Field Of Analytical Chemistry Research Articles

A Green Analytical Methodology for Detecting Adulteration in Automotive Urea-SCR Products Using Microfluidic-Paper Analytical Devices

The application of urea-based selective catalytic reduction products (i.e., Urea-SCR) provides a reduction of NOx and, therefore, minimizes pollution emissions from vehicles fueled by diesel. Such products can be easily found in the market; however, they are often susceptible to adulteration, mainly in terms of the urea content and dilution with non-mineralized water. In this study, we propose a simple, low-cost, disposable, and straightforward paper-based microfluidic device for the quality-control of Urea-SCR products for the first time by quantifying urea and water hardness simultaneously via colorimetric reactions using a small volume of sample. 4-(dimethylamino)benzaldehyde and Eriochrome T were used as colorimetric indicators for urea and water hardness determination, respectively. Each reagent (1.5 µL) was combined with 6 µL of sample for analysis, contributing to an expressive reduction of waste generation. Digital images of the µPAD were obtained, and linear relations between color intensity and urea and Ca2+ and Mg2+ concentrations in the range of 0.2 to 1.0% and 0.1 to 3.5 mmol L−1 were obtained with a correlation coefficient higher than 0.99. Recovery experiments were employed to evaluate the accuracy of the methodology, revealing suitable values between 91.5 and 115%. Brazilian Urea-SCR samples were acquired from different distributors and submitted to the proposed procedure to evaluate its applicability. The application of microfluidic paper-based devices with colorimetric reactions enables the quality control of Urea-SCR products with high accuracy, portability, low consumption of reagents, and no generation of toxic residues; thereby contributing to the green analytical chemistry field.

Recent trends in layered double hydroxides based electrochemical and optical (bio)sensors for screening of emerging pharmaceutical compounds

The rapid expansion of the human population has given rise to new environmental and biomedical concerns, contributing to different advancements in the pharmaceutical industry. In the field of analytical chemistry over the last few years, layered double hydroxides (LDHs) have drawn significant attention, owing to their extraordinary properties. Furthermore, the novel advancement of LDH-based optical and electrochemical platforms to detect different pharmaceutical materials has acquired substantial attention because of their outstanding specificity, actual-time controlling, and user-friendliness. This review aims to recapitulate advanced LDHs-based optical and electrochemical sensors and biosensors to identify and measure important pharmaceutical compounds, such as anti-depressant, anti-inflammatory, anti-viral, anti-bacterial, anti-cancer, and anti-fungal drugs. Additionally, fundamental parameters, namely interactions between sensor and analyte, design rationale, classification, selectivity, and specificity are considered. Finally, the development of high-efficiency techniques for optical and electrochemical sensors and biosensors is featured to deliver scientists and readers a complete toolbox to identify a broad scope of pharmaceutical substances. Our goals are: (i) to elucidate the characteristics and capabilities of available LDHs for the identification of pharmaceutical compounds; and (ii) to deliver instances of the feasible opportunities that the existing devices have for the developed sensing of pharmaceuticals regarding the protection of ecosystems and human health at the global level.

Mass-to-Charge Ratio Set Matching: A Novel and Efficient Compound Identification Method.

GC-MS is a powerful tool for component analysis of unknown compounds, especially in the fields of analytical chemistry and detection of biological samples. To effectively identify compounds in GC-MS, one of the most important ways is to use a matching algorithm to compare the similarity between the reference spectrum and the query spectrum. To propose a novel way to improve compound identification accuracy. This article proposes a method based on an m/z set match. First of all, select the maximum m/z and the m/z corresponding to the highest peak intensity in a pre-search. Next, employ the space vector model to carry on a refined search in the remaining spectra after the pre-search. Then, distinguish stereoisomers according to the order of the G value. Compared with the 10 peaks and the method based on an m/z number matching pre-search, the method based on m/z set matching showed higher accuracy and fewer remaining (missing) spectra. Furthermore, the refined search which is based on the m/z set matching method possesses shorter calculation time compared with no pre-search. The method can reduce the remaining spectra and speed up the identification of compounds. The accuracy is higher, the number of remaining spectra is less, and the computational time is shorter.

High-Aspect-Ratio Microfluidic Channel with Parallelogram Cross-Section for Monodisperse Droplet Generation.

Droplet-based microfluidics has been widely used as a potent high-throughput platform due to various advantages, such as a small volume of reagent consumption, massive production of droplets, fast reaction time, and independent control of each droplet. Therefore, droplet microfluidic systems demand the reliable generation of droplets with precise and effective control over their size and distribution, which is critically important for various applications in the fields of chemical analysis, material synthesis, lab-on-a-chip, cell research, diagnostic test, and so on. In this study, we propose a microfluidic device with a high-aspect-ratio (HAR) channel, which has a parallelogram cross-section, for generating monodisperse droplets. The HAR channel was fabricated using simple and cheap MEMS processes, such as photolithography, anisotropic wet etching, and PDMS molding, without expensive equipment. In addition, the parallelogram cross-section channel structure, regarded as a difficult shape to implement in previous fabrication methods, was easily formed by the self-alignment between the silicon channel and the PDMS mold, both of which were created from a single crystal silicon through an anisotropic etching process. We investigated the effects of the cross-sectional shape (parallelogram vs. rectangle) and height-to-width ratio of microfluidic channels on the size and uniformity of generated droplets. Using the developed HAR channel with the parallelogram cross-section, we successfully obtained smaller monodisperse droplets for a wider range of flow rates, compared with a previously reported HAR channel with a rectangular cross-section.

Recent Applications of Derivatization Techniques for Pharmaceutical and Bioanalytical Analysis through High-performance Liquid Chromatography

Background: Derivatization of analytes is a quite convenient practice from an analytical perspective. Its vast prevalence is accounted by the availability of distinct reagents, primarily pragmatic for obtaining desired modifications in an analyte structure. Another reason for its handiness is typically to overcome limitations such as lack of sensitive methodology or instrumentation.The past decades have witnessed various new derivatization techniques including in-situ, enzymatic, ultrasound-assisted, microwave-assisted, and photochemical derivatization which have gain popularity recently. Methods: The online literature available on the utilization of derivatization as prominent analytical tools in recent years with typical advancements is reviewed. The illustrations of the analytical condition together with the structures of different derivatizing reagents (DRs) are provided to acknowledge the vast capability of derivatization to resolve analytical problems. Results: The derivatization techniques have enabled analytical chemists throughout the globe to develop an enhanced sensitivity method with the simplest of the instrument like High-Performance Liquid Chromatography (HPLC). The HPLC, compared to more sensitive Liquid chromatography coupled to tandem mass spectrometer, is readily available and can be readily utilized for routine analysis in fields of pharmaceuticals, bioanalysis, food safety, and environmental contamination. A troublesome aspect of these fields is the presence of a complex matrix with trace concentrations for analyses. Liquid chromatographic methods devoid of MS detectors do not have the desired sensitivity for this. A possible solution for overcoming this is to couple HPLC with derivatization to enable the possibility of detecting trace analytes with a less expensive instrument. Running cost, enhanced sensitivity, low time consumption, and overcoming the inherent problems of analyte are critical parameters for which HPLC is quite useful in high throughput analysis. Conclusion: The review critically highlights various kinds of derivatization applications in different fields of analytical chemistry. The information primarily focuses on pharmaceutical and bioanalytical applications in recent years. The various modes, types, and derivatizing reagents with brief mechanisms have been ascribed briefly Additionally, the importance of HPLC coupled to fluorescence and UV detection is presented as an overview through examples accompanied by their analytical conditions.

Implementation of Project-based Learning Innovation to Develop Students’ Critical Thinking Skills as a Strategy to Achieve Analytical Chemistry Competencies

Abstract: Background: The ability to think critically is one of the life skill targets that pharmacists and scientists want to achieve in learning, therefore it is necessary to do project-based learning innovations to guide students to learn actively and independently in developing critical thinking skills. Objectives: This study aims to implement project-based learning to facilitate active and independent learning through project implementation to build students’ critical thinking skills and at the same time to facilitate students to achieve competencies in the analytical chemistry required by pharmaceutical and chemical scientists. Materials and Methods: Research includes the development of project packages and the integration of information technology on the topic of Distillation, standardization of learning resources, and implementation of Analytical Chemistry teaching. Results: An innovative project-based learning resource package was successfully developed for the Distillation topic. Implementation of learning resource packages effectively guides students to carry out their own projects in separating target compound contextually through distillation method. The learning facilities available in the learning package have proven to be able in guiding students to design project assignments suit to target analyte. The learning potential of students has been optimized. Students’ knowledge and skills in separating target analytes by distillation have been fully mastered as desired in the competency-based curriculum. The results of the assessment showed that the students’ critical thinking skills were very good (M = 84.51±7.41). Student learning outcomes based on the portfolio value of the project proposal (M = 88.46±6.74) and project reports (M = 92.85±1.98), and from the objective score of the formative exam (M = 85.59±3.09) are all classified very good, namely the competence in the analytical field is achieved. Conclusion: Project-based learning innovations are very effective in improving critical thinking skills as well as increasing student competence in the field of analytical chemistry. Recommendation: Project-based learning is suitable for implementation in teaching other subjects to achieve the competencies required by scientists. This learning model is effective in building student competence in a normal learning atmosphere, or when social restrictions are imposed during the COVID-19 pandemic. Key words: Project-based learning, Learning innovation, Critical thinking skills, Students competence, Learning outcomes.

Smartphone-coupled three-layered paper-based microfluidic chips demonstrating stereoscopic capillary-driven fluid transport towards colorimetric detection of pesticides.

The existence of pesticide residues in the hydrosphere, biosphere, and anthroposphere can cause acute or chronic diseases and deteriorate the environment. Therefore, efficient detection of pesticide residues is of great significance to prevent food poisoning, control food pollution, and protect human lives by recognizing their distribution and concentration. Herein, a novel smartphone-coupled three-layered paper-based microfluidic chip is proposed as a facile platform to detect the pesticides. The stereoscopic capillary-driven fluid transport is enabled by the three-layered microfluidic chip configuration. The detection mechanism is based on the enzyme inhibition reaction and the chromatic reaction. The detection results are obtained by a smartphone and figured out by colorimetric quantitative analysis. Taking advantages of the above merits, we demonstrate the utilization of this smartphone-coupled three-layered paper-based microfluidic chip for the effective analysis of typical pesticides (profenofo and methomyl). The linear ranges of profenofo and methomyl are 0.27-2.1μmol L-1 and 0.14-1.85μmol L-1, respectively. The corresponding limits of detection in the chips are 55nM and 34nM, respectively. The paper-based chips are also highly cost-effective with a total cost of 0.082 ¥ per piece. It can be anticipated that this technique will open new avenues for the mass fabrication of paper-based microfluidic chips and provide state-of-the-art methods in the field of analytical chemistry.

Magnetic Nanorobots as Maneuverable Immunoassay Probes for Automated and Efficient Enzyme Linked Immunosorbent Assay.

As a typical, classical, but powerful biochemical sensing technology in analytical chemistry, enzyme-linked immunosorbent assay (ELISA) shows excellence and wide practicability for quantifying analytes of ultralow concentration. However, long incubation time and burdensome laborious multistep washing processes make it inefficient and labor-intensive for conventional ELISA. Here, we propose rod-like magnetically driven nanorobots (MNRs) for use as maneuverable immunoassay probes that facilitate a strategy for an automated and highly efficient ELISA analysis, termed nanorobots enabled ELISA (nR-ELISA). To prepare the MNRs, the self-assembled chains of Fe3O4 magnetic particles are chemically coated with a thin layer of rigid silica oxide (SiO2), onto which capture antibody (Ab1) is grafted to further achieve magnetically maneuverable immunoassay probes (MNR-Ab1s). We investigate the fluid velocity distribution around the MNRs at microscale using numerical simulation and empirically identify the mixing efficiency of the actively rotating MNRs. To automate the analysis process, we design and fabricate by 3-D printing a detection unit consisting of three function wells. The MNR-Ab1s can be steered into different function wells for required reaction or wishing process. The actively rotating MNR-Ab1s can enhance the binding efficacy with target analytes at microscale and greatly decrease incubation time. The integrated nR-ELISA system can significantly reduce the assay time, more importantly during which process manpower input is greatly minimized. Our simulation of the magnetic field distribution generated by Helmholtz coils demonstrates that our approach can be scaled up, which proves the feasibility of using current strategy to construct high throughput nR-ELISA detection instrument. This work of taking magnetic micro/nanobots as active immunoassay probes for automatic and efficient ELISA not only holds great potential for point-of-care testing (POCT) in future but also extends the practical applications of self-propelled micro/nanorobots into the field of analytical chemistry.

REDGIM COMO APLICATIVO DE SMARTPHONE PARA APLICAÇÕES QUIMIOMÉTRICAS POR MEIO DE ANÁLISE DE IMAGENS: UM USO EM PLS

REDGIM AS A SMARTPHONE APP FOR CHEMOMETRICS APPLICATIONS THROUGH IMAGE ANALYSIS: A USE IN PLS. The study of the spectrum of light has increased its range of action in the field of chemistry, with the help of several advanced equipment and innovative techniques that have become a strong ally of analytical chemistry. However, the simplicity of obtaining results integrated with mobile devices appears as an interesting path to be taken in the field of chemical analysis. This work addresses the dissemination of an application called REDGIM for smartphones on the Android platform capable of working with multivariate image analysis using chemometric methods through the luminous intensities of photos and R (red), G (green) and B (blue) channels. In order to show the potential of REDGIM, we propose two applications using the partial least squares (PLS) regression method: 1) quantification of free chlorine in tap water; and 2) quantification of cannabinol, (CBN, a type of cannabinoid) in marijuana and hashish samples. The free chlorine concentration obtained for two investigated samples was 0.73 and 0.74 mg L–1 and 0.74 and 0.76 mg L–1 by the spectrophotometer and by the application (container: cuvette), respectively. For the quantification of CBN in marijuana and hashish samples, the mean concentration ranged from 6.137 to 8.823 mg mL–1. The results obtained by the application are compatible with results from traditional techniques, such as UV-Vis spectrophotometry, for example. Therefore, REDGIM was proved to be a simple and accessible technological tool for the scientific community, being viable for chemical tests of a multivariate nature.

Analysis of total content of petroleum products in water by using FTIR spectroscopy

Contamination of aquatic and terrestrial environment with oil products is a major problem in processes of extraction, transport and processing of crude oil. Derived organic compounds, resulting from fractional distillation of crude oil often end up in wastewater and surface water causing irreversible effects on aquatic ecosystems. Thus, it’s necessary to identify and qualitatively determine the total content of petroleum products in water, by classical chemical, chromatographic and infrared spectroscopy methods. Gathering high-resolution spectral data was performed by a modern method, Fourier transform infrared spectrometry (FTIR), a relatively precise, high accuracy data method. The study’s main purpose is to describe most important steps to be followed to obtain representative results for the use of FTIR spectrometry in determining total content of petroleum products in water. Steps described in the study involve drawing the baseline, calibrating the method with certified reference materials and estimating the uncertainty degree of the analysis method used. The study of total content of petroleum products is addressed especially to researchers in the field of analytical chemistry to update the methods used, environmental engineers to estimate the pollution degree of a body of water and (PhD) students who want to deepen the field of petroleum compounds analysis.

Sensing the Anti-Epileptic Drug Perampanel with Paper-Based Spinning SERS Substrates.

The applications of SERS in therapeutic drug monitoring, or other fields of analytical chemistry, require the availability of sensitive sensors and experimental approaches that can be implemented in affordable ways. In this contribution, we show the production of cost-effective SERS sensors obtained by depositing Lee-Meisel Ag colloids on filter paper either by natural sedimentation or centrifugation. We have characterized the morphological and plasmonic features of the sensors by optical microscopy, SEM, and UV-Vis spectroscopy. Such sensors can be used to quantify by SERS the anti-epileptic drug Perampanel (in the concentration range 1 × 10−4–5 × 10−6 M) by spinning them during the micro-Raman measurements on the top of a custom device obtained from spare part hard disk drives. This approach minimizes laser-induced heating effects and allows averaging over the spatial non-uniformity of the sensor.

A highly sensitive D-type photonic crystal fiber infrared sensor with indium tin oxide based on surface plasmon resonance

A highly sensitive surface plasmon resonance (SPR) sensor composed of a photonic crystal fiber (PCF) with the D-type structure is designed and analyzed by the full-vector finite element method (FEM). Indium tin oxide (ITO) is adopted as the plasmonic substance on account of the low cost and controllable infrared range (1500–2600 nm). By optimizing the structural parameters, the sensor shows a maximum wavelength sensitivity of 46,000 nm/RIU and average sensitivity of 13,166.67 nm/RIU for analyte refractive indexes between 1.355 and 1.385. This PCF combining a circular layout and D-type structure offers excellent sensitivity while the deposition and manufacturing complexity can be reduced. This sensor will possess an extremely expansive development space in the field of chemical analysis and environmental safety.

Applications of Plasma-Activated Liquid in the Medical Field

Much progress has been made since plasma was discovered in the early 1900s. The first form of plasma was thermal type, which was limited for medical use due to potential thermal damage on living cells. In the late 1900s, with the development of a nonthermal atmospheric plasma called cold plasma, profound clinical research began and ‘plasma medicine’ became a new area in the academic field. Plasma began to be used mainly for environmental problems, such as water purification and wastewater treatment, and subsequent research on plasma and liquid interaction led to the birth of ‘plasma-activated liquid’ (PAL). PAL is currently used in the fields of environment, food, agriculture, nanoparticle synthesis, analytical chemistry, and sterilization. In the medical field, PAL usage can be expanded for accessing places where direct application of plasma is difficult. In this review, recent studies with PAL will be introduced to inform researchers of the application plan and possibility of PAL in the medical field.

Click reaction triggered turn-on fluorescence strategy for highly sensitive and selective determination of steroid hormones in food samples

The copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) click reaction has becoming noticeable in the field of analytical chemistry. Mild reaction conditions, simple operation, high efficiency, and good regioselectivity make this classical click reaction a perfect strategy for chemical derivatization. Herein, we proposed a promising click fluorescent labeling method with high selectivity for the determination of five steroid hormones in food samples. The labeling strategy depends on the reaction between 3-Azido-7-hydroxycoumarin and the alkynyl group of steroid hormones, which shows a turn-on fluorescence response in the presence of copper (I). The formed fluorescent products were detected by HPLC-FLD. Under the optimized conditions, the proposed method presented excellent performance with good linearity (R2 ≥ 0.9998) and low detection limit (1.8–7.3 μg L-1). Further, satisfactory recoveries were obtained to be 82–107% in spiked meats with relative standard deviations (RSDs) ≤ 5.7%. Finally, the established method was successfully applied for the determination of steroid hormones in meat, indicating the potential prospect of the click reaction in chemical derivatization.

A miniaturized analytical method based on molecularly imprinted absorbents for selective extraction of (S)-1,1'-binaphthyl-2,2'-diamine and combinatorial screening of polymer precursors by computational simulation.

Chiral resolution of binaphthylamine is often a toilful conundrum in the field of analytical chemistry and biomedicine. The work puts forward a selective, sensitive, and miniaturized analytical method based on molecularly imprinted polymers (MIPs) as adsorbent for miniaturized tip solid-phase extraction (MTSPE) in the separation of binaphthylamine enantiomer. This method combines the advantages of MIPs (high selectivity), MTSPE (low consumption), and high-performance liquid chromatography (HPLC, high sensitivity). A simple synthesis methodology of MIP (P2) was conducted through bulk polymerization with (S)-(-)-1,1'-binaphthyl-2,2'-diamine (S-DABN) as template together with methacrylic acid monomer, and ethylene glycol dimethacrylate as cross-linker in proper porogen, realizing a selective recognition and efficient enrichment for S-DABN. The method exhibited appreciable linearity (0.06-1.00 mg ml-1 ), low quantification limit (0.056 mg ml-1 ), good absolute recoveries (45.70%-69.29%), and high precision (relative standard deviations ≤ 3.54%), along with low consumption (0.50ml sample solution and 25.0mg adsorbent). Based on the density functional theory, computational simulation was used to make a preliminary prediction for rational design of MIPs and gave a reasonable elaboration involving the potential mechanism of templates interacting with functional monomers. The adsorption kinetics and thermodynamics were investigated to evaluate the recombination process of substrates. In addition, the selectivity of MIPs for S-DABN was obtained by MIP-MTSPE coupled with HPLC, which supports the feasibility of this convenient design process. The proposed method was employed for selective extraction of S-DABN and exhibited promising potential in the application of chiral analysis.

Immunological Analytical Techniques for Cosmetics Quality Control and Process Monitoring

Cosmetics analysis represents a rapidly expanding field of analytical chemistry as new cosmetic formulations are increasingly in demand on the market and the ingredients required for their production are constantly evolving. Each country applies strict legislation regarding substances in the final product that must be prohibited or regulated. To verify the compliance of cosmetics with current regulations, official analytical methods are available to reveal and quantitatively determine the analytes of interest. However, since ingredients, and the lists of regulated/prohibited substances, rapidly change, dedicated analytical methods must be developed ad hoc to fulfill the new requirements. Research focuses on finding innovative techniques that allow a rapid, inexpensive, and sensitive detection of the target analytes in cosmetics. Among the different methods proposed, immunological techniques are gaining interest, as they make it possible to carry out low-cost analyses on raw materials and finished products in a relatively short time. Indeed, immunoassays are based on the specific and selective antibody/antigen reaction, and they have been extensively applied for clinical diagnostic, alimentary quality control and environmental security purposes, and even for routine analysis. Since the complexity and variability of the matrices, as well as the great variety of compounds present in cosmetics, are analogous with those from food sources, immunological methods could also be applied successfully in this field. Indeed, this would provide a valid approach for the monitoring of industrial production chains even in developing countries, which are currently the greatest producers of cosmetics and the major exporters of raw materials. This review aims to highlight the immunological techniques proposed for cosmetics analysis, focusing on the detection of prohibited/regulated compounds, bacteria and toxins, and allergenic substances, and the identification of counterfeits.

A compound post-column re-focusing approach in supercritical fluid chromatography

Supercritical-fluid chromatography (SFC) is regaining popularity in various fields of analytical chemistry owning to significant advances in instrumentation made in the past decade. However, due to the CO2 based mobile phase and the high flow rates often employed, detection of trace amounts of analytes and coupling with certain detectors or other chromatography techniques are still difficult under many circumstances. In this study we propose a post-column re-focusing approach for SFC analysis to achieve not only signal enhancement in UV-Vis detection, but also actual concentration enhancement of the analyte. By heart-cutting and transporting a selected fraction from the SFC flow into a trapping column with a flushing solvent, re-focusing of the collected analytes can be achieved by re-mobilization with another solvent once the depressurized CO2 is eliminated. By carefully selecting the trapping stationary phase and the two solvents, signal-enhancement ratios between 2.2 and 6.4 were realized for four representative compounds eluting with very different percentages of SFC modifier (methanol). The actual concentration enhancement was lower (ratios between 1.7 to 2.9), because the UV response of the analytes was found to differ significantly under SFC and LC conditions.

Time-Resolved ATR-FTIR Spectroscopy and Macro ATR-FTIR Spectroscopic Imaging of Inorganic Treatments for Stone Conservation.

In this study, the novel application of ATR–FTIR spectroscopy and macro ATR–FTIR spectroscopic imaging overcame an analytical challenge in conservation science: the time-resolved, chemical, and spatial investigation of the reaction of inorganic treatments for stone conservation (ammonium oxalate, AmOx; ammonium phosphate, DAP) occurring in water-based solutions. The aim was to (1) assess the composition and localization of reaction products and their phase variation during the reaction in real time and directly in an aqueous environment and (2) investigate the reaction of AmOx and DAP with calcite and the transformations induced to the substrate with a time-resolved approach. The new analytical results showed that for both treatments, the formation of new crystalline phases initiated at the early stages of the reaction. Their composition changed during the treatment and led to more stable phases. The reactivity of the stone substrate to the treatments varied as a function of the stone material features, such as the specific surface area. A clear influence of post-treatment rinsing on the final composition of reaction phases was observed. Above all, our research demonstrates the actual feasibility, practicality, and high potential of an advanced ATR–FTIR spectroscopic approach to investigate the behavior of conservation treatments and provided new analytical tools to address the choices of conservation in pilot worksites. Lastly, this study opens novel analytical perspectives based on the new possible applications of ATR–FTIR spectroscopic imaging in the field of conservation science, materials science, and analytical chemistry.

A fluorescent sensor recognized by the FA1 site for highly sensitive detection of HSA

Human serum albumin (HSA), as the most abundant protein in blood plasma, plays a crucial role in many physiological processes. The abnormal HSA level in serum or in urine is often associated with various diseases. Therefore, to achieve highly sensitive and selective quantification of HSA is of great importance for disease diagnosis and preventive medicine. Herein, an HSA-selective light-up fluorescent sensor, DCM-ML, was successfully developed for quantitative detection of HSA. DCM-ML exhibited good (photo-) stability and strong fluorescence enhancement around 630 nm in the presence of HSA in complex samples containing numerous biological analytes. Upon addition of HSA into DCM-ML containing solution, a good linear relationship (R2 > 0.99) between the fluorescence intensity of DCM-ML and HSA concentration from 0 to 0.08 mg/mL was obtained with the detection limit of 0.25 μg/mL. The sensing mechanism of the sensor towards HSA was demonstrated to be via recognition in the fatty acid site 1 (FA1), instead of the most reported binding sites (Sudlow I and II) in HSA, for the first time, by both the displacement experiments and molecular docking simulation. Thus, DCM-ML can also be assumed as a potential FA1 site-binding marker for examining drugs binding to the FA1 site in HSA. At last, the utilization of sensor DCM-ML for quantification and validation of HSA in urine samples and cell culture medium was effectively demonstrated. Therefore, the development of DCM-ML should find great application potentials in the fields of analytical chemistry and clinical medicine as a highly sensitive HSA sensor.

Sequential storage and release of microdroplets

Droplet microfluidic methods have opened up the possibility of studying a plethora of phenomena ranging from biological to physical or chemical processes at ultra low volumes and high throughput. A key component of such approaches is the ability to trap droplets for observation, and many device architectures for achieving this objective have been developed. A challenge with such approaches is, however, recovering the droplets following their confinement for applications involving further analysis. Here, we present a device capable of generating, confining and releasing microdroplets in a sequential manner. Through a combination of experimental and computational simulations, we shed light on the key features required for successful droplet storage and retrieval. Moreover, we explore the effect of the flow rate of the continuous phase on droplet release, determining that a critical rate is needed to ensure complete droplet deformation through constrictions holding the droplets in place prior to release. Finally, we find that once released, droplets can be retrieved and collected off chip. The ability to generate, store and sequentially release droplets renders such a device particularly promising for future applications where reactions may not only be monitored on-chip, but droplets can also be retrieved for further analysis, facilitating new exploratory avenues in the fields of analytical chemistry and biology.