Dr. Valdes-Morales, Hector

In this work, a facile green approach for the synthesis of graphene quantum dots (GQDs) embedded on silicate network silver nanocrystals (GQDs-AgNCs(APTS)) is reported. Moreover, glassy carbon-GC electrodes were modified with the prepared nanocomposite containing graphene quantum dots supported on silver nanocrystals (GQDs-AgNCs(APTS)) and applied for simultaneous detection of guanine (GA) and adenine (AD). The chemically modified electrode was assessed during the determination of purine bases by cyclic voltammetry-CV and differential pulse voltammetry-DPV. The incorporation of GQDs-AgNCs(APTS) nanocomposites over the surface of the GC electrode considerably enhances the anodic peak currents and decreases the adenine and guanine peak potentials. Compared to other electrodes, GQDs-AgNCs(APTS)/GC improved the electrochemical behavior towards the detection of adenine and guanine. At optimal conditions, calibration curves were obtained by DPV being linear in the range of 0.1–6.0 μM and 0.1–5.0 μM for guanine and adenine, respectively. The detection limits of both guanine and adenine were estimated as 0.1 μM. Additionally, interferences analyses were performed on the existence of other interferent compounds. Furthermore, the method developed for the identification of GA and AD was proved using fish sperm DNA samples.

Gold nanocrystals (AuNCs) were synthesized by economical and green strategy in aqueous medium by using N[3(trimethoxysilyl)propyl]ethylenediamine (TMSPED) as both a reducing and stabilizing mediator to avoid the aggregation of gold nanocrystals. Then, the AuNCs were capped with graphene quantum dots (GQDs) using an ultrasonic method. The resulting nanocomposites of GQD-TMSPED-AuNCs were characterized by X-ray photoelectron, X-ray diffraction, Raman, UV-vis and FTIR spectroscopies. The size and shape of the nanocomposites were confirmed by using transmission electron microscopy and atomic force microscopy. The GQD-TMSPED-AuNCs placed on a glassy carbon electrode enable simultaneous determination of dopamine (DA) and epinephrine (EP) with peak potentials at 0.21 and 0.30 V (vs. Ag/AgCl). The response is linear in the 5 nM – 2.1 μM (DA) and 10 nM – 4.0 μM (EP) concentration ranges, with detection limits of 5 and 10 nM, respectively. The sensor shows good selectivity toward DP and EP in the presence of other molecules, facilitating its rapid detection in practical applications.

The huge demand for the clinical diagnosis of diabetes mellitus has prompted the development of great-performance sensing platforms for glucose detection. Non-enzymatic glucose sensors are getting closer to their use in realistic applications. In this work, polyvinylpyrrolidone (PVP)-conjugated bimetallic Pt–Pd nanosuperlattices were synthesized precisely through a simple synthesis procedure, leading to controllable spherical morphologies with significantly fine and precise nanostructures in a size range of ∼3–5 nm by the reduction of Pt and Pd precursors in ethylene glycol, using an ultrasonic method. High-resolution transmission electron microscopy (HRTEM) measurements evidenced the formation of Pt–Pd bimetallic nanosuperlattices (BMNSLs). The superlattice-fringe patterns (111) of bimetallic Pt–Pd NSLs were identified in the HRTEM images, clearly showing their crystalline nature. The prepared material was used in the electrochemical oxidation of glucose using voltammetry analyses. The experimental evidence indicates that the Pt–Pd BMNSL modified glassy carbon electrode is effective for the selective amperometric detection of glucose in the presence of galactose, sucrose, fructose, lactose, and ascorbic acid. Moreover, its application in the detection of glucose in real serum and urine samples was assessed and good recoveries are achieved. The results show that a Pt–Pd bimetallic nanosuperlattice with high surface area, catalytic activity, and superior selectivity could be a promising material in the generation of novel electrodes for low-cost non-enzymatic glucose sensors.

The goethite (α-FeOOH) nanoparticles were wrapped on the reduced graphene oxide (rGO) to synthesize the α-FeOOH/rGO nanocomposites. The nanocomposites (NCs) were initially examined for their optical, structural, and morphological properties. The XRD data obtained the crystallite size of the α-FeOOH, showed that the average crystal size for pristine α-FeOOH and α-FeOOH/rGO nanocomposites were about 85 and 90 nm, respectively. The transmission electron microscope confirmed the nanoparticles (NPs) were evenly distributed throughout the reduced graphene oxide sheets. The nanocomposites improved glassy carbon electrodes (GCE), making them efficient sensors for detecting the arsenic(III) (As+3) in a pH 5 phosphate buffer solution with an Ag/AgCl reference electrode. The detection limit for As+3 was 0.07 μgL−1 and the resulting sensitivity was 0.39 μA−1 μgL−1 in the linear dynamic range of 0.1–10 μgL−1. The α-FeOOH/rGO/GCE was more sensitive than its original and showed a synergistic effect due to the influence of α-FeOOH on the properties of rGO. The α-FeOOH/rGO NCs-modified GCE electrode performed as a promising sensor, by separating the common interfering ions. Moreover, the modified electrode exhibited remarkable stability, repeatability, and potential real-time application towards the detection of arsenic(III). Additionally, the proposed approach has been successfully applied to the detection of As+3 in the real water sample.

Hybrid nanocomposites consisting of carbon nanotubes (CNT)/nanomaterial heterostructure play a key part in the excellent performance of nano-devices by coupling different functionalities. In this study, a glucose sensor was fabricated by immobilizing zinc oxide quantum dots (ZnO QDs) on multiwall carbon nanotubes (MWCNTs) nanocomposites using ultrasonication in an ease and economical method. ZnO QDs with ~ 3–8 nm diameters were grown and anchored on the surface of MWCNTs. These nanocomposites were characterized using different spectroscopy and microscopy techniques. XRD reveals the wurtzite structure of ZnO. TEM confirmed that ZnO QDs were anchored onto MWCNTs. The synthesized nanocomposites were applied as a sensor for electrochemical detection of glucose and as a photoelectric effect for photoelectric current measurements. The electrochemical properties of the MWCNT/ZnO QDs nanocomposite were enhanced significantly for glucose sensing when compared to pristine ZnO and MWCNTs. Results showed that ZnO QDs anchored over MWCNTs have a sensitivity of 9.36 µA µM− 1 with repeatable results. The detection limit was found to be 0.208 µM. By applying nanocomposites on the sensor, the linear range could be extended from 0.1 to 2.5 µM, which increases the response time to less than 3 s. Experimental results also indicate that the sensor response is unaffected by the common interference agents during glucose-sensing such as sucrose, ascorbic acid, dopamine and uric acid. The proposed sensor was successfully employed to detect glucose levels in human urine samples with satisfactory outcomes.