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ABSTRACT Lactate is a useful analytical indicator in various fields. The lactate monitoring benefits from evaluating the body's condition, as excessive muscle use or fatigue can result in injury. Further, it is useful for alerting to emergencies like haemorrhage, hypoxia, respiratory distress, and sepsis. Additionally, the determination of the food's lactate level is very important in examining freshness, storage stability, and fermentation degree. Given such benefits, the determination of lactate in various samples has been widely explored, especially using electrochemical sensor technology. Despite enzymatic sensors being the focus of numerous studies, enzyme‐free platforms have gained focus over the last few years to address the matter of enzyme stability. This review article respectfully offers an overview of the concepts, applications, and recent advances of electrochemical lactate detection platforms. A comparison of hot research for enzymatic and enzyme‐free lactate sensors in terms of electrode surface engineering, enzymes and their immobilisation matrices, and several analytical parameters, including linear dynamic range, the limit of detection, sensitivity, and stability, have been discussed. In addition, future perspectives have been highlighted in this review.

The diversity of materials proposed for non-enzymatic glucose detection and the lack of standardized protocols for assessing sensor performance have caused considerable confusion in the field. Therefore, methods for pre-evaluation of working electrodes, which will enable their conscious design, are currently intensively sought. Our approach involved comprehensive morphologic and structural characterization of copper sulfides as well as drop-casted suspensions based on three different polymers—cationic chitosan, anionic Nafion, and nonionic polyvinylpyrrolidone (PVP). For this purpose, scanning electron microscopy (SEM), X-ray diffraction (XRD), and Raman spectroscopy were applied. Subsequently, comparative studies of electrochemical properties of bare glassy carbon electrode (GCE), polymer- and copper sulfides/polymer-modified GCEs were performed using electrochemical impedance spectroscopy (EIS) and voltammetry. The results from EIS provided an explanation for the enhanced analytical performance of Cu-PVP/GCE over chitosan- and Nafion-based electrodes. Moreover, it was found that the pH of the electrolyte significantly affects the electrocatalytic behavior of copper sulfides, indicating the importance of OHads in the detection mechanism. Additionally, diffusion was denoted as a limiting step in the irreversible electrooxidation process that occurs in the proposed system.

Urea, a nitrogenous organic compound resulting from protein metabolism, is excreted as a waste product in urine. Elevated blood urea levels are associated with severe health conditions, including chronic kidney disease (CKD) and liver failure. Thus, monitoring urea levels is essential for CKD patients and individuals with metabolic disorders that heighten the risk of CKD. While existing diagnostic technologies offer high sensitivity and specificity, they are often expensive, require skilled operators, involve lengthy processing times, and are typically invasive and discontinuous. To address these challenges, researchers have developed various biosensor systems for rapid and cost‐effective urea detection. This review provides a comprehensive overview of recent advancements in urea biosensing technologies, highlighting key challenges and potential solutions in biosensor design. It examines enzymatic and non‐enzymatic urea biosensors, focusing on electrochemical detection techniques such as amperometry and potentiometry for enzymatic sensors and cyclic voltammetry for non‐enzymatic sensors. Additionally, it explores material innovations, technological advancements, and strategies to enhance sensitivity, selectivity, portability, and stability. The integration of biosensors with IoT for real‐time monitoring and their applications in medical diagnostics are also discussed. This review explores advances in enzymatic and non‐enzymatic biosensors, emphasizing electrochemical detection, material innovations, and IoT integration for real‐time tracking. Key challenges and future opportunities in enhancing sensitivity, selectivity, and portability are highlighted, showcasing biosensors as promising tools for next‐generation medical diagnostics.

Nanocrystalline ZSM‐5 was prepared using propyltriethoxysilane. Materials were characterized by a complementary combination of X‐ray diffraction, nitrogen sorption, and scanning electron microscopy. Transition‐metal ion exchanged nanocrystalline ZSM‐5‐modified electrodes were constructed for the electrocatalytic oxidation of glucose and methanol. A non‐enzymatic electrochemical sensor based on a Ni2+‐exchanged nanocrystalline ZSM‐5‐modified electrode exhibits the highest sensing ability, whereas the corresponding Cu2+‐exchanged electrode exhibits the highest current sensitivity for glucose oxidation. Among the variety of electrodes modified with transition‐metal ion exchanged nanocrystalline ZSM‐5, the Ni2+‐exchanged electrode exhibits high current sensitivity and sensing ability in methanol oxidation. Electrocatalytic activity of conventional ZSM‐5‐modified electrodes was significantly low compared to nanocrystalline ZSM‐5‐modified electrodes. Enhancement in the electrocatalytic activities of nanocrystalline ZSM‐5‐modified electrodes can be correlated with the enhanced accessibility of glucose/methanol to M2+ active centers in the nanocrystalline ZSM‐5 owing to its large specific surface area and intercrystalline mesopores. The sensor was applied directly to determine glucose concentration in adult human blood serum, and the precision of the method was found to be satisfactory. The non‐enzymatic sensor exhibited excellent reproducibility, repeatability, stability, and antifouling ability for direct determination of glucose in human blood serum. Nanocrystalline ZSM‐5‐modified electrodes exhibit high electrocatalytic activity towards oxidation of glucose and methanol (see figure). Enhancement in the electrocatalytic activity is correlated with the accessibility of glucose/methanol to M2+ active centers in the nanocrystalline ZSM‐5 owing to its large surface area and intercrystalline mesopores. Glucose concentration in human blood serum was determined.

Glucose biosensors play an extremely important role in health care systems worldwide. Therefore, the field continues to attract significant attention leading to the development of innovative technologies. Due to their characteristics, Molecularly Imprinted Polymers (MIPs) represent a promising alternative to commercial enzymatic sensors. In this work, a low‐cost, flexible MIP‐based platform for glucose sensing by integrating MIP particles directly into screen‐printed electrodes (SPEs) is realized. The sensor design allows the detection of glucose via two different transducer principles, the so‐called “heat‐transfer method” (HTM) and electrochemical impedance spectroscopy (EIS). The sensitivity and selectivity of the sensor are demonstrated by comparing the responses obtained toward three different saccharides. Furthermore, the application potential of the MIP‐SPE sensor is demonstrated by analyzing the response in urine samples, showing a linear range of 14.38–330 µm with HTM and 1.37–330 µm with EIS. To bring the sensor closer to a real life application, a handheld dipstick sensor is developed, allowing the single‐shot detection of glucose in urine using EIS. This study illustrates that the simplicity of the dipstick readout coupled with the straightforward manufacturing process opens up the possibility for mass production, making this platform a very attractive alternative to commercial glucose sensors. Fabrication of a low‐cost MIP‐based platform for glucose sensing by integrating MIP particles directly into screen‐printed electrodes (SPEs). The design of the MIP‐SPE handheld dipstick sensor allows the single‐shot detection of glucose in human urine samples via two different transducer principles, the so‐called “Heat‐Transfer Method” (HTM) and Electrochemical Impedance Spectroscopy (EIS).

This study introduces a novel microneedle‐based lactate sensor with SU‐8 micropillar enhancement, designed for real‐time monitoring in dynamic environments. Utilizing inkjet‐printing technology, the sensor demonstrates enhanced sensitivity and a reduced limit of detection (LoD), addressing critical challenges in clinical applications like hemodialysis and patient monitoring in ICU. Design enhancements in the medical steel needle improve stress resistance during insertion, contributing to the sensor's reliability. The experimental findings demonstrate that the microneedle is capable of achieving a high level of linearity at 0.99, with a sensitivity of 3.38 µA mM−1/mm−2–0.5 µA mM−1/mm−2 observed within the range of 0.1–0.5 mM and 1–10 mM, respectively. Meanwhile, the microneedle exhibits a low limit of detection (LoD) of 0.01 mM when tested in phosphate‐buffered saline (PBS) with varying lactate concentrations. Moreover, it demonstrates a linearity of 0.98, sensitivity of 1.13 µA mM−1 mm−2, and the same LoD of 0.01 mM in urine. The sensor maintains its performance at flow rates up to 500 mL min−1. Overall, this flexible and inkjet‐printed lactate sensor represents a significant advancement in real‐time clinical monitoring technology. The microneedle‐based lactate sensor shows potential for real‐time clinical applications, such as hemodialysis and cardiac surgery, with a linearity of 0.98, sensitivity of 1.13 µA mM−1 mm−2, and consistent performance at flow rates up to 500 mL min−1, maintaining a LoD of 0.01 mM.

Introducing oxygen-vacancy into the surface of the non-enzymatic sensor is supposed to be an effective way to improve inherently low catalytic activity and specificity of non-enzymatic sensors. In this work, CuO/C was synthesized at different temperatures using metal-organic frameworks as sacrificial templates to receive additional content of oxygen-vacancy. The product with the highest oxygen vacancy was found at 400 °C (named CuO/C-400 °C), which increased catalytically active sites and enhanced the charge-transfer efficiency. The sensing performance was afterward explored by amperometry under an optimal applied potential at 0.5 V (vs. SCE), presenting a broad detection range from 5.0 µM to 25.325 mM (R 2  = 0.9998) with a sensitivity of 244.71 µA mM − 1  cm − 2 , and a detection limit of 1 µM. Furthermore, the reliability and selectivity of CuO/C-400 °C sensors were extensively explored in the presence of artificial serum/saliva samples with gradient glucose concentrations. The human blood samples were also detected with high recoveries compared with the clinical Hexokinase method. Hence, the prepared CuO/C-400 °C sensor with a broad detection range and high selectivity can be applied for the diabetes diagnosis ex vivo without further dilution for real-time analysis in practical applications.

Copper-doped zinc oxide nanoparticles (NPs) CuxZn1−xO (x = 0, 0.01, 0.02, 0.03, and 0.04) were synthesized via a sol-gel process and used as an active electrode material to fabricate a non-enzymatic electrochemical sensor for the detection of glucose. Their structure, composition, and chemical properties were characterized using X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infrared (FTIR) and Raman spectroscopies, and zeta potential measurements. The electrochemical characterization of the sensors was studied using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and differential pulse voltammetry (DPV). Cu doping was shown to improve the electrocatalytic activity for the oxidation of glucose, which resulted from the accelerated electron transfer and greatly improved electrochemical conductivity. The experimental conditions for the detection of glucose were optimized: a linear dependence between the glucose concentration and current intensity was established in the range from 1 nM to 100 μM with a limit of detection of 0.7 nM. The proposed sensor exhibited high selectivity for glucose in the presence of various interfering species. The developed sensor was also successfully tested for the detection of glucose in human serum samples.

Analytical chemistry is now developing mainly in two areas: automation and the creation of complexes that allow, on the one hand, for simultaneously analyzing a large number of samples without the participation of an operator, and on the other, the development of portable miniature devices for personalized medicine and the monitoring of a human habitat. The sensor devices, the great majority of which are biosensors and chemical sensors, perform the role of the latter. That last line is considered in the proposed review. Attention is paid to transducers, receptors, techniques of immobilization of the receptor layer on the transducer surface, processes of signal generation and detection, and methods for increasing sensitivity and accuracy. The features of sensors based on synthetic receptors and additional components (aptamers, molecular imprinted polymers, biomimetics) are discussed. Examples of bio- and chemical sensors’ application are given. Miniaturization paths, new power supply means, and wearable and printed sensors are described. Progress in this area opens a revolutionary era in the development of methods of on-site and in-situ monitoring, that is, paving the way from the “test-tube to the smartphone”.

The non-enzymatic electrochemical sensors are attractive due to their high sensitivity, quick detection, low cost, and simple construction. Hence, in this work, a non-enzymatic biosensor was constructed with NiCo2O4 nanoparticles (~ 82 nm) decorated over Ti2NbC2 nanosheets by an in-situ method. The crystal structure, phase purity, morphology and elemental composition of the synthesized NiCo2O4/Ti2NbC2 nanohybrid was investigated using XRD, Raman and FESEM analysis. The electrocatalytic and electrochemical behaviour of the prepared nanohybrid was investigated using cyclic voltammetry and amperometry analysis. Hybrid of NiCo2O4/Ti2NbC2 produces a biocompatible, electrochemically active surface with enhanced electrical conductivity. The enhanced surface area of NiCo2O4 and superior electrical conductivity of Ti2NbC2 nanosheets helped to develop non-enzymatic electrochemical glucose sensor with enhanced sensitivity (425.6 µA mM−1cm−2), low limit of detection and quick response time that satisfy glucose detection applications. Thus, the developed non-enzymatic electrochemical glucose sensor has excellent electrochemical properties and making it as a strong candidate for the detection of glucose concentration in sweat.