been tested but only 30 out of 3452 studies met our inclusion criteria. Different FTIR methods were used with the Attenuated Total Reflection (ATR) variant being the most common (21 studies). Investigated solutions included sodium hypochlorite (NaOCl), ethylenediaminetetraacetic-acid (EDTA), 1-hydroxyethylidene-1-1-diphosphonic-acid (HEDP), peracetic-acid (PAA), glycolic-acid (GA), and citric-acid (CA) though most focused on NaOCl and EDTA. All solutions had detectable effects on the FTIR signature of dentin. NaOCl mainly affects the organic signatures, revealing reduced amide/phosphate ratios with increasing concentrations. EDTA mainly effects the inorganic component, increasing with time and concentration, yet glycolic acid has stronger effects than EDTA on dentin. Beyond the type of irrigant and dentin exposure durations, concentration and protocol of application had strong effects. There is a lack of studies comparing similar irrigants under conditions that mimic clinical scenarios analyzing bulk sample because FTIR of powder dentin differs from bulk measurements.

SIGNIFICANCE

The ideal root-canal irrigant should combine local disinfection properties with minimal compositional effects on healthy dentin. FTIR methods appear reliable to identify important changes in root dentin chemical composition. Such information can help understand when endodontic irrigation might lead to root degradation or possibly contribute to long term failures such as vertical fractures. Awareness of chemical damage from irrigation procedures may help clinicians select procedures that reduce deleterious effects on the root canal structures.

Inverted Transflection Spectroscopy of Live Cells Using Metallic Grating on Elevated Nanopillars

Water absorption of mid-infrared (MIR) radiation severely limits the options for vibrational spectroscopy of the analytes-including live biological cells-that must be probed in aqueous environments. While internal reflection elements, such as attenuated total reflection prisms and metasurfaces, partially overcome this limitation, such devices have their own limitations: ATR prisms are difficult to integrate with multiwell cell culture workflows, while metasurfaces suffer from a limited spectral range and small penetration depth into analytes. In this work, we introduce an alternative live cell biosensing platform based on metallic nanogratings fabricated on top of elevated dielectric pillars. For the MIR wavelengths that are significantly longer than the grating period, reflection-based spectroscopy enables broadband sensing of the analytes inside the trenches separating the dielectric pillars. Because the depth of the analyte twice-traversed by the MIR light excludes the highly absorbing thick water layer above the grating, we refer to the technique as inverted transflection spectroscopy (ITS). The analytic power of ITS is established by measuring a wide range of protein concentrations in solution, with the limit of detection in the single-digit mg mL-1. The ability of ITS to interrogate live cells that naturally wrap themselves around the grating is used to characterize their adhesion kinetic.

A review of concepts and methods for FTIR imaging of biomarker changes in the post-stroke brain

Stroke represents a core area of study in neurosciences and public health due to its global contribution toward mortality and disability. The intricate pathophysiology of stroke, including ischemic and hemorrhagic events, involves the interruption in oxygen and nutrient delivery to the brain. Disruption of these crucial processes in the central nervous system leads to metabolic dysregulation and cell death. Fourier transform infrared (FTIR) spectroscopy can simultaneously measure total protein and lipid content along with a number of key biomarkers within brain tissue that cannot be observed using conventional techniques. FTIR imaging provides the opportunity to visualize this information in tissue which has not been chemically treated prior to analysis, thus retaining the spatial distribution and in situ chemical information. Here we present a review of FTIR imaging methods for investigating the biomarker responses in the post-stroke brain.

The Involvement of Lactic Acid Bacteria and Their Exopolysaccharides in the Biosorption and Detoxication of Heavy Metals in the Gut

Heavy metal pollution has become one of the most important global environmental issues. The human health risk posed by heavy metals encountered through the food chain and occupational and environmental exposure is increasing, resulting in a series of serious diseases. Ingested heavy metals might disturb the function of the gut barrier and cause toxicity to organs or tissues in other sites of the body. Probiotics, including some lactic acid bacteria (LAB), can be used as an alternative strategy to detoxify heavy metals in the host body due to their safety and effectiveness. Exopolysaccharides (EPS) produced by LAB possess varied chemical structures and functional properties and take part in the adsorption of heavy metals via keeping the producing cells vigorous. The main objective of this paper was to summarize the roles of LAB and their EPS in the adsorption and detoxification of heavy metals in the gut. Accumulated evidence has demonstrated that microbial EPS play a pivotal role in heavy metal biosorption. Specifically, EPS-producing LAB have been reported to show superior absorption, tolerance, and efficient abatement of the toxicity of heavy metals in vitro and/or in vivo to non-EPS-producing species. The mechanisms underlying EPS-metal binding are mainly related to the negatively charged acidic groups and unique steric structure on the surface of EPS. However, whether the enriched heavy metals on the bacterial cell surface increase toxicity to local mammal cells or tissues in the intestine and whether they are released during excretion remain to be elucidated.

Application of spectrochemical analysis with chemometrics to profile biochemical alterations in nanoplastic-exposed HepG2 cells

Humans are routinely exposed to nanoplastics (NPs) in various ways, and this exposure presents a significant health risk. Nevertheless, there remain gaps in our knowledge, particularly in the mechanisms of toxicity of NPs with different surface charges at very low environmental concentrations. Herein, a spectrochemical approach was used to profile the cytotoxicity of NPs with different surface charges in HepG2 cells. It was found that all three NPs can cause some biomolecular alterations in cells, affecting cellular lipids, proteins, amino acids, and genetic material. Of these, PS and PS-COOH led to a non-linear dose-response, which may be related to a biphasic dose-response, whereas PS-NH2 led to a linear dose-response with a gradual increase in toxicity with increasing exposure concentration. In addition, the spectroscopic results showed that surface modifications led to cellular biochemical changes and caused adverse biological effects, with PS-NH2 exhibiting higher toxicity compared to PS or PS-COOH along with an inhibition of cell proliferation. Surprisingly PS-COOH, although considered the least toxic NP, appears to cause DNA damage. Overall, the toxic effects of different surface-modified NPs in cells were detected for the first time by applying spectrochemical techniques, and these findings provide important data towards understanding the emerging widespread environmental pollution of NPs and their effects on humans.

Inhibitory mechanism of carboxymethyl chitosan-lotus seedpod oligomeric procyanidin nanoparticles on dietary advanced glycation end products released from glycated casein during digestion

Lotus seedpod oligomeric procyanidins (LSOPC) are potent inhibitors of advanced glycation end products (AGEs), whose gastrointestinal susceptibility to degradation limits their use in vivo. In this study, carboxymethyl chitosan-lotus seedpod oligomeric procyanidin nanoparticles (CMC-LSOPC NPs) were constructed with a binding ratio of 1:6.51. CMC-LSOPC NPs significantly inhibited the release of AGEs from glycated casein (G-CS) during digestion, increasing the inhibition rate by 25.76% in the gastric phase and by 14.33% in the intestinal phase compared with LSOPC alone. To further investigate the inhibition mechanism, fluorescence microscopy, scanning electron microscopy and FTIR were used to find that CMC-LSOPC NPs could form cohesions to encapsulate G-CS in the gastric phase and hinder G-CS hydrolysis. In the intestinal phase, LSOPC was targeted for release and bound to trypsin through hydrophobic interactions and hydrogen bonding, resulting in protein peptide chain rearrangement, changes in secondary structure and significant reduction in trypsin activity. In addition, CMC-LSOPC NPs increased the antioxidant capacity of digestive fluid and could reduce the oxidative stress in the gastrointestinal tract caused by the release of AGEs. It's the first time that CMC-LSOPC NPs were constructed to enhance the stability of LSOPC during digestion and explain the mechanism by which CMC-LSOPC NPs inhibit the release of AGEs from G-CS in both stomach and intestine. This finding will present a novel approach for reducing AGEs during gastrointestinal digestion.

Fullerenols Mitigate Radiation-Induced Myocardial Injury

Radiation-induced heart disease is a serious side effect of radiation therapy that can lead to severe consequences. However, effective and safe methods for their prevention and treatment are presently lacking. This study reports the crucial function of fullerenols in protecting cardiomyocytes from radiation injury. First, fullerenols are synthesized using a simple base-catalyzed method. Next, the as-prepared fullerenols are applied as an effective free radical scavenger and broad-spectrum antioxidant to protect against X-ray-induced cardiomyocyte injury. Their ability to reduce apoptosis via the mitochondrial signaling pathway at the cellular level is then verified. Finally, it is observed in animal models that fullerenols accumulate in the heart and alleviate myocardial damage induced by X-rays. This study represents a timely and essential analysis of the prevention and treatment of radiological myocardial injury, providing new insights into the applications of fullerenols for therapeutic strategies.

AFM-IR for Nanoscale Chemical Characterization in Life Sciences: Recent Developments and Future Directions

Despite the ubiquitous absorption of mid-infrared (IR) radiation by virtually all molecules that belong to the major biomolecules groups (proteins, lipids, carbohydrates, nucleic acids), the application of conventional IR microscopy to the life sciences remained somewhat limited, due to the restrictions on spatial resolution imposed by the diffraction limit (in the order of several micrometers). This issue is addressed by AFM-IR, a scanning probe-based technique that allows for chemical analysis at the nanoscale with resolutions down to 10 nm and thus has the potential to contribute to the investigation of nano and microscale biological processes. In this perspective, in addition to a concise description of the working principles and operating modes of AFM-IR, we present and evaluate the latest key applications of AFM-IR to the life sciences, summarizing what the technique has to offer to this field. Furthermore, we discuss the most relevant current limitations and point out potential future developments and areas for further application for fruitful interdisciplinary collaboration.

Inverted transflection spectroscopy of live cells using metallic grating on elevated nanopillars

Water absorption of mid-infrared (MIR) radiation severely limits the options for vibrational spectroscopy of the analytes - including live biological cells - that must be probed in aqueous environments. While internal reflection elements, such as attenuated total reflection prisms and metasurfaces, partially overcome this limitation, such devices have their own limitations: high cost, incompatibility with standard cell culture workflows, limited spectral range, and small penetration depth into the analyte. In this work, we introduce an alternative live cell biosensing platform based on metallic nanogratings fabricated atop elevated dielectric pillars. For the MIR wavelengths that are significantly longer than the grating period, reflection-based spectroscopy enables broadband sensing of the analytes inside the trenches separating the dielectric pillars. Because the depth of the analyte twice-traversed by the MIR light excludes the highly absorbing thick water layer above the grating, we refer to the technique as Inverted Transflection Spectroscopy (ITS). We demonstrate the analytic power of ITS by measuring protein concentrations in solution. The ability of ITS to interrogate live cells that naturally wrap themselves around the grating is also exploited to characterize their adhesion kinetics.

Thermal, chemical and physical analysis of VDW.1Seal, Fill Root ST, and ADseal root canal sealers

This study aimed to evaluate the thermal, chemical, and physical properties of VDW.1Seal, Fill Root ST, and ADseal sealers. Thermal properties were analyzed using Thermogravimetric analysis (TGA) and Differential thermal analysis (DTA). Attenuated total reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR) analysis was performed as a complementary test to confirm TGA/DTA analysis. The chemical composition of the set sealer material was identified using an X-ray powder diffraction (XRD) system. Other physical properties of each sealer were investigated; ten specimens were used to measure the solubility (at 24 h and 28 days), and another ten specimens were used to assess pH changes and calcium ion release (after 7 and 14 days). Film thickness was done according to ISO 6876 specs. The data were analyzed using the two-way ANOVA test. Results showed that for all sealers, TGA analysis revealed a direct relationship between sealer mass loss and temperature rise. In addition, the decomposition of the tested sealers started at 145 °C, 135 °C and 91 °C for VDW.1Seal, ADseal sealer, and Fill Root ST, respectively. XRD analysis revealed a higher degree of crystallinity for VDW.1Seal and ADseal. ADseal showed the least solubility; VDW.1Seal exhibited the highest alkalinity, calcium ion release, and the lowest film thickness.

Advancement of non-destructive spectral measurements for the quality of major tropical fruits and vegetables: a review

The quality of tropical fruits and vegetables and the expanding global interest in eating healthy foods have resulted in the continual development of reliable, quick, and cost-effective quality assurance methods. The present review discusses the advancement of non-destructive spectral measurements for evaluating the quality of major tropical fruits and vegetables. Fourier transform infrared (FTIR), Near-infrared (NIR), Raman spectroscopy, and hyperspectral imaging (HSI) were used to monitor the external and internal parameters of papaya, pineapple, avocado, mango, and banana. The ability of HSI to detect both spectral and spatial dimensions proved its efficiency in measuring external qualities such as grading 516 bananas, and defects in 10 mangoes and 10 avocados with 98.45%, 97.95%, and 99.9%, respectively. All of the techniques effectively assessed internal characteristics such as total soluble solids (TSS), soluble solid content (SSC), and moisture content (MC), with the exception of NIR, which was found to have limited penetration depth for fruits and vegetables with thick rinds or skins, including avocado, pineapple, and banana. The appropriate selection of NIR optical geometry and wavelength range can help to improve the prediction accuracy of these crops. The advancement of spectral measurements combined with machine learning and deep learning technologies have increased the efficiency of estimating the six maturity stages of papaya fruit, from the unripe to the overripe stages, with F1 scores of up to 0.90 by feature concatenation of data developed by HSI and visible light. The presented findings in the technological advancements of non-destructive spectral measurements offer promising quality assurance for tropical fruits and vegetables.

Metasurface-Enhanced Infrared Spectroscopy: An Abundance of Materials and Functionalities

Infrared spectroscopy provides unique information on the composition and dynamics of biochemical systems by resolving the characteristic absorption fingerprints of their constituent molecules. Based on this inherent chemical specificity and the capability for label-free, noninvasive, and real-time detection, infrared spectroscopy approaches have unlocked a plethora of breakthrough applications for fields ranging from environmental monitoring and defense to chemical analysis and medical diagnostics. Nanophotonics has played a crucial role for pushing the sensitivity limits of traditional far-field spectroscopy by using resonant nanostructures to focus the incident light into nanoscale hot-spots of the electromagnetic field, greatly enhancing light-matter interaction. Metasurfaces composed of regular arrangements of such resonators further increase the design space for tailoring this nanoscale light control both spectrally and spatially, which has established them as an invaluable toolkit for surface-enhanced spectroscopy. Starting from the fundamental concepts of metasurface-enhanced infrared spectroscopy, a broad palette of resonator geometries, materials, and arrangements for realizing highly sensitive metadevices is showcased, with a special focus on emerging systems such as phononic and 2D van der Waals materials, and integration with waveguides for lab-on-a-chip devices. Furthermore, advanced sensor functionalities of metasurface-based infrared spectroscopy, including multiresonance, tunability, dielectrophoresis, live cell sensing, and machine-learning-aided analysis are highlighted.

Cuticles and postharvest life of tomato fruit: A rigid cover for aerial epidermis or a multifaceted guard of freshness?

Fruit cuticle is a specialized cell wall hydrophobic architecture covering the aerial surfaces of fruit, which forms the interface between the fruit and its environment. As a specialized seed-bearing organ, fruit utilize cuticles as physical barriers, water permeation regulator and resistance to pathogens, thus appealing extensive research interests for its potential values in developing postharvest freshness-keeping strategies. Here, we provide an overview for the composition and functions of fruit cuticles, mainly focusing on its functions in mechanical support, water permeability barrier and protection over pathogens, further introduce key mechanisms implicated in fruit cuticle biosynthesis. Moreover, currently available state-of-art techniques for examining compositional diversity and architecture of fruit are also compared.

Metasurface-enhanced infrared spectroscopy in multiwell format for real-time assaying of live cells

Fourier transform infrared (FTIR) spectroscopy is a popular technique for the analysis of biological samples, yet its application in characterizing live cells is limited due to the strong attenuation of mid-IR light in water. Special thin flow cells and attenuated total reflection (ATR) FTIR spectroscopy have been used to mitigate this problem, but these techniques are difficult to integrate into a standard cell culture workflow. In this work, we demonstrate that the use of a plasmonic metasurface fabricated on planar substrates and the probing of cellular IR spectra through metasurface-enhanced infrared spectroscopy (MEIRS) can be an effective technique to characterize the IR spectra of live cells in a high-throughput manner. Cells are cultured on metasurfaces integrated with multiwell cell culture chambers and are probed from the bottom using an inverted FTIR micro-spectrometer. To demonstrate the use of MEIRS as a cellular assay, cellular adhesion on metasurfaces with different surface coatings and cellular response to the activation of the protease-activated receptor (PAR) signaling pathway were characterized through the changes in cellular IR spectra.

The Potential Use of Near- and Mid-Infrared Spectroscopy in Kidney Diseases

Traditional renal biomarkers such as serum creatinine and albuminuria/proteinuria are rather insensitive since they change later in the course of the disease. In order to determine the extent and type of kidney injury, as well as to administer the proper therapy and enhance patient management, new techniques for the detection of deterioration of the kidney function are urgently needed. Infrared spectroscopy is a label-free and non-destructive technique having the potential to be a vital tool for quick and inexpensive routine clinical diagnosis of kidney disorders. The aim of this review is to provide an overview of near- and mid-infrared spectroscopy applications in patients with acute kidney injury and chronic kidney disease (e.g., diabetic nephropathy and glomerulonephritis).

Beyond Karl Fischer titration: a monolithic quantum cascade sensor for monitoring residual water concentration in solvents

Quality control of liquids is an important part of analytical chemistry. The gold standard for measuring residual water in organic solvents and pharmaceutical applications is Karl Fischer titration. It has a high sensitivity, selectivity and accuracy. The downsides are a time-consuming offline analysis, together with the need for toxic reagents producing waste, and it suffers from poor inter-laboratory reproducibility. In this work, we present a high-performance lab-on-a-chip sensor exploiting mid-IR spectroscopy for liquid sensing. It is operating at 6.1 μm wavelength and is suitable for robust and flexible real-time in situ analysis of the residual water concentration in isopropyl alcohol. This is demonstrated in two experiments. A custom-made 60 μL flow cell is employed to measure only minute amounts of analyte in an inline configuration. In a second approach, the whole sensor is immersed into the analyte to demonstrate sensitive and rapid in situ operation on the millisecond time scale. This is confirmed by the ability for time resolved single water-droplet monitoring, while they are mixed into the liquid sample. We obtain a limit of detection between 120 ppm and 150 ppm with a concentration coverage spanning three orders of magnitude from 1.2 × 10^-2%_vol to 25%_vol for the flow cell and 1.5 × 10^-2%_vol to 19%_vol in the in situ configuration, respectively.

Accurate identification of traumatic lung injury (TLI) by ATR-FTIR spectroscopy combined with chemometrics

Traumatic lung injury (TLI), which is a common mechanical injury, is receiving increasing attention because of its serious hazards. In forensic practices, accurately identifying TLI is of great importance for investigations and case trials. The main goal of this research was to identify TLI utilizing attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy in combination with chemometrics. The macroscopic appearance of lung tissue showed that identifying TLI in lung tissue at the decomposition stage is not feasible by only visualization, and significant pulmonary hypostasis was observed in the lungs regardless of whether the lung tissue was injured. Average spectra and principal component analysis (PCA) suggested that the biochemical difference between injured lung tissue samples from the TLI group and noninjured lung tissue samples from the negative control group was mainly attributed to the different structures and contents of proteins. Partial least squares discriminant analysis (PLS-DA) was then utilized to identify TLI with an accuracy of 96.4% and 98.6% based on the training set and the test set, respectively. Next, we focused on samples that were misclassified in the model and proposed that the misclassification could be caused by the pulmonary hypostasis effect. Therefore, two additional PCA and PLS-DA models were created to identify the pulmonary hypostatic areas between the TLI group and the negative control group and the nonpulmonary hypostatic areas between the TLI group and the negative control group. The PCA results indicated that the biochemical difference between the two groups was still associated with proteins, and the two PLS-DA models achieved 100% accuracy based on both the training and test sets. This result indicated that when pulmonary hypostasis was considered and the lung tissue was divided into pulmonary hypostatic areas and nonpulmonary hypostatic areas for separate comparisons, TLI identification was achieved with a greater accuracy than that obtained when the two areas were combined. This research confirms that the combined application of ATR-FTIR spectroscopy and chemometrics can be utilized to accurately identify TLI.

ATR-FTIR spectrum analysis of plasma samples for rapid identification of recovered COVID-19 individuals

The development of fast, cheap and reliable methods to determine seroconversion against infectious agents is of great practical importance. In the context of the COVID-19 pandemic, an important issue is to study the rate of formation of the immune layer in the population of different regions, as well as the study of the formation of post-vaccination immunity in individuals after vaccination. Currently, the main method for this kind of research is enzyme immunoassay (ELISA, enzyme-linked immunosorbent assay). This technique is sufficiently sensitive and specific, but it requires significant time and material costs. We investigated the applicability of attenuated total reflection (ATR) Fourier transform infrared (FTIR) spectroscopy associated with machine learning in blood plasma to detect seroconversion against SARS-CoV-2. The study included samples of 60 patients. Clear spectral differences in plasma samples from recovered COVID-19 patients and conditionally healthy donors were identified using multivariate and statistical analysis. The results showed that ATR-FTIR spectroscopy, combined with principal components analysis (PCA) and linear discriminant analysis (LDA) or artificial neural network (ANN), made it possible to efficiently identify specimens from recovered COVID-19 patients. We built classification models based on PCA associated with LDA and ANN. Our analysis led to 87% accuracy for PCA-LDA model and 91% accuracy for ANN, respectively. Based on this proof-of-concept study, we believe this method could offer a simple, label-free, cost-effective tool for detecting seroconversion against SARS-CoV-2. This approach could be used as an alternative to ELISA.

Forensic Discrimination of Drug Powder Based on Drug Mixing Condition Determined Using Micro Fourier Transform Infrared Spectroscopy

The quantitative evaluation of the drug mixing condition was conducted for application in the forensic discrimination of drug powders using micro Fourier transform infrared (FT-IR) spectroscopy. Bromhexine hydrochloride (BHCl) and p-hydroxybenzoic acid (PHBA) were used as the simulated drug and additive, respectively. Equal masses of two chemicals were (1) simply mixed, (2) homogenized using agate mortar, or (3) dissolved in methanol and dried, and then (4) homogenized using agate mortar. The mixed powders dispersed on BaF₂ plates were subjected to mapping analysis of micro FT-IR spectroscopy using synchrotron radiation (SR) or globar light in transmission mode with aperture sizes of 2.5 x 2.5 and 10 x 10μm², and x-y scanning steps of 2.5 and 10 μm, respectively. The areas of the vibration bands specific to BHCl (C-N bending) and PHBA (C=O stretching) were converted to the molar contents (C_BHCl, C_PHBA), and the relative content ratio (RCR: C_PHBA/[C_BHCl + C_PHBA]) was used as one mixing parameter. The resulting two-dimensional distribution map provided the relative spatial localizations of the two species, and frequency histograms with a horizontal axis of RCR were plotted to evaluate the RCR distribution. The percentage frequency of the extreme value in which RCR was 0 or 1 (%EV) was used as one mixing index. After excluding the extreme values, the coefficient of variation (CV) of the RCR distribution was used as another mixing index. The differentiation among four mixing modes could be evaluated from the standpoint of %EV and CV, and the discrimination capacity by SR instrument was superior to that by globe light instrument.

Infrared spectroscopy and flow cytometry studies on the apoptotic effect of nano-chrysin in HeLa cells

Mapping the structural changes in membrane lipids, proteins, polysaccharides and nucleic acids has opened new channels for understanding the mode of action of anticancer natural products. Earlier, we synthesized chrysin nanoparticles (NChr) with good bioavailability, and characterized its size, surface charge, entrapment efficiency, and drug release pattern using PLGA polymer. NChr induced concentration dependent cytotoxicity in HeLa cells with an IC₅₀ of 61.54 ± 1.2 µM in comparison with free chrysin with IC₅₀ of 86.51 ± 2.9 µM. Since nanoparticles interact dynamically with cell membranes, organelles, proteins and DNA, it is necessary to understand the interplay of nanodrug induced macromolecular changes in cancer cells. In this work, we obtained signatures of NChr-induced biochemical changes in HeLa cells by Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy technique coupled with flow cytometry. NChr induced cell membrane disruption, G1 phase cell cycle arrest, and increased externalization of phosphatidylserine leading to apoptosis indicating the biochemical perturbations in membrane lipids and DNA of HeLa cells in comparison with untreated cells. The 1300-1000 cm^-1 spectral region indicated NChr interaction with the ribose sugar backbone and DNA denaturation. Spectral range 1800-1400 cm^-1 indicated a concentration dependent decrease in α helical and β sheet structures which may lead to protein degradation during apoptosis. The spectral range 3000-2800 cm^-1 indicated the lipid peroxidation in response to NChr treatment. This is the first study describing the bio-macromolecular changes induced by a nano encapsulated drug and can pave the way to investigate unconventional modes of action for bioactive formulations.

Effect of Antibiotic Amphotericin B Combinations with Selected 1,3,4-Thiadiazole Derivatives on RPTECs in an In Vitro Model

4-(5-methyl-1,3,4-thiadiazole-2-yl) benzene-1,3-diol (C1) and 4-[5-(naphthalen-1-ylmethyl)-1,3,4-thiadiazol-2-yl] benzene1,3-diol (NTBD) are representative derivatives of the thiadiazole group, with a high antimycotic potential and minimal toxicity against normal human fibroblast cells. The present study has proved its ability to synergize with the antifungal activity of AmB. The aim of this work was to evaluate the cytotoxic effects of C1 or NTBD, alone or in combination with AmB, on human renal proximal tubule epithelial cells (RPTECs) in vitro. Cell viability was assessed with the MTT assay. Flow cytometry and spectrofluorimetric techniques were used to assess the type of cell death and production of reactive oxygen species (ROS), respectively. The ELISA assay was performed to measure the caspase-2, -3, and -9 activity. ATR-FTIR spectroscopy was used to evaluate biomolecular changes in RPTECs induced by the tested formulas. The combinations of C1/NTBD and AmB did not exert a strong inhibitory effect on the viability/growth of kidney cells, as evidenced by the negligible changes in the apoptotic/necrotic rate and caspase activity, compared to the control cells. Both NTBD and C1 displayed stronger anti-oxidant activity when combined with AmB. The relatively low nephrotoxicity of the thiadiazole derivative combinations and the protective activity against AmB-induced oxidative stress may indicate their potential use in the therapy of fungal infections.

Investigation of bactericidal effect of a mid-infrared free electron laser on Escherichia coli

The rapid increase in the number of bacteria that are resistant to many commonly used antimicrobial agents and their global spread have become a major problem worldwide. In particular, for periodontal disease, which is a localized infection, there is a growing need for treatment methods that do not primarily involve antimicrobial agents, and antimicrobial photodynamic therapy (aPDT) is attracting attention. In this study, the bactericidal effects of a mid-infrared free electron laser (MIR-FEL) on E. coli were investigated as a basic study to examine the applicability of MIR-FELs, which can selectively excite molecular vibrations due to their wavelength tunability, to aPDT. The optimal irradiation wavelengths to be examined in this study were determined from the infrared spectrum of the bacteria, which was obtained using Fourier transform infrared spectroscopy. Five irradiation wavelengths (6.62, 6.88, 7.14, 8.09 and 9.26 µm) were selected from the FT-IR spectrum, and we found that the bactericidal effects at a wavelength of 6.62 µm were markedly stronger than those observed at the other wavelengths. At this wavelength corresponding to the Amide II band, the bacterial survival rate decreased significantly as the irradiation time increased. On the contrary, irradiation of a neodymium-doped yttrium aluminum garnet (Nd: YAG) laser at 1.06 µm exhibited no distinct bactericidal effect. No morphological changes were observed after MIR-FEL irradiation, suggesting that a bacterial organelle molecule may be the target of MIR-FEL irradiation, but the exact target was not identified. Furthermore, the temperature change induced in the culture medium by the laser irradiation was ± 1.5 °C at room temperature. These results suggest that the bactericidal effects of MIR-FEL are derived from photochemical reactions involving infrared photons, since E. coli is usually killed by heating it to 75 °C for 1 min or longer.

Machine Learning Enhanced Optical Spectroscopy for Disease Detection

Optical spectroscopy plays an important role in disease detection. Improving the sensitivity and specificity of spectral detection has great importance in the development of accurate diagnosis. The development of artificial intelligence technology provides a great opportunity to improve the detection accuracy through machine learning methods. In this Perspective, we focus on the combination of machine learning methods with the optical spectroscopy methods widely used for disease detection, including absorbance, fluorescence, scattering, FTIR, terahertz, etc. By comparing the spectral analysis with different machine learning methods, we illustrate that the support vector machine and convolutional neural network are most effective, which have potential to further improve the classification accuracy to distinguish disease subtypes if these machine learning methods are used. This Perspective broadens the scope of optical spectroscopy enhanced by machine learning and will be useful for the development of disease detection.

Infrared Spectroscopy–Quo Vadis?

Given the exquisite capability of direct, non-destructive label-free sensing of molecular transitions, IR spectroscopy has become a ubiquitous and versatile analytical tool. IR application scenarios range from industrial manufacturing processes, surveillance tasks and environmental monitoring to elaborate evaluation of (bio)medical samples. Given recent developments in associated fields, IR spectroscopic devices increasingly evolve into reliable and robust tools for quality control purposes, for rapid analysis within at-line, in-line or on-line processes, and even for bed-side monitoring of patient health indicators. With the opportunity to guide light at or within dedicated optical structures, remote sensing as well as high-throughput sensing scenarios are being addressed by appropriate IR methodologies. In the present focused article, selected perspectives on future directions for IR spectroscopic tools and their applications are discussed. These visions are accompanied by a short introduction to the historic development, current trends, and emerging technological opportunities guiding the future path IR spectroscopy may take. Highlighted state-of-the art implementations along with novel concepts enhancing the performance of IR sensors are presented together with cutting-edge developments in related fields that drive IR spectroscopy forward in its role as a versatile analytical technology with a bright past and an even brighter future.

Characterizing biological macromolecules with attenuated total reflectance-Fourier transform infrared spectroscopy provides hands-on spectroscopy experiences for undergraduates

Infrared (IR) spectra of biologically derived materials display distinct absorption bands correlating to individual macromolecules: protein, polysaccharide, lipid, and nucleic acids. A series of experiments aimed at teaching qualitative bioorganic spectroscopy using attenuated total reflectance (ATR) Fourier transform infrared (IR) with biological polymers as samples is proposed. Labs targeting 1st and 4th year undergraduate students at St. Francis College are being developed. During 2014 ➔ 2017, an integrated biology/chemistry exercise featuring elementary spectroscopy as an addition to an existing lab on light microscopy was administered to three sections of a 1st year general biology course. Students were taught the concept of a spectral fingerprint and to identify carbohydrate and protein based materials by looking for key vibrational bands. The success of that effort as determined by the results of an assessment quiz became the motivation for developing an advanced 4th year exercise involving four macromolecules. In a trial lab (Spring 2019) students gathered reference spectra from materials homogeneous in a single biopolymer followed by spectra of whole tissues which they were expected to fully characterize. Assessment data suggest that 1st year students benefited most from the experience. A detailed discussion of reference and sample spectra (as obtained by students) and relevant bond vibrations along with suggestions for instructors are presented.

Probing the Drug Dynamics of Chemotherapeutics Using Metasurface-Enhanced Infrared Reflection Spectroscopy of Live Cells

Infrared spectroscopy has drawn considerable interest in biological applications, but the measurement of live cells is impeded by the attenuation of infrared light in water. Metasurface-enhanced infrared reflection spectroscopy (MEIRS) had been shown to mitigate the problem, enhance the cellular infrared signal through surface-enhanced infrared absorption, and encode the cellular vibrational signatures in the reflectance spectrum at the same time. In this study, we used MEIRS to study the dynamic response of live cancer cells to a newly developed chemotherapeutic metal complex with distinct modes of action (MoAs): tricarbonyl rhenium isonitrile polypyridyl (TRIP). MEIRS measurements demonstrated that administering TRIP resulted in long-term (several hours) reduction in protein, lipid, and overall refractive index signals, and in short-term (tens of minutes) increase in these signals, consistent with the induction of endoplasmic reticulum stress. The unique tricarbonyl IR signature of TRIP in the bioorthogonal spectral window was monitored in real time, and was used as an infrared tag to detect the precise drug delivery time that was shown to be closely correlated with the onset of the phenotypic response. These results demonstrate that MEIRS is an effective label-free real-time cellular assay capable of detecting and interpreting the early phenotypic responses of cells to IR-tagged chemotherapeutics.

Recent advances and applications to cultural heritage using ATR-FTIR spectroscopy and ATR-FTIR spectroscopic imaging

Scientific investigation of cultural heritage objects plays a vital role in a responsible modern approach to conservation and archaeology. Recent advances in spectroscopy, such as the development of Attenuated Total Reflection Fourier Transform Infrared (ATR-FTIR) spectroscopy and ATR-FTIR spectroscopic imaging, have opened up a window of opportunities for characterisation of materials in artefacts and collections from museums. This review summarises some of the recent advances and applications of these ATR-FTIR spectroscopic analytical techniques in the area of cultural heritage studies, including examples of cross-sections of oil paintings, paper, textiles, plastic objects, potteries, glasses and mineral artefacts. Two of the major advantages of ATR mode measurements are minimal or no requirements for sample preparation and its provision for high lateral spatial resolution. In addition to conventional single point detection, two-dimensional mapping and imaging is especially beneficial for chemical visualisation of multi-layered structure cultural objects. This review also explores the implications of these advantages as well as some limitations and provides a brief outlook for the possible future developments in this area.

Non-destructive molecular FTIR spectromicroscopy for real time assessment of redox metallodrugs

Recent emergence of FTIR spectromicroscopy (micro-FTIR) as a dynamic spectroscopy for imaging to study biological chemistry has opened new possibilities for investigating in situ drug release, redox chemistry effects on biological molecules, DNA and drug interactions, membrane dynamics, and redox reactions with proteins at the single cell level. Micro-FTIR applied to metallodrugs has been playing an important role since the last decade because of its great potential to achieve more robust and controlled pharmacological effects against several diseases, including cancer. An important aspect in the development of these drugs is to understand their cellular properties, such as uptake, accumulation, activity, and toxicity. In this review, we present the potential application of micro-FTIR and its importance for studying metal-based drugs, highlighting the perspectives of chemistry of living cells. We also emphasise bioimaging, which is of high importance to localize the cellular processes, for a proper understanding of the mechanism of action.

Analysis and comparison of protein secondary structures in the rachis of avian flight feathers

Avians have evolved many different modes of flying as well as various types of feathers for adapting to varied environments. However, the protein content and ratio of protein secondary structures (PSSs) in mature flight feathers are less understood. Further research is needed to understand the proportions of PSSs in feather shafts adapted to various flight modes in different avian species. Flight feathers were analyzed in chicken, mallard, sacred ibis, crested goshawk, collared scops owl, budgie, and zebra finch to investigate the PSSs that have evolved in the feather cortex and medulla by using nondestructive attenuated total reflection Fourier transform infrared spectroscopy (ATR-FTIR). In addition, synchrotron radiation-based, Fourier transform infrared microspectroscopy (SR-FTIRM) was utilized to measure and analyze cross-sections of the feather shafts of seven bird species at a high lateral resolution to resolve the composition of proteins distributed within the sampled area of interest. In this study, significant amounts of α-keratin and collagen components were observed in flight feather shafts, suggesting that these proteins play significant roles in the mechanical strength of flight feathers. This investigation increases our understanding of adaptations to flight by elucidating the structural and mechanistic basis of the feather composition.

Attenuated Total Reflection (ATR) Micro-Fourier Transform Infrared (Micro-FT-IR) Spectroscopy to Enhance Repeatability and Reproducibility of Spectra Derived from Single Specimen Organic-Walled Dinoflagellate Cysts

The chemical composition of recent and fossil organic-walled dinoflagellate cyst walls and its diversity is poorly understood and analyses on single microscopic specimens are rare. A series of infrared spectroscopic experiments resulted in the proposition of a standardized attenuated total reflection micro-Fourier transform infrared-based method that allows the collection of robust data sets consisting of spectra from individual dinocysts. These data sets are largely devoid of nonchemical artifacts inherent to other infrared spectrochemical methods, which have typically been used to study similar specimens in the past. The influence of sample preparation, specimen morphology and size and spectral data processing steps is also assessed within this methodological framework. As a result, several guidelines are proposed which facilitate the collection and qualitative interpretation of highly reproducible and repeatable spectrochemical data. These, in turn, pave the way for a systematic exploration of dinocyst chemistry and its assessment as a chemotaxonomical tool or proxy.

Nondestructive assessment of tissue engineered cartilage based on biochemical markers in cell culture media: application of attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy

ATR spectral data obtained from cell culture medium discards can be used to assess glucose and lactate content, which are shown here to be a surrogate for matrix development in tissue engineered cartilage.

One-step zwitterionization and quaternization of thick PDMAEMA layer grafted through subsurface-initiated ATRP for robust antibiofouling and antibacterial coating on PDMS

In this work, we demonstrate the grafting of thick poly((2-dimethylamino) ethyl methacrylate) (PDMAEMA) layer on PDMS via subsurface-initiated atom transfer radical polymerization (SSI-ATRP). The self-migration of DMAEMA monomers into the subsurface of PDMS is proven to be the dominant factor for the success of SSI-ATRP. The as-prepared thick microscale graft layer on PDMS shows much better abrasion resistance than nanoscale graft layer obtained by conventional surface-initiated atom transfer radical polymerization (SI-ATRP) under identical condition. Taking advantage of the tertiary amines of PDMAEMA, the simultaneous zwitterionization and quaternization of the PDMAEMA thick layer is realized through a facile one-step process. The effect of zwitterionization and quaternization degree on the antibiofouling and antibacterial properties is investigated. The results show that a relatively high zwitterionization degree (75 mol%) and a low quaternization degree (25 mol%) exhibit a good well-balanced effect on both fouling repellence and bactericidal activity. This work may lead to the development of robust bifunctional antibiofouling and antibacterial surfaces via SSI-ATRP strategy.

Addressable graphene encapsulation of wet specimens on a chip for optical, electron, infrared and X-ray based spectromicroscopy studies

Label-free spectromicroscopy methods offer the capability to examine complex cellular phenomena. Electron and X-ray based spectromicroscopy methods, though powerful, have been hard to implement with hydrated objects due to the vacuum incompatibility of the samples and due to the parasitic signals from (or drastic attenuation by) the liquid matrix surrounding the biological object of interest. Similarly, for many techniques that operate at ambient pressure, such as Fourier transform infrared spectromicroscopy (FTIRM), the aqueous environment imposes severe limitations due to the strong absorption of liquid water in the infrared regime. Here we propose a microfabricated multi-compartmental and reusable hydrated sample platform suitable for use with several analytical techniques, which employs the conformal encapsulation of biological specimens by a few layers of atomically thin graphene. Such an electron, X-ray, and infrared transparent, molecularly impermeable and mechanically robust enclosure preserves the hydrated environment around the object for a sufficient time to allow in situ examination of hydrated bio-objects with techniques operating under both ambient and high vacuum conditions. An additional hydration source, provided by hydrogel pads lithographically patterned in the liquid state near/around the specimen and co-encapsulated, has been added to further extend the hydration lifetime. Note that the in-liquid lithographic electron beam-induced gelation procedure allows for addressable capture and immobilization of the biological cells from the solution. Scanning electron microscopy and optical fluorescence microscopy, as well as synchrotron radiation based FTIR and X-ray fluorescence microscopy, have been used to test the applicability of the platform and for its validation with yeast, A549 human carcinoma lung cells and micropatterned gels as biological object phantoms.

Cell wall polymer distribution in bamboo visualized with in situ imaging FTIR

To better understand the high recalcitrance of bamboo during bioconversion, the fine spatial distribution of polymers in bamboo was studied with Imaging FTIR microscopy under both transmission and ATR modes, combined with PCA data processing. The results demonstrated that lignin, xylan and hydroxycinnamic acid (HCA) were more concentrated in the fibers near the xylem conduit, while cellulose was evenly distributed across the whole fiber sheath. PCA processing produced a clear separation between bamboo fibers and parenchyma cells, indicating that the parenchyma cells contains more pectin and HCA than fibers. It also demonstrated that cellulose, xylan and S-lignin were concentrated most heavily in bamboo fiber secondary cell walls, while G-lignin, pectin and HCA were found more in the compound middle lamella. The revealed information regarding polymer distribution is of great significance for better understanding of the inherent design mechanism of plant cell wall and its efficient utilization.

Regional differences in clonal Japanese knotweed revealed by chemometrics-linked attenuated total reflection Fourier-transform infrared spectroscopy

BACKGROUND

Japanese knotweed (R. japonica var japonica) is one of the world's 100 worst invasive species, causing crop losses, damage to infrastructure, and erosion of ecosystem services. In the UK, this species is an all-female clone, which spreads by vegetative reproduction. Despite this genetic continuity, Japanese knotweed can colonise a wide variety of environmental habitats. However, little is known about the phenotypic plasticity responsible for the ability of Japanese knotweed to invade and thrive in such diverse habitats. We have used attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy, in which the spectral fingerprint generated allows subtle differences in composition to be clearly visualized, to examine regional differences in clonal Japanese knotweed.

RESULTS

We have shown distinct differences in the spectral fingerprint region (1800-900 cm^- 1) of Japanese knotweed from three different regions in the UK that were sufficient to successfully identify plants from different geographical regions with high accuracy using support vector machine (SVM) chemometrics.

CONCLUSIONS

These differences were not correlated with environmental variations between regions, raising the possibility that epigenetic modifications may contribute to the phenotypic plasticity responsible for the ability of R. japonica to invade and thrive in such diverse habitats.

Scanning Aperture Approach for Spatially Selective ATR-FTIR Spectroscopy: Application to Microfluidics

We present a novel spectroscopy accessory that can easily convert any Fourier transform infrared (FTIR) spectrometer into a fully automated mapping and assaying system. The accessory uses a multiridge attenuated total reflection (ATR) wafer as the sensing element coupled with a moving aperture that is used to select the regions of interest on the wafer. In this demonstration, the accessory is combined with a series of parallel micropatterned channels, which are positioned co-linear with the light-coupling ridges on the opposite side of the ATR wafer. The ATR spectroscopy microfluidic assay accessory (ASMAA) was used in continuous mapping mode to scan perpendicular to the ATR ridges, revealing complex but repeatable oscillations in the spectral intensities. To understand this behavior, the light path through the optical components was simulated with consideration of the aperture position, ridge-to-channel alignment, and excitation beam profile. With this approach, the simulation reproduced the experimental mapping results and provided evidence that the measurement position and area changed with the aperture position. To demonstrate the assay mode, we obtained spectra along the centerline of individual microchannels and determined noise baselines and limits of detection.

Securely anchored Prussian blue nanocrystals on the surface of porous PAAm sphere for high and selective cesium removal

Prussian blue (PB) has been well known as a pigment crystal to selectively sequestrate the radioactive cesium ion released from aqueous solutions owing to PB cage size similar to the cesium ion. Because the small size of PB is hard to deal with, the adsorbents containing PB have been prepared in the form of composites causing low sequestration efficiency of cesium. In this study, securely anchored PB nanocrystals on the surface of millimeter-sized porous polyacrylamide (PAAm) spheres (PB@PAAm) have been prepared by the crystallization of PB on the Fe³⁺ adsorbed PAAm. The securely anchored PB nanocrystals have been demonstrated to be selective and efficient adsorbents for sequestration of the radioactive cesium. The well-interconnected-spherical pores and millimeter-sized diameter of the PB@PAAm adsorbents facilitated permeation of Cs⁺ into the adsorbent and ease of handling respectively. Especially the well-interconnected-spherical pores allowed that PB@PAAm showed 90% of its maximum Cs⁺ adsorption capacity within 30 min. The PB@PAAm showed an outstanding Cs⁺ capture ability of 374 mg/g, high removal efficiency of 85% even at low concentration of Cs⁺ (10 ng/L), and superior selectivity of Cs⁺ against interference ions of Na⁺, K⁺, Mg²⁺, and Ca²⁺.

Determination of Klebsiella pneumoniae Susceptibility to Antibiotics Using Infrared Microscopy

Klebsiella pneumoniae (K. pneumoniae) is one of the most aggressive multidrug-resistant bacteria associated with human infections, resulting in high mortality and morbidity. We obtained 1190 K. pneumoniae isolates from different patients with urinary tract infections. The isolates were measured to determine their susceptibility regarding nine specific antibiotics. This study's primary goal is to evaluate the potential of infrared spectroscopy in tandem with machine learning to assess the susceptibility of K. pneumoniae within approximately 20 min following the first culture. Our results confirm that it was possible to classify the isolates into sensitive and resistant with a success rate higher than 80% for the tested antibiotics. These results prove the promising potential of infrared spectroscopy as a powerful method for a K. pneumoniae susceptibility test.

Monitoring the effects of chemical stimuli on live cells with metasurface-enhanced infrared reflection spectroscopy

Infrared spectroscopy has found wide applications in the analysis of biological materials. A more recent development is the use of engineered nanostructures - plasmonic metasurfaces - as substrates for metasurface-enhanced infrared reflection spectroscopy (MEIRS). Here, we demonstrate that strong field enhancement from plasmonic metasurfaces enables the use of MEIRS as a highly informative analytic technique for real-time monitoring of cells. By exposing live cells cultured on a plasmonic metasurface to chemical compounds, we show that MEIRS can be used as a label-free phenotypic assay for detecting multiple cellular responses to external stimuli: changes in cell morphology, adhesion, and lipid composition of the cellular membrane, as well as intracellular signaling. Using a focal plane array detection system, we show that MEIRS also enables spectro-chemical imaging at the single-cell level. The described metasurface-based all-optical sensor opens the way to a scalable, high-throughput spectroscopic assay for live cells.

Fatty Acids and Their Metal Salts: A Review of Their Infrared Spectra in Light of Their Presence in Cultural Heritage

In a cultural heritage context, fatty acids are usually found as breakdown products of lipid-containing organic remains in archaeological findings, binders in aged oil paintings, and additives in modern art-related materials. They may further interact with the ionic environment transforming into metal soaps, a process that has been recognized as a threat in aged paintings but has received less attention in archaeological objects. The investigation of the above related categories of materials with infrared spectroscopy can provide an overall picture of the organic components' identity and demonstrate their condition and prehistory. The capability of investigating and distinguishing fatty acids and their metal soaps through their rich infrared features, such as the acidic carbonyl, the carboxylate shifts, the variable splits of alkyl chain stretching, bending, twisting, wagging, and rocking vibrations, as well as the hydroxyl peak envelopes and acid dimer bands, allows for their direct detailed characterization. This paper reviews the infrared spectra of selected saturated fatty monoacids and diacids, and their corresponding sodium, calcium, and zinc salts and, supported by newly recorded data, highlights the significance of their spectroscopic features.

"Wax On, Wax Off": In Vivo Imaging of Plant Physiology and Disease with Fourier Transform Infrared Reflectance Microspectroscopy

Analysis of the epicuticular wax layer on the surface of plant leaves can provide a unique window into plant physiology and responses to environmental stimuli. Well-established analytical methodologies can quantify epicuticular wax composition, yet few methods are capable of imaging wax distribution in situ or in vivo. Here, the first report of Fourier transform infrared (FTIR) reflectance spectroscopic imaging as a non-destructive, in situ, method to investigate variation in epicuticular wax distribution at 25 µm spatial resolution is presented. The authors demonstrate in vivo imaging of alterations in epicuticular waxes during leaf development and in situ imaging during plant disease or exposure to environmental stressors. It is envisaged that this new analytical capability will enable in vivo studies of plants to provide insights into how the physiology of plants and crops respond to environmental stresses such as disease, soil contamination, drought, soil acidity, and climate change.

Design Considerations for Discrete Frequency Infrared Microscopy Systems

Discrete frequency infrared chemical imaging is transforming the practice of microspectroscopy by enabling a diversity of instrumentation and new measurement capabilities. While a variety of hardware implementations have been realized, design considerations that are unique to infrared (IR) microscopes have not yet been compiled in literature. Here, we describe the evolution of IR microscopes, provide rationales for design choices, and catalog some major considerations for each of the optical components in an imaging system. We analyze design choices that use these components to optimize performance, under their particular constraints, while providing illustrative examples. We then summarize a framework to assess the factors that determine an instrument's performance mathematically. Finally, we provide a validation approach by enumerating performance metrics that can be used to evaluate the capabilities of imaging systems or suitability for specific intended applications. Together, the presented concepts and examples should aid in understanding available instrument configurations, while guiding innovations in design of the next generation of IR chemical imaging spectrometers.

ATR-FTIR spectroscopy probing of structural alterations in the cellular membrane of abscopal liver cells

In this study, we utilize ATR-FTIR spectroscopy to investigate the structural damages in the cell membrane lipids and proteins as a result of the oxidative stress in abscopal liver tissue of rats either whole-body, cranially or lower limb irradiated as compared with sham-irradiated group. We also question whether the original irradiation region would influence the induction of the abscopal effect. The data present compelling evidence that an abscopal effect was induced in the liver tissue following both cranial and lower limb irradiations, marked by damage in the membrane-associated lipids and proteins. Lipid damage manifestation is evident by; 1) decrease in the lipid/protein ratio. 2) Degradation of lipid as marked by the decrease in the area ratio CH ₂ asymmetric/CH ₃ asymmetric stretching bands. 3) Increase in the carbonyl content evident by the increase in the band area ratio of carbonyl ester/lipid. 4) Increase in the degree of methylation as indicated by the increase in the band area ratio of CH₃/lipid. 5) Disorder in the phospholipid acyl chains marked by the shift in the CH₂ asymmetric stretching and olefinic HCCH absorption bands. Protein damage was indicated by 1) Shifts in the position of amide I and amide II bands. 2) Decrease in the area ratio amide I/amide II. 3) Broadening in amide II band. Our data strongly suggest similar induction of the abscopal effect as a result of either cranial or lower limb irradiation, which means that the original irradiation region did not influence the induced abscopal effect in the examined system.

Multi-modal image sharpening in fourier transform infrared (FTIR) microscopy

Mid-infrared Spectroscopic Imaging (MIRSI) provides spatially-resolved molecular specificity by measuring wavelength-dependent mid-infrared absorbance. Infrared microscopes use large numerical aperture objectives to obtain high-resolution images of heterogeneous samples. However, the optical resolution is fundamentally diffraction-limited, and therefore wavelength-dependent. This significantly limits resolution in infrared microscopy, which relies on long wavelengths (2.5 μm to 12.5 μm) for molecular specificity. The resolution is particularly restrictive in biomedical and materials applications, where molecular information is encoded in the fingerprint region (6 μm to 12 μm), limiting the maximum resolving power to between 3 μm and 6 μm. We present an unsupervised curvelet-based image fusion method that overcomes limitations in spatial resolution by augmenting infrared images with label-free visible microscopy. We demonstrate the effectiveness of this approach by fusing images of breast and ovarian tumor biopsies acquired using both infrared and dark-field microscopy. The proposed fusion algorithm generates a hyperspectral dataset that has both high spatial resolution and good molecular contrast. We validate this technique using multiple standard approaches and through comparisons to super-resolved experimentally measured photothermal spectroscopic images. We also propose a novel comparison method based on tissue classification accuracy.

The Progress of Label-Free Optical Imaging in Alzheimer's Disease Screening and Diagnosis

As the major neurodegenerative disease of dementia, Alzheimer's disease (AD) has caused an enormous social and economic burden on society. Currently, AD has neither clear pathogenesis nor effective treatments. Positron emission tomography (PET) and magnetic resonance imaging (MRI) have been verified as potential tools for diagnosing and monitoring Alzheimer's disease. However, the high costs, low spatial resolution, and long acquisition time limit their broad clinical utilization. The gold standard of AD diagnosis routinely used in research is imaging AD biomarkers with dyes or other reagents, which are unsuitable for in vivo studies owing to their potential toxicity and prolonged and costly process of the U.S. Food and Drug Administration (FDA) approval for human use. Furthermore, these exogenous reagents might bring unwarranted interference to mechanistic studies, causing unreliable results. Several label-free optical imaging techniques, such as infrared spectroscopic imaging (IRSI), Raman spectroscopic imaging (RSI), optical coherence tomography (OCT), autofluorescence imaging (AFI), optical harmonic generation imaging (OHGI), etc., have been developed to circumvent this issue and made it possible to offer an accurate and detailed analysis of AD biomarkers. In this review, we present the emerging label-free optical imaging techniques and their applications in AD, along with their potential and challenges in AD diagnosis.

Critical angle reflection imaging for quantification of molecular interactions on glass surface

Quantification of molecular interactions on a surface is typically achieved via label-free techniques such as surface plasmon resonance (SPR). The sensitivity of SPR originates from the characteristic that the SPR angle is sensitive to the surface refractive index change. Analogously, in another interfacial optical phenomenon, total internal reflection, the critical angle is also refractive index dependent. Therefore, surface refractive index change can also be quantified by measuring the reflectivity near the critical angle. Based on this concept, we develop a method called critical angle reflection (CAR) imaging to quantify molecular interactions on glass surface. CAR imaging can be performed on SPR imaging setups. Through a side-by-side comparison, we show that CAR is capable of most molecular interaction measurements that SPR performs, including proteins, nucleic acids and cell-based detections. In addition, we show that CAR can detect small molecule bindings and intracellular signals beyond SPR sensing range. CAR exhibits several distinct characteristics, including tunable sensitivity and dynamic range, deeper vertical sensing range, fluorescence compatibility, broader wavelength and polarization of light selection, and glass surface chemistry. We anticipate CAR can expand SPR′s capability in small molecule detection, whole cell-based detection, simultaneous fluorescence imaging, and broader conjugation chemistry.

Here, the authors present a method for quantifying molecular interactions on a glass surface, based on measuring surface refractive index changes via the reflectivity near the critical angle. They demonstrate tunable sensitivity and dynamic range, deep vertical sensing range, also for intracellular signals.