Miniaturization through lab-on-a-chip: Utopia or reality for routine laboratories? A review

Target-induced DNA nanomachine operation for the detection of proteins

Accurate and sensitive detection of disease-associated proteins in early stage of patients plays an important role in timely treatment and successfully extending patients' lives. To meet this demand, we herein rationally designed a flexible target-induced DNA nanomachine operation (TIDNMO) sensor for the detection of proteins. The TIDNMO system was composed of DNA nanoswitch and DNA walker. Triplex DNA nanoswitch was triggered by specific target, followed by the release of the walking strand, which initiated the DNA walker amplification as signal output. In addition, the Exo III could drive walking strand autonomously move on gold nanoparticle surface to realize 2 orders of magnitude signal amplification. What's more, this sensor could transform its suitable functional recognition element of DNA nanoswitch to recognize other specific molecule and realize different targets sensing based on identical walking tracks. Considering the facile reporter elements and efficient amplification performance, the present DNA nanomachine as a sensor could achieve a detection limit of 68 pM for anti-Dig antibody, 0.95 pM for mucin-1 respectively, along with a superb specificity. Furthermore, the method reported here opened a new chapter in disease-related protein sensing for the development of clinical early diagnosis.

Polymer Waveguide Sensor Based on Evanescent Bragg Grating for Lab-on-a-Chip Applications

In this work, an evanescent Bragg grating sensor inscribed in a few-mode planar polymer waveguide was integrated into microchannel structures and characterized by various chemical applications. The planar waveguide and the microchannels consisted of epoxide-based polymers. The Bragg grating structure was postprocessed by using point-by-point direct inscription technology. By monitoring the central wavelength shift of the reflected Bragg signal, the sensor showed a temperature sensitivity of -47.75 pm/K. Moreover, the functionality of the evanescent field-based measurements is demonstrated with two application examples: the refractive index sensing of different aqueous solutions and gas-phase hydrogen concentration detection. For the latter application, the sensor was additionally coated with a functional layer based on palladium nanoparticles. During the refractive index sensing measurement, the sensor achieved a sensitivity of 6.5 nm/RIU from air to 99.9% pure isopropyl alcohol. For the gas-phase hydrogen detection, the coated sensor achieved a reproducible concentration detection up to 4 vol% hydrogen. According to the reported experimental results, the integrated Bragg-grating-based waveguide sensor demonstrates high potential for applications based on the lab-on-a-chip concept.

User-friendly analysis of droplet array images

Water-in-oil droplets allow performing massive experimental parallelization and high-throughput studies, such as single-cell experiments. However, analyzing such vast arrays of droplets usually requires advanced expertise and sophisticated workflow tools, which limits accessibility for a wider user base in the fields of chemistry and biology. Thus, there is a need for more user-friendly tools for droplet analysis. In this article, we deliver a set of analytical pipelines for user-friendly analysis of typical scenarios in droplet experiments. We built pipelines that combine various open-source image-analysis software with a custom-developed data processing tool called "EasyFlow". Our pipelines are applicable to the typical experimental scenarios that users encounter when working with droplets: i) mono- and polydisperse droplets, ii) brightfield and fluorescent images, iii) droplet and object detection, iv) signal profile of droplets and objects (e.g., fluorescence).

Surface Modification of Cyclic-Olefin-Copolymer (COC)-Based Microchannels for the Large-Scale Industrial Production of Droplet Microfluidic Devices

The copolymers of cycloolefin (COC), a type of thermoplastic material, have been widely used for the large-scale industrial fabrication of droplet microfluidic devices, which is often performed using hot-embossing or injection-molding techniques. The generation of droplets and the uniformity of droplet sizes are significantly affected by the surface wettability of COC during fabrication and the pressure stability of the employed fluid pump during operation. In order to alleviate the effects of undesirable surface wettability and pressure variation on the generation of droplets in COC-based devices, a simple surface modification procedure was applied to hydrophobically modify the surfaces of COC-based microchannels for large-scale industrial production. The surface modification procedure consisted of an oxygen plasma treatment of the polymer surface followed by a solution-phase reaction in fluorocarbon solvent. The experimental results demonstrate that following the proposed surface modification, the COC droplet microfluidic devices could stably generate microvolume water droplets with a small coefficient of variation, even if the pressure of the dispersed phase (water) fluctuated. The durability test results regarding the modified surfaces show that the hydrophobicity of the modified COC surfaces could be sustained for up to four months, deteriorating with time thereafter. Our study can provide a potential solution useful in and guidance for the large-scale industrial production of droplet microfluidic devices for various applications, including polymerase chain reaction and single-cell analysis.

Integrated Glass Microfluidics with Electrochemical Nanogap Electrodes

We present a framework for the fabrication of chip-based electrochemical nanogap sensors integrated with microfluidics. Instead of polydimethylsiloxane (PDMS), SU-8 aided adhesive bonding of silicon and glass wafers is used to implement parallel flow control. The fabrication process permits wafer-scale production with high throughput and reproducibility. Additionally, the monolithic structures allow simple electrical and fluidic connections, alleviating the need for specialized equipment. We demonstrate the utility of these flow-incorporated nanogap sensors by performing redox cycling measurements under laminar flow conditions.

Miniaturized Protein Digestion Using Acoustic Levitation with Online High Resolution Mass Spectrometry

The combination of acoustically levitated droplets, mid-IR laser evaporation, and subsequent post-ionization by secondary electrospray ionization was applied for monitoring the enzymatic digestion of various proteins. Acoustically levitated droplets are an ideal, wall-free model reactor, readily allowing compartmentalized microfluidic trypsin digestions. Time-resolved interrogation of the droplets yielded real-time information on the progress of the reaction and thus provided insights into reaction kinetics. After 30 min of digestion in the acoustic levitator, the obtained protein sequence coverages were identical to the reference overnight digestions. Importantly, our results clearly demonstrate that the applied experimental setup can be used for the real-time investigation of chemical reactions. Furthermore, the described methodology only uses a fraction of the typically applied amounts of solvent, analyte, and trypsin. Thus, the results exemplify the use of acoustic levitation as a green analytical chemistry alternative to the currently used batch reactions.

Design and Fabrication of a Fully-Integrated, Miniaturised Fluidic System for the Analysis of Enzyme Kinetics

The lab-on-a-chip concept, enabled by microfluidic technology, promises the integration of multiple discrete laboratory techniques into a miniaturised system. Research into microfluidics has generally focused on the development of individual elements of the total system (often with relatively limited functionality), without full consideration for integration into a complete fully optimised and miniaturised system. Typically, the operation of many of the reported lab-on-a-chip devices is dependent on the support of a laboratory framework. In this paper, a demonstrator platform for routine laboratory analysis is designed and built, which fully integrates a number of technologies into a single device with multiple domains such as fluidics, electronics, pneumatics, hydraulics, and photonics. This facilitates the delivery of breakthroughs in research, by incorporating all physical requirements into a single device. To highlight this proposed approach, this demonstrator microsystem acts as a fully integrated biochemical assay reaction system. The resulting design determines enzyme kinetics in an automated process and combines reservoirs, three-dimensional fluidic channels, optical sensing, and electronics in a low-cost, low-power and portable package.

Multi-well plate as headspaces for paper-based colorimetric detection of sulfur dioxide gas: An alternative method of sulfite titration for determination of formaldehyde

This work describes the analysis of formaldehyde using a 96-well microplate as multiple headspaces for the separation of sulfur dioxide gas generated from the sulfite remaining after its reaction with the formaldehyde in the sample. The quantitation of the gas is by colorimetric detection of an indicator paper placed over the microplate. The samples are aqueous extracts of various foods that are possibly adulterated with formaldehyde. A known excess amount of sulfite is added to the extract solution aliquoted in the well. The remaining sulfite is acidified with hydrochloric acid to generate sulfur dioxide gas which diffuses through the headspace above the solution to be absorbed at the moist strip of the indicator paper placed over the mouth of the wells. Anthocyanins extracted from the butterfly pea flower is used as the pH indicator giving a color change from the increase of hydrogen ions by hydrolysis of the absorbed sulfur dioxide gas. The exposed paper strip is scanned, and the digital images of the colored region analyzed using ImageJ software. The optimized method has a linear range of 200-1000 mg L^-1 formaldehyde with limit of detection ((2.57*SD of intercept)/(slope of calibration line)) of the aqueous extract of 40 mg L^-1 and coefficient of determination (r²) > 0.9979. Samples of fresh produce, such as seafood, meat, and vegetables, and various processed food were analyzed for their possible formaldehyde content. The results obtained from the headspace paper-based colorimetric detection are not statistically different from the values obtained from the titration method by paired t-tests.

On-Chip Electromembrane Surrounded Solid Phase Microextraction for Determination of Tricyclic Antidepressants from Biological Fluids Using Poly(3,4-ethylenedioxythiophene)-Graphene Oxide Nanocomposite as a Fiber Coating

In the present study, on-chip electromembrane surrounded solid phase microextraction (EM-SPME) was employed in the determination of tricyclic antidepressants (TCAs), including amitriptyline, nortriptyline, imipramine, desipramine, maprotiline, and sertraline, from various biological fluids. In this regard, poly(3,4-ethylenedioxythiophene)-graphene oxide (PEDOT-GO) was electrodeposited on an SPME fiber as a conductive coating, then the fiber played the acceptor-electrode role during the extraction. Thus, the immigration of the analytes under the influence of an electric field and their absorption onto the fiber coating were accomplished simultaneously. Under the optimized conditions, the limits of detection for the target analytes were acquired in the range of 0.005-0.025 µg L^-1 using gas chromatography-mass spectrometry. The linearity of the method was 0.010-500 µg L^-1 for the imipramine and sertraline, 0.025-500 µg L^-1 for the amitriptyline, nortriptyline, and desipramine, and 1.000-250 µg L^-1 for the maprotiline (R² ≥ 0.9984). Moreover, this method provided suitable precision and fiber-to-fiber reproducibility, with RSDs ≤ 8.4%. The applicability of the proposed setup was eventually investigated for extraction of the drugs from human bone marrow aspirate, urine, plasma, and well water samples, in which satisfactory relative recoveries, from 93-105%, were obtained.

A handheld 3D-printed microchip for simple integration of the H2O2-producing enzymatic reactions with subsequent chemiluminescence detection: Application for sugars

Herein, a novel lab-on-a-chip (LoC) device fabricated by 3D printing based on H₂O₂-producing enzymatic reactions with sensitive chemiluminescence (CL) detection was developed to measure different sugars, including glucose, fructose, sucrose, and maltose, in honey, juice, and rice flour samples. The pumpless microchip included two main parts, separated by new cone-shape blocking valves; part A for sample introduction and subsequent enzymatic reaction, besides the CL reagent (luminol) container, and part B for detection. The specific enzyme(s) were embedded into the pores of the zinc zeolite-imidazole framework (ZIF-8) to improve their storage stability. By opening the valves, H₂O₂ produced by enzymatic reaction and luminol could flow through the designed channels into the detection zone on part B, where a 2D cobalt-imidazole framework was embedded to improve the luminol-H₂O₂ CL emission. The obtained signal was proportional to the considered sugar concentration, with the detection limits range of 20-268 µM.

Microfluidics for detection of exosomes and microRNAs in cancer: State of the art

Exosomes are small extracellular vesicles with sizes ranging from 30-150 nanometers that contain proteins, lipids, mRNAs, microRNAs, and double-stranded DNA derived from the cells of origin. Exosomes can be taken up by target cells, acting as a means of cell-to-cell communication. The discovery of these vesicles in body fluids and their participation in cell communication has led to major breakthroughs in diagnosis, prognosis, and treatment of several conditions (e.g., cancer). However, conventional isolation and evaluation of exosomes and their microRNA content suffers from high cost, lengthy processes, difficult standardization, low purity, and poor yield. The emergence of microfluidics devices with increased efficiency in sieving, trapping, and immunological separation of small volumes could provide improved detection and monitoring of exosomes involved in cancer. Microfluidics techniques hold promise for advances in development of diagnostic and prognostic devices. This review covers ongoing research on microfluidics devices for detection of microRNAs and exosomes as biomarkers and their translation to point-of-care and clinical applications.

Ion chromatograph with three-dimensional printed absorbance detector for indirect ultraviolet absorbance detection of phosphate in effluent and natural waters

An ion chromatography system employing a low-cost three-dimensional printed absorbance detector for indirect ultraviolet detection towards portable phosphate analysis of environmental and industrial waters has been developed. The optical detection cell was fabricated using stereolithography three-dimensional printing of nanocomposite material. Chromatographic analysis and detection of phosphate were carried out using a CS5A 4 × 250 mm analytical column with indirect ultraviolet detection using a 255 nm light-emitting diode. Isocratic elution using a 0.6 mM potassium phthalate eluent combined with 1.44 mM sodium bicarbonate was employed at a flow rate of 0.75 ml/min. A linear calibration range of 0.5 to 30 mg/L PO₄ ^3- applicable to environmental and wastewater analysis was achieved. For retention time and peak area repeatability, relative standard deviation values were 0.68% and 4.09%, respectively. Environmental and wastewater samples were analyzed with the optimized ion chromatography platform and the results were compared to values obtained by an accredited ion chromatograph. For the analysis of environmental samples, relative errors of <14 % were achieved. Recovery analysis was also carried out on both freshwater and wastewater samples and recovery results were within the acceptable range for water analysis using standard ion chromatography methods.

Lab-on-a-chip technologies for food safety, processing, and packaging applications: a review

The advent of microfluidic systems has led to significant developments in lab-on-a-chip devices integrating several functions onto a single platform. Over the years, these miniature devices have become a promising tool for faster analytical testing, displaying high precision and efficiency. Nonetheless, most microfluidic systems are not commercially available. Research is actually undergoing on the application of these devices in environmental, food, biomedical, and healthcare industries. The lab-on-a-chip industry is predicted to grow annually by 20%. Here, we review the use of lab-on-a-chip devices in the food sector. We present fabrication technologies and materials to developing lab-on-a-chip devices. We compare electrochemical, optical, colorimetric, chemiluminescence and biological methods for the detection of pathogens and microorganisms. We emphasize emulsion processing, food formulation, nutraceutical development due to their promising characteristics. Last, smart packaging technologies like radio frequency identification and indicators are highlighted because they allow better product identification and traceability.

Fully 3D printed fluidic devices with integrated valves and pumps for flow injection analysis

The use of a PolyJet 3D printer to create a microfluidic device that has integrated valves and pumps is described. The process uses liquid support and stacked printing to result in fully printed devices that are ready to use within minutes of fabrication after minimal post-processing. A unique feature of PolyJet printing is the ability to incorporate several different materials of varying properties into one print. In this work, two commercially available materials were used: a rigid-transparent plastic material (VeroClear) was used to define the channel regions and the bulk of the device, while the pumps/valves were printed in a flexible, rubber-like material (Agilus30). The entire process, from initial design to testing takes less than 4 hours to complete. The performance of the valves and pumps were characterized by fluorescence microscopy. A flow injection analysis device that enabled the discrete injections of analyte plugs was created, with on-chip pumps being used to move the fluid streams. The injection process was found to be reproducible and linearly correlated with changes in analyte concentration. The utility was demonstrated with the injection and rapid lysis of fluorescently-labeled endothelial cells. The ability to produce a device with integrated pumps/valves in one process significantly adds to the applicability of 3D printing to create microfluidic devices for analytical measurements.

Pump-Free Microfluidic Device for the Electrochemical Detection of α1-Acid Glycoprotein

α₁-Acid glycoprotein (AGP) is a glycoprotein present in serum, which is associated with the modulation of the immune system in response to stress or injuries, and a biomarker for inflammatory diseases and cancers. Here, we propose a pump-free microfluidic device for the electrochemical determination of AGP. The microfluidic device utilizes capillary-driven flow and a passive mixing system to label the AGP with the Os (VI) complex (an electrochemical tag) inside the main channel, before delivering the products to the electrode surface. Furthermore, thanks to the resulting geometry, all the analytical steps can be carried out inside the device: labeling, washing, and detection by adsorptive transfer stripping square wave voltammetry. The microfluidic device exhibited a linear range from 500 to 2000 mg L^-1 (R² = 0.990) and adequate limit of detection (LOD = 231 mg L^-1). Commercial serum samples were analyzed to demonstrate the success of the method, yielding recoveries around 83%. Due to its simplicity, low sample consumption, low cost, short analysis time, disposability, and portability, the proposed method can serve as a point-of-care/need testing device for AGP.

Manipulation and Mixing of 200 Femtoliter Droplets in Nanofluidic Channels Using MHz-Order Surface Acoustic Waves

Controllable manipulation and effective mixing of fluids and colloids at the nanoscale is made exceptionally difficult by the dominance of surface and viscous forces. The use of megahertz (MHz)-order vibration has dramatically expanded in microfluidics, enabling fluid manipulation, atomization, and microscale particle and cell separation. Even more powerful results are found at the nanoscale, with the key discovery of new regimes of acoustic wave interaction with 200 fL droplets of deionized water. It is shown that 40 MHz-order surface acoustic waves can manipulate such droplets within fully transparent, high-aspect ratio, 100 nm tall, 20-130 micron wide, 5-mm long nanoslit channels. By forming traps as locally widened regions along such a channel, individual fluid droplets may be propelled from one trap to the next, split between them, mixed, and merged. A simple theory is provided to describe the mechanisms of droplet transport and splitting.

Portable analyser using two-dimensional ion chromatography with ultra-violet light-emitting diode-based absorbance detection for nitrate monitoring within both saline and freshwaters

A portable and automated IC system with a dual-capability for the analysis of both fresh and saline environmental waters has been developed. Detection of nitrate in complex matrices such as seawater was achieved by the employment of an automated two-dimensional (heart-cut) IC method utilised in tandem with on-column matrix elimination, using a sodium chloride eluent. The system also demonstrated the capability to switch to a second mode of analysis, whereby direct one-dimensional IC analysis was employed to rapidly detect nitrite and nitrate in freshwater, with direct UV LED based absorption detection in under 3 minutes. Calibration curves using a 195 µL sample loop were generated for both freshwater and artificial seawater samples. For marine analysis, an analytical range of 0.1 mg L^-1 - 40 mg L^-1 NO₃^- was possible, while an analytical range (0.1 mg L^-1 - 15 mg L^-1 NO₂^-, 0.2 - 30 mg L^-1 NO₃^-) appropriate for freshwater analysis was also achieved. Chromatographic repeatability for both marine and freshwater analysis was verified over 40 sequential runs with RSD values of < 1% demonstrated for both peak area and retention times for each mode of analysis. The selectivity of both methods was demonstrated with interference tests with common anions present in environmental waters. Recovery analysis was carried out on marine samples from Tramore Bay, Co. Waterford, Ireland, and the systems analytical performance was compared with that of an accredited IC following environmental sample analysis.

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.

Membrane integration into PDMS-free microfluidic platforms for organ-on-chip and analytical chemistry applications

Membranes play a crucial role in many microfluidic systems, enabling versatile applications in highly diverse research fields. However, the tight and robust integration of membranes into microfluidic systems requires complex fabrication processes. Most integration approaches, so far, rely on polydimethylsiloxane (PDMS) as base material for the microfluidic chips. Several limitations of PDMS have resulted in the transition of many microfluidic approaches to PDMS-free systems using alternative materials such as thermoplastics. To integrate membranes in those PDMS-free systems, novel alternative approaches are required. This review provides an introduction into microfluidic systems applying membrane technology for analytical systems and organ-on-chip as well as a comprehensive overview of methods for the integration of membranes into PDMS-free systems. The overview and examples will provide a valuable resource and starting point for any researcher that is aiming at implementing membranes in microfluidic systems without using PDMS.

Numerical simulation of three-dimensional passive micromixer based on the principle of Koch fractal

In this paper, We arrange the obstacles based on the Koch fractal principle (OKF) in the micromixer. By changing the fluid flow and folding the fluid, a better mixing performance is achieved. We improve the mixing efficiency by placing OKF and changing the position of OKF, then we studied the influence of the number of OKF and the height of the micromixer on the mixing performance. The results show that when eight OKF are staggered in the microchannel and the height is 0.2 mm, the mixing efficiency of the OKF micromixer can reach 97.1%. Finally, we compared the velocity cross section and velocity streamline of the fluid, and analyzed the influence of OKF on the concentration trend. Through analysis, it is concluded that OKF can generate chaotic convection in the fluid, and enhance the mixing of fluids by generating vortices and folding the fluid. It can effectively improve the mixing efficiency of the micromixer.

Microfluidics for Peptidomics, Proteomics, and Cell Analysis

Microfluidics is the advanced microtechnology of fluid manipulation in channels with at least one dimension in the range of 1-100 microns. Microfluidic technology offers a growing number of tools for manipulating small volumes of fluid to control chemical, biological, and physical processes relevant to separation, analysis, and detection. Currently, microfluidic devices play an important role in many biological, chemical, physical, biotechnological and engineering applications. There are numerous ways to fabricate the necessary microchannels and integrate them into microfluidic platforms. In peptidomics and proteomics, microfluidics is often used in combination with mass spectrometric (MS) analysis. This review provides an overview of using microfluidic systems for peptidomics, proteomics and cell analysis. The application of microfluidics in combination with MS detection and other novel techniques to answer clinical questions is also discussed in the context of disease diagnosis and therapy. Recent developments and applications of capillary and microchip (electro)separation methods in proteomic and peptidomic analysis are summarized. The state of the art of microchip platforms for cell sorting and single-cell analysis is also discussed. Advances in detection methods are reported, and new applications in proteomics and peptidomics, quality control of peptide and protein pharmaceuticals, analysis of proteins and peptides in biomatrices and determination of their physicochemical parameters are highlighted.

Enzyme embedded microfluidic paper-based analytic device (μPAD): a comprehensive review

Low-cost paper-based analytical devices are the latest generation of portable lab-on-chip designs that offers an innovative platform for the on/off-site analysis (biosensing) of target analytes, especially in rural and remote areas. Recently, microfluidic paper-based analytical devices (μPADs) have attained significant recognition owing to their exciting fundamental features such as: ease of fabrication, rapid operation, and precise interpretations. The incorporation of enzymes with paper-based analytical devices significantly improves analytical performance while exhibiting excellent chemical and storage stability. In addition to that, these devices are highly compact, portable, easy-to-use, and do not require any additional sophisticated equipment for the detection and quantification of target analytes. This review provides a holistic insight into design, fabrication, and enzyme immobilization strategies for the development of enzyme-μPADs, which enables them to be widely implemented for in-field analysis. It also highlights the recent application of enzyme-μPADs in the area of: biomedical, food safety, and environmental monitoring while exploring the mechanisms of detection involved. Further, in order to improve the accuracy of analysis, researchers have designed a smartphone-based scanning tool for multi-variant point-of-care devices, which is summarized in the latter part of the review. Finally, the future perspectives and outlook of major challenges associated with enzyme-μPADs are discussed with their possible solutions. The development of enzyme integrated μPADs will open a new avenue as an exceptional analytical tool to explore various applications.HIGHLIGHTSEnzyme embedded paper-based analytical devices are a revolution in the field of biosensing.The design, fabrication, and enzyme immobilization on μPADs have been comprehensively discussed.The application of enzyme-μPADs food safety, environmental monitoring, and clinical diagnostic have been reviewed.Smartphones can be used as an on-site, user-friendly, and compact next-gen scanning tool for biosensing.

Mixing performance of an electroosmotic micromixer with Koch fractal structure

In this paper, we have designed a Koch fractal electroosmotic micromixer (KFEM). A low-voltage electroosmotic micromixer. In order to optimize the electrode position, Koch microchannel is designed according to the Koch fractal principle and the electrode pairs based on the fractal are arranged. Then the effect of electrode voltage, electrode distribution positions, the number of electrode pairs, two kinds of Koch fractal structures, Reynolds (Re) number and the frequency of alternating current (AC) on the mixing performance are studied. The results show that the mixing efficiency can reach 99% in a short time when the AC voltage is 1 V, the AC frequency is 12 Hz and the electroosmotic micromixer has two sets of electrode pairs.

A novel three-dimensional electroosmotic micromixer based on the Koch fractal principle

Mixing performance of micromixers. (a) The voltage value is 0 V. (b) The voltage value is 3 V. (c) The voltage value is 10 V.

Advances in Electrochemical Aptasensors Based on Carbon Nanomaterials

Carbon nanomaterials offer unique opportunities for the assembling of electrochemical aptasensors due to their high electroconductivity, redox activity, compatibility with biochemical receptors and broad possibilities of functionalization and combination with other auxiliary reagents. In this review, the progress in the development of electrochemical aptasensors based on carbon nanomaterials in 2016–2020 is considered with particular emphasis on the role of carbon materials in aptamer immobilization and signal generation. The synthesis and properties of carbon nanotubes, graphene materials, carbon nitride, carbon black particles and fullerene are described and their implementation in the electrochemical biosensors are summarized. Examples of electrochemical aptasensors are classified in accordance with the content of the surface layer and signal measurement mode. In conclusion, the drawbacks and future prospects of carbon nanomaterials’ application in electrochemical aptasensors are briefly discussed.

Simultaneous determination of total phenolic acids and total flavonoids in tea and honey samples using an integrated lab on a chip device

A microfluidic device for simultaneous analysis of total flavonoids and total phenolic acids is presented for the first time. The process was based on the utilization of magnetic zinc-imidazole frameworks (ZIF-4), as a highly efficient media for on-line separation of phenolic acids and flavonoids, which were subsequently detected by a sensitive chemiluminescence (CL) method. Acrylate-based polymeric microchips containing a separation column (12.5 mm length, 3 mm width and 1 mm depth) were fabricated using a 3D-printer, and magnetic ZIF-4 was fixed into the column. The high porosity of the magnetic ZIF-4 made it a suitable adsorbent, guaranteeing an effective separation. The detection limits were in the range of 0.04-0.10 µg mL^-1 with relative standard deviation values of (2.19-4.38%). The system was successfully applied for the analysis of flavonoids and phenolic acids in tea and honey samples. The recovery was from 95.4 to 104.1%, indicating a good accuracy of the developed method.

Finite-Size Charged Species Diffusion and pH Change in Nanochannels

Molecular transport through nanofluidic structures exhibits properties that are unique at the nanoscale. The high surface-to-volume ratio of nanometer-sized confined spaces renders particle interactions with the surface of central importance. The electrical double layer (EDL) at the solid-liquid interface of charged surfaces generates an enrichment of counterions and the exclusion of co-ions that lead to a change in their diffusivity. In addition, the diffusive transport is altered by steric and hydrodynamic interactions between fluid molecules and the boundaries. An extensive body of literature investigates molecular transport at the nanoscale. However, most studies account for ionic species as point charges, severely limiting the applicability of the results to "large" nanofluidic systems. Moreover, and even more importantly, the change of pH in the nanoconfined region inside nanochannels has been completely overlooked. Corroborated by experimental data, here we present an all-encompassing analysis of molecular diffusion from the micro- to the ultra-nanoscale. While accounting for finite-size ions, we compute self-consistently the pH inside the channels. Surprisingly, we found that the concentration of ions H⁺ can change by more than 2 orders of magnitude compared to the bulk, hugely affecting molecular transport. Further, we found that counterions exhibit both enrichment and exclusion, depending on the size of nanochannels. Achieving a greater understanding of the effective transport properties of fluids at the nanoscale will fill the gap in knowledge that still limits development of innovative systems for medicine and industrial applications alike.

High-throughput electrochemical sensing platform for screening nanomaterial-biomembrane interactions

A high-throughput, automated screening platform has been developed for the assessment of biological membrane damage caused by nanomaterials. Membrane damage is detected using the technique of analyzing capacitance-current peak changes obtained through rapid cyclic voltammetry measurements of a phospholipid self-assembled monolayer formed on a mercury film deposited onto a microfabricated platinum electrode after the interaction of a biomembrane-active species. To significantly improve wider usability of the screening technique, a compact, high-throughput screening platform was designed, integrating the monolayer-supporting microfabricated electrode into a microfluidic flow cell, with bespoke pumps used for precise, automated control of fluid flow. Chlorpromazine, a tricyclic antidepressant, and a citrate-coated 50 nm diameter gold nanomaterial (AuNM) were screened to successfully demonstrate the platform's viability for high-throughput screening. Chlorpromazine and the AuNM showed interactions with a 1,2-dioleoyl-sn-glycero-3-phosphocholine (DOPC) monolayer at concentrations in excess of 1 µmol dm^-3. Biological validity of the electrochemically measured interaction of chlorpromazine with DOPC monolayers was confirmed through quantitative comparisons with HepG2 and A549 cytotoxicity assays. The platform also demonstrated desirable performance for high-throughput screening, with membrane interactions detected in <6 min per assay. Automation contributed to this significantly by reducing the required operating skill level when using the technique and minimizing fluid consumption.

Electroosmotic Flow Behavior of Viscoelastic LPTT Fluid in a Microchannel

In many research works, the fluid medium in electroosmosis is considered to be a Newtonian fluid, while the polymer solutions and biological fluids used in biomedical fields mostly belong to the non-Newtonian category. Based on the finite volume method (FVM), the electroosmotic flow (EOF) of viscoelastic fluids in near-neutral (pH = 7.5) solution considering four ions (K+, Cl-, H+, OH-) is numerically studied, as well as the viscoelastic fluids' flow characteristics in a microchannel described by the Linear Phan-Thien-Tanner (LPTT) constitutive model under different conditions, including the electrical double layer (EDL) thickness, the Weissenberg number (Wi), the viscosity ratio and the polymer extensibility parameters. When the EDL does not overlap, the velocity profiles for both Newtonian and viscoelastic fluids are plug-like and increase sharply near the charged wall. Compared with Newtonian fluid at Wi = 3, the viscoelastic fluid velocity increases by 5 times and 9 times, respectively, under the EDL conditions of kH = 15 and kH = 250, indicating the shear thinning behavior of LPTT fluid. Shear stress obviously depends on the viscosity ratio and different Wi number conditions. The EOF is also enhanced by the increase (decrease) in polymer extensibility parameters (viscosity ratio). When the extensibility parameters are large, the contribution to velocity is gradually weakened.

Barcoded point-of-care bioassays

Barcoded bioassays are ready to promote bioanalysis and biomedicine toward the point of care.

Enhanced Sensitivity in Nanopore Sensing of Cancer Biomarkers in Human Blood via Click Chemistry

Cancer biomarkers are expected to be indicative of the occurrence of certain cancer diseases before the tumors form and metastasize. However, many biomarkers can only be acquired in extremely low concentrations, which are often beyond the limit of detection (LOD) of current instruments and technologies. A practical strategy for nanopore sensing of cancer biomarkers in raw human blood down to the femtomolar level is developed here. This strategy first converts the detection of cancer biomarkers to the quantification of copper ions by conducting a sandwich assay involving copper oxide nanoparticles. The released Cu²⁺ is then taken to catalyze the "click" reaction which ligates a host-guest modified DNA probe. Finally, this DNA probe is subjected to single-channel recordings to afford the translocation events that can be used to derive the concentrations of the original biomarkers. Due to the amplification effects of nanoparticle loadings and the "click" reaction, the LOD of this strategy can be as low as the subfemtomolar level. Further, the acid treatment step could effectively eliminate the interferences from plasma proteins in raw human blood and make the strategy highly suitable for the detection of cancer biomarkers in clinical samples.

Rapid two-dimensional characterisation of proteins in solution

Microfluidic platforms provide an excellent basis for working with heterogeneous samples and separating biomolecular components at high throughput, with high recovery rates and by using only very small sample volumes. To date, several micron scale platforms with preparative capabilities have been demonstrated. Here we describe and demonstrate a microfluidic device that brings preparative and analytical operations together onto a single chip and thereby allows the acquisition of multidimensional information. We achieve this objective by using a free-flow electrophoretic separation approach that directs fractions of sample into an on-chip analysis unit, where the fractions are characterised through a microfluidic diffusional sizing process. This combined approach therefore allows simultaneously quantifying the sizes and the charges of components in heterogenous mixtures. We illustrate the power of the platform by describing the size distribution of a mixture comprising components which are close in size and cannot be identified as individual components using state-of-the-art solution sizing techniques on their own. Furthermore, we show that the platform can be used for two-dimensional fingerprinting of heterogeneous protein mixtures within tens of seconds, opening up a possibility to obtain multiparameter data on biomolecular systems on a minute timescale.

Sensors Based on Bio and Biomimetic Receptors in Medical Diagnostic, Environment, and Food Analysis

Analytical chemistry is now developing mainly in two areas: automation and the creation of complexes that allow, on the one hand, for simultaneously analyzing a large number of samples without the participation of an operator, and on the other, the development of portable miniature devices for personalized medicine and the monitoring of a human habitat. The sensor devices, the great majority of which are biosensors and chemical sensors, perform the role of the latter. That last line is considered in the proposed review. Attention is paid to transducers, receptors, techniques of immobilization of the receptor layer on the transducer surface, processes of signal generation and detection, and methods for increasing sensitivity and accuracy. The features of sensors based on synthetic receptors and additional components (aptamers, molecular imprinted polymers, biomimetics) are discussed. Examples of bio- and chemical sensors' application are given. Miniaturization paths, new power supply means, and wearable and printed sensors are described. Progress in this area opens a revolutionary era in the development of methods of on-site and in-situ monitoring, that is, paving the way from the "test-tube to the smartphone".