Infrared-attenuated Reflection Spectroscopy Research Articles

Novel thermal synthesis of ternary Cu-CuO-Cu2O nanospheres supported on reduced graphene oxide for the sensitive non-enzymatic electrochemical detection of pyruvic acid as a cancer biomarker

In this present research, we have developed a novel electrochemical sensing platform based on ternary Cu-CuO-Cu2O nanospheres supported on reduced graphene oxide (rGO-Cu-CuO-Cu2O) for the practical non-enzymatic detection of Pyruvic acid (PA) as a metabolism-based cancer biomarker. The facile route of this synthesis was mainly based on two steps, including the physical adsorption of a copper complex into reduced graphene oxide followed by thermal calcination at 700°C. The characterization of the rGO-Cu-CuO-Cu2O nanocomposite was performed using X-ray Diffraction (XRD), attenuated reflectance infrared spectroscopy (ATR-FTIR), scanning electron microscopy (SEM), Raman Spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy (EIS). The findings showed that GCE/Nafion/ rGO-Cu-CuO-Cu2O exhibits excellent electrocatalytic activity toward Pyruvic acid reduction. The quantitative analysis of Pyruvic acid was carried out using differential pulse voltammetry (DPV), where the limit of detection (LOD) and the limit of quantification (LOD) were calculated to be 1.21 µM and 3.68 µM, respectively; also, a wide linear range was achieved covering the natural PA values in biological fluids from 5 to 370 µM with excellent selectivity and reproducibility. Furthermore, the reliability of the proposed sensor was demonstrated using real human serum samples, and good recoveries were obtained.

Self-Cross-Linking p(APM-co-AA) Microstructured Thin Films as Biomimetic Scaffolds.

In nature, cells reside within an extracellular matrix (ECM) that provides biophysical and biochemical cues to direct cell development and behavior. Traditional methods for studying cells involve using in vitro models that are convenient and cost-effective, but often use two-dimensional supports that are poor mimics for three-dimensional natural cell microenvironments. In this work, a synthetic polyampholyte, p(APM-co-AA) [poly(N-(3-aminopropyl)methacrylamide hydrochloride-co-acrylic acid)], was coated onto prestressed polystyrene support films that were then thermally shrunken, which concomitantly induced self-cross-linking of the polyampholyte. The cross-linking process involved a two-step sequence of anhydride formation from pairs of adjacent acrylic acid units, followed by amide cross-linking through reaction with primary amines on other chains. Attenuated reflectance infrared spectroscopy (ATR-IR) confirmed the formation of anhydride and amide bonds during heating, and the cross-linked films remained intact in cell culture media and basic solutions. Furthermore, the compressive stress from the shrinking substrate wrinkled the polyampholyte film, producing 3D scaffolds that were used to study the effect of topography on cell cultures. Cell viability tests confirmed the noncytotoxicity of the microstructured polyampholyte films. The surface wettability of the films was tuned by postfunctionalizing with different amines, with decylamine-functionalized films showing decreased fibroblast attachment, and d-glucamine-functionalized films showing reduced fibroblast spreading, compared to the control. Furthermore, the topography of the p(APM-co-AA) scaffolds could be tuned by changing the polyampholyte film thickness. Different topographies of the microstructured films elicited different fibroblast morphologies, with larger structures contributing to less complex cell boundaries, lower cell areas, and higher cell circularities. Overall, this tunable, self-cross-linking p(APM-co-AA) system can be fabricated into microstructured films, which can be used to study the effects of surface chemistry, topography, and other physical properties of biomimetic scaffolds on cell behavior and contribute to the library of existing biomimetic scaffolds.

The effect of the particle size on the fundamental vibrations of the [CO3(2-)] anion in calcite.

This study examines the effects of particle sizes between 3 and 121 μm on the fundamental vibrations of the [CO3(2-)] anion in calcite [CaCO3] as analyzed by total attenuated reflectance infrared spectroscopy (ATR-IR) and Raman spectroscopy (RS). The ATR-IR absorbance intensity ratios of the [ν4/ν3] [712 cm(-1)/1393 cm(-1)], [ν4/ν2] [712 cm(-1)/871 cm(-1)], and [ν2/ν3] [871 cm(-1)/1393 cm(-1)] share the same profile for grain size fractions 121 μm through to 42 μm mode. Between 42 and 3 μm mode the three ratios sharply decline in a systematic manner, consistent with a nonuniform decrease in spectral contrast of the [CO3(2-)] internal modes. Raman intensity increased with decreasing particle size from 121 μm until 19 μm mode particle size fraction thereafter decreasing sharply. The [ν4/ν3], [ν1/ν3], and [ν4/ν1] intensity ratios normalized against the corresponding intensity ratio of the 121 μm particle size fraction indicate that the [ν4/ν3] ratio changes by 22%. Both ATR-IR and Raman indicate two critical points in internal mode behavior of the Raman and infrared active ν4 and ν3 internal modes, the first between 42 and 59 μm size range and the second between 19 and 5 μm. Results are interpreted in terms of specular to volume (diffuse) coherent transitions of internal modes and with further grain refinement internal mode specific optically thick to thin transitions.

Monomer Exchange Dynamics of Self‐Assembled Surfactant Monolayers at the Solid–Liquid Interface

Self-assembly of surface-active agents at solid–liquid interfaces is critical for many processes in nature and technology, including the stability of suspension, detergency, wetting and mineral separation. Historically, a detailed understanding of nanometer-scale layers has emerged. However, surprisingly little is known about their dynamics—the key to non-equilibrium phenomena. Even in equilibrium, there is constant exchange of monomers between bulk and monolayer. Determination of the associated rate constants has been undertaken by evaluating adsorption and desorption kinetics. These methods are not practical near equilibrium adsorption as they rely upon a changing surface concentration. Hence, little can be learned about the true equilibrium state of a monolayer. The importance of dynamical properties at solution interfaces has long been realized and relaxation techniques, utilizing the system’s response to perturbation from equilibrium, have developed into powerful tools. Unfortunately, these methods do not adapt easily to the rather slow kinetics typically found at the solid–liquid interface. The nature of the solid–liquid boundary as a buried interface, together with the vanishingly small fraction of monolayer to bulk molecules poses a serious experimental challenge. Certain spectroscopic techniques are applicable, and in fact infrared attenuated reflection spectroscopy (IR-ATR) has been used to study exchange reactions of aggregates at interfaces. However, this linear IR technique probes an interfacial region extending to hundreds of nanometers—including molecules far beyond the monolayer. Higher interfacial specificity is obtained with nonlinear optical methods. Kinetic studies at the air–water interface by second harmonic generation have been reported. The related but more powerful vibrational sum-frequency spectroscopy (VSFS) exploits resonant effects of vibrational transitions, and has demonstrated its applicability for the study of monolayers at mineral–water interfaces. However, its current use for such systems has heretofore been limited to static investigations. Herein, we exploit a wide-band, rapidly tunable IR source within a VSFS system to investigate dynamic phenomena. A simplified, three step, monomer exchange process is described in Figure 1. The surfactant (sodium dodecanoate, C12) is first released from the monolayer (rate constant kD). Secondly monomer adsorption occurs from the bulk into a randomly oriented state (kA) on the substrate (fluorite CaF2). Finally an ordered monolayer is reformed (kO).

Degradation of agar films in a humid tropical climate: Thermal, mechanical, morphological and structural changes

Agar films were subjected to natural weathering exposure in a humid tropical climate for 90 days to determine their biodegradation behavior and functionality. Exposed samples were taken at 15, 30, 45, 60 and 90 days. Mechanical, thermal, structural and morphological properties were determined using tensile test, differential scanning calorimetry (DSC), attenuated reflectance infrared spectroscopy (ATR-FTIR), X-ray diffraction and environmental scanning electron microscopy (ESEM). The photodegradation process and temperature–relative humidity fluctuations promoted a decrease in agar mechanical properties in early exposure stages (30–45 days) caused by a reduction in agar molecular size and a decrease in the number of sulfate groups. These changes alter agar crystallinity, causing contraction that leads to formation of micro-fractures and embrittlement, and promote microbial attack. Accelerated weathering exposure of agar films showed that outdoor climate parameters play an important role in their degradation. These results will aid in further research to determine the potential use of agar as an environmentally friendly solution to the problem of biodegradable composites disposal.