Immobilization of phenylalanine-dehydrogenase on nano-sized polytaurine: A new platform for application of nano-polymeric materials on enzymatic biosensing technology

Taurine Electrografting onto Porous Electrodes Improves Redox Flow Battery Performance

The surface properties of porous carbonaceous electrodes govern the performance, durability, and ultimately the cost of redox flow batteries (RFBs). State-of-the-art carbon fiber-based electrode interfaces suffer from limited kinetic activity and incomplete wettability, fundamentally limiting the performance. Surface treatments for electrodes such as thermal and acid activation are a common practice to make them more suitable for aqueous RFBs; however, these treatments offer limited control over the desired functional properties. Here, we propose, for the first time, electrografting as a facile, rapid, and versatile technique to enable task-specific functionalization of porous carbonaceous electrodes for use in RFBs. Electrografting allows covalent attachment of organic molecules on conductive substrates upon application of an electrochemical driving force, and the vast library of available organic molecules can unlock a broad range of desired functional properties. To showcase the potential of electrografting for RFBs, we elect to investigate taurine, an amine with a highly hydrophilic sulfonic acid tail. Oxidative electrografting with cyclic voltammetry allows covalent attachment of taurine through the amine group to the fiber surface, resulting in taurine-functionalized carbon cloth electrodes. In situ polarization and impedance spectroscopy in single-electrolyte flow cells reveal that taurine-treated cloth electrodes result in 40% lower charge transfer and 25% lower mass transfer resistances than off-the-shelf cloth electrodes. We find that taurine-treated electrode interfaces promote faster Fe³⁺ reduction reaction kinetics as the electrochemical surface area normalized current densities are 2-fold and 4-fold higher than oxidized and untreated glassy carbon surfaces, respectively. Improved mass transfer of taurine-treated electrodes is attributed to their superior wettability, as revealed by operando neutron radiography within a flow cell setup. Through demonstrating promising results for aqueous systems with the model molecule taurine, this work aims to bring forth electrografting as a facile technique to tailor electrode surfaces for other RFB chemistries and electrochemical technologies.

Human Serum Phenylpyruvate Quantification Using Responsive 2D Photonic Crystal Hydrogels via Chemoselective Oxime Ligation: Progress toward Developing Phenylalanine-Sensing Elements

There is a need to develop at-home phenylalanine (Phe) test kits, analogous to home glucose meters, for phenylketonuria patients who must measure their blood Phe levels frequently to adjust their diet. Unfortunately, such test kits are not available yet because of the lack of simple and inexpensive Phe-sensing elements. With the goal of developing a Phe-sensing element, we fabricated two-dimensional photonic crystal (2DPC) hydrogels that quantify human serum phenylpyruvate (PhPY), which is the product of the reaction between Phe and the enzyme phenylalanine dehydrogenase. The PhPY-sensing hydrogels have oxyamine recognition groups that link PhPY to the hydrogel polymer network via chemoselective oxime ligation. This structural modification induces the hydrogel to swell, which then increases interparticle spacings within the embedded 2DPC. The PhPY-induced particle spacing changes are measured from light diffraction and used to quantify the PhPY concentrations. The estimated limit of detection of PhPY in human serum for a detection time of 30 min is 19 μM, which is comparable to the minimum blood Phe concentrations of healthy people. Besides the potential application for developing Phe-sensing elements, this new hydrogel sensing approach via chemoselective oxime ligation is generalizable to the development of other chemical sensors working in complex biological environments.

Characterization methods in porous materials for the rational design of multi-step processing in the context of a paper microfluidic phenylalanine test

A promising application of paper microfluidics is the translation of gold-standard multi-step laboratory tests to a disposable paper-based format for decentralized diagnostic or therapeutic testing. This often entails conversion of bench-top processing of macro-volume samples to the processing of micro-volume samples within a porous matrix, and requires detailed characterization of fluid and reagent interactions within the porous material(s) of the device. The current study focuses on rational device design through the characterization of fluid and reagent interactions in polysulfone and glass fiber substrates for multi-step sample processing. Specifically, we demonstrate how the characterization of fluidic compatibility between substrates, chemical compatibility between reagents and substrates, sample pH, and sample transport can be used to inform device design in the context of a two-reaction detection scheme for phenylalanine in porous materials. Finally, we demonstrate detection of phenylalanine from human whole blood, and discuss the multiple strengths of the current design over a previous version.

Bioassays: The best alternative for conventional methods in detection of Legionella pneumophila

Fastidious bacteria are group of bacteria that not only grow slowly but also have complex nutritional needs. In this review, recent progress made on development of biosensing strategies towards quantification of Legionella pneumophila as fastidious bacteria in microbiology was investigated. In coincidence with medical bacteriology, it is the most widely used bio-monitoring, biosensors based on DNA and antibody. Also, all of legionella pneumophila genosensors and immunosensors that developed in recent years were collected analyzed. This review is meant to provide an overview of the various types of bioassays have been developed for determination of Legionella Legionella, along with significant advances over the last several years in related technologies. In addition, this review described: i) Most frequently applied principles in bioassay/biosensing of Legionellaii) The aspects of fabrication in the perspective of bioassay/biosensing applications iii) The potential of various electrochemical and optical bioassay/biosensing for the determination of Legionella and the circumvention of the most serious problem in immunosensing/immunoassay was discussed. iv) Some of bioassay/biosensing has been discussed with and without labels. v) We also summarize the latest developments in the applications of bioassay/biosensing methods for detection of Legionella. vi) The development trends of optical and electrochemical based bioassay/biosensing are also introduced.

Non-enzymatic Determination of L-Proline Amino Acid in Unprocessed Human Plasma Sample Using Hybrid of Graphene Quantum Dots Decorated with Gold Nanoparticles and Poly Cysteine: A Novel Signal Amplification Strategy

An innovative electrochemical interface for quantitation of L-proline (L-Pro) based on ternary amplification strategy was fabricated. In this work, gold nanoparticles prepared by soft template methodology were immobilized onto green and biocompatible nanocomposite containing poly as a conductive matrix and graphene quantum dots as the amplification element. Therefore, a novel multilayer film based on poly-L-cysteine, graphene quantum dots (GQDs), and gold nanoparticles (GNPs) was exploited to develop a highly sensitive electrochemical sensor for the detection of L-Pro. Fully electrochemical methodology was used to prepare a new transducer on a glassy carbon electrode, which provided a high surface area towards sensitive detection of L-Pro. The prepared electrode was employed for the detection of L-Pro. Under optimized conditions, the calibration curve for L-Pro concentration was linear in 0.5 nM - 10 mM with a low limit of quantification of 0.1 nM. The practical analytical utility of the modified electrode was illustrated by determination of L-Pro in unprocessed human plasma samples.

Ultrasensitive immunoassay of carcinoma antigen 125 in untreated human plasma samples using gold nanoparticles with flower like morphology: A new platform in early stage diagnosis of ovarian cancer and efficient management

Ovarian cancer, as one of the most life-threatening malignancies among women worldwide, is usually diagnosed at the late stage despite up regulation of molecular markers such as carcinoma antigen 125 (CA 125) at the early stages of the malignancy. CA 125 is the only tumor marker recommended for clinical use in the diagnosis and management of ovarian cancer. The potential role of CA-125 for the early detection of ovarian cancer is controversial and has not yet been adopted for widespread screening efforts in asymptomatic women. Therefore, early detection of CA 125 in human biofluids is highly demanded. In the present study, a novel method was proposed for the fabrication of electrochemical immunosensor based reduced graphene oxide (RGO). Cysteamine capped gold nanoparticle (Cys-AuNPs) were deposited over the surface of ERGO probe using electrophoretic deposition method. These Cys-AuNPs/ERGO probes provide the favorable sites to attach the monoclonal antibody specific to CA 125 antigen. Cyclic voltammetry (CV), and square wave voltammetry (SWV) were applied for the electrochemical recognition of the biolayer. The represented signals demonstrates excellent figure of merits and good capability of the engineered immunosensor towards sensitive detection of CA 125. Quantitative measurements of CA 125 in human plasma samples have been demonstrated, showing the potential of the practical application of this novel immunosensor for the analysis of this biomarker in blood serum samples. This immunosensor has the ability of direct electron transfer as compared to earlier reported electrochemical immunosensors based electrochemical methods. Further, this immunosensor provides a very suitable and convenient alternative to replace the expensive commercially available methods such as immunohistochemistry. The following regression equation between the electrochemical current response and the CA 125 concentration range from 0.1 to 400 U/mL was found. The low limit of quantification for this immunosensor was 0.1 U/mL. To the best of our knowledge, this is the first reported on the direct immobilization of antibody on the surface of Cys-AuNPs/ERGO for fabrication of immunosensors.

Aptamer-based assay for monitoring genetic disorder phenylketonuria (PKU)

The genetic disorder phenylketonuria (PKU) is the inability to metabolize phenylalanine because of a lack of the enzyme phenylalanine hydroxylase. Phenylalanine is used to biochemically form proteins, coded for by DNA. The development of an apta-assay for detection of l-Phenylalanine is presented in this work. A highly specific DNA-aptamer, selected to l-Phenylalanine was immobilized onto a gold nanostructure and electrochemical measurements were performed in a solution containing the phosphate buffer solution with physiological pH. We have constructed an aptamer immobilized gold nanostructure mediated, ultrasensitive electrochemical biosensor (Apt/AuNSs/Au electrode) for l-Phenylalanine detection without any additional signal amplification strategy. The aptamer assemble onto the AuNSs makes Apt/AuNSs/Au electrode an excellent platform for the l-Phenylalanine detection in physiological like condition. Differential pulse voltammetry were used for the quantitative l-Phenylalanine detection. The Apt/AuNSs/Au electrode offers an ultrasensitive and selective detection of l-Phenylalanine down to 0.23 μM level with a wide dynamic range from 0.72 μM-6 mM. The aptasensor exhibited excellent selectivity and stability. The real sample analysis was performed by spiking the unprocessed human serum samples with various concentration of l-Phenylalanine and obtained recovery within 2% error value. The sensor is found to be more sensitive than most of the literature reports. The simple and easy way of construction of this apta-assay provides an efficient and promising diagnosis of phenylketonuria.

Nanomaterials for biocatalyst immobilization – state of the art and future trends

Advantages, drawbacks and trends in nanomaterials for enzyme immobilization.