Organic Bioelectronic Devices for Metabolite Sensing

Electrochemical detection of metabolites is essential for early diagnosis and continuous monitoring of a variety of health conditions. This review focuses on organic electronic material-based metabolite sensors and highlights their potential to tackle critical challenges associated with metabolite detection. We provide an overview of the distinct classes of organic electronic materials and biorecognition units used in metabolite sensors, explain the different detection strategies developed to date, and identify the advantages and drawbacks of each technology. We then benchmark state-of-the-art organic electronic metabolite sensors by categorizing them based on their application area (in vitro, body-interfaced, in vivo, and cell-interfaced). Finally, we share our perspective on using organic bioelectronic materials for metabolite sensing and address the current challenges for the devices and progress to come.

Silky Co3O4 nanostructures for the selective and sensitive enzyme free sensing of uric acid

In this study, simple, new and functional silky nanostructures of Co₃O₄ are prepared by hydrothermal method. These nanostructures are successfully used for the enzyme free sensing of uric acid in 0.1 M phosphate buffer solution of pH 7.3. Physical characterization experiments were carried out to explore the morphology, composition and crystalline phase of the newly prepared Co₃O₄ nanostructures. Scanning electron microscopy (SEM) shows a silk like morphology and energy dispersive spectroscopy (EDS) revealed the presence of Co and O as the main elements. Powder X-ray diffraction (XRD) demonstrates a cubic crystallography with well resolved diffraction patterns. The electrochemical activity of these silky Co₃O₄ nanostructures was evaluated by cyclic voltammetry (CV) in a 0.1 M phosphate buffer solution at pH 7.3. The high purity and unique morphology of Co₃O₄ shows a highly sensitive and selective response towards the non-enzymatic sensing of uric acid. This uric acid sensor exhibits a linear range of 0.5 mM to 3.5 mM uric acid and a 0.1 mM limit of detection. The anti-interference capability of this uric acid sensor was monitored in the presence of common interfering species. Furthermore, electrochemical impedance spectroscopy confirms a low charge transfer resistance value of 5.11 K Ω cm² for silky Co₃O₄ nanostructures which significantly supported the CV results. The proposed modified electrode is stable, selective and reproducible which confirms its possible practical use. Silky Co₃O₄ nanostructures can be of great importance for diverse electrochemical applications due to their excellent electrochemical activity and large surface area.

Synthesis of Heart/Dumbbell-Like CuO Functional Nanostructures for the Development of Uric Acid Biosensor

It is always demanded to prepare a nanostructured material with prominent functional properties for the development of a new generation of devices. This study is focused on the synthesis of heart/dumbbell-like CuO nanostructures using a low-temperature aqueous chemical growth method with vitamin B₁₂ as a soft template and growth directing agent. CuO nanostructures are characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) techniques. CuO nanostructures are heart/dumbbell like in shape, exhibit high crystalline quality as demonstrated by XRD, and have no impurity as confirmed by XPS. Apparently, CuO material seems to be porous in structure, which can easily carry large amount of enzyme molecules, thus enhanced performance is shown for the determination of uric acid. The working linear range of the biosensor is 0.001 mM to 10 mM with a detection limit of 0.0005 mM and a sensitivity of 61.88 mV/decade. The presented uric acid biosensor is highly stable, repeatable, and reproducible. The analytical practicality of the proposed uric acid biosensor is also monitored. The fabrication methodology is inexpensive, simple, and scalable, which ensures the capitalization of the developed uric acid biosensor for commercialization. Also, CuO material can be used for various applications such as solar cells, lithium ion batteries, and supercapacitors.

Green synthesis of carbon dots from pork and application as nanosensors for uric acid detection

In this work, a green, simple, economical method was developed in the synthesis of fluorescent carbon dots using pork as carbon source. The as-prepared carbon dots exhibit exceptional advantages including high fluorescent quantum yield (17.3%) and satisfactory chemical stability. The fluorescence of carbon dots based nanosensor can be selectively and efficiently quenched by uric acid. This phenomenon was used to develop a fluorescent method for facile detection of uric acid within a linear range of 0.1-100μM and 100-500μM, with a detection limit of 0.05μM (S/N=3). Finally, the proposed method was successfully applied in the determination of uric acid in human serum and urine samples with satisfactory recoveries, which suggested that the new nanosensors have great prospect toward the detection of uric acid in human fluids.

Poly(brilliant green) and poly(thionine) modified carbon nanotube coated carbon film electrodes for glucose and uric acid biosensors

Poly(brilliant green) (PBG) and poly(thionine) (PTH) films have been formed on carbon film electrodes (CFEs) modified with carbon nanotubes (CNT) by electropolymerisation using potential cycling. Voltammetric and electrochemical impedance characterisation were performed. Glucose oxidase and uricase, as model enzymes, were immobilised on top of PBG/CNT/CFE and PTH/CNT/CFE for glucose and uric acid (UA) biosensing. Amperometric determination of glucose and UA was carried out in phosphate buffer pH 7.0 at -0.20 and +0.30 V vs. SCE, respectively, and the results were compared with other similarly modified electrodes existing in the literature. An interference study and recovery measurements in natural samples were successfully performed, indicating these architectures to be good and promising biosensor platforms.

A new approach for noninvasive transdermal determination of blood uric acid levels

The aims of this study were to investigate the most effective combination of physical forces from laser, electroporation, and reverse iontophoresis for noninvasive transdermal extraction of uric acid, and to develop a highly sensitive uric acid biosensor (UAB) for quantifying the uric acid extracted. It is believed that the combination of these physical forces has additional benefits for extraction of molecules other than uric acid from human skin. A diffusion cell with porcine skin was used to investigate the most effective combination of these physical forces. UABs coated with ZnO₂ nanoparticles and constructed in an array configuration were developed in this study. The results showed that a combination of laser (0.7 W), electroporation (100 V/cm²), and reverse iontophoresis (0.5 mA/cm²) was the most effective and significantly enhanced transdermal extraction of uric acid. A custom-designed UAB coated with ZnO₂ nanoparticles and constructed in a 1×3 array configuration (UAB-1×3-ZnO₂) demonstrated enough sensitivity (9.4 μA/mM) for quantifying uric acid extracted by the combined physical forces of laser, electroporation, and RI. A good linear relationship (R²=0.894) was demonstrated to exist between the concentration of uric acid (0.2–0.8 mM) inside the diffusion cell and the current response of the UAB-1×3-ZnO₂. In conclusion, a new approach to noninvasive transdermal extraction and quantification of uric acid has been established.

Development of an amperometric screen-printed galactose biosensor for serum analysis

The development of a disposable amperometric biosensor for the measurement of circulating galactose in serum is described. The biosensor comprises a screen-printed carbon electrode (SPCE), incorporating the electrocatalyst cobalt phthalocyanine (CoPC), which is covered by a permselective cellulose acetate (CA) membrane and a layer of immobilized galactose oxidase (GALOX). The optimal response of the biosensor, designated as GALOX-CA-CoPC-SPCE, was obtained by systematically examining the effects of enzyme loading, temperature, pH, and buffer strength. The optimal performance of the biosensor occurred with 2U of GALOX, at 35°C, using 50mM phosphate buffer solution (pH 7.0). The sensitivity was 7.00μAmM(-1)cm(-2) and the linear range from 0.1 to 25mM with a calculated limit of detection (LOD) of 0.02mM; this concentration range and LOD are appropriate to diagnose galactosemia, i.e., concentrations >1.1mM in infants. When the biosensor was used in conjunction with amperometry in stirred solution for the analysis of serum, the precision values obtained on unspiked (endogenous level of 0.153mM) and spiked serum (1mM added) (n=6) were 1.10% and 0.11%, respectively, with a calculated recovery of 99.9%.

Thermal inactivation of uricase (urate oxidase): mechanism and effects of additives

Uricase (Urc) is an oxidoreductase enzyme of both general and commercial interest, the former because of its lack of a cofactor and the latter because of its use in the treatment of hyperuricemic disorders. Results of fluorometry and circular dichroism (CD) spectroscopy indicate that the main phase of thermal Urc inactivation follows an irreversible two-state mechanism, with loss of ~20% of the helical structure, loss of the majority of the tertiary structure, and partial exposure of tryptophan residues to solution being approximately concurrent with activity loss. Results of size exclusion chromatography and 8-anilinonaphthalene-1-sulfonate binding studies confirm that this process results in the formation of aggregated molten globules. In addition to this process, CD studies indicate the presence of a rapid reversible denaturation phase that is not completely coupled to the main phase. Urc inactivation is inhibited by the presence of glycerol and trimethylamine oxide, stabilizers of hydrophobic interactions and backbone structure respectively, confirming that loss of hydrophobic bonding and loss of helical structure are key events in the loss of Urc activity. NaCl, however, destabilizes the enzyme at elevated temperature, emphasizing the importance of ionic interactions to Urc stability. A model is developed in which interfacial disruption, involving local loss of hydrophobic interactions, ionic bonds, and helical structure, leads to Urc inactivation and aggregation. Additional studies of Urc inactivation at a more ambient temperature indicate that the inactivation process followed under such conditions is different from that followed at higher temperatures, highlighting the limitations of high-temperature enzyme stability studies.

Development of a sandwich format, amperometric screen-printed uric acid biosensor for urine analysis

A screen-printed carbon electrode (SPCE) incorporating the electrocatalyst cobalt phthalocyanine (CoPC), fabricated using a water-based ink formulation, has been investigated as the base transducer for a uric acid biosensor. A sandwich biosensor was fabricated by first depositing cellulose acetate (CA) onto this transducer (CoPC-SPCE), followed by uricase (UOX) and finally a polycarbonate (PC) membrane; this device is designated PC-UOX-CA-CoPC-SPCE. This biosensor was used in conjunction with chronoamperometry to optimize the conditions for the analysis of urine: temperature, 35°C; buffer, pH 9.2; ionic strength, 50 mM; uricase, 0.6 U; incubation time, 180 s. The proposed biosensor was applied to urine from a healthy subject. The precision determined on unspiked urine (n=6) was 5.82%. Urine was fortified with 0.225 mM UA, and the resulting precision and recovery were 4.21 and 97.3%, respectively. The linear working range of the biosensor was found to be 0.015 to 0.25 mM (the former represents the detection limit), and the sensitivity was calculated to be 2.10 μA/mM.

A potentiometric indirect uric acid sensor based on ZnO nanoflakes and immobilized uricase

In the present work zinc oxide nanoflakes (ZnO-NF) structures with a wall thickness around 50 to 100 nm were synthesized on a gold coated glass substrate using a low temperature hydrothermal method. The enzyme uricase was electrostatically immobilized in conjunction with Nafion membrane on the surface of well oriented ZnO-NFs, resulting in a sensitive, selective, stable and reproducible uric acid sensor. The electrochemical response of the ZnO-NF-based sensor vs. a Ag/AgCl reference electrode was found to be linear over a relatively wide logarithmic concentration range (500 nM to 1.5 mM). In addition, the ZnO-NF structures demonstrate vast surface area that allow high enzyme loading which results provided a higher sensitivity. The proposed ZnO-NF array-based sensor exhibited a high sensitivity of ∼66 mV/ decade in test electrolyte solutions of uric acid, with fast response time. The sensor response was unaffected by normal concentrations of common interferents such as ascorbic acid, glucose, and urea.

Disposable luminol copolymer-based biosensor for uric acid in urine

A new electrochemiluminescent (ECL) disposable biosensor for uric acid was manufactured by immobilization in a double-layer design of luminol as a copolymer with 3,3',5,5'-tetramethylbenzidine (TMB) and the enzyme uricase in chitosan on gold screen-printed cells. The good mechanical and improved electroluminescent characteristics of the new copolymer poly(luminol-TMB) make it possible to determine uric acid by measuring the growing ECL emission with the analyte concentration. The combination of enzymatic selectivity with ECL sensitivity results in a disposable analytical device with a linear range for uric acid from 1.5×10(-6) to 1.0×10(-4) M, a limit of detection of 4.4×10(-7) M and a precision of 13.1% (1.0×10(-5) M, n=10) as relative standard deviation. Satisfactory results were obtained for uric acid determination in 24h-urine samples compared to a reference procedure. This uric acid biosensor can be used as a low-cost alternative to conventional methods.