Highly sensitive and selective nanostructured microbiosensors for glucose and lactate simultaneous measurements in blood serum and in vivo in brain tissue

Amperometric bio-sensing of lactate and oxygen concurrently with local field potentials during status epilepticus

Epilepsy is a prevalent neurological disorder with a complex pathogenesis and unpredictable nature, presenting limited treatment options in >30 % of affected individuals. Neurometabolic abnormalities have been observed in epilepsy patients, suggesting a disruption in the coupling between neural activity and energy metabolism in the brain. In this study, we employed amperometric biosensors based on a modified carbon fiber microelectrode platform to directly and continuously measure lactate and oxygen dynamics in the brain extracellular space. These biosensors demonstrated high sensitivity, selectivity, and rapid response time, enabling in vivo measurements with high temporal and spatial resolution. In vivo recordings in the cortex of anaesthetized rats revealed rapid and multiphasic fluctuations in extracellular lactate and oxygen levels following neuronal stimulation with high potassium. Furthermore, real-time measurement of lactate and oxygen concentration dynamics concurrently with network electrical activity during status epilepticus induced by 4-aminopyridine (4-AP) demonstrated phasic changes in lactate levels that correlated with bursts of electrical activity, while tonic levels of lactate remained stable during seizures. This study highlights the complex interplay between lactate dynamics, electrical activity, and oxygen utilization in epileptic seizures.

An inexpensive paracetamol sensor based on an acid-activated carbon fiber microelectrode

Paracetamol, a contaminant of emerging concern, has been detected in different bodies of water, where it can impact ecological and human health. To quantify this paracetamol, electroanalytical methods have gained support. Thus, the present study developed a simple, inexpensive, and environmentally friendly method for paracetamol quantification using a carbon fiber microelectrode based on commercial carbon fiber. To improve the carbon fiber microelectrode's paracetamol sensitivity and selectivity, it was subjected to an activation process via electrochemical oxidation in an acid medium (H2SO4 or HNO3), using 20 consecutive cycles of cyclic voltammetry. The treated (activated) carbon fiber microelectrode was characterized using scanning electron microscopy and electrochemical techniques, including chronoamperometry and electrochemical impedance spectroscopy. The H2SO4-activated carbon fiber microelectrode exhibited enhanced figures of merit, with a linear dynamic range of paracetamol detection from 0.5 to 11 μmol L-1 and a limit of detection of 0.21 μmol L-1 under optimized conditions. The method was optimized by quantifying paracetamol in commercial pharmaceutical tablets, spiked running tap water, and river water (Pita River, Quito, Ecuador, latitude -0.364955°, longitude -78.404538°); the respective recovery values were 102.89, 103.93, and 112.40%. The results demonstrated an acceptable level of accuracy and the promising applicability of this carbon fiber microelectrode as a sensor to detect paracetamol.

Challenges and strategies faced in the electrochemical biosensing analysis of neurochemicals in vivo: A review

Our brain is an intricate neuromodulatory network, and various neurochemicals, including neurotransmitters, neuromodulators, gases, ions, and energy metabolites, play important roles in regulating normal brain function. Abnormal release or imbalance of these substances will lead to various diseases such as Parkinson's and Alzheimer's diseases, therefore, in situ and real-time analysis of neurochemical interactions in pathophysiological conditions is beneficial to facilitate our understanding of brain function. Implantable electrochemical biosensors are capable of monitoring neurochemical signals in real time in extracellular fluid of specific brain regions because they can provide excellent temporal and spatial resolution. However, in vivo electrochemical biosensing analysis mainly faces the following challenges: First, foreign body reactions induced by microelectrode implantation, non-specific adsorption of proteins and redox products, and aggregation of glial cells, which will cause irreversible degradation of performance such as stability and sensitivity of the microsensor and eventually lead to signal loss; Second, various neurochemicals coexist in the complex brain environment, and electroactive substances with similar formal potentials interfere with each other. Therefore, it is a great challenge to design recognition molecules and tailor functional surfaces to develop in vivo electrochemical biosensors with high selectivity. Here, we take the above challenges as a starting point and detail the basic design principles for improving in vivo stability, selectivity and sensitivity of microsensors through some specific functionalized surface strategies as case studies. At the same time, we summarize surface modification strategies for in vivo electrochemical biosensing analysis of some important neurochemicals for researchers' reference. In addition, we also focus on the electrochemical detection of low basal concentrations of neurochemicals in vivo via amperometric waveform techniques, as well as the stability and biocompatibility of reference electrodes during long-term sensing, and provide an outlook on the future direction of in vivo electrochemical neurosensing.

Focus Review on Nanomaterial-Based Electrochemical Sensing of Glucose for Health Applications

Diabetes management can be considered the first paradigm of modern personalized medicine. An overview of the most relevant advancements in glucose sensing achieved in the last 5 years is presented. In particular, devices exploiting both consolidated and innovative electrochemical sensing strategies, based on nanomaterials, have been described, taking into account their performances, advantages and limitations, when applied for the glucose analysis in blood and serum samples, urine, as well as in less conventional biological fluids. The routine measurement is still largely based on the finger-pricking method, which is usually considered unpleasant. In alternative, glucose continuous monitoring relies on electrochemical sensing in the interstitial fluid, using implanted electrodes. Due to the invasive nature of such devices, further investigations have been carried out in order to develop less invasive sensors that can operate in sweat, tears or wound exudates. Thanks to their unique features, nanomaterials have been successfully applied for the development of both enzymatic and non-enzymatic glucose sensors, which are compliant with the specific needs of the most advanced applications, such as flexible and deformable systems capable of conforming to skin or eyes, in order to produce reliable medical devices operating at the point of care.

Microfluidic Platform Integrated with Carbon Nanofibers-Decorated Gold Nanoporous Sensing Device for Serum PSA Quantification

Prostate cancer is a disease with a high incidence and mortality rate in men worldwide. Serum prostate-specific antigens (PSA) are the main circulating biomarker for this disease in clinical practices. In this work, we present a portable and reusable microfluidic device for PSA quantification. This device comprises a polymethyl methacrylate microfluidic platform coupled with electrochemical detection. The platinum working microelectrode was positioned in the outflow region of the microchannel and was modified with carbon nanofibers (CNF)-decorated gold nanoporous (GNP) structures by the dynamic hydrogen bubble template method, through the simultaneous electrodeposition of metal precursors in the presence of CNF. CNF/GNP structures exhibit attractive properties, such as a large surface to volume ratio, which increases the antibody's immobilization capacity and the electroactive area. CNFs/GNP structures were characterized by scanning electron microscopy, energy dispersive spectrometry, and cyclic voltammetry. Anti-PSA antibodies and HRP were employed for the immune-electrochemical reaction. The detection limit for the device was 5 pg mL^-1, with a linear range from 0.01 to 50 ng mL^-1. The coefficients of variation within and between assays were lower than 4.40%, and 6.15%, respectively. Additionally, its clinical performance was tested in serum from 30 prostate cancer patients. This novel device was a sensitive, selective, portable, and reusable tool for the serological diagnosis and monitoring of prostate cancer.

Fabrication of a Lactate-Specific Molecularly Imprinted Polymer toward Disease Detection

The development of sensitive and selective robust sensor materials for targeted biomarker detection aims to contribute to self-health monitoring and management. Molecularly imprinted polymeric (MIP) materials can perform as biomimetic recognition elements via tailored routes of synthesis for specific target analyte extraction and/or detection. In this work, a sensitive- and selective-lactate MIP has been developed utilizing methacrylic acid and ethylene glycol dimethacrylate as the functional monomer and cross-linker, respectively. The sensitivity of the as-synthesized imprinted species was evaluated by determining the target analyte retention, imprinting factor, and selectivity adsorption of up to 63.5%, 6.86, and 0.82, respectively. MIP selectivity elucidated the imprinting mechanism between the functional monomers and target analyte lactate, further experimentally evidenced by using structurally competitive analytes malic acid and sodium 2-hydroxybutyrate, where retentions of 22.6 and 25.2%, respectively, were observed. Understanding the specific intermolecular mechanisms of both the template analyte and structural interferents with the MIP enables experimentalists to make informed decisions regarding monomer-target and porogen selections and possible sites of interaction for improved molecular imprinting. This imprinting system highlights the potential to be further developed into artificial receptor sensor materials for the detection of disease.

In Vivo Electrochemical Biosensors: Recent Advances in Molecular Design, Electrode Materials, and Electrochemical Devices

Electrochemical biosensors provide powerful tools for dissecting the dynamically changing neurochemical signals in the living brain, which contribute to the insight into the physiological and pathological processes of the brain, due to their high spatial and temporal resolutions. Recent advances in the integration of in vivo electrochemical sensors with cross-disciplinary advances have reinvigorated the development of in vivo sensors with even better performance. In this Review, we summarize the recent advances in molecular design, electrode materials, and electrochemical devices for in vivo electrochemical sensors from molecular to macroscopic dimensions, highlighting the methods to obtain high performance for fulfilling the requirements for determination in the complex brain through flexible and smart design of molecules, materials, and devices. Also, we look forward to the development of next-generation in vivo electrochemical biosensors.

Multi-Spatiotemporal Probing of Neurochemical Events by Advanced Electrochemical Sensing Methods

Neurochemical events involving biosignals of different time and space dimensionalities constitute the complex basis of neurological functions and diseases. In view of this fact, electrochemical measurements enabling real-time quantification of neurochemicals at multiple levels of spatiotemporal resolution can provide informative clues to decode the molecular networks bridging vesicles and brains. This Minireview focuses on how scientific questions regarding the properties of single vesicles, neurotransmitter release kinetics, interstitial neurochemical dynamics, and multisignal interconnections in vivo have driven the design of electrochemical nano/microsensors, sensing interface engineering, and signal/data processing. An outlook for the future frontline in this realm will also be provided.

Accelerating the development of implantable neurochemical biosensors by using existing clinically applied depth electrodes

In this study, an implantable stereo-electroencephalography (sEEG) depth electrode was functionalised with an enzyme coating for enzyme-based biosensing of glucose and L-glutamate. This was done because personalised medicine could benefit from active real-time neurochemical monitoring on small spatial and temporal scales to further understand and treat neurological disorders. To achieve this, the sEEG depth electrode was characterised using cyclic voltammetry (CV), differential pulse voltammetry (DPV), square wave voltammetry (SWV), and electrochemical impedance spectroscopy (EIS) using several electrochemical redox mediators (potassium ferri/ferrocyanide, ruthenium hexamine chloride, and dopamine). To improve performance, the Pt sensors on the sEEG depth electrode were coated with platinum black and a crosslinked gelatin-enzyme film to enable enzymatic biosensing. This characterisation work showed that producing a useable electrode with a good electrochemical response showing the expected behaviour for a platinum electrode was possible. Coating with Pt black improved the sensitivity to H₂O₂ over unmodified electrodes and approached that of well-defined Pt macro disc electrodes. Measured current showed good dependence on concentration, and the calibration curves report good sensitivity of 29.65 nA/cm²/μM for glucose and 8.05 nA/cm²/μM for L-glutamate with a stable, repeatable, and linear response. These findings demonstrate that existing clinical electrode devices can be adapted for combined electrochemical and electrophysiological measurement in patients and obviate the need to develop new electrodes when existing clinically approved devices and the associated knowledge can be reused. This accelerates the time to use and application of in vivo and wearable biosensing for diagnosis, treatment, and personalised medicine.

Recent Development of Neural Microelectrodes with Dual-Mode Detection

Neurons communicate through complex chemical and electrophysiological signal patterns to develop a tight information network. A physiological or pathological event cannot be explained by signal communication mode. Therefore, dual-mode electrodes can simultaneously monitor the chemical and electrophysiological signals in the brain. They have been invented as an essential tool for brain science research and brain-computer interface (BCI) to obtain more important information and capture the characteristics of the neural network. Electrochemical sensors are the most popular methods for monitoring neurochemical levels in vivo. They are combined with neural microelectrodes to record neural electrical activity. They simultaneously detect the neurochemical and electrical activity of neurons in vivo using high spatial and temporal resolutions. This paper systematically reviews the latest development of neural microelectrodes depending on electrode materials for simultaneous in vivo electrochemical sensing and electrophysiological signal recording. This includes carbon-based microelectrodes, silicon-based microelectrode arrays (MEAs), and ceramic-based MEAs, focusing on the latest progress since 2018. In addition, the structure and interface design of various types of neural microelectrodes have been comprehensively described and compared. This could be the key to simultaneously detecting electrochemical and electrophysiological signals.