In purine metabolism, the xanthine oxidoreductase enzyme converts hypoxanthine (HXN) to xanthine (XN) and XN to uric acid (UA). This leads to the deposition of UA crystals in several parts of the body and the serum UA level might be associated with various multifunctional disorders. The dietary intake of caffeine (CF) and ascorbic acid (AA) decreases the UA level in the serum, which leads to cellular damage. Hence, it is highly needed to monitor the UA level in the presence of AA, XN, HXN, and CF and vice versa. Considering this sequence of complications, the present paper reports the fabrication of an electrochemical sensor using low-cost N-doped carbon dots (CDs) for the selective and simultaneous determination of UA in the presence of AA, XN, HXN, and CF at the physiological pH. The colloidal solution of CDs was prepared by the pyrolysis of asparagine and fabricated on a GC electrode by cycling the potential from -0.20 to +1.2 V in a solution containing CDs and 0.01 M H2SO4. Here, the surface -NH2 functionalities of CDs were used to make a thin film of CDs on the GC electrode. FT-IR spectroscopy confirmed the involvement of the -NH2 group in the formation of the CD film. HR-TEM analysis depicts that the formed CDs showed spherical particles with a size of 1.67 nm and SEM analysis exhibits the 89 nm CD film on the GC electrode surface. The fabricated CD film was successfully used for the sensitive and selective determination of UA. The determination of UA was achieved selectively in a mixture consisting of AA, XN, HXN, and CF with 50-fold high concentration. The CDs-film fabricated electrode has several benefits over the bare electrode: (i) well-resolved oxidation peaks for five analytes, (ii) boosted sensitivity, (iii) shifted oxidation as well as on-set potentials toward less positive potentials, and (iv) high stability. The practical utility of the present sensor was tested by simultaneously determining the multifactorial disorders-causing agents in human fluids. The electrocatalyst developed in the present study is sustainable and can be used for multiple analyses; besides, the electrochemical method used for the fabrication of the CD film is environmentally benign.
Tannic acid (TA) is a water-soluble polyphenol and used in beverages, medical fields as clarifying and additive agents. In daily life, TA is unavoidable, and excessive consumption of tannin containing foods can harm health. Thus, rapid and sensitive quantification is highly necessary. Herein, an eco-friendly fluorometric and electrochemical sensing of TA was developed based on a dysprosium(III)-metal-organic framework (Dy(III)-MOF). An aqueous dispersion of Dy(III)-MOF exhibits strong dual emissions at 479 and 572 nm with an excitation at 272 nm, due to the 4f-4f electronic transition and "antenna effect". Chromophore site of the functional ligand, and Dy(III) ion could potentially serve as a sensing probe for TA via quenching (fluorescence). The fluorometric sensor worked well in a wide linear range concentrations from 0.02 to 25 μM with a limit of detection (LOD) of 0.0053 μM. Secondly, the cyclic voltammetric of TA at Dy(III)-MOF modified screen-printed carbon electrode (SPCE) has been investigated. The Dy(III)-MOF/SPCE showed an anodic peak signal at +0.22 V with a five-fold stronger current than the control electrode surface. Under optimized sensing parameters, the Dy(III)-MOF/SPCE delivered wide linear concentrations from 0.01 to 200 μM with a LOD of 0.0023 μM (S/N = 3). Accessibility of real practical samples in alcoholic and juice-based beverages were quantified, resulting in superior recovery rates (98.13-99.53%), F-test, and t-test confirmed high reliability (<95% confidence level (n = 3)). Finally, practicability result of the electrochemical method was validated by fluorometric with a relative standard deviation (RSD) of 0.18-0.46 ± 0.17% (n = 3). The designed probe has proven to be a key candidate for the accurate analysis of TA in beverage samples to ensure food quality.
Excess levels of nitrite ion in drinking water interact with amine functionalized compounds to form carcinogenic nitrosamines, which cause stomach cancer. Thus, it is indispensable to develop a simple protocol to detect nitrite. In this paper, a Cu-metal-organic framework (Cu-MOF) with graphene oxide (GO) composite was synthesized by ultrasonication followed by solvothermal method and then fabricated on a glassy carbon (GC) electrode for the sensitive and selective determination of nitrite contamination. The SEM image of the synthesized Cu-MOF showed colloidosome-like structure with an average size of 8 μm. Interestingly, the Cu-MOF-GO composite synthesized by ultrasonic irradiation followed by solvothermal process produce controlled size of 3 μm colloidosome-like structure. This was attributed to the formation of an exfoliated sheet-like structure of GO by ultrasonication in addition to the obvious influence of GO providing the oxygen functional groups as a nucleation node for size-controlled growth. On the other hand, the composite prepared without ultrasonication exhibited 6.6 μm size agglomerated colloidosome-like structures, indicating the crucial role of ultrasonication for the formation of size-controlled composites. XPS results confirmed the presence of Cu(II) in the as-synthesized Cu-MOF-GO based on the binding energies at 935.5 eV for Cu 2p3/2 and 955.4 eV for Cu 2p1/2. The electrochemical impedance studies in [Fe(CN)6]3-/4- redox couple at the composite fabricated electrode exhibited more facile electron transfer than that with Cu-MOF and GO modified electrodes, which helped to utilize Cu-MOF-GO for trace level determination of nitrite in environmental effluent samples. The Cu-MOF-GO fabricated electrode offered a superior sensitive platform for nitrite determination than the Cu-MOF and GO modified electrodes demonstrating oxidation at less positive potential with enhanced oxidation current. The present sensor detects nitrite in the concentration range of 1 × 10-8 to 1 × 10-4 M with the lowest limit of detection (LOD) of 1.47 nM (S/N = 3). Finally, the present Cu-MOF-GO electrode was successfully exploited for nitrite ion determination in lake and dye contaminated water samples.
A novel organic-inorganic nile-blue - CeO2 (CeO2/NB) nanohybrid has been synthesized by environmentally benign ultrasonic irradiation method for the selective determination of the environmental pollutant, carcinogenic hydrazine (HZ) in environmental water samples. Hydrophobic dyes have generally been as redox mediators in electrochemical sensors fabrication due to strong electron transfer capacity and they would allow the oxidation and reduction of the analytes at lower potentials. The CeO2 nanoparticles were initially synthesized by the ultrasonic irradiation of Ce(NO3)2, NH4OH and ethylene glycol mixture for 6 h using probe sonicator (20 kHz, 100 W) followed by calcination. The organic-dye NB was then added and ultrasonicated further 30 min for the formation of CeO2/NB nanohybrid material. Various spectroscopic and microscopic tools such as UV-vis and FT-IR spectroscopy, XRD, SEM and high-solution TEM and surface analysis tool Brunauer-Emmett-Teller (BET) confirm the formation of the nanohybrid. HR-TEM images showed the well-covered CeO2 on NB molecules and the average size of the nanohybrid is ~35 nm. For the fabrication of environmental pollutant electrochemical sensor, the prepared CeO2/NB nanohybrid was drop-casted on the electrode surface and utilized for the determination of HZ. The nanohybrid modified electrode exhibits higher electrocatalytic activity by showing enhanced oxidation current and less positive potential shift towards HZ oxidation than the bare and individual CeO2 and NB modified electrodes. The fabricated sensor with excellent reproducibility, repeatability, long-term storage stability and cyclic stability exhibited the sensational sensitivity (484.86 µA mM-1 cm-2) and specificity in the presence of 50-fold possible interfering agents with the lowest limit of detection of 57 nM (S/N = 3) against HZ. Utilization of the present sensor in environmental samples with excellent recovery proves it practicability in the determination of HZ in real-time application.
A copper-1,4-naphthalenedicarboxylic acid-based organic framework (Cu-NDCA MOF) with different morphologies was synthesized by solvothermal synthetic route via a simple protonation-deprotonation approach. The synthesized Cu-NDCA MOFs were analyzed by diverse microscopic and spectral techniques. The FE-SEM and TEM image results exhibited the flake-like (FL), partial anisotropic (PAT), and anisotropic (AT)-Cu-NDCA MOFs formation obtained at different pH (3.0, 7.0, and 9.0) of the reaction medium. The AT-Cu-NDCA MOF/GC electrode not only increases the electroactive surface area but also boosts the electron transfer rate reaction compared to other modified electrodes (PAT- and FL-Cu-NDCA MOFs/GCEs). Under the optimized conditions, the modified electrode (AT-Cu-NDCA MOF) exhibited a sharp oxidation peak (+ 0.46 V vs. Ag/AgCl) and higher current response for rutin. The electrode provides a wide linear range from 1 × 10-9 to 50 × 10-6 M, a low detection limit of 1.21 × 10-10 M, LOQ of 0.001 μM, and sensitivity of 0.149 μA μM-1 cm-2. The AT-Cu-NDCA MOF/GC electrode exhibited good stability (RSD = 3.52 ± 0.02% over 8 days of storage), and excellent reproducibility (RSD = 2.62 ± 0.02% (n = 3)). The modified electrode was applied to the determination of rutin in apple, orange, and lemon samples with good recoveries (99.79-99.91, 99.24-99.69, and 99.53-99.83, respectively). Graphical abstract Anisotropic structure of Cu-NDCA MOFs and its modification on glassy carbon electrode for ultra-sensitive determination of rutin in fruit samples.
An efficient electrochemical biosensor has been developed for the simultaneous evaluation of DNA bases using AgNPs-embedded covalent organic framework (COF). The COF (p-Phenylenediamine and terephthalaldehyde) was synthesized by reflux (DMF; 150 °C; 12 h) and the nanoparticles were embedded from the aqueous solutions of AgNO3 and NaBH4. The nanocomposite-modified COF was confirmed by spectral, microscopic, and electrochemical techniques. The nanocomposite material was deposited on a glassy carbon electrode (GCE) and the redox behavior of AgNPs was confirmed by cyclic voltammetry. The electrocatalytic activities of DNA bases were analyzed by differential pulse voltammetry (DPV) in a physiological environment (PBS; pH = 7.0) based on simple and easy-to-use electrocatalyst. The AgNPs-COF/GCE showed well-defined anodic peak currents for the bases guanine (+ 0.63 V vs. Ag/AgCl), adenine (+ 0.89 V vs. Ag/AgCl), thymine (+ 1.10 V vs. Ag/AgCl), and cytosine (+ 1.26 V vs. Ag/AgCl) in a mixture as well as individuals with respect to the conventional, COF, and AgNPs/GCEs. The AgNPs-COF/GCE showed linear concentration range of DNA bases from 0.2-1000 µM (guanine; (G)), 0.1-500 µM (adenine (A)), 0.25-250 µM (thymine (T)) and 0.15-500 µM (cytosine (C)) and LOD of 0.043, 0.056, 0.062, and 0.051 µM (S/N = 3), respectively. The developed sensor showed reasonable selectivity, reproducibility (RSD = 1.53 ± 0.04%-2.58 ± 0.02% (n = 3)), and stability (RSD = 1.22 ± 0.06%-2.15 ± 0.04%; n = 3) over 5 days of storage) for DNA bases. Finally, AgNPs-COF/GCE was used for the determination of DNA bases in human blood serum, urine and saliva samples with good recoveries (98.60-99.11%, 97.80-99.21%, and 98.69-99.74%, respectively).
A simple and rapid screening of biomarkers in clinical and food matrices is urgently needed to diagnose cardiovascular diseases. The cholesterol (Chol) and hydrogen peroxide (H2O2) are critical bio-indicators, which require more inventive detection techniques to be applied to real food, and bio-samples. In this study, a robust dual sensor was developed for Chol and H2O2 using hybrid catalyst. Bovine serum albumin (BSA)-capped nanocatalyst was potentially catalyzed 3,3',5,5'-tetramethylbenzidine (TMB), and H2O2. The enzymatic nanoelectrocatalyst delivered a wide range of signaling concentrations from 250 nM to 3.0 mM and 100 nM to 10 mM, limit of detection (LOD) of 53.2 nM and 18.4 nM for Chol and H2O2. The cholesterol oxidase-BSA-AuNPs-metal-free organic framework (ChOx-BSA-AuNPs-MFOF) based electrode surface effectively operated in live-cells and real-food samples. The enzymatic sensor exhibits adequate recovery of real-food samples (96.96-99.44%). Finally, the proposed system is a suitable choice for the potential applications of Chol and H2O2 in clinical and food chemistry.
Different modes of attachment of graphene oxide (GO) on an electrode surface resulted in unusual catalytic behavior respective of attachment because of film thickness. The present work investigates the direct adsorption of GO to the surface of a glassy carbon (GC) electrode. Scanning electron microscopy images revealed that multilayers of GO get adsorbed on the GC substrate and the adsorption was limited by folding up of the GO sheets at their edges. π-π and hydrogen bonding interactions between the GO and GC substrate flagged the adsorption of GO. pH studies revealed that higher adsorption of GO was achieved at pH = 3 rather than at pH = 7 and 10. Even though the electroactive surface area of adsorbed GO (GOads) was not remarkable (0.069 cm2), upon electrochemical reduction of GOads (Er-GOads), the electroactive surface area was escalated to be 0.174 cm2. Similarly, the RCT of Er-GOads was boosted to 2.9 kΩ compared to GOads which is 19 kΩ. Open circuit voltage was recorded to study the adsorption of GO on the GC electrode. Multilayered GO best fitted with the Freundlich adsorption isotherm, and the Freundlich constants like n and KF were found to be 4 and 0.992, respectively. The Freundlich constant "n" revealed the adsorption of GO on the GC substrate to be a physisorption process. Furthermore, the electrocatalytic performance of Er-GOads was demonstrated by taking uric acid as a probe. The modified electrode showed excellent stability toward the determination of uric acid.
Small biomolecules play a critical role in the fundamental processes that sustain life and are essential for the proper functioning of the human body. The detection of small biomolecules has garnered significant interest in various fields, including disease diagnosis and medicine. Electrochemical techniques are commonly employed in the detection of critical biomolecules through the principle of redox reactions. It is also a very convenient, cheap, simple, fast, and accurate measurement method in analytical chemistry. Zeolitic imidazolate frameworks (ZIFs) are a unique type of metal-organic framework (MOF) composed of porous crystals with extended three-dimensional structures. These frameworks are made up of metal ions and imidazolate linkers, which form a highly porous and stable structure. In addition to their many advantages in other applications, ZIFs have emerged as promising candidates for electrochemical sensors. Their large surface area, pore diameter, and stability make them ideal for use in sensing applications, particularly in the detection of small molecules and ions. This review summarizes the critical role of small biomolecules in the human body, the standard features of electrochemical analysis, and the utilization of various types of ZIF materials (including carbon composites, metal-based composites, ZIF polymer materials, and ZIF-derived materials) for the detection of important small biomolecules in human body fluids. Lastly, we provide an overview of the current status, challenges, and future outlook for research on ZIF materials.
Hydroquinone (HQ), a phenolic compound is expansively used in many industrial applications and due to the utilization of HQ, water pollution tragedies frequently found by the improper handling and accidental outflows. When HQ is adsorbed directly through the skin that create toxic effects to human by affecting kidney, liver, lungs, and urinary tract and hence, a highly selective and sensitive technique is required for its quantification. Herein, we have developed the ultrasonic synthesis of copper oxide nanoflakes (CuO-NFs) using ultrasonic bath (20 kHz, 100 W) and successfully employed for the sensitive detection of the environmental hazardous pollutant HQ. The formed CuO-NFs were confirmed by X-ray diffraction, field emission scanning electron microscopy (FE-SEM), FT-IR spectroscopy and UV-visible spectroscopy and fabricated with the screen-printed carbon electrode (SPCE). The SEM images exhibited the uniform CuO-NFs with an average width of 85 nm. The linker-free CuO-NFs fabricated electrode showed the appropriate wide range of concentrations from 0.1 to 1400 µM and the limit of detection was found to be 10.4 nM towards HQ. The fabricated sensor having long term stability and sensitivity was successfully applied for the environmental and commercial real sample analysis and exhibited good recovery percentage, implying that the SPCE/CuO-NFs is an economically viable and benign robust scaffold for the determination of HQ.
The incorporation of noble metals with metal-organic frameworks (MOFs) are conducive to the simultaneous electrochemical detection of analytes owing to multiple accessible reaction sites. Herein, Au@Cu-metal organic framework (Au@Cu-MOF) is successfully synthesized and modified as a screen-printed carbon electrode (SPCE), which serves as an excellent electrocatalyst for the oxidation of dopamine (DA) and uric acid (UA). The sensor shows a linear range from 10 μM to 1000 μM, with sensitivity and detection limit of 0.231 μA μM-1 cm-2 and 3.40 μM for DA, and 0.275 μA μM-1 cm-2 and 10.36 μM for UA. Au@Cu-MOF could realize the individual and simultaneous electrochemical sensing of DA and UA, with distinguishable oxidation peak potentials. Moreover, it exhibits reproducibility, repeatability, and stability. Ultimately, the sensor provides an avenue for an ultrasensitive label-free electrochemical detection of DA and UA.
Calcium carbonate has slowly paved its way into the field of nanomaterial research due to its inherent properties: biocompatibility, pH-sensitivity, and slow biodegradability. In our efforts to synthesize calcium carbonate nanoparticles (CSCaCO3NP) from blood cockle shells (Anadara granosa), we developed a simple method to synthesize CSCaCO3NP, and loaded them with gefitinib (GEF) and paclitaxel (PTXL) to produce mono drug-loaded GEF-CSCaCO3NP, PTXL-CSCaCO3NP, and dual drug-loaded GEF-PTXL-CSCaCO3NP without usage of toxic chemicals. Fourier-transform infrared spectroscopy (FTIR) results reveal that the drugs are bound to CSCaCO3NP. Scanning electron microscopy studies reveal that the CSCaCO3NP, GEF-CSCaCO3NP, PTXL-CSCaCO3NP, and GEF-PTXL-CSCaCO3NP are almost spherical nanoparticles, with a diameter of 63.9 ± 22.3, 83.9 ± 28.2, 78.2 ± 26.4, and 87.2 ± 26.7 (nm), respectively. Dynamic light scattering (DLS) and N2 adsorption-desorption experiments revealed that the synthesized nanoparticles are negatively charged and mesoporous, with surface areas ranging from ~8 to 10 (m2/g). Powder X-ray diffraction (PXRD) confirms that the synthesized nanoparticles are aragonite. The CSCaCO3NP show excellent alkalinization property in plasma simulating conditions and greater solubility in a moderately acidic pH medium. The release of drugs from the nanoparticles showed zero order kinetics with a slow and sustained release. Therefore, the physico-chemical characteristics and in vitro findings suggest that the drug loaded CSCaCO3NP represent a promising drug delivery system to deliver GEF and PTXL against breast cancer.