Synchrotron FTIR mapping of mineralization in a microfluidic device

IR-EcoSpectra: Exploring sustainable ex situ and in situ FTIR applications for green chemical and pharmaceutical analysis

In various industries, particularly in the chemical and pharmaceutical fields, Fourier transform infrared spectroscopy (FTIR) spectroscopy provides a unique capacity to detect and characterise complex chemicals while minimising environmental damage by minimal waste generation and reducing the need for extensive sample preparation or use of harmful reagents. This review showcases the versatility of ex situ and in situ FTIR applications for substance identification, analysis, and dynamic monitoring. Ex situ FTIR spectroscopy's accuracy in identifying impurities, monitoring crystallisation processes, and regulating medication release patterns improves product quality, safety, and efficacy. Furthermore, its quantification capabilities enable more effective drug development, dosage procedures, and quality control practices, all of which are consistent with green analytical principles. On the other hand, in situ FTIR spectroscopy appears to be a novel tool for the real-time investigation of molecular changes during reactions and processes, allowing for the monitoring of drug release kinetics, crystallisation dynamics, and surface contacts, as well as providing vital insights into material behaviour. The combination of ex situ FTIR precision and in situ FTIR dynamic capabilities gives a comprehensive analytical framework for developing green practices, quality control, and innovation in the chemical and pharmaceutical industries. This review presents the wide range of applications of ex situ and in situ FTIR spectroscopy in chemical, pharmaceutical and medical fields as an analytical green chemistry tool. However, further study is required to fully realise FTIR's potential and develop new applications that improve sustainability in these areas.

Review: Advanced Atomic Force Microscopy Modes for Biomedical Research

Visualization of biomedical samples in their native environments at the microscopic scale is crucial for studying fundamental principles and discovering biomedical systems with complex interaction. The study of dynamic biological processes requires a microscope system with multiple modalities, high spatial/temporal resolution, large imaging ranges, versatile imaging environments and ideally in-situ manipulation capabilities. Recent development of new Atomic Force Microscopy (AFM) capabilities has made it such a powerful tool for biological and biomedical research. This review introduces novel AFM functionalities including high-speed imaging for dynamic process visualization, mechanobiology with force spectroscopy, molecular species characterization, and AFM nano-manipulation. These capabilities enable many new possibilities for novel scientific research and allow scientists to observe and explore processes at the nanoscale like never before. Selected application examples from recent studies are provided to demonstrate the effectiveness of these AFM techniques.

X-ray compatible microfluidics for in situ studies of chemical state, transport and reaction of light elements in an aqueous environment using synchrotron radiation

This paper presents an X-ray compatible microfluidic platform for in situ characterization of chemical reactions at synchrotron light sources. We demonstrate easy to implement techniques to probe reacting solutions as they first come into contact, and study the very first milliseconds of their reaction in real-time through X-ray absorption spectroscopy (XAS). The devices use polydimethylsiloxane (PDMS) microfluidic channels sandwiched between ultrathin, X-ray transparent silicon nitride observation windows and rigid substrates. The new approach has three key advantages: i) owing to the assembly techniques employed, the devices are suitable for both high energy and tender (1-5 keV) X-rays; ii) they can operate in a vacuum environment (a must for low energy X-rays) and iii) they are robust enough to survive a full 8 hour shift of continuous scanning with a micro-focused beam, providing higher spatial and thus greater time resolution than previous studies. The combination of these opens new opportunities for in situ studies. This has so far not been possible with Kapton or glass-based flow cells due to increased attenuation of the low energy beam passing through these materials. The devices provide a well-defined mixing region to collect spatial maps of spatially stable concentration profiles, and XAS point spectra to elucidate the chemical structure and characterize the chemical reactions. The versatility of the approach is demonstrated through in situ XAS measurements on the mixing of two reactants in a microfluidic laminar flow device, as well as a segmented droplet based system for time resolved analysis.

Mineralogical Characteristics and Luminescent Properties of Natural Fluorite with Three Different Colors

Fluorite is rich in mineral resources and its gorgeous colors and excellent luminescence characteristics have attracted the attention of many scholars. In this paper, the composition, structure, luminescent properties, and the potential application value of three fluorites with different colors and are systematically analyzed. The results show that REE and radioactive elements have effects on the structure, color, and luminescence of fluorite. Radioactive elements Th and U will aggravate the formation of crystal defects in fluorite. The green color is related to Ce³⁺ and Sm²⁺. Colloidal calcium and F⁻ center are responsible for the blue-purple color of fluorite. There are many luminescent centers, such as Eu, Pr, Dy, Tb, Er, and Sm, in fluorite. The blue fluorescence is mainly caused by 4f⁷-4f⁶5d¹ of Eu²⁺. In addition, it is found that fluorite has certain temperature sensing properties in the temperature range of 303–343 K.

Nucleation kinetics of calcium oxalate monohydrate as a function of pH, magnesium, and osteopontin concentration quantified with droplet microfluidics

A droplet-based microfluidic platform is presented to study the nucleation kinetics of calcium oxalate monohydrate (COM), the most common constituent of kidney stones, while carefully monitoring the pseudo-polymorphic transitions. The precipitation kinetics of COM is studied as a function of supersaturation and pH as well as in the presence of inhibitors of stone formation, magnesium ions (Mg2+), and osteopontin (OPN). We rationalize the trends observed in the measured nucleation rates leveraging a solution chemistry model validated using isothermal solubility measurements. In equimolar calcium and oxalate ion concentrations with different buffer solutions, dramatically slower kinetics is observed at pH 6.0 compared to pHs 3.6 and 8.6. The addition of both Mg2+ and OPN to the solution slows down kinetics appreciably. Interestingly, complete nucleation inhibition is observed at significantly lower OPN, namely, 3.2 × 10-8 M, than Mg2+ concentrations, 0.875 × 10-4 M. The observed inhibition effect of OPN emphasizes the often-overlooked role of macromolecules on COM nucleation due to their low concentration presence in urine. Moreover, analysis of growth rates calculated from observed lag times suggests that inhibition in the presence of Mg2+ cannot be explained solely on altered supersaturation. The presented study highlights the potential of microfluidics in overcoming a major challenge in nephrolithiasis research, the overwhelming physiochemical complexity of urine.

Design and Parameter Research of Time-Harmonic Magnetic Field Sensor Based on PDMS in Microfluidic Technology

In order to improve the throughput and sensitivity of the inductive metal micro-abrasive particle detection sensor, this paper uses microfluidic detection technology to design a high-throughput abrasive particle detection sensor based on PDMS (Polydimethylsiloxane). Theoretical modeling analyzes the magnetization of metal abrasive particles in the coil's time-harmonic magnetic field, and uses COMSOL simulation to calculate the best performance parameters of the sensor. Through the experiment of the control variable method, the corresponding signal value is obtained and the signal-to-noise ratio (SNR) is calculated. The SNR value and error value are calculated, and the SNR is corrected. The detection limit of the sensor is determined to be 10 μm iron particles and 60 μm copper particles. The optimal design parameters of the 3-D solenoid coil and the frequency characteristics of the sensor are obtained. Finally, through high-throughput experiments and analysis, it was found that there was a reasonable error between the actual throughput and the theoretical throughput. The design ideas suggested in this article can not only improve the sample throughput, but also ensure the detection accuracy. This provides a new idea for the development of an inductive on-line detection method of abrasive particle technology.

Synchrotron infrared nanospectroscopy on a graphene chip

A recurring goal in biology and biomedicine research is to access the biochemistry of biological processes in liquids that represent the environmental conditions of living organisms. These demands are becoming even more specific as microscopy techniques are fast evolving in the era of single cell analysis. In the modality of chemical probes, synchrotron infrared spectroscopy (μ-FTIR) is a technique that is extremely sensitive to vibrational responses of materials; however, the classical optical limits prevent the technique to access the biochemistry of specimens at the subcellular level. In addition, due to the intricate environmental requirements and strong infrared absorption of water, μ-FTIR of bioprocesses in liquids remains highly challenging. In phase with these challenges, on-chip liquid cells emerge as a versatile alternative to control the water thickness while providing a biocompatible chemical environment for analytical analyses. In this work we report the development of a liquid platform specially designed for nanoscale infrared analysis of biomaterials in wet environments. A key advantage of our designed platform is the use of graphene as an optical window that interfaces wet and dry environments in the liquid cell. By combining near-field optical microscopy and synchrotron infrared radiation, we measure the nanoscale fingerprint IR absorbance of a variety of liquids often used in biological studies. Further, we demonstrate the feasibility of the platform for the chemical analysis of protein clusters immersed in water with a clear view of the proteins' secondary structure signatures. The simplicity of the proposed platform combined with the high quality of our data makes our findings a template for future microfluidic devices targeting dynamic nanoscale-resolved chemical analysis.

Understanding Secondary Structures of Silk Materials via Micro- and Nano-Infrared Spectroscopies

The secondary structures (also termed conformations) of silk fibroin (SF) in animal silk fibers and regenerated SF materials are critical in determining mechanical performance and function of the materials. In order to understand the structure-mechanics-function relationships of silk materials, a variety of advanced infrared spectroscopic techniques, such as micro-infrared spectroscopies (micro-IR spectroscopies for short), synchrotron micro-IR spectroscopy, and nano-infrared spectroscopies (nano-IR spectroscopies for short), have been used to determine the conformations of SF in silk materials. These IR spectroscopic methods provide a useful toolkit to understand conformations and conformational transitions of SF in various silk materials with spatial resolution from the nano-scale to the micro-scale. In this Review, we first summarize progress in understanding the structure and structure-mechanics relationships of silk materials. We then discuss the state-of-the-art micro- and nano-IR spectroscopic techniques used for silk materials characterization. We also provide a systematic discussion of the strategies to collect high-quality spectra and the methods to analyze these spectra. Finally, we demonstrate the challenges and directions for future exploration of silk-based materials with IR spectroscopies.

A microfluidic approach for probing hydrodynamic effects in barite scale formation

Crystallization of mineral scale components ubiquitously plagues industrial systems for water treatment, energy production, and manufacturing. Chemical scale inhibitors and/or dissolvers are often employed to control scale formation, but their efficacy in flow conditions remains incompletely understood. We present a microfluidic platform to elucidate the time-resolved processes controlling crystallization and dissolution of barite, a highly insoluble and chemically resistant component of inorganic scale, in the presence of flow. In a growth environment, increasing the flow rate leads to a crossover from a transport-limited to a reaction-limited kinetic regime. In situ optical microscopy reveals that addition of diethylenetriaminepentaacetic acid (DTPA), a common dissolution agent, alters the morphology of barite crystals grown under flow. In a dissolution environment (i.e. alkaline solutions without barium sulfate), increasing the flux of DTPA, whether by increasing the flow rate or DTPA concentration, enhances the rate of dissolution of barite. Trends in the rate of barite dissolution with DTPA concentration and flow rate indicate an optimal combination of these parameters. The combined use of microfluidics and optical microscopy provides a robust and broadly-useful platform for capturing crystallization kinetics and morphological transformation under dynamic flow conditions.

Solution rheological parameters modulate calcium phosphate mineralization in a microfluidic device

Mineralization of calcium phosphate and other materials in vivo and in natural water sources occurs in solutions that are not stagnant, but are flowing. Flow conditions could influence solution mixing and, therefore, mineralization kinetics or mechanism. This work describes the design and characterization of a multi-stream parallel flow microfluidic device that allows for controlled solution mixing and indirect control of laminar flow by altering the microfluidic device width, shape, length, flow rate, and flow velocity. Measurement of solution mixing was accomplished using the protonation of quinine to produce a fluorescent molecule and the rate of calcium phosphate mineralization was monitored by optical microscopy and analysis with Image J software. Experiments were designed to hold the flow rate constant, allowing the solution velocity to vary and to hold the velocity constant, allowing the flow rate to vary. It was found that small changes in laminar flow conditions do not correlate to mineral growth, but solution velocity and flow rate have a substantial effect on calcium phosphate mineralization. AFM and SEM characterization of the mineral produced shows an amorphous material and varying degrees of mineralization possibly due to variation in supersaturation conditions across the solution mixing area. This microfluidic device and analysis procedure allows for improved study of mineralization and the effect of flow conditions relevant to those seen in biological settings.

Passive Picoinjection Enables Controlled Crystallization in a Droplet Microfluidic Device

Segmented flow microfluidic devices offer an attractive means of studying crystallization processes. However, while they are widely employed for protein crystallization, there are few examples of their use for sparingly soluble compounds due to problems with rapid device fouling and irreproducibility over longer run-times. This article presents a microfluidic device which overcomes these issues, as this is constructed around a novel design of "picoinjector" that facilitates direct injection into flowing droplets. Exploiting a Venturi junction to reduce the pressure within the droplet, it is shown that passive injection of solution from a side-capillary can be achieved in the absence of an applied electric field. The operation of this device is demonstrated for calcium carbonate, where highly reproducible results are obtained over long run-times at high supersaturations. This compares with conventional devices that use a Y-junction to achieve solution loading, where in-channel precipitation of calcium carbonate occurs even at low supersaturations. This work not only opens the door to the use of microfluidics to study the crystallization of low solubility compounds, but the simple design of a passive picoinjector will find wide utility in areas including multistep reactions and investigation of reaction dynamics.

Flash crystallization kinetics of methane (sI) hydrate in a thermoelectrically-cooled microreactor

The crystallization kinetics of methane (sI) hydrate were investigated in a thermoelectrically-cooled microreactor with in situ Raman spectroscopy. Step-wise and precise control of the temperature allowed acquisition of reproducible data within minutes, while the nucleation of methane hydrates can take up to 24 h in traditional batch reactors. The propagation rates of methane hydrate (from 3.1-196.3 μm s^-1) at the gas-liquid interface were measured for different Reynolds' numbers (0.7-68.9), pressures (30.0-80.9 bar), and sub-cooling temperatures (1.0-4.0 K). The precise measurement of the propagation rates and their subsequent analyses revealed a transition from mixed heat-transfer-crystallization-rate-limited to mixed heat-transfer-mass-transfer-crystallization-rate-limited kinetics. A theoretical model, based on heat transfer, mass transfer, and intrinsic crystallization kinetics, was derived for the first time to understand the non-linear relationship between the propagation rate and sub-cooling temperature. The molecular diffusivity of methane within a stagnant film (ahead of the propagation front) was discovered to follow Stokes-Einstein, while calculated Hatta (0.50-0.68), Lewis (128-207), and beta (0.79-116) numbers also confirmed that the diffusive flux influences crystal growth. Understanding methane hydrate crystal growth is important to the atmospheric, oceanic, and planetary sciences and to energy production, storage, and transportation. Our discoveries could someday advance the science of other multiphase, high-pressure, and sub-cooled crystallizations.