A needle-type glucose biosensor based on PANI nanofibers and PU/E-PU membrane for long-term invasive continuous monitoring

Wearable filamentary continuous sensor for interstitial glucose detection in diabetes management

The development of novel diabetes monitoring sensors is important for the diabetes management of millions of diabetic patients. This work reports a flexible filamentary continuous glucose monitoring (CGM) sensor. A multilayer CGM sensor has been constructed on titanium filament with low cost and ease of use. The sensor, made of flexible material, offers better adaptability and comfort than traditional rigid filament CGM sensors, allowing continuous monitoring of subcutaneous blood glucose levels to provide patients with treatment strategies. The performance and reliability of the sensor were verified through rat experiments. The trend of the increase and decrease of the detected current was generally consistent with the actual blood glucose, and the detected values were located in regions A and B of the Clarke error grid. The results show that the sensor has the advantages of high sensitivity, high accuracy and fast response speed, which is suitable for monitoring the blood glucose level for a long time and has a broad application prospect in diabetes monitoring, exercise monitoring, health management and clinical application.

Disposable Polyaniline/m-Phenylenediamine-Based Electrochemical Lactate Biosensor for Early Sepsis Diagnosis

Lactate serves as a crucial biomarker that indicates sepsis assessment in critically ill patients. A rapid, accurate, and portable analytical device for lactate detection is required. This work developed a stepwise polyurethane-polyaniline-m-phenylenediamine via a layer-by-layer based electrochemical biosensor, using a screen-printed gold electrode for lactate determination in blood samples. The developed lactate biosensor was electrochemically fabricated with layers of m-phenylenediamine, polyaniline, a crosslinking of a small amount of lactate oxidase via glutaraldehyde, and polyurethane as an outer membrane. The lactate determination using amperometry revealed the biosensor's performance with a wide linear range of 0.20-5.0 mmol L-1, a sensitivity of 12.17 ± 0.02 µA·mmol-1·L·cm-2, and a detection limit of 7.9 µmol L-1. The developed biosensor exhibited a fast response time of 5 s, high selectivity, excellent long-term storage stability over 10 weeks, and good reproducibility with 3.74% RSD. Additionally, the determination of lactate in human blood plasma using the developed lactate biosensor was examined. The results were in agreement with the enzymatic colorimetric gold standard method (p > 0.05). Our developed biosensor provides efficiency, reliability, and is a great potential tool for advancing lactate point-of-care testing applications in the early diagnosis of sepsis.

A Novel Polyurethane-Based Polyion Complex Material with Tunable Selectivity against Interferents for Selective Dopamine Determination

Polyion complex (PIC) materials have been widely used in biosensors due to their molecular selectivity. However, achieving both widely controllable molecular selectivity and long-term solution stability with traditional PIC materials has been challenging due to the different molecular structures of polycations (poly-C) and polyanions (poly-A). To address this issue, we propose a novel polyurethane (PU)-based PIC material in which the main chains of both poly-A and poly-C are composed of PU structures. In this study, we electrochemically detect dopamine (DA) as the analyte and L-ascorbic acid (AA) and uric acid (UA) as the interferents to evaluate the selective property of our material. The results show that AA and UA are significantly eliminated, while DA can be detected with a high sensitivity and selectivity. Moreover, we successfully tune the sensitivity and selectivity by changing the poly-A and poly-C ratios and adding nonionic polyurethane. These excellent results were employed in the development of a highly selective DA biosensor with a detection range from 500 nM to 100 μM and a 3.4 μM detection limit. Overall, our novel PIC-modified electrode has the potential to advance biosensing technologies for molecular detection.

Development of Smartphone-Controlled and Microneedle-Based Wearable Continuous Glucose Monitoring System for Home-Care Diabetes Management

Continuous glucose monitoring (CGM) can mini-invasively track blood glucose fluctuation and reduce the risk of hyperglycemia and hypoglycemia, and this is is in great demand for diabetes management. However, cost-effective manufacture of CGM systems with continuously improved convenience and performance is still the persistent goal. Herein, we developed a smartphone-controlled and microneedle (MN)-based wearable CGM system for long-term glucose monitoring. The CGM system modified with a sandwich-type enzyme immobilization strategy can satisfy the clinical requirement of interstitial fluid (ISF) glucose monitoring for 14 days with a mean absolute relative difference of 10.2% and a cost of less than $15, which correlated well with the commercial glucometer and FDA-approved CGM system FreeStyle Libre (Abbott Inc., Illinois, USA). The self-developed CGM system is demonstrated to accurately monitor glucose fluctuations and provide abundant clinical information. It is better to find the cause of individual blood glucose changes and beneficial for the guide of precise glucose control. On the whole, the intelligently wearable CGM system may provide an alternative solution for home-care diabetes management.

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.

Nanofiber Based on Electrically Conductive Materials for Biosensor Applications

Biosensors are analytical tools that enable the transmission of different signals produced from the target analyte to a transducer for the production of real-time clinical diagnostic devices by obtaining meaningful results. Recent research demonstrates that the production of structured nanofiber through various methods has come to light as a potential platform for enhancing the functionality of biosensing devices. The general trend is towards the use of nanofibers for electrochemical biosensors. However, optical and mechanical biosensors are being developed by functionalization of nanofibers. Such nanofibers exhibit a high surface area to volume ratio, surface porosity, electroconductivity and variable morphology. In addition, nanosized structures have shown to be effective as membranes for immobilizing bioanalytes, offering physiologically active molecules a favorable microenvironment that improves the efficiency of biosensing. Cost effective, wearable biosensors are crucial for point of care diagnostics. This review aims to examine the electrically conductive materials, potential forming methods, and wide-ranging applications of nanofiber-based biosensing platforms, with an emphasis on transducers incorporating mechanical, electrochemical and optical and bioreceptors involving cancer biomarker, urea, DNA, microorganisms, primarily in the last decade. The appealing properties of nanofibers mats and the attributes of the biorecognition components are also stated and explored. Finally, consideration is given to the difficulties now affecting the design of nanofiber-based biosensing platforms as well as their future potential.

An Optically Controlled Virtual Microsensor for Biomarker Detection In Vivo

Current technologies for the real-time analysis of biomarkers in vivo, such as needle-type microelectrodes and molecular imaging methods based on exogenous contrast agents, are still facing great challenges in either invasive detection or lack of active control of the imaging probes. In this study, by combining the design concepts of needle-type microelectrodes and the fluorescence imaging method, a new technique is developed for detecting biomarkers in vivo, named as "optically controlled virtual microsensor" (OCViM). OCViM is established by the organic integration of a specially shaped laser beam and fluorescent nanoprobe, which serve as the virtual handle and sensor tip, respectively. The laser beam can trap and manipulate the nanoprobe in a programmable manner, and meanwhile excite it to generate fluorescence emission for biosensing. On this basis, fully active control of the nanoprobe is achieved noninvasively in vivo, and multipoint detection can be realized at sub-micrometer resolution by shifting a nanoprobe among multiple positions. By using OCViM, the overexpression and heterogenous distribution of biomarkers in the thrombus is studied in living zebrafish, which is further utilized for the evaluation of antithrombotic drugs. OCViM may provide a powerful tool for the mechanism study of thrombus progression and the evaluation of antithrombotic drugs.

Progress in Probe-Based Sensing Techniques for In Vivo Diagnosis

Advancements in robotic surgery help to improve the endoluminal diagnosis and treatment with minimally invasive or non-invasive intervention in a precise and safe manner. Miniaturized probe-based sensors can be used to obtain information about endoluminal anatomy, and they can be integrated with medical robots to augment the convenience of robotic operations. The tremendous benefit of having this physiological information during the intervention has led to the development of a variety of in vivo sensing technologies over the past decades. In this paper, we review the probe-based sensing techniques for the in vivo physical and biochemical sensing in China in recent years, especially on in vivo force sensing, temperature sensing, optical coherence tomography/photoacoustic/ultrasound imaging, chemical sensing, and biomarker sensing.

Investigating lytic polysaccharide monooxygenase-assisted wood cell wall degradation with microsensors

Lytic polysaccharide monooxygenase (LPMO) supports biomass hydrolysis by increasing saccharification efficiency and rate. Recent studies demonstrate that H₂O₂ rather than O₂ is the cosubstrate of the LPMO-catalyzed depolymerization of polysaccharides. Some studies have questioned the physiological relevance of the H₂O₂-based mechanism for plant cell wall degradation. This study reports the localized and time-resolved determination of LPMO activity on poplar wood cell walls by measuring the H₂O₂ concentration in their vicinity with a piezo-controlled H₂O₂ microsensor. The investigated Neurospora crassa LPMO binds to the inner cell wall layer and consumes enzymatically generated H₂O₂. The results point towards a high catalytic efficiency of LPMO at a low H₂O₂ concentration that auxiliary oxidoreductases in fungal secretomes can easily generate. Measurements with a glucose microbiosensor additionally demonstrate that LPMO promotes cellobiohydrolase activity on wood cell walls and plays a synergistic role in the fungal extracellular catabolism and in industrial biomass degradation.

A Platinized Carbon Fiber Microelectrode-Based Oxidase Biosensor for Amperometric Monitoring of Lactate in Brain Slices

BACKGROUND

Direct and real-time monitoring of lactate in the extracellular space can help elucidate the metabolic and modulatory role of lactate in the brain. Compared to in vivo studies, brain slices allow the investigation of the neural contribution separately from the effects of cerebrovascular response and permit easy control of recording conditions.

METHODS

We have used a platinized carbon fiber microelectrode platform to design an oxidase-based microbiosensor for monitoring lactate in brain slices with high spatial and temporal resolution operating at 32 °C. Lactate oxidase (Aerococcus viridans) was immobilized by crosslinking with glutaraldehyde and a layer of polyurethane was added to extend the linear range. Selectivity was improved by electropolymerization of m-phenylenediamine and concurrent use of a null sensor.

RESULTS

The lactate microbiosensor exhibited high sensitivity, selectivity, and optimal analytical performance at a pH and temperature compatible with recording in hippocampal slices. Evaluation of operational stability under conditions of repeated use supports the suitability of this design for up to three repeated assays.

CONCLUSIONS

The microbiosensor displayed good analytical performance to monitor rapid changes in lactate concentration in the hippocampal tissue in response to potassium-evoked depolarization.

A Power-Harvesting CGM Chiplet Featuring Silicon-Based Enzymatic Glucose Sensor

Diabetes has become a leading cause of death and disability in the past decades. Continuous glucose monitoring (CGM) is a prevailing technique to determine the glucose level and provide in-time treatment. However, conventional CGM systems combine an electrochemical sensor with a CMOS chip, suffering from bulky size and interface issues. Integrating the CGM sensor on silicon is potential to miniaturize the CGM system and reduce the cost, while the recent silicon-based sensors show limited detection range and sensitivity. In this work, we present a silicon-based CGM chip let with wireless power transfer (WPT) and real-time wireless telemetry. Fabricated on a single silicon substrate, the chiplet consists of a silicon-based CGM sensor, a power-harvesting wireless-telemetry chip, and a silicon-based antenna. Measured results show that the chip let achieves a sensitivity of 4 μA.mM.cm-2 and a linear detection range of 0-10 mM. Based on WPT and backscattering communication, the chip let consumes 18.8 μ W power in glucose telemetry.

Closed-Loop Diabetes Minipatch Based on a Biosensor and an Electroosmotic Pump on Hollow Biodegradable Microneedles

Developing a miniaturized, low-cost, and smart closed-loop system for diabetes could significantly improve life quality and benefit millions of people. Conventional closed-loop devices are large in size and exorbitant. Here, we unprecedentedly demonstrate an electrically controlled flexible closed-loop patch for continuous diabetes management by integrating hollow biodegradable microneedles with a biosensing device and an electroosmotic pump. The hollow microneedles were fabricated using a combination of soft lithography and micromachining. The outer layer of the microneedles was functionalized to serve as a biosensing device for the in situ sensitive and accurate monitoring of interstitial glucose. The inner layer of the microneedles was integrated with a flexible electroosmotic pump to deliver insulin, and the delivery rate was electrically controlled by the glucose level from the biosensing device. The closed-loop system successfully stabilized the blood glucose levels of diabetic rats in a normal and safe range. The system is painless, miniaturized, cost-effective, and flexible. It is anticipated that it could open up exciting new avenues for fundamental studies of new closed-loop devices as well as practical applications for diabetes management.

Progress of Polyaniline Glucose Sensors for Diabetes Mellitus Management Utilizing Enzymatic and Non-Enzymatic Detection

Glucose measurement is a fundamental tool in the daily care of Diabetes Mellitus (DM) patients and healthcare professionals. While there is an established market for glucose sensors, the rising number of DM cases has promoted intensive research to provide accurate systems for glucose monitoring. Polyaniline (PAni) is a conductive polymer with a linear conjugated backbone with sequences of single C-C and double C=C bonds. This unique structure produces attractive features for the design of sensing systems such as conductivity, biocompatibility, environmental stability, tunable electrochemical properties, and antibacterial activity. PAni-based glucose sensors (PBGS) were actively developed in past years, using either enzymatic or non-enzymatic principles. In these devices, PAni played roles as a conductive material for electron transfer, biocompatible matrix for enzymatic immobilization, or sensitive layer for detection. In this review, we covered the development of PBGS from 2015 to the present, and it is not even exhaustive; it provides an overview of advances and achievements for enzymatic and non-enzymatic PBGB PBGS for self-monitoring and continuous blood glucose monitoring. Additionally, the limitations of PBGB PBGS to advance into robust and stable technology and the challenges associated with their implementation are presented and discussed.

Differential Amperometric Microneedle Biosensor for Wearable Levodopa Monitoring of Parkinson's Disease

Levodopa (L-Dopa) is considered to be one of the most effective therapies available for Parkinson's disease (PD) treatment. The therapeutic window of L-Dopa is narrow due to its short half-life, and long-time L-Dopa treatment will cause some side effects such as dyskinesias, psychosis, and orthostatic hypotension. Therefore, it is of great significance to monitor the dynamic concentration of L-Dopa for PD patients with wearable biosensors to reduce the risk of complications. However, the high concentration of interferents in the body brings great challenges to the in vivo monitoring of L-Dopa. To address this issue, we proposed a minimal-invasive L-Dopa biosensor based on a flexible differential microneedle array (FDMA). One working electrode responded to L-Dopa and interfering substances, while the other working electrode only responded to electroactive interferences. The differential current response of these two electrodes was related to the concentration of L-Dopa by eliminating the common mode interference. The differential structure provided the sensor with excellent anti-interference performance and improved the sensor's accuracy. This novel flexible microneedle sensor exhibited favorable analytical performance of a wide linear dynamic range (0-20 μM), high sensitivity (12.618 nA μM^-1 cm^-2) as well as long-term stability (two weeks). Ultimately, the L-Dopa sensor displayed a fast response to in vivo L-Dopa dynamically with considerable anti-interference ability. All these attractive performances indicated the feasibility of this FDMA for minimal invasive and continuous monitoring of L-Dopa dynamic concentration for Parkinson's disease.

Fully integrated flexible biosensor for wearable continuous glucose monitoring

Continuous physiological monitoring is a promising alternative to current chronic disease management for obtaining big data sets to help individualized therapy. Here, we present a continuous glucose monitoring platform consisting of a screen-printed electrochemical biosensor and a fully integrated wireless electrochemical analysis system. A biocompatible conjugated polymer (poly (N-phenylglycine)) was employed as the support material for enzyme immobilization. Specifically, a polyurethane outer layer was decorated onto the working electrode of the biosensor to construct a diffusion limiting membrane and improve the linear range of the glucose sensor. We optimized the fabricated glucose sensor so that it achieves a linear range of 1-30 mM and a sensitivity of 12.69 μA mM^-1·cm^-2 in vitro. The long-term stability is up to 30 days by storing in PBS solution at 4°C. The overall system design was very small (0.8 × 1.8 cm) and consisted of a signal conditioning part, a programmable electrochemical chip, and a wireless connection using Bluetooth Low Energy with a smartphone. Finally, we carried out biocompatibility tests and animal experiments to demonstrate the device can successfully monitor blood glucose in vivo.

Nanomaterials for IoT Sensing Platforms and Point-of-Care Applications in South Korea

Herein, state-of-the-art research advances in South Korea regarding the development of chemical sensing materials and fully integrated Internet of Things (IoT) sensing platforms were comprehensively reviewed for verifying the applicability of such sensing systems in point-of-care testing (POCT). Various organic/inorganic nanomaterials were synthesized and characterized to understand their fundamental chemical sensing mechanisms upon exposure to target analytes. Moreover, the applicability of nanomaterials integrated with IoT-based signal transducers for the real-time and on-site analysis of chemical species was verified. In this review, we focused on the development of noble nanostructures and signal transduction techniques for use in IoT sensing platforms, and based on their applications, such systems were classified into gas sensors, ion sensors, and biosensors. A future perspective for the development of chemical sensors was discussed for application to next-generation POCT systems that facilitate rapid and multiplexed screening of various analytes.

Addressing the Selectivity of Enzyme Biosensors: Solutions and Perspectives

Enzymatic biosensors enjoy commercial success and are the subject of continued research efforts to widen their range of practical application. For these biosensors to reach their full potential, their selectivity challenges need to be addressed by comprehensive, solid approaches. This review discusses the status of enzymatic biosensors in achieving accurate and selective measurements via direct biocatalytic and inhibition-based detection, with a focus on electrochemical enzyme biosensors. Examples of practical solutions for tackling the activity and selectivity problems and preventing interferences from co-existing electroactive compounds in the samples are provided such as the use of permselective membranes, sentinel sensors and coupled multi-enzyme systems. The effect of activators, inhibitors or enzymatic substrates are also addressed by coupled enzymatic reactions and multi-sensor arrays combined with data interpretation via chemometrics. In addition to these more traditional approaches, the review discusses some ingenious recent approaches, detailing also on possible solutions involving the use of nanomaterials to ensuring the biosensors' selectivity. Overall, the examples presented illustrate the various tools available when developing enzyme biosensors for new applications and stress the necessity to more comprehensively investigate their selectivity and validate the biosensors versus standard analytical methods.

Electrochemical Sensors Based on Conducting Polymers for the Aqueous Detection of Biologically Relevant Molecules

Electrochemical sensors appear as low-cost, rapid, easy to use, and in situ devices for determination of diverse analytes in a liquid solution. In that context, conducting polymers are much-explored sensor building materials because of their semiconductivity, structural versatility, multiple synthetic pathways, and stability in environmental conditions. In this state-of-the-art review, synthetic processes, morphological characterization, and nanostructure formation are analyzed for relevant literature about electrochemical sensors based on conducting polymers for the determination of molecules that (i) have a fundamental role in the human body function regulation, and (ii) are considered as water emergent pollutants. Special focus is put on the different types of micro- and nanostructures generated for the polymer itself or the combination with different materials in a composite, and how the rough morphology of the conducting polymers based electrochemical sensors affect their limit of detection. Polypyrroles, polyanilines, and polythiophenes appear as the most recurrent conducting polymers for the construction of electrochemical sensors. These conducting polymers are usually built starting from bifunctional precursor monomers resulting in linear and branched polymer structures; however, opportunities for sensitivity enhancement in electrochemical sensors have been recently reported by using conjugated microporous polymers synthesized from multifunctional monomers.

Recent advances of nanomedicine-based strategies in diabetes and complications management: Diagnostics, monitoring, and therapeutics

Diabetes mellitus (DM) is a metabolic disorder characterized by the presence of chronic hyperglycemia driven by insulin deficiency or resistance, imposing a significant global burden affecting 463 million people worldwide in 2019. This review has comprehensively summarized the application of nanomedicine with accurate, patient-friendly, real-time properties in the field of diabetes diagnosis and monitoring, and emphatically discussed the unique potential of various nanomedicine carriers (e.g., polymeric nanoparticles, liposomes, micelles, microparticles, microneedles, etc.) in the management of diabetes and complications. Novel delivery systems have been developed with improved pharmacokinetics and pharmacodynamics, excellent drug biodistribution, biocompatibility, and therapeutic efficacy, long-term action safety, as well as the improved production methods. Furthermore, the effective nanomedicine for the treatment of several major diabetic complications with significantly improved life qualities of diabetic patients were discussed in detail. Going through the literature review, several critical issues of the nanomedicine-based strategies applications need to be addressed such as stabilities and long-term safety effects in vivo, the deficiency of standard for formulation administration, feasibility of scale-up, etc. Overall, the review provides an insight into the design, advantages and limitations of novel nanomedicine application in the diagnostics, monitoring, and therapeutics of DM.

Antibody-based biosensor to detect oncogenic splicing factor Sam68 for the diagnosis of lung cancer

OBJECTIVE

The present work aimed to investigate the potential utility of Sam68 protein as a prognostic marker in lung cancer. Then an electrochemical immunosensor is fabricated that is sufficiently sensitive to detect Sam68.

RESULTS

Analysis of stage-specific Lung cancer microarray data shows that differential expression of Sam68 is associated with cancer stage and monotonically increases from early tumor stage to advanced metastatic stage. Moreover, the higher expression of Sam68 results in reduced survival of lung cancer patients. Based on these observations, an electrochemical immunosensor was developed for the quantification of Sam68 protein. The target protein was captured by the Anti-Sam68 antibody that was immobilized on the modified Glassy carbon electrode. The stepwise assembly process was characterized by cyclic voltammetry and electrochemical impedance spectroscopy. This fabricated immunosensor displayed good analytical performance in comparison to commercial ELISA kit with good sensitivity, lower detection limit (LOD) of 10.5 pg mL^-1, and wide linear detection range from 1 to 5 μg mL^-1. This method was validated with satisfactory detection of Sam68 protein in lung adenocarcinoma cell line, NCI-H23. Besides, spike and recovery assay reconfirm that the sensor can precisely quantify Sam68 protein in a complex physiological sample.

CONCLUSION

We conclude Sam68 as a valuable prognostic biomarker for early detection of lung cancer. Moreover, we report the first study on the development of an electrochemical immunosensor for the detection of Sam68. The fabricated immunosensor exhibit excellent analytical performance, which can accurately predict the lung cancer patient pathological state.

One-step modification of nano-polyaniline/glucose oxidase on double-side printed flexible electrode for continuous glucose monitoring: Characterization, cytotoxicity evaluation and in vivo experiment

The single-step modification of the nanostructured polyaniline (PANI)/glucose oxidase (GOD) enzyme on double-sided, screen-printed, flexible electrodes doped with Prussian blue (PB), has been achieved and successfully applied in continuous glucose monitoring in vivo, and its biocompatibility has been evaluated systematically. The proposed fabrication procedure is simple, low cost, and suitable for large-scale production. PB doped with carbon ink catalyzes the reduction of hydrogen peroxide (H₂O₂) in low-voltage conditions, which could help eliminate interferences. And the PANI/GOD nanostructure makes the GOD enzyme more stable for long-term, in vivo monitoring. More importantly, a polyurethane (PU) layer is deposited on the electrode's surface as a diffusion limiting membrane that enhanced the linear range and biocompatibility. In tests in vitro, the proposed biosensor achieved a linear range of 0-12 mM and a good sensitivity of 16.66 μA·mM^-1·cm^-2(correlation coefficient R² = 0.9962) with an excellent specificity to glucose. The biosensor exhibits long-term stability, with a maximum lifespan of 14 days when stored in phosphate buffer solution at 4 °C, and achieves a sensitivity of 120%. The biocompatibilities of the electrode materials have also been systematically evaluated in cytotoxicity and cell adhesion tests to ensure the safety of implantation. In experiments in vivo, the biosensor can successfully monitor the glucose level fluctuation of rats after 24 h following implantation. Overall, the biosensor fabricated with the double-side, screen-printing process, satisfies the glucose monitoring range in vivo and eliminates various types of interference, thus establishing a new, large-scale production procedure for flexible in vivo biosensors.

Microscale Biosensor Array Based on Flexible Polymeric Platform toward Lab-on-a-Needle: Real-Time Multiparameter Biomedical Assays on Curved Needle Surfaces

In vivo sensing of various physical/chemical parameters is gaining increased attention for early prediction and management of various diseases. However, there are major limitations on the fabrication method of multiparameter needle-based in vivo sensing devices, particularly concerning the uniformity between sensors. To address these challenges, we developed a microscale biosensor array for the measurement of electrical conductivity, pH, glucose, and lactate concentrations on a flexible polymeric polyimide platform with electrodeposited electrochemically active layers. The biosensor array was then transferred to a medical needle toward multiparametric in vivo sensing. The flexibility of the sensor platform allowed an easy integration to the curved surface (φ = 1.2 mm) of the needle. Furthermore, the electrodeposition process was used to localize various active materials for corresponding electrochemical sensors on the microscale electrodes with a high precision (patterning area = 150 μm × 2 mm). The biosensor array-modified needle was aimed to discriminate cancer from normal tissues by providing real-time discrimination of glucose, lactate concentration, pH, and electrical conductivity changes associated with the cancer-specific metabolic processes. The sensor performance was thus evaluated using solution samples, covering the physiological concentrations for cancer discrimination. Finally, the possibility of in vivo electrochemical biosensing during needle insertion was confirmed by utilizing the needle in a hydrogel phantom that mimicked the normal and cancer microenvironments.

Design of a Sandwich Hierarchically Porous Membrane with Oxygen Supplement Function for Implantable Glucose Sensor

This study aims to develop an oxygen regeneration layer sandwiched between multiple porous polyurethanes (PU) to improve the performance of implantable glucose sensors. Sensors were prepared by coating electrodes with platinum nanoparticles, Nafion, glucose oxidase and sandwich hierarchically porous membrane with an oxygen supplement function (SHPM-OS). The SHPM-OS consisted of a hierarchically porous structure synthesized by polyethylene glycol and PU and a catalase (Cat) layer that was coated between hierarchical membranes and used to balance the sensitivity and linearity of glucose sensors, as well as reduce the influence of oxygen deficiency during monitoring. Compared with the sensitivity and linearity of traditional non-porous (NO-P) sensors (35.95 nA/mM, 0.9987, respectively) and single porous (SGL-P) sensors (45.3 nA /mM, 0.9610, respectively), the sensitivity and linearity of the SHPM-OS sensor was 98.45 nA/mM and 0.9989, respectively, which was more sensitive with higher linearity. The sensor showed a response speed of five seconds and a relative sensitivity of 90% in the first 10 days and remained 78% on day 20. This sensor coated with SHPM-OS achieved rapid responses to changes of glucose concentration while maintaining high linearity for long monitoring times. Thus, it may reduce the difficulty of back-end hardware module development and assist with effective glucose self-management for people with diabetes.

3D Printed Multi-Functional Hydrogel Microneedles Based on High-Precision Digital Light Processing

Traditional injection and extraction devices often appear painful and cumbersome for patients. In recent years, polymer microneedles (MNs) have become a novel tool in the field of clinical medicine and health. However, the cost of building MNs into any shapes still remains a challenge. In this paper, we proposed hydrogel microneedles fabricated by high-precision digital light processing (H-P DLP) 3D printing system. Benefits from the sharp protuberance and micro-porous of the hydrogel microneedle, the microneedle performed multifunctional tasks such as drug delivery and detection with minimally invasion. Critical parameters for the fabrication process were analyzed, and the mechanical properties of MNs were measured to find a balance between precision and stiffness. Results shows that the stiffness and precision were significantly influenced by exposure time of each layer, and optimized printing parameters provided a balance between precision and stiffness. Bio-compatible MNs based on our H-P DLP system was able to execute drug injection and drug detection in our experiments. This work provided a low-cost and fast method to build MNs with 3D building, qualified the mechanical performance, drug injection, drug detection ability of MNs, and may be helpful for the potential clinical application.

Novel lavender oil and silver nanoparticles simultaneously loaded onto polyurethane nanofibers for wound-healing applications

Synthetic polymers, especially those with biocompatible and biodegradable characteristics, may offer effective alternatives for the treatment of severe wounds and burn injuries. Ideally, the scaffold material should induce as little pain as possible, enable quick healing, and direct the growth of defect-free epidermal cells. The best material with this multifunctionality, such as self-healing dressings, should be hydrophilic and have uninterrupted and direct contact with the damaged tissue. In addition, the ideal biomaterial should have some antibacterial properties. In this study, a novel technique was used to fabricate composite electrospun wound-dressing nanofibers composed of polyurethane encasing lavender oil and silver (Ag) nanoparticles (NPs). After electrospinning, the fabricated nanofibers were identified using various techniques, including scanning electron microscopy (SEM) and transmission electron microscopy (TEM). An abundance of Ag NPs in the fibers decreased the diameter of the fibers while increased concentration of the lavender oil increased the diameter. Fourier transform infrared (FTIR) and X-ray diffraction (XRD) studies showed the presence of the lavender oil and Ag NPs in the fiber dressings. The Ag NPs and lavender oil improved the hydrophilicity of the nanofibers and ensured the proliferation of chicken embryo fibroblasts cultured in-vitro on these fiber dressings. The antibacterial efficiency of the nanofiber dressings was investigated using E. coli and S. aureus, which yielded zones of inhibition of 16.2 ± 0.8 and 5.9 ± 0.5 mm, respectively, indicating excellent bactericidal properties of the dressings. The composite nanofiber dressings have great potential to be used as multifunctional wound dressings; offering protection against external agents as well as promoting the regeneration of new tissue.

Top-Down Strategy of Implantable Biosensor Using Adaptable, Porous Hollow Fibrous Membrane

Fabrication of an outer membrane is crucial for an implantable biosensor to enhance the long-term stability and accuracy of sensors. Herein, an adaptable, controllable, porous outer membrane for an implantable biosensor was fabricated using a "top-down" method, allowing maximum retention of enzyme activity and fine control over membrane microstructure. Polysulfone hollow fibrous membranes with different pore sizes and porosities were used as a base membrane. Chitosan (CH) and sodium alginate (SA) were self-assembled on the inner surface of PSfHM to construct a biocompatible and conductive interface between PSfHM and the electrode. In vitro and in vivo experiments were used to evaluate the performance of implantable glucose biosensors with PSfHM and CH/SA modified PSfHM (PSfHM-CH/SA). The glucose biosensor with PSfHM-CH/SA exhibited a more stable output current than bare sensors and a quick response time (<50 s). The glucose biosensor with PSfHM-CH/SA linear sensing range was between 0 and 22 mM ( R² = 0.9905), and relative sensitivity remained at >87% within 7 days and >76% within 15 days. Furthermore, response currents recorded by implanted sensors closely followed the blood glucose trend from the tail vein blood during in vivo experiments.

Wearable All-Solid-State Potentiometric Microneedle Patch for Intradermal Potassium Detection

A new analytical all-solid-state platform for intradermal potentiometric detection of potassium in interstitial fluid is presented here. Solid microneedles are modified with different coatings and polymeric membranes to prepare both the potassium-selective electrode and reference electrode needed for the potentiometric readout. These microneedle-based electrodes are fixed in an epidermal patch suitable for insertion into the skin. The analytical performances observed for the potentiometric cell (Nernstian slope, limit of detection of 10^-4.9 potassium activity, linear range of 10^-4.2 to 10^-1.1, drift of 0.35 ± 0.28 mV h^-1), together with a fast response time, adequate selectivity, and excellent reproducibility and repeatability, are appropriate for potassium analysis in interstitial fluid within both clinical and harmful levels. The potentiometric response is maintained after several insertions into animal skin, confirming the resiliency of the microneedle-based sensor. Ex vivo tests based on the intradermal detection of potassium in chicken and porcine skin demonstrate that the microneedle patch is suitable for monitoring potassium changes inside the skin. In addition, the dimensions of the microneedles modified with the corresponding layers necessary to enhance robustness and provide sensing capabilities (1000 μm length, 45° tip angle, 15 μm thickness in the tip, and 435 μm in the base) agree with the required ranges for a painless insertion into the skin. In vitro cytotoxicity experiments showed that the patch can be used for at least 24 h without any side effect for the skin cells. Overall, the developed concept constitutes important progress in the intradermal analysis of ions related to an electrolyte imbalance in humans, which is relevant for the control of certain types of diseases.

Intracellular calcium ions and morphological changes of cardiac myoblasts response to an intelligent biodegradable conducting copolymer

A novel biodegradable conducting polymer, PLA-b-AP-b-PLA (PAP) triblock copolymer of poly (l-lactide) (PLA) and aniline pentamer (AP) with electroactivity and biodegradability, was synthesized and its potential application in cardiac tissue engineering was studied. The PAP copolymer presented better biocompatibility compared to PANi and PLA because of promoted cell adhesion and spreading of rat cardiac myoblasts (H9c2 cell line) on PAP/PLA thin film. After pulse electrical stimulation (5 V, 1 Hz, 500 ms) for 6 days, the proliferation ratio, and intracellular calcium concentration of H9c2 cells on PAP/PLA were improved significantly. Meanwhile, cell morphology changed by varying the pulse electrical signals. Especially, the oriented pseudopodia-like structure was observed from H9c2 cells on PAP/PLA after electrical stimulation. It is regarded that the novel conducting copolymer could enhance electronic signals transferring between cells because of its special electrochemical properties, which may result in the differentiation of cardiac myoblasts.

A wearable electrochemical glucose sensor based on simple and low-cost fabrication supported micro-patterned reduced graphene oxide nanocomposite electrode on flexible substrate

In this study, a reduced graphene oxide (rGO)-based nanostructured composite working electrode of high quality was successfully microfabricated and micro-patterned on a flexible polyimide substrate using simple low-cost fabrication processes. Gold and platinum alloy nanoparticles were electrochemically deposited onto the microfabricated rGO surface and chitosan-glucose oxidase composites were integrated onto the modified surface of the working electrode to develop a human sweat-based wearable glucose sensor application. The fabricated biosensor exhibited excellent amperometric response to glucose at a detection range of 0-2.4 mM (covers the glucose range in sweat), with a sensitivity of 48 μA/mMcm², a short response time (20 s), and high linearity (0.99). The detection limit for glucose was calculated as 5 µm. The human sweat/mixing glucose samples initially used for testing indicated acceptable detection performance and stability for low glucose concentrations. These results confirm that the proposed nanostructured composite flexible working electrode and fabrication process are highly promising for application as human sweat-based electrochemical glucose sensors.

Intrinsically Conductive Polymer Nanocomposites for Cellular Applications

Intrinsically conductive polymer nanocomposites have a remarkable potential for cellular applications such as biosensors, drug delivery systems, cell culture systems and tissue engineering biomaterials. Intrinsically conductive polymers transmit electrical stimuli between cells, and induce regeneration of electroactive tissues such as muscle, nerve, bone and heart. However, biocompatibility and processability are common issues for intrinsically conductive polymers. Conductive polymer composites are gaining importance for tissue engineering applications due to their excellent mechanical, electrical, optical and chemical functionalities. Here, we summarize the different types of intrinsically conductive polymers containing electroactive nanocomposite systems. Cellular applications of conductive polymer nanocomposites are also discussed focusing mainly on poly(aniline), poly(pyrrole), poly(3,4-ethylene dioxythiophene) and poly(thiophene).