New Electrochemical Flow-Cell Configuration Integrated into a Three-Dimensional Microfluidic Platform: Improving Analytical Application in the Presence of Air Bubbles

Merging 3D-printing technology and disposable materials for electrochemical purposes: A sustainable alternative to ensure greener electroanalysis

3D-printing technology has revolutionized electrochemical applications by enabling rapid prototyping of various devices with high precision, even in highly complex structures. However, a significant challenge remains in developing less costly and more sustainable analytical approaches and methods aimed at mitigating the negative environmental impacts of chemical analysis procedures. In this study, we propose a solution to these challenges by creating a simple and versatile electrochemical system that combines 3D-printing technology with recyclable disposable materials, such as graphite from an exhausted battery and a stainless-steel screw. Our results demonstrate a novel strategy for developing electrodes and other laboratory-made devices that align with the principles of sustainability and green chemistry. Furthermore, we provide evidence of the effectiveness of the proposed system in an analytical application involving the simultaneous determination of tert-butylhydroquinone, acetaminophen, and levofloxacin using the voltammetric technique in lake and groundwater samples. The results indicate sufficient accuracy, with recovery values ranging from 91 to 110%. Additionally, we utilized the Analytical GREEnness calculator as a metric system to evaluate the environmental friendliness of the proposed electroanalytical protocol. The final score confirms a favorable level of sustainability, reaffirming the eco-friendly nature of our approach.

Threads in tubing: an innovative approach towards improved electrochemical thread-based microfluidic devices

Thread-based microfluidic analytical devices have received growing attention since threads have some advantages over other materials. Compared to paper, threads are also capable of spontaneously transporting fluid due to capillary action, but they have superior mechanical strength and do not require hydrophobic barriers. Therefore, thread-based microfluidic devices can be inexpensively fabricated with no need for external pumps or sophisticated microfabrication apparatus. Despite these outstanding features, achieving a controlled and continuous flow rate is still a challenging task, mainly due to fluid evaporation. Here, we overcome this challenge by inserting a cotton thread into a polyethylene tube aiming to minimize fluid evaporation. Also, a cotton piece was inserted into the outlet reservoir to improve the wicking ability of the device. This strategy enabled the fabrication of an innovative electrochemical thread in a tubing microfluidic device that was capable to hold a consistent flow rate (0.38 μL s^-1) for prolonged periods, allowing up to 100 injections in a single device by simply replacing the cotton piece in the outlet reservoir. The proposed device displayed satisfactory analytical performance for selected model analytes (dopamine, hydrogen peroxide, and tert-butylhydroquinone), in addition to being successfully used for quantification of nitrite in spiked artificial saliva samples. Beyond the flow rate improvement, this "thread-in-tube" strategy ensured the protection of the fluid from external contamination while making it easier to connect the electrode array to the microchannels. Thus, we envision that the thread in a tube strategy could bring interesting improvements to thread-based microfluidic analytical devices.

Microfluidics for Electrochemical Energy Conversion

Electrochemical energy conversion is an important supplement for storage and on-demand use of renewable energy. In this regard, microfluidics offers prospects to raise the efficiency and rate of electrochemical energy conversion through enhanced mass transport, flexible cell design, and ability to eliminate the physical ion-exchange membrane, an essential yet costly element in conventional electrochemical cells. Since the 2002 invention of the microfluidic fuel cell, the research field of microfluidics for electrochemical energy conversion has expanded into a great variety of cell designs, fabrication techniques, and device functions with a wide range of utility and applications. The present review aims to comprehensively synthesize the best practices in this field over the past 20 years. The underlying fundamentals and research methods are first summarized, followed by a complete assessment of all research contributions wherein microfluidics was proactively utilized to facilitate energy conversion in conjunction with electrochemical cells, such as fuel cells, flow batteries, electrolysis cells, hybrid cells, and photoelectrochemical cells. Moreover, emerging technologies and analytical tools enabled by microfluidics are also discussed. Lastly, opportunities for future research directions and technology advances are proposed.

Simultaneous separation and electroanalysis in a single polydimethylsiloxane-based platform

Channel-based microfluidic devices integrating the separation step and detection system are key factors to expand microanalysis application. However, these devices still depend on macroscale external equipment for pre-treatment of the sample, separation, or detection. The integration of all steps in only one stage is critical to improving feasibility. Herein, we use a low-cost protocol to solve part of the challenge by designing a dual-mode system onto single polydimethylsiloxane (PDMS)-based platform - overall dimensions of 65 mm length × 20 mm width × 14 mm height and the inner diameter of 297±10 μm height × 605±19 μm width - for column-free separation and simultaneous detection. As a proof-of-concept, we used this all-in-one PDMS platform to separate - without the packet-based phase - and determine salicylic acid (SA) and caffeine (CAF) with a detection limit of 0.20 and 0.18 μmol L^-1 and quantification limit of 0.70 and 0.60 μmol L^-1 for SA and CAF, respectively. We separated the mixture using forced convection into a chemically treated microchannel while detecting the analytes in amperometric mode. Here, we report new insights into how integrating analytes separation and further electroanalysis into a single miniaturized device.

Microfluidic Device for the Determination of Water Chlorination Levels Combining a Fluorescent meso-Enamine Boron Dipyrromethene Probe and a Microhydrocyclone for Gas Bubble Separation

Chlorination procedures are commonly applied in swimming pool water and wastewater treatment, yet also in food, pharmaceutical, and paper production. The amount of chlorine in water needs to be strictly controlled to ensure efficient killing of pathogens but avoid the induction of negative health effects. Miniaturized microfluidic fluorescence sensors are an appealing approach here when aiming at online or at-site measurements. Two meso-enamine-substituted boron dipyrromethene (BODIPY) dyes were found to exhibit favorable indication properties, their reaction with hypochlorite leading to strong fluorescence enhancement. Real-time assays became possible after integration of these fluorescent probes with designed two-dimensional (2D) and three-dimensional (3D) microfluidic chips, incorporating a passive sinusoidal mixer and a microhydrocyclone, respectively. A comparison of the two microfluidic systems, including their abilities to prevent accumulation or circulation of microbubbles produced by the chemical indication reaction, showed excellent fluidic behavior for the microhydrocyclone-based device. After coupling to a miniaturized optical reader for fluorescence detection, the 2D microfluidic system showed a promising detection range of 0.04-0.5 mg L^-1 while still being prone to bubble-induced fluctuations and suffering from considerably low signal gain. The microhydrocyclone-based system was distinctly more robust against gas bubbles, showed a higher signal gain, and allowed us to halve the limit of detection to 0.02 mg L^-1. The use of the 3D system to quantify the chlorine content of swimming pool water samples for sensitive and quantitative chlorine monitoring was demonstrated.

Advances in Chemical and Biological Methods to Identify Microorganisms-From Past to Present

Fast detection and identification of microorganisms is a challenging and significant feature from industry to medicine. Standard approaches are known to be very time-consuming and labor-intensive (e.g., culture media and biochemical tests). Conversely, screening techniques demand a quick and low-cost grouping of bacterial/fungal isolates and current analysis call for broad reports of microorganisms, involving the application of molecular techniques (e.g., 16S ribosomal RNA gene sequencing based on polymerase chain reaction). The goal of this review is to present the past and the present methods of detection and identification of microorganisms, and to discuss their advantages and their limitations.