Microfluidic chips for chirality exploration

Online-Monitoring of the Enantiomeric Ratio in Microfluidic Chip Reactors Using Chiral Selector Ion Vibrational Spectroscopy

A novel experimental approach for the rapid online monitoring of the enantiomeric ratio of chiral analytes in solution is presented. The charged analyte is transferred to the gas phase by electrospray. Diastereomeric complexes are formed with a volatile chiral selector in a buffer-gas-filled ion guide held at room temperature, mass-selected, and subsequently spectrally differentiated by cryogenic ion trap vibrational spectroscopy. Based on the spectra of the pure complexes in a small diastereomer-specific spectral range, the composition of diastereomeric mixtures is characterized using the cosine similarity score, from which the enantiomeric ratio in the solution is determined. The method is demonstrated for acidified alanine solutions and using three different chiral selectors (2-butanol, 1-phenylethanol, 1-amino-2-propanol). Among these, 2-butanol is the best choice as a selector for protonated alanine, also because the formation ratio of the corresponding diastereomeric complexes is found to be independent of the nature of the enantiomer. Subsequently, a microfluidic chip is implemented to mix enantiomerically pure alanine solutions continuously and determine the enantiomeric ratio online with minimal sample consumption within one minute and with competitive accuracy.

Chirality in Light-Matter Interaction

The scientific effort to control the interaction between light and matter has grown exponentially in the last 2 decades. This growth has been aided by the development of scientific and technological tools enabling the manipulation of light at deeply sub-wavelength scales, unlocking a large variety of novel phenomena spanning traditionally distant research areas. Here, the role of chirality in light-matter interactions is reviewed by providing a broad overview of its properties, materials, and applications. A perspective on future developments is highlighted, including the growing role of machine learning in designing advanced chiroptical materials to enhance and control light-matter interactions across several scales.

Role of microfluidics in accelerating new space missions

Numerous revolutionary space missions have been initiated and planned for the following decades, including plans for novel spacecraft, exploration of the deep universe, and long duration manned space trips. Compared with space missions conducted over the past 50 years, current missions have features of spacecraft miniaturization, a faster task cycle, farther destinations, braver goals, and higher levels of precision. Tasks are becoming technically more complex and challenging, but also more accessible via commercial space activities. Remarkably, microfluidics has proven impactful in newly conceived space missions. In this review, we focus on recent advances in space microfluidic technologies and their impact on the state-of-the-art space missions. We discuss how micro-sized fluid and microfluidic instruments behave in space conditions, based on hydrodynamic theories. We draw on analyses outlining the reasons why microfluidic components and operations have become crucial in recent missions by categorically investigating a series of successful space missions integrated with microfluidic technologies. We present a comprehensive technical analysis on the recently developed in-space microfluidic applications such as the lab-on-a-CubeSat, healthcare for manned space missions, evaluation and reconstruction of the environment on celestial bodies, in-space manufacturing of microfluidic devices, and development of fluid-based micro-thrusters. The discussions in this review provide insights on microfluidic technologies that hold considerable promise for the upcoming space missions, and also outline how in-space conditions present a new perspective to the microfluidics field.

Recent advances in microchip enantioseparation and analysis

This review summarizes recent developments (over the past decade) in the field of microfluidics-based solutions for enantiomeric separation and detection. The progress in various formats of microchip electrodriven separations, such as MCE, microchip electrochromatography, and multidimensional separation techniques, is discussed. Innovations covering chiral stationary phases, surface coatings, and modification strategies to improve resolution, as well as integration with detection systems, are reported. Finally, combinations with other microfluidic functional units are also presented and highlighted.

Absolute Chiral Sensing in Dielectric Metasurfaces Using Signal Reversals

Sensing molecular chirality at the nanoscale has been a long-standing challenge due to the inherently weak nature of chiroptical signals, and nanophotonic approaches have proven fruitful in accessing these signals. However, in most cases, complete sensing of the chiral part of the molecule's refractive index (magnitude and sign of both its real and imaginary part) has not been possible, while the strong inherent signals from the nanostructures themselves obscure the weak chiroptical signals. Here, we propose a dielectric metamaterial system that overcomes these limitations and allows for complete measurements of the total chirality and discrimination of the effects of its real and imaginary part, possible also in an absolute manner via the application of a crucial signal reversal (excitation with reversed polarization) that enables chirality measurements without the need for sample removal. As proof of principle, we demonstrate signal enhancements by a factor of 200 for ultrathin, subwavelength, chiral samples over a uniform and accessible area.

Some thoughts about enantioseparations in capillary electrophoresis

In this overview the goal of the authors was to analyze from the historical perspective the reasons of success and failure of chiral capillary electrophoresis. In addition, the current trends are analyzed, unique advantages of capillary electrophoresis are highlighted and some future directions are discussed.

Bioresponsive Release System for Visual Fluorescence Detection of Carcinoembryonic Antigen from Mesoporous Silica Nanocontainers Mediated Optical Color on Quantum Dot-Enzyme-Impregnated Paper

An all-in-one paper-based analytical device (PAD) was successfully developed for visual fluorescence detection of carcinoembryonic antigen (CEA) on CdTe/CdSe quantum dot (QD)-enzyme-impregnated paper by coupling with a bioresponsive controlled-release system from DNA-gated mesoporous silica nanocontainers (MSNs). The assay was carried out in a centrifuge tube by using glucose-loaded MSNs with a CEA aptamer and a QD-enzyme-paper attached on the lid. Initially, single-strand complementary DNA to a CEA aptamer was covalently conjugated to the aminated MSN, and then glucose (enzyme substrate) molecules were gated into the pore with the help of the aptamer. Glucose oxidase (GOD) and CdTe/CdSe QDs were coimmobilized on paper for the visual fluorescence signal output. Upon target CEA introduction in the detection cell, the analyte specifically reacted with the immobilized aptamer on the MSN to open the pore, thereby resulting in the glucose release. The released glucose was oxidized by the immobilized GOD on paper to produce gluconic acid and hydrogen peroxide, and the latter quenched the fluorescence of CdTe/CdSe QDs, which could be determined by the naked eye on a portable smartphone and a commercial fluorospectrometer. Under optimal conditions, the PAD-based sensing system enabled sensitive discrimination of target CEA against other biomarkers or proteins in a linear range of 0.05-20 ng mL^-1 with a limit of detection of 6.7 pg mL^-1 (ppt). In addition, our strategy displayed high specificity, good reproducibility, and acceptable accuracy for analyzing human serum specimens with a commercial human CEA ELISA kit. Importantly, this methodology offers promise for simple analysis of biological samples and is suitable for use in the mass production of miniaturized devices, thus opening new opportunities for protein diagnostics and biosecurity.

Improving the sensitivity in chiral capillary electrophoresis

CE is known for being one of the most powerful analytical techniques when performing enantioseparations due to its numerous advantages such as excellent separation efficiency and extremely low solvents and reagents consumption, all of them derived from the capillary small dimensions. Moreover, it is worth highlighting that unlike in chromatographic techniques, in CE the chiral selector is generally within the separation medium instead of being attached to the separation column which makes the method optimization a more versatile task. Despite its numerous advantages, when using UV-Vis detection, CE lacks of sensitivity detection due to its short optical path length derived from the narrow separation capillary. This issue can be overcome by means of different approaches, either by sample treatment procedures or by in-capillary preconcentration techniques or even by employing detection systems more sensitive than UV-Vis, such as LIF or MS. The present review assembles the latest contributions regarding improvements of sensitivity in chiral CE published from June 2013 until May 2015, which follows the works included in a previous review reported by Sánchez-Hernández et al. [Electrophoresis 2014, 35, 12-27].

Microscale technology and biocatalytic processes: opportunities and challenges for synthesis

Despite the expanding presence of microscale technology in chemical synthesis and energy production as well as in biomedical devices and analytical and diagnostic tools, its potential in biocatalytic processes for pharmaceutical and fine chemicals, as well as related industries, has not yet been fully exploited. The aim of this review is to shed light on the strategic advantages of this promising technology for the development and realization of biocatalytic processes and subsequent product recovery steps, demonstrated with examples from the literature. Constraints, opportunities, and the future outlook for the implementation of these key green engineering methods and the role of supporting tools such as mathematical models to establish sustainable production processes are discussed.

On-chip monitoring of chemical syntheses in microdroplets via surface-enhanced Raman spectroscopy

An approach for inline monitoring of organic syntheses in a microfluidic droplet chip via surface-enhanced Raman spectroscopy is presented. In a proof of concept it was successfully applied to follow thiazole syntheses in real-time.

Microfluidic chip capillary electrophoresis coupled with electrochemiluminescence for enantioseparation of racemic drugs using central composite design optimization

Optimization based on central composite design (CCD) for enantioseparation of anisodamine (AN), atenolol (AT), and metoprolol (ME) in human urine was developed using a microfluidic chip-CE device. Coupling the flexible and wide working range of microfluidic chip-CE device to CCD for chiral separation of AN, AT, and ME in human urine, a total of 15 experiments is needed for the optimization procedure as compared to 75 experiments using the normal one variable at a time optimization. The optimum conditions obtained are found to be more robust as shown by the curvature effects of the interaction factors. The developed microfluidic chip-CE-ECL system with adjustable dilution ratios has been validated by satisfactory recoveries (89.5-99% for six enanotiomers) in urine sample analysis. The working range (0.3-600 μM), repeatability (3.1-4.9% RSD for peak height and 4.0-5.2% RSD for peak area), and detection limit (0.3-0.6 μM) of the method developed are found to meet the requirements for bedside monitoring of AN, AT, and ME in patients under critical conditions. In summary, the hyphenation of CCD with the microfluidic chip-CE device is shown to offer a rapid means for optimizing the working conditions on simultaneous separation of three racemic drugs using the microfluidic chip-CE device developed.

Recentchiral selectors for separation in HPLC and CE

Enantiomers (stereoisomers) can exhibit substantially different properties if present in chiral environments. Since chirality is a basic property of nature, the different behaviors of the individual enantiomers must be carefully studied and properly treated. Therefore, enantioselective separations are a very important part of separation science. To achieve the separation of enantiomers, an enantioselective environment must be created by the addition of a chiral selector to the separation system. Many chiral selectors have been designed and used in various fields, such as the analyses of drugs, food constituents and agrochemicals. The most popular have become the chiral selectors and/or chiral stationary phases that are of general use, i.e., are applicable in various separation systems and allow for chiral separation of structurally different compounds. This review covers the most important chiral selectors / chiral stationary phases described and applied in high performance liquid chromatography and capillary electrophoresis during the period of the last three years (2008–2011).