Photochemical synthesis of Prussian blue film from an acidic ferricyanide solution and application

Investigation of H2O2 Electrochemical Behavior on Ferricyanide-Confined Electrode Based on Ionic Liquid-Functionalized Silica-Mesostructured Cellular Foam

In this work, ionic liquid (IL) of 1-propyl-3-methyl imidazolium chloride-functionalized silica-mesostructured cellular foam (MCF) was prepared. The obtained MCF-IL was used to construct the Fe(CN)₆^3--confined electrode (MCF-IL-Fe(CN)₆^3-/PVA) and H₂O₂ electrochemical behavior on the electrode was investigated. It was found that H₂O₂ was oxidized on the freshly prepared electrode while catalytically electro-reduced on the acid pretreated one. Cyclic voltametric results revealed that the real catalyst for catalytic reduction of H₂O₂ was Prussian blue (PB) rather than Fe(CN)₆^3-. The electrocatalytic ability of the acid-pretreated MCF-IL-Fe(CN)₆^3-/PVA electrode offered a wide linear range for H₂O₂ detection. The present study on H₂O₂ electrochemical behavior on an MCF-IL-Fe(CN)₆^3-/PVA electrode might provide useful information for further developing integrated Fe(CN)₆^3--mediated biosensors as H₂O₂ is extensively involved in the classic reaction containing oxidase enzymes.

A Novel Approach to the Facile Growth and Organization of Photothermal Prussian Blue Nanocrystals on Different Surfaces

We report here a novel "one-pot" approach for the controlled growth and organization of Prussian blue nanostructures on three different surfaces: pure Au0, cysteamine-functionalized Au0, and SiO2-supported lipid bilayers with different natures of lipids. We demonstrate that fine control over the size, morphology, and the degree and homogeneity of the surface coverage by Prussian Blue (PB) nanostructures may be achieved by manipulating different parameters, which are the precursor concentration, the nature of the functional groups or the nature of lipids on the surfaces. This allows the growth of isolated PB nanopyramids and nanocubes or the design of thin dense films over centimeter square surfaces. The formation of unusual Prussian blue nanopyramids is discussed. Finally, we demonstrate, by using experimental techniques and theoretical modeling, that PB nanoparticles deposited on the gold surface exhibit strong photothermal properties, permitting a rapid temperature increase up to 90 °C with a conversion of the laser power of almost 50% for power source heat.

Wireless Battery-Free Generation of Electric Fields on One-Dimensional Asymmetric Au/ZnO Nanorods for Enhanced Raman Sensing

Wearable electronics have great potential in enhancing health monitoring, disease diagnosis, and environmental pollution tracking. Development of wearable surface-enhanced Raman spectroscopy (SERS) substrates with target sampling and sensitive sensing functions is a promising way to obtain physical and chemical information. This study describes a facile and effective approach for constructing an electrically modulated SERS (E-SERS) substrate as a wearable and wireless battery-free substrate with improved sensitivity. By integrating zinc oxide nanorods (ZnO NRs) with asymmetric gold decoration, controllable enhanced piezoelectric potentials were achieved using magnets to supply the adjustable pressure force. Owing to spatially oriented electron-hole pair separation on the asymmetric NRs, the local hotspot intensity at the Au tips is significantly improved, increasing the SERS signal by 6.7 times. This mechanism was quantitatively analyzed using Raman spectra by in situ formation of Prussian blue (PB). As a proof-of-concept, the E-SERS substrate was further used as a wearable flexible device to directly collect the sweat on a runner's skin and then monitor the lactate status of the runner. This study offers new insight into the development of E-SERS substrates and provides new design options for the construction of wearable sampling and sensing devices for the noninvasive monitoring of metabolites in healthcare and biomedical fields.

Target-Driven Nanozyme Growth in TiO2 Nanochannels for Improving Selectivity in Electrochemical Biosensing

Nanozymes have been used in colorimetric and electrochemical sensing because of their low cost and high stability. However, the wide applications of nanozymes in sensing devices are largely limited due to their poor selectivity. In this study, unlike traditional methods using prepared nanozymes for target detection, we designed a target-driven nanozyme growth strategy in TiO₂ nanochannels to detect analytes. Using telomerase as an example, the established recognition event was used to expand the photocatalytic activity of TiO₂ to visible-light region, thus triggering Prussian blue nanoparticle (PBNP) growth in visible light. Benefiting from the peroxidase (POD)-like activity of PBNPs, the uncharged 3,5,3',5'-tetramethylbenzidine (TMB) is oxidized to positively charged oxTMB, which induces significant ionic transport changes in nanochannels, and thus in turn provides information about telomerase activity. Such a nanozyme-triggered sensing system exhibited excellent performance in telomerase detection in urine specimens from patients with bladder cancer. This innovative target-driven signal generation strategy might provide a new method for applying nanozymes in developing sensitive, rapid, and accurate biological sensing systems.

Electrochemical synthesis of Prussian blue from iron impurities in 3D-printed graphene electrodes: Amperometric sensing platform for hydrogen peroxide

This communication shows the electrochemical synthesis of Prussian blue (PB) films on additive manufactured (3D-printed) electrodes from iron impurities found at the graphene-polylactic acid (G/PLA) substrate and its application as a highly selective sensor for H₂O₂. The 3D-printed G/PLA electrode was immersed in dimethylformamide for 30 min to exposure the iron impurities within the PLA matrix. Next, cyclic voltammograms (200 cycles) in the presence of potassium ferricyanide in 0.1 mol L^-1 KCl + 0.01 mol L^-1 HCl were performed to grow the PB films. The sensing properties of this novel PB/G/PLA platform were evaluated for the amperometric detection of H₂O₂ using batch-injection analysis, with a limit of detection of 0.56 μmol L^-1 under the application of 0.0 V (vs Ag/AgCl/KCl_sat.). The applicability of the sensor was demonstrated for the analysis of milk samples (10-fold diluted in the supporting electrolyte), resulting in proper recovery values (94-101%).

Disposable electrodes from waste materials and renewable sources for (bio)electroanalytical applications

The numerous advantages of disposable and screen-printed electrodes (SPEs) particularly in terms of portability, sensibility, sensitivity and low-cost led to the massive application of these electroanalytical devices. To limit the electronic waste and recover precious materials, new recycling processes were developed together with alternative SPEs fabrication procedures based on renewable, biocompatible sources or waste materials, such as paper, agricultural byproducts or spent batteries. The increased interest in the use of eco-friendly materials for electronics has given rise to a new generation of highly performing green modifiers. From paper based electrodes to disposable electrodes obtained from CD/DVD, in the last decades considerable efforts were devoted to reuse and recycle in the field of electrochemistry. Here an overview of recycled and recyclable disposable electrodes, sustainable electrode modifiers and alternative fabrication processes is proposed aiming to provide meaningful examples to redesign the world of disposable electrodes.

Exploring the Confinement Effect of Carbon Nanotubes on the Electrochemical Properties of Prussian Blue Nanoparticles

A novel and efficient photochemical method has been proposed for the encapsulation of Prussian blue nanoparticles (PBNPs) inside the channels of carbon nanotubes (PB-in-CNTs) in an acidic ferrocyanide solution under UV/vis illumination, and the confinement effect of CNTs on the electrochemical properties of PBNPs is systematically explored. PB-in-CNTs show a faster electron-transfer process, an enhanced electrocatalytic activity toward the reduction of H₂O₂, and an increased anti-base ability compared to PBNPs loaded outside of CNTs (PB-out-CNTs). In addition, PB-in-CNTs show an increased electrochemical reversibility and an unexpected diameter-independent catalytic activity with the decrease of CNT diameters. The improved electrochemical properties of PB-in-CNTs are attributed to the modified electronic properties and dimensions of PBNPs induced by the confinement effect of CNTs. This work provides further insights into the confinement effect on the properties of nanomaterials and will inspire extensive relevant investigations in the development of novel composites or excellent catalysts.

Incorporating doped carbon nanodots and metal ions as an excellent artificial peroxidase for H2O2 detection

Novel nitrogen-doped carbon nanodots (NCdots) were successfully synthesized by a hydrothermal method using 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC) as a carbon–nitrogen source.

Lanthanide Coordination Polymer Nanoparticles as an Excellent Artificial Peroxidase for Hydrogen Peroxide Detection

Lanthanide coordination polymer nanoparticles (Ln-CPNs) have been recently demonstrated as excellent platforms for biomolecule detection. In this work, we synthesized novel cerium coordination polymer nanoparticles ATP-Ce-Tris CPNs in a simple and quick way using ATP molecules as the biocompatible ligands to Ce(3+) ions in tris(hydroxymethyl)aminomethane hydrochloric (Tris-HCl) solution. In view of the excellent free radical scavenging property of cerium compounds, which is ascribed to the mixed valence state (Ce(3+), Ce(4+)) and the reversible switch from Ce(3+) to Ce(4+), the synthesized ATP-Ce-Tris CPNs was used as artificial peroxidase to selectively and sensitively detect H2O2. The sensing mechanism depends on the oxidation of the fluorescent ATP-Ce(III)-Tris CPNs to nonfluorescent ATP-Ce(IV)-Tris CPNs by H2O2. Compared with those inorganic cerium oxide sensors, this kind of fluoresence ATP-Ce-Tris CPNs sensor needs no additional organic redox dye, such as ABTS (2,20-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid), TMB (3,3,5,5-tetramethylbenzidine), or fluorescein as signal molecules. Moreover, such ATP-Ce-Tris CPNs sensor exhibited a more sensitive response to H2O2 with a detection limit down to 0.6 nM, which is 2 orders of magnitude lower than those of cerium oxide sensors. This sensing platform was further extended to the detection of glucose in combination with the specific catalytic effect of glucose oxidase (GOx) for the oxidation of glucose and formation of H2O2.

Electrochemical response of nitrite and nitric oxide on graphene oxide nanoparticles doped with Prussian blue (PB) and Fe2O3 nanoparticles

Electrocatalytic behaviour of graphene oxide (GO), iron(iii) oxide (Fe₂O₃) and Prussian blue (PB) nanoparticles towards nitrite (NO₂⁻) and nitric oxide (NO) oxidation was investigated on a platinum modified electrode.

Electrochemical and Photoelectrochemical Investigation of New Self-Assembled Films Based on Prussian Blue and a Terpyridyl RuII Complex

A new hybrid multilayer film containing Prussian blue (PB) and a bis-terpyridyl RuII complex of RuII(L)2(ClO4)2 (in which L = 4′-(4-(imidazol-1-yl)phenyl)-2,2′:6′,2″-terpyridine), was fabricated though covalently and electrostatic layer-by-layer self-assembly techniques, and characterised by UV-vis absorption spectroscopy, cyclic voltammetry, and photoelectrochemical techniques. The results demonstrated that the two film-forming components were successfully transferred into the hybrid film, which exhibited three quasi-reversible redox couples centred at 0.06, 0.76, and 1.0 V. The photoelectrochemical studies showed that an 11-layer film exhibited a large cathodic photocurrent density of 7.72 μA cm–2 while irradiated with 100 mW cm–2 polychromatic light (325 < λ < 730 nm) at an applied potential of –0.2 V versus a saturated calomel electrode.

Fluorescent hydrogen peroxide sensor based on cupric oxide nanoparticles and its application for glucose and L-lactate detection

A novel fluorescent hydrogen peroxide sensor was developed based on the peroxidase-like activity of cupric oxide nanoparticles. Cupric oxide nanoparticles effectively catalyzed the decomposition of hydrogen peroxide into hydroxyl radicals. Then terephthalic acid was oxidized by hydroxyl radical to form a highly fluorescent product. The linear range of hydrogen peroxide estimated to be 5.0 × 10(-6)-2.0 × 10(-4)M with a detection limit of 3.4 × 10(-7)M. Moreover, this detection system enabled the sensing of analytes which can enzymatically generate hydrogen peroxide. By coupling the oxidation of glucose or L-lactate catalyzed by their corresponding oxidase enzymes with terephthalic acid oxidation catalyzed by cupric oxide nanoparticles, sensitive assays of glucose and l-lactate with detection limits of 1.0 × 10(-6) and 4.5 × 10(-8)M were realized. The successful applications of this approach in human serum samples have also been demonstrated.

Spontaneous Deposition of Prussian Blue on Multi-Walled Carbon Nanotubes and the Application in an Amperometric Biosensor

A simple method has been developed for the spontaneous deposition of Prussian blue (PB) particles from a solution containing only ferricyanide ions onto conducting substrates such as indium tin oxide glass, glassy carbon disk and carbon nanotube (CNT) materials. Formation of PB deposits was confirmed by ultraviolet-visible absorption spectrometry and electrochemical techniques. The surface morphology of the PB particles deposited on the substrates was examined by atomic force microscopy and scanning electron microscopy. CNT/PB composite modified glassy carbon electrodes exhibited an electrocatalytic property for hydrogen peroxide reduction. These modified electrodes exhibited a high sensitivity for electrocatalytic reduction of hydrogen peroxide at −0.05 V (vs. Ag|AgCl), probably due to the synergistic effect of CNT with PB. Then, CNT/PB modified electrodes were further developed as amperometric glucose biosensors. These biosensors offered a linear response to glucose concentration from 0.1 to 0.9 mM with good selectivity, high sensitivity of 0.102 A M⁻¹ cm⁻² and short response time (within 2 s) at a negative operation potential of −0.05 V (vs. Ag|AgCl). The detection limit was estimated to be 0.01 mM at a signal-to-noise ratio of 3.

Layer-by-layer self-assembly aluminum Keggin ions/Prussian blue nanoparticles ultrathin films towards multifunctional sensing applications

In this study we described the nanocomposites films of specially synthesized inorganic Prussian blue (PB) nanoparticles and polyoxocation Al(13) Keggin ions that possess the excellent sensing activities. Film fabrication using layer-by-layer (LBL) self-assembly technique was followed by electrochemical characterization. The assembled multilayer Al(13)/PB films as sensor devices for both the catalytic reduction of H(2)O(2) and detecting the change of relative humidity were also investigated. The sensitivity of the biosensor was 0.886 mA cm(-2)mM(-1), and about two orders of magnitude change in resistance was observed as the relative humidity increasing from 5 to 95%. Both sensors exhibited good reproducibility, wide linear range. The performance and multifunctional abilities of these nanocomposites promise potential applications in biosensors, environmental controlling system and biomedical devices.

Synthesis, characterization, and immobilization of Prussian blue-modified Au nanoparticles: application to electrocatalytic reduction of H2O2

Au nanoparticles modified with electroactive Prussian blue (PB) were for the first time synthesized by a simple chemical method. Transmission electronic microscopy showed that the average size of the Prussian blue shell/Au core hybrid composite (PB@Au) was about 50 nm, and Fourier transform IR, UV-vis spectra, and cyclic voltammetry confirmed the existence of PB on the surface of Au nanoparticles. Using the LbL technique, multilayer thin films of PB@Au nanoparticles were prepared by the alternate adsorption of oppositely charged linear polyelectrolyte poly(allylamine hydrochloride) (PAH) onto ITO glass for the construction of a hydrogen peroxide sensor. The novel multilayer films were characterized by SEM, cyclic voltammetry, and UV-visible absorption spectroscopy. The {PAH/PB@Au}n multilayer-modified electrode showed a well-defined pair of redox peaks and dramatic catalytic activity toward the reduction of hydrogen peroxide.

Electrocatalytic reduction of hydrogen peroxide on modified graphite electrodes: application to the development of glucose biosensors

The electrocatalytic activities of a series of compact graphites modified with microquantities of platinum metals (Pd or Pt+Pd) towards the electrochemical reduction of hydrogen peroxide were characterised. Operational parameters such as the optimal working potential, the influence of temperature and the resulting electrode characteristics were examined. The benefits of using graphite modified with Pt+Pd (mixture ratio 30%:70%) as the basic transducer in a glucose biosensor with improved sensitivity were demonstrated. It was proven that, under the working conditions chosen, the selected electrode (whether bare or covered with an enzyme layer) did not respond to any glutathione, uric acid or ascorbic acid (which all normally occur in biological fluids) present.

Improved surface-enhanced Raman scattering on optimum electrochemically roughened silver substrates

In this work, the effects of preparation conditions used in roughening silver substrates by electrochemical triangular-wave oxidation-reduction cycles (ORC) on surface-enhanced Raman scattering (SERS) were first investigated. The optimum roughening conditions for obtaining strongest SERS of Rhodamine 6G (R6G) are as follows. Ag electrodes were cycled in deoxygenated aqueous solutions containing 0.1 M NaCl from -0.3 to +0.2 V versus Ag/AgCl at 25 mV s(-1) for five scans. The SERS of R6G adsorbed on this optimum procedure-prepared roughened Ag substrate exhibits a higher intensity by one order of magnitude, as compared with that of R6G adsorbed on a normally roughened Ag substrate.