The use of nanoparticles in electroanalysis: an updated review

Removable Composite Electrode Made of Silver Nanoparticles on Pyrolyzed Photoresist Film for the Electroreduction of 4-Nitrophenol

Access to removable nanocomposite electrodes for electrosensing of pollutants is of great importance. However, the preparation of reproducible and reliable carbon electrodes decorated with metallic nanoparticles, a prerequisite for trustworthy devices, remains a challenge. Here we describe an innovative and easy method to prepare such electrodes. These latter are silicon-coated with a thin carbon film on which controlled silver nanostructures are grafted. Different silver nanostructures and surface coverage of the carbon electrode (16, 36, 51, and 67%) can be obtained through a careful control of the time of the hydrogenolysis of the N-N' isopropyl butylamidinate silver organometallic precursor (t = 1, 5, 15, and 60 min, respectively). Importantly, all nanocomposite surfaces are efficient for the electrodetection of 4-nitrophenol with a remarkable decrease of the overpotential of the reduction of such molecule up to 330 mV. The surfaces are characterized by atomic force microscopy, grazing incidence X-ray diffraction, scanning electronic microscopy, and Raman spectroscopy. Furthermore, surface-enhanced Raman scattering effect is also observed. The exaltation of the Raman intensity is proportional to the surface coverage of the electrode; the number of hot spots increases with the surface coverage.

Design and Characterization of Effective Ag, Pt and AgPt Nanoparticles to H₂O₂ Electrosensing from Scrapped Printed Electrodes

The use of disposable screen-printed electrodes (SPEs) has extraordinarily grown in the last years. In this paper, conductive inks from scrapped SPEs were removed by acid leaching, providing high value feedstocks suitable for the electrochemical deposition of Ag, Pt and Ag core-Pt shell-like bimetallic (AgPt) nanoparticles, onto screen-printed carbon electrodes (M_L@SPCEs, M = Ag, Pt or AgPt, L = metal nanoparticles from leaching solutions). M_L@SPCEs were characterized by scanning electron microscopy, cyclic voltammetry and electrochemical impedance spectroscopy. The results were compared to those obtained when metal nanoparticles were synthesised using standard solutions of metal salts (M_S@SPCEs). Both M_L@SPCEs and M_S@SPCEs exhibited similar cyclic voltammetric patterns referred to the electrochemical stripping of silver or the adsorption/desorption of hydrogen/anions in the case of platinum, proving leaching solutions extremely effective for the electrodeposition of metallic nanoparticles. The use of both M_L@SPCEs and M_S@SPCEs proved effective in enhancing the sensitivity for the detection of H₂O₂ in phosphate buffer solutions (pH = 7). The AgPt_L@SPCE was used as proof of concept for the validation of an amperometric sensor for the determination of H₂O₂ within laundry boosters and antiseptic samples. The electrochemical sensor gave good agreement with the results obtained by a spectrophotometric method with H₂O₂ recoveries between 100.6% and 106.4%.

Cyclic Voltammetry Characterization of Au, Pd, and AuPd Nanoparticles Supported on Different Carbon Nanofibers

Three types of carbon nanofibers (pyrolytically stripped carbon nanofibers (PS), low-temperature heat treated carbon nanofibers (LHT), and high-temperature heat treated carbon nanofibers (HHT)) with different graphitization degrees and surface chemistry have been used as support for Au, Pd, or bimetallic AuPd alloy nanoparticles (NPs). The carbon supports have been characterized using Raman, X-ray photoelectron spectroscopy (XPS), and cyclic voltammetry (CV). Moreover, the morphology of the metal nanoparticles was investigated using transmission electron microscopy (TEM) and CV. The different properties of the carbon-based supports (particularly the graphitization degree) yield different electrochemical behaviors, in terms of potential window widths and electrocatalytic effects. Comparing the electrochemical behavior of monometallic Au and Pd and bimetallic AuPd, it is possible to observe the interaction of the two metals when alloyed. Moreover, we demonstrate that carbon surface has a strong effect on the electrochemical stability of AuPd nanoparticles. By tuning the Au-Pd nanoparticles’ morphology and modulating the surface chemistry of the carbon support, it is possible to obtain materials characterized by novel electrochemical properties. This aspect makes them good candidates to be conveniently applied in different fields.

Overview and recent advances in electrochemical sensing of glutathione - A review

The present paper is aimed at providing an overview of the recent advances in the electrochemical sensing of glutathione (GSH), an important electrochemically and biologically active molecule, for the period 2012-2018. Herein, the analytical performances of newly developed electrochemical methods, procedures and protocols for GSH sensing are comprehensively and critically discussed with respect to the type of method, electrodes used (new electrode modifications, advanced materials and formats), sample matrices, and basic validation parameters obtained (limit of detection, linear dynamic range, precision, selectivity/evaluation of interferences). This paper considers electrochemical methods used alone as well as the hyphenated methods with electrochemical detection (ECD), such as HPLC-ECD or CE-ECD. The practical applicability of the platforms developed for GSH detection and quantification is mostly focused on pharmaceutical and biomedical analysis. The most significant electrochemical approaches for GSH detection in multicomponent analyte samples and multicomponent matrices and for real-time in vivo GSH analysis are highlighted. The great variability in the electrochemical techniques, electrode approaches, and obtainable performance parameters, discussed in this review, brought new insights not only on current GSH and glutathione disulfide (GSSG) determinations, but, along with this, on the advances in electrochemical analysis from a more general point of view.

Graphene-derived nanomaterials as recognition elements for electrochemical determination of heavy metal ions: a review

This review (with 155 refs.) summarizes the progress made in the past few years in the field of electrochemical sensors based on graphene-derived materials for the determination of heavy metal ions. Following an introduction of this field and a discussion of the various kinds of modified graphenes including graphene oxide and reduced graphene oxide, the review covers graphene based electrodes modified (or doped) with (a) heteroatoms, (b) metal nanoparticles, (c) metal oxides, (d) small organic molecules, (e) polymers, and (f) ternary nanocomposites. Tables are provided that afford an overview of representative methods and materials for fabricating electrochemical sensors. Furthermore, sensing mechanisms are discussed. A concluding section presents new perspectives, opportunities and current challenges. Graphical Abstract Schematic illustration of electrochemical sensor for heavy metal ion sensing based on heteroatom-doped graphene, metal-modified graphene, metal-oxide-modified graphene, organically modified graphene, polymer-modified graphene, and ternary graphene based nanocomposites.

Highly Sensitive AgNP/MWCNT/Nafion Modified GCE-Based Sensor for the Determination of Heavy Metals in Organic and Non-organic Vegetables

Silver nanoparticles/multi-walled carbon nanotubes/Nafion modified glassy carbon electrodes (AgNPs/MWCNTs/Nafion-GCE) were fabricated and were used as working electrode in anodic stripping voltammetry (ASV) for trace level determination of lead (Pb²⁺) and cadmium (Cd²⁺). The fabricated electrodes were characterized using scanning electron microscopy and cyclic voltammetry. The amounts of the electrode modifiers and the ASV parameters were optimized. It was found that the electrode modified with 1 mg AgNPs and 2 mg MWCNTs exhibited the best analytical response towards the determination of Pb²⁺ and Cd²⁺. The optimized ASV parameters were 60 s for the deposition time, 90 s for the accumulation time, and 100 mV/s for the scan rate. The electrode exhibited linearity from 0.493 ppb to 157.2 ppb for Pb²⁺ and 1.864 ppb to 155.1 ppb for Cd²⁺. The limit of detection was found to be 0.216 ppb for Pb²⁺ and 0.481 ppb for Cd²⁺. Real sampling analysis was carried out using organic vegetables from Sitio San Ysiro, Antipolo and Daraitan, Rizal and commercially available vegetables from Divisoria, all in Luzon, Philippines. Trace amounts of lead, cadmium, and copper were detected in the samples. Unwashed vegetables contained more heavy metal concentration compared to the washed vegetables. Atomic absorption spectroscopy was performed to validate the presence of the heavy metals in the vegetables.

In Situ Metalorganic Deposition of Silver Nanoparticles on Gold Substrate and Square Wave Voltammetry: A Highly Efficient Combination for Nanomolar Detection of Nitrate Ions in Sea Water

The electro-reduction of nitrate ions in artificial sea water was investigated at a gold substrate (EAu) functionalized by silver nanoparticles (AgNPs). These AgNPs were generated in situ on the gold substrate by the direct decomposition of the metalorganic N,N′-diisopropylacetamidinate silver precursor [Ag(Amd)] in the liquid phase. Very small and well dispersed AgNPs were deposited on the gold electrode and then used as working electrode (EAu/AgNPs). Square wave voltammetry (SWV) was successfully employed to detect nitrate ions (NO3−) with a detection limit (LOD) of 0.9 nmol∙L−1 in artificial sea water (pH = 6.0) without pre-concentration or pH adjustment.

Nanomaterials: Electrochemical Properties and Application in Sensors

The unique properties of nanoparticles make them an extremely valuable modifying material, being used in electrochemical sensors. The features of nanoparticles affect the kinetics and thermodynamics of electrode processes of both nanoparticles and redox reactions occurring on their surface. The paper describes theoretical background and experimental studies of these processes. During the transition from macro- to micro- and nanostructures, the analytical characteristics of sensors modify. These features of metal nanoparticles are related to their size and energy effects, which affects the analytical characteristics of developed sensors. Modification of the macroelectrode with nanoparticles and other nanomaterials reduces the detection limit and improves the degree of sensitivity and selectivity of measurements. The use of nanoparticles as transducers, catalytic constituents, parts of electrochemical sensors for antioxidant detection, adsorbents, analyte transporters, and labels in electrochemical immunosensors and signal-generating elements is described.

Monitoring the Phenolic Ripening of Red Grapes Using a Multisensor System Based on Metal-Oxide Nanoparticles

The maturity of grapes is usually monitored by means of the sugar concentration. However, the assessment of other parameters such as the phenolic content is also important because the phenolic maturity has an important impact on the organoleptic characteristics of wines. In this work, voltammetric sensors able to detect phenols in red grapes have been developed. They are based on metal oxide nanoparticles (CeO2, NiO, and TiO2,) whose excellent electrocatalytic properties toward phenols allows obtaining sensors with detection limits in the range of 10-8 M and coefficients of variation lower than 7%. An electronic tongue constructed using a combination of the nanoparticle-based sensors is capable to monitor the phenolic maturity of red grapes from véraison to maturity. Principal Component Analysis (PCA) can be successfully used to discriminate samples according to the ripeness. Regression models performed using Partial Least Squares (PLS-1) have established good correlations between voltammetric data obtained with the electrochemical sensors and the Total Polyphenolic Index, the Brix degree and the Total Acidity, with correlation coefficients close to 1 and low number of latent variables. An advantage of this system is that the electronic tongue can be used for the simultaneous assessment of these three parameters which are the main factors used to monitor the maturity of grapes. Thus the electronic tongue based on metal oxide nanoparticles can be a valuable tool to monitor ripeness. These results demonstrate the exciting possible applications of metal oxide nanoparticles in the field of electronic tongues.

Numerical insights into the early stages of nanoscale electrodeposition: nanocluster surface diffusion and aggregative growth

Fundamental understanding of the early stages of electrodeposition at the nanoscale is key to address the challenges in a wide range of applications. Despite having been studied for decades, a comprehensive understanding of the whole process is still out of reach. In this work, we introduce a novel modelling approach that couples a finite element method (FEM) with a random walk algorithm, to study the early stages of nanocluster formation, aggregation and growth, during electrochemical deposition. This approach takes into account not only electrochemical kinetics and transport of active species, but also the surface diffusion and aggregation of adatoms and small nanoclusters. The simulation results reveal that the relative surface mobility of the nanoclusters compared to that of the adatoms plays a crucial role in the early growth stages. The number of clusters, their size and their size dispersion are influenced more significantly by nanocluster mobility than by the applied overpotential itself. Increasing the overpotential results in shorter induction times and leads to aggregation prevalence at shorter times. A higher mobility results in longer induction times, a delayed transition from nucleation to aggregation prevalence, and as a consequence, a larger surface coverage of smaller clusters with a smaller size dispersion. As a consequence, it is shown that a classical first-order nucleation kinetics equation cannot describe the evolution of the number of clusters with time, N(t), in potentiostatic electrodeposition. Instead, a more accurate representation of N(t) is provided. We show that an evaluation of N(t), which neglects the effect of nanocluster mobility and aggregation, can induce errors of several orders of magnitude in the determination of nucleation rate constants. These findings are extremely important towards evaluating the elementary electrodeposition processes, considering not only adatoms, but also nanoclusters as building blocks.

Ultrasensitive Determination of Malathion Using Acetylcholinesterase Immobilized on Chitosan-Functionalized Magnetic Iron Nanoparticles

A renewable, disposable, low cost, and sensitive sensor for the detection of organophosphorus pesticides was constructed by immobilizing the acetylcholinesterase enzyme (AChE), via glutaraldehyde, on magnetic iron nanoparticles (Fe₃O₄) previously synthesized and functionalized with chitosan (CS). The sensor was denoted AChE/CS/Fe₃O₄. The magnetic nanoparticles were characterized by Fourier transform infrared spectroscopy and transmission electron microscopy. Acetylthiocholine (ATCh) was incubated with AChE/CS/Fe₃O₄ and attached to a screen-printed electrode using a magnet. The oxidation of thiocholine (from ATCh hydrolysis) was monitored at an applied potential of +0.5 V vs. Ag/AgCl(KCl_sat) in 0.1 mol L⁻¹ phosphate buffer solution (pH 7.5) as the supporting electrolyte. A mixture of the pesticide malathion and ATCh was investigated using the same procedure, and the results were compared and expressed as inhibition percentages. For determination of malathion, the proposed sensor presented a linear response in the range from 0.5 to 20 nmol L⁻¹ (R = 0.9942). The limits of detection (LOD) and quantification (LOQ) were 0.3 and 0.8 nmol L⁻¹, respectively. Real samples were also investigated, with recovery values of 96.0% and 108.3% obtained for tomato and pond water samples, respectively. The proposed sensor is a feasible option for malathion detection, offering a linear response, good sensitivity, and a low detection limit.

The influence of amine structures on the stability and catalytic activity of gold nanoparticles stabilized by amine-modified hyperbranched polymers

Amine-modified amphiphilic hyperbranched polymers (MePEG-H104-Nx) were prepared from hyperbranched 2,2-bis(methylol)propionic acid polyester (H104) by decoration with polyethylene glycol monomethyl ether (MePEG) and different classes of oligo(ethylenimine)s. By using the MePEG-H104-Nx polymers as stabilizers, gold nanoparticles (AuNPs) were prepared in an aqueous medium by the reduction of HAuCl₄ with NaBH₄. The AuNPs were sphere-like with diameters of 2-4 nm, which were dependent on the structure of the amines. Further, the catalytic activity of these AuNPs was evaluated by monitoring the reduction reaction of 4-nitrophenol by sodium borohydride. The results demonstrate that the longer chain length and the branched structure of the amine moieties are beneficial for the stability and catalytic activity of the AuNPs. The AuNPs stabilized by MePEG-H104-N4 and MePEG-H104-Nb3 showed high catalytic activity for the reduction of 4-nitrophenol to 4-aminophenol.

Particle morphology: an important factor affecting drug delivery by nanocarriers into solid tumors

INTRODUCTION

Efficient delivery of drugs by nanoparticles deep into solid tumors is the precondition of valid cancer therapy. Despite profound understanding of the delivery of spherical nanoparticles into solid tumor attained, insufficient attention was paid to anisotropic particles. Actually, owing to their structural asymmetry, some non-spherical particles exhibit significant advantages over their spherical counterparts.

AREAS COVERED

This review will focus on particles with different shapes (discoidal particle, nanorod, filamentous particle, single-walled carbon nanotube) and the influence of their morphological characteristics (size, aspect ratio, rigidity) on the process of drug delivery to solid tumor in view of systemic circulation, transport from circulation system to tumor tissue, intratumoral transport and uptake by tumor cells, on the basis of introduction of challenges for drug delivery to solid tumor. In addition, the morphological characteristics will be briefly introduced to provide an understanding of anisotropic particle morphology.

EXPERT OPINION

Anisotropic particles exhibit desirable properties such as enhanced circulation time and efficient tumor penetration that could serve as an enlightenment in the exploitation of novel non-spherical nanocarriers to clinical therapy. Yet, current understanding of how anisotropic particles interact with organism is insufficient, which restricts the biomedical application of anisotropic particles. Further work is desired for the development of practical fabrication of anisotropic particles, quantitative analysis of particle morphology, as well as profound understanding of new targeting mechanism and intratumoral penetration of anisotropic particles.

Electrochemical carbon based nanosensors: A promising tool in pharmaceutical and biomedical analysis

Nanotechnology has become very popular in the sensor fields in recent times. It is thought that the utilization of such technologies, as well as the use of nanosized materials, could well have beneficial effects for the performance of sensors. Nano-sized materials have been shown to have a number of novel and interesting physical and chemical properties. Low-dimensional nanometer-sized materials and systems have defined a new research area in condensed-matter physics within past decades. Apart from the aforesaid categories of materials, there exist various materials of different types for fabricating nanosensors. Carbon is called as a unique element, due to its magnificent applications in many areas. Carbon is an astonishing element that can be found many forms including graphite, diamond, fullerenes, and graphene. This review provides an overview of some of the important and recent developments brought about by the application of carbon based nanostructures to nanotechnology for both chemical and biological sensor development and their application in pharmaceutical and biomedical area.

Electrodeposition of Highly Porous Pt Nanoparticles Studied by Quantitative 3D Electron Tomography: Influence of Growth Mechanisms and Potential Cycling on the Active Surface Area

Nanoporous Pt nanoparticles (NPs) are promising fuel cell catalysts due to their large surface area and increased electrocatalytic activity toward the oxygen reduction reaction (ORR). Herein, we report on the influence of the growth mechanisms on the surface properties of electrodeposited Pt dendritic NPs with large surface areas. The electrochemically active surface was studied by hydrogen underpotential deposition (H UPD) and compared for the first time to high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) quantitative 3D electron tomography of individual nanoparticles. Large nucleation overpotential leads to a large surface coverage of roughened spheroids, which provide a large roughness factor (R_f) but low mass-specific electrochemically active surface area (EASA). Lowering the nucleation overpotential leads to highly porous Pt NPs with pores stretching to the center of the structure. At the expense of smaller R_f, the obtained EASA values of these structures are in the range of those of large surface area supported fuel cell catalysts. The active surface area of the Pt dendritic NPs was measured by electron tomography, and it was found that the potential cycling in the H adsorption/desorption and Pt oxidation/reduction region, which is generally performed to determine the EASA, leads to a significant reduction of that surface area due to a partial collapse of their dendritic and porous morphology. Interestingly, the extrapolation of the microscopic tomography results in macroscopic electrochemical parameters indicates that the surface properties measured by H UPD are comparable to the values measured on individual NPs by electron tomography after the degradation caused by the H UPD measurement. These results highlight that the combination of electrochemical and quantitative 3D surface analysis techniques is essential to provide insights into the surface properties, the electrochemical stability, and, hence, the applicability of these materials. Moreover, it indicates that care must be taken with widely used electrochemical methods of surface area determination, especially in the case of large surface area and possibly unstable nanostructures, since the measured surface can be strongly affected by the measurement itself.

Magnetite-platinum nanoparticles-modified glassy carbon electrode as electrochemical detector for nitrophenol isomers

A glassy carbon electrode was modified with magnetite and platinum nanoparticles stabilized with 3-n-propyl-4-picoline silsesquioxane chloride. This chemically-modified electrode is proposed for the first time for the individual or simultaneous electrochemical detection of nitrophenol isomers. Nanoparticles act as catalysts and also increase the surface area. The polymer stabilizes the particles and provides the electrochemical separation of isomers. Under optimized conditions, the reduction peak currents, obtained by differential-pulse voltammetry, of 2-, 3-, and 4-nitrophenol increased linearly with increases in their concentration in the range of 0.1-1.5μmolL^-1. In individual analysis, the detection limits were 33.7nmolL^-1, 45.3nmolL^-1 and 48.2nmolL^-1, respectively. Also, simultaneous analysis was possible for 2-, and 4-nitrophenol. In this case, the separation of the peak potentials was 0.138V and the detection limits were 69.6nmolL^-1 and 58.0nmolL^-1, respectively. These analytical figures of merit evidence the outstanding performance of the modified electrode, which was also successfully applied to the individual determination of isomers in environmental and biological samples. The magnetite and platinum nanoparticles modified glassy carbon electrode was able to detect nitrophenol isomers at the ppm level in rain water and human urine samples.