EDTA assisted synthesis of hydroxyapatite nanoparticles for electrochemical sensing of uric acid

Ingenious fabrication of bamboo leaf-like ferric vanadate intertwined multi-walled carbon nanotubes nanocomposite as a sensitive sensor for determination of uric acid in fetal bovine serum

A novel nanocomposite material, ferric vanadate intertwined multi-walled carbon nanotubes (FeV/MWCNTs), has been designed which was drop-coated onto a glassy carbon electrode (GCE). The constructed sensor was used for the sensitive determination of uric acid (UA) in fetal bovine serum (FBS) and human serum (HS). A series of characterization and electrochemical tests showed that the ultrasound-assisted assembly of FeV with MWCNTs not only overcame the disadvantages of low conductivity and easy (unwanted) aggregation, but also avoided the decrease in effective surface area due to the severe aggregation of each individual raw material. The fabricated FeV/MWCNTs nanocomposites exhibited higher conductivity, larger effective surface area, and better electrocatalytic activity. In addition, under optimized conditions, the developed electrochemical sensor FeV/MWCNTs/GCE has a lower limit of detection (LOD, 0.05 µM; Ep = 0.268 V vs. Ag/AgCl) and wider linear range (0.20-100 µM), which can satisfy the criteria of trace UA detection. The results of UA determination in FBS (recovery = 95.5-103%; RSD ≤ 3.1%) and HS (recovery = 95.5-103%; RSD ≤ 4.3%) further validated the feasibility of FeV/MWCNTs-based electrochemical sensors for the determination of UA in biological fluids.

Electrochemical and Structural Characterization of Lanthanum-Doped Hydroxyapatite: A Promising Material for Sensing Applications

In the quest to find powerful modifiers of screen-printed electrodes for sensing applications, a set of rare earth-doped Ca_10-xRE_x(PO₄)₆(OH)₂ (RE = La, Nd, Sm, Eu, Dy, and Tm and x = 0.01, 0.02, 0.10, and 0.20) hydroxyapatite (HAp) samples were subjected to an in-depth electrochemical characterization using electrochemical impedance spectroscopy and cyclic and square wave voltammetry. Among all of these, the inorganic phosphates doped with lanthanum proved to be the most reliable, revealing robust analytical performances in terms of sensitivity, repeatability, reproducibility, and reusability, hence paving the way for their exploitation in sensing applications. Structural data on La-doped HAp samples were also provided by using different techniques, including optical microscopy, X-ray diffraction, Rietveld refinement from X-ray data, Fourier transform infrared, and Raman vibrational spectroscopies, to complement the electrochemical characterization.

A novel non-enzymatic electrochemical uric acid sensing method based on nanohydroxyapatite from eggshell biowaste immobilized on a zinc oxide nanoparticle modified activated carbon electrode (Hap-Esb/ZnONPs/ACE)

Hydroxyapatite-derived eggshell biowaste (Hap-Esb) has been fabricated and developed for the electrochemical detection of uric acid (UA). The physicochemical characteristics of the Hap-Esb and modified electrodes were evaluated using a scanning electron microscope and X-ray Diffraction analysis. Utilized as UA sensors, the electrochemical behavior of modified electrodes (Hap-Esb/ZnONPs/ACE) was assessed using cyclic voltammetry (CV). The superior peak current response observed for the oxidation of UA at Hap-Esb/ZnONPs/ACE, which was 13 times higher than that of the Hap-Esb/activated carbon electrode (Hap-Esb/ACE) is attributed to the simple immobilization of Hap-Esb on zinc oxide nanoparticle-modified ACE. The UA sensor exhibited a linear range at 0.01 to 1 μM, low detection limit (0.0086 μM), and excellent stability, which surpass the existing Hap-based electrodes reported in the literature. The facile UA sensor subsequently realized is also advantaged by its simplicity, repeatability, reproducibility, and low cost, applicable for real sample analysis (human urine sample).

Hydroxyapatite/L-Lysine Composite Coating as Glassy Carbon Electrode Modifier for the Analysis and Detection of Nile Blue A

An amperometric sensor was developed by depositing a film coating of hydroxyapatite (HA)/L-lysine (Lys) composite material on a glassy carbon electrode (GCE). It was applied for the detection of Nile blue A (NBA). Hydroxyapatite was obtained from snail shells and its structural properties before and after its combination with Lys were characterized using X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and Brunauer-Emmett-Teller (BET) surface area analyses. The coupling of Lys to HA was attributed to favorable interaction between negatively charged -COO^- groups of Lys and divalent ions Ca²⁺ of HA. Electrochemical investigations pointed out the improvement in sensitivity of the GCE/Lys/HA sensor towards the detection of NBA in solution. The dependence of the peak current and potential on the pH, scan rate, and NBA concentration was also investigated. Under optimal conditions, the GCE/Lys/HA sensor showed a good reproducibility, selectivity, and a NBA low detection limit of 5.07 × 10^-8 mol L^-1. The developed HA/Lys-modified electrode was successfully applied for the detection of NBA in various water samples.

Surface functionalization of natural hydroxyapatite by polymerization of β-cyclodextrin: application as electrode material for the electrochemical detection of Pb(II)

A composite material prepared by polymerization of β-cyclodextrin (β-CD) on the surface of natural hydroxyapatite using citric acid as cross linker, was employed as electrode material for the detection of Pb(II). Hydroxyapatite was obtained from bovine bones, following a three-step procedure including pre-calcination, chemical treatment with (NH₄)₂HPO_4, and calcination. The structure and morphology of the pristine hydroxyapatite (NHAP_P0.5) and its functionalized counterpart (NHAP_p0.5-CA-β-CD) were examined using XRD, FTIR, and SEM. Upon deposition as thin film on a glassy carbon electrode (GCE), the ion exchange ability of NHAP_p0.5-CA-β-CD was exploited to elaborate a sensitive sensor for the detection of lead. The electroanalytical procedure was based on the chemical accumulation of Pb(II) ions under open-circuit conditions, followed by the detection of the preconcentrated species using differential pulse anodic stripping voltammetry. The reproducibility of the proposed method, based on a series of 8 measurements in a solution containing 2 μM Pb(II) gave a coefficient of variation of 1.27%. Significant parameters that can affect the stripping response of Pb(II) were optimized, leading to a linear calibration curve for lead in the concentration range of 2 × 10^-8 mol L^-1 - 20 × 10^-8 mol L^-1 (R² = 0.998). The detection limit (3S/m) and the sensitivity of the proposed sensor were 5.06 × 10^-10 mol L^-1 and 100.80 μA.μM^-1, respectively. The interfering effect of several ions expected to affect the determination of lead was evaluated, and the proposed sensor was successfully applied in the determination of Pb(II) ions in spring water, well water, river water and tap water samples.

Ultrasonic assisted functionalization of MWCNT and synergistic electrocatalytic effect of nano-hydroxyapatite incorporated MWCNT-chitosan scaffolds for sensing of nitrofurantoin

In the present work, we report the fabrication of stable composite of chitosan hydrogels (CHI) on multiwalled carbon nanotubes (MWCNT) using a simple ultrasonic-assisted method. Also, rod-like hydroxyapatite nanoparticles (HA NPs) were synthesised using a hydrothermal route and were incorporated into the highly conductive MWCNT-CHI scaffolds using an ultrasonication method. The functionalization of MWCNT and preparation of HA NPs on MWCNT-CHI nanocomposite were done using the sonication over the frequency of 37 kHz with the ultrasonic power capable of 150 W (Elmasonic Easy 60H bath sonicator). The resulting hybrid HA NPs/MWCNT-CHI nanocomposites have an excellent surface area and high surface to volume ratio, which leads to the sensitive detection of nitrofurantoin than pristine MWCNT and HA NPs. The complete elemental and morphological analyses of the HA NPs/MWCNT-CHI nanocomposites were characterised by XRD, FTIR, RAMAN, FESEM, TEM, EDX, and elemental mapping techniques. Electrochemical analysis of the HA NPs/MWCNT-CHI nanocomposites was carried out by cyclic voltammetry, electrochemical impedance spectroscopy and amperometry methods. The modified glassy carbon electrode (GCE) of HA NPs/MWCNT-CHI nanocomposites exhibit the nitrofurantoin detection activity at the linear range of 0.005-982.1 µM with the detection limit of 1.3 nM. The synergistic electrocatalytic activity of HA NPs/MWCNT-CHI nanocomposites modified GCE is correlated to the sensitivity of 0.16 µAµM^-1 cm^-2 with excellent precision and accuracy towards the sensing of nitrofurantoin.

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.

Hydrothermal Synthesis and Biocompatibility Study of Highly Crystalline Carbonated Hydroxyapatite Nanorods

Highly crystalline carbonated hydroxyapatite (CHA) nanorods with different carbonate contents were synthesized by a novel hydrothermal method. The crystallinity and chemical structure of synthesized nanorods were studied by Fourier transform infrared spectroscopy (FTIR), X-ray photo-electronic spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM). The biocompatibility of synthesized CHA nanorods was evaluated by cell viability and alkaline phosphatase (ALP) activity of MG-63 cell line. The biocompatibility evaluation results show that these CHA nanorods are biologically active apatites and potentially promising bone-substitute biomaterials for orthopedic application.

Electrochemical detection of mercury using biosynthesized hydroxyapatite nanoparticles modified glassy carbon electrodes without preconcentration

An electrochemical method for the determination of trace levels of mercury(ii) ions using Aloe vera (Av) assisted hydroxyapatite (HA) nanoparticles modified glassy carbon electrode (GCE) by square wave voltammetry is described for the first time.