Portable, Disposable, Biomimetic Electrochemical Sensors for Analyte Detection in a Single Drop of Whole Blood

Nanotechnology-Based Wearable Electrochemical Biosensor for Disease Diagnosis

Recently, flexible electronics have significantly transformed information and communications technology (ICT). In particular, wearable devices, via integration with attachable biosensors, have driven the development of new types of biosensors and diagnostic devices for point-of-care testing (POCT). Moreover, wearable electrochemical biosensors can be applied to diagnose diseases in real time based on the synergistic effect generated from the incorporation of the electrochemical technique. Besides, to improve the sensitivity of electrochemical biosensors while retaining their wearability, novel nanomaterials and nanotechnologies have been introduced. In this review, recent studies on nanotechnology-based wearable electrochemical biosensors for accurate disease diagnosis are discussed. First, widely used techniques for developing flexible electrodes, including nanolithography- and nano/microneedle-based patches, are presented. Next, the latest studies on developing wearable electrochemical biosensors for the diagnosis of diseases such as diabetes and dermatitis are discussed by categorizing the biosensors into nanolithography- and nano/microneedle-based categories. Finally, this review explores the latest research trends on the application of nanotechnology-enabled nanopatterning and nano/microneedle technologies to electrochemical wearable biosensors. This review suggests novel approaches and methods for developing wearable electrochemical biosensors for real-time disease diagnosis under POCT applications.

Highly Reusable Electrochemical Immunosensor for Ultrasensitive Protein Detection

The detection and quantification of protein biomarkers in bodily fluids is important for many clinical applications, including disease diagnosis and health monitoring. Current techniques for ultrasensitive protein detection, such as enzyme-linked immunosorbent assay (ELISA) and electrochemical sensing, involve long incubation times (1.5-3 hr) and rely on single-use sensing electrodes which can be costly and generate excessive waste. This work demonstrates a reusable electrochemical immunosensor employing magnetic nanoparticles (MNPs) and dually labeled gold nanoparticles (AuNPs) for ultrasensitive measurements of protein biomarkers. As proof of concept, this platform was used to detect C-X-C motif chemokine ligand 9 (CXCL9), a biomarker associated with kidney transplant rejection, immune nephritis from checkpoint inhibitor therapy, and drug-associated acute interstitial nephritis, in human urine. The sensor successfully detected CXCL9 at concentrations as low as 27 pg/mL within ~1 hr. This immunosensor was also adapted onto a handheld smartphone-based diagnostic device and used for measurements of CXCL9, which exhibited a lower limit of detection of 65 pg/mL. Lastly, we demonstrate that the sensing electrodes can be reused for at least 100 measurements with a negligible loss in analytical performance, reducing the costs and waste associated with electrochemical sensing.

Flow injection amperometric uric acid biosensor based on AuNPs-GO-CS porous composite cryogel coated on PB-PEDOT:PSS modified screen-printed carbon electrode

An enzymatic amperometric uric acid (UA) biosensor was successfully developed by modifying a screen-printed carbon electrode (SPCE) with Prussian blue-poly(3,4-ethylene dioxythiophene) polystyrene sulfonate composite (PB-PEDOT:PSS). The modified SPCE was coated with gold nanoparticles-graphene oxide-chitosan composite cryogel (AuNPs-GO-CS cry). Uricase (UOx) was directly immobilized via chemisorption on AuNPs. The nanocomposite was characterized by scanning electron microscopy, transmission electron microscopy, ultraviolet-visible spectroscopy, and Fourier transform infrared spectroscopy. The electrochemical characterization of the modified electrode was performed by cyclic voltammetry and electrochemical impedance spectroscopy. UA was determined using amperometric detection based on the reduction current of PB which was correlated with the amount of H2O2 produced during the enzymatic reaction. Under optimal conditions, the fabricated UA biosensor in a flow injection analysis (FIA) system produced a linear range from 5.0 to 300 μmol L-1 with a detection limit of 1.88 μmol L-1. The proposed sensor was stable for up to 221 cycles of detection and analysis was rapid (2 min), with good reproducibility (RSDs < 2.90 %, n = 6), negligible interferences, and recoveries from 94.0 ± 3.9 to 101.1 ± 2.6 %. The results of UA detection in blood plasma were in agreement with the enzymatic colorimetric method (P > 0.05).

Mechanistic Insight into Intestinal α-Synuclein Aggregation in Parkinson's Disease Using a Laser-Printed Electrochemical Sensor

Aggregated deposits of the protein α-synuclein and depleting levels of dopamine in the brain correlate with Parkinson's disease development. Treatments often focus on replenishing dopamine in the brain; however, the brain might not be the only site requiring attention. Aggregates of α-synuclein appear to accumulate in the gut years prior to the onset of any motor symptoms. Enteroendocrine cells (specialized gut epithelial cells) may be the source of intestinal α-synuclein, as they natively express this protein. Enteroendocrine cells are constantly exposed to gut bacteria and their metabolites because they border the gut lumen. These cells also express the dopamine metabolic pathway and form synapses with vagal neurons, which innervate the gut and brain. Through this connection, Parkinson's disease pathology may originate in the gut and spread to the brain over time. Effective therapeutics to prevent this disease progression are lacking due to a limited understanding of the mechanisms by which α-synuclein aggregation occurs in the gut. We previously proposed a gut bacterial metabolic pathway responsible for the initiation of α-synuclein aggregation that is dependent on the oxidation of dopamine. Here, we develop a new tool, a laser-induced graphene-based electrochemical sensor chip, to track α-synuclein aggregation and dopamine level over time. Using these sensor chips, we evaluated diet-derived catechols dihydrocaffeic acid and caffeic acid as potential inhibitors of α-synuclein aggregation. Our results suggest that these molecules inhibit dopamine oxidation. We also found that these dietary catechols inhibit α-synuclein aggregation in STC-1 enteroendocrine cells. These findings are critical next steps to reveal new avenues for targeted therapeutics to treat Parkinson's disease, specifically in the context of functional foods that may be used to reshape the gut environment.

Solution-Induced Degradation of the Silicon Nanobelt Field-Effect Transistor Biosensors

Field-effect transistor (FET)-based biosensors are powerful analytical tools for detecting trace-specific biomolecules in diverse sample matrices, especially in the realms of pandemics and infectious diseases. The primary concern in applying these biosensors is their stability, a factor directly impacting the accuracy and reliability of sensing over extended durations. The risk of biosensor degradation is substantial, potentially jeopardizing the sensitivity and selectivity and leading to inaccurate readings, including the possibility of false positives or negatives. This paper delves into the documented degradation of silicon nanobelt FET (NBFET) biosensors induced by buffer solutions. The results highlight a positive correlation between immersion time and the threshold voltage of NBFET devices. Secondary ion mass spectrometry analysis demonstrates a gradual increase in sodium and potassium ion concentrations within the silicon as immersion days progress. This outcome is ascribed to the nanobelt's exposure to the buffer solution during the biosensing period, enabling ion penetration from the buffer into the silicon. This study emphasizes the critical need to address buffer-solution-induced degradation to ensure the long-term stability and performance of FET-based biosensors in practical applications.

Affinity-based electrochemical sensors for biomolecular detection in whole blood

The detection and/or quantification of biomarkers in blood is important for the early detection, diagnosis, and treatment of a variety of diseases and medical conditions. Among the different types of sensors for detecting molecular biomarkers, such as proteins, nucleic acids, and small-molecule drugs, affinity-based electrochemical sensors offer the advantages of high analytical sensitivity and specificity, fast detection times, simple operation, and portability. However, biomolecular detection in whole blood is challenging due to its highly complex matrix, necessitating sample purification (i.e., centrifugation), which involves the use of bulky, expensive equipment and tedious sample-handling procedures. To address these challenges, various strategies have been employed, such as purifying the blood sample directly on the sensor, employing micro-/nanoparticles to enhance the detection signal, and coating the electrode surface with blocking agents to reduce nonspecific binding, to improve the analytical performance of affinity-based electrochemical sensors without requiring sample pre-processing steps or laboratory equipment. In this article, we present an overview of affinity-based electrochemical sensor technologies that employ these strategies for biomolecular detection in whole blood.