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Abnormal cell growth and proliferation can lead to tumor formation and cancer, one of the most fatal diseases worldwide. Hydrogen peroxide (H2O2) has emerged as a cancer biomarker, with its concentration being crucial for distinguishing cancer cells from normal cells. Herein, a cost-effective and enzymeless electrochemical sensing system for the monitoring of intracellular H2O2 has been constructed. The sensor is fabricated using gold nanoparticles embedded bimetallic copper/nickel metal organic framework (Au-CNMOF) immobilized reduced graphene oxide (RGO) modified screen printed electrode (SPE). The synthesized materials were characterized and confirmed by XRD, FTIR, SEM with EDS, and electrochemical analysis. The fabricated sensor displayed a redox peak at a formal potential (E°) of -0.155 V, corresponding to CuII/I redox couple of CNMOF in 0.1 M phosphate buffer. Electrochemical investigations revealed that the proposed sensor has a large electrochemical active surface area (1.113 cm2) and a higher surface roughness (5.67). Additionally, the sensor demonstrated excellent electrocatalytic activity towards H2O2 at -0.3 V, over a wide linear detection range from 28.5 µM to 4.564 mM with a limit of detection of 4.2 µM (S/N=3). Furthermore, the proposed sensor exhibits excellent stability, repeatability, reproducibility, and good anti-interference activity. Ultimately, the sensor was validated through real-time analysis of H2O2 released from cancer cells, successfully quantifying the released H2O2. The developed sensor holds great promise for real-time H2O2 analysis, with potential applications in clinical diagnostics, biological research and environmental monitoring.

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Electrochemical biosensors are superior technologies that are used to detect or sense biologically and environmentally significant analytes in a laboratory environment, or even in the form of portable handheld or wearable electronics. Recently, imprinted and implantable biosensors are emerging as point-of-care devices, which monitor the target analytes in a continuous environment and alert the intended users to anomalies. The stability and performance of the developed biosensor depend on the nature and properties of the electrode material or the platform on which the biosensor is constructed. Therefore, the biosensor platform plays an integral role in the effectiveness of the developed biosensor. Enormous effort has been dedicated to the rational design of the electrode material and to fabrication strategies for improving the performance of developed biosensors. Every year, in the search for multifarious electrode materials, thousands of new biosensor platforms are reported. Moreover, in order to construct an effectual biosensor, the researcher should familiarize themself with the sensible strategies behind electrode fabrication. Thus, we intend to shed light on various strategies and methodologies utilized in the design and fabrication of electrochemical biosensors that facilitate sensitive and selective detection of significant analytes. Furthermore, this review highlights the advantages of various electrode materials and the correlation between immobilized biomolecules and modified surfaces.

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Design and development of inexpensive, portable, and eco-friendly electrochemical non-enzymatic sensors with high selectivity and sensitivity is pivotal in analytical chemistry. In this regard, we have developed a highly porous graphitic-activated carbon (GAC, derived from tamarind fruit shell biomass) coated iron oxide (Fe2O3) nanocomposite (Fe2O3/GAC) for the efficient detection of rutin (vitamin p). Fe2O3/GAC nanocomposite was prepared using a facile green synthesis method and thoroughly characterized using SEM, XRD, and XPS techniques. As-prepared Fe2O3/GAC nanocomposite was deposited over a screen printed electrode (SPE) to fabricate Fe2O3/GAC/SPE and utilized as a non-enzymatic sensor for the electrochemical determination of rutin in food and environmental samples. The modified electrode was characterized using cyclic voltammetry and electrochemical impedance spectroscopy techniques, which witnessed the excellent conductivity of the developed sensor. The fabricated Fe2O3/GAC/SPE nanocomposite exhibited a set of redox peaks in the presence of rutin, corresponding to the electrochemical redox feature of rutin (rutin to 3',4'-diquinone). Further, the modified electrode displayed excellent electrocatalytic characteristics towards the oxidation of rutin, based on which a differential pulse voltammetry-based sensor was developed for rutin determination. The developed non-enzymatic sensor has shown prominent performance towards rutin detection in a wide linear range from 0.1 to 130 µM with an excellent detection limit of 0.027 µM. The enhanced electrocatalytic response could be ascribed to the synergistic effect of Fe2O3 and GAC on the developed probe. Moreover, the developed sensor was successfully utilized for real-time detection of rutin in various samples.

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Monitoring the concentration levels of hydrogen peroxide (H2O2) is significant in both clinical and industrial applications. Herein, we develop a facile biosensor for the detection of H2O2 based on direct electron transfer of hemoglobin (Hb), which was covalently immobilized on a hydrophobic naphthylimidazolium butyric acid ionic liquid (NIBA-IL) over a multiwalled carbon nanotube (MWCNT) modified glassy carbon electrode (GCE) to obtain an Hb/NIBA-IL/MWCNT/GCE. Highly water-soluble Hb protein was firmly immobilized on NIBA-IL via stable amide bonding between the free NH2 groups of Hb and COOH groups of NIBA-IL via EDC/NHS coupling. Thus fabricated biosensor showed a well resolved redox peak with a cathodic peak potential (Epc) at -0.35 V and anodic peak potential (Epa) at -0.29 V with a formal potential (E°') of -0.32 V, which corresponds to the deeply buried FeIII/FeII redox centre of Hb, thereby direct electrochemistry of Hb was established. Further, the modified electrode demonstrated very good electrocatalytic activity towards H2O2 reduction and showed a wide linear range of detection from 0.01 to 6.3 mM with a limit of detection and sensitivity of 3.2 µM and 111 µA mM-1 cm-2, respectively. Moreover, the developed biosensor displayed high operational stability under dynamic conditions as well as during continuous potential cycles and showed reliable reproducibility. The superior performance of the fabricated biosensor is attributed to the effective covalent immobilization of Hb on the newly developed highly conducting and biocompatible NIBA-IL/MWCNT/GCE platform.

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Facile yet simple platforms for the immobilization of biomolecules have always been a substantial requirement for the fabrication of proficient biosensors. In this study, we report a naphthyl substituted acetate functionalized ionic liquid (NpAc-IL) for the covalent anchoring of horseradish peroxidase (HRP), using which the direct electrochemistry of HRP was successfully accomplished and a H2O2 biosensor was developed. The naphthyl substitution on the NpAc-IL was utilized for the π-π stacking with the MWCNT modified GCE and the terminal -OCH3 group of NpAc-IL was used for the covalent attachment with the free -NH2 group of HRP via amide bond formation. High conducting nature of the newly designed ionic liquid (NpAc-IL), facilitated an improved communication with the deeply buried redox centre of the HRP, while the covalent bonding provided enhanced stability to the fabricated biosensor by stably holding the water soluble HRP enzyme on the electrode surface. Furthermore, incorporation of MWCNT on the sensor setup synergistically enhanced the sensitivity of the developed biosensor. Under optimized conditions, the fabricated biosensor showed an enhanced electrocatalytic reduction of H2O2 in the range of 0.01 to 2.07 mM with a limit of detection and sensitivity of 2.7 µM and 55.98 µA mM-1 cm-2 respectively. Further, the proposed biosensor was utilized for the sensing of H2O2 spiked in real samples. Moreover, the newly fabricated biosensor demonstrated excellent stability with improved sensitivity and selectivity towards H2O2 reduction. The superior analytical characteristics are attributed to the facile fabrication strategy using this newly developed acetate functionalized ionic liquid platform.

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Herein, we have designed and demonstrated a facile and effective platform for the covalent anchoring of a tetrameric hemoprotein, hemoglobin (Hb). The platform comprises of naphthyl substituted amine functionalized gel type hydrophobic ionic liquid (NpNH2-IL) through which the heme protein was covalently attached over a glassy carbon electrode (Hb-NpNH2-IL/GCE). UV-vis and FT-IR spectral results confirmed that the Hb on NpNH2-IL retains its native structure, even after being covalently immobilized on NpNH2-IL platform. The direct electron transfer of redox protein could be realized at Hb-NpNH2-IL/GCE modified electrode and a well resolved redox peak with a formal potential of -0.30 V and peak separation of 65 mV was observed. This is due to the covalent attachment of highly conducting NpNH2-IL to the Hb, which facilitates rapid shuttling of electrons between the redox site of protein and the electrode. Further, the fabricated biosensor favoured the electrochemical reduction of bromate in neutral pH with linearity ranging from 12 to 228 µM and 0.228 to 4.42 mM with a detection limit and sensitivities of 3 µM, 430.7 µA mM-1 cm-2 and 148.4 µA mM-1 cm-2 respectively. Notably, the fabricated biosensor showed good operational stability under static and dynamic conditions with high selectivity and reproducibility.

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An aldehyde functionalized ionic liquid, (3-(3-formyl-4-hydroxybenzyl)-3-methylimidazolium hexafluorophosphate) (CHO-IL) has been employed herein as a multiple host platform for the covalent immobilization of mediator as well as enzyme. The CHO-IL was immobilized on electrochemically reduced graphene oxide (ERGO) through the π-π stacking of hydroxybenzyl and imidazolium groups with ERGO and subjected to further covalent attachment of Azure A (Azu-A) mediator or glucose oxidase (GOx) enzyme. Electroactive, water soluble organic dye Azu-A was effectively immobilized to the host IL through simple Schiff base reaction. Azu-A was rendered leak-free in the electrode setup and also responded well for the amperometric determination of H2O2 over a linear range of 0.03-1mM with a detection limit and sensitivity of 11.5µM and 133.2µAmM-1cm-2, respectively. Further, attempts were made to explore the CHO-IL platform for the covalent immobilization of GOx enzyme which served well in retaining the enzyme nativity, reactivity and stability. Under optimized conditions, mediatorless GOx biosensor developed based on direct electrochemistry has exhibited an impressive analytical signal towards glucose detection in the linear range of 0.05-2.4mM with a detection limit and sensitivity of 17µM and 17.7µAmM-1cm-2, respectively. The reliability of the proposed Azu-A based chemical sensor and GOx based biosensor towards the determination of H2O2 and glucose in the real samples have been demonstrated. The remarkable analytical parameters and long term stability of both the sensors could be envisioned as a result of facile immobilization platform and immobilization strategy.

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