Metabolites are the intermediatory products of metabolic processes catalyzed by numerous enzymes found inside the cells. Detecting clinically relevant metabolites is important to understand their physiological and biological functions along with the evolving medical diagnostics. Rapid advances in detecting the tiny metabolites such as biomarkers that signify disease hallmarks have an immense need for high-performance identifying techniques. Low concentrations are found in biological fluids because the metabolites are difficult to dissolve in an aqueous medium. Therefore, the selective and sensitive study of metabolites as biomarkers in biological fluids is problematic. The different non-electrochemical and conventional methods need a long time of analysis, long sampling, high maintenance costs, and costly instrumentation. Hence, employing electrochemical techniques in clinical examination could efficiently meet the requirements of fully automated, inexpensive, specific, and quick means of biomarker detection. The electrochemical methods are broadly utilized in several emerging and established technologies, and electrochemical biosensors are employed to detect different metabolites. This review describes the advancement in electrochemical sensors developed for clinically associated human metabolites, including glucose, lactose, uric acid, urea, cholesterol, etc., and gut metabolites such as TMAO, TMA, and indole derivatives. Different sensing techniques are evaluated for their potential to achieve relevant degrees of multiplexing, specificity, and sensitivity limits. Moreover, we have also focused on the opportunities and remaining challenges for integrating the electrochemical sensor into the point-of-care (POC) devices.

Synthesis of an l-cys_rGO hydrogel and fabrication of a BSA/anti-TNF-α/l-cys_rGO hydrogel/gSPE immunosensor.

Nanohybrid based non-invasive biosensing platforms are emerging as promising alternatives to detect biomarkers in complex and diverse bio-fluids toward ultrasensitive point-of-care diagnostics. Herein, we report the development of a highly sensitive, facile, non-invasive, label free, affordable, and innovative electrochemical screen printed immunosensor for identifying CYFRA 21-1, an established and crucial biomarker for oral cancer. Until now, no work has been reported utilizing a titanium carbide Ti₃C₂ MXene nanosheet and L-cysteine (L-Cyst) functionalized magnetite nanoparticle (MNPs) nanohybrid based immunosensor for electrochemical detection of CYFRA 21-1. The L-Cyst@MNPs/Ti₃C₂-MXene nanohybrid was synthesized via the co-precipitation method and later deposited on a gold screen printed electrode (GSPE) offering enhanced surface area and electrochemical properties. The nanohybrid modified GSPE was then surface immobilized with monoclonal antibodies (anti-CYFRA-21-1) to fabricate an anti-CYFRA-21-1/L-Cyst@MNPs/Ti₃C₂-MXene/GSPE immunoelectrode and the non-specific locations of the immunoelectrode were covered with bovine serum albumin (BSA). The spectroscopic, morphological, and structural analyses of the synthesized nanohybrid and the fabricated electrodes were performed using different analytical techniques. The electrochemical studies of modified electrodes were evaluated using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV). The fabricated BSA/anti-CYFRA-21-1/L-Cyst@MNPs/Ti₃C₂-MXene/GSPE immunosensor has shown an excellent limit of detection of 0.023 ng mL⁻¹, a linear detection range of (0.5–30) ng mL⁻¹, a sensitivity of 277.28 μA (ng mL⁻¹)⁻¹ cm⁻² and a lower limit of quantification of 0.618 ng mL⁻¹ for electrochemical CYFRA 21-1 determination. Hence, this L-Cyst@MNPs/Ti₃C₂-MXene nanohybrid could also be explored as a potential candidate for determining other cancer biomarkers.

The pandemic of COVID-19 and its widespread transmission have made us realize the importance of early, quick diagnostic tests for facilitating effective cure and management. The primary obstacles encountered were accurately distinguishing COVID-19 from other illnesses including the flu, common cold, etc. While the polymerase chain reaction technique is a robust technique for the determination of SARS-CoV-2 in patients of COVID-19, there arises a high demand for affordable, quick, user-friendly, and precise point-of-care (POC) diagnostic in therapeutic settings. The necessity for available tests with rapid outcomes spurred the advancement of POC tests that are characterized by speed, automation, and high precision and accuracy. Paper-based POC devices have gained increasing interest in recent years because of rapid, low-cost detection without requiring external instruments. At present, microfluidic paper-based analysis devices have garnered public attention and accelerated the development of such POCT for efficient multistep assays. In the current review, our focus will be on the fabrication of detection modules for SARS-CoV-2. Here, we have included a discussion on various strategies for the detection of viral moieties. The compilation of these strategies would offer comprehensive insight into the detection of the causative agent preparedness for future pandemics. We also provide a descriptive outline for paper-based diagnostic platforms, involving the determination mechanisms, as well as a commercial kit for COVID-19 as well as their outlook.

The generation of gut microbiota-derived trimethylamine N-oxide (TMAO) from the metabolism of dietary L-carnitine and choline is associated with a high risk of major adverse effects on humans. For this purpose, cheap, rapid, highly sensitive, and accurate electrochemical sensors are needed to detect TMAO in real samples clinically. Thus, a sensor showing all these features is developed based on a molecularly imprinted technique and characterized using X-ray diffraction, scanning electron microscopy, UV-Visible spectroscopy, and Fourier transform infrared spectroscopy in this study. The MIP sensor is fabricated using a novel nanocomposite (PANI–ZnSNPs) that comprises a polyaniline polymer (PANI) and zinc sulphide nanoparticles (ZnSNPs) that serve as a receptor and are deposited on an indium tin oxide (ITO) coated glass substrate using the electrophoretic deposition technique. The chemical interaction responsible for bonding between the gut metabolite TMAO and PANI–ZnSNPs is hydrogen bonding occurring between the oxygen atoms of N-oxides and NH of PANI on the addition of TMAO concentrations resulting in a decrement in the current (after 10 min of incubation time) and electro-activity of the sensor. The developed MIP sensor exhibited a linear range from 5 μM to 180 μM having a limit of detection of 4.35 μM. Moreover, the sensor showed a high sensitivity of 0.276 μA μM⁻¹ cm⁻² (R² = 0.984), as well as relative standard deviation (RSD) values for selectivity analysis, which were found to be in the range of 3.12% to 7.50% for several interfering agents. It also showed promising results related to reproducibility (RSD = 4.34%), repeatability (RSD = 0.08%), and the potential to determine TMAO in spiked urine samples with acceptable RSD, as well as % recovery values ranging from 96.67–110.58% and 0.55–7.11%, respectively. The current strategy is potent and opens a new pathway for developing fast diagnostic tools for TMAO detection and other metabolites.

Over the past four decades, additive manufacturing (AM), particularly 3D printing, has emerged as a disruptive force in chemical and biosensing technologies, revolutionizing prototyping and production across laboratories and industries. Recent advancements in 3D printing techniques and materials have accelerated the development of novel sensors for diverse applications, offering unparalleled advantages such as rapid prototyping, customization, and cost efficiency. Unlike traditional fabrication methods, 3D printing creates intricate, high-precision structures while reducing multi-step processes, making it ideal for biosensor development. Its interdisciplinary potential spans physics, chemistry, engineering, biology, and medicine, positioning it as a transformative tool in biomedical applications, particularly for biosensing. Despite its promise, challenges such as limited multi-material integration, standardization hurdles, resolution constraints, biocompatibility concerns, and scalability issues persist. Addressing these gaps through interdisciplinary collaboration could unlock the full potential of AM-enabled sensing devices. This review critically evaluates the evolution and latest progress in AM technologies, including fused deposition modelling, stereolithography, and inkjet printing for designing sensitive, customizable, and affordable biosensors. Additionally, this article explores recent innovations in 3D-printed chemical and biological sensors, analyzing their performance in detecting various analytes. A comprehensive summary of cutting-edge developments is provided, alongside an examination of future directions for refining and inventing 3D printing techniques in biosensor fabrication. Finally, the review highlights current challenges and opportunities in 3D-printed sensing devices, emphasizing the need for material optimization, improved printing resolution, and enhanced device functionality. By overcoming these barriers, 3D printing can serve as a cornerstone for next-generation diagnostic platforms, driving innovation in chemical and biosensing technologies. This review underscores AM’s transformative role as a catalyst for future breakthroughs in the field.