Processable and nanofibrous polyaniline:polystyrene-sulphonate (nano-PANI:PSS) for the fabrication of catalyst-free ammonium sensors and enzyme-coupled urea biosensors

Materials design and characterization of injectable and degradable oxidized alginate PANI:PSS hydrogels for photothermal therapy

Photothermal therapy has gained great attention as an alternative candidate for radiation therapy or chemotherapy for cancers. However, photothermal agents for photothermal therapy are generally in the form of nanoparticles that are too small to remain in the target tissue, and therefore, the agents are rather quickly removed from the targeted site. Furthermore, conventional photothermal agents are generally expensive or complicated to synthesize. As an approach to these issues, here we present new hydrogels with oxidized alginate ionically crosslinked with Ca2+, bearing polyaniline:poly(sodium 4-styrenesulfonate) (PANI:PSS) nanoparticles in the polymer network. The presented oxidized alginate PANI:PSS hydrogels exhibited excellent injectability as well as a gradual degradation rate from several days to several months depending on the oxidation degree of alginate chains. The presented oxidized alginate PANI:PSS hydrogels showed an excellent photothermal effect even under a neutral pH environment by showing temperature increased to 53 °C in 5 min upon NIR irradiation, which provide strong potential as a candidate for photothermal agent in photothermal therapy.

Sulfonated-polypyrene aniline/polyaniline composite fortified with Cu-GQD@ZIF8 as an electrochemical enzymatic urea biosensor

The determination of urea concentration is essential for human health owing to its crucial role in the ability to metabolize nitrogen-containing substances. This study developed new electrochemical enzymatic detection systems via the synergistic effect of the superior features of novel electropolymerizable pyranine-aniline (PA, 4), polyaniline (PANI) compounds, graphene quantum dots (GQDs) and zeolitic imidazolate framework-8 (ZIF8). The novel compound 4 was characterized via1H-NMR, 13C-NMR, FTIR, and MALDI-TOF mass spectroscopies. Furthermore, Cu-GQD@ZIF8 hybrid materials containing GQD and integrated electroactive Cu metal were prepared in this study. The surface morphology of the prepared Cu-GQD@ZIF8 hybrid material was investigated through microscopic methods such as SEM and TEM, and chemical characterizations were performed using FTIR, XPS, XRD, and TGA analyses. After the characterization of the novel materials, the urease (Urs) enzyme was bound to the new modified electrode surface. Next, the enzymatic biosensor properties of the Urs/Cu-GQD@ZIF8/PANI/PA/GCE sensor electrode for urea detection via reduction of PANI were investigated by DPV and CV techniques. The LOD and LOQ values of the presented sensor were calculated to be 0.77 μM and 2.31 μM, respectively, in the linear range of 1.0-80.0 μM, based on DPV measurements. The presented biosensor system determined the amount of urea in an artificial serum sample, and its accuracy was confirmed via the recovery test and GC-MS analysis.

High-Throughput Automatic Laser Printing Strategy toward Cost-effective Portable Integrated Urea Tele-Monitoring System

A portable sweat urea sensing system is a promising solution to satisfy the booming requirement of kidney function tele-monitoring. However, the complicated manufacturing route and the cumbersome electrochemical testing system still need to be improved to develop the urea point-of-care testing (POCT) and tele-monitoring devices. Here, a universal technical route based on a high-throughput automatic laser printing strategy for fabricating the portable integrated urea monitoring system is proposed. This integrated system includes a high-performance laser-printed urea sensing electrode, a planar three-electrode system, and a self-developed wireless mini-electrochemical workstation. A precursor donor layer is activated by laser scribing and in situ transferred into functional nanoparticles for the drop-on-demand printing of the urea sensing electrode. The obtained electrodes show high sensitivity, low detection limit, fast response time, high selectivity, good average recovery, and long-term stability for urea sensing. Additionally, a laser-induced graphene circuit-based miniature planar three-electrode system and a wireless mini-electrochemical workstation are designed for sensing data collection and transmitting, achieving real-time urea POCT and tele-monitoring. This scalable method provides a universal solution for high-throughput and ultra-fast fabrication of urea-sensing electrodes. The portable integrated urea monitoring system is a competitive option to achieve cost-effective POCT and tele-monitoring for kidney function.

Urea-Self Powered Biosensors: A Predictive Evolutionary Model for Human Energy Harvesting

The objective of this study is to create a reliable predictive model for the electrochemical performance of self-powered biosensors that rely on urea-based biological energy sources. Specifically, this model focuses on the development of a human energy harvesting model based on the utilization of urea found in sweat, which will enable the development of self-powered biosensors. In the process, the potential of urea hydrolysis in the presence of a urease enzyme is employed as a bioreaction for self-powered biosensors. The enzymatic reaction yields a positive potential difference that can be harnessed to power biofuel cells (BFCs) and act as an energy source for biosensors. This process provides the energy required for self-powered biosensors as biofuel cells (BFCs). To this end, initially, the platinum electrodes are modified by multi-walled carbon nanotubes to increase their conductivity. After stabilizing the urease enzyme on the surface of the platinum electrode, the amount of electrical current produced in the process is measured. The optimal design of the experiments is performed based on the Taguchi method to investigate the effect of urea concentration, buffer concentration, and pH on the generated electrical current. A general equation is employed as a prediction model and its coefficients calculated using an evolutionary strategy. Also, the evaluation of effective parameters is performed based on error rates. The obtained results show that the established model predicts the electrical current in terms of urea concentration, buffer concentration, and pH with high accuracy.

Multi-Parameter Detection of Urine Based on Electropolymerized PANI: PSS/AuNPs/SPCE

Urine analysis is widely used in clinical practice to indicate human heathy status and is important for diagnosing chronic kidney disease (CKD). Ammonium ions (NH₄⁺), urea, and creatinine metabolites are main clinical indicators in urine analysis of CKD patients. In this paper, NH₄⁺ selective electrodes were prepared using electropolymerized polyaniline-polystyrene sulfonate (PANI: PSS), and urea- and creatinine-sensing electrodes were prepared by modifying urease and creatinine deiminase, respectively. First, PANI: PSS was modified on the surface of an AuNPs-modified screen-printed electrode, as a NH₄⁺-sensitive film. The experimental results showed that the detection range of the NH₄⁺ selective electrode was 0.5~40 mM, and the sensitivity reached 192.6 mA M^-1 cm^-2 with good selectivity, consistency, and stability. Based on the NH₄⁺-sensitive film, urease and creatinine deaminase were modified by enzyme immobilization technology to achieve urea and creatinine detection, respectively. Finally, we further integrated NH₄⁺, urea, and creatinine electrodes into a paper-based device and tested real human urine samples. In summary, this multi-parameter urine testing device offers the potential for point-of-care testing of urine and benefits the efficient chronic kidney disease management.

Application of Polypyrrole-Based Electrochemical Biosensor for the Early Diagnosis of Colorectal Cancer

Although colorectal cancer (CRC) is easy to treat surgically and can be combined with postoperative chemotherapy, its five-year survival rate is still not optimistic. Therefore, developing sensitive, efficient, and compliant detection technology is essential to diagnose CRC at an early stage, providing more opportunities for effective treatment and intervention. Currently, the widely used clinical CRC detection methods include endoscopy, stool examination, imaging modalities, and tumor biomarker detection; among them, blood biomarkers, a noninvasive strategy for CRC screening, have shown significant potential for early diagnosis, prediction, prognosis, and staging of cancer. As shown by recent studies, electrochemical biosensors have attracted extensive attention for the detection of blood biomarkers because of their advantages of being cost-effective and having sound sensitivity, good versatility, high selectivity, and a fast response. Among these, nano-conductive polymer materials, especially the conductive polymer polypyrrole (PPy), have been broadly applied to improve sensing performance due to their excellent electrical properties and the flexibility of their surface properties, as well as their easy preparation and functionalization and good biocompatibility. This review mainly discusses the characteristics of PPy-based biosensors, their synthetic methods, and their application for the detection of CRC biomarkers. Finally, the opportunities and challenges related to the use of PPy-based sensors for diagnosing CRC are also discussed.

Electrochemical Signal Amplification Strategies and Their Use in Olfactory and Taste Evaluation

Biosensors are powerful analytical tools used to identify and detect target molecules. Electrochemical biosensors, which combine biosensing with electrochemical analysis techniques, are efficient analytical instruments that translate concentration signals into electrical signals, enabling the quantitative and qualitative analysis of target molecules. Electrochemical biosensors have been widely used in various fields of detection and analysis due to their high sensitivity, superior selectivity, quick reaction time, and inexpensive cost. However, the signal changes caused by interactions between a biological probe and a target molecule are very weak and difficult to capture directly by using detection instruments. Therefore, various signal amplification strategies have been proposed and developed to increase the accuracy and sensitivity of detection systems. This review serves as a reference for biosensor and detector research, as it introduces the research progress of electrochemical signal amplification strategies in olfactory and taste evaluation. It also discusses the latest signal amplification strategies currently being employed in electrochemical biosensors for nanomaterial development, enzyme labeling, and nucleic acid amplification techniques, and highlights the most recent work in using cell tissues as biosensitive elements.

Amperometric biosensors for L-arginine and creatinine assay based on recombinant deiminases and ammonium-sensitive Cu/Zn(Hg)S nanoparticles

There are limited data on amperometric biosensors (ABSs) based on deiminases that produce ammonium as a byproduct of enzymatic reaction. The most frequently proposed biosensors utilizing such a mode are based on potentiometric transducers, which contain at least two enzymes in the bioselective layer; this complicates the procedure and increases the cost of analysis. Thus, the construction of a one-enzyme ABS is a practical problem. In our manuscript ABSs for the direct measurement of creatinine (Crn) and l-arginine (Arg), based on the recombinant bacterial creatinine deiminase (CDI) and arginine deiminase (ADI), are described. To choose the best chemosensor on ammonium ions, a number of nanoparticles (NPs) were synthesized and characterized using cyclic voltammetry. Hybrid Cu/Zn(Hg)S-NPs, having a good selectivity and an extremely high sensitivities towards ammonium ions (5660 A M^-1 m^-2 at +170 mV and 1870 A M^-1 m^-2 at -300 mV, respectively), was selected for the development of deiminase-based ABSs. The novel biosensors exhibited very high sensitivities (2660 A M^-1 m^-2 to Crn for CDI-ABS; 1570 A M^-1 m^-2 to Arg for ADI-ABS), broad linear ranges, low limits of detection, satisfactory storage stabilities and good selectivities towards natural substrates. The constructed CDI-ABS and ADI-ABS were tested on real samples of biological fluids and juices for Crn and Arg assay, respectively. High correlations of the obtained results with the reference methods were demonstrated for the target analytes.

Evaluation on the Intrinsic Physicoelectrochemical Attributes and Engineering of Micro-, Nano-, and 2D-Structured Allotropic Carbon-Based Papers for Flexible Electronics

Flexible electronics have gained more attention for emerging electronic devices such as sensors, biosensors, and batteries with advantageous properties including being thin, lightweight, flexible, and low-cost. The development of various forms of allotropic carbon papers provided a new dry-manufacturing route for the fabrication of flexible and wearable electronics, while the electrochemical performance and the bending stability are largely influenced by the bulk morphology and the micro-/nanostructured domains of the carbon papers. Here, we evaluate systematically the intrinsic physicoelectrochemical properties of allotropic carbon-based conducting papers as flexible electrodes including carbon-nanotubes-paper (CNTs-paper), graphene-paper (GR-paper), and carbon-fiber-paper (CF-paper), followed by functionalization of the allotropic carbon papers for the fabrication of flexible electrodes. The morphology, chemical structure, and defects originating from the allotropic nanostructured carbon materials were characterized by scanning electron microscopy (SEM) and Raman spectroscopy, followed by evaluating the electrochemical performance of the corresponding flexible electrodes by cyclic voltammetry and electrochemical impedance spectroscopy. The electron-transfer rate constants of the CNTs-paper and GR-paper electrodes were ∼14 times higher compared with the CF-paper electrode. The CNTs-paper and GR-paper electrodes composed of nanostructured carbon showed significantly higher bending stabilities of 5.61 and 4.96 times compared with the CF-paper. The carbon-paper flexible electrodes were further functionalized with an inorganic catalyst, Prussian blue (PB), forming the PB-carbon-paper catalytic electrode and an organic conducting polymer, poly(3,4-ethylenedioxythiophene) (PEDOT), forming the PEDOT-carbon-paper capacitive electrode. The intrinsic attribute of different allotropic carbon electrodes affects the deposition of PB and PEDOT, leading to different electrocatalytic and capacitive performances. These findings are insightful for the future development and fabrication of advanced flexible electronics with allotropic carbon papers.

Enzyme-free detection of hydrogen peroxide with a hybrid transducing system based on sodium carboxymethyl cellulose, poly(3,4-ethylenedioxythiophene) and prussian blue nanoparticles

Herein, we report a two-layered hybrid catalytic interface composed of carboxymethyl cellulose (CMC), poly (3,4-ethylene dioxythiophene) (PEDOT), Prussian blue (PB) nanoparticles and Nickel-Hexacyanoferrate (Ni-HCF) layer for the enzyme-free detection of hydrogen peroxide (H₂O₂). Whereas the first layer, CMC:PEDOT:PB, is responsible for generating amperometric signals toward H₂O₂, Ni-HCF on CMC:PEDOT:PB layer is playing an active role as an operational stability-enhancer. In the study, where the systematic optimization of the sensor electrode is presented using cyclic voltammetry (CV), amperometry and electrochemical impedance spectroscopy (EIS) technique, the physical and chemical properties of the hybrid composite systems constructed is also supported by scanning electron microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR) techniques. The amperometric signal generation of the H₂O₂ sensor was linear between 1 and 100 μM (R² = 0.999) with a sensitivity of 416.11 μA mM^-1cm^-2, providing a limit of detection (LOD) of 0.33 μM. The sensing system, which was not affected by the various interfering molecules, creates a successful sensor platform for H₂O₂ measurements in tap water with a high recovery value between 94.0% and 110.5% and relatively small RSD in the range of 0.4-5.2%.