Colorimetric Detection of Extracellular Hydrogen Peroxide Using an Integrated Microfluidic Device.

It is well known that hydrogen peroxide (H2O2) is a signaling molecule essential for vital physiological reactions in mammalian cells, such as cell survival, intercellular communication, and cancer metabolism. However, to fully understand the function of H2O2, it is critical to monitor its intracellular and/or extracellular concentrations. Current techniques implemented to address this need require large sample volumes, expensive instrumentation, and long sample preparation and analysis times, inapplicable to inline or online monitoring. In this paper, a new integrated microfluidic device capable of overcoming these limitations is demonstrated for the colorimetric detection of extracellular hydrogen peroxide H2O2. The device contains an optical waveguide to determine absorbance changes and micromixers to enable complete mixing of reagents using a passive approach. This novel H2O2-sensing device has allowed the detection of H2O2 in the range of 0.5-60 µM with a detection limit of 167 ± 5.8 nM and a sensitivity of 13.5 ± 0.1 AU/mM. Proof of concept of the device was demonstrated by quantifying H2O2 release from benign prostatic epithelial (BPH-1) cells upon stimulation with phorbol 12-myristate 13-acetate (PMA). Results show that this integrated device can be potentially utilized to continuously monitor cell-released metabolites autonomously without constant human supervision during the process. Furthermore, this can be achieved without interfering with the cell culture conditions, as only a very small volume of conditioned media (less than 0.4 µL), and not the cells, is required.

Microfluidic Electrochemical Sensor for Cerebrospinal Fluid and Blood Dopamine Detection in a Mouse Model of Parkinson's Disease.

Parkinson's disease (PD) is a progressive neurodegenerative disorder involving dopaminergic neurons from the substantia nigra. The loss of dopaminergic neurons results in decreased dopamine (DA) release in the striatum and thus impaired motor functions. DA is one of the key neurotransmitters monitored for the diagnosis and during the progression and treatment of PD. Therefore, sensitive and selective DA detection methods are of high clinical relevance. In this study, a new microfluidic device utilized for electrochemical DA detection is reported. The microfluidic sensing device operates in the range of 0.1-1000 nM DA requiring only ∼2.4 µL sample volume, which corresponds to detectable 240 amol of DA. Using this sensor, we were able to monitor the changes in DA levels in cerebrospinal fluid and plasma of a mouse model of PD and following the treatment of drug l-3,4-dihydroxyphenylalanine.

Recent progress in nanomaterial-based electrochemical and optical sensors for hypoxanthine and xanthine. A review.

This review (with 160 ref.) summarizes the progress that has been made in the methods for chemical or biochemical sensing of hypoxanthine and xanthine, which are produced as part of purine metabolism and are precursors of uric acid. An introduction discusses the importance of hypoxanthine and xanthine as analytes due to their significance in the clinical and food science, together with the conventional methods of analysis. A large section covers methods for the electrochemical hypoxanthine and xanthine sensing. It is divided into subsections according to the nanomaterials used including carbon nanomaterials, meal oxide nanoparticles, metal organic frameworks, conductive polymers, and bio-nanocomposites. A further large section covers optical methods for hypoxanthine and xanthine sensing, with subsections on nanomaterials including carbon nanomaterials, nanosheets, nanoclusters, nanoparticles, and their bio-nanocomposites. A concluding section summarizes the current status, addresses current challenges, and discusses future perspectives. Graphical abstractSchematic representation of the hypoxanthine and xanthine electrochemical and optical sensors incorporating various nanomaterials like graphene, carbon nanotubes (CNT), quantum dots (QD), nanoparticles and polymers, which are implemented in clinical and food analysis.

Recent Progress in Lab-On-a-Chip Systems for the Monitoring of Metabolites for Mammalian and Microbial Cell Research.

Lab-on-a-chip sensing technologies have changed how cell biology research is conducted. This review summarises the progress in the lab-on-a-chip devices implemented for the detection of cellular metabolites. The review is divided into two subsections according to the methods used for the metabolite detection. Each section includes a table which summarises the relevant literature and also elaborates the advantages of, and the challenges faced with that particular method. The review continues with a section discussing the achievements attained due to using lab-on-a-chip devices within the specific context. Finally, a concluding section summarises what is to be resolved and discusses the future perspectives.

Wearable microneedle array-based sensor for transdermal monitoring of pH levels in interstitial fluid.

Microneedle-based wearable sensors offer an alternative approach to traditional invasive blood-based health monitoring and disease diagnostics techniques. Instead of blood, microneedle-based sensors target the skin interstitial fluid (ISF), in which the biomarker type and concentration profile resemble the one found in the blood. However, unlike blood, interstitial fluid does not have the same pH-buffering capacity causing deviation of pH levels from the physiological range. Information about the skin ISF pH levels can be used as a biomarker for a wide range of pathophysiological conditions and as a marker for the calibration of a wearable sensor. The ISF pH can significantly affect the detection accuracy of other biomarkers as it influences enzyme activity, aptamer affinity, and antibody-antigen interaction. Herein, we report the fabrication of a high-density polymeric microneedle array-based (PMNA) sensing patch and its optimization for the potentiometric transdermal monitoring of pH levels in ISF. The wearable sensor utilizes a polyaniline-coated PMNA having a density of ∼10,000 microneedles per cm2, containing individual microneedles with a height of ∼250 µm, and a tip diameter of ∼2 µm. To prevent interference from other body fluids like sweat, an insulating layer is deposited at the base of the PMNA. The wearable pH sensor operates from pH 4.0 to 8.6 with a sensitivity of 62.9 mV per pH unit and an accuracy of ±0.036 pH units. Furthermore, testing on a mouse demonstrates the ability of the PMNA to provide a real-time reading of the transdermal pH values. This microneedle-based system will significantly contribute to advancing transdermal wearable sensors technology, simplifying the fabrication process, and improving the cost-effectiveness of such devices.

High-Frequency Ultrasound Boosts Bull and Human Sperm Motility.

Sperm motility is a significant predictor of male fertility potential and is directly linked to fertilization success in both natural and some forms of assisted reproduction. Sperm motility can be impaired by both genetic and environmental factors, with asthenozoospermia being a common clinical presentation. Moreover, in the setting of assisted reproductive technology clinics, there is a distinct absence of effective and noninvasive technology to increase sperm motility without detriment to the sperm cells. Here, a new method is presented to boost sperm motility by increasing the intracellular rate of metabolic activity using high frequency ultrasound. An increase of 34% in curvilinear velocity (VCL), 10% in linearity, and 32% in the number of motile sperm cells is shown by rendering immotile sperm motile, after just 20 s exposure. A similar effect with an increase of 15% in VCL treating human sperm with the same setting is also identified. This cell level mechanotherapy approach causes no significant change in cell viability or DNA fragmentation index, and, as such, has the potential to be applied to encourage natural fertilization or less invasive treatment choices such as in vitro fertilization rather than intracytoplasmic injection.

High-Aspect-Ratio SU-8-Based Optofluidic Device for Ammonia Detection in Cell Culture Media.

Miniaturization of sensing technology has led to the development of multifunctional micro total analysis systems (µTAS) that benefit from microfluidic technology. Optical sensing is one of the most commonly used sensing approaches integrated into µTAS devices and features high sensitivity and low detection limits. Different materials have been used for the fabrication of µTAS devices, each having their advantages and disadvantages. Herein, a high-aspect-ratio optofluidic waveguide fabricated from SU-8 is presented for the first time. The suitable optical properties and chemical inertness of SU-8 provide a durable device made by a flexible and cost-efficient fabrication process. The optofluidic device was used for colorimetric ammonia (NH3) sensing with a dynamic range of 3-70 µM, a detection limit of 2.5 µM, a response time of 8 min, and close to 10 times better analytical performance compared to using a standard microplate reader. The µTAS device was capable of monitoring NH3 accumulating in the cell culture media of prostatic epithelial cell (BPH-1) culture.

Enhanced electrochemical sensing performance by insitu electrocopolymerization of pyrrole and thiophene-grafted chitosan.

Nowadays, there is increasing number of electrochemical biosensors which utilize chitosan (Ch); as an enzyme immobilization matrix, and conductive nanomaterials; as electron carriers improving sensitivity of the biosensor. However, the challenge these sensors face is the lack of uniform dispersion of nanomaterials throughout the Ch film, which can negatively affect analytical performance of the biosensor. In this study, we report the development of an enzyme immobilization matrix that displays enhanced electrochemical performance thanks to a novel conductive thin film prepared via in situ electrocopolymerization of pyrrole (Py) and thiophene-grafted chitosan (Th-Ch). This is a simple thin film preparation method that can help overcome aforementioned challenges by providing a uniformly distributed conductive layer on the electrode. We are also for the first time reporting the synthesis and characterization of Th-Ch, where grafted Th plays an essential role as a linking group between Ch and Py. The resulting conductive Ch-based thin film was modified with glucose oxidase (GOx) which served as a model enzyme. In situ electrocopolymerization of Py with Th-Ch resulted in a highly conductive thin film enabling approximately 40% higher sensitivity when compared to a Py-Ch composite. This new type of composite thin film is promising in biosensor technology due to its biocompatibility, the chemically and physically modifiable structure, as well as its electrical conductivity.

Novel electrochemical xanthine biosensor based on chitosan-polypyrrole-gold nanoparticles hybrid bio-nanocomposite platform.

The aim of this study was the electrochemical detection of the adenosine-3-phosphate degradation product, xanthine, using a new xanthine biosensor based on a hybrid bio-nanocomposite platform which has been successfully employed in the evaluation of meat freshness. In the design of the amperometric xanthine biosensor, chitosan-polypyrrole-gold nanoparticles fabricated by an in situ chemical synthesis method on a glassy carbon electrode surface was used to enhance electron transfer and to provide good enzyme affinity. Electrochemical studies were carried out by the modified electrode with immobilized xanthine oxidase on it, after which the biosensor was tested to ascertain the optimization parameters. The Biosensor exhibited a very good linear range of 1-200 µM, low detection limit of 0.25 µM, average response time of 8 seconds, and was not prone to significant interference from uric acid, ascorbic acid, glucose, and sodium benzoate. The resulting bio-nanocomposite xanthine biosensor was tested with fish, beef, and chicken real-sample measurements.

Construction of ferrocene modified conducting polymer based amperometric urea biosensor.

Herein, an electrochemical urea sensing bio-electrode is reported that has been constructed by firstly electropolymerizing 4-(2,5-Di(thiophen-2-yl)-1H-pyrrol-1-yl)aniline monomer (SNS-Aniline) on Pencil Graphite Electrode (PGE), then modifying the polymer coated electrode surface with di-amino-Ferrocene (DAFc) as the mediator, and lastly Urease enzyme through glutaraldehyde crosslinking. The effect of pH, temperature, polymer thickness, and applied potential on the electrode current response was investigated besides performing storage and operational stability experiments with the interference studies. The resulting urea biosensor's amperometric response was linear in the range of 0.1-8.5mM with the sensitivity of 0.54µA/mM, detection limit of 12µM, and short response time of 2s. The designed bio-electrode was tested with real human blood and urine samples where it showed excellent analytical performance with insignificant interference.